DRAINS User Manual

DRAINS User Manual
Watercom Pty Ltd
User Manual
A manual on the DRAINS program
for urban stormwater drainage system
design and analysis
Geoffrey O’Loughlin and Bob Stack
This manual coincides with DRAINS Version 2014.11
It is available electronically and on paper and is updated regularly
- to download a PDF file of the latest version,
visit www.watercom.com.au.
November 2014
CONTENTS WELCOME 1. INTRODUCTION TO DRAINS 1.1 Outline.............................................................................................................. 1.1 1.1.1 1.1.2 1.1.3 1.1.4 1.1.5 1.1.6 Description ............................................................................................................................. 1.1 Modelling Aspects .................................................................................................................. 1.2 Computer Aspects ................................................................................................................. 1.4 Support................................................................................................................................... 1.4 Installation .............................................................................................................................. 1.5 Starting Up ............................................................................................................................. 1.5 1.2 Examples of DRAINS in Operation .................................................................. 1.5 1.2.1 1.2.2 1.2.3 1.2.4 Running a Model of a Simple Pipe System ........................................................................... 1.5 Running the Rational Method and Extended Rational Method Models ............................... 1.23 Running the Premium Hydraulic Model ............................................................................... 1.26 Running Storage Routing Models ........................................................................................ 1.28 2. MENUS, TOOLS AND DATA BASES 2.1 Introduction ...................................................................................................... 2.1 2.2 Menus .............................................................................................................. 2.1 2.2.1 2.2.2 2.2.3 2.2.4 2.2.5 2.2.6 2.2.7 2.2.8 The Menu Bar ........................................................................................................................ 2.1 The File Menu ........................................................................................................................ 2.1 The Edit Menu ........................................................................................................................ 2.2 The Project Menu ................................................................................................................... 2.2 The View Menu ...................................................................................................................... 2.2 The Draw Menu...................................................................................................................... 2.2 The Run Menu ....................................................................................................................... 2.3 The Help Menu....................................................................................................................... 2.3 2.3 Tools and Associated Components.................................................................. 2.3 2.3.1 General .................................................................................................................................. 2.3 2.3.2 Pits ......................................................................................................................................... 2.4 2.3.3 Simple Nodes ......................................................................................................................... 2.8 2.3.4 Pipes ...................................................................................................................................... 2.9 2.3.5 Sub-Catchments .................................................................................................................. 2.11 2.3.6 Overflow Routes .................................................................................................................. 2.17 2.3.7 Detention Basins .................................................................................................................. 2.22 2.3.8 Special Weirs and Orifices ...................................................................................................2.27 2.3.9 Pumps .................................................................................................................................. 2.28 2.3.10 Prismatic Open Channels .................................................................................................... 2.28 2.3.11 Irregular Open Channels ...................................................................................................... 2.29 2.3.12 Multi-Channels ..................................................................................................................... 2.31 2.3.13 Stream Routing Reaches ..................................................................................................... 2.32 2.3.14 Headwalls............................................................................................................................. 2.34 2.3.15 Culverts ................................................................................................................................ 2.35 2.3.16 Bridges ................................................................................................................................. 2.35 2.3.17 Combining Components ...................................................................................................... 2.37 DRAINS User Manual
November 2014
2.4 Data Bases .................................................................................................... 2.38 2.4.1 2.4.2 2.4.3 2.4.4 2.4.5 2.4.6 2.4.7 General................................................................................................................................ 2.38 Standardised Data Bases ................................................................................................... 2.38 Hydrological Models ............................................................................................................ 2.39 Rainfall Data Bases ............................................................................................................. 2.40 Pipe Data Base ................................................................................................................... 2.48 Pit Data Base ...................................................................................................................... 2.50 Overflow Route Data Base.................................................................................................. 2.53 3. OPTIONS WITHIN DRAINS 3.1 Introduction ...................................................................................................... 3.1 3.2 Input Options.................................................................................................... 3.1 3.2.1 General.................................................................................................................................. 3.1 3.2.2 Importing DXF Files .............................................................................................................. 3.2 3.2.3 Spreadsheet Imports ............................................................................................................. 3.4 3.2.4 GIS File Imports .................................................................................................................... 3.4 3.2.5 ILSAX File Imports ................................................................................................................ 3.9 3.2.6 Merging Files ......................................................................................................................... 3.9 3.2.7 Transferring to and from CAD Programs ............................................................................ 3.10 3.2.8 Transferring Data to and from the 12d Program ................................................................. 3.10 3.2.9 CADApps Advanced Road Design Link .............................................................................. 3.11 3.2.10 Transferring from MXROADS ............................................................................................. 3.12 3.2.11 Transferring from CatchmentSIM ........................................................................................ 3.12 3.2.12 Setting Up New Pipe, Pit and Overflow Route Data Bases ................................................ 3.12 3.3 Display Options .............................................................................................. 3.13 3.3.1 Introduction.......................................................................................................................... 3.13 3.3.2 Screen Presentation Options .............................................................................................. 3.13 3.4 Run Options ................................................................................................... 3.16 3.4.1 3.4.2 3.4.3 3.4.4 3.4.5 Design and Analysis Runs .................................................................................................. 3.16 Run Logs ............................................................................................................................. 3.18 Warning and Error Messages ............................................................................................. 3.19 Options for Modifying Pit Pressure Change Factors ........................................................... 3.19 Quantities ............................................................................................................................ 3.21 3.5 Output Options ............................................................................................... 3.22 3.5.1 3.5.2 3.5.3 3.5.4 3.5.5 3.5.6 3.5.7 3.5.8 3.5.9 Transfers of Displays and Screen Print-Outs...................................................................... 3.22 DRAINS Print Diagram Option ............................................................................................ 3.23 DXF Exports ........................................................................................................................ 3.23 Spreadsheet Outputs (and Inputs) ...................................................................................... 3.25 GIS File Exports .................................................................................................................. 3.30 Hydrograph Outputs in TUFLOW Format ........................................................................... 3.35 Outputs to Linked Applications ........................................................................................... 3.35 Merge Outputs (and Inputs) ................................................................................................ 3.35 Template File Exports ......................................................................................................... 3.37 3.6 Help Options .................................................................................................. 3.37 4. OPERATIONS 4.1 Introduction ...................................................................................................... 4.1 4.2 DRAINS Workings ........................................................................................... 4.1 4.2.1 Units ...................................................................................................................................... 4.1 DRAINS User Manual
November 2014
4.2.2 Programming.......................................................................................................................... 4.1 4.2.3 Data Storage and Files .......................................................................................................... 4.1 4.2.4 Processes .............................................................................................................................. 4.2 4.2.5 Initial Processes ..................................................................................................................... 4.3 4.2.6 Hydrological Calculations....................................................................................................... 4.3 4.2.7 Hydraulic Calculations ........................................................................................................... 4.4 4.2.8 Calibration .............................................................................................................................. 4.7 4.2.9 Interpretation of Results ......................................................................................................... 4.7 4.2.10 Design Procedures ................................................................................................................ 4.8 4.3 Applying DRAINS ........................................................................................... 4.11 4.3.1 4.3.2 4.3.3 4.3.4 4.3.5 4.3.6 4.3.7 4.3.8 Integration ............................................................................................................................ 4.11 Designing Subdivision Piped Drainage Systems ................................................................. 4.11 Designing Infill Developments with On-Site Stormwater Detention Systems ...................... 4.13 Analysing Established Drainage Systems ........................................................................... 4.14 Asset Management ..............................................................................................................4.17 Performing Flood Studies with Storage Routing Models ..................................................... 4.18 Methods and Parameters Applied in DRAINS ..................................................................... 4.19 Choice of Model ................................................................................................................... 4.19 5. TECHNICAL REFERENCE 5.1 Introduction ...................................................................................................... 5.1 5.2 Predecessors ................................................................................................... 5.1 5.2.1 DRAINS.................................................................................................................................. 5.2 5.3 Hydrology ......................................................................................................... 5.2 5.3.1 5.3.2 5.3.3 5.3.4 5.3.5 General .................................................................................................................................. 5.2 The ILSAX Hydrological Model .............................................................................................. 5.3 Testing and Verification of DRAINS ..................................................................................... 5.14 Rational Method Procedures ............................................................................................... 5.17 The Extended Rational Method ........................................................................................... 5.18 5.4 Storage Routing Models................................................................................. 5.19 5.5 Pit Inlet Capacities ......................................................................................... 5.22 5.5.1 General ................................................................................................................................ 5.22 5.5.2 Pit Inlet Capacities in DRAINS ............................................................................................. 5.23 5.5.3 US Federal Highway Administration (HEC22) Procedures ................................................. 5.28 5.6 Pipe System Hydraulics ................................................................................. 5.31 5.6.1 5.6.2 5.6.3 5.6.4 5.6.5 5.6.6 5.6.7 General ................................................................................................................................ 5.31 Pipe Design Calculations .....................................................................................................5.32 Basic Hydraulic Calculations................................................................................................ 5.32 Unsteady Flow Calculations in Standard and Premium Hydraulic Models .......................... 5.32 Pipe Friction Equations ........................................................................................................ 5.33 Pit Pressure Changes ..........................................................................................................5.34 Tailwater Levels ................................................................................................................... 5.36 5.7 Hydraulics of Open Channels ........................................................................ 5.36 5.8 Detention Basin Hydraulics ............................................................................ 5.37 5.8.1 5.8.2 5.8.3 5.8.4 Routing ................................................................................................................................. 5.37 Overflows from Basins .........................................................................................................5.39 On-Site Stormwater Detention ............................................................................................. 5.41 Infiltration..............................................................................................................................5.42 DRAINS User Manual
November 2014
5.9 Culvert and Bridge Hydraulics........................................................................ 5.43 5.9.1 Culverts ............................................................................................................................... 5.43 5.9.2 Bridges ................................................................................................................................ 5.43 5.10 File Formats ................................................................................................... 5.43 5.10.1 General................................................................................................................................ 5.43 5.10.2 Drawing File Formats .......................................................................................................... 5.43 5.10.3 GIS File Formats ................................................................................................................. 5.44 5.10.4 Spreadsheet File Formats ................................................................................................... 5.46 5.10.5 TUFLOW TS1 File Formats ................................................................................................ 5.47 A. THE DRAINS VIEWER A.1 Introduction ..................................................................................................... A.1 A.2 Setting Up and Running the Viewer ................................................................ A.1 A.3 Information Required for Checking ................................................................. A.3 A.3.1 A.3.2 A.3.3 A.3.4 A.3.5 A.3.6 General.................................................................................................................................. A.3 Property Drainage Systems .................................................................................................. A.3 Inter-Allotment Drainage Systems ........................................................................................ A.4 Street Drainage Systems ...................................................................................................... A.5 Trunk Drainage Systems....................................................................................................... A.6 Localised Flood Studies ........................................................................................................ A.6 A.4 Assessing Models and Inputs ......................................................................... A.7 A.4.1 A.4.2 A.4.3 A.4.4 A.4.5 A.4.6 General.................................................................................................................................. A.7 Rainfall Inputs ....................................................................................................................... A.7 Hydrology .............................................................................................................................. A.8 Comparison of Hydrological Methods for Piped Drainage Systems ................................... A.14 Pipe, Pit and Overflow Route Data Bases .......................................................................... A.18 Hydraulics............................................................................................................................ A.19 A.5 Checking Model Components, Flowrates and Water Levels ......................... A.21 A.5.1 Viewing Pipe System Components ..................................................................................... A.21 A.5.2 Viewing Pipe System Results ............................................................................................. A.22 A.5.3 Reviewing Stormwater Detention and Retention Systems ................................................. A.26 Reviewing Open Channel Systems ................................................................................................ A.29 A.6 Analyses ....................................................................................................... A.29 A.7 Conclusion .................................................................................................... A.30 REFERENCES INDEX DRAINS User Manual
November 2014
This manual, available in both printed and electronic forms, provides the information you need to run the
DRAINS program to design and analyse urban stormwater drainage systems. Together with the Help
system that accompanies DRAINS, it will guide you to understand what DRAINS can do, and how to use
it to model many situations. The data files included in the Manual Example Files folder among the
files supplied with DRAINS, which are also obtainable from www.watercom.com.au, can be used to
explore the operation of DRAINS.
The manual covers the operation of Version 2014.07 of DRAINS. An appendix provides information on
the DRAINS Viewer, a free program that can be used to review DRAINS models and result files.
DRAINS uses hydrological and hydraulic methods developed by generations of engineers. If you have
formal training in water engineering and experience in using models and encountering practical problems,
you should find the program easy to use and to interpret.
If you are a beginner in the fields of hydrology, hydraulics or stormwater system design, or are out of
practice, this manual and the Help system will assist you towards understanding the program’s operations
and outputs. DRAINS can apply four types of alternative hydrological models and two hydraulic
modelling procedures.
This manual can be used as a learning guide for DRAINS or as a reference manual that you can dip into.
There is an index at the end, and you can use PDF search functions to find topics in the electronic
version. Most displays of screens are in Microsoft Windows 7 style; these displays may appear different
in XP or 'classic style', but the contents are the same.
Chapter 1 describes what DRAINS is and does, and how it can be installed. To get you started, it
provides a simple example that takes you through the steps of entering data, running the program, and
inspecting some of its outputs. (The examples supplied run with the demo version of DRAINS, and cover
most of the methods available in DRAINS.)
Chapter 2 deals with the many items and facilities in DRAINS. It presents the menus that control
operation, the tools that define drainage system components (pits, pipes, etc.), and the data bases used
to store standard data. It describes the data required for all components. To illustrate these, it works with
a larger example involving both pipes and open channels.
Chapter 3 is about processes. It describes the options within DRAINS for inputting and displaying
information, running the program, outputting data and results, and obtaining help.
Chapter 4 describes how DRAINS operates, covering computing and computational aspects. It also
describes how DRAINS can be applied to design and analysis tasks, indicating how runs can be made
and how results can be interpreted.
Chapter 5 provides the technical background to DRAINS and the methods that it uses. There are
explanations and references relating to material on rainfall data, overland flows, pit inlet capacities and
pressure change coefficients, detention basins, culverts and bridges.
The examples that were explained in earlier versions of this manual are now included in the
DRAINS Help system. They use files that are available at C:\Program Files\Drains or C:\Program
Files (x86)\Drains.
Previous versions of this manual described some features that have become obsolete and have been
deleted. To avoid confusion, these descriptions are not given here, but the information remains in the
DRAINS Help system to provide guidance when models created by earlier versions of DRAINS are
As DRAINS develops and new features are added, there will be revisions of this manual, available
electronically from www.watercom.com.au and on paper.
DRAINS User Manual
November 2014
The authors’ contact information is:
Bob Stack
Watercom Pty Ltd
15 Little River Close
Wooli NSW 2462
phone/fax: (02) 6649 8005
[email protected]
DRAINS User Manual
Geoffrey O’Loughlin
Anstad Pty Limited
72 Laycock Road
Penshurst NSW 2222
(02) 9570 6119, fax (02) 9570 6111, 0438 383 841
[email protected]
November 2014
DRAINS is a multi-purpose Windows program for designing and analysing urban stormwater drainage
systems and catchments. It was first released in January 1998 and is marketed by Watercom Pty Ltd,
based in Wooli, NSW.
DRAINS can model drainage systems of all sizes, from small to very large (up to 10 km2 using subcatchments with ILSAX hydrology, and greater using storage routing model hydrology). Working through
a number of time steps that occur during the course of a storm event, it simulates the conversion of
rainfall patterns to stormwater runoff hydrographs and routes these through networks of pipes, channels
and streams. In this process, it integrates:
design and analysis tasks,
hydrology (four alternative models) and hydraulics (two alternative procedures),
closed conduit and open channel systems,
headwalls, culverts and other structures,
stormwater detention systems, and
large-scale urban and rural catchments.
Within a single package, DRAINS can carry out hydrological modelling using ILSAX, rational method and
storage routing models, together with unsteady hydraulic modelling of systems of pipes, open channels
and, and in the premium hydraulic model, surface overflow routes. It includes an automatic design
procedure for piped drainage systems, connections to CAD and GIS programs, and an in-built Help
system. Figure 1.1 shows areas where DRAINS can be used.
Figure 1.1 DRAINS Applications
Three significant functions that are not included in DRAINS are (a) continuous modelling over long
periods including wet and dry conditions, (b) water quality modelling, and (c) 2-dimensional unsteady flow
DRAINS is continuously being improved and expanded. Although users need to adapt to new features
and modes of operation in the program, this continuing development process provides benefits from
improvements to DRAINS’ modelling techniques and breadth of coverage.
DRAINS User Manual
November 2014
DRAINS is available in versions for 20, 50 and unlimited numbers of pipes or channels. The ILSAX
hydrology or rational method can be chosen. Optional ILSAX or rational method procedures, storage
routing models, GIS capabilities and unsteady flow hydraulics in overflow routes are available at extra
cost. Current prices are available from Bob Stack of Watercom Pty Ltd on (02) 6649 8005 or
[email protected]
Modelling Aspects
(a) Hydrology to Estimate Flows
The ILSAX hydrological model, illustrated in Figure 1.2, is the original model used to simulate the
operation of urban stormwater drainage systems in DRAINS. It comes from the ILSAX program
(O'Loughlin, 1993), described in Section 5.3.2. This model uses time-area calculations and Horton
infiltration procedures to calculate flow hydrographs from sub-catchments. The various sub-catchment
flows are combined and routed through a pipe and channel system. Calculations are performed at
specified times after the start of each storm, using time intervals of one minute or less. At each time step,
a hydraulic grade line analysis is performed throughout the drainage network, determining flowrates and
water levels.
Figure 1.2 Operation of the DRAINS Rainfall-Runoff Simulation Model Incorporating the ILSAX
Hydrological Model and Hydraulic Calculations
The design of a piped drainage system can be performed automatically, followed by an analysis, and
results can be checked, viewed and exported as CAD (computer aided drafting) files, GIS (geographical
information system) files and spreadsheet tables.
In addition to the ILSAX model, three other hydrological models are available as options in DRAINS:
Peak flowrates can be calculated by the rational method, traditionally used for calculating flowrates
for piped urban drainage design. Using the formula Q=C.I.A, it converts a statistical rainfall intensity
I to a flowrate Q using a runoff coefficient C and catchment area A (see Section 5.3.3). The rational
method’s main drawback that it does not calculate flow hydrographs, and it is gradually being
superseded by hydrograph-producing methods. DRAINS includes a search procedure that
determines the time duration that gives the greatest value of Q = C.I.A, thus resolving 'partial area'
DRAINS User Manual
November 2014
An optional, 'extended' rational method (ERM) model that produces flow hydrographs based on
rational method calculations is also provided with the rational method, for modelling detention
DRAINS incorporates optional storage routing models of the type used in the RORB, RAFTS and
WBNM programs that have been used in Australia since the 1970s, and are applicable to broadscale rural and urban catchments of virtually any size. As shown in Figure 1.3, they involve the
division of a catchment into sub-catchments based on streams and internal ridge lines.
Figure 1.3 Layout of a RORB style of Storage Routing Model within DRAINS
Storage routing models treat sub-catchments and stream reaches as storages (similar to reservoirs or
detention basins) that can be modelled by the non-linear equation, S = k.Qm, where S is the storage in an
element, Q is the flow or discharge out of the element, and k and m are model parameters. These
models work downwards through a catchment, adding runoff from the various sub-catchments and
performing routing catchments that reshape the hydrographs.
The runoff routing modelling facilities in DRAINS can be configured to emulate the RORB, RAFTS and
WBNM modelling structures. They can also be combined with ILSAX sub-catchments and open channel
hydraulic calculations, so that quite diverse flooding and urban drainage systems can be described.
(b) Hydraulic Calculations for Pipes, Open Channels and Surface Overflows
The procedures in DRAINS originally were intended to be of a medium level of complexity, providing
stable, fast and sufficiently accurate methods to compute flowrates and water surface profiles. The needs
of users have prompted considerable advances.
The original basic hydraulic model combined (i) hydraulic grade lines (HGLs) projected backwards from
tailwater levels at drainage system outlets with (ii) a pressure pipe calculation procedure, to calculate
flowrates and HGL levels at pits and other locations using a quasi-unsteady process. DRAINS then
computed the characteristics of surface overflows that cannot be carried by pipes.
This model has been replaced by a one-dimensional unsteady flow procedure. In the standard hydraulics
model, this is applied to pipe and open channel flows, and in the premium hydraulic model, surface
overflows are also modelled by full unsteady flow calculations.
DRAINS User Manual
November 2014
(c) Additional Information on Models
A more detailed coverage of the hydrological and hydraulic models available in DRAINS is provided in
Chapter 5. These procedures reflect Australian urban stormwater drainage management practice, which
considers hydrological and hydraulic features in considerable detail, as described in this manual and in
the DRAINS Help system. DRAINS is also adaptable for use outside Australia. The ILSAX model is
based on the American ILLUDAS program, using the U.S. Soil Conservation Service soil classification,
and the Horton infiltration model is the same as that used in the US EPA Stormwater Management Model
(SWMM) program (Huber and Dickinson, 1998). The rational method and ERM procedures are similar to
one applied in the U.S. The hydraulic procedures are the same as those used in all English-speaking
countries, using Colebrook-White and Manning’s equations.
Computer Aspects
DRAINS follows Microsoft Windows conventions and runs on all version of the Windows operating
system, from Windows 95 to Windows 7. PC users will find the standard Main Window, menu bar, toolbar
and Help system easy to navigate. There are four alternative forms of data entry:
• by drawing drainage system components on the screen and inserting information for each component
in property sheets,
• by entering data from ILSAX files, CAD drawing files or GIS files,
• by direct entry from other programs such as 12d, CADApps Advanced Road Design and MX, and
• by modifying spreadsheet output files created by DRAINS, or building such files directly in a
spreadsheet program or as an exported file from another program.
There is also a large choice of outputs - screen print-outs, CAD, GIS and spreadsheet files.
In most cases, revised data can be transferred back to the originating programs using these files.
Installation and updating of DRAINS is quick and easy using a self-extracting file named
DainsSetup.exe that can be supplied on CD-ROM or downloaded from www.watercom.com.au. The
file installs the latest release version of DRAINS, which also operates as a demonstration program with a
limit of five pipes or channels, and restrictions on changes to detention basins and culverts.
When installed on a PC using Microsoft Windows, the program resides in the folder C:\Program
Files\Drains\Program, along with related files. It also places a default data base file named
Drains.db1 in C:\ProgramData\Drains to meet Microsoft Vista requirements' At present, the
Drains.exe file is about 4 Mb in size, and is accompanied by a HTML Help file of 4 Mb.
To run with capabilities beyond those of the demonstration version, a hardware lock or dongle must be
inserted into a USB port, or with earlier types, the 25 pin printer port of the PC. DRAINS can be installed
and run on any PC or server system to which a hardware lock has been attached. The hardware lock will
control the number of conduits that can be modelled (20, 50 and unlimited), and whether rational method,
storage routing GIS modelling or premium hydraulic modelling facilities are implemented.
The DRAINS Viewer described in Appendix A is a separate program, but operates in the same way as
DRAINS. Both programs can be opened at the same time. The Viewer is installed from a self-extracting
file, and users can navigate through DRAINS models, property sheets and outputs of results in the same
way as DRAINS. However, they cannot modify or run models. There is no size limitation on the Viewer
and it can be freely distributed. To read the latest DRAINS models, the Viewer needs to be periodically
updated. To obtain the latest version, contact Bob Stack or Geoffrey O’Loughlin at the numbers given in
the next section.
Microsoft Vista and Windows 7 impose restrictions that may affect users’ ability to change the standard
data base stored in the Drains.db1 file (see Section 2.4.2). The user should have permission to modify
files in C:\ProgramData\Drains.
For support, contact Watercom Pty Ltd at phone/fax (02) 6649 8005 or [email protected]
Training workshops are conducted by Dr. Geoffrey O’Loughlin, who can be contacted on phone
(02) 9570 6119 or 0438 383 841, fax (02) 9570 6111 and [email protected] They are
communicated to DRAINS users by e-mail, and advertised by mail-outs to organisations involved with
urban stormwater management.
DRAINS User Manual
November 2014
If you are setting up the demonstration version, or updating a DRAINS program that is already installed,
you only need the file DrainsSetup.exe, which can be downloaded from the website
www.watercom.com.au or obtained on CD.
Click your mouse on the icon for DrainsSetup.exe and, when prompted, enter the password provided
by Watercom Pty Ltd, or enter 'DEMO' to install the demonstration version. Then follow the instructions,
acknowledging the Conditions of Use.
For the first installation of DRAINS on a PC that is to be used with a hardware lock, you should install
from the CD-ROM provided when DRAINS is purchased. The USB locks that are currently supplied do
not require a driver.
Installations can be made on any number of PCs. Running DRAINS requires that the moveable hardware
lock or dongle be connected to the PC’s USB or printer ports. Locks are programmed to model certain
sizes of drainage network (up to 20, 50 or unlimited links), to implement additional rational method, ILSAX
and storage routing model calculations, to import and export data from GIS files and to undertake full
premium hydraulic calculations. DRAINS can be uninstalled in the usual way for Windows programs.
The version number of the DRAINS program being used can be found in the About DRAINS…. Option in
the Help menu. The License Details item provides information on the capabilities of the attached
hardware lock.
The DRAINS Viewer installs in the same way as the demonstration version of DRAINS. No password is
Starting Up
Once installed, DRAINS can be opened by:
using the Start menu, selecting Programs and choosing DRAINS,
clicking on a DRAINS shortcut if one is created on your desktop (This may be necessary with some
server systems.), or
clicking on Drains.exe in the C:\Program Files\Drains\Program folder.
When opened, the Main Window of DRAINS appears as shown in Figure 1.4.
You can define a drainage system graphically on this blank screen by drawing components such as pits
and pipes, using the facilities in the menus and toolbar located at the top.
To operate DRAINS, you can enter data directly using the keyboard and mouse, or open or import an
existing file from the File menu. If you are entering an entirely new system, you must follow the steps
that are explained in detail in the following section.
Examples of DRAINS in Operation
Running a Model of a Simple Pipe System
This example illustrates how a pipe system, assumed to be located at Orange, New South Wales, can be
set up in DRAINS and how design and analysis runs can be made. You will learn best by constructing
the model in the demonstration or full versions of DRAINS using the instructions set out below.
Alternatively, you can inspect and run the finished model files Orange1.drn and Orange2.drn
provided in the set of examples accompanying this manual.
The instructions do not cover all DRAINS options or procedures, but are adequate to set up this model.
DRAINS User Manual
November 2014
Drop-Down Menu
Main Window
(Drainage Systems are drawn here)
Figure 1.4 The Main DRAINS Window with the Project Menu Selected
(a) Defining Hydrological Models, Rainfall Data and Other Options
The hydrological model, rainfall patterns and component data bases should be established first. Most of
this information can be changed later. If you open and close an existing DRAINS model, the hydrological
model and rainfall from that model will remain. To start afresh, you need to exit from DRAINS and start
up again. In this case, the databases for the hydrological model and rainfall data will be empty, while
those for pipes, pits and overflow routes will be taken from the file Drains.db1, located in the
From the Project menu at the top of the screen you can select Hydrological Models…. The window in
Figure 1.5 appears, showing a dialog that is used to establish hydrological models. (Not all of the options
shown may be available with your hardware lock.)
Figure 1.5 The Hydrological Model Specification Dialog Box
DRAINS User Manual
November 2014
ILSAX hydrology is used in this example. Clicking the Add ILSAX Model button opens the property
sheet shown in Figure 1.6, in which the characteristics of the hydrological model can be entered.
Figure 1.6 ILSAX Type Hydrological Model Property Sheet (Top Portion)
Enter the name and numbers shown. These will be explained later, but if you require an immediate
explanation, press the Help button to open the Help screen shown in Figure 1.7.
Figure 1.7 Help Window opened from the ILSAX Hydrological Model Property Sheet
You should then click OK in the property sheet and the Hydrological Model Specification dialog box,
ensuring that 'Orange Soils' is defined as the default model in the drop-down list box at the top left corner
of Figure 1.5.
Next, you must define the rainfall patterns to be used, using the Rainfall Data… option in the Project
menu. This opens the window shown Figure 1.8, in which you can set up a data base of rainfall patterns
or hyetographs. In this example, two patterns are to be set up, both of 25 minutes duration, for average
recurrence intervals (ARIs) of 2 years and 100 years, corresponding to average intensities of 40.2 and
101 mm/h. For most design and analysis tasks in Australia, the required rainfall data will come from
Australian Rainfall and Runoff (Institution of Engineers, Australia, 1987) or from updated intensityfrequency-duration data to be made available on the Bureau of Meteorology website, www.bom.gov.au.
DRAINS User Manual
November 2014
Figure 1.8 Rainfall Data Property Sheet
Storm patterns or hyetographs can be defined easily in DRAINS by clicking the Add one ARR87 Storm
button, which opens the dialog box shown in Figure 1.9.
Figure 1.9 Australian Rainfall and Runoff Pattern Dialog Box
Enter the information shown in this figure and press the OK button. The pattern will be displayed in the
Rainfall Data property sheet, as shown in Figure 1.10. (Note that there are other ways of entering rainfall
data, described in Section 2.4.4).
Next, change the antecedent moisture condition value in the Rainfall property sheet to 2.5. Set up a
second pattern using the same process, this time for an ARI of 100 years and an intensity of 101 mm/h.
Then click the OK button.
The next step is to select storms from the data base to be used for design and for analysis. This is done
using the Select Minor Storms option in the Project menu, which opens the dialog box shown in Figure
1.11. Click the Selected storms button in the top left corner and then click the downwards arrow on the
first drop down list box to show the names of the rainfall patterns in the data base. For this example, click
on the 2 year ARI, 25 minute pattern to select this storm as the one to be used to design the pipe
DRAINS User Manual
November 2014
Close this dialog box by clicking OK, and then follow the same procedure with Select Major Storms to
select the 100 year ARI, 25 minute storm for major storm runs.
Figure 1.10 2 Year ARI, 25 Minute Rainfall Pattern for Orange, NSW
Figure 1.11 Select Minor Storms Dialog Box
(The design process defines the pipe sizes and depths needed to carry runoff from minor ARI storms
satisfactorily, while meeting certain criteria. The system must also 'fail-safe' in runoff from major ARI
storms. The system performance is checked using various analyses.)
Now choose Options … in the Project menu to open the sheet shown in Figure 1.12. This sets the
values of parameters used in design calculations. The only items to be entered in the present example
are the blocking factors - enter 0.5 for sag pits and 0.0 for on-grade pits.
With this model, you will be using New South Wales pits. To select these, choose the Default Data Base
option in the Project menu. The dialog box shown in Figure 1.13 appears, allowing you to select the data
base to be used. (Note that this must be done before any pits are entered into the Main Window. The
selected data base stays in the .drn file for each model. New pit, pipe and overflow route types can be
added, and existing information can be altered, but for programming reasons it is not possible to remove
pipe and pit specifications.)
At this point, you should save the file using the Save option in the File menu, or the diskette symbol on
the Toolbar, naming the file Orange1.drn. The above processes create a template or shell, containing
the base information that will be used to run the model, and the pipe, pit and overflow route types to be
referred to when setting up drainage systems. The DRAINS .drn file can be saved at this stage, to be
used later as a starting point for models that use this base information. (The saved file might be named
Orange template.drn or something similar.)
DRAINS User Manual
November 2014
Figure 1.12 The Options Property Sheet
(Note that not all options may appear. Some may not be available with the hardware lock that is being used, and
others may be obsolete features in an older DRAINS model.)
Figure 1.13 Dialog Box Selecting a Data Base for Pipes, Pita and Overflow Routes
(b) Defining the Drainage System
Suppose that the system to be designed is that shown in Figure 1.14.
Figure 1.14 A Simple Drainage System
DRAINS User Manual
November 2014
This system can be drawn in the Main Window using five tools from the Toolbar:
As you guide your mouse arrow over the Toolbar items, tool-tips will appear, indicating the purpose of
each button. Once you click one of the Toolbar button, the cursor will change to a pencil, which can be
used to place that component in the Main Window.
You can use the pit and node tools,
Main Window, as shown in Figure 1.15.
, to draw five drainage pits and three outlet nodes in the
Nodes at Pipe
and Overflow
Figure 1.15 Initial Drawing of Drainage System
Note that the overflow paths
can be drawn as a polyline,
., allowing them to be
placed to the side in cases where both the pipe and any overflows travel to the same destination. Points
along the overflow route are selected using the left mouse button, and the end-point is defined by clicking
the right mouse button.
The names of components (mostly given as ???? to start with) can be dragged to more convenient
locations. The components themselves can be moved round the screen. You can select a component by
clicking it to make 'handles' appear, holding the left mouse button down on it so that horizontal and
vertical arrows appear, and then dragging the component to the required location. A pipe or channel can
be moved as a single unit by dragging near its centre. Alternatively, their ends can be moved by dragging
the handles.
As well as entering data directly onto a blank Main Window, as shown above, you can insert a
background from a CAD drawing file, together with a layout of pits and pipes. A drawing file for the
current example, Orange Base.dxf, is shown in Figure 1.17. This can be entered into a DRAINS Main
Window, after the hydrological, rainfall and options settings have been defined, using the Import DXF
File… option in the File menu, shown in Figure 1.18. This takes you through a set of dialog boxes in
which you must nominate layers containing data on the background, pipes (as lines) and pits (as circles),
and other information. The first of these is also shown in Figure 1.18.
The pipe system appears as shown in Figure 1.19. This model should be saved as file Orange2.drn.
This view can be enlarged using the magnifying tool or mouse wheel, and you can pan across the model
using the pan tool in the toolbar. All pipe lengths can be scaled by setting the length of one pipe. The
other components of the system: pits, sub-catchments, overland flow paths and outlets, can then be
DRAINS User Manual
November 2014
Figure 1.16 More Complete Orange Drainage System Drawing
The background is an image created from vector objects (lines, polylines and arcs) in the nominated layer
of the CAD file. It can be switched on and off, and its colour can be changed, using options in the View
Figure 1.17 CAD Display showing Pipe System Layout and Background
Data for parts of the drainage system can be entered and edited using property sheets that appear when
you right-click a component, and select Edit Data from the pop-up menu, as shown in Figure 1.20.
The property sheet for Pit 1 is shown in Figure 1.21. This has two pages, the first with pit properties and
another optional page for factors to be applied if pit pressure change coefficients are to be calculated
using the Queensland Urban Drainage Manual (QUDM) charts (refer to Section 3.4.4). These include an
aligned/misaligned choice (explained in the DRAINS Help system) and the width of the pit wall on which
the outlet pipe is located.
DRAINS User Manual
November 2014
Figure 1.18 Menu and Dialog Box for Nominating CAD Layers
Figure 1.19 Inputted Drainage System from the CAD File
From Figure 1.14 you can see that any overflows from Pit 1 will flow to Pit 2, so that this first pit should be
selected as an on-grade pit, on a slope so that no pond will form over the pit. Note how pit types and
sizes are selected from a data base of pit types using two drop-down list boxes. (When entering data,
you can move from box to box using the Tab key on your PC’s keyboard.)
DRAINS User Manual
November 2014
Figure 1.20 Pop-Up (Right Mouse Button) Menu
Figure 1.21 A Drainage Pit Property Sheet
The pit pressure change coefficient value of 4.5 is suitable for a pit at the top of a drainage line. You can
obtain further information about these factors, which influence the water levels in the pipe system, from
the Help system or from Section 0.
DRAINS User Manual
November 2014
After closing the Drainage Pit property sheet, you will find that the pit name has changed and the question
marks have disappeared. As data is entered, the allocated names appear in the Main Window. DRAINS
will not run until all the required data is entered. Even if the data for all components are entered, question
marks will remain if the connections between components are incomplete.
Table 1.1 defines the data for the pits in this system. If you are following this example, enter the
appropriate values for the five pits. The names of pits can be up to 10 characters long, and those of other
components may be slightly larger. Assume all pits to be NSW RTA (Roads and Traffic Authority, now
Roads and Maritime Services) SA2 pits, at the slopes shown in the table.
Table 1.1 Pit and Outlet Node Data for the Orange Example
Pit Type
Slope (%)
Pit 1
Pit 2
1, say
Pit 3
Pit 4
Coeff. Ku
Pit 5
Outlet 1
Outlet 2
Outlet 3
Pit 2 is a sag pit, located in a hollow in which stormwater can form a pond over the pit. For this type of pit,
there is an additional page on the property sheet, labelled Pond Properties, where extra information has
to be provided - an allowable ponding depth and a maximum ponded volume, here taken to be 0.15 m
and 2 m3.
Figure 1.22 A Drainage Pit Property Sheet
Next, you can enter the sub-catchments,
as shown in Figure 1.20. The sub-catchment symbol
should no be placed over a pit. If this is done, it will snap to the top right corner of a pit, and can then be
moved to another location around the pit if you wish. The data for sub-catchments is entered into their
property sheets, which are opened from a pop-up menu in the same way as for pits. The simplest form of
the property sheet is shown in Figure 1.23.
The sub-catchment draining to each pit is divided into three types of land-use:
paved areas (impervious areas directly connected to the drainage system),
supplementary areas (impervious areas not directly connected to the drainage system), and
grassed areas (pervious areas).
A time of entry is assigned to each land-use. This is the time that it takes for stormwater to flow from the
furthest boundary of each type to the point nearest to the pit. The supplementary area drains onto the
pervious area. If the grassed area does not extend to the pit, a lag time is specified to account for the
time taken for this grassed area runoff to pass over the section of paved area near the pit. Times can be
calculated using the equations and guidelines presented in Section 5.3.2(d).
DRAINS User Manual
November 2014
The parameters for all sub-catchments are presented in Table 1.2. After entering values for Catchment
Cat 1, enter parameters for the four other sub-catchments. The displayed names of all should change
from '?????' to the names you provide - if not, check that the symbol for each sub-catchment touches the
symbol for the related pit.
Figure 1.23 The Sub-Catchment Data Property Sheet
Table 1.2 Sub-Catchment Data for Orange Example
Pit or
Cat 1
Pit 1
Cat 2
Pit 2
Cat 3
Pit 3
Cat 4
Pit 4
Cat 5
Pit 5
Pipe data is entered by right-clicking on pipes to open their property sheets. You need to click on the
object and not on its name, as the latter will open the dialog box (illustrated later in Figure 3.19) that
defines the information shown in the Main Window. Figure 1.24 shows the sheet for the first pipe.
It is not necessary to specify invert levels or slopes because DRAINS will calculate these during the
design. You must, however, specify the pipe name, length and type, selecting the type from a list box. (If
you have inserted a background, pipe lengths can be automatically scaled after the first length is
entered.) You can also take the lengths of the remaining pipes from Table 1.3.
When you close the property sheet, you will find that the pipe name is prefixed with '??', indicating that
the data are still incomplete.
Overflow routes are the next components to be defined. You must define a name and an estimated time
of flow, as shown in Figure 1.25, and you must also define overflow route cross-sections from the
overflow route data base, with slopes and percentages of downstream sub-catchments, as shown in
Figure 1.26.
DRAINS User Manual
November 2014
Figure 1.24 The Pipe Property Sheet – Page 1
Table 1.3 Pipe Data for Orange Example
Length (m)
Pipe 1
Pit 1
Pit 2
Pipe 2
Pit 2
Pit 3
Pipe 3
Pit 3
Pit 5
Pipe 4
Pit 4
Pit 5
Pipe 5
Pit 5
Figure 1.25 The Overflow Route Property Sheet - Page 1 (Top Portion)
(Note that Figure 1.25 may include additional data entry boxes if the storage routing or premium
hydraulic model options are available. Only the information shown above is required in the Orange
example.) The overflow route information for this example is shown in Table 1.4.
The percentages of downstream areas are used to define flow characteristics along the overflow route, as
explained in Section 2.3.6.
DRAINS User Manual
November 2014
Finally, the outlet names and levels must be defined. Here it is assumed that the main outlet operates as
a free outfall. The tailwater level for the pipe system will be the higher of the normal and critical depths
for the outlet pipe, unless this is running full. Outlet surface levels are specified in Table 1.1.
This adds a percentage of the sub-catchment flow
at the downstream pit to the overflow rate, allowing
flow characteristics to be calculated at points all
along the overflow route
Figure 1.26 The Overflow Route Property Sheet - Page 2
Table 1.4 Overflow Data for Orange Example
Travel Time
% of D/S
Flow Path
Slope (%)
OF 1
Pit 1
Pit 2
OF 2
Pit 2
Pit 3
OF 3
Pit 3
Outlet 3
OF 4
Pit 4
Outlet 2
OF 5
Pit 5
Outlet 1
As these changes are made, you should periodically save the file and tidy it up so that it looks like the
arrangement in Figure 1.28. If you have Property Balloons switched on in the View menu, details of the
data for various components can be seen without opening property sheets.
(a) Running the Program
You can now run the program in Design mode from the Run menu, shown in Figure 1.27.
After a Design run, the message in Figure 1.29 appears advising that the process is complete and that
you should run an analysis with minor or major storms to assess the results. You can do this my
choosing the Analyse minor storms and Analyse major storms options. The standard hydraulic model
is available in all DRAINS model. The optional, premium model requires more detailed information on
overflow routes, in order to model them with unsteady flow hydraulics.
DRAINS User Manual
November 2014
When performing an analysis, DRAINS is likely to display the message shown in Figure 1.30.
Figure 1.27 Run Options
Figure 1.28 Orange Drainage System Ready to Run (with Property Balloon shown)
Figure 1.29 Run Completion Message
Figure 1.30 Multi Core Processing Query
DRAINS User Manual
November 2014
If you agree, DRAINS will display the Project Options property sheet (Figure 1.12) in which you can click
the box titled Enable multi core processing to reduce the processing time. Whatever choice is made,
the analysis run proceeds, and a report is displayed after it finishes, as shown in Figure 1.31.
Figure 1.31 The Result of a Design Run and Minor Storm Analysis
After you close this window you will see that the names of components have changed to coloured
numbers as follows:
the black numbers are the maximum flowrates from the sub-catchments, in m3/s,
the blue numbers are the greatest flowrates in each pipe, in m3/s,
the red numbers are the greatest overflows from pits, in m3/s, in the standard hydraulics model, or
the flowrates at the centre of an overflow path in the premium hydraulic model (which will include any
flows from the downstream sub-catchment),
the green numbers are the highest levels reached by the hydraulic grade lines (HGLs) throughout
the pipe system, in m elevation, defining the highest water levels during the 2 year ARI, 25 minute
storm event considered. (At sag pits, the highest surface ponding level is also shown.)
Since it calculates conditions at a number of time intervals, DRAINS produces hydrographs or time series
of runoff flowrates from the rainfall hyetographs. It is possible to view what happens at all times during
the storm event, as shown in Figure 1.32.
(a) Reviewing Results
You can now inspect the results and check the pipe inverts and sizes determined by DRAINS. There are
a number of ways of doing this, the most comprehensive being the transfer of information to a
spreadsheet using options within the Edit menu. The data spreadsheet for the Orange Example is shown
in Figure 1.33.
Results of particular runs of DRAINS can also be exported to worksheets using the Edit menu, as shown
in Figure 1.34. These can be, for example, minor and major storm results from design procedures.
The major/minor system is usually employed in Australian drainage design. Pipes are sized to carry flows
of a minor ARI, from 2 to 10 years, and a check is made to ensure the safe working of the system during
a major storm event, with an ARI of about 100 years.
So far, DRAINS has performed the design, determining pipe sizes and invert levels. You can now also
perform an analysis using the 100 year ARI, 25 minute rainfall pattern. Simply run Analyse major
storms from the Run menu to produce the results shown in Figure 1.35.
DRAINS User Manual
November 2014
In all DRAINS runs,
tables of results are
available as well as
Figure 1.32 Hydrograph and Hydraulic Grade Line Results for a Minor Storm
Data for
Pits and
Data for
Figure 1.33 Spreadsheet Output for Data
The flowrates are now larger and some overflows occurring. These can be inspected using the Cross
Section Data page of the Overflow Route property sheet, as shown in Figure 1.36. With the standard
hydraulic model, these characteristics are based on normal depth calculations (The premium hydraulic
model calculations apply a more rigorous and accurate unsteady flow analysis.)
The suitability of the overflows during minor or major storms can be assessed and the system enlarged if
flow characteristics such as widths exceed acceptable limits.
DRAINS User Manual
November 2014
Results for Pits
and Nodes
Figure 1.34 Spreadsheet Output for Minor Storm Results
Figure 1.35 Analysis Run Results for a Major Storm
(a) Saving Data and Results
This last step involves the storage of results. The input data is all stored in the DRAINS data file
Orange2.drn. There is plenty of opportunity to make comments, in the spaces provided in the property
sheets for individual components, and in a Description … option in the Project menu.
The spreadsheet results can also be stored, and, as is detailed in Chapter 3, it is also possible to transfer
the results via a DXF file to drawing programs that can print plans and longitudinal cross-sections of pipe
systems. Additional results from analysis runs are shown in Figure 1.37
DRAINS User Manual
November 2014
Figure 1.36 Overflow Route Property Sheet, showing Flow Characteristics
Figure 1.37 Long-Section Display for a Pipe showing 2 Year and 100 Year ARI Results
The pipe design is performed on the basis of the allowable flow along the overflow route. The method
determines this flowrate, taking into account the flows from of the sub-catchment immediately
downstream of each pit. It then works backwards to define a set of pit inlets and pipe sizes that will limit
overland flows to safe levels in both minor and major storms. Safety requirements are defined in terms of
flow depths and velocity-depth products in the Overflow Route Data Base, as shown in Figure 1.26.
Running the Rational Method and Extended Rational Method Models
To illustrate the rational method procedure, the same Orange system can be modelled using a rational
method hydrological model in the file named Orange2Rat.drn. You can run this if your hardware lock
is enabled to run the rational method, or if you are using the DEMO version.
This file can be created in the same way as the ILSAX model, but it is also possible to adapt the model to
run with the rational method procedures. Only three of the property sheets for data entry differ from those
DRAINS User Manual
November 2014
for the ILSAX hydrological model. In the setting up of project options, the Hydrological Model for a
rational method model called from the dialog box in Figure 1.5 takes the form shown in Figure 1.38.
Before you leave this
dialog box, you must
select the rational
method model here
Figure 1.38 Hydrological Model Property Sheet for the Rational Method
There are three choices on the type of rational method procedure to be used. The version from
Australian Rainfall and Runoff, 1987 is selected, as shown in Figure 1.39.
Figure 1.39 Rational Method Model Specification
The 10 year ARI runoff coefficient C10 for the pervious area is set at 0.26, based on a 10 year ARI, 1 hour
rainfall intensity, 10I1 of 37.2 mm/h entered into Equation 14.12 in Australian Rainfall and Runoff, 1987:
C10 = 0.1 + 0.0133 x (10I1 – 25).
The selection of a rational method hydrological model acts as a switch that affects other parts of the
program. When the Rainfall Data… option is selected in the Project menu, the property sheet that
appears (Figure 1.40) is different to that shown previously in Figure 1.8.
Into this sheet you can enter the minor and major ARIs you require and the corresponding design rainfall
intensities for durations of 6 minutes, 1 hour, 12 hours and 72 hours. This information is available from
Australian Rainfall and Runoff, 1987, the Bureau of Meteorology’s CDIRS procedure, or from councils’
drainage design manuals or codes. Updated information soon will be available from the Bureau of
Meteorology’s website, www.bom.gov.au.
DRAINS User Manual
November 2014
Figure 1.40 The 'Rainfall Data for Rational Method' Property Sheet
The ARR Wizard button allows this information to be obtained from nine factors that can be found from
Volume 2 of Australian Rainfall and Runoff, 1987. These are entered in the property sheet shown in
Figure 1.41. The intensities are calculated from this information, and are used to establish the full
intensity-frequency-drainage relationship used by DRAINS for rational method calculations.
Figure 1.41 Factors from Australian Rainfall and Runoff, 1987, Volume 2
The remaining property sheet that is different is for sub-catchments, shown in Figure 1.42. The rational
method does not distinguish between directly-connected and non-directly-connected impervious areas.
The paved and supplementary area percentages are added to produce a percentage impervious, and the
ILSAX model grassed area becomes the pervious area. The data that needs to be entered for subcatchments is presented in Table 1.5, and run results are shown in Figure 1.43. (The flowrates differ from
those provided by the ILSAX model in Figure 1.31. The results provided by the alternative models are
discussed in Section A.4.4 of the Appendix.)
Figure 1.42 Sub-Catchment Data Property Sheet with Rational Method
DRAINS User Manual
November 2014
Table 1.5 Rational Method Sub-Catchments
Pit or
Imperv- Pervious Imperv- Pervious
ious tc
Cat 1
Pit 1
Cat 2
Pit 2
Cat 3
Pit 4
Cat 5
Pit 5
Cat 4
Pit 4
Figure 1.43 Results of Rational Method Design Run
DRAINS also provides an Extended Rational Method (ERM) model, using many of the assumptions in the
Australian Rainfall and Runoff version of the rational method. This can use design storm patterns like
those employed by the ILSAX hydrological model. The method is described fully in Section 5.3.5.
Running the Premium Hydraulic Model
The unsteady flow model used in the standard hydraulic model makes allowance for the storage effects of
flows along pipes and open channels. The premium model extends this to overflow routes, allowing
accurate determination of water levels and flow characteristics during large storm events.
Some additional data is required for premium hydraulic model calculations. This is revealed when you
attempt to run an existing model such as the Orange2.drn with premium model calculations, using the
second or third options in the Run menu in Figure 1.27. For each overflow route, a route length must be
specified in addition to the travel time in the Overflow Route property sheet, as shown in Figure 1.44.
Figure 1.44 also shows the entry of required invert levels at the beginning and end of the overflow route.
You can enter this yourself, or allow DRAINS to provide values at the start of a run, checking these later.
The remaining issue is to specify outlet controls at sag pits. These are usually weirs representing barriers
such as road crowns or centrelines. Only one sag pit occurs in the Orange2 - premium. Drn model,
and the control will be modelled as a parabolic weir, as shown in Figure 1.45.
In Step (b) of the process of setting up a DRAINS model, the other data, for pits, pipes overflow routes
and nodes, is entered in the same way as for runs using the ILSAX hydrological model.
DRAINS User Manual
November 2014
Figure 1.44 Overflow Route Property Sheet for Premium Hydraulic Model Calculations
Figure 1.45 Specification of Overflow Weir for a Sag Pit
In Step (c), when a Design run is made and followed by an analysis, the results appear similar to those
obtained with the ILSAX hydrology, as shown in Figure 1.43. A difference is that only peak flows are
generated, rather than a full hydrograph, as shown in Figure 1.32 and Figure 1.35, so that detention
storages cannot be modelled using the rational method.
Steps (d) and (e) proceed in the same manner as with the ILSAX hydrology. An Analysis run can be
made to determine major storm effects, but this will not be as accurate as major system results derived
using hydrographs in the ILSAX model.
The run proceeds, with DRAINS adding invert levels for overflow routes. The cross-sections and
roughnesses specified for overflow routes are used with the lengths to performing routing calculations
that will usually reduce flowrates. A more detailed modelling of sag pit storages will add to this effect.
Results for the Orange examples are shown in Figure 1.46. It is possible to plot long sections for
overflow routes, determining flow characteristics along these.
An animation (Figure 1.47) of the changing HGL levels in a selected part of the system can also be run
from premium hydraulic model results.
DRAINS User Manual
November 2014
Figure 1.46 Results from Premium Hydraulic Model for a Major Storm
Figure 1.47 Animation of Flow Along Main Line of Orange System in a Major Storm
Running Storage Routing Models
Storage routing models can be implemented using many of the same features and processes used with
the ILSAX and rational method programs. To illustrate this, consider the RAFTS Model shown in Figure
1.48, modelling a hypothetical creek at Shepparton, Victoria.
This rural catchment has been divided into four sub-areas, and a RAFTS model has been superimposed
on this. The four sub-catchments shown by the symbol
are sites where conversions from rainfall to
runoff and routing processes occur. Routing can also occur, if required, in the stream routing reaches
(shown dashed).
DRAINS User Manual
November 2014
Figure 1.48 Shepparton RAFTS Model
Loss information and the routing parameter BX are entered in the hydrological model property sheet
shown in Figure 1.49. Rainfall data is entered in the same way as for ILSAX models. Property sheets for
a sub-catchment and a stream routing reach are shown in Figure 1.48 and Figure 1.50.
Figure 1.49 RAFTS Hydrological Model Property Sheet
The stream reach property sheet offers a choice of translation of the hydrograph (movement of flows
without changing the hydrograph shape) or an approximate routing procedure based on kinematic wave
hydraulic principles.
A name must be entered for nodes, but surface levels are not required, as the routing is not tied to
particular elevations or datum levels. Detention basins and completely-defined open channels can be
added if desired.
DRAINS User Manual
November 2014
Results from a major storm run involving four storms of different durations are shown in Figure 1.51.
The black numbers at the sub-catchments represent the routed sub-catchment flows, while the pairs of
red numbers represent the peak flowrates at the top and bottom ends of a reach. Hydrographs can be
examined easily and data can be transferred to a spreadsheet.
Figure 1.50 RAFTS Stream Routing Reach Property Sheet
Figure 1.51 Results of Storage Routing Run
DRAINS User Manual
November 2014
This chapter presents the options and tools that are used to create and tailor DRAINS models. Drainage
systems can be created with the tools on the Toolbar, or can be partially imported using menu options.
With optional modules covering rational method, storage routing, GIS transfers, GIS transfers, and
premium hydraulic modelling, there are different forms of some menus and property sheets to those
described here.
These facilities are explained in the following sections together with the data bases that store information
on hydrological models, rainfall patterns and components such as pits. The exposition is detailed and
systematic, and is likely to be boring unless you check through each item using the DRAINS
demonstration examples, or if you have a hardware lock to run the program fully, the example file
Toowoomba Estate. Drn, shown in Figure 2.1.
Figure 2.1 Hypothetical Toowoomba Example
The Menu Bar
DRAINS employs seven drop-down menus opened from the items in the menu bar:
The broad functions of each menu are described below. You will find material on individual functions in
other parts of this manual. Refer to the index for the locations of these.
The File Menu
This menu controls most ways of inputting and outputting data. The functions of creating new files,
opening and closing stored files, saving and 'saving as' files, and exiting are carried out using standard
Windows procedures. Through the additional menus shown below, called through the Import ► and
Export ► options in the File menu, information can be taken in and out of DRAINS in various file
formats, which are covered in detail in Chapters 3 and 5.
DRAINS User Manual
November 2014
If a DRAINS model already has a background, the first
option in the File → Import ► option will be
Import DXF background… instead of Import DXF file...
in a new model. This enables the background to be
changed or updated.
The Edit Menu
This contains functions like Undo and Redo, and Find facilities for
locating components in large drainage networks.
The commands for transferring data and results to and from
spreadsheets are also included here.
The Project Menu
This menu accesses information for the particular drainage system
being analysed by DRAINS, as well as the pipe, pit and overflow
route data bases.
It also allows a new data base to be loaded as the standard data
The View Menu
This menu provides options for
viewing data and results in
different ways.
It controls what is shown in the
Main Window. See Section 3.3
for a description of the options.
The Draw Menu
This duplicates the Toolbar choices.
Selecting an option has the same effect as
clicking on a button in the toolbar.
DRAINS User Manual
November 2014
The Run Menu
This includes various options for making runs, and for
varying these. Depending on circumstances, this menu
can take different forms, the first, shown to the right, being
for new models.
For models created prior to December 2010, it is also
possible to run with the obsolete basic hydraulic model,
which has been replaced by the standard model.
The run menus for rational method models and for storage
routing models will be less complicated than those
The Help Menu
This contains an access point to the Help system through the Contents
option, and also identifies the version of DRAINS and allows the
capabilities set by the hardware lock to be upgraded using passwords.
Where an item in a menu list is followed by '…' or ' ►' it opens another
menu, a dialog box or property sheet.
Tools and Associated Components
DRAINS provides 21 buttons in the Toolbar:
The first four buttons are for creating a new file, opening an existing file, saving a file and printing the
Main Window, duplicating functions in the File menu. The last two buttons are the Zoom Factor function
that is also available in the View window, and the Pan function.
The remaining fifteen buttons can be used to draw components in drainage systems in the Main Window.
The first group of five are all nodes or junctions; the next group of nine are links, and the remaining subcatchment button provides a source of water as runoff derived from rainfalls. If you hold your mouse
arrow over each button, a ScreenTip will appear to indicate its function.
Clicking on these buttons changes the cursor from an arrow to a pencil, which is used to place
components in the Main Window. Holding down the Shift key while entering a component retains the
pencil cursor after you have entered a component, allowing you to add another component of the same
type. If you become 'stuck', with the cursor still in pencil form when you no longer want to enter a
component, simply enter the component and then delete it.
Components should connect properly. The ends of links should be placed near the centre of nodes, and
sub-catchments should clearly connect to pits and nodes. Sub-catchments must not be placed over pits,
or overflow routes over pipes, as it will be difficult to select particular components later. The layout should
be tidy, to enable components to be viewed and accessed easily. Names and positions of components
can be shifted to clarify the layout.
A background layer imported as a DXF file from a CAD program, as described in Section 3.2.2, or as part
of the importation of GIS files (Section 3.2.4), provides a guide for locating pits and other components.
DRAINS User Manual
November 2014
Behind each of the components provided in DRAINS is a computer algorithm (logic + equations + data)
that is employed within calculation frameworks. There are often alternative ways to describe the
operations of components such as pits or detention basins. When performing analysis work with
DRAINS, you should assess the methods and equations used in the program (detailed in Chapter 6) and
examine results, to confirm that the program operates as you expect.
You may encounter situations that are not fully described by the standard components, such as a
complex system of detention basins. It will then be up to your judgement and modelling skills to use the
available tools to describe the situation. This may involve 'tweaking' of the model. An example of this
type of manipulation is the use of detention basins to simulate stormwater infiltration systems or pumps,
as noted in Section 2.3.7.
The following sections describe the features of each component, starting with those that you are likely to
use most frequently.
(a) General
Pits, like other forms of node, act as entry points for water into the pipe system. They can represent a
street gully pit, a manhole, a junction, a flow diversion or other components.
On-grade pits are located on slopes, while sag pits are in hollows or depressions, as shown in Figure 2.2.
When stormwater runoff reaches an on-grade pit, at smaller flowrates all flows are collected. As
approach flowrates increase, a point is reached where some bypass flow occurs. This will flow away from
the pit, perhaps to another pit downstream, with additional flows joining it along the way. To model ongrade pits, a relationship between the approach flow and the flow captured by the pit must be specified.
These cannot be established by theory and are usually determined from modelling studies or tests on
installed pits, as is discussed further in Section 5.5.
Figure 2.2 On-Grade and Sag Pits
(b) On-Grade Pits
The Drainage Pit property sheet can take two forms, depending on the type of pit selected.
The on-grade pit property sheet, shown in Figure 2.3, requires the following inputs:
a pit name of up to 10 characters (including blanks);
a surface elevation (m) (This can be arbitrary, but it is recommended that you work with a standard
datum such as Australian Height Datum (AHD).);
a pit family and size, defined using drop-down lists linked to inlet capacity information set up in the
Pit Data Base, as described in Section 2.4.6. (A pit type must be established in the Pit Data Base for
all the pit families used.);
a dimensionless pit pressure change coefficient for full pipe flow, which defines the change in the
hydraulic grade line (HGL) at a pit, due to turbulence and other effects. (Pit pressure changes are
explained in Section 0 and DRAINS offers methods for automatically calculating these. Some typical
values are presented in Table 2.1.)
DRAINS User Manual
November 2014
Figure 2.3 Drainage Pit Property Sheet for an On-Grade Pit - First Page
Table 2.1 Approximate Pit Pressure Change Coefficients, ku
Type of Pit
Pit at the top of a line
Pit with a straight through flow, no sidelines, no grate inflow
Pit with a straight through flow, no sidelines, 50% grate inflow
Pit with a right angle direction change, no sidelines
Pit with a straight through flow, one or more sidelines
Pit with a right angle direction change from two opposed inflow pipes
On this property sheet there is also a check box with the label 'Pit has bolt-down impermeable lid' that
allows pits to be sealed, and the HGL may rise above the surface. A sealed pit cannot accept flows at the
surface, and cannot overflow.
In the sheet there is also provision for specifying blocking factors, default values of which can be set in
the Options property sheet opened from the Project menu as shown in Figure 1.12. The inlet capacity
calculated from the relationship obtained from the Pit Data Base is multiplied by 1 minus the blocking
factor. Thus a factor of 0.2 will reduce the inlet capacity or capture rate by 20%. More restrictive blocking
factors are usually applied for sag pits than for on-grade pits. Values of 0.5 for sag pits and 0.2 for ongrade pits are typically used, though the latter in particular is questionable.
On the second page with the tag ‘QUDM’ shown in Figure 2.4, you can nominate whether the pit is
aligned or misaligned and to provide the pit wall width (in mm) at the location of the outlet pipe. (This is
only required if you wish to apply the QUDM Chart procedure to define pit pressure change coefficients.
DRAINS User Manual
November 2014
Information for QUDM
determination of pit
pressure coefficients
Figure 2.4 Drainage Pit Property Sheet for an On-Grade Pit - Second Page
The original blockage calculation process in DRAINS simply multiplied the inflow capacities for an ongrade pit by a constant blockage factor. The same percentage reduction applied for low and high
approach flows. The blocking theory that is now applied results in a lower reduction at low approach
flows and an increasing blockage effect with increasing flowrates, up to the specified factor. An further
explanation is shown in Figure 2.5.
Figure 2.5 Inlet Capacity Relationships allowing for 0.5 (50%) Blocking Factor
In older DRAINS models the method to be applied could be set in the Options property sheet (
Figure 1.12
A pit can be excluded from the design process using the This pit is buttons at the bottom left of the
property sheet.
(c) Sag Pits
For sag pits, the Drainage Pit property sheet appears as shown in Figure 2.6. It is necessary to enter the
same information as for an on-grade pit, with additional data required for water that might form a pool
over the pit. It is necessary to specify the maximum ponded depth and the corresponding volume of
ponded water over the pit.
DRAINS User Manual
November 2014
for sag pit
Information for QUDM
determination of pit
pressure coefficients
Figure 2.6 Drainage Pit Property Sheet for a Sag Pit (Upper Part)
DRAINS will make the ponding area overflow if the water depth exceeds the maximum ponded depth
specified in the pit property sheet. Where two sag pits are connected by an overflow route, the overflow
level of the upper one (its surface level + ponding depth) should be higher than the overflow level of the
lower pit, as shown in Figure 2.7. Otherwise, in basic and standard hydraulic model calculations,
DRAINS will have overflows going 'uphill' and will display a warning message, either prior to running a
model, or in the report at the end of a run.
Between On-Grade
and Sag Pits
Pit A/5
Overflow Level
Between Sags
Sag Pit
Sag Pit
Figure 2.7 Relative Overflow Levels
The overflow level of a sag pit is below the surface level of an on-grade pit that overflows to the sag pit,
otherwise messages regarding uphill overflows will appear. In reality, on-grade pits may be submerged
by ponding over a nearby sag pit, as is the case in Figure 2.7.
(d) Baseflows and Direct Hydrographs
As well as receiving surface flows, a pit can receive a constant baseflow or a user-provided inflow
hydrograph, specified using the buttons at the top of the Drainage Pit property sheet. These can be
introduced at the surface or inside the pit. Flows introduced inside the pit are not subject to the pit inlet
capacity relationship.
DRAINS User Manual
November 2014
When the Baseflow… button is clicked, the property sheet shown in Figure 2.8 appears. Only a single
flowrate is entered.
Figure 2.8 Baseflow Property Sheet
When the Inflow Hydrograph… button is clicked, the window shown in Figure 2.9 is opened.
To specify a hydrograph a set of hydrograph ordinates, or flowrates at particular times, must be entered in
the text boxes labelled 'Time (mins)' and 'Flow (cu.m/s)'. The graph assists the entry of data by providing
a visual guide. Specific ordinates can be located and altered using the arrows in the spin box associated
with the times.
Figure 2.9 User-Provided Inflow Hydrograph for Pits
Hydrographs can also be entered from a spreadsheet. You must prepare two columns in a spreadsheet
program such as Excel, one containing times at fixed intervals in minutes, starting at zero, and the other
containing the values of flowrates in m3/s. You then select these columns and copy them to the
Clipboard. Switching from the spreadsheet program to DRAINS, you can then open the Pit Inflow
Hydrograph property sheet and import the data by clicking the Paste button.
The presence of baseflows or input hydrographs is not obvious when models are inspected. They can be
located by exporting the data to a spreadsheet, as shown in Section 3.5.4, and inspecting the pit and
node data. Columns I and P of the spreadsheet output (Figure 1.33) show the values of baseflows and
the presence of direct hydrographs.
Simple Nodes
The most basic type of node, called a simple node, can be used for several purposes:
to represent an outlet,
to act as a junction linking reaches in an open channel drainage system,
to provide a junction for stream reaches in a storage routing model,
to act as a closed, no-loss junction in a pipe system, and
DRAINS User Manual
November 2014
to provide a joining point for sections of overflow routes.
DRAINS detects whether a node is at an outlet to a system, and if so, it presents the property sheet
shown in Figure 2.10. As explained in Chapter 5, for part-full pipe flows DRAINS projects hydraulic grade
lines upstream through a drainage system. If a free outfall is specified, the starting point for this upwards
projection at each time step is the higher of the pipe’s normal and critical depths for the current flowrate.
If a tailwater level higher than these depths is specified in the Outlet Node property sheet, this becomes
the starting level.
Figure 2.10 Outlet Node Property Sheet
Intermediate nodes connecting pipes, open channel systems and overflow routes appear as shown in
Figure 2.11, with a surface level required. Nodes that link stream routing reaches in a storage routing
model have the same property sheet, but no surface level is required, only the node name.
A baseflow or user-provided inflow hydrograph can be entered at each node, by clicking on the
corresponding buttons in the node property sheet. This will open property sheets similar to those in
Figure 2.8 and Figure 2.9.
Figure 2.11 Property Sheet for an Intermediate Node
The Pipe property sheet shown in Figure 2.12 requires, as a minimum, that you enter a name, length and
number of parallel pipes (default value 1), and specify a pipe type from the drop-down list box.
DRAINS User Manual
November 2014
This only
appears for the
outlet of a
detention basin
or the last pipe
in a network
This only
appears for the
last pipe in a
Figure 2.12 Pipe Property Sheet
This information is sufficient for a Design run, in which DRAINS will specify the pipe diameter and invert
levels. The pipe type chosen must be defined beforehand in the Pipe Data Base located under the
Project menu options. Pipe lengths can be scaled from coordinates if the system is drawn to scale.
Rectangular pipes can be used, though not for design, and minimum pipe diameters can be set for design
in the manner described in Section 2.4.5.
If the pipe’s characteristics are already known, its diameter and invert levels can be specified. If it is not
to intended to change these in a Design run, the second or third choices in the ‘During Design runs’ box
should be selected. The fourth choice only applies to the last pipe in a network. It allows the system to
be designed to match a specified pipe invert level at the outlet, even if this violates constraints on the
minimum allowable pipe cover and minimum slope.
The Survey Data… button at the bottom of the sheet opens the property sheet shown in Figure 2.13.
Figure 2.13 Survey Data Property Sheet for Defining Intermediate Levels along a Pipe Line and
Positions of Services
DRAINS User Manual
November 2014
Surface levels can be entered at given chainages along the line of the pipe, so that the design procedure
can allow for minimum cover all along the pipe. Intermediate points can be plotted in a long-section
drawing, as shown in Figure 2.14. This property sheet also allows the positions of other services to be
defined so that DRAINS can avoid these (allowing for a vertical clearance defined in the Options…
property sheet in the Project menu, as shown below.
In Design runs, DRAINS tries to locate pipes between services, going under them if no other route is
possible. If this is unacceptable, the designer can selectively remove services, or make manual
adjustments to the pipe cross-section and/or alignment.
The long section display in Figure 2.14 shows how the ground levels and service positions appear after a
Design run is carried out, using the Long Section option in the pop-up menu for the pipe. The position of
the pipe is defined by the intermediate low point in the surface. The pipe fits comfortably under the
services, shown in red, and the required clearance, shown in yellow.
Intermediate Survey
Points on Surface
Surface Ponding
Level at a Sag Pit
Figure 2.14 Pipe Long Section Display
In some cases, a non-return device such as a flap gate may be installed in a pipe, preventing flows from
moving upstream. This can be modelled by ticking the Include Non Return Valve box in the Pipe
property sheet.
ILSAX Model Sub-Catchments
The form of the property sheet for a sub-catchment depends on the hydrological model defined in the
Hydrological Models… option in the Project menu, as shown in Figure 1.4 and Figure 1.5. If an ILSAX
type model is chosen, the sub-catchment can be divided into the paved, grassed and supplementary
land-surface types illustrated in Figure 2.15:
paved area (impervious areas directly connected to the drainage system),
supplementary areas (impervious areas not directly connected to the drainage system), and
grassed areas (pervious areas, which can be lawn, bare earth, landscaped areas, bushland, porous
pavement or any other pervious surface).
The supplementary area models any impervious surfaces that drain onto pervious or grassed areas,
where the runoff might be absorbed into the soil. These could be sheds, swimming pools, parking lots
DRAINS User Manual
November 2014
and other impervious areas that do not drain through pipes or over impervious surfaces to the subcatchment outlet.
In the original specification of these land-uses in the ILLUDAS Model, Terstriep and Stall (1974) defined
them using the diagrams in Figure 2.16. These indicate that the supplementary area was used to model
systems where downpipes discharged directly onto grassed areas. Thus, this feature can be used to
model certain water sensitive urban design (WSUD) options.
Figure 2.15 ILSAX Catchment Model Land-Use Types
Figure 2.16 Original Definition of Land Use Areas for ILLUDAS Model
The full form of the Sub-Catchment property sheet for the ILSAX Model is shown in Figure 2.17, with the
more detailed data option chosen in the check boxes labelled Use.
Figure 1.23 in the previous chapter displayed the abbreviated data option. In both this and the more
detailed data option, you must enter the total area in hectares, and the percentages of the three land-use
categories that make up the total area. The detailed option in Figure 2.17 requires additional information
to establish times of entry using different flow-path components, applying the kinematic wave equation
described in Section 5.3.2(d).
DRAINS User Manual
November 2014
This can be the
sum of constant
times for one or
more flow path
A flow time can be calculated from
these three inputs. This varies with
the mean intensity of each rainfall
pattern. It is added to the constant,
additional time.
Figure 2.17 Sub-Catchment Data Property Sheet
For each of the three land-uses, there are two flow components – a constant component and a kinematic
wave calculation component. A typical flow path is shown in Figure 2.18, consisting of:
Figure 2.18 Flow Paths to a Pit
a constant time for the segment from the roof of the furthest building in the sub-catchment to its
property boundary (usually 1 minute for a new property drainage system or 2 minutes for an older
one with possible blockages),
a time to be calculated by the kinematic wave equation for the overland flow segment, using the
specified length, slope and surface roughness n*, and
DRAINS User Manual
November 2014
a street gutter or channel segment (where a flow time can be calculated from an estimated velocity
along the gutter).
Times (a) and (c) can be added to form the constant time in the property sheet.
A lag time can be used to delay the grassed are area runoff hydrograph by a time representing the travel
time of runoff over an area of impervious surface between the lowest point on the grassed surface and
the pit or node at the catchment outlet. This is illustrated in Figure 2.19. It might be used to model a
constant flow time along a street gutter or channel.
Figure 2.19 Explanation of Lags
(b) Rational Method Sub-Catchments
The property sheet has a very similar format to the ILSAX model sub-catchment property sheet, the main
difference being that sub-catchments are being divided into pervious and impervious areas, instead of
paved, supplementary and grassed. An example is shown in Figure 2.20.
Figure 2.20 Rational Method Sub-Catchment Property Sheet
DRAINS User Manual
November 2014
The sheet is similar for the three available types of rational method model (General, Australian Rainfall
and Runoff, 1987, and Standards Australia AS/NZS 3500.3:2003). The only difference is the need to
enter roofed percentages for the AS/NZS 3500.3 method.
If a DRAINS model is converted to a rational method model, the paved and supplementary area
percentages will be added to form the impervious area percentage. The impervious area constant time
will be the paved area constant time and the pervious area constant time will be the grassed area
constant time. With the current version of DRAINS, no adjustments are made for supplementary area
times or for grassed area lag factors. If allowance is to be made it will have to be done for each subcatchment individually.
(c) Extended Rational Method Sub-Catchments
The property sheet used is the same as that for the rational method, as shown in Figure 2.20.
(d) Storage Routing Model Sub-Catchments
The three storage routing model described in Section 5.4, RORB, RAFTS and WBNM, require different
inputs, due to their different structures and parameters.
Figure 2.21 shows a RORB sub-catchment input. Since no routing calculations occur in a RORB subcatchment in DRAINS, only the sub-catchment area and impervious area percentage are required.
Figure 2.21 RORB Model Sub-Catchment Property Sheet
The sheet for a RAFTS sub-catchment shown in Figure 2.22 requires more information. In addition to
catchment area and percentage impervious, a sub-catchment slope and a Manning's n for the pervious
portion of the catchment are required to calculate hydrological losses and to define a routing parameter.
Figure 2.22 RAFTS Model Sub-Catchment Property Sheet
DRAINS User Manual
November 2014
The property sheet for the Watershed Bounded Network Model (WBNM), shown in Figure 2.23, is the
same as that for the RORB Model. However, routing does occur in WBNM sub-catchments, using
equations based on the sub-catchment area.
Figure 2.23 WBNM Model Sub-Catchment Property Sheet
(e) Customising Storms
The Customise Storms button near the bottom of the ILSAX model Sub-Catchment property sheet
allows special features to be chosen, using the property sheet shown in Figure 2.24. These features are
useful in special studies involving gauged rainfall and flow data, or where you wish to explore the effects
of varying the rainfall intensity, pattern and timing of storms over the catchment area.
Figure 2.24 Property Sheet for Customising Storms
You can select a particular storm to apply to this sub-catchment, in Design or Analysis calculations. The
storm is selected from the rainfall pattern data base using the list box shown. A time lag can also be
specified and the storm patterns can be multiplied by a constant rainfall multiplier. These allow for the
following situations:
Areally-varying intensities across a catchment with the same storm pattern can be modelled by
setting up a rainfall pattern in the Storm Data Base for each intensity used and selecting appropriate
ones for each sub-catchment. A simpler alternative is to set a suitable multiplier for each subcatchment in the property sheet shown in Figure 2.24.
Varying storm patterns across a catchment can be modelled in the same way, by selecting patterns
from the data base that apply to each sub-catchment, and applying multipliers if necessary.
A moving storm can be described by specifying different lag times for the start of the storm for each
DRAINS User Manual
November 2014
These options allow you to specify a different rainfall pattern and intensity at every sub-catchment in a
drainage network. They can be used to model climate change effects.
Overflow Routes
(a) General
These paths define the routes taken by stormwater flows that bypass on-grade pits and/or overflow from
pressurised pipe systems. DRAINS uses this information to calculate flow characteristics along the
routes. The property sheet takes different forms depending on the hydraulic model being enabled. Three
different routing processes may be involved:
translation (shifting of a hydrograph by a time lag without changing its shape), employed in the
standard and obsolete basic hydraulic calculations,
kinematic wave calculations, employed in stream routing channels with RAFTS storage routing
full unsteady flow modelling, employed in premium hydraulic model calculations.
Overflow routes between pits or nodes can be divided into a number of overflow route segments,
separated by nodes. They can also combine at a node, as shown below:
A path made of two or more segments can have differing cross-sections, slopes, etc. In premium
hydraulic model calculations DRAINS traces a HGL through these segments, defining a backwater curve
on mild slopes.
(b) Basic and Standard Hydraulic Model Inputs
With the standard or obsolete basic hydraulic models, clicking on an overflow route opens a two- or
three-page property sheet . As shown in Figure 2.25, all that is required on the Basic Data page is a
name and an estimated time of travel,. During calculations, any overflow hydrographs will be delayed by
this time of travel. The information on the second, Cross Section Data page, which is the same for all
hydraulic models, is described in Section (e).
Figure 2.25 First Page of the Overflow Route Property Sheet (Top Portion)
(c) Premium Hydraulic Model Inputs
If premium hydraulic model calculations are enabled, the first page of the property sheet should have the
form shown in Figure 2.26. Rather than specifying a travel time, the length of the overflow route and
invert levels at each end of the flow path are required. DRAINS uses this with information from the Cross
Section Data page to route flows along the route.
If an overflow route leaves a sag pit, you must also specify control weir information in a third, Overflow
Weir Properties page of the overflow route property sheet, shown in Figure 2.27
DRAINS User Manual
November 2014
Time estimate
used with basic
or standard
The kinematic wave option is
only available when storage
routing calculations are
Length of overflow path,
used with basic or standard
hydraulic calculations and
with kinematic wave routing
Invert levels at the ends of the
overflow route – these only
appear if premium hydraulic
model calculations can be made.
Figure 2.26 First Page of Property Sheet for Premium Hydraulic Model Calculations
Figure 2.27 Weir Properties Page in Overflow Route Property Sheet
This is to provide a hydraulic control representing a barrier such as the crown of a road or an entrance to
a property. There are three choices on the page:
a rectangular weir,
a parabolic weir representing a vertical road alignment, and
DRAINS User Manual
November 2014
a general depth-discharge relationship that can be set up on a spreadsheet and transferred to
The rectangular weir requires a weir width (the coefficient is taken to be 1.7); the parabolic relationship
requires a depth at a given distance from the low point (as shown below), while the elevation-discharge
relationship is more general.
Since the premium hydraulic model must deal with potentially very high flowrates in 100 year ARI and
PMP storms, it models situations where there are chains of storages and overflow routes. The storages
are likely to be at sag pits, but can also occur at ponding locations that are created in large storms. The
overflow routes connect the storages. Both storages and overflow routes can be small or extensive.
A typical situation is shown in Figure 2.28. The overflow route will connect the ponded water on each
side of the street. It will begin at the road crown and end at the downstream pit.
Flow CrossSection
Figure 2.28 Flow Through a Road Low Point
During premium hydraulic model calculations, DRAINS will monitor the ponded levels in sag pits at each
time interval. When the defined ponding level, assumed to be the level at which a spill will start to occur,
is exceeded, overflow rates and ponding levels will be determined using the weir control specified in the
overflow route property sheet (Figure 2.27). DRAINS will also calculate depths of flow in the overflow
route and allow for a 'tailwater level' due to ponding downstream, if the overflow route terminates in a sag
pit or detention basin. If the water level in the overflow route is greater than the weir crest level, the weir
discharge will be reduced using a submerged weir equation, as described in Section 5.6.4.
It is important to establish pipe and overflow route levels and other details correctly. DRAINS provides a
large number of checks to detect errors, but final responsibility for the accuracy of the model remains with
the user.
(d) Kinematic Wave Routing Inputs
Overflow routes can also be used to model stream linkages in a RAFTS type of storage routing model,
with the inputs shown in Figure 2.29. If this feature is enabled your hardware lock you can model urban
overland flow paths using the kinematic wave routing procedure. While this has some advantages over
the basic calculations for overflow routes from pits, the best procedure is to employ the premium hydraulic
model if this is available.
DRAINS User Manual
November 2014
Figure 2.29 First Page of the Overflow Route Property Sheet with Kinematic Wave Routing
(Top Portion)
(e) Definition of the Flow Cross Section
On the second page, you should specify an overflow path cross-section from the Data Base set up in the
Project menu, described in Section 2.4.7. The section may be a roadway, as shown in Figure 2.30, or a
trapezoidal, rectangular or other channel shape.
Figure 2.30 Cross-Section Data Entry in Overflow Path Property Sheet
Here it is necessary to select:
a shape from the list box,
the percentage of flows estimated to come from the downstream sub-catchment, and
a flow path channel slope.
(With the storage routing model option shown in Figure 2.29, DRAINS uses the cross-section in its
kinematic wave calculations. In both procedures, it will calculate flow characteristics such as depths and
widths, assuming that normal depth occurs in the flow cross-section at the slope indicated.)
DRAINS User Manual
November 2014
DRAINS can define flow characteristics at a selected critical location, which may be at a pit receiving
overflows from this overflow route, combined with flows from its local sub-catchment. This location could
also be just downstream of the pit from which the overflow occurs. The position is effectively defined by
the percentage of the downstream catchment’s flow that is carried by the cross-section, which must be
entered into the property sheet in Figure 2.30.
Figure 2.31 shows how a downstream sub-catchment may contribute to flows. Here the critical point is
the downstream pit, which is in a sag. An estimated 65% of Catchment 2 drains to this point, on the left
side of Pit 2.
Figure 2.31 Effect of a Lower Sub-Catchment upon Overflows
If the property sheet for the overflow between Pit 1 and Pit 2 specifies a percentage of downstream
catchment of 0%, the flowrate displayed in the results will be the overflow from Pit 1. This applies to a
point just below Pit 1. If the percentage is set at 65%, the flowrate displayed will be the overflow from Pit
1 plus 65% of the flow from Catchment 2. This sum is calculated from addition of hydrographs, and
represents the flow at a point just upstream of Pit 2. By varying the specified percentage between 0%
and 65%, we can define surface flows at any point along the flow path.
Using this feature, you can examine the flows approaching pits at the top of a pipeline, as shown below.
Although the overflow routes originate from a node with no connected sub-catchment, a percentage of the
flows from sub-catchment Cat A.1 can be specified and the flow characteristics along the flow path
When applying the Design procedure, DRAINS focuses upon the flow at the point defined by the specified
percentage of the downstream catchment. This can represent a critical feature such as a child care
centre or bus stop that needs to be specially protected. (Note that this feature will only be meaningful on
long overflow routes. The flows calculated will not be accurate for short flow paths where the calculated
normal depth cannot be established and paths across streets or around corners.)
By changing the value in the box labelled 'Channel slope (%)', the slope can be varied along the entire
flow path length to reflect a concave or convex longitudinal profile, as opposed to a constant slope.
Overflow routes can be divided into several segments, linked through simple nodes. These segments
can have different properties such as cross-sections and slopes. Two or more overflow routes can be
connected to a node, and their flows combined, as shown later in Error! Reference source not found..
DRAINS User Manual
November 2014
As described in the next section, the overflow path from a detention basin acts as a high-level outlet to
the basin, and requires additional information to an overflow from a pit, this being set out on an additional
page of the property sheet.
Detention Basins
DRAINS can incorporate large or small detention and retention basins into drainage networks. To define
a basin or storage fully, at least two components are required. The first is the basin, which is defined in
the Detention Basin property sheet, an example of which is shown in Figure 2.32. This includes a basin
name, options to set an initial water level and infiltration characteristics, an elevation-surface area (or
elevation-volume) relationship, and a low level outlet specification.
Figure 2.32 Detention Basin Property Sheet
DRAINS applies as a default an elevation-surface area relationship rather than an elevation-storage
volume relationship, which will be easier for users, since volumes are calculated from surface areas in
most cases. Previously-developed models that specify volumes, shown in Figure 2.33, are still supported
in DRAINS, but both types of elevation-based relationship cannot be used in the same model. Elevationvolume relationships can be used in projects by selecting an option in the Project Options property sheet
opened from the Project menu.
When working with elevation-surface area relationships, DRAINS
employs an interpolation procedure for calculating volumes
corresponding to certain elevations, with a fitted curve rather than the
set of straight-line segments. The elevation-surface area relationship
must use levels to the same datum as the rest of the drainage network.
Relationships can be calculated in a spread-sheet and pasted into
DRAINS Using the Paste Table button. Numbers must be arranged
into two columns, as shown to the right.
These are then selected and the Edit → Copy option is used to place the data on the clipboard.
Transferring from the spreadsheet program to DRAINS, the data can be entered using the Paste Table
The Low Level Outlet Type (connecting to a pipe) option buttons offer five choices:
an orifice acting as a free outfall of the type commonly used in on-site stormwater detention (OSD)
storages in Sydney;
DRAINS User Manual
November 2014
Figure 2.33 Detention Basin Property Sheet with Elevation-Storage Relationship
a pit or sump outlet;
a circular conduit (the example shown above);
a rectangular channel, similar to the circular outlet; and
no low-level outlet.
These are then selected and the Edit → Copy option is used to place the data on the clipboard.
Transferring from the spreadsheet program to DRAINS, the data can be entered using the Paste Table
For pipes, it is only necessary to specify the entry and bend losses,
as shown in Figure 2.32. The rest of the information is included in
the property sheet for the outlet pipe. This is the same as the sheet
for a pipe located between pits, as shown in Figure 2.12 , except
that there is provision for an exit loss different from the loss of 0.0
assumed by DRAINS.
If an orifice outlet is selected, the property sheet takes the form shown in Figure 2.34. You must supply a
diameter (mm) for a circular orifice, and the elevation of its centre. The check box labelled High Early
Discharge allows the modelling of a high early discharge pit, a special type of OSD system. You must
provide a crest level and length for an internal weir that is a feature of this kind of storage. Further details
of these options are given in Section 5.8.3.
The pit/sump outlet type may apply in situations where basins are created unintentionally by the creation
of a barrier such as a road embankment. If this outlet type is selected, the outlet changes to that shown
in Figure 2.35. A pit family and size is to be selected using the same drop-down list box as in the
Drainage Pit property sheet.
Since this type of outlet is prone to instabilities in calculations where there are incoming pipes that are
below the surface of the basin, it is usually necessary to locate the basin 'off-line', connecting to a sealed
pit through a large, artificial pipe with a capacity well in excess of the inlet. An arrangement of this type is
shown in Figure 2.36. Surface overflows are directed to the basin, and the main overflow comes out of it.
The pipe leaving a basin is specified in the same way as a normal pipe. If this is rectangular, it may be
necessary to set up a special pipe type and size in the Pipe Data Base, as described in Section 2.4.5.
DRAINS User Manual
November 2014
Figure 2.34 Detention Basin Property Sheet with Orifice Outlet
Figure 2.35 Detention Basin Property Sheet for a Pit/Sump Outlet
For some basins in low-lying areas where backflows may occur, a non-return valve may be specified in
the Pipe property sheet. Only one low level pipe can exit from a detention basin, with specified invert
levels. The required size and invert levels cannot by determined in Design runs, but must be established
by trial and error using analysis runs.
DRAINS User Manual
November 2014
Figure 2.36 Arrangement for a Basin with a Pit/Sump Outlet
Where the 'basin' is a ponding area in a street with a sag pit that acts as an unintended storage, the
above method can be used with the standard hydraulic model. If the premium hydraulic model is
available, this pit should be modelled as a sag pit with a table of elevation-area values describing the
The fifth and last type of outlet is a 'None' option. If this is selected, water can only leave the basin
through a high-level outlet (to be described below), and the outflows will not be affected by downstream
hydraulic grade lines or backwater effects. If a height-outflow relationship is specified for a high level
outlet, the detention basin modelling will be carried out in the relatively simple way used in ILSAX, rather
than having HGLs projected upwards through the basin.
A new development is the provision of an in-built infiltration calculation facility on the second page of the
Detention Basin property sheet. This appears as shown in Figure 2.37.
Figure 2.37 Infiltration Data Specification
Allowance is made for a flat floor, as provided in infiltration chambers and trenches, and for walls through
which infiltration will occur when the stored water level rises above the floor level. The perimeter of the
walls at different elevations can be defined in the table. The hydraulic conductivity depends on the type
of strata through while infiltration occurs. Further information is provided in Argue (2004). Conductivities
DRAINS User Manual
November 2014
are quite small and in most cases need to be specified in scientific notation. For example, a conductivity
of 2 x 10-6 m/s can be specified as '2e-6'. DRAINS specifies these as 2e-006.
The page on the Detention Basin property sheet tagged ‘Initial
Water Level’, shown to the right, can be used to make a basin
part-full at the start of a storm. Usually it is assumed that the basin
is empty. (Use of this facility may result in some reverse flows at
the start of a storm,)
The last component required to define a detention storage is the
high level outlet, which is described in the property sheet for the
overflow route from a basin. When an overflow route originates in
a basin, the property sheet has three pages instead of the two shown in Figure 2.25 and Figure 2.30.
Two of these pages are the same as those in those figures. On the third page, labelled 'Weir Data' you
have the choice of specifying a weir outlet, as shown in Figure 2.38, or an elevation-discharge (or heightoutflow) relationship, as shown in Figure 2.39.
Figure 2.38 Outlet Definition of a Weir (Top Portion of Page)
Figure 2.39 Elevation-Discharge Table for a High-Level Outflow (Top Portion)
For a weir, you must provide a weir coefficient, a width (m) (at right angles to the direction of flow) and a
crest level (m). Further details are given in Section 5.8.2. A suitable coefficient for the earth
embankments used as high-level outlets for many detention basins is 1.7.
If used alone, the elevation-discharge relationship must be determined using equations relating to both
the low and high level outlets. If it is certain that no backwater effect can submerge the outlets, this
relationship will be constant. As noted earlier, if 'None' is specified for the low level outlet in the Detention
Basin property sheet and an elevation-discharge relationship is given in the Overflow Route property
sheet, a simplified basin routing can be applied.
DRAINS User Manual
November 2014
There can be any number of overflow routes from a basin, representing high level outlets at various
levels. Pumped discharges and stormwater infiltration can be modelled using overflow routes with
suitable water level - discharge relationships, but it is best to use the specific pumping and infiltration
methods provided.
Elevation-discharge relationships can be calculated in a spreadsheet and pasted into the Overflow Route
property sheet using the Paste Table button in Figure 2.39.
Special Weirs and Orifices
Two new components in DRAINS, the orifice,
and the weir
, are only available with the premium
hydraulic model. These facilitate the modelling of complex detention basins that have multiple orifice or
weir outlets that can connect to various outlet points with different tailwater levels. With the standard
hydraulic model, it is possible to model a single pipe or orifice-controlled outlet and multiple weirs that are
located above tailwater influences. However, it is difficult to model a second pipe or orifice even when
this leads to a free outfall. The new components make such modelling easy and accurate under complex
tailwater conditions.
Figure 2.40 shows an example named Premium Detention Basin.drn that has two orifice and two
weir outlets. The orifice and weir links can be bent or kinked to allow several links to go to a common
point. This can be done by clicking on the link, so the ‘handles’ appear at the ends, placing the mouse
pointer on the line, holding down the mouse button, and moving the pointer.
Figure 2.40 Detention Basin with Special Orifice and Weir Outlets
The property sheets for the Orifice and weir are shown in Figure 2.41.
Figure 2.41 Special Orifice and Weir Property Sheets
DRAINS User Manual
November 2014
As described in the previous section, pumps can be modelled with an overflow route coming out of a
detention basin. Howe However, this can cause problems when applying the premium hydraulic model,
and a specific pumping link has been provided.
When the tool
is selected a pump link
can be drawn. This must come out of a
detention basin and can be directed to a pit, a simple node or another detention basin. The associated
property sheet, shown in Figure 2.42, requires a level at which the pump switches on and off (relative to
the water level in the basin out of which it comes), and a table of water elevation vs. flowrate.
Figure 2.42 Specification of a Pump from a Detention Basin
The pump starts operating when the storage water level rises above 222.0 m. The pump rate increases
from 160 to 300 L/s as the water level rises to 223.5 m, reflecting the characteristic head versus
discharge relationship for the pump and the friction and shock losses through the delivery pipe. A
worksheet in the DRAINS Utility Spreadsheet (Section 3.2.3) can assist in developing an appropriate
pumping relationship, which can be imported into the Pump property sheet using the Paste Table button.
Pump links can be bent of kinked, like those for special orifices and weirs.
2.3.10 Prismatic Open Channels
The Prismatic Open Channel property sheet, shown in Figure 2.43, enables easy entry of the parameters
needed to define trapezoidal. Rectangular or triangular channels of uniform cross-section and slope.
(Rectangular channels have zero side-slope factors, and triangular channels have a zero base width.)
If calculations determine that the channel depth exceeds that specified in this property sheet, the sides of
the channel will be extrapolated upwards, and a warning message will be provided. DRAINS does not
allow for overflows from channels. In the majority of cases, where overflows will follow the same route as
the main stream channel, they can be accommodated by defining a channel cross-section large enough
to carry them. If necessary, the channel should be defined as an irregular open channel, as explained in
the following section, to include overbank flow areas.
Where an overflow from a channel will cause a breakout that follows a different path to the main stream,
special ways of modelling the separation of flows are required (see Table 2.2 in Section 2.3.17).
DRAINS User Manual
November 2014
Figure 2.43 Prismatic Open Channel Property Sheet
2.3.11 Irregular Open Channels
(a) General
This component, with the property sheet in Figure 2.44, allows you to set up stream reaches to model a
stream or channel with varying cross-sections and slopes.
It can also be used to model closed and open conduits with cross-sections other than circular, rectangular
or trapezoidal.
The information required differs between the obsolete basic hydraulic models calculations and the
unsteady flow calculations used in the standard and premium hydraulic models.
(b) Basic Hydraulic Model Calculations
It is necessary to define channel reaches over which flowrates are the same, and to define for each reach
at least two cross-sections, at the upstream and downstream ends of the reach. At each cross-section,
you must enter:
the channel name, total length and chainages or lengths of reaches along a stream; a set of X-Y
coordinates (m) that define the cross-section, with the X datum being at an arbitrary point on the left
bank of a channel, and the Y datum being Australian Height Datum (AHD) or some other standard
datum (as shown in Figure 2.45).
distances from the upstream node (m) and Manning’s roughnesses for the left overbank, main
channel and right overbank areas;
coordinate locations of the left and right banks (m), and expansion and contraction coefficients
Various features assist the entry of cross-sections. Sections can be copied and pasted. The top section
of a reach must be the same as the bottom section of the reach above it. If reaches are entered in a
downwards direction, DRAINS automatically enters data from the previous reach. Sections can be
viewed and checked using the View Cross Sections and View maximum water level profile options in
the pop-up menu for an irregular channel component, as shown in Figure 2.46.
DRAINS User Manual
November 2014
Figure 2.44 The Irregular Channel Property Sheet
Figure 2.45 Coordinate System for Irregular Channel Cross-Section (looking downstream)
(c) Standard and Premium Hydraulic Model Calculations
The same inputs as those shown in Figure 2.44 are required, with the additional information specified at
the bottom of the property sheet. The additional inputs are the invert levels at the upstream and
downstream ends of the reach, and the number of the cross section to be considered as representative of
the channel reach.
The two hydraulic calculation options use entirely different procedures. The basic method uses methods
akin to the steady flow modelling carried out by the well-known HEC-RAS program (Hydrologic
Engineering Center, US Army Corps of Engineers, 1997), in which cross-sections are required at each
end of an irregular channel.
DRAINS User Manual
November 2014
Figure 2.46 Irregular Channel Cross-Sections and Longitudinal Profiles
Like HEC-RAS, DRAINS allows cross-sections, roughnesses and bed slopes to vary along a channel,
though it is not possible to change the flowrate along a channel. This can be done by specifying two or
more irregular channels in series.
The unsteady calculations assume that each open channel has a constant cross-section and slope. This
will suit lined channels well, but for natural channels, it may be necessary to define several sections of
channel to allow for changes of cross-section.
2.3.12 Multi-Channels
The prismatic and irregular channel types do not adequately cover the situation where two or more
channels with different characteristics connect the same two points. This is handled in the basic hydraulic
calculations by multi-channels that use the property sheet shown in Figure 2.47 to call up the boxes for
prismatic or irregular channels, or a box for circular channels.
The data required is similar to that for other open channels. Conduit lengths, roughnesses, slopes and
even starting and ending levels can vary. DRAINS distributes flows between the different conduits. At
present, DRAINS does not report on the separate flowrates.
Situations requiring multi-channels occur where inadequate open drainage systems are amplified by
building a parallel channel or pipe, and where grassed floodway channels have a piped underdrain.
DRAINS User Manual
November 2014
Figure 2.47 Multi-Channel Property Sheet
2.3.13 Stream Routing Reaches
This link type, shown as
, is used with the RORB and WBNM storage routing models to connect
nodes and sub-catchments as described in Section 5.4, and to perform non-linear routing. Its exact
function differs between the two models as they have differing structures. (The RAFTS storage routing
model describes stream reaches using the same overflow routes that were used for pipe systems,
described in Section 2.3.6.)
If a RORB storage routing model is selected, the property sheet for its stream routing reaches appears as
shown in Figure 2.48. A reach name and length must be specified, and a Channel condition selected. If
a channel condition of 'excavated unlined' or 'lined or piped' are selected, it is also necessary to provide
the reach slope.
The RAFTS stream channel property sheet, shown in Figure 2.49, is identical to that for an overflow route
from a pit. A name is required, and if Simple translation (no attenuation) is chosen in the box labelled
Flow Routing Method, a travel time through the reach must be entered. With a RAFTS model, this can
be zero if a conservative result is required.
Figure 2.48 RORB Stream Routing Reach Property Sheet
DRAINS User Manual
November 2014
Figure 2.49 First Form of the RAFTS Stream Routing Reach Property Sheet (Top Part)
If the second option in the Flow Routing Method box is chosen, the property sheet changes to the form
shown in Figure 2.50. It is now necessary to provide a reach length and, using the second page of the
property sheet shown in Figure 2.51, a cross-section is to be selected from the Overflow Route Data
Base. This section is meant to be representative of the whole stream reach and to be used in a kinematic
wave routing procedure derived from Chapter 9 of Open Channel Hydraulics by F.M Henderson (1966).
Figure 2.50 Second Form of the RAFTS Stream Routing Reach Property Sheet (Top Part)
Figure 2.51 Second Page of the RAFTS Stream Routing Reach Property Sheet
DRAINS User Manual
November 2014
When run, the kinematic wave option will produce two hydrographs, at the top and bottom ends of the
reach, with a small reduction in peak flows. (As noted in Section 2.3.6, this specification can also be
applied to conventional overflow routes in piped urban drainage systems, but the premium hydraulic
model calculations are preferable.)
The WBNM stream routing reach property sheet shown in Figure 2.52 requires only a name and a stream
lag factor. When this factor is not zero, routing occurs along the reach using parameters based on the
area of the sub-catchment at the node at the end of the reach.
Figure 2.52 WBNM Stream Routing Reach Property Sheet (Top Portion)
2.3.14 Headwalls
The headwall
allows open channels to be connected directly into a pipe system, and overflows to be
directed to other locations. It is not to be used as the outlet of a pipe system, which is modelled as a
node. The Headwall property sheet is shown in Figure 2.53
Figure 2.53 Headwall Property Sheet
The overflow level entered on this sheet is critical to the operation of this component at higher flows. As
water levels increase to this level, the flow into the pipe is governed by the culvert equations described in
Section 5.8.2. Once this level is reached, the inflow is assumed to be that corresponding to the
nominated overflow level, while the headwater level (the level of the water level upstream) is assumed to
be governed by the property sheet for the overflow route provided, which takes the form shown in Figure
2.38 and Figure 2.39. Assuming the overflow rate to be the upstream flowrate minus the pipe capacity,
DRAINS calculates a flow depth based on the weir or elevation-discharge relationship, and adds this to
the overflow level to obtain the headwater level.
This process will set a headwater level that is slightly conservative, as the depth of the overflow path flow
is not considered in determining the flow through the pipe. This is necessary to avoid considerable
iterative calculations caused by the splitting of the flows and the uncertainty of the effects of changing
flowrates on the calculations for downstream pipes. An alternative way of handling this situation is by
terminating an open channel at a detention basin and starting a pipe from there.
The headwall can be used to model culverts, as described in the next section.
DRAINS User Manual
November 2014
2.3.15 Culverts
Initially, culverts were modelled in DRAINS using the Culvert component
the concentrated all the
functions of culverts into a single object. This has now been replaced by the combination of a headwall
with a pipe and overflow route, as shown in Figure 2.54, and the culvert object has been removed from
the DRAINS Toolbar. This is similar to the arrangement used for detention basins.
Figure 2.54 Culvert Constructed from Headwalls and Other Components
The inputs for these components are described in other parts of this chapter, while the inputs for the
discontinued culvert object will be described in the Help System. If the obsolete culvert object has been
used in an older DRAINS model, it will re-appear when this model is opened with the current version of
2.3.16 Bridges
The property sheet for Bridges is shown in Figure 2.55. Because of the differences in shapes, abutment
and pier arrangements and approach conditions, bridges are more complex that culverts. In DRAINS,
calculations are performed using a relatively-simple method provided in the AUSTROADS (1994) manual,
which is based on the US Federal Highway Administration report by Bradley (1970). More complex
bridge modelling procedures are available in HEC-RAS, MIKE-11 and other open channel hydraulics
programs. DRAINS results should be checked using these programs if the accurate determination of
levels is critical.
You will need to refer to the original references to understand the inputs required fully. It is necessary to
the name of the bridge, and the levels of the deck (m) and the soffit (underside of deck) (m);
the weir coefficient for overflows over the bridge deck, typically 1.7;
pier width, locations of piers (as noted in Figure 2.56), and pier type;
the abutment type and the X-Y coordinates at the bridge section (m), left overbank, main channel
and right overbank Manning’s roughnesses, and the X locations of the left and right banks that divide
the zones of different roughness (m).
With the standard and premium hydraulic models, the data shown in Figure 2.57 must be entered in the
second page of the property sheet. This provides instructions on choosing the values to be entered.
DRAINS User Manual
November 2014
Figure 2.55 Bridge Property Sheet
Figure 2.56 Pier and Abutment Locations
Figure 2.57 Second Page of Bridge Property Sheet (Top Part)
DRAINS User Manual
November 2014
This information might be obtained by running the DRAINS model without a bridge to estimate the
maximum flowrate, and inserting the bridge later. The upstream and downstream water levels can be
estimated from the level without the bridge, making the upstream level higher and the downstream level
lower. The differences might also be determined from relationships from texts or manuals.
2.3.17 Combining Components
Some arrangements of the components described in the preceding sections cannot be modelled because
they are not logical, or they create computational difficulties.
Table 2.2 describes the possible connections between nodes and links noting those that cannot be made.
The footnotes provide suggestions as to how you can get around some of these limitations. Experienced
modellers can use dummy components to model complex situations.
Table 2.2 Allowable Connections between DRAINS Nodes and Links
Link into Node from Upstream (U/S) or Downstream (D/S)
U/S - yes1
D/S - yes1
U/S - yes
D/S - yes
U/S - yes
D/S - yes
U/S - yes
D/S - yes
U/S - yes2
D/S - maybe3
U/S - yes
D/S - yes4
U/S - yes
D/S - no
U/S - yes
D/S - no
U/S - yes
D/S - no
U/S - yes
D/S - yes5
U/S - no
D/S - yes4
U/S - yes
D/S - no
U/S - yes
D/S - no
U/S - yes
D/S - no
U/S - yes
D/S - yes
Culvert object
U/S - no6
D/S - no6
U/S - yes
D/S - yes
U/S - yes
D/S - yes
U/S - yes
D/S - yes
U/S - yes
D/S - no7
U/S - no6
D/S - no6
U/S - yes
D/S - yes
U/S - yes
D/S - yes
U/S - yes
D/S – no7
U/S - yes
D/S - no7
U/S - yes
D/S - yes
U/S - no
D/S – no8
U/S - no
D/S – no8
U/S - no
D/S – no8
U/S - yes
D/S - yes
1 - If a node has pipes both upstream and downstream, it acts as a closed junction, and can be pressurised, with the
HGL rising above the surface. Generally, however, it is better to connect pipes through sealed or unsealed pits,
where a head loss can be specified.
2 - You need to be aware that nodes will accept all flows coming to them, and check whether this is realistic. Where
there are likely to be overflows, a pit should be substituted if the node is in a pipe system, and a detention basin if
the node is in an open channel system.
3 - In the standard hydraulic model, overflows are permitted from a node, but not if there is also a pipe or channel
leaving the node. For an open channel where overflows will run along the banks, you should raise the height of
the channel cross-section so that overbank areas are included. The open channel downstream will need to be
defined as an irregular open channel. Where channel overflows are to be directed out of a channel, you can
place a detention basin at the location of the low point where overflows might occur, with an elevation-storage
relationship based on the storage within the upstream channel. High-level outlets with weir data or a heightdischarge table can be used to control the overflows. The premium hydraulic model allows a channel and
overflow route to come out of the same node.
4 - Overflow links from a detention basin or headwall require more information than a normal overflow link, to define
high level outlets. It is possible to have several high-level outlets from a basin.
5 - Culverts and bridges must have open channels or routing reaches upstream and downstream. Where a road is
located at a point where stormwater emerges from a pipe, or goes from on open channel into a pipe, it is probably
inappropriate to model this situation as a bridge or culvert. If cross-sections change under road in these
circumstances, the transitions can be modelled by pipe or open channel sections.
6 - While water may pond behind a bridge or culvert, and even overflow over the top of the road, DRAINS does not
allow for any diversion of flows away from the downstream channel. This might be modelled by locating a
detention basin upstream of the device, or perhaps by modelling a culvert as a detention basin.
7 - Bridges have more restrictions than culverts in DRAINS. You cannot have two upstream channels meeting at a
bridge, as they can at a culvert. It is necessary to insert a section of combined channel upstream of the bridge.
A multi-channel cannot be placed downstream of a bridge - a short section of single channel can be interposed,
8 - You cannot have an open channel coming out of a pit. However, a short section of pipe and a simple node might
be used to link the pit and a channel.
DRAINS User Manual
November 2014
In a DRAINS Main Window, it is possible to have several, separate drainage systems. These may be
completely independent, or may be connected by overflow links. When DRAINS runs, it applies the same
rainfall and loss data to all systems, unless local options are selected in the Hydrological Model and
Customise Storms options in the Sub-Catchment property sheet described in Section 2.3.5. This
feature allows systems to be analysed together, to provide 'before' and 'after' comparisons.
The example file Sydney OSD.drn provides such a comparison for an on-site stormwater detention
system. As shown in Figure 2.58, the pre-developed catchment is set out on the lower left, and the
developed drainage system around a house and backyard occupies most of the window. These two
systems are run together using the same project specifications, allowing a direct comparison of results.
Post-development model,
with on-site stormwater
Figure 2.58 Two Drainage Systems Set Up in DRAINS for Comparison
Data Bases
By storing data about inputs and common components in five data bases that are easily accessible from
drop-down list boxes, DRAINS makes it easy to select and alter hydrological models, rainfall patterns,
pipe types, pit types and overflow route cross-sections. By referring to standardised types, the amount of
data that has to be entered into files is greatly reduced.
The role of data bases is particularly important in the DRAINS pipe design procedure. Pipes and pits are
both organised into types or families of different sizes from which the program can select.
Data bases can be set up, element by element, using the editing procedures described in the following
sections. Hydrological model and rainfall pattern data bases can be stored in template files, and
retrieved, as described in the next section. Pipe, pit and overflow route data bases can be imported
directly into DRAINS using the Default Data Base option in the Project menu (for a new project) and the
Import ► DRAINS Database (DB1) File… in the File menu (for existing DRAINS files).
Standardised Data Bases
When you start DRAINS it loads the standardised data base file, Drains.db1, located on the
C:\ProgramData\Drains folder. This contains information on pipe, pit and overflow route components
that are likely to be used in your model..
If you work in only one geographical area, always with the same hydrological model and set of storms,
this file need not change. In this case, when you first use DRAINS you should set up the storms and
hydrological model for your area, set up the pipe, pit and overflow route data bases, then save the file as
a template or base that can be used whenever you begin a new project in the area. This file should not
DRAINS User Manual
November 2014
contain pipes or other components. If you work in different locations, you will need to set up a different
template file for each geographical area.
Another way to set up a file with required data bases is to open a DRAINS file with the data bases that
are required, and then close this. The drainage system disappears, hydrological model and data bases
remain. The data for pits, pipes and overflow routes can be changed using the Project → Default Data
Base option, and editing the entries. You can then copy this file as a template file and start a new job
with a different filename.
Hydrological Models
The set ups for ILSAX, the rational method and storage routing hydrological models are described in
Chapter 1. DRAINS is structured to deal with two categories of hydrological model:
• ILSAX, extended rational method and storage routing models that produce hydrographs, developing a
time series of flowrates, and
• rational method models that produce only peak flows,
and to apply different forms of rainfall data (hyetograph patterns and intensity-frequency-duration (I-F-D
relationships) with these model types.
It is possible to develop a number of different ILSAX models, say for different soils, and to mix these in a
model. The storage routing models can be mixed with ILSAX models, although it is only possible to have
one type. You cannot mix RORB and WBNM models, for example. However, it would be possible to
create a DRAINS model that used three kinds of ILSAX model and two kinds of RORB model. The
extended rational method cannot be mixed with any other model. Three different kinds of rational method
model can be applied, as shown in Figure 2.59, and you can inter-mix these.
Figure 2.59 Rational Method Selection Property Sheets
Many models of different types can be stored in the Hydrological Model data base. The hydrological
model that is selected in the Hydrological Specifications dialog box acts as a default model that applies to
DRAINS User Manual
November 2014
all sub-catchments. However, in many cases a local model can be selected in the property sheet for a
particular sub-catchment, as shown in Figure 2.60.
Figure 2.60 Selection of a Default and a Local Hydrological Model
Rainfall Data Bases
(a) New ARR2013 Procedures
At the time of updating this manual, the Commonwealth Bureau of Meteorology and Engineers Australia
are in the process of introducing new sets of design rainfall for all of Australia, as set out in
http://www.bom.gov.au/water/designRainfalls/ifd/index.shtml, shown below:
Figure 2.61 Bureau of Meteorology Website
DRAINS User Manual
November 2014
Rather than recommending that the new design rainfall estimates be adopted in preference to the older
ones from Australian Rainfall and Runoff, 198, the initial advice from these organisations is to use these
cautiously, perhaps because these estimates are lower than the 1987 values at many locations.
Other changes are that the new intensity-frequency-duration (I-F-D) values are expressed as depths of
rainfall over a number of durations, rather than intensities, and that frequencies are defined as
exceedances per year (EY) and annual exceedance probabilities (AEPs) in %, rather than average
recurrence intervals (ARIs). It appears that this situation will take some time to sort out, so DRAINS
retains inputs for older procedures, and will accommodate the new procedures when users require these.
While the Bureau has issued new rainfall intensity or depth information, there is, as yet, no new rainfall
temporal patterns to accompany these. New patterns will not be available for two or more years, and it
appears that the only choice for designers requiring hyetographs will be to use the new I-F-D data with
the old 1987 temporal patterns.
The new design rainfall intensities can be converted to design patterns in DRAINS using the Single Entry
procedure described in Section 1.2.1(a) in Figure 1.8 to Figure 1.11. The steps required are
Define a table of rainfall depths for the design location (specified by latitude and
longitude), entering additional Standard Durations as required.
Figure 2.62 Depth-Frequency-Duration Table
For each duration, divide the depth by the duration in minutes, and multiply by 60 to obtain the
required intensity. For example, for a 20% AEP, 30 minute duration, the depth of 16.0 mm
corresponds to an intensity of 16.0 / 30 * 60 = 32 mm/h.
This needs to be applied with a 30 minute duration pattern from ARR87, which can be done applying
the procedure in Section 1.2.1(a), as shown below:
DRAINS User Manual
November 2014
Figure 2.63 Date Entry for 2013 Design Rainfall Pattern
Pressing OK will produce the required pattern. A suitable title for this 2013 interim estimate can be
This procedures needs to be repeated for each design storm pattern required.
(b) Entering Single and Multiple ARR87 Patterns
The setting up of standardised Australian patterns in the Rainfall Patterns dialog box has been
demonstrated in Section 1.2.1(a) in Figure 1.8 to Figure 1.11, with patterns being entered one by one . It
is also possible to enter multiple patterns in a single operation, using 1987 intensity-frequency-duration (IF-D) data from the Bureau of Meteorology website, www.bom.gov.au.
Multiple patterns can be entered by downloading data from the Bureau of Meteorology's site
http://reg.bom.gov.au/hydro/has/cdirswebx/cdirswebx.shtml shown in Figure 2.64, and pasting it into
Figure 2.64 Bureau of Meteorology Web-Page
To apply the process in DRAINS, click the Add multiple ARR87 storms button in the Rainfall Data
property sheet, which will open the dialog box shown in Figure 2.65
DRAINS User Manual
November 2014
Figure 2.65 Add Multiple Storms Dialog Box
The Zone of Australia, ARIs and durations required can be entered, as shown above. Note that different
antecedent moisture conditions (AMCs) can be provided for ILSAX models. When the option of using
BOM format table selected and the Next button is clicked, this will open the following dialog box:
Figure 2.66 Paste BOM Format Table Dialog Box
Now go to the 'flash' BOM page, and press the Create an IFD button. The dialog box shown below will
DRAINS User Manual
November 2014
Figure 2.67 Create an IFD Dialog Box
Enter the latitude, longitude and name of the site, click the Conditions of Use box, and press the Submit
button to produce the following web page:
Figure 2.68 Output from CDIRS Procedure
Next, click the Coefficients button to open Figure 2.69. Click the Copy Table button, and then go back to
DRAINS, to the Paste BOM format table dialog box, and click the Paste Table button, which displays
Figure 2.70
The text shown is a set of polynomial coefficients in csv (comma separated variable) format. When the
OK button is clicked, the desired storms are added to the rainfall pattern database, as shown in Figure
2.71 . As an alternative, you can select IFD Table rather than Coefficients in the BOM output that shows
the IFD curves, and go through a similar process.
(c) Entering Synthetic Storms for the Extended Rational Method
As an alternative to working with design storm patterns from Australian Rainfall and Runoff 1987, the
Extended Rational Method can be applied using synthetic patterns derived from the local intensityfrequency-duration (I-F-D) relationships.
DRAINS User Manual
November 2014
Figure 2.69 I-F-D Coefficients
Figure 2.70 Paste BOM Dialog Box with Coefficients Displayed
The latter will give the same peak rainfall values as the rational method because they are derived directly
from the I-F-D data. They can be added to the rainfall pattern data base by pressing the Add Synthetic
Storm button in the Rainfall Data property sheet and completing the dialog box shown in Figure 2.72 to
produce the pattern shown in Figure 2.73.
The four intensities must be obtained from the local I-F-D data. A block duration of 1 minute is
recommended to allow exact matching of 5, 6, 7, 8, etc. minute intensities in the I-F-D data. The volume
of the hydrograph will increase for longer storm durations. The storm duration selected should be
considerably longer than the time of concentration of the catchment.
The 2/3 - 1/3 option pushes the peak of the rainfall pattern to the right so that its peak occurs at two-thirds
of the specified storm duration. Further information on this can be obtained in the San Diego County
Hydrological Manual available on the internet. This is claimed to be more conservative for detention
basin design.
DRAINS User Manual
November 2014
Figure 2.71 Added Multiple Storms
Figure 2.72 Dialog Box for Setting Up Synthetic Storms
Synthetic storm patterns consist of a number of nested storms, with the average intensity for any duration
equalling the intensity specified by the I-F-D relationship for that duration. Originally known as the
Chicago storm patterns, these relationships have been used in the United States for some time and are
also applied in the UK and Hong Kong.
(d) Adding Storms by Hand or by Spreadsheet Transfer
It is also possible to set up non-standard patterns by clicking the Add a New Storm button in the Rainfall
Data property sheet to open the box shown in Figure 2.74.
DRAINS User Manual
November 2014
Figure 2.73 Synthetic Rainfall Pattern
Figure 2.74 Manual Data Entry of a Rainfall Hyetograph
The duration of the pattern and the time step can be set, and the rainfall intensities
entered directly in the text box labelled 'Intensity (mm/h)'. Corrections can be
made by locating a value using the spin box for the intensities, and altering the
contents of the text box.
An average recurrence interval is required to specify factors used to determine
runoff coefficients in the Extended Rational Method. It is possible to enter values
between 0.1 and 999 years. If actual storms are being modelled, a rough estimate
of the ARI should be entered. If probable maximum precipitation storms are to be
modelled, a value of 999 might be used.
It is also possible to enter data from a spreadsheet by setting up two spreadsheet
columns as shown to the right. The left one should contain the times in minutes of
the start of each block, beginning with zero. The time divisions used must be the
same throughout; they cannot be varied. The right column should contain the
DRAINS User Manual
November 2014
rainfall intensities corresponding to the given times in mm/h. This facility allows complex patterns such as
that shown in Figure 2.75 to be entered.
You should copy both columns to the Windows Clipboard and then transfer from the spreadsheet
program to DRAINS. Clicking on the <- Paste button in the property sheet in Figure 2.74 will
automatically enter the rainfall pattern. This is an effective way of entering patterns for probable
maximum precipitation and extreme flood modelling.
At times DRAINS may not calculate hydrographs for as long a period as you may require. The calculation
period can be easily extended by increasing the given storm duration in Figure 2.74. This automatically
assumes that the extra rainfall ordinates are zero, and extends the calculation period.
Paste from
Figure 2.75 Observed Actual Rainfall Pattern (from file Ilsax10.drn)
Whatever data are entered into the rainfall database, they must be nominated as major or minor storms
using the options shown in Figure 1.11, in order to run with the available options (as set out in Section
3.4). There is the only way that rainfall date can be applied in runs. There is no way of storing a specific
set of rainfall patterns outside of the major-minor setup.
Pipe Data Base
The Pipe Data Base property sheet shown in Figure 2.76 is opened by selecting the Pipe Data Base …
option in the Project menu. This operates in two stages. The first is to define a pipe type, and to specify
its name, whether it is circular or rectangular, its roughness (according to the pipe friction formula set in
the Options property sheet called from the Project menu), and its minimum cover (m). The second
stage is to provide data for specific pipe sizes in the property sheet shown to the right in Figure 2.76. For
circular pipes, the nominal diameter, internal diameter (I.D.) and wall thickness must be supplied in mm.
For rectangular pipes, the width (m), height (m) and wall thickness (mm) must be supplied.
The check box labelled 'Not available for selection in design runs' allows you to omit pipe sizes that
are considered too small or are unavailable. If you wish to vary cover depths with pipe sizes, or to have
different classes of pipes (with different wall thicknesses), specific pipes classes should be entered as
pipe types.
Once established, the data base is easy to apply. Pipe types and sizes are readily accessed from the
Pipe Data property sheet. The data base can be edited, and factors such as cover depths can be altered.
When such changes are made, the title should also be changed to note that the default set of pipe data
has been altered. Additional pipe types can be added using Import ► DRAINS Database (DB1)
File… in the File menu, which requests the name of a .db1 file to be added. These are usually located in
the C:\Program Files\Drains\Program folder. When a file is nominated, DRAINS opens the
dialog box shown in Figure 2.77. You can then select the particular data you wish to transfer.
DRAINS User Manual
November 2014
Note that deletion of pipe types and sizes is not possible if pipes are present in the Main Window. It can
be done on a template file that does not contain any drainage system components.
When a DRAINS file is opened and closed, its pipe, pit, overflow profile data bases remain in DRAINS,
and some may be inherited by the new system. Template files can also supply suitable data bases.
Figure 2.76 Main Pipe Data Base and Pipe Type Property Sheets
Figure 2.77 Dialog Box for Importation of Additional Pipe, Pit and Overflow Data
DRAINS User Manual
November 2014
Pit Data Base
The Pit Data Base is accessed through the Pit Data Base… option in the Project menu. As shown in
Figure 2.78, pits are organised into types or families of different sizes, in a similar way to pipes. The pit
type is described in the Pit Type property sheet, also shown in Figure 2.78.
Figure 2.78 Main Pit Data Base Property Sheet and Pit Type Property Sheet
Data for each individual pit is entered in the triple property sheet shown in Figure 2.79. The relationships
are entered directly, as tables. This provides flexible relationships, particularly at the top end of the
curves. It is possible to set an upper limit on inlet capacities if required.
As part of the DRAINS design method, sets of relationships for pits in various regions have been provided
in.db1 data files contained in the C:/Program Files/Drains/Program or C:/Program Files
(x86)/Drains/Program folder, under names such as NSW Pits June 2008.db1. Relationships
for NSW, Queensland, Victoria, the Australian Capital Territory, South Australia and Western Australia
are now available. Instead of a single data base, these are made up of sets of relationships that can be
combined as required, using the Import ► DRAINS Database (DB1) File… option in the File menu. Via
the dialog box shown in Figure 2.77, additional pit types can be entered into the data base.
This process can be assisted by the Paste Data and Copy Data buttons in the On-Grade Data and Sag
Data windows shown in Figure 2.79. The first function can bring in data from two columns of a
spreadsheet, in the same way as for rainfall patterns (Section 2.4.4). The Copy Data function can
transfer data to a spreadsheet, or directly to another DRAINS pit data base. A pit data base can be
selected for a new project using the Default Data Base option in the Project menu, in the dialog box
shown in Figure 2.80.
Through Watercom Pty Ltd, inlet capacity relationships are available for many Australian pit types, as
indicated in Table 5.13 to Table 5.19.
DRAINS User Manual
November 2014
These may be periodically updated. To update a DRAINS model it will be necessary to import the data in
the revised .db1 file using the Import ► DRAINS Database (DB1) File… option in the File menu, and
then change the name of the old relationship to show that it is obsolete. The pit types nominated for
particular pits can then be changed one by one, or altered by exporting the system data to a spreadsheet,
as described in Section 3.5.4, altering pit type and size names in the columns, and then exporting the
altered spreadsheet back to the DRAINS model.
DRAINS User Manual
November 2014
Figure 2.79 Inlet Capacity Data for an Individual Pit
Figure 2.80 Dialog Box for Selecting a Default Data Base
However, there are many types of pit for which no relationships are available. Using the HEC22
procedures in the wizards for on-grade and sag pits implemented by the buttons shown in Figure 2.79,
inlet capacity relationships can be estimated for these. A 'generic' pit spreadsheet that calculates
capacities using methods from the US Federal Highway Administration HEC-22 manual (US FHWA,
2001) can also be applied. More explanation is provided in Section 5.5.3.
If a Pit Data Base is opened, and a change is made to the data for one of the pits, the following message
appears when this is closed by clicking on the OK button: Clicking the Yes button sets up the file’s pit
data base as the selected one.
Various regional pit types are available as .db1 files in the C:/Program Files/Drains/
Program folder. If ACT Pits June 2008.db1 or Queensland Pits June 2008.db1 is copied as
Drains.db1 into the folder C:/ProgramData/Drains, the ACT or Queensland pit types will be
installed. DRAINS uses separate folders in C:/Program Files and C:/ProgramData because of
Microsoft Vista rules for handling files for applications.
DRAINS still accepts old files that use the ILSAX equations described in Section 5.5.1 for pit inlet
capacities. However, if you attempt to run the Design method, the following message will appear. It
would then be possible to import a new Pit Data Base and to alter each pit’s type to conform to this.
DRAINS User Manual
November 2014
Overflow Route Data Base
The property sheet opened from the Overflow Route Data Base… in the Project menu is shown in
Figure 2.81. Using X-Y coordinates, a cross section can be defined for a roadway, footpath or other route
that may operate as a path for overflows.
Figure 2.81 Overflow Route Cross Section Data Base Property Sheet
At present, the section may be divided into two zones with different Manning’s n roughnesses, by
specifying these, and the X value of the dividing line. As X-Y values are entered, the picture shows the
section being produced.
In the boxes at the bottom, you can specify safe depths for minor and major storms and a safe depthvelocity product. These are applied at selected cross-sections in the Design method. DRAINS works
backwards to ensure that overflows from pits are kept to levels that will meet these safety criteria. It does
this by providing pits and pipes with the appropriate capacities to do this, following procedures within the
Queensland Urban Drainage Manual (Neville Jones & Associates et al., 1992).
DRAINS User Manual
November 2014
DRAINS User Manual
November 2014
Most of the functions or processes within DRAINS are presented here, referring to the example files that
accompany this manual. They are arranged into:
Input Options,
Display Options,
Run Options,
Output Options, and
Help Options.
Input Options
The example file in Chapter 1 was established using the screen tools provided on the Toolbar, and their
associated property sheets. Other options are available that allow a substantial part of the information
required to be inputted by other means. These are mainly implemented through the File menu shown in
Figure 3.1, and the two additional menus that are opened using the Import ► and Export ► options.
(Note that not all options may appear when the hydrological model in DRAINS is set to be a rational
method model.)
Figure 3.1 The File Menu and Sub-Menus showing Import and Export Options
In design work, it is likely that considerable data will be available from CAD files created by surveyors and
used by designers to set out street layouts, cadastral (land boundary) data and positions of services.
Some of this data can be taken directly into DRAINS by importing CAD files in DXF format. This includes
a background showing streets, lot boundaries and other information. Other data obtainable from CAD
drawing files, such as sub-catchment areas, will have to be entered into property sheets, or via a
For investigation of established drainage systems, data is likely to be available in a number of forms:
paper plans, CAD drawings, spreadsheet tables, data bases from GIS systems and aerial photographs.
DRAINS can accept ESRI (ArcView, ArcInfo, and ArcMap) files and MapInfo files. A background can be
imported as a DXF file, and spreadsheets can be assembled into a form accepted by DRAINS.
DRAINS User Manual
November 2014
Importing DXF Files
(a) New Systems
Where a drainage system has been drawn in a drawing package or digital terrain model, it can be
imported into DRAINS in DXF format. This is one of the oldest drawing formats, which can be created in
almost all technical graphics packages. Newer formats such as DWG, the widely-used AutoCAD binary
format, can be converted to DXF format before transfer to DRAINS.
The external software package must include three layers:
one for pits, with the location of each pit marked by a circle,
one for pipes, with pipes shown as lines, and
a background, which may show street boundaries, cadastral information and contours.
Other layers can also be present, but will not be used. Lines, poly-lines and arcs on the background layer
will be imported into DRAINS as a bitmap.
Figure 3.2 shows a drawing created in AutoCAD LT, representing a drainage system assumed to be at
Figure 3.2 Drawing of Drainage Network
Information that is in this file can be imported by opening DRAINS and selecting Import a DXF File… from
the File menu. You will be requested to nominate a file with a .dxf suffix. You will then see a dialog box
that asks you to nominate the names of the layers on which pipes, pits and background are located, as
shown in Figure 3.3. This is saved as a file Brisbane.dxf.
Using the drop-down list box, you can select the appropriate layers. Pits and pipes can be placed on the
same layer if you wish. Once layers are selected, a number of information windows appear. The first one
shown in Figure 3.4 allows pipe lengths to be automatically scaled off the DXF drawing, according to the
length allocated to the first pipe for which full data is entered.
The DRAINS Main Window then appears with the drainage system and background shown as in Figure
3.5. This can be enlarged if necessary, using the Zoom tool. The colour of the background and its
intensity can be changed using the Background Colour… option in the View menu. If the background
has a much greater extent than the pipes in the model, DRAINS will reduce the field of view. This can be
extended again using the View → Extend Drawing Area… option. Dummy pipes and pits can also be
inserted to provide a large background, as shown to the left of Figure 3.5.
DRAINS User Manual
November 2014
Figure 3.3 Layer Selection Dialog Box
Figure 3.4 Messages in DXF Import Procedure
You must now enter information for pits and pipes, and draw in sub-catchments, overflow routes and
outfall nodes, as shown in the example in Chapter 1. Directions of pipes will have to be changed if the
pipes in the CAD drawing are drawn from 'the bottom up'.
Lettering for features such as street names can be brought into DRAINS from a CAD file if it is in an
acceptable format. If AutoCAD is being used, text in the Standard style on a single line (created using
Draw → Text ► → Single Line Text) can be transferred.
(b) Replacement of Backgrounds
It is possible to import a new background or to
exchange the current background with another.
Using the File → Import → Import DXF
background… option brings up a dialog box from
which a DXF file can be opened. When a file is
selected, the window shown to the right appears.
DRAINS User Manual
November 2014
Figure 3.5 Imported DXF File Information
Note that if you replace a background, it does not open the dialog box shown in Figure 3.3 and will not
transfer pits and pipes. All layers in the replacement CAD file will be shown. For example, if the Brisbane
background is read in again, the contours and pipes will appear in the background. You must be careful
that the replacement file only contains the layers that you want. This will probably involve the creation of
an additional CAD file containing only those layers that you want to display.
If you have a DRAINS model without a background, you will be able to insert a background provided that
it has a similar extent (in x-y coordinates) to the coverage of the x-y coordinates of the pits and nodes
used in the model, which are displayed in the spreadsheet data output. Backgrounds can be inserted into
models that include saved results.
Spreadsheet Imports
Information about a drainage system can also be imported from a spreadsheet file. Since this file will
usually be created by outputting information from a DRAINS file, both the spreadsheet output and input
processes are described later, in Section 3.5.4 of this chapter.
Some sets of information can be pasted into DRAINS property sheets for rainfall patterns, hydrographs,
pits, detention basins, headwalls and culverts as columns from a spreadsheet.
A DRAINS Utility Spreadsheet and a Generic Pit Inlet Capacity Sheet are available to DRAINS Users,
with the former being on the www.watercom.com site. Information from these can be pasted into
DRAINS as shown in Figure 3.6.
GIS File Imports
(a) Importing ESRI (ArcView) Files
This process enables you to import data into DRAINS from one to six sets of ESRI or ArcView files, plus
an optional background from a DXF file. The procedure is the reverse of the exporting process for ESRI
files described in Section 3.5.5(a).
If you wish to model an existing drainage system in DRAINS, importing data from available ArcView
records, you must edit these into the format required by DRAINS, described in Section 5.10.3(b). You
can also scrutinise this format by exporting a small drainage system and examining the resulting DBASE
tables. The six sets of files contain data for nodes (pits and outlets), pipes, overflow routes, subcatchments, survey levels along pipe routes and the positions of other services along a pipe routes. Each
set includes three files with SHP, SHX and DBF suffixes.
DRAINS User Manual
November 2014
Figure 3.6 Transfer of a PMP Rainfall Pattern from a Utility Spreadsheet to DRAINS Rainfall Data
The transfer must include the files for nodes, but the rest are optional. In a first transfer, it is unlikely that
all the information required by DRAINS will be available in the GIS. Information that is already in the GIS
should be included in the files to be transferred. You can then choose whether to add additional data in
these files, or to use dummy values and enter the required values later, in DRAINS.
The example shown in Figure 3. illustrates the process. The data for nodes (including pits and outlets)
and pipes, each contained in a 'theme', needs to be entered in the data base tables shown in Figure 3.8,
which can be created by editing in ArcMap or other GIS programs. A DXF file containing a background
for the DRAINS model can be created from GIS layers.
Figure 3.7 The 'Oldtown' Example in ArcMap
To make the transfer, you must place all files to be transferred into the same Windows folder, set up a
DRAINS model with the ILSAX hydrological model and pit and pipe data bases that you require, and then
use the File -> Import -> ESRI Shapefiles… option, which will display the message in Figure 3.9.
After entering 'Yes', you must select one of the ESRI files to be transferred, as shown in Figure 3.10 The
transfer will then take place, and the pits and pipes will come into view, as shown in Figure 3.11.
DRAINS User Manual
November 2014
Figure 3.8 ArcView Tables of Characteristics of Nodes and Pipes,
ready for Import into DRAINS
Figure 3.9 Shapefile Transfer Message
DRAINS User Manual
November 2014
Figure 3.10 Choosing a Shapefile
Figure 3.11 Transferred Data
(b) Importing MapInfo Files
This process enables you to import data into DRAINS from one to six sets of MapInfo files, plus an
optional background from a DXF file. The procedure is the reverse of the exporting process for MapInfo
files described in Section 3.5.5(b), and is similar to the ESRI transfer process described in the previous
section of this chapter. The six sets of files cover nodes (pits and outlets), pipes, overflow routes, subcatchments, location of ground levels along the pipe routes, and the location of other services along these
To transfer MapInfo data to DRAINS, you need to edit the available MapInfo data into pairs of MID and
MIF files in the format required by DRAINS, specified in Section 5.10.3(c). This is the same as the format
generated in the export process that creates MapInfo files from DRAINS data, which you can see by
exporting a small system and examining the resulting tables.
All the required information that is already in the GIS should be included in the files to be transferred. It is
then a matter of choice as to whether you add additional data in these files, or enter dummy values, and
enter the missing data later in DRAINS.
DRAINS User Manual
November 2014
The following example illustrates the process, paralleling the ESRI file import example. Figure 3.12 shows
the Oldtown System in MapInfo, with the data for one pipe being displayed. This can be set up in
MapInfo or in a text editor. The corresponding node data is similar.
Figure 3.12 The 'Oldtown' Example in MapInfo
From the MapInfo layers, a DXF file containing a background for the DRAINS model can be created.
This will appear in the same form as Figure 3.10.
To make a transfer, you will need to place all the files to be transferred into the same Windows folder, set
up a DRAINS model with the ILSAX hydrological model and pit and pipe data bases that you require, and
then use the File -> Import -> MapInfo MIF files… option, which will display the following message:
After you enter 'Yes', you must select one of the MapInfo MIF files to be transferred, as shown in Figure
3.13. The transfer will then take place, and the pits and pipes will come into view, in the same form as
Figure 3.11.
DRAINS User Manual
November 2014
Figure 3.13 Choosing a MIF File
As with the ESRI transfers, with this setup it is possible to import a new or additional background. Using
the File -> Import -> Import DXF background… option brings up a dialog box from which a DXF file can
be opened. When a file is selected, the following window appears. When a choice is made, the
background is replaced.
ILSAX File Imports
DRAINS is partly based on the ILSAX program that was used widely in Australia since 1986. Many
Government organisations developed ILSAX files describing their drainage systems that could be
converted to DRAINS files using the Import ILSAX Files … option in the File menu. However, there
have been changes to DRAINS that mean that now it is hardly worthwhile to make transfers by these
means. These changes include the use of a different type of pit inlet capacity relationship and the
omission of the ILLUDAS type pit that was employed in the transfer (refer to the DRAINS Help system).
It is therefore recommended that this feature not be used, and that models be created by other means.
However, the transfer facility is still available, and instructions are available in the DRAINS Help system
under the topic 'Importing ILSAX files'.
Merging Files
There is an option in the File menu to merge DRAINS files together. Since this first involves an output
process, it is described in Section 3.5.8.
DRAINS User Manual
November 2014
ansferring to
t and from
m CAD Pro grams
Drafting prog
grams such as
a AutoCAD, Microstatio
on, IntelliCAD
D, Bricscad and
a TurboCA
AD can be us
sed for
creating the network geo
ometry. In th
he drawing, a
all pipes mus
st be on a lay
yer and all pitts on a sepa
layer. Pipess must be dra
awn as lines and pits as ccircles. (If th
he drawing uses other syymbols for pitts, a
separate layyer should be
e created, witth a circle ovver each pit.)) The file sho
ould be saveed in DXF forrmat. At
the time of im
mport to DRA
AINS you willl be asked to
o nominate the respective layers, as described in Section
3.2.2 using tthe File → Im
mport ► Imp
port DXF file
e… comman
ansferring Data
to and
d from the 12d Progra
Data for settting up DRAIINS models can
c be impo rted directly from the 12d
d digital terraain modelling
arried out in DRAINS, us
program. Affter design and analysis have
been ca
sing the ILSA
AX or ERM models,
the resulting
g system info
ormation can be returned to 12d for fu
urther analysis and plottinng. An important
requirement is to ensure
e consistency
y in pit and p ipe names used. The procedure doees not work with
DRAINS ratiional method
d calculations
2d, Version 7
7. For more current inforrmation contaact 12d direc
ctly at
The following instructions relate to 12
Assuming th
hat you have set up a dra
ainage system
m in 12d, deffining pits, piipes, sub-cattchments and
overflow rou
utes, the step
ps involved in
n the transferr process are
While 12d is open, start up a DRAINS
del with the required
hydrrology, rainfaall, pipe, pit and
ow route datta bases. Op
pen the pit da
ata base in the DRAINS Project mennu and then close
this, cclicking OK. When asked
d if you wish to save the altered
data base, reply ''Yes'. (This ensures
that th
he required data
base is stored
in a fi le that 12d can
c access.)
Next, in 12d open the dialog box selected ffrom the menus, Design → Drainag
ge-Sewer → More
→ Dra
ains to drain
nage 4d → drains.
Thiss appears as shown in Fig
gure 3.14.
Figurre 3.14 DRA
AINS Transffer Dialog Box Specifica
ations in 12 d
Checkk the databasses making sure
that the
e required DR
RAINS pipe and
a pit relatioonships appe
Click tthe Read Drrains databa
ase button an
nd check the
e displayed in
nformation annd the pit gro
separator. Separa
ators ',' or '-' are used in tthe names contained in different
AINS pit data
a bases.
If the d
data is not what
you wan
nt, return to S
Step (a).
ge-Sewer → Drainage Network
Then open the win
ndow Design
n → Drainag
Ediitor, shown as
e 3.15. From
m this you ca
an check deffine sub-catc
chments, pits, pipes and ooverflow routtes
using 12d procedu
ures. Set ap
ppropriate de
efaults and us
se the Set Pit Names buutton to provide a set
of uniq
que pit name
es. Then pre
ess Set Pit D
Details and Set
S Catchme
ents and nom
minate the Regrade
s option.
Now tthe transfer can
c be made
e using the Im
mport/Exporrt button on the
t Drainagee Network Ed
which opens the dialog
box sh
hown in Figurre 3.16. For I/O format, select
'Drainss Clipboard - Ver 5
X' or 'Drains Clipboard
- Ver
V 5 Rationa
al' depending
g on the hydrological moodel you are running
in DRA
AINS. Clickk the Run bu
DRAINS Userr Manual
mber 2014
e 3.16 12d Im
mport/Export Window
Figure 3.15 12d Drainage
e Network E
Now switch to
o the DRAINS model note
ed in Step (a
a), and from the
t Edit mennu, select Pa
aste Data
frrom Spreads
sheet. The model shoulld then appear, ready for a Design ru n.
Run the mode
el in DRAINS
S, using ILSA
AX or rationa
al method hyd
drology and the standard
d or premium
hydraulic mod
dels. Inspect the results, and when satisfied,
send data to thee Clipboard using
Copy Data to
o Spreadshe
eet option in the Edit menu.
12d Drainage Network Editor, bring thhe data back
Using the Imp
port/Export button in the 1
k to 12d.
Going back to
o DRAINS, press
Edit → Copy Resu
ults to Sprea
adsheet, andd in 12d pres
ss the
mport/Exportt button again to bring the
e remainder of the requirred informatioon into 12d. (Note that
his reverse data
transfer must be don
ne in two stag
ges, first data
a and then reesults.)
For furth
her details, contact
s Advanced
d Road Des
sign Link
The Advvanced Road
d Design (AR
RD) program
m is used insid
de Autodesk
k Civil 3D. It has purpose
e-built tools
for creating drainage
e network ge
eometry and assigning th
he catchmentt/overflow rouute/surface profile
geometry informatio
on required by DRAINS. ARD was de
eveloped by Peter Bloom
mfield and CA
adapps.com.au, www.civ
u). This transfer proceduure works wh
has ILSAX or ERM specified,
ut not for the rational method. When this is speciffied as the hy
model, tthe links to ARD
in the File menu, me
entioned belo
ow, do not ap
To make
e a transfer, from the AR
RD 'Drainage
e' menu use the
t command
Drainage ► Data Exchange
► Write to D
With Civvil 3D the data is written to
t the Drains
s-n.mdb file in the DrawingName_Daata\AdvRoad
ds directory
under th
he directory holding
the drawing
In DRAIINS use the File → Impo
ort ► Importt Advanced Road Desig
gn file… com
mmand to import the
data. A
After making a run in DRA
AINS, use the
e File → Exp
port ► Adva
anced Road
d Design file
e… command
S User Manual
November 2014
to export the data. This command writes the Design data back to the Advanced Road Design data file
from where it is exported back to the Advanced Road Design data file for plotting with the Drainage ►
Data Exchange ► Read in Drains data command. For further details, view the educational video at
or contact Andrew English on (03) 9568 0077 or [email protected]
3.2.10 Transferring from MXROADS
The Bentley MX ROAD software has a connection to DRAINS that operates in the same way as the
Advanced Road Design procedure described in the previous section. The commands:
File → Import ► Import Advanced Road Design file…
File → Export ► Advanced Road Design file…
can be used to import and export MXROADS files. For detailed information, contact support at Bentley.
Like the other connections, this does not work when DRAINS has a rational method hydrological model.
It operates when the DRAINS model has an ILSAX or ERM model specified.
3.2.11 Transferring from CatchmentSIM
CatchmentSIM, developed by Chris Ryan (2005), is a program that manipulates topographic data to
define catchments and to determine catchment characteristics. Starting with data in a 3-dimensional
vector format such as MID/MIF or TIN files, CatchmentSIM converts these to a raster grid, from which
catchments and sub-catchments can be defined. For urban catchments, barriers to flow along fences
and road crowns can be specified, and the sub-catchments derived reflect these.
This information can be used to develop DRAINS models. For further information, contact Catchment
Simulation Solutions at www.csse.com.au.
3.2.12 Setting Up New Pipe, Pit and Overflow Route Data Bases
New data bases can be established using the Default Data Base Option in the Project menu. This
opens the dialog box shown in Figure 3.17, from which a base can be selected from the .db1 files stored
in the C:/Program Files/Drains/Program folder. This is followed by a warning indicating that the
default .db1 file, Drains.db1, will be overwritten.
Note that this can only be done with a DRAINS file that has an empty main window. Once components
are entered, the only way to add pipe or pit types is by hand. In addition, it is not possible to delete pipe
and pit types in this situation, though their characteristics can be edited and changed. (.db1 files are
related to the new pit data bases and .db files to the older system described in Section 2.4.6.)
An additional feature, implemented through the Import ► DRAINS Database (DB1) File… option in the
File menu can be used to add extra pipe, pit and overflow route types to a data base, as described in
Section 2.4.5.
DRAINS User Manual
November 2014
Figure 3.17 Default Data Base Dialog Box
Display Options
DRAINS provides several options for viewing data on screen in addition to usual Windows facilities such
as scrolling bars. The options available before calculations are performed are demonstrated in this
section using the Toowoomba Estate.drn example that is ready to run in Design mode, which will
define the pipe diameters and invert levels.
Screen Presentation Options
You can vary the way that a drainage system is presented on screen
using options that are mainly included in the View menu ( Figure 3.18).
(a) Customise Text
The Customise Text … option at the top of the View menu produces the
dialog box shown in Figure 3.19. By selecting options here, you can
change the information provided, as indicated in Figure 3.20. Many
choices are only available after a Design or Analysis run. The custom
display numbers are coloured purple to distinguish them from names of
components (black) and numerical outputs (black, green, blue and red).
This dialog box can also be opened by right-clicking on the name of any
component, though not the component itself.
(b) Index Sheet
Selecting Index Sheet from the DRAINS View menu produces the view
of the system shown in Figure 3.21. The rectangle represents the screen
size. Placing this 'mask' in a certain position and clicking sets the screen
to that position, as shown in Figure 3.22.
Figure 3.18 View Menu
(c) Zoom
There are three zoom options for enlarging or reducing the image in the Main Window. The Zoom
Factor, which is also available through a button on the Toolbar, changes the cursor to a magnifying
glass, which you should place over the area to which you wish to zoom. Clicking on this opens the
dialog box shown in Figure 3.23, in which you can nominate the magnification. If you accept the default
value of 1.5, an enlarged presentation is obtained. Entering a factor less than 1 reduces the size of the
system, but the size of lettering remains the same.
DRAINS User Manual
November 2014
Figure 3.19 Dialog Box for Customising or Changing the Text Displayed
Figure 3.20 Drainage System with Surface Levels (coloured purple) replacing Pit Names and
Upstream and Downstream Invert Levels replacing Pipe Names
The wheel on a mouse can also be used to zoom in and out of DRAINS models. To pan, you can press
the Pan button on the Toolbar
, or the sliding bars on the margins. In large drainage systems, you
can use the Index Sheet facility described in the previous section.
DRAINS User Manual
November 2014
Figure 3.21 Index Sheet View
Figure 3.22 Toowoomba Pipe System selected using the Index Sheet
Figure 3.23 Zoom Window
DRAINS User Manual
November 2014
The Zoom Window option in the View menu changes the cursor to crosshairs that can be used to define
the rectangular area that is to be enlarged. When the mouse button is released, the enlarged area fills
the Main Window.
The Zoom Extents option zooms out, but not to the full extent of the model. It can provide the desired
extent when applied a number of times.
(d) Property Balloons
These can be switched on and off by clicking on Property Balloons in the View menu.
(e) Description Option
Note that the Main Window area includes a title block in the lower right corner. Text can be inserted into
this block using the Description… option in the Project menu, which opens the property sheet shown in
Figure 3.24. Comments and lines for the title block can be entered. If no block is required, the three
TITLE BLOCK lines can be made blank.
(f) Removing Items from View
Facilities like the Status Bar at the bottom of the Main Window and components such as sub-catchments
can be removed from the window if desired, using the options in the central part of the View menu.
Figure 3.24 The Description Property Sheet
(g) Changes to the Main Window Coverage
The Drawing Area can be extended at the four corners, cropped (reduced selectively) or trimmed all
round, using options in the View menu – Extend Drawing Area ..., Crop Drawing Area ..., and Trim
Drawing Edges.
(h) Pop-Up Menu Displays
The pop-up menus opened by right-clicking on an object are the main means of presenting results of
calculations on-screen. They also provide some information prior to calculations. Two displays from the
Toowoomba example are shown in Figure 3.25.
Run Options
Design and Analysis Runs
In the Run menu shown in Figure 3.26 there are at least three run options:
the Analyse major storms (standard hydraulic model),
the Analyse minor storms (standard hydraulic model),
the Design option.
DRAINS User Manual
November 2014
Detention Basin Elevation-Storage Relationship Display
Irregular Channel Cross-Section Display
Figure 3.25 Sample Displays from the Pop-Up Menus for Components
Figure 3.26 Run Menus for New DRAINS Models and for Older Models
DRAINS User Manual
November 2014
If the premium hydraulic model is enabled by the hardware lock being used, there are two more options:
the Analyse major storms (premium hydraulic model),
the Analyse minor storms (premium hydraulic model),
and, if the model was created prior to the end of 2010, there are the options:
the Analyse major storms (basic hydraulic model),
the Analyse minor storms (basic hydraulic model).
There is also the Design option that sets pipe sizes and invert levels, and options for revising pit pressure
change factors and outputting pipe quantities.
The alternative hydraulic models are described in Sections 4.2.7 and 0. The standard model that
replaces the obsolete basic model applies unsteady flow calculations to pipes and open channels, but not
to overflow routes. The premium model applies the unsteady calculations to all three types of conduits.
The models can be run with either the set of minor or the set of major storms established in the rainfall
inputs using Select Storms ► Minor storms or Select Storms ► Major storms options in the
Project menu (see Section 2.4.4).
When any of the above options are chosen, DRAINS launches into a run. There may be warnings and a
request to use parallel processing. Once these are noted are acted upon, the run begins. Rational
method calculations are quick because only peak flows are generated and there are no unsteady flow
calculations. The simulation runs used with the other, hydrograph-producing models will take longer to
run, and will produce much more comprehensive results.
Analysis runs treat all pipes as fixed, and do not alter the given pipe diameters and invert levels.
Complex situations, such as pits with the invert of the outgoing pipe being higher than those of the
incoming pipes, can usually be modelled.
For pipes that have the specification shown in Figure 3.27, the Design option selects pit sizes from the
specified pit family for each pit, and defines the pipe diameters and invert levels for circular pipes.
(Design cannot be performed with rectangular pipes.) If you have already specified invert levels, these
will most probably be changed in a design. (In calculations, the second option in Figure 3.27 is treated
exactly the same as the third, except that when DRAINS calculates quantities of soil volumes for
excavation, volumes for pipes defined under Option 2 are included in the table of quantities along with
those defined under Option 1; volumes for Option 3 pipes are not.)
Figure 3.27 Specification of Pipe Types
DRAINS does not specifically try to design around existing pipes with fixed invert levels, so situations will
be encountered where it is not possible to do this while obeying the restrictions set in the Options
property sheet opened from the Project menu. In these cases, the invert levels at the downstream end of
designed pipes may be specified as being lower than the existing pipe to which they connect.
The design method applied, based on the Queensland Urban Drainage Manual (Neville Jones &
Associates et al., 1992) varies both pits and pipes to obtain an optimal result. It is possible to set the pit
size and the pipe diameter and invert levels as fixed, using options in the Pit and Pipe property sheets.
Both procedures allow for intermediate levels along a pipeline route between pits. These are considered
when pipe invert levels are determined, allowing for minimum cover depths.
Run Logs
Following a run, DRAINS presents a log reporting on the results, as shown in Figure 3.28, indicating
problems and possible causes. The first example shows a trouble-free run and the
second one that has complex results.
DRAINS User Manual
November 2014
Figure 3.28 Examples of Messages Reporting Results from Design and Analysis Runs
The report must be closed (by clicking on the X at the top right of the window), but it can be recalled using
the Last Run Report option in the View menu. The information in the log is also reproduced in the
spreadsheet output for results.
Warning and Error Messages
DRAINS performs a number of checks as data is entered. One is to ensure that all the required data is
provides. In some instances DRAINS requires values to be within certain ranges of expected values, in
others it queries values that appear to be unusual. Warnings like those shown in Figure 3.29 also appear
when a run is initiated, and after a run. It is important to heed these, and to try to eliminate the causes.
Figure 3.29 Warning Messages (see also Figure 3.28)
If a serious computational problem occurs, and DRAINS cannot resolve this, an error message may
appear, and the program will shut down after this is closed. Sometimes such messages will request that
you contact Watercom Pty Ltd to resolve the problem.
Options for Modifying Pit Pressure Change Factors
The Revise Pit Loss Coefficients option alters the pit pressure change coefficients using an algorithm
based on an approximate relationship developed by Mills or a method based on the Queensland Urban
Drainage Manual, QUDM (see Section 0). Before using these procedures, you must run DRAINS to
obtain a set of flows and HGLs, as shown in Figure 3.30.
DRAINS User Manual
November 2014
Figure 3.30 Sample System with Initial Pressure Change Coefficients
For example, you might set up a system as shown below, guessing Ku factors, or setting all factors to the
default value of 1.5. You would than run the models and select the method you wish to apply, in this case
the QUDM Chart procedure, as shown in Figure 3.31.
Figure 3.31 Applying the QUDM Charts Procedure
The following messages will appear.
DRAINS User Manual
November 2014
A table of changes can be pasted from the Clipboard to a spreadsheet and displayed:
The Chart referred to in Column D is the one selected from those in the Queensland Urban Drainage
Manual, and the Ratios are those used to enter the chart to determine the ku or K values. Further details
are given in Section 5.6.6(c).
The model will contain the revised coefficients. The process of running the model and adjusting the
coefficients should be repeated once or twice more to allow the procedure to converge to a fixed set of ku
values. Since values depend on flowrates and HGL levels, this process must be run separately for minor
and major flows in pipe system design, generating different sets of coefficients.
The procedure for the Mills equation is similar, but simpler. Strictly speaking, both procedures need to be
applied iteratively, since changing ku values will alter flowrates and HGLs, which in turn influence the
selection of the ku values. Two iterations might be usually required when using Mills Method while three
or four iterations may be required using the QUDM procedure. As indicated in the second message
displayed for the QUDM procedure, the changes made are presented in a spreadsheet placed on the
Clipboard, and this can be used to check that convergence has occurred. ku values created by this
method can be manually overwritten.
The Quantities option in the Run menu displays or prints out a
table of quantities for the pipes in the current system, as shown in
Figure 3.33. This complements the information printed for each
completely-defined pipe at the bottom of its property sheet, as
shown in
DRAINS calculates excavation volumes from pipe lengths and
invert levels, assuming the trench widths given in Table 3.1
Table 3.1, with 200 mm and the diameter being added for each
additional parallel pipe. The bedding depth is assumed to be
50 mm below the outside of the pipe wall.
DRAINS User Manual
Figure 3.32 Quantities Information
in Pipe Property Sheet
November 2014
Figure 3.33 The Summary of Quantities
Table 3.1 Default Trench Width Table
Nominal Diameter (mm)
Trench Width (mm)
300 mm or less
550 mm
301 - 375 mm
650 mm
376 - 450 mm
750 mm
451 - 525 mm
850 mm
526 - 600 mm
950 mm
601 - 675 mm
1050 mm
676 - 750 mm
1150 mm
751 - 900 mm
1400 mm
902 - 1000 mm
1550 mm
1001 - 1200 mm
1800 mm
1201 mm or greater
Diameter + 750 mm
Output Options
Transfers of Displays and Screen Print-Outs
Section 3.3.2 described the various screen displays that are provided by DRAINS prior to run
calculations. Additional displays become available once a run is made. These include hydrographs, HGL
level plots, tables of flowrates and HGLs.
Data and results can be printed from many of the display windows using the File and Edit options in their
windows, such as the hydrograph display in
. These can also be copied to
reports and calculation files. You can also use the screen capture techniques available in all Windows
applications, such as the Print Screen key and Alt + Print Screen keys, or specialist screen capture
programs to produce outputs such as Figure 3.34.
DRAINS User Manual
November 2014
Figure 3.34 DRAINS Results showing Main Window, Hydrograph and HGL Plot Windows
DRAINS Print Diagram Option
DRAINS has a facility for printing out the system
displayed on a screen, either completely, or as the view
shown on the screen. This is implemented in the Print
Diagram option in the File menu, using the dialog box
shown in
Figure 3.35. Font sizes can be altered. The OK button
starts the printout, while the Setup... button opens a
Printer Setup dialog box.
In the past, this facility has not worked with some printers,
due to problems with printer drivers. Trying the options
now available should produce a satisfactory image.
Another way around printing problems is to print to a pdf
file, if you have Adobe Acrobat or another program
capable of doing this, and then to print from the pdf file.
Figure 3.35 Print Diagram Dialog Box
DXF Exports
The process of importing data in DXF format was presented
in Section 3.2.2. There are two types of output via DXF file
format, one of the most common formats used for drawings.
With the Toowoomba Estate.drn file, you can export a
plan view to scale using the Export DXF File… option in the
File menu. This opens a Save As dialog box, and after a file
name and location are specified, opens the DXF File dialog
box shown in
Figure 3.36. The resulting file can be opened in a
drawing program, appearing as shown in Figure 3.37. The
background and pipes are supplied on different CAD layers.
Figure 3.36 DXF File Details Dialog Box
DRAINS User Manual
November 2014
Figure 3.37 Drawing Transferred Out of DRAINS in DXF Format
A longitudinal section can be exported by nominating a path between neighbouring pits, and then
specifying drawing characteristics. The option Export ► DXF Long Section… in the File menu opens
the dialog boxes shown in Figure 3.38.
Figure 3.38 Dialog Boxes for setting Paths for Plotting Long Sections
The smaller box is used to define a continuous pipe route. You need to specify the starting and ending
node names exactly, allowing for blanks and the case of words.
Once a route is selected and the Next button is clicked, a preview like that shown in Figure 3.39 appears.
This is in a window that can be enlarged by clickin on the Maximize button (circled) at the top right of the
The Customise button opens the dialog box shown in Figure 3.40, which can be used to set drawing
features. Changes are reflected in the preview.
DRAINS User Manual
November 2014
Figure 3.39 Preview of Long Section Plot
Once a satisfactory layout is achieved, clicking the Save as DXF button opens a window in which the file
name and location can be specified. This creates the DXF file, which can then be viewed and
manipulated in a CAD program, as shown in Figure 3.41 and printed from this.
Figure 3.40 Dialog Box for Customising a Long Section
Spreadsheet Outputs (and Inputs)
The spreadsheet option provides a convenient way to view and store data and results, as well as a
medium for transferring information between DRAINS and other programs. It effectively supersedes the
text file output described in the previous section, although this is retained for the convenience of users.
To exchange information with a spreadsheet program, say Excel, both programs must be opened.
Information is exchanged via the Windows Clipboard by selecting the copy and paste options in the Edit
menu. After selecting Copy Data to Spreadsheet in DRAINS, as shown in Figure 3.42, transfer to Excel
and select Paste from its Edit menu.
DRAINS User Manual
November 2014
Figure 3.41 The Exported Longitudinal Section, with Hydraulic Grade Line
The information shown in Figure 3.43 appears. Almost all the information entered for components is
presented, organised by type of component - PIPE/NODE, SUB-CATCHMENT, etc. This worksheet can
be given a name such as 'Data' by double-clicking on the tag at the bottom of the sheet and writing in the
name in the space that is highlighted. X-Y coordinates are given for pits and nodes, referring to their
positions in the Main Window. If a base drawing is imported from a CAD or GIS file the coordinate
system will be consistent with this.
Figure 3.42 Copying Spreadsheet Data to the Clipboard after a Design Run
DRAINS User Manual
November 2014
Figure 3.43 Transferred Data
The results from a Design can then be transferred using the Copy Results to Spreadsheet option from
the Edit menu. This can be pasted into a second worksheet with the tag 'Design' or 'Minor', as shown in
Figure 3.44.
Figure 3.44 Transferred Design Results
As with the data, results are organised by the type of component, in the same order. Calculated
flowrates, times, velocities and other information are presented. Where multiple rainfall patterns are
specified, the information presented is for the worst-case result - the greatest flowrate, highest HGL level,
etc. among the results for the various storms.
DRAINS User Manual
November 2014
The particular storm that causes this worst condition is noted in the last column for each component.
(DRAINS does not transfer the specific results for each individual storm. If you wish to do this, you
should use the Select Storms option in the Project menu to run DRAINS with single storms and transfer
the results one at a time.) The velocities shown correspond to the peak flowrates and may be part-full or
full pipe velocities, depending on the conditions when the maximum flowrate occurred.
A continuity check of inflow and outflow hydrograph volumes at each node (presented at the bottom of the
spreadsheet shown in Figure 3.45) applies for the most severe storm. It shows up differences in
continuity, due to factors such as the absence of an overflow route when overflows occur. However, it
does not show any discontinuity due to the introduction of a baseflow or a user-provided inflow
hydrograph. Where there is a lack of continuity at a node, the cause can be explored by examining the
inputs and outputs to the relevant node using the View Hydrographs and View Hydrographs as Tables
options in the pop-up menus for pipes, channels, overflow routes and sub-catchments. The run log that
appeared after the run completed is also presented at the end of the Results output.
Figure 3.45 Continuity Checks
When a Design run is followed up by an Analysis run, the results can also be transferred, being pasted in
the 'Major' worksheet shown in Figure 3.45. These spreadsheets can be saved and used to document a
design or analysis. They can also be transferred from the spreadsheet program to a word processor for
inclusion in a report.
In connection with rational method calculations, DRAINS has the option Edit → Copy Check HGL to
Spreadsheet that presents results of a simplified analysis of the drainage system, using assumptions
similar to those in the manual analysis procedures set out in Chapter 14 of Australian Rainfall and Runoff,
1987 and Chapter 5 of the Queensland Urban Drainage Manual. These results are not available for other
hydrological models such as the ILSAX and extended rational method models.
For the rational method example shown in Figure 3.46, we can determine pit pressure change
coefficients using the method from the outlined in Section 3.4.4 and run this model for minor and major
storms. We can then transfer the results of the simplified analysis to Excel in the form shown in
Figure 3.47. Overflow routes from nodes have been provided at the tops of lines. By specifying
percentages of downstream sub-catchments contributing, it is possible to define the hydraulic
DRAINS User Manual
November 2014
characteristics of approach flows in the spreadsheet output (see Columns L to O of the Excel worksheet
Figure 3.47).
This feature has been provided to assist persons documenting or checking designs. It is more
conservative than the DRAINS calculation procedures, and will specify higher HGLs that might
sometimes exceed the freeboard limits at pits. It should therefore be considered as a guide or 'sanity
check' rather than as a true representation of the peak HGL levels. Among the reasons for conservatism
are that peak flowrates in all pipes are assumed to occur simultaneously.
Figure 3.46 Rational Method Example
DRAINS User Manual
November 2014
Figure 3.47 Transferred Check HGL Results
Queensland users will be able to convert the DRAINS Check HGL outputs to forms set out in QUDM and
manuals from Brisbane City Council and Pine Rivers Shire Council, using a ‘DRAINS Rational Method
Output Converter’ spreadsheet available from www.watercom.com.au. An output from this is shown in
Figure 3.48.
Figure 3.48 Rational Method Converter Results
Data for pipes, pits, nodes and sub-catchments can be transferred back into DRAINS using the Paste
Data from Spreadsheet option in the Edit menu. You must first make the required changes and then
copy the entire spreadsheet to the Clipboard using the Copy option in the spreadsheet. (A quick way of
selecting an entire Excel spreadsheet is to click the cell top-left cell between the '1' and 'A' cells.) The
changes can then be pasted into DRAINS using the Paste Data from Spreadsheet option in the Edit
menu. Because the transfers are made via the Clipboard, it is not necessary to have any direct
connection between the spreadsheet file and the DRAINS file.
A similar output spreadsheet using ILSAX hydrology can be obtained from Geoffrey O’Loughlin at
[email protected]
GIS File Exports
(a) Exporting ESRI (ArcView, ArcInfo, ArcMap) Files
It is first necessary to establish a system that is capable of being run, such as the example shown in
Figure 3.49.
DRAINS User Manual
November 2014
Selecting the ESRI Shapefiles… option
from the File -> Export menu presents
the message shown to the right:
If you continue, you will then need to
nominate a filename for shapefiles in the
dialog box shown in Figure 3.50. You
can see from the existing files in this
example how six ESRI SHP files are
established. Another 12 SHX and DBF
files will also be produced.
After a name is entered, the process is
complete if there are no results. If results
are available, the dialog box shown in
Figure 3.51 appears. A suitable name
should be added describing the results; here they are for a 2 year average recurrence interval storm. The
limited size is due to restrictions on the size of column headings in the database files used in ArcMap.
After this is entered, the process is finished.
Figure 3.49 System to be Exported to GIS
DRAINS User Manual
November 2014
Figure 3.50 Nomination of Shapefile Name
Figure 3.51 Naming of Set of Results
If a background is present in the DRAINS model, this will be transferred with the ESRI files. The
transferred files can now be viewed in ArcMap as shown in Figure 3.52.
Figure 3.52 Display of Results in ArcMap
A database table is associated with each theme, as shown in Figure 3.53. Note that most values are
specified as strings of characters, and must be converted to numerical values using procedures within
ESRI programs if these are required to provide thematic displays where colours, line thicknesses or other
attributes indicate properties.
Figure 3.53 Table of Pit Data
Note that this includes results with the '2Yr' added to headings as a suffix. If another run is made and the
process is repeated with one of the existing shapefiles nominated in the Save As dialog box, additional
DRAINS User Manual
November 2014
results will be appended, as shown in Figure 3.54 and Figure 3.55, where 100 year ARI results are added
to the 5 year ARI results.
If data from a GIS data base can be assembled into this same format, less the results, the File ► Import
option ESRI Shapefiles… can be used to import data into DRAINS.
Figure 3.54 Naming of Second Set of Results
Figure 3.55 Expanded Table of Pipe Data
(b) Exporting MapInfo Files
It is first necessary to establish a system that is capable of being run in DRAINS, such as the
demonstration example shown in Figure 3.49. Selecting the MapInfo files… option from the File ->
Export menu presents the message in Figure 3.56. If you continue, you will then need to nominate a
filename for MID/MIF files in the dialog box shown in Figure 3.57.
Figure 3.56 Message in MapInfo File Export Procedure
DRAINS User Manual
November 2014
Figure 3.57 Nomination of MID/MIF File Name
You can see from the existing files in this example how six MapInfo MIF files are established. Another six
MID files are also produced. After a name is entered, it will be necessary to nominate the projection to be
used if the data has not been brought in from MapInfo files. This can be done in the dialog box shown in
Figure 3.58 that appears. This has a similar format to the equivalent window in MapInfo.
Figure 3.58 Nomination of Projection
The process is then complete if there are no results. If results are available, a dialog box similar to that
shown in Figure 3.51 appears. A suitable name should be added describing the results; such as '10Yr' for
a 10 year average recurrence interval storm.
A background in the DRAINS model will be transferred with the MapInfo files. If there are any problems
with the projections, these can be overcome by editing the ASCII MIF file, inserting a line giving the
appropriate projection. The transferred files can now be viewed in MapInfo, as shown in Figure 3.59.
DRAINS User Manual
November 2014
Figure 3.59 Display of Data transferred to MapInfo
'2Yr' and '100Yr' are added to headings as a suffix. If another run is made and the process is repeated
with one of the existing shapefiles nominated in the Save As dialog box, additional results will be
Hydrograph Outputs in TUFLOW Format
Using the File → Export → Tuflow TS1
Files… option, you can export hydrographs
in a format used by the 2-dimensional
TUFLOW hydraulics program (BMT WBM,
2010). Hydrographs are produced for subcatchments, pipes and overflow routes for
all storm runs made prior to exporting. This
format can be read by spreadsheets and
editors, and can be used by other programs
than TUFLOW. When a transfer is made,
the message to the right appears:
Outputs to Linked Applications
As part of the dedicated links from Autodesk Land Desktop, Advanced Road Design and 12d to DRAINS,
results are transferred back to these applications via database files and the spreadsheet outputs, as
described in Section 0 and Section 3.2.7.
Merge Outputs (and Inputs)
The merge options allow you to add DRAINS systems together. It is first necessary to export a system as
a merge file, before importing it into another system. The two systems are linked the pits at each end of a
common pipe, which is the lowest pipe in the system to be added. The procedure is as follows:
Edit the files so that both include two adjacent pits with the same names. Make sure that you have
zoomed in to the model so that there is an observable distance between pits. (If the model is at a
low magnification, so that individual pipes cannot be seen, there may be round-off errors in the
process that DRAINS applies when creating a merge file. This may lead to sub-catchments and
other components being connected wrongly.)
In the file to be added, use the Export a Merge File... option in the File menu to create and name a
.mrg merge file.
DRAINS User Manual
November 2014
Then close the file to be added, and open the file with the receiving system. Using the Import a
Merge File… option in the File menu, read in the .mrg merge file created in Step (b).
The merged system will appear. The orientation of pipes will be that of the receiving system. You
can then tidy this up, save the combined file and make runs as required.
This process is demonstrated by opening the file shown as Toowoomba Addition.drn in Figure 3.60
and creating a merge file named Toowoomba Addition.mrg with the Export a Merge File option in
the File menu.
This can then be imported into Toowoomba Estate.drn, displayed in Figure 3.23, using the Import a
Merge File option in the File menu. The joined system is shown in Figure 3.61.
It is possible to join models together when these do not have common pits, by drawing top dummy pits.
The process is as follows:
On the first model, draw two dummy pits 100 m or 200 m apart. Give them distinctive names. Pit
details should be filled in, but the exact information entered is not important.
Export the model data to a spreadsheet using the procedures in Section 3.5.4.
Open the second DRAINS model and export the data from this to another worksheet in the spread
sheet. Among the PIT/NODE outputs insert two additional rows.
Return to the worksheet created from the first DRAINS model and copy the two rows describing the
dummy pits. Paste these into the two blank rows in the worksheet for the second model. Then
copy the whole worksheet to the clipboard.
Return to the second DRAINS model and use the Edit → Paste Data from Spreadsheet option to
bring the two dummy pits into this model.
Figure 3.60 The File that is to be Added using the Merge Options
DRAINS User Manual
November 2014
Figure 3.61 The Combined File
Both models should than have two common pits and can then be joined using the merge procedure
described earlier in this section. If necessary, the background can be replaced using the procedures
described in Section 3.2.2(b). A problem may occur if there is a conflict in the 'id' numbers that are used
by DRAINS for internal purposes, and which appear in the spreadsheet output. Contact Watercom Pty
Ltd if this occurs.
Template File Exports
To assist in the preparation of files that can be used as the basis of other models, DRAINS has a function
implemented by selecting File → Export → Drains template file…. This opens the following window:
After selecting a file type and clicking the Next button, a window appears allowing the file name and path
to be nominated, and it can then be saved.
Figure 3.62 Dialog Box for Exporting Template Files
Help Options
The Help system in DRAINS can be called in three ways: (a) by choosing Contents in the Help menu, (b)
by pressing the F1 key, or (c) by pressing a Help button in a property sheet or dialog box to deliver
context-sensitive Help.
DRAINS User Manual
November 2014
It is implemented as a HTML Help system in a three-pane window with an index as well as topics, as
shown in Figure 3.63. The panes can be re-sized as required.
Figure 3.63 A Typical HTML Help Message
Within particular Help topics, the underlined links open additional topics. The index can also be used to
find specific topics.
With well over 200 topics, the DRAINS Help system provides a comprehensive guide to the program, and
a glossary of urban stormwater drainage terms and concepts. It complements the material in this manual,
and provides timely advice on enhancements to DRAINS.
DRAINS User Manual
November 2014
This chapter outlines how DRAINS works and how to perform design and analysis tasks. The detailed
procedures within the program cannot be explained in simple terms, so only a general description is
provided here. Likewise, DRAINS can be put to many uses, and it is not possible to cover all of these.
The DRAINS training workshops provide information of this type though examples and exercises.
DRAINS Workings
DRAINS uses metric units throughout. Where possible, it follows SI conventions for these, but in many
displays and outputs it is not possible to show superscripts. Thus, 'cu.m' and 'cu.m/s' are frequently used
in place of 'm3' and 'm3/s'.
DRAINS is written in C++ and works on PCs with Microsoft Windows operating systems from Windows 95
to Windows 7. The calculation procedures from the PIPES program are used to model pressurised flow
situations. It inputs and outputs data in binary, spreadsheet CSV, DXF, ESRI shapefile, MapInfo
MID/MIF and data base formats.
DRAINS is structured so that different hydrological and hydraulic models can be run via the same
interface, with many functions being shared, such as the display of hydrographs. There are choices of:
Hydrological models - ILSAX, storage routing and extended rational method (producing hydrographs)
and rational method (producing peak flowrates);
Hydraulic calculations – standard or premium hydraulic model calculations, and perhaps for older
models, the obsolete basic model calculations; and
Procedures – design of pipe systems or analysis of pipe, open channel and detention systems.
The free DRAINS Viewer operates in the same way as DRAINS, but is limited to inspecting data and
results saved in a .drn file. It can also export spreadsheet and CAD outputs.
Data Storage and Files
To run, DRAINS requires run specifications, rainfall data and a pipe or channel system. This data is
stored temporarily in the computer’s memory and, more permanently, in a binary data file with a .drn
suffix, such as the sample files that have been described in this manual. After a data file has been saved,
you can re-open it in DRAINS and modify the data. Since it is saved in binary format, it cannot be viewed
or changed using a text editor. The binary file formats change as DRAINS is updated, but will always be
back-compatible. That is, the current version of DRAINS will open and operate with files created in
previous versions. You will probably not be able to open files created with a later version of DRAINS than
the one you are using - it is not forward-compatible.
Each DRAINS .drn file is effectively a data base describing a drainage system and its components,
together with reference data bases for pipes, pits and overflow routes, and possible the results of a run.
Most of the data on the drainage system can be readily accessed in ASCII or text form, using the
spreadsheet output option described in Section 3.5.4. Data on rainfall patterns, hydrological models and
run specifications are not transferred to spreadsheets.
As well as the sets of pipe, pit and overflow route types and associated information contained in the .drn
file, a set called Drains.db1 is contained in the C:/Program Data/Drains folder. This is set that is
applied when DRAINS is first .opened. The regional sets of pipe, pit and overflow route data for New
South Wales, Queensland and other states are stored as .db1 files in the C:/Program
Files/Drains/Program folder, along with the Drains.exe file. These sets can be installed using
the Default Data Base option in the Project menu, which copies these to Drains.db1. (It is important
that users determine what they require before starting a project, as it may be awkward to change the
available options later.)
DRAINS User Manual
November 2014
As shown in Figure 4.1, you can operate DRAINS through a number of processes, such as:
(a) Data entry and file storage,
(b) Performing calculations,
(c) Inspection and possible storage of results,
(d) Changing or correcting data, and re-running calculations,
(e) Transferring data and results to files and other programs.
12d Digital
Terrain Model
DRAINS model in
computer memory from
keyboard and other
sources, displaying this on
Autodesk LD
Or Civil Design
Spreadsheet file
Run DRAINS using
calculation engine in
Design or Analysis
Results stored in
computer memory, to
be inspected
Data stored in
binary file
Data in Data base and
GIS programs
Stored data and results
in spreadsheet, DXF,
GIS or Data base
Figure 4.1 Typical Processes in DRAINS
Performing calculations in Action (b) is a batch process. Once started it continues without intervention by
the user, unless it is aborted by pressing the Esc key. On the other hand, Actions (a), (c) and (d) are
event-driven. They can be carried out in many different ways, depending on your preferences. The
programming style follows Microsoft Windows conventions, so that it will be familiar to most users.
The main calculation procedures in DRAINS are:
hydrological calculations, which produce the flowrates to be transported through the drainage
the hydraulic design procedure for pipes, which determines pipe diameters and invert levels allowing
for minor and major storms, and,
hydraulic analysis calculations for pipes and channels, which define flow characteristics such as
discharge rate, velocity and depth, and determine whether systems can convey flows without
Applications using hydrological storage routing models may only apply the first of these procedures.
DRAINS User Manual
November 2014
Initial Processes
The various run options are described in Section 3.4. Before these become available in the Run menu,
DRAINS performs checks to confirm that:
a hydrological model and rainfall patterns have been specified,
the components of a system are joined correctly,
the drainage system components have been fully specified.
The run options in the menu are greyed out if these conditions are not met.
Once a run begins, DRAINS sorts through the various components to define linkages throughout the
system and the order in which calculations should occur. Using the coordinates of the objects, it identifies
connections between pits or nodes and links, such as pipes or channels where the positions of the ends
of a link are within the symbol of a node in the Main Window. The connections between pits and subcatchments are established where the symbols overlap. The pits or nodes at the extremities of drainage
systems are identified as those having no incoming links. DRAINS also checks inputs for any
inconsistencies that have escaped the checks in property sheets during data entry.
Hydrological Calculations
With the ILSAX model, hydrological calculations involve the computation of the hydrographs from the
paved and grassed surfaces of each sub-catchment using the Horton loss model and the time-area
routing methods described in Section 5.3.2(b). They are carried out in the same way for both Design and
Analysis runs. With the extended rational method and the storage routing models, hydrographs are
calculated by different procedures. The rational method procedure only calculates peak flowrates.
In calculated hydrographs, flowrates are defined at times that are multiples of the calculation time step
that is (a) defined in the Options property sheet called from the Project menu, or (b) automatically
defined by DRAINS using various criteria, including the requirement that unpressurised flows should take
at least one time step to travel through any pipe in the system.
DRAINS results change when it is run with different time steps. Most of the time, users should accept the
time step defined by the program. This is determined so that it will take at least one time step for water to
travel through each conduit. The minimum time step is 0.005 minutes or 0.3 seconds, and the maximum
for pipe calculations is 1 minute. Sensitivity tests can be carried out to determine a suitable time step. If
two time steps provide essentially the same results, the longer one can be used. Generally, smaller time
steps will give more accurate and stable results, but this may not always be the case.
The hydrographs in all links begin at the same time, the start of the storm rainfall pattern. Any baseflows
and user-provided inflow hydrographs introduced at pits or nodes begin at this starting time. Userprovided hydrographs can be specified at any time step, but flowrates will be converted to the calculation
time step by linear interpolation.
Where flow values are zero, due to:
losses absorbing the initial rainfalls,
a lag time or factor being specified for a grassed area hydrograph in the ILSAX model (see Section
2.3.5), or
a delay used to model a moving storm (also see Section 2.3.5),
an appropriate number of zero flows will be placed at the start of the hydrograph so that it begins at the
rainfall pattern’s starting time. This common starting time simplifies the combination of hydrographs at
With the rational method model, peak flows are calculated and stored with the data for each component.
Hydrographs produced by other models for sub-catchments, pipes, channels, overflow links and detention
basins can be viewed as graphs or tables using the pop-up menus for individual components, and can be
transferred to the Clipboard, as shown in Figure 5.3. They also can be printed out in the Print Data and
Results… option in the File menu. Calculated hydrographs and HGL levels are stored temporarily as
part of each sub-catchment ‘object’, and can be retained in the saved .drn file.
DRAINS User Manual
November 2014
The procedures for the storage routing models emulating the RORB, RAFTS and WBNM models, are
simpler than those from ILSAX. Results are presented in the same way as ILSAX hydrograph outputs in
Figure 4.2. .
Figure 4.2 DRAINS Hydrograph Outputs for an ILSAX Sub-Catchment
Hydraulic Calculations
(a) General
Once hydraulic calculations begin, DRAINS determines the inflow into the pipe and channel system at
each time step. At each node, the following flows are combined: flows off areas on the local subcatchment, any overflows from upstream pits or detention basins that are directed to this destination, any
baseflows or flows from user-provided inflow hydrographs applied at the surface for a pit or simple node.
This surface flow is assumed to enter the system without restriction at a simple node, detention basin,
culvert or bridge. For an on-grade or sag pit, the pit capacity relationship defined in the Pit property sheet
is applied to estimate the inflow rate, as described in Section 2.3.2.
For Design calculations, a pipe system will be sized to carry all flows that enter the system. The only
overflows will be the bypasses caused by restrictions on inlet capacities. In Analysis, there may be
upwelling of flows from the pit due to the capacity of the downstream pipe system being insufficient to
carry the assumed flows. As shown in Figure 4.3, these are added to any bypass flows to define the total
overflow from the pit.
Approach Flow
Bypass Flow
Pipe Flows
Pipe Flows
Figure 4.3 Pit Inflows and Outflows
DRAINS User Manual
November 2014
No overflows can occur at simple nodes or from ILLUDAS type pits (now obsolete). Situations where
overflows or breakouts occur from channels might be modelled by adding a detention basin at the
overflow location, as noted in Table 2.2.
The calculated inflow rates at each time step can then be used as boundary conditions for the main set of
calculations through a pipe or open channel system. These provide information on HGLs and water
surfaces at nodes, and flowrates through the various links within a system.
With the rational method, only peak flow conditions are considered, but for hydrograph models, conditions
are calculated at each time step..
(b) Basic Hydraulic Calculations
In the basic calculations that are now obsolete, drainage systems are analysed by making downwards
and upwards passes through the pipe or channel network at each time step, going from each pit or node
to the next one downstream or upstream. The first pass moves downwards from the top of each line in
the system, establishing the surface flows arriving at each node by adding flows from the local catchment,
overflows from upstream and user-provided flows. Using the pit inlet capacity relationship, bypass flows
are determined. The flow entering the pit is then added to any flows through upstream pipes and possible
user-provided inflow hydrographs to define provisional pipe flows.
When the calculations reach the system outlet or outlets, DRAINS makes the upwards pass, starting from
the tailwater level at the outlet. Allowing for pipe friction and pressure changes at pits, it defines the
position of the HGLs at pits and nodes, and if necessary, modifies the flowrates in the pipes and the
corresponding overflows. For part-full pipe flow, this process is carried out by projecting HGLs upwards
and allowing for pressure changes at pits. If a pipe flows full, a pressurised flow calculation procedure is
used to define HGLs at pits and flowrates in pipes. Whenever it encounters a junction, DRAINS projects
HGLs up both branches from the pit water level. If the calculated water level in a drop pit is determined to
be below the invert level of an incoming pipe, the tailwater is set at the critical depth in this pipe, and
upwards HGL projections are continued.
This model provides information on water levels at pits and nodes and flowrates through pipes. When
there is subcritical open channel flow, the standard step method employing the Colebrook-White or
Manning's equation is used to compute backwater curves in pipes and channels. Where pipe flow is
supercritical, the water surface is assumed to follow the normal depth. (In open channels, the basic
model conservatively assumes surfaces to be no lower than the critical depth.)
The basic calculations define HGLs at nodes and inside pipes for subcritical part-full flows, but they only
presents the results at nodes. They define flowrates in links such as pipes or channels, and provides
continuity checks in the spreadsheet output summing the inflows and outflows at each node. The
flowrates presented for pipes are those calculated at their upper ends, so that the flows displayed in
DRAINS outputs at a particular time will probably differ from the flowrates emerging from the pipe at that
time. If a pipe is unpressurised, these outflows will be the same as the flows that entered a conduit a
certain number of time steps previously (depending on the pipe length and flow velocity). If it is
pressurised, there is no time delay. DRAINS manages the transfers between part-full and full-pipe flow
so that there are only small continuity errors.
(c) Unsteady Hydraulic Calculations
The unsteady flow calculations carried out with the standard and premium hydraulic models are quite
different, using the equations of mass and momentum conservation (Section 5.6.4) to set up a matrix
specifying the equations to be solved over a space-time grid. The space or x dimension represents the
conditions at various points in a system, with conditions being calculated at multiple points in longer
conduits. The time or t dimension relates to the time steps used. While results are reported at fixed
times, calculations can be carried out at smaller time intervals. The main quantities being calculated are
water elevations H and flowrates Q. The main calculation involves the solution of the matrix equations to
determine H and Q values at all locations at each time step during the simulation. As well as the core
calculation procedures, this involves the determination of states at many boundaries in the system (such
as pits where water enters, and outflow locations).
Water or HGL levels are presented at pits and nodes and also appear on some plots of pipe, overflow
route and open channel long-sections. The flowrates displayed apply at the centre of the link.
The DRAINS hydraulic calculation procedures permit two outlet pipes to be specified for each pit, and can
model looped or branching pipe systems, where there is a bifurcation with two pipes coming out of a pit.
The premium hydraulic model permits two or more overflow routes from sag and on-grade pits, so the
DRAINS User Manual
November 2014
invert levels of overflow routes from a pit can be at different levels. This allows modelling of situations
that cannot be adequately modelled using the basic or standard models (e.g. overflow from an on-grade
pit down a gutter and across the road crown).
(d) Pit Modelling
As flows pass through pits, a pit pressure change relationship is applied, using the ku factor shown in
Figure 4.4, which is specified by the user in the pit’s property sheet.
Grate Flow
k LV0
k uV0
Figure 4.4 Pit Pressure Change Relationships
The change from part-full to full pipe flow often results in a large increase in the pit pressure change.
This raises the HGL level and causes a rise of HGL that moves upwards through the system. A jump in
pressure at a pit may actually be due to filling of another pit somewhere downstream. A similar drop in
HGL and pressure may occur when a full-flowing pipe changes to part-full flow.
While pit pressure changes have been studied for full-pipe flows, there is little information available about
pit pressure changes and energy losses in pits with part-full flow. Currently, DRAINS assumes that ku
coefficients are constant , and the same for both full- and part-full flows. This is likely to be conservative,
overestimating changes for part-full flows. It also provides more stable results.
If a sag or on-grade pit is defined as being sealed using the check box labelled 'Pit has bolt down lid' in
the Pit property sheet, the HGL can rise above the surface without any upwelling occurring. DRAINS
calculates upwelling flows using hydraulic analyses. With the basic hydraulic model, no outlet restrictions
are placed on upwelling flows unless the pit has a bolt-down lid. With the standard and premium
hydraulic models, a hydraulic loss is assumed to occur when water upwells. This is based on the sag pit
depth-inflow relationship for the pit type and size being used.
(e) Tailwater Levels
At system outlets, DRAINS sets a tailwater level, depending on the entries in the Outlet property sheet. If
a free outfall is specified, it determines the higher of the normal and critical depths for the current flowrate.
If a higher tailwater level is specified in the property sheet for the particular storm being analysed, this
level becomes the starting point for an upwards projection in the obsolete basic hydraulic model and a
boundary condition in the current unsteady models.
Where a drop pit is so deep that the pit water surface is below the invert of the upstream pipe, the starting
level for upstream HGL projections will be set in the same way as for a free outlet. It will be the higher of
the normal and critical depths in the upstream pipe. In effect, the calculations start again at this pit.
(f) Surface Overflows
Overflows follow the defined overland flow path to a destination, with flows being lagged by the specified
time delay, which must be at least one calculation time step.
Although a slope and cross-section must be specified for flow paths, the standard hydraulic method
calculations allow a flow to go from one pit or node to another at a higher surface level, despite warnings
that are displayed by DRAINS. The premium model is stricter, and all overflow paths must have
downwards slopes. In this model, overflow routes are modelled in the same way as open channels, and
backwater effects can apply.
DRAINS User Manual
November 2014
(g) Detention Basins
The calculations for detention basins in DRAINS can be complex because the elevation-discharge
relationship will change if the downstream tailwater level submerges the outlet. This can happen at many
time steps during a DRAINS run, so that the relationship changes. By contrast, ILSAX and most other
models for trunk drainage systems assume that the relationship is fixed. Thus, DRAINS can model
interconnected basins.
Flows through culverts and bridges are modelled using the same equations as outflows from detention
basins, since they obstruct flows and can have low level outlets (the channel under the roadway) and high
level outlets (overflows over the road). They do not have any associated storage. Where this may be
significant, the situation can be modelled as a detention basin. DRAINS returns similar information in the
Main Window for detention basins, culverts and bridges - the upstream and downstream water levels.
This process of fitting a hydrological computer model to observed or recorded information is done by
varying the model parameters. Some calibrations made using DRAINS and similar models are presented
in Sections 5.3.3 and 5.3.5. In DRAINS, the main factors that can be varied are:
the soil type, depression storages, and AMC,
the proportions of paved, supplementary and grassed areas,
the times of entry for paved, supplementary and grassed areas.
All of these relate to physical quantities that are easily understandable, so that values that are estimated,
as is usually the case, will not be greatly wide of the mark.
Where rainfall and runoff data for storms is available, the hydrological modelling in DRAINS can be
improved by calibration, though not to a large extent (O’Loughlin, Haig, Attwater and Clare, 1991). Times
of entry and travel through a drainage system can be defined more accurately. Less accurate calibrations
can also be carried out based on ponded volumes. If rainfall is available for a storm, DRAINS can
estimate the stored volume at a location where depths have been observed. The volume from DRAINS
can be compared with that corresponding to the maximum depth observed.
Calibration of drainage system hydraulics is usually performed by altering the roughnesses of conduits to
match observed water levels. Observations may often be available for open channels, but are unlikely to
be available for closed pipe systems, unless a special gauging programme is undertaken. If such
information is available, it can be used to verify the DRAINS model, though it is likely to be difficult to
refine the model because of the many pipe links that may be involved.
Interpretation of Results
Most DRAINS hydrographs and HGL plots are simple 'rise and fall' patterns, reflecting the simple design
rainfall patterns that are commonly used. However, in complex or badly-implemented pipe systems,
complex patterns such as the hydrograph shown in Figure 4.5 can occur.
A DRAINS plot may show frequent rises and falls at some times, giving rise to 'black ink'. The plot also
shows a flow peak that has caved in, or reversed itself. This can occur when the HGL at the pit upstream
of a pipe overflows, while the HGL at the pit at the downstream end is still below the ground surface. As
flowrates increase, or tailwater levels rise higher, the HGL level in the downstream pit rises, flattening the
HGL for the pipe and reducing the flowrate through it. This produces the 'hollowed out' effect.
The hydrograph in Figure 4.5 also displays negative flows, indicating that there has been a flow reversal.
Flows can reverse in any DRAINS model if the HGL slope is negative, but this occurs rarely. In this case,
a high HGL downstream causes flows to run backwards.
These can also be sudden 'spikes' and instabilities that occur at very low flows, due to waves that are
numerically generated. Users should interpret plots with strange patterns to understand what is going on.
Often this requires inspection of two or more flow and HGL plots together.
DRAINS User Manual
November 2014
'Hollow' Peak
'Black Ink'
Negative Flow
Figure 4.5 Complex Flow Hydrograph
4.2.10 Design Procedures
The pipe design process in DRAINS makes a pass down the various branches of a drainage network
from pits at the tops of lines to the main outlet. At each pit, it determines the maximum pipe outflow,
allowing for inlet flows, flows in upstream pipes, and any baseflows or user-provided direct hydrograph
flows. It then determines suitable pipe sizes and invert levels, taking account of:
• the roughness and the allowable cover depth associated with the chosen pipe type,
• the values set of minimum pipe slope, pit freeboard and fall in the Options property sheet opened
from the Project menu,
• a restriction preventing pipes decreasing in diameter as the calculations move downstream,
• likely pit pressure changes at pits in full or part-full pipe flows, and
• the hydraulic capacities of pipes with various diameters and slopes.
In 2014, an enhanced design procedure has been introduced. Following a design by the original
procedure, a review is carried out that reduces pipe sizes where possible. It provides a message saying
how many pipes were able to be downsized. Pipes reduced by more than one size increment will only be
counted as one pipe downsize.
It may still be possible to improve on a DRAINS design by manually downsizing pipes, although there is
much less scope to do this than with the original design procedure. If you try to do this, some things to
keep in mind are:
• You should not make any pipe smaller than the biggest pipe upstream (i.e. if you have a run of say,
1200 mm pipes, you could try to downsize the one furthest upstream. If you can'y downsize this, you
will not be able to downsize any pipes in the run.
• For major storms you should use the same freeboard criterion as set in Project → Options. If you
want to relax this criterion for major storms, you should also relax it in Project → Options prior to a
design run in DRAINS.
The selection of invert levels is mainly based on allowable cover depths and slope restrictions. The aim
is to keep the pipe as shallow as possible, and pipe sizes are increased where necessary to achieve this.
(In cases where pipes need to be set deep enough to pass under other services, such as water supply
pipes, increased cover depths can be defined in the Project → Options property sheet, effectively
specifying a minimum pipe depth.)
DRAINS User Manual
November 2014
Allowance is made for cover depths at intermediate levels along a pipeline, as defined in the Survey Data
property sheet called from a Pipe property sheet (see Section 2.3.4). A result is shown graphically in
Figure 4.6. This output also shows a pit with a significant drop, which might be a consequence of aiming
to keep the pipe system as shallow as possible. If you wish to grade the upstream pipe down to the pit, it
will be necessary to adjust the invert levels and run the model in Analysis mode, or make the pipe inverts
Figure 4.6 Display showing a Drop Pit and Intermediate Levels
DRAINS can automatically design to avoid fixed services, where possible, using service location
information entered in the Survey Data property sheet and a minimum design clearance to services set in
the Options property sheet called from the Project menu. One such service is shown in Figure 4.6 and
also in Figure 4.7.
If a Design run is made with the positions of some of the pipes fixed, the results must be carefully
checked, especially if these are located in the middle of lines. In some complex Design cases, pipes
entering pits might be lower than a fixed pipe flowing out. The fallback in this case is to run in Analysis
mode with pits and pipes made 'existing', and to vary pipe sizes and invert levels individually to achieve a
satisfactory design.
Where multiple storm patterns are specified, the program repeats the downwards pass for each storm
and selects the pipe diameters and invert levels that convey the most critical flows.
DRAINS User Manual
November 2014
Figure 4.7 Long Section Display (from Pop-Up Menu for a Pipe
The design procedure also determines the sizes of inlet pits, using a method that was first presented in
the Queensland Urban Drainage Manual (Neville Jones & Associates et al., 1992). The method focuses
upon the flows along overflow routes. It sets appropriate safety levels for these, in terms of tolerable flow
depths in the minor and major storms and a maximum velocity x depth product. A point along each flow
path must be nominated, by specifying a cross-section from the Overflow Route data base as shown in
Figure 4.8, a percentage of downstream catchment contributing to the flow, and a longitudinal slope.
The basis for selecting the percentage of the downstream sub-catchment is explained in Section 2.3.6.
Figure 4.8 The Overflow Route Property Sheet
Having established safe flows for each flow path, the method then determines the pit and pipe sizes
needed to restrict the surface overflows to the safe limits, considering both minor and major flows.
DRAINS User Manual
November 2014
This process requires that pit types be classified into families and sizes, in a similar way to the
classification of pipe types and diameters. With the user having defined the pit and pipe types required,
DRAINS searches through the available sizes to determine the required ones at each overflow location.
It also selects pipe sizes so that at a major storm level, such as the 100 year ARI storm event, HGL levels
at pits are still below the ground surface. This ensures that the drainage system does not completely fill
with water, and the pipe flows will be maintained even when stormwater ponds over pits.
In some cases, DRAINS cannot arrive at a solution that meets the safety requirements, most obviously
when the flow from a sub-catchment is much larger than the capacity of any of the pits that can be
selected. DRAINS returns the notice in Figure 4.9, advising that the pipe system must be changed or that
different pits are required.
Figure 4.9 Warning of Failure to Define a Feasible Design
The results can be checked by Analysis runs to ensure that the design conditions are met. By taking full
advantage of allowable surface flow capacities, the sizes and costs of pipe systems can be minimised.
Applying DRAINS
A key feature of DRAINS is integration. This occurs internally, with the data inputs, hydrology, hydraulics
and presentation of results operating in the same package, and the ability to model different parts and
scales of stormwater systems together. It also occurs externally, with the linkages to other programs
shown in Figure 4.10.
System Asset
Data Base
GIS Programs
CAD Files,
Access Files
Figure 4.10 Integrated Linkages between DRAINS and other programs.
The general operation of DRAINS have been illustrated in Chapter 1. This section provides guidance on
applications to specific types of stormwater drainage system.
Designing Subdivision Piped Drainage Systems
Design runs are mainly made for new systems on greenfields sites where the developer and designer
have considerable scope to alter the system. The available information will be:
a survey of the area showing contours to a standard datum such as AHD and a mapping grid such
as MGA94, available on paper and electronically as a CAD file in a format such as DXF or DWG.
the planned layout for roads, either on plans, or as a partly- or fully-completed road design model;
DRAINS User Manual
November 2014
cadastral (property boundary) data, available on plans and as drawing layers over which the contour
drawing can be overlaid;
the technical requirements of the consent authority for the project;
local design rainfall data and other local information.
There is usually some give and take in design, so that the road and allotment layout can be altered to suit
drainage requirements. However, the initial layout made by an experienced subdivision and road
designer should anticipate potential conflicts.
The products or 'deliverables' of the design will be a drainage layer in the drawings with all drains and
channels detailed, together with design calculations. Plans, specifications, tables of quantities and
estimated costs can be derived from these.
The main aims in designing pipe networks with DRAINS are to develop a file that describes the proposed
system, and to produce the deliverables - plans and documentation. The single .drn file can be run for
both Design and checking by Analysis, and can quickly be re-run, with data and results being transferred
to a spreadsheet or report. It forms the basis for the design variations and checks that may be required.
For a small system, data can be entered from the keyboard into property sheets, as described in Chapter
1. For larger systems, it is likely that information will be transferred from a CAD file, as described in
Section 3.2.2, or from DTMs such as 12d and Advanced Road Design. Imported data can be augmented
with data entered directly into the property sheets for components. The information for a component is
retained when it is copied and pasted using the Copy Shape option in the pop-up menu for a component
and the associated Paste Shape option. It is often easier to copy and paste an existing component and
to modify its data, rather than to enter all data each time an object is created.
For large systems, the spreadsheet outputs and inputs described in Section 3.5.4 can provide an efficient
means of entering repetitive data. Components can be entered with nominal values and can then be
edited in the Data spreadsheet, before transferring the information back to DRAINS. The process is
shown diagrammatically in Figure 4.11.
Figure 4.11 The Design Process
Using CAD and DTM programs, catchment areas can be defined as polygons and the areas directly
measured. The lengths of flowpaths, and in some models, their slopes, can also be determined. In some
models, the automatic definition of impervious and pervious areas will be possible where suitable
overlays are available.
DRAINS User Manual
November 2014
For convenience in design, the parts of the system can be separated into small sub-systems. For
example, where several branched pipe systems in steep terrain flow to a common open channel, the pipe
systems can be analysed independently, as long as there are no backwater effects. In flat terrain with
backwater influences the system must be designed as a whole. Individual systems can be joined using
the merging procedures described in Section 3.5.8.
DRAINS produces information on pipe sizes, invert levels and locations that can be transferred to drawing
programs to produce detailed plans and longitudinal sections. The spreadsheet tables act as
documentation that can be printed or supplied in electronic form to a consent authority, together with the
DRAINS data files. Diagrams of the network can be printed, say as a PDF file using the File → Print
Diagram option.
Models and results can be checked by persons inside or outside the designer’s organisation using the
DRAINS Viewer, which is free. A reviewer can open all property sheets in a model and export data
summaries in spreadsheet format. If a DRAINS file contains stored results, these can also be viewed and
exported to spreadsheets. CAD outputs and system diagrams can also be exported, but other types of
output are not available. It is not possible to edit or run files in the Viewer. Since reviewers have direct
access to models, it should not be necessary to provide elaborate printed sets of results to reviewers.
However, some converter spreadsheets have been developed to transfer results from ILSAX and rational
method models to tables similar to those in Australian Rainfall and Runoff and the Queensland Urban
Drainage Manual. These are available as downloads from www.watercom.com.au (see the last item on
the downloads page).
Since DRAINS runs rapidly and its results are quite apparent, it is easy for consent authorities such as
municipal councils to run files and inspect the results, or else to view these using the DRAINS Viewer. As
discussed in Section 4.3.4, files prepared by consultants can be retained and incorporated into the
authority's DRAINS model of its overall drainage system.
The results provided by an appropriate ILSAX hydrological model are likely to be superior to those
obtained using the rational method, since allowance can be made for multiple storms and detention
storages, and major system modelling is more accurate. The extended rational method gets overcomes
most of these difficulties, as it produces hydrographs using a rational method loss model.
The pipe system design method employed in DRAINS is dependent on having good information on pit
inlet capacity relationships. The best data is available from Queensland where overflows are larger than
in southern states, and more attention has been given to controlling them. If good quality pit capacity
data is unavailable, the Design method cannot be realistically employed.
The design method can be applied with the rational method and extended rational method as well as the
ILSAX hydrological model. The design calculations for sizing pipes and determining invert levels are
carried out using simplified assumptions, and need to be followed by one or more analysis runs.
DRAINS allows hydrological models to be swapped easily, so that it is not difficult to convert rational
method models to ones using ILSAX hydrology. Only the hydrological model and rainfall data need to be
changed, and the impervious areas for each sub-catchment to be split into paved and supplementary
areas. The reverse change, from an ILSAX Model to the rational method, can be done even more easily.
This might be done to compare the results given by the models, or to check an older design using rational
method hydrology.
Designing Infill Developments with On-Site Stormwater Detention Systems
Design work for re-developments, and developments located within established urban areas, is more
complex that greenfields design. There are many more constraints, such as:
the presence of existing infrastructure such as water pipes and electricity cables,
the need to connect into an existing drainage system, which may create problems due to low
availability of head and limited downstream capacity,
the presence of multiple land-owners,
difficulties of construction due to limited space and conflicts with traffic and other activities in the
It is unlikely that designs of pipe systems can be carried out automatically, as in a new subdivision.
Analysis capabilities are required when exploring solutions. Users will probably have to vary some
DRAINS User Manual
November 2014
features by hand to develop a trial and error solution. Fortunately, DRAINS can be easily edited and reruns can be carried out rapidly.
While DRAINS allows users to mix pipes that have fixed inverts with pipes with positions that can be
varied, it may not be able to develop with a suitable design in some cases. When dealing with a complex
situation, a suitable strategy would be to see whether DRAINS can come up with a satisfactory design
first, and then make modifications by hand to cope with problems such as conflicting services and the
inability of a pipe system to match the inverts of the downstream pipe to which it must connect, while
carrying the required design flows.
DRAINS can 'design around' existing services or utilities, and can allow for surface levels all the way
along a pipe if suitable survey data is provided in the Pipe property sheet. However, the solution provided
may set pipe inverts too deep, so that it will be necessary to make adjustments by hand. It may be
necessary to use stronger pipe classes (with greater wall thicknesses), multiple pipes or box-section
conduits to reduce the cover requirements. In complex cases, relocation of existing stormwater pipes or
other services may be the best solution.
Because re-developments usually involve an increase in the density of development and the percentage
of impervious area, several drainage authorities have imposed on-site stormwater detention (OSD)
requirements. These have become an important and often complicated issue for designers. The Upper
Parramatta River Catchment Trust has been the most influential developer of OSD design procedures in
New South Wales, introducing requirements such as a permissible site discharge (PSD) in L/s/ha of
catchment, and site storage requirement (SSR) in m3/ha.
DRAINS models detention basins by simulation, presenting several relationships, such as storage vs.
time, upstream and downstream water levels vs. time, and inflow and outflow hydrographs. It can also
handle multiple outlets, infiltration into soils and pumped systems. The high early discharge (HED)
system can also be modelled. Details are given in Section 2.3.7.
The detention basin routing has to be explored by trial and error, but the ability to edit the data quickly
and re-run the model makes this a fast process.
Analysing Established Drainage Systems
Established systems may need to be examined for deficiencies at particular locations, such as problem
areas, where complaints of flooding have been made by householders, or on an area-wide basis, taking
in all drainage system components. This latter type of investigation may be prompted by asset
management or liability concerns, rather than by particular experiences of flooding.
The processes in creating DRAINS files for Analysis are almost the same as for Design. However, all pits
and pipes should be defined as 'existing'. Invert levels of all conduits must be defined.
The sources of the information required include:
scaled plans showing road and cadastral layouts and contours,
information on additions and remedial works for the drainage system,
information on detention storage systems on sites or on public land,
files detailing reports and complaints stemming from storm events and drainage system defects,
any previous analysis studies relating to the area being considered,
information on past storm events.
Since an existing system has to be modelled in some detail, it will be necessary to draw information from
GIS and data base sources. If these are unavailable or inadequate, it will be necessary to carry out
topographic surveys to determine the exact positions and levels of system components, including:
surface levels of pits,
invert levels of pipes, including if possible, those in sealed pits and junctions,
lengths of pipes,
floor levels of houses and businesses, and driveway levels where flows may enter properties and
yard levels where ponding may occur.
DRAINS User Manual
November 2014
Techniques such as GPS measurements and LIDAR aerial laser scanning, supplemented by
conventional surveying, can be used to obtain large amounts of levels efficiently.
Inspections are needed to define many aspects of drainage systems, such as low points on roadways
and likely overflow paths. It is likely that the same areas may have to be inspected two or three times
during modelling to define drainage components and paths exactly. Information can also be sought from
residents about their experiences of flooding during these visits. Closed circuit television (CCTV)
investigations can provide detailed information on pipes and defects such as erosion, cracks and faulty
If resources are available, the drainage system may be gauged to record storms rainfalls and
corresponding drainage system flows that can be used to calibrate models. Rainfalls are usually
recorded by tipping-bucket raingauges and pipe and channel flows by magnetic or laser-Doppler flow
meters. Gauging for a period of at least 3 months will probably be necessary. When the model is run
with recorded data, the times of flow can be varied by altering values in the spreadsheet output and reinserting these into DRAINS. The DRAINS model can be calibrated or 'tuned' so that the times of the
calculated hydrograph peaks match those of the recorded ones. A similar process can be carried out by
varying the Hydrological Model parameters and percentages of land use, to make the calculated flow
peaks or volumes match the recorded ones. This is more difficult because pervious areas may only
contribute flows in larger storms, and the gauging period may be too short or dry to record significant
runoff-producing storms.
From the available mapping and the survey data, DXF or DWG drawings can be prepared, and a suitable
file prepared with the three layers containing pits (as circles), pipes and a background. DXF files then
can be imported into DRAINS to provide the initial file for the data entry and modelling processes.
As in Design, it will be necessary to develop a set of guidelines on matters such as:
the definition and modelling of flow paths,
the factors used in pit inlet capacity relationships for the various kinds of pits encountered in the
drainage system,
pit blockage factors,
existing pipe roughnesses and shapes, and
the modelling of ponding of stormwater in streets and backyards.
In modelling existing systems, a difficult issue will be the definition of the flow paths taken by flows from
paved and grassed surfaces, as shown in Figure 4.12. These will be greatly influenced by the size and
arrangement of allotments and the buildings on them, and especially by the style of fencing along
allotment boundaries.
If there was no fencing, or if flows could easily pass under fences, the flows would follow the land
contours and the definition of paths and overland flow lengths, slopes and roughnesses would be
relatively easy. Once flows have to pass through fences, or be directed along them, the situation
becomes quite complex, with some storage effects probably coming into play. Even in a detailed analysis
with abundant scope for survey data collection, it would be prohibitively expensive and complex to model
each property’s drainage system and to include possible storages. Some judgements about overall or
average effects must therefore be made. Calibration with gauged data would be particularly useful for
refining these judgements.
Another difficult issue will be the ponding of stormwater on streets and in backyards. This occurs where
development has occurred in the natural floodway areas, and various barriers to flow have been erected,
including road crowns, road embankments, walls and fences. It is fairly easy to see where stormwater
will run into properties. Usually those on the downstream side of a road at a low point will be affected, as
shown in Figure 4.13.
DRAINS User Manual
November 2014
Figure 4.12 Flow Paths to a Pit
Figure 4.13 Ponding Storages on Streets and in Allotments
Storages on streets might be modelled as detention basins with a height-storage relationship and a lowlevel outlet to the pipe system. Their high level outlet or outlets can be modelled as one or more weirs,
usually located a driveways into properties.
Storages within allotments can be very complicated, with flows being blocked by gates and fences, so
that several instances of ponding may occur on the one property. Some situations can be modelled
readily, such as flow under a fence represented as a sluice gate, or flow over a low wall as a weir flow.
However, in many Australian situations, the barrier may be a metal Colorbond fence extending to the
ground. Such fences can probably hold back stormwater to a depth of 1 m or more. When failure occurs,
there may be catastrophic effects from the resulting rush of water and debris. Modelling such events is
difficult. Our knowledge of how they are initiated is poor, and DRAINS does not model 'dambreaks' of this
Existing systems that have been augmented can have two pipes with different characteristics running
more or less parallel. These might be modelled as multi-channels if there are no significant inflows along
one of these that will change the distribution of flows. If this is the case, they can still be modelled as two
DRAINS User Manual
November 2014
outlet pipes from a pit. DRAINS can model these using its full-pipe and open channel network calculation
The spreadsheet documentation provided by DRAINS is very useful for recording results, which can be
separated into worksheets and suitably tagged.
When analysing very large systems (say 500 pipes and over) computation times can be quite long with
multiple storms. It is therefore necessary to plan the analysis work, starting with storm events likely
produce the highest flowrates. Once the system has been refined, final runs can be made with a wider
range of rainfall patterns of different average recurrence intervals and durations.
Once a working model has been established, the likely flowrates, heights of storages, flooding impacts
and resulting damages can be assessed. Flooding trouble spots can be identified, and remedial works
can be considered. The initial DRAINS model can then be varied to produce a number of models for
assessing different remedies. In some cases the remedies will interact with each other, some reinforcing
the beneficial effects of other remedies, others diminishing these. This makes the consideration of
options quite complex.
The rational method analysis procedure should not be used to simulate the behaviour of existing systems,
since the various flow peaks calculated can occur at different times, and the flowrates obtained from
combining peak flows are approximate. This procedure should only be used to check newly-designed
systems. The extended rational method can be used as a valid analysis procedure, but the ILSAX
hydrology is a more accurate and proved hydrological procedure.
Analyses should be carried out using the unsteady standard and premium hydraulic model calculations.
These are superior to the basic hydraulic model in the following respects:
• They are more soundly based on theory, including all the terms of the St. Venant equations of mass
and momentum conservation (see Section 5.6.4), so that they can model sub- and supercritical flows
in pipes, channels, and with the premium hydraulic model, overflow routes
• They are more stable, and will give more accurate results for pipe and open channel flows.
• The premium model permits modelling of overflows and other configurations that are not possible in
the basic model. (For example, it is possible to model two or more outflows from a sag or on-grade
pit, or a node. Situations such as flows spilling from a street gutter or channel into a driveway or
across a road centreline can be modelled in this way.)
• The premium model can model situations where on-grade pits are submerged by water ponding over
adjacent sag pits, with the on-grade pit operating as a sag pit while it is submerged.
• The premium model provides greater allowance for storage in surface flow systems, such as ponded
water over sag pits and surface flows between these, leading to generally lower flowrates.
With the availability of multi core processing, running times for the standard and premium models are
faster than those for calculations with the older basic model. The basic model should only be used for
checking older models, using the methods that applied when such models were developed.
Asset Management
Once developed and used to prepare construction plans and specifications, DRAINS models should be
retained by the authority that maintains the system. Besides being a record of the system, with its own
readily-accessible database, the DRAINS model is a working model of the system, which can be altered
to reflect any changes. It can form part of the authority's asset management system, especially when it is
integrated with drainage system data base and a geographic information system (GIS).
When the drainage system is constructed, it is likely that some details will have been changed during
construction. The model should be updated to reflect the work-as-executed information. It will then
require further modification as, whenever:
additional drainage systems are connected,
rezonings and re-developments create more impervious areas and increase runoff volumes and
possible flow diversions occur within the catchment, and between it and other catchments,
compensatory detention storages are provided,
additional information and experience about the drainage system accumulates,
DRAINS User Manual
November 2014
design rainfalls are revised, and climatic change effects occur,
the system deteriorates and defects due to damage and ageing of assets become apparent,
remedial works are constructed, and
design standards change.
DRAINS can be easily updated to reflect all these changes. Periodic reviews can be made using the
DRAINS model, which becomes a permanent feature of the drainage authority’s asset management
Many municipalities and stormwater authorities do not have full information on their systems.
Nevertheless, they can start with this incomplete data, setting up data bases and models with the
available information, and then refining these. Experience during storm events special surveys to
determine pit and pipe invert levels, CCTV inspections, preparation of lists of trouble spots and asset
registers will provide added information, so the records can be gradually expanded and the modelling
As shown in Figure 4.14, DRAINS provides transfers to GIS programs in the form of ArcView shapefiles
and MapInfo MID/MIF files. The connection of DRAINS to the GISs of drainage authorities allows the
results of DRAINS analyses to be included in the GIS. These can include flowrates and hydraulic grade
line levels for average recurrence intervals of 1, 2, 5, 10, 20, 50 and 100 years, plus probable maximum
precipitation (PMP) storms - see Bureau of Meteorology (2003). These results can be mapped and
displayed in many ways, using colour-coded symbols and lines. The GIS can also act as a means of
querying the underlying database, so that flows or HGL levels at particular locations can be checked onscreen.
19 files – three ESRI SHP, SHX and
DBF files for nodes, pipes, subcatchments, overflow routes, survey
points along pipes and conflicting
services, plus an optional DXF file of
the DRAINS background
DRAINS .drn File
13 files – two MapInfo MID and MIF
files for nodes, pipes, sub-catchments,
overflow routes, survey points along
pipes and conflicting services, plus an
optional DXF file of the DRAINS
DRAINS .drn File
Figure 4.14 Transfers of Data Between DRAINS and GIS Programs
DRAINS does not export overflow routes as polylines, but as lines connecting the first and last points of
the overflow route polyline. To display complex routes such as those passing through properties, it is
recommended that these be represented by two or more segments joined at nodes.
Ultimately, drainage system managers can develop systems where revised DRAINS models can be
created from information on previous DRAINS models in their GIS. As new developments and redevelopments occur, it will be possible to include these. Results from various models can be retained in
the GIS system. The combination of DRAINS with GIS allows managers to maintain and ongoing record
of their drainage systems that included records of performance and flooding risk.
Performing Flood Studies with Storage Routing Models
The catchment must be defined on a contour map and sub-catchments defined using the stream pattern
and the internal ridge lines as shown in Figure 4.15. The CatchmentSIM software (Ryan, 2005) can do
this if suitable topographic information is available. Sub-catchment areas, channel reach lengths and
other characteristics are then measured. The number of sub-areas should reflect the detail of the
information required and the important features of the catchment, such as reservoirs and changes in the
type of channel.
DRAINS User Manual
November 2014
Streamflows and other data suitable for calibration of the model are then assembled. Ideally, there
should be at least three recorded flood events. Loss parameters and initial values of the parameters (kc
in RORB, BX in RAFTS and C in WBNM) are established.
The program is then run and the outflows are compared with the calibration data, or rural catchment flood
estimates developed by methods in Chapter 5 of Australian Rainfall and Runoff (Institution of Engineers,
Australia, 1987). The parameters are then adjusted and the final calibration flowrates determined. If
more than one storm event is available for calibration, it may require different parameters to obtain exact
matches to recorded peak flows. A compromise set of parameters must then be selected.
Figure 4.15 Layout of a RAFTS Storage Routing Model
With the parameters established, the model can be used to estimate the flows from large floods such as a
100 year ARI flood. The effects of detention basins and stream break-outs or diversions can be
If you wish to combine the storage routing model results with the open channel hydraulic calculations
available in DRAINS and/or an ILSAX model, this can be done to obtain more detailed results. The open
channel and ILSAX models can be set up in the usual way. This integration of models should be useful in
situations where there is interaction between a large watershed and a smaller urban catchment.
Methods and Parameters Applied in DRAINS
Usually, designers must follow guidelines established by drainage consent authorities, such as local
councils or state road authorities, supplemented by authoritative guides such as Australian Rainfall and
Runoff, the Queensland Urban Drainage Manual or AS/NZS 3500.3. Nevertheless, there will be many
situations that are not covered completely in these sources. It is the responsibility of the designer to
choose how these situations are to be modelled and what parameters are to be applied.
DRAINS is a flexible tool that can be used with many different procedures and parameters, and it is
inappropriate for this manual to recommend specific methods or values, or to specify how DRAINS should
be applied in specific situations. There is a discussion of alternative hydrological models in Appendix A.
Choice of Model
DRAINS offers a choice of hydrological and hydraulic models. Some are available to all purchasers,
while others can be purchased as optional add-ons. The choice of hydrological model will depend on the
task to be undertaken with the model, and by the likelihood of acceptance of the model by approval
DRAINS User Manual
November 2014
authorities or assessors. Comparisons of alternative models are presented in the guidance on the
DRAINS Viewer that is included in Appendix A.
All hydrological models except the rational model produce hydrographs, which are necessary for
modelling detention storages and complex networks. The ILSAX and storage routing models (RORB,
RAFTS and WBNM) are backed by testing programs in which their performance has been tested against
gauged rainfall and runoff data. The rational method models have not been extensively tested, but have
been the most commonly-used models in many applications. Some authorities consider them to be
acceptable benchmarks. The extended rational model included in DRAINS is an extension of the rational
The storage routing models are the accepted methods of modelling broad-scale urban catchments and
can cope with the hydrological effects of urbanisation. The various models produce different flow
estimates due to (a) use of different rainfall data, notable I-F-D statistical relationships and Australian
Rainfall and Runoff patterns, (b) models being derived for different purposes, scales of operation (pipe
system sub-catchments compared to larger broad-area sub-catchments), and calibration to different data
sets, and (c) modelling choices by users. (Some models allow users much more scope than others.)
For routine applications such as OSD calculations, designers probably should choose models accepted
by approval authorities, while for more complex or critical applications, the more scientifically-proven and
calibrated models will be the ones that can best model situations and be most easily justified.
The basic hydraulic model that was used from the first release of DRAINS has been replaced by the
standard and premium hydraulic models, which are based on different principles and are more rigorous
and stable. Because both of these models allow for volumetric effects in stored and flowing runoff, they
calculate lower flowrates than the old basic hydraulic model, with the premium model usually giving the
lowest flowrates and HGL levels.
DRAINS User Manual
November 2014
This chapter sets out the background and the technical basis for the procedures used in DRAINS. Some
features, such as the ILSAX hydrological model, were inherited from other programs while others were
developed specially for DRAINS.
DRAINS is the result of a chain of development that originated with the U.K. Transport and Road
Research Laboratory (TRRL) Method in the early 1960s:
TRRL Method (UK, 1962)
ILLUDAS (US, 1974)
ILLUDAS-SA (South Africa, 1981)
ILSAX (Australia, 1986)
PIPES++ ⇒ DRAINS (Australia, 1998)
Figure 5.1 The Initial Development Path of DRAINS
The TRRL method was developed by Watkins (1962) following extensive studies in which storm rainfalls
and runoff were recorded for several years on twelve catchments. Flow estimates from the rational
method and other hydrological models were compared with the recorded data. A design procedure using
the time-area method (Ross, 1921) applied to impervious areas was developed from this research (UK
Transport and Road Research Laboratory, 1976). A simple procedure was applied to route flows through
pipe systems. This was released as a FORTRAN program in 1963, replacing the rational method.
The Illinois Urban Drainage Area Simulator, ILLUDAS, was developed and extensively tested by Terstriep
and Stall (1974), who adapted the TRRL Method to cope with pervious area runoff and added other
features. Tests involving gauged data from 21 catchments were made. Although ILLUDAS was popular
among researchers, it has not been widely used by designers in North America. For most design tasks,
ILLUDAS and SWMM (Stormwater Management Model) have been overshadowed by U.S. Soil
Conservation Service programs TR20 and TR55 and other, relatively-simple methods.
After testing ILLUDAS on two South African gauged catchments, Watson (1981) produced a version
named ILLUDAS-SA, with many additional features. This was the basis for the ILSAX program. In
Australia, ILLUDAS-SA and various development versions of ILSAX were applied to data from gauged
urban catchments in Sydney and Melbourne by Cartwright (1983), Mein and O'Loughlin (1985), Vale,
Attwater and O'Loughlin (1986), and others. The first practical application was in a large-scale drainage
study of Keswick and Brownhill Creeks in suburban Adelaide in 1982-83.
ILSAX was developed by Geoffrey O’Loughlin between 1982 and 1986, with the aim of producing a better
stormwater drainage design program than the rational method. The later part of this development
occurred alongside the preparation of the chapter on urban stormwater drainage in Australian Rainfall
and Runoff, 1987. ILLUDAS-SA was adapted to model overflows from pits, so that it could model major
storm flows in the major/minor design system recommended in Australian Rainfall and Runoff. However,
the program did not calculate HGLs. ILSAX started to be used widely in 1986, when it was released in a
public domain version for IBM PCs. Its flexibility, low cost and robustness made it acceptable, despite the
limitations of its hydraulic calculation method. The early testing showed that the hydrological model was
at least as accurate as alternative urban hydrology models. In the 1990s, it was commonly used for
analysis of on-site stormwater detention systems. It has now been superseded by DRAINS and is no
longer supported.
PIPES and PIPES++ are hydraulic network analysis programs developed in the 1990s by Bob Stack for
the design and analysis of piped water supply systems. Full pipe flows were modelled using steady flow
DRAINS User Manual
November 2014
equations, and a graphical user interface was provided, which became the bases for the interface in
DRAINS grew out of attempts by Geoffrey O’Loughlin to provide a successor program to ILSAX. A joint
venture with Bob Stack of Watercom Pty Ltd yielded a program that combines an effective user interface
from Watercom’s PIPES programs with the ILSAX model and a much-improved pipe and channel
hydraulics system. Development took place from 1994 to 1997, and has continued to the present time,
with important developments being shown in Table 5.1.
Table 5.1 Significant Developments in the Capabilities of DRAINS
Development of DRAINS from ILSAX and PIPES with HGL projection
procedures for pipes and open channels
January 1998
Commercial release of DRAINS
Early 1998
Addition of pressurised models to allow for sealed pits
Addition of spreadsheet input-output
Introduction of rational method procedures,
Introduction of the Advanced Design Method (with new pipe, pit and
overflow route data bases)
Introduction of storage routing models emulating procedures in the RORB,
RAFTS and WBNM programs
Early 2003
Allowance for looped pipe systems
Mid 2003
Introduction of transfers to and from GIS programs
Late 2004
Addition of the extended rational method
Mid 2005
Addition of HEC22 procedures for calculation pit inlet capacities
March 2006
Introduction of fully dynamic (unsteady) calculations for pipes, open
channels and overflow routes
Use of DRAINS Utility Spreadsheet to prepare input data externally.
February 2008
Introduction of Queensland Urban Drainage Manual (QUDM) procedures
for automatically determining pit pressure change coefficients.
March 2009
Release of the free DRAINS Viewer
December 2010
Replacement of the basic hydraulic model by the standard and premium
models. Parallel processing introduced to greatly reduce run times.
Multiple rainfall pattern entry, New orifice and weir components
Enhancements to unsteady flow calculations, improving speed and stability.
Enhanced pipe system design procedure.
The rational method, the extended rational method and storage routing models have been added to the
original ILSAX hydrological model. The basic hydraulic model, which underwent considerable
development between 1989 and 2010, has now been replaced by unsteady flow models.
Simulation models such DRAINS require a model to transform rainfall patterns to runoff hydrographs in
the part of the hydrological cycle shown in Figure 5.2.
Urban stormwater drainage design can be carried out by three categories of models:
simple models that produce a peak flow estimate only (such as the rational method),
hydrograph-producing models (such as the time-area model in ILSAX) applied to storm events,
DRAINS User Manual
November 2014
more complex models, capable of continuous simulation of hydrographs (such as the Stormwater
Management Model, SWMM).
Channel Precipitation
Surface Runoff
(very slow)
Deep Groundwater Flow
or Runoff
Figure 5.2 The Rainfall-Runoff Process
Models can be split into loss models and routing models, as shown in Figure 5.3. Loss models represent
hydrological processes such as interception, depression storage, evaporation and infiltration, which
prevent water from running off catchments immediately. The most common types are: (a) initial loss –
continuing loss models, and (b) infiltration models using procedures such as Horton’s equation.
Routing models allow for the distribution of rainfall across a catchment surface, with some rainfall inputs
being closer to the outlet than others, and so spreading out the pattern of flow or hydrograph at the outlet.
They also account for storage effects on the catchment. The main types are (a) time-area routing, (b)
unit hydrographs, (c) routing through artificial storages, (d) kinematic wave routing, and (e) unsteady flow
hydraulic modelling across catchment surfaces.
The ILSAX hydrological model in DRAINS is a medium-level rainfall-runoff model that combines a Horton
loss model with time-area routing. The rational method only calculates peak flowrates. The ERM applies
a loss model based on the rational method with time-area routing. These models are adaptable to many
situations, but do not perform continuous simulation. The storage routing models that emulate the RORB,
RAFTS and WBNM models commonly used in Australia are also 'event models', designed to produce
hydrographs for flood estimation, but not capable of modelling long periods of runoff under wet and dry
The ILSAX Hydrological Model
(a) General Description
This model relates to an urban or semi-urban catchment, subdivided into sub-catchments linked to a
drainage system of pipe and channel sections as shown in Figure 5.4. Sub-catchments are divided into
three surface types - paved, supplementary and grassed. Runoff hydrographs generated from inputted
DRAINS User Manual
November 2014
rainfall patterns are used to model system behaviour and to perform design tasks. The model works to a
fixed time scale, beginning at the start of a storm, performing calculations at specified time steps.
Defines rainfall excess,
equivalent to runoff at
the point where it begins
to occur
Combines rainfall excess
from different areas, and
allows for delaying effects
of time of travel and storage.
Figure 5.3 Loss and Routing Models
(directly-connected impervious)
(impervious area not
(pervious area
DRAINS User Manual
November 2014
Fiigure 5.4 Th
he Layout of the ILSAX Model
Since th
his is an even
nt model, conditions at th
he start of ea
ach storm eve
ent must be established by defining a
value off the anteced
dent moisture
e condition, A
AMC, for the
e soil underlying the perviious portions
s of the
ent. The loss model subtracts depresssion storage
es from all su
urfaces and calculates additional
losses ffor grassed or
o pervious areas using H
Horton’s infiltration model. The soil tyype and AMC
C parameterss
d to identifiable soils and
are easily understan
ndable and can
c be related
d rainfall deptths preceding a storm.
Results are quite se
ensitive to the
e AMC and u
users must consider the effects
of theeir choices us
sensitivity studies. Despite
this, few problem
ms with employing this mo
odel have beeen reported.
The model relies on times of trav
vel as the ma
ain paramete
ers used in ro
outing. Thesse can be de
etermined to
an acce
eptable level of accuracy for urban ca
atchments, bu
ut are very variable for ruural catchments. Thus,
while the ILSAX model can be applied to perrvious sub-ca
atchments off a drainage system, it is not strictly
ble to rural ca
atchments. This reflects the lack of suitable
studies to calibraate the mode
el in rural
ons, rather than any defec
ct in the mod
del itself.
me-Area Rou
(b) Tim
The bassis of the ILS
SAX model’s hydrograph generation is
s the time-arrea method, illustrated in Figure 5.5,
which 'cconvolves' the rainfall hye
etograph with
h a time-area
a diagram, in
n a similar maanner to unitt hydrograph
calculattions. A time
e of entry (orr time of conccentration) must
be determined for a drained area
a using
methodss discussed later in Section (d).
5 Time-Area
a Calculatio
Figure 5.5
e that the rain
nfall hyetogra
aph has had
d losses remo
oved and so represents rrainfall exces
ss, and that
the hyettograph is divvided into tim
me steps of Δ
Δt. The time-area diagram, a plot of tthe catchment area
uting after a given
er of time ste ps is divided
d in the same
e intervals. T
This diagram
m can be
ed by drawin
ng isochrones, or lines off equal time of
o travel to th
he catchmentt outlet. For times
greater than the time
e of concentration, the co
ontributing area equals th
he total area of the catch
mences on a catchment tthat has a tim
me of entry of 5Δt, the inittial flow Q0 is
s zero. Afterr
When a storm comm
one time
e step Δt, on
nly sub-area A1
A contribute
es to the flow
w at the outle
et. Any runofff from otherr sub-areas iss
S User Manual
November 2014
still in transit to the outlet. Thus the flowrate at the end of the first time step can be approximated by
Q1 = c.A1 . I1, where c represents the conversion factor from mm/h to m3/s units, and I1 is the average
rainfall intensity during the first time step.
At the end of the second time step, there are two contributions to the outlet flow, Q2, due to the second
block of rainfall falling on the sub-area nearest to the outlet, c. A1 .I2, and to runoff from the first rainfall
block on the second sub-area, c. A2 . I1. At the end of the third time step, there are three contributions,
Q3 = c. (A1 . I3 + A2 . I2 + A3 . I1), and so the process continues, as shown in Figure 5.5. The hydrograph
builds up to a peak and then recedes once rainfall stops and the catchment drains.
In practice, losses can be subtracted from the rainfalls and flows before or after these time-area
calculations are made. The latter choice is recommended for grassed or paved areas, as this allows
infiltration to occur from flows moving across a sub-catchment after rainfall has stopped. In this case, the
hydrograph of Q values represents a 'supply rate', from which losses must be subtracted later.
In DRAINS, as in ILSAX, it is assumed that all time-area diagrams are straight-lines. It is conceivable that
they could be concave or convex, depending on catchment shape on other factors, however,
investigations conducted in the U.K. with the TRRL Method concluded that this degree of accuracy was
not necessary.
(c) Catchment Surface Types
The sub-catchments draining to each entry point on the pipe and channel system can be obtained from
maps, aerial photographs and GIS information, as well as field inspections. The likely effects of fences
along property boundaries and other barriers must be assessed.
In the ILSAX model used in DRAINS, each sub-catchment must be divided into the sub-areas shown in
Figure 5.6, with the following surface and drainage characteristics:
paved areas, impervious areas directly connected to the pipe system, including road surfaces,
driveways, roofs connected to street gutters, etc.,
supplementary areas, impervious areas not directly connected to the pipe system, but draining onto
pervious surfaces which connect to this system (These may include tennis courts surrounded by
lawns, house roofs draining onto pervious ground, etc. distributed evenly next to the grassed area.),
grassed areas, pervious areas directly connected to the pipe system, including bare ground and
porous pavements as well as lawns.
Figure 5.6 ILSAX Model Surface Types
In DRAINS, the total sub-catchment area and the percentages of paved, supplementary and grassed
areas must be specified for each sub-catchment. If there is some part of a sub-catchment that does not
drain to the drainage system, for example, a hollow or depression in volcanic areas, it should be excluded
from the model.
Generally, fully-developed medium density residential catchments will have areas impervious between 30
and 70%. Dayaratne (2000) has obtained the following relationships from modelling of storms on 16
gauged residential catchments in four Victorian municipalities:
DRAINS User Manual
November 2014
Directly connected impervious area (or paved area) percentage,
DCIA (%) = -0.85 hhd2 + 23.38 hhd - 101.19 (r2 = 0.90)
… (Equation 5.1)
Supplementary area percentage,
SA (%) = -0.04 hhd2 + 1.13 hhd - 3.79 (r2 = 0.91)
… (Equation 5.2)
where hhd is the number of houses/ha.
These equations produce the numbers shown in Table 5.2.
Table 5.2 Estimates Paved and Supplementary Area Percentages
Housing Density, hhd
Paved Area, DCIA
Area (%)
As noted in connection with Figure 2.16, supplementary areas may be used to model systems where
roofwater is discharged onto grassed areas.
(d) Overland Flows and Times of Entry
Times of entry must be specified for the paved and grassed areas (and also for the supplementary area in
DRAINS). These are effectively the same as the times of concentration or times of travel used in the
rational method. They set the base lengths of the time-area diagrams used to create hydrographs.
The DRAINS property sheet for a sub-catchment is shown in Figure 5.7. Information on surface types is
arranged in three columns. The length of these varies according to the level of detail selected in the Use
box. For many applications, fixed times can be entered.
However, it is also possible to calculate a time by the steady-state 'kinematic wave' equation for overland
flows (Ragan and Duru, 1972):
toverland = 6.94 .
(L ⋅ n * )0.6
…(Equation 5.3)
⋅ S 0.3
where time toverland is in minutes, flow path length L is in m, rainfall intensity I is in mm/h and slope S is in
The surface roughness n* is similar to the coefficient n in Manning's Formula for open channel flows, but
is of a different magnitude. It typically takes the values set out in Table 5.3. Values for lawns and
grassed surfaces show considerable variation, depending on the depth of flow relative to the height of
grass blades. Values from 0.05 to 1.0 have been obtained by various researchers, as described by
Engman (1986).
In DRAINS, intensity I is taken as the mean intensity of the rainfall pattern supplied. This should be
satisfactory for design rainfall bursts such as those supplied in Australian Rainfall and Runoff, 1987, but
may be erroneous for some more variable or patchy patterns that occur naturally.
DRAINS User Manual
November 2014
For paved areas, it is also possible to calculate a gutter flow time using (a) an equation for flows in street
gutters or channels (U.S. Federal Highway Administration, 1984) , (b) Manning’s equation, or (c) more
simply, by dividing a flow path length by a speed to obtain a time.
Figure 5.7 Sub-Catchment Property Sheet with Text Boxes for Entry of Data
Table 5.3 Surface Roughness Factors
Surface Type
Roughness Coefficient n
Concrete or Asphalt
0.010 - 0.013
Bare Sand
0.010 - 0.016
Gravelled Surface
0.012 - 0.030
Bare Clay-Loam Soil (eroded)
0.012 - 0.033
Sparse Vegetation
0.053 - 0.130
Short Grass Prairie (Veldt or Scrub)
0.100 - 0.200
0.170 - 0.480
[Source: Woolhiser (1975)]
In DRAINS, a kinematic wave flow time can be added to a constant time, as follows:
Total time = Constant time, which can represent property drainage time plus gutter flow time
+ Overland flow time calculated from length, slope and roughness … (Equation 5.4)
Users can specify the times associated with paved, supplementary and grassed areas as (a) a constant
time, (b) a constant time, now called an 'additional' time, plus a kinematic wave calculation, or (c) a
kinematic wave time only, by specifying the additional time as zero. Up to 2005, there was a third term
that modelled street gutter flow times using equations based on road cross-sections. This has been
omitted in the current version of DRAINS but may appear in older models. It is described in the DRAINS
Help system.
DRAINS User Manual
November 2014
The property drainage time is that required for all water to contribute to flow at the boundary outlet. There
is conflicting evidence on property drainage times (Stephens and Kuczera, 1999, Goyen and O’Loughlin,
1999, Dayaratne, 2000), with some pointing to short times, 1 or 2 minutes, and some to longer times, 5 to
10 minutes). 1 to 2 minutes is recommended as being reasonably conservative.
In DRAINS, a lag time for grassed area flows can be applied where flows from such areas pass over
paved surfaces before reaching a pit, as shown in the lower part of Figure 5.8. The time to be entered is
the flow time over the paved area.
Figure 5.8 Lag Times and Factors
The Queensland Urban Drainage Manual, QUDM (2008) recommends a simplified procedure for setting
inlet times, using the values in Table 5.4. Should the calculated tc be less than 5 minutes, this minimum
value is customarily adopted as the tc.
Table 5.4 Recommended Standard Inlet Times in Queensland Urban Drainage Manual
Inlet Time (minutes)
Road surfaces and paved areas
Urban and residential areas where:
- average land slope is greater than 15%
- average land slope is between 10% and 15%
- average land slope is between 6% and 10%
- average land slope is between 3% and 6%
- average land slope is up to 3%
(e) ILSAX Loss Models
Losses from paved and supplementary areas are calculated simply in the ILSAX model. Depression
storages are considered as initial losses subtracted from rainfall hyetographs prior to time-area
calculations. The general range of depression storages is from 0 to 2 mm for impervious surfaces and 2
to 10 mm for pervious surfaces. Commonly-used values for paved, supplementary and grassed areas
are 1, 1 and 5 mm, respectively. Dayaratne (2000) recommends values of 0 to 1 mm for impervious
The procedures for grassed areas are more complex. They are based on the general equation
developed by Horton in the 1930s:
f = fc + (f0 - fc) . e-kt
… (Equation 5.5)
f is infiltration capacity (mm/h),
f0 and fc are initial and final rates on the curve (constants, mm/h),
k is a shape factor, here taken as 2 h-1,
and t is the time from the start of rainfall (minutes).
DRAINS User Manual
November 2014
This describes the curves shown in Figure 5.9. These only apply when there is sufficient rainfall to satisfy
completely the infiltration capacities, and accumulated infiltration is increasing at its full rate.
Figure 5.9 Horton Infiltration Curves
The curves represent soil types which follow the classification used by Terstriep and Stall (1974), based
on the system developed by the U.S. Department of Agriculture, and described in references such as
Chow (1964) and U.S. Natural Resources Conservation Service (2007). These are used in North
American procedures such as Technical Release 55 of the U.S. Soil Conservation Service (1975). The
four main soil classifications, designated A, B, C and D (corresponding to 1, 2, 3 and 4 in the ILSAX type
model), are described as:
1 (or A)
- low runoff potential, high infiltration rates (consists of sand and gravel);
2 (or B)
- moderate infiltration rates and moderately well-drained;
3 (or C)
- slow infiltration rates (may have layers that impede downward movement of water);
4 (or D)
- high runoff potential, very slow infiltration rates (consists of clays with a
permanent high water table and a high swelling potential).
These soil types are used in conjunction with antecedent moisture conditions (AMCs) that define the
points on the infiltration curves at which calculations commence. This is specified, not by an initial
infiltration rate in mm/h, but by an antecedent depth of moisture, corresponding to the area under the
curve to the left of the starting point. On each curve in the above figure, four starting points (numbered 1,
2, 3 and 4) are shown, representing possible AMCs.
AMCs can be estimated from Table 5.5. Both soil types and AMCs can be interpolated between the
levels of 1, 2, 3 and 4.
Table 5.5 Antecedent Moisture Conditions
Total rainfall in 5 days
preceding the storm (mm)
Completely dry
Rather dry
0 to 12.5
Rather wet
12.5 to 25
Over 25
DRAINS User Manual
November 2014
For the curve and AMC selected, the model calculates an infiltration loss in each time step. This is
subtracted from the rainfall inputs to the pervious area.
Values of parameters involved with various combinations of soil types and AMCs are set out in Table 5.6.
Table 5.6 Infiltration Model Parameters
Soil Type
A (or 1)
B (or 2)
C (or 3)
D (or 4)
Initial Rate, f0 (mm/h)
Final Rate, fc (mm/h)
Shape Factor, k (h )
Antecedent Rainfall Depths
(mm) for AMCs:
Initial Infiltration Rates (mm/h)
for AMCs:
Users also can also provide their own values. One method to do this is to analyse daily rainfall records
and on a spreadsheet calculate the rainfalls for the 5 days preceding each day. Daily rainfalls can then
be ranked and the antecedent rainfalls for the highest 100 rainfalls, say, can be analysed, as shown in
Figure 5.10 which gives results for Observatory Hill rainfall records in Sydney. From the mean or median
antecedent rainfalls and classification numbers, a most-likely value of AMC can be selected.
DRAINS User Manual
November 2014
Figure 5.10 Procedure for Determining AMCs for Design Purposes from Daily Rainfalls
This classification involving soil type and AMC has been found to give good fits to recorded storm
hydrographs from gauged catchments in Australia, and the soil types have been accepted by ILSAX and
DRAINS users. Siriwardena, Cheung and Perera (2003) compared the infiltration rates in Table 6.4 with
those measured with infiltrometers at eight urban gauged catchments in Victoria. They found that the f0
and fc values measured were generally higher than those for the same soil classification in Table 5.6.
They obtained f0 values of 28 to 503 mm/h compared to 13 mm/h for a Type B soil, and fc values of 4 to
135 mm/h, compared to values of 31 to 200 mm/h. They also obtained a shape factor, k, of 0.85 h-1
compared to 2 h-1 in the table.
Siriwardena, Cheung and Perera did not explore the implications of changing these parameters in
modelling hydrographs from the test catchments. It is not possible to assess the effects of this at present,
but Victorian users of DRAINS and similar programs should take the above results into consideration
when setting parameters. DRAINS s allows user-provided parameter values to be specified in the
hydrological model inputs.
In ILLUDAS-SA and ILSAX, the following form of Horton's equation was used to determine the infiltration
rate from the accumulated depth of infiltration. This allows for variable rainfall intensities that might be
less than the infiltration capacities at some times.
f = f + fc . ⎜1 −
(f0 −kF − f )/ f ⎟
fc + (f0 − fc ).e
... (Equation 5.6)
f is the current infiltration capacity (mm/h), and
F is accumulated depth of infiltration (mm).
The infiltration rate calculated from this is subtracted from the hyetograph or supply rate, and should any
water remain, depression storage is subtracted. Once the depression storage has been fully satisfied,
any excess over infiltration is assumed to be runoff. The accumulated infiltration depth is increased by
the amount assumed to be infiltrated. For porous soils and light rainfalls, it is quite possible that there will
be zero runoff from pervious surfaces.
Malcolm Watson, the developer of ILLUDAS-SA, suggested that an alternative method could be used
which would not involve iterative calculations, and this was incorporated into ILSAX. This procedure,
described by Watson (1981b), involved the division of the infiltration curve equation into diminishing and
constant components (f0 - fc) . e-kt and fc. Watson used this concept in the following analysis:
The actual depth of infiltration, ΔF, over time step Δt is the lesser of I . Δt , where I is rainfall intensity,
⎛( − )
Fcap = (1 - e-kΔt) . ⎜ f 0 f c − Fd ⎟ + fc . Δt
… (Equation 5.7)
⎝ k
where Fd is the accumulated diminishing infiltration, determined at each time step by
Fd = Fd -
Δ Fcap
. (ΔFcap - fc. Δt)
… (Equation 5.8)
which apportions actual infiltration depths between diminishing and constant components, as shown in
Figure 5.11.
DRAINS User Manual
November 2014
ΔFcap - f c Δ t
ΔFd =
(ΔF - f c . Δ t)
ΔFc =
.f .Δt
ΔFcap c
Figure 5.11 Infiltration Capacity Calculation Procedure
(f) Combination of Hydrographs
The time-area method is applied separately to the paved, supplementary and grassed area portions of
the catchment. DRAINS allows for a supplementary area depression storage and time of travel. (These
must both be set to zero if you wish to exactly reproduce ILSAX hydrographs.)
The process for paved and supplementary areas is shown in Figure 5.12. Hyetograph values are scaled
(by area/360) to convert intensities to flowrates in m3/s.
The more complex process for grassed area runoff is shown in Figure 5.13. This diagram is actually an
oversimplification. Some details not shown are that:
the process is actually a step-by-step one, mixing loss and routing calculations for a number of strips
across a sub-catchment, and allowing for water running from one strip to another;
supplementary area runoff is added to the grassed area flows; and
depression storage is actually calculated after the infiltration is calculated.
(m3 /s)
Area (ha)
Full Area
... convolved
with ...
Storage (mm)
... produces ...
Time of Travel
or Time of Entry
Figure 5.12 Calculation of Hydrographs from Paved and Supplementary Areas
DRAINS User Manual
November 2014
Area (ha)
Horton Infiltration Curve
(m3 /s)
Full Area
... convolved
with ...
... produces ...
Time of
Storage (mm)
Subtract Horton
Infiltration (mm/h)
Figure 5.13 Calculation of Hydrographs from Grassed Areas
As explained earlier, grassed area hydrographs can be delayed to allow for any time lag occurring when
grassed area flows travels over paved surfaces to the pipe system.
All hydrographs in the program are linked to the same time base and are synchronised, and combination
of input hydrographs is a straightforward addition process. As shown in Figure 5.14, the supplementary
area hydrograph is incorporated in the grassed area hydrograph. This is added to the paved area
hydrograph and possible user-provided hydrographs or baseflow, to obtain the total runoff hydrograph
coming off the local sub-catchment. Overflows from upstream pits, if present, are then added to this to
obtain the total approach flow to a pit, simple node or detention basin.
from the
Figure 5.14 Flows between Strips in Time-Area Calculations
At pits, an entry capacity relationship applies, and bypass flows and overflows from the pipe system can
occur. With the elaborate hydraulic routing calculations that are applied in DRAINS, it is not possible to
explain these processes in detail, but generally, various inflow hydrographs are added at each time step,
and combined with calculated flows through the upstream pipe system.
Testing and Verification of DRAINS
Testing during development has shown that the ILSAX hydrological model has been reproduced exactly
in DRAINS, with the additional feature of more detailed calculations of supplementary area flows
operating satisfactorily. In comparisons with data from gauged urban catchments, ILSAX has been
shown to provide results that are at least as good as other urban hydrology programs such as SWMM
(see Vale, Attwater and O’Loughlin, 1986; O’Loughlin et al, 1991; and Diamante, 1997, 2000). Table 5.7
Table 5.8 show comparative results between recorded data, SWMM, ILLUDAS-SA (a predecessor of
ILSAX) and ILSAX, showing that the ILSAX Hydrological Model provides a reasonable reproduction of
storm flow characteristics.
Table 5.7 ILLUDAS-SA and Observed Results (Mein and O'Loughlin, 1985)
Storm Date
Vine Street
DRAINS User Manual
Peak Flowrate (m3/s)
Volume (m3)
November 2014
Table 5.8 SWMM and ILSAX Results for Bunnerong Catchment, Maroubra, Sydney
(Vale, Attwater and O'Loughlin, 1986)
Peak Flowrate (m3/s)
Runoff Volume (m3)
27. 0
Table 5.9 and Figure 5.15 present more recent comparisons between ILSAX, DRAINS and observed data
for 25 storms recorded at the University of Technology, Sydney gauging station at Hewitt, Penrith. This
and other comparisons with data recorded at Penrith (Pereira, 1998; Tran, 1998) have shown that ILSAX
and DRAINS produce similar hydrographs at catchment outlets, except in large storms where backwater
effects influence the pipe system hydraulics.
Table 5.9 Comparisons between ILSAX and DRAINS Calculated Flows and Observed Flows at the
Hewitt Gauging Station, Penrith, Sydney
(O'Loughlin, Stack and Wilkinson, 1998; Shek and Lao, 1998; Chan, 1998)
DRAINS User Manual
Peak Flowrate (m3/s)
Runoff Volume (m3)
November 2014
DRAINS User Manual
November 2014
Rational Method Procedures
DRAINS offers three options for the rational method, which can be mixed together in a single system. If
your version of DRAINS is enabled to run the rational method, it is chosen by selecting a rational method
model as a default in the Hydrological Model Specifications dialog box opened from the Project menu.
The first option available in the Rational Method Model property sheet that is called from the Hydrological
Model Specifications box is a general rational method procedure. It is necessary to specify four runoff
coefficients - an impervious and a pervious area coefficient for design, and another set of these for
For a particular sub-catchment, the rational method is applied as follows:
Q = (Cimp . Aimp + Cperv . Aperv) . I
… (Equation 5.9)
Q is the design flowrate in m3/s,
Cimp and Cperv are impervious and pervious area runoff coefficients
Aimp and Aperv are the impervious and pervious areas (ha), and
I is the rainfall intensity (mm/h) corresponding to the appropriate
time of concentration.
Calculated Flowrates (m 3/s)
Linear (ILSAX)
Linear (DRAINS)
Recorded Flowrates (m /s)
Figure 5.15 Hewitt Results
DRAINS performs a search between 5 minutes and the (usually longer) times specified for the impervious
and pervious areas, to find the time that provides the greatest value of Q = C.I.A, overcoming the partialarea problem whereby the lower part of a catchment produce a higher estimate of a flowrate than the total
Rational method times of concentration are specified in exactly the same way as ILSAX model times of
entry in the property sheet for sub-catchments, as described in Section 5.3.2(d).
The first, general method is a 'plain' implementation that has no special fixed features, and can be applied
outside Australia, or within Australia if the user wants to depart from the Australian Rainfall and Runoff,
1987 method. The second method, from Australian Rainfall and Runoff (institution of Engineers,
Australia, 1987), is fully explained in that publication. C10 values must be entered for impervious and
pervious areas. These are 10 year average recurrence interval (ARI) runoff coefficients that are adjusted
for other ARIs by multiplying the C10 values by the frequency factors shown in Table 5.10. The value for
the impervious area is always 0.9.
DRAINS User Manual
November 2014
Table 5.10 Rational Method Frequency Factors
ARI (years)
Frequency Factor
The pervious area runoff coefficient is calculated from the formula:
C10 = 0.1 + 0.0133 (10I1 - 25)
with upper and lower values of 0.1 and 0.7.
index of the rainfall climate.
…(Equation 5.10)
I1 is the 10 year ARI, 1 hour rainfall intensity, used as an
The third method is taken from the Australian / New Zealand Standard AS/NZS 3500.3.2. This gives
different procedures for Australia and New Zealand, and only the Australian procedure is implemented in
DRAINS at present. In the Rational Method Model property sheet, this option requires that only the 10
year ARI, 1 hour rainfall intensity 10I1 be entered. This is used to determine the pervious area C value
using the above equation. This runoff coefficient is adjusted upwards by 0.1 for clay soils and downwards
by 0.1 for sandy soils. The frequency factors from Table 5.10 are applied with a factor of 1.25 being used
for ARIs greater than 100 years. The runoff coefficient for roofs is assumed to be 1.0 and that for
impervious surfaces at ground level to be 0.9.
Only a property site itself is considered in these calculations. The rational method formula is expanded to
allow for the three surface types:
Q = I (CrAr + CiAi + CpAp) / 3600
… (Equation 5.11)
where Ar, Ai and Ap are the areas of roofs, impervious areas and pervious areas in the sub-catchment
being considered. In calculations, the time of concentration is fixed, at 5 minutes.
All methods require intensity-frequency-duration (I-F-D) data that is entered in the Rational Method
Rainfall Data property sheet opened from the Rainfall Data… option in the Project menu.
The Extended Rational Method
A number of methods have been developed for extending the rational method to produce hydrographs,
usually by assuming a triangular or trapezoidal shape. In the US, a Modified Rational Method (Poertner,
1981) has been applied in many locations. This produces hydrographs corresponding to uniform rainfall
blocks of various durations, which can be used to model detention basins in the same way that can be
done using Australian Rainfall and Runoff design rainfall patterns.
DRAINS presents a variation on this method named the Extended Rational Method (ERM), which is
available if the rational method is enabled in the hardware lock used. It was introduced to meet the needs
of users who wish to develop hydrographs that are consistent with Rational Method flowrates derived
using the methods from Australian Rainfall and Runoff, 1987 and the Queensland Urban Drainage
Manual, 1992. While the ILSAX hydrological model in DRAINS should produce superior results to the
rational method due to the testing and verification described in Section 5.3.3 and previous parts of this
chapter, it cannot provide similar peak flowrates to the rational method across a range of ARIs and storm
The ERM employs the same time-area routing procedure as the ILSAX model rather than assuming
hydrograph shapes. The loss model is different, applying a continuing loss to all blocks of rainfall. When
the ERM was first released, it assumed a constant continuing loss but inconsistencies were found when it
was applied with storms of various durations. The ERM assumes a continuing loss proportional to rainfall
The ERM requires the same input data as the ARR87 rational method (Figure 1.39) but runs with rainfall
patterns or hyetographs, rather than intensities from an I-F-D relationship. When applied with the design
storm patterns from Australian Rainfall and Runoff, 1987 Chapter 3 the peak flows obtained from a set of
DRAINS User Manual
November 2014
design storms will differ from those given by the ARR87 rational method. The synthetic storm option in
the Rainfall Data property sheet (Figure 2.73) has been provided to produce rainfall patterns that
incorporate many blocks of rainfall of different average durations that are consistent with the I-F-D
duration curves of the design rainfalls. Using these patterns with the ERM, rather than the
The volumetric runoff coefficient (the ratio of volume of runoff to volume of rainfall) obtained from a
pervious area with the ERM will be the same as the C10 coefficient supplied, adjusted by a frequency
factor. The validity of this has been checked using data collected at the Jamison Park Gauging Station in
Western Sydney, as shown in Figure 5.16. Results from 80 storms shown in indicate that this is
reasonable for this locality. (Peak flow coefficients were derived assuming a time of entry of 20 minutes.)
Storage Routing Models
Traditionally, storage routing or 'runoff routing' models such as RORB, RAFTS and WBNM have been
used for flood studies for larger rural catchments and somewhat smaller semi-urban catchments. These
models were introduced in the 1970s as computer models became more widely-used than previously,
and methods for modelling urban areas became more important.
Figure 5.16 Jamison Park Volumetric vs. Peak Flow Runoff Coefficients
Previous models, notably synthetic unit hydrograph procedures, provided a flow estimate at the outlet to a
catchment. By dividing the catchment into sub-areas, the storage routing models provided flood
estimates at several points throughout the stream system. They also allowed hydrological losses to be
varied across the catchment area, reflecting various soil types. Since these models are essentially
networks of storages, detention basins and reservoirs can be easily incorporated.
RORB, RAFTS and WBNM belong to a class of models termed runoff routing models, which also includes
models based on unit hydrograph and kinematic wave calculations. Runoff routing models can 'route' a
hydrograph from one geographical location to another, allowing for changes such as translation and
attenuation of the hydrograph, as shown in Figure 5.17.
Figure 5.17 Translation and Attenuation Effects on Hydrographs
DRAINS User Manual
November 2014
The basic non-linear model used in Australian storage routing models was developed by Eric Laurenson.
RORB, a practical computer application of this model, was produced by Eric Laurenson, Russell Mein
and Tom McMahon at Monash University, Melbourne in the mid-1970s. At the same time, the RSWM
(Regional Stormwater Model) was developed by Allan Goyen of Willing & Partners and Tony Aitken of
SMEC. These models were immediately popular, as they filled a need for modelling mixed rural and
urban catchments, allowing for soil and rainfall variability, and providing flow estimates at points
throughout the catchment. In 1979, they were followed by the WBNM (Watershed Bounded Network
Model) of Michael Boyd , David Pilgrim and Ian Cordery.
Initially, these models were run on mainframe and mini computers. RAFTS (Runoff Analysis and Flow
Training Simulation), an enhanced version of RSWM, was released in 1983 and sold commercially by
Willing & Partners (later WP Software and XP-Software). This includes continuous modelling processes
as well as the storage routing model discussed here. A version for PCs was released in 1987. A PC
version of RORB was released in 1988.
WBNM was revised in 1987 and a new version was produced by Michael Boyd, Ted and Rudy VanDrie
in 1994, which modelled urban catchments. WBNM2000, introduced in 1999, used a different structure to
earlier models and added many features.
Storage routing calculations are carried out over a series of time steps, with the information obtained from
solving equations at one time step being used as an input to the next step. Each of the models available
in DRAINS has been developed on different principles. RORB performs calculations based on the
S = kc . kr . Qm = kc . (li / lc) . Qm
… (Equation 5.12)
S is storage (m3),
kc and m are parameters, with m being in the range 0.65 to 0.85,
kr is a routing factor for a particular sub-catchment, being the ratio of the stream length running
through that sub-catchment, li, and the average flow distance from sub-catchments to the
catchment outlet, lc, calculated by dividing the sum of catchment areas multiplied by their
distances from the outlet by the total catchment area, Σ(Ar.dr) / A, and
Q is flowrate (m3/s).
kc acts as a calibration parameter, enabling the model's results to be varied and fitted to recorded
hydrographs. A kc of 0.0 will perform no routing, so that values of rainfall excess and flows from upstream
storages will pass through a sub-catchment unchanged. A kc that is very large will delay flows
considerably, so that flowrates will be very low. By adjusting kc, the peak of a calculated hydrograph can
be varied over the range from the peak rate of rainfall excess to zero. Decreasing kc increases flowrates.
Allowance is made for different channel conditions by multiplying the routing factors by the values in
Table 5.11, in which Sc is the reach slope (%).
Table 5.11 Reach Adjustment Factors in RORB Model
Reach Type
Excavated and unlined
Lined or piped
Drowned (by a reservoir)
The routing through a sub-catchment in a RORB model will depend on the length of the stream channel
through the sub-catchment and the average distance to the outlet, lc. When combining a RORB model
with an ILSAX model, the lengths of channels and pipes in the ILSAX model will be used to calculate lc.
If a kc value from a stand-alone RORB model is used in this case, it will result in an incorrect routing
calculation. It will be necessary to use a different kc that can be derived or by dividing the kc derived for a
stand-alone model by lc for the new model multiplied by lc for the original RORB model. Since DRAINS
does not reveal the lengths to outlets, it will be easiest to determine a new kc by trial and error, matching
the peak flowrates defined by the original model.
For sub-catchment routing, RAFTS uses the equation:
S = BX . IBFL . PERN . 0.285 A0.52. (1+U)-1.97. Sc-0.50. Q0.715
DRAINS User Manual
… (Equation 5.13)
November 2014
where BX is a calibration factor similar to RORB's kc,
IBFL is a factor for modelling overbank flow,
PERN is a factor that adjusts the catchment routing factor to allow for catchment roughness,
A is the sub-catchment area (km2),
U is the fraction of the catchment that is urbanized, and
Sc is the main drainage slope of the sub-catchment.
For routing along stream reaches, RAFTS applies a translation over a nominated time, or performs
Muskingum-Cunge routing based on the stream cross-section and roughness.
For sub-catchments, WBNM uses the routing equation:
S = 60 . LP. A0.57. Q0.77
… (Equation 5.14)
where LP is a lag parameter and A is catchment area (ha).
Values of the WBNM lag parameter are typically between 1.3 and 1.8. This can be used to calibrate the
model in a similar way to the RORB parameter, kc. WBNM2003 also allows for translation and
Muskingum routing in stream reaches.
For stream reaches, a similar equation is used:
S = 0.6. 60 .LP.A0.57.Q0.77
… (Equation 5.15)
with the 0.6 allowing for the routing effects in the reach, the length of which is related to the area of the
catchment through which it runs, A. A stream lag factor can be applied to allow for different types of
channel. Indicative values are shown in Table 5.12.
Table 5.12 Stream Lag Factors used in WBNM
Reach Type
Stream Lag Factor
Natural channel
Gravel bed with rip-rap
Excavated earth
Concrete lined
Drowned (by a reservoir)
No lag, artificial link
Modelling facilities based on RORB, RAFTS and WBNM have been included in DRAINS. The three
models have different structures, as shown in Figure 6.18: RORB has a well-defined structure, with
nodes located close to sub-catchment centroids. Routing is only carried out in the stream reaches.
There is modelling of losses at nodes but no routing.
By contrast, RAFTS can carry out routing at nodes representing sub-catchments, and also in stream
reaches, where flows can be translated or routed using the Muskingum-Cunge method, based on the
reach cross-section and roughness. The routing within sub-catchments differs from RORB and WBNM in
that flows are commonly routed through 10 successive non-linear storages, as indicated in one of the
sub-catchments in Figure 5.18.
In WBNM, routing occurs at the sub-catchment nodes and in stream reaches that convey runoff from
upstream sub-catchments through the local sub-catchment. Like RAFTS, it is flexible, and can be set out
in different configurations.
To fit these different structures into the DRAINS framework, it has been necessary to apply different
property sheets and relationships between model sub-catchments and stream routing reaches. These
are described in Chapter 2. For stream channels, routing can also be undertaken by methods such as
the Muskingum Method, lag and route methods, Muskingum-Cunge routing and hydraulic routing using
methods such as kinematic wave calculations. DRAINS employs the latter in RAFTS-style stream routing
reaches, following a method given in Chapter 9 of Open Channel Hydraulics by F.M. Henderson (1966).
DRAINS User Manual
November 2014
Figure 5.18 Structure of Three Storage Routing Models
Pit Inlet Capacities
The inlet capacity of pits is a vital factor in the modelling of piped stormwater drainage systems in major
storm events, separating surface overflows from underground pipe flows. Pits can be distinguished by
their form, as grated pits, kerb inlets, or as combinations of these. The latter two types are preferred in
Australia. Pits can also be distinguished by the situation in which they are applied. On-grade pits, shown
in Figure 5.19, are located on slopes in a channel such as a street gutter, with water flowing to them, and
with any bypass flows escaping. Sag pits are located in hollows or depression, where the incoming flows
for a pond over the pit. These situations are hydraulically different and different forms of relationships
are used to describe their inlet capacities.
Bypass Flow
Kerb and
On-Grade Pit
Sag Pit
Figure 5.19 On-Grade and Sag Pits
On-grade pit inlet capacities are defined as a relationship between the inlet flow or capture and the
approaching flow. This flow is affected by the road cross-section properties and its longitudinal slope, as
well as the characteristics of the inlet. Different road and gutter cross-sections and roughnesses will
create different widths and velocities of flow approaching the pit. Since there is no direct theoretical
relationship covering all of these factors, empirical relationships have been established from laboratory
tests and field observations.
Figure 5.20 shows the relationships for kerb inlets on grade measured in hydraulic model studies
published by the N.S.W. Department of Main Roads (1979). As the magnitude of the approach flow
increases, the percentage of the flow captured will decrease. This is represented by the curved line
becoming gradually flatter and crossing the dotted lines that indicate various percentages of capture.
Sag pits can be modelled more easily, as the theory of weir and orifice flow can be applied to relate inlet
capacities to depths of ponding. Experimental investigations have confirmed the following weir equation
given in Australian Rainfall and Runoff (Institution of Engineers, Australia, 1987, page 303).
DRAINS User Manual
November 2014
Qi = 1.66 . P . d1.5
up to about 0.12 m of ponding
… (Equation 5.16)
where Qi is inlet flowrate (m3/s),
P is the perimeter length of a grated pit, excluding the section against the
kerb, and
d is the average depth of ponding (m).
Orifice flow can occur above 0.12 m for a grate and 1.4 times the slot height for a kerb inlet, though there
is a large transition zone for grates, in which either flow mechanism may occur. Most cases of interest to
designers, including major flows, are described by the weir equation.
At low flows all of the approach flow will be captured, but at a certain flow, some bypass will start to occur.
Figure 5.20 Entry Capacities for Kerb Inlets on Grade
There have been many sets of hydraulic tests undertaken to define inlet capacities. Tests have been
conducted in Australia by the NSW Public Works Department for the NSW Department of Main Roads
(now NSW Roads and Maritime Services) and NSW Department of Housing, by the University of South
Australia for various Queensland, Australian Capital Territory and South Australian bodies, and by the
Victorian Country Roads Board (VicRoads). These have produced a rather confusing array of results,
from which it is difficult to generalise.
In addition, the published relationships do not cover the range of high flows expected to occur in severe
storm events such as 100 year average recurrence interval and probable maximum precipitation events.
Almost all studies were intended to develop relationships for routine design, and did not deal with very
high flows. Extrapolation of these relationships is an uncertain process.
The main factors influencing inlet capacity of on-grade pits are the length of the pit, the depression or
crossfall of the gutter at the pit, and the longitudinal slope. Generally the greater the longitudinal slope,
the lower the capture rate. Pit size and grate type are the main factors affecting sag pit capacities.
The US Federal Highway Administration Hydraulic Engineering Circular No. 22, Urban Drainage Design
(2009) includes a set of semi-theoretical procedures for defining inlet capacity relationships. Pezzaniti,
O’Loughlin and Argue (2005) have used these as a basis for extrapolating existing relationships, and for
developing relationships where none are available.
Pit Inlet Capacities in DRAINS
At every time step in DRAINS calculations, the program applies pit inlet capacity relationships to the
surface flow arriving at each inlet. If the flowrate arriving at an on-grade pit causes the storage to exceed
its specified volume, the surplus flow becomes a bypass. If overflows occur due to limitations on pipe
reach capacity, these are added to the bypass flows.
Two types of entry conditions can be modelled in DRAINS:
sag pit, at a low point where water will pond, up to some limit, with any overflows being directed
downstream or out of the system, when the ponded water level rises to the spill level.
DRAINS User Manual
November 2014
on-grade inlet, on a sloping gutter, from which any flows bypassing the inlet can run away, with
bypasses or overflows being directed to downstream pits or out of the system.
At one stage there was also an ILLUDAS pit type that no longer appears in DRAINS. It is described in
the Help System.
Initially, DRAINS followed ILSAX (O’Loughlin, 1993) by using equations employing various curve-fitting
factors, but this approach was superseded by inlet capacity relationships defined as a series of points, as
shown in Section 2.4.6, rather than by equations. Further information is given in the DRAINS Help
system. Sets of inlet capacity relationships are available to users of DRAINS in the new format. These
were obtained from published sources, mostly smoothed graphs fitted to experimental data from the
testing rigs operated by the University of South Australia (www.unisa.edu.au/uwrc/rig.htm) and the New
South Wales Government Manly Hydraulics Laboratory (http://mhl.nsw.gov.au/www/welcome.html).
The new relationships have been extrapolated well beyond the ranges of the published relationships
using hydraulic principles, allowing for approach flows up to 2.5 m3/s for on-grade pits and depths of
ponding of up to 0.6 m for sag pits. None of these relationships have been approved by the originating
authorities. It is up to each user of DRAINS to determine whether they are suitable for their purposes.
Users can readily modify the relationships.
The available relationships for New South Wales apply to the pits described in Table 5.13.
Table 5.13 New South Wales Pits
Pit Type
Kerb Inlet
Grate Size
NSW Roads
and Maritime
(formerly called
the RTA and
DMR) pits
(DMR, 1979;
Darlington and
House, 1992)
and tests
carried out for
the RTA in the
1.0 m wide x 0.15
m high
1 m x 0.45 m
A kerb inlet-grate combination
depressed by 25 mm below
normal gutter levels
1.83 m wide x
0.15 m high
0.915 m x 0.45
As above
2.745 m wide x
0.15 m high
0.915 m x 0.45
As above
Median pit with
As above
SO V-Channel
0.7 x 0.7 m or
0.7 x 1.4 m
V shaped pits located in VChannels
SK V-Channel
0.825 x 0.7 m or
0.825 x 1.4 m
V shaped pits located in VChannels
Council Pits
0.9, 1.2, 1.8,
2.4, 3.0, 3.6
and 4.2 m
wide lintel
0.9, 1.2, 1.8, 2.4,
3.0, 3.6 or 4.2 m
wide x 0.15 m
0.915 m x 0.45
Essentially the same type as
the RTA Pits
NSW Dept. of
Housing (1987)
RM10 Pit
1.68, 1.8, 2.4
or 3.0 m lintel
1.68, 1.8, 2.4 or
3.0 m wide by
0.15 m high
0.9 m x 0.5 m
A similar type of pit to the RTA
0.9 m x 0.5 m
A grated pit used on
0.85, 1.2, 1.8, 2.4
and 3.0 m wide by
0.15 m high
0.9 m x 0.5 m
No grate or Durham Cast iron
NSW Dept. of
Housing (1987)
RM7 Pit
Shire Council
0.85, 1.2, 1.8,
2.4 and 3.0 m
The set of pits shown in Figure 5.21 was the basis of both the RMS (RTA) and Hornsby Council
relationships, which have different forms. The former allows for longitudinal slopes while the latter
provides a single relationship for all slopes.
Relationships developed for Australian Capital Territory are detailed in Table 5.14
DRAINS User Manual
November 2014
Fiigure 5.21 Type
SA1, SA2
and SA5
5 Pits tested
d for the NSW
W Departmeent of Main Roads
able 5.14 AC
CT Pits
(Source: AC
CT Governme
ent Urban S
Stormwater, Standard
gineering Praactices, Editiion 1,
Kerb In
Dimensi ons
ate Size
0.6 m lo
Only for saggs, in three types
1.3 m lo
n three typess of gutters: KG,
Double R
2.6 m lo
As above
Triple R
3.9 m lo
As above
Victorian relationships obtained by extrapola
ating the curv
ves given in the
t VicRoadss Road Desiign
nes Part 7, Drainage,
95 are availa
able for the pits
p shown in Table 5.15.
Table 5.15
5 Victorian VicRoads Pits
urce: VicRoads Manual)
Ke rb Inlet
ate Size
1.0 and 1.5 m
entry pitts
and 1.5 m
1.0 a
wide by 0.10 m
1 m grated inlet
e grates A & B 1.0 m wid
de x 0.75, 1.00,
1.5, 2.0 or
o 2.5 m longg
Grrated side en
1.0 m wide x 0.1
m deep
assumed 1.0
1 m x 0.45 m
Queenssland relation
nships are ou
utlined in Tab
ble 5.16. Qu
ueensland ha
as the most ccomprehensiive data of
any Ausstralian state. There has been an exttensive revision of the original Queennsland 2003
relationsships, becau
use of the intrroduction of new pit types and relatio
onships, and new extrapo
S User Manual
November 2014
Table 5.16 Queensland Pits
(2008 Version, Various sources, see Column 1)
Kerb Inlet
Grate Size
City Council
Pits (from
S, M and L,
2400, 3600
and 4800
mm lintel
lintels - 2.04,
3.24 and
4.44 m long x
0.12 or 0.14
m deep
0.90 m x 0.61
Separate lip in line (recessed)
relationships for D (mountable) and E
(barrier) kerbs and two sets of kerb in
line relationships for both D & E kerbs.
The new relationships supersede the
older ones that appear in the DMR Road
Drainage design Manual (2002) and
other manuals. Relationships are given
for 2.5 and 3.3% crossfalls and grades
from 0.25% to 16% plus sags.
Gold Coast
City Council
(from GCCC
As above
As above
0.90 m x 0.50
Separate lip in line relationships for
(a) barrier or roll-top kerbs and
(b) transverse or longitudinal grates,
(c) 2.5% or 3% crossfalls and
(d) grades from 0.25% to 16% and sags.
Max Q
Plus (from
Max Q
2TP/X and
1.0, 2.3, 3.6
and 4.0 m
wide x 0.1 m
deep lintels
0.66 m x 0.614
m Maxflow
and Mannflow
Grates or
With (a) mountable kerb, barrier kerbs
with 300 mm and 450 mm channels,
(b) 2.5% or 3% crossfalls, (c) 0.25 to
16% grades and sags.
Max Q
(from Max Q
1.0, 2.3, 3.6
and 4.0 m
wide x 0.1 m
deep lintels
0.85 x 0.51m
Grates or
With (a) mountable kerb, rollover kerb,
barrier kerbs with 300 mm and 450 mm
channels, (b) 2.5% or 3% crossfalls,
(c) 0.25 to 16% grades and sags.
Max Q
1.0 m lintel
0.675 x 0.31 m
Hazen Grate
For mountable kerbs, 2.5 and 3%
crossfalls and grades from 1% to 16%
and sags
0TC, 1TC,
2TC and
1.35, 2.7,
4015 and 5.4
m wide x
0.14 m deep
One or two
0.5 m x 0.5 m
grate or infill
A modular system built around one or
two pits with grates
0.75 m, 2.1
m and 3.45
m wide x
0.10 m deep
A modular system made up of pits (C)
and troughs (T)
DMR Field
Single and
0.6 x 0.9 m or
0.6 x 1.8 m
Nominally for sags only, but an on-grade
relation assuming 1% grade is included
South Australian relationships are provided in
Table 5.17. Relationships for Western Australian and Tasmanian Pits derived using US Federal Highway
Administration HEC-22 procedures are shown in
Table 5.18 and Table 5.19.
For both on-grade and sag pits, a choke factor can be applied to simulate blockage of the pit. This is 0.0
for no blockage and 1.0 for complete blockage. There is considerable uncertainty about appropriate
factors. Australian Rainfall and Runoff 1987 indicated typical values of 0.2 for an on-grade pit and 0.5 for
a sag. Some Queensland practice applies values of 0.1 for both. It could be argued that a factor of 0.0
should be applied to on-grade pits, which are much less likely to block than sag pits. These are multiplied
by the capacity defined by the inlet capacity relationships, whatever magnitude this may be. While this is
acceptable for the type of blockage that might occur for sag pits, it may not be realistic for on-grade pits.
If you have doubts about this, it would be better to define the required inlet capacity relationship in the pit
data base, and to employ this with a blocking factor of zero.
DRAINS User Manual
November 2014
Table 5.17 South Australian Pits
(Source: html files developed by the Urban Water Research Centre of the University of South Australia)
Kerb Inlet
Grate Size
Single Bay
0.9 m long
On-grade relationships with and
without deflectors
Double Bay
1.9 m long
On-grade and sag relationships
with and without deflectors
Single Pit
0.9 m long
0.5 m long x
0.54 m wide
On-grade and sag
Double Pit
1.9 m long
As above
Sag only
Double Pit
1.9 m long
On-grade and sag,
with and without deflectors
Transport SA
City of Adelaide
City of
Single Pit
0.9 m long
City of Charles
On-grade and sag, with and without
deflectors and transitions
Double Pit
1.9 m long
As above
City of Marion
Double Pit
1.9 m long
On-grade and sag, with and without
Single Bay
0.9 m long
0.9m x 0.45m
On-grade without deflectors
City of Mitcham
Double Bay
1.9 m long
On-grade and sag, with and without
City of
Double Pit
1.9 m long
As above
City of Playford
Double Pit
1.9 m long
As above
City of Port
Double Pit
1.9 m long
On-grade, with and without
Triple Pit
1.9 m long
Different bay arrangement, Ongrade, with and without deflectors
City of Salisbury
Double Pit
1.9 m long
On-grade and sag,’ with and
without deflectors
City of Tea Tree
Double Pit
1.9 m long
On-grade and sag, without
City of West
Double Pit
1.9 m long
On-grade and sag, with and without
Table 5.18 Western Australian Pits
(Developed from Department of Main Roads drawings and Generic Spreadsheet using HEC-22 procedures. None
are based on measured data.)
Kerb Inlet
Grate Size
Main Roads Side
Entry Gully, Type
0.88 m long
On-grade relationships with
allowance for deflectors
Main Roads Gully,
Single Pit
0.92 m long x
0.425 m wide
On-grade and sag
Main Roads
Normal Catchpit
As above
On-grade and sag, assumed
to be used in swales
Main Roads High
Flow Catchpit
As above,
150 mm above
As above
Pit Type
DRAINS User Manual
November 2014
Table 5.19 Tasmanian Pits
(Developed from government drawings and Generic Spreadsheet using HEC-22 procedures. No measured data.)
Pit Type
Kerb Inlet
Grate Size
Single grated
Grated deflector
0.9 m wide
1.865 m wide
Double grated
1.9 m wide
0.9 x 0.45 m
0.9 x 0.45 m +
1.9 x 0.45 m
At some slopes the double
grate pit has the highest
capacity; at other grades it
is the grated deflector pit
City of
Double grated
extended kerb
1.68 m wide
0.89 x 0.40 m
Dept. of
Energy &
Mountable kerb
1.0 m wide
1.8 m wide
0.9 x 0.35 m +
0.9 x 0.35
Barrier kerb
0.9 m wide
As above
As above
0.98 m x 0.64 m
US Federal Highway Administration (HEC22) Procedures
The Hydraulic Engineering Circular No. 22 of the US Federal Highway Administration (2009) (available
from www.fhwa.dot.gov/bridge/hyd.htm) contains the only general methodology available for defining inlet
capacities for all kinds of rectangular pit. It is applied as a series of equations and procedures, with a
semi-theoretical basis. These procedures have been included in a comprehensive 'generic' pit capacity
spreadsheet available to DRAINS users and the on-grade pit procedures have been incorporated into
DRAINS via wizards located in the Pit Data base opened from the Project menu.
For the gutter and pit shown in Figure 5.22, the on-grade procedure shown in Figure 5.23 applies.
Figure 5.22 Road and Pit Characteristics
Flow is assumed to approach a pit along a gutter. At the pit, the gutter crossfall may become steeper to
provide a depression. The pit may be a kerb inlet, a grate, or a combination inlet with both. The latter
kerb inlet is assumed to project beyond the grate so that the approaching flow encounters this first. The
method requires information on the road cross-section as well as on the inlet characteristics. The grate
types detailed in the HEC22 manual are shown in Figure 5.24.
DRAINS User Manual
November 2014
Figure 5.23 HEC22 On-Grade Input Procedure
30o Tilt Bar
45o Tilt Bar
P-50 and P-50 x 100
DRAINS User Manual
November 2014
Figure 5.24 HEC22 Pit Types
Once the required data is entered, the required relationship will appear in the Pit Data Base property
sheet. This can be checked by copying this and displaying it in a spreadsheet. This procedure can be
applied to pits in swales, as well as in street gutters or channels. The dialog box is shown in Figure 5.25,
covering the situation shown in Figure 5.26.
Figure 5.25 Dialog Box for a Pit in a Swale
Figure 5.26 Pit in Swale
A similar procedure applies for sag pits. The DRAINS wizard shown in Figure 5.27 only operates for
grated inlets. This requires information on grate dimensions. (For kerb inlets or combination (kerb inlet +
grate) inlets, you can use the 'generic' spreadsheet supplied to DRAINS users to develop relationships
that can be pasted into the DRAINS pit data base.)
The calculations associated with these methods produce results that match laboratory results on pit
capacities well in some cases, but rather poorly in others. This issue has been studied by Pezzaniti,
O’Loughlin and Argue (2005), who produced the assessments of the accuracy of the HEC22 procedures
for on-grade pits shown in Table 5.20. This can be used as a guide to adjusting relationships produced
by the HEC22 procedure. Adjustments can be made by copying the relationship produced to a
spreadsheet, modifying this as required, and then pasting it back into the Pit Data Base table. Using
these procedures, it is possible to derive inlet capacity relationships for all types of pits, including unusual
or modified ones.
DRAINS User Manual
November 2014
Figure 5.27 Dialog Box for Sag Pit
Pipe System Hydraulics
The hydraulic models used in design and analysis of urban stormwater drainage systems can be
considered to operate at three levels:
open channel hydraulics assuming steady flow and normal depth conditions, described as 'pipe full
but not under pressure' in Australia,
part- or full-pipe flow calculations determining hydraulic grade lines (HGLs) and water surface
full hydrodynamic modelling, usually involving a finite difference solution of the partial differential
equations for conservation of mass and momentum, the St. Venant Equations.
ILSAX calculations operate at the first level, so their hydraulics is quite limited. The same applies to the
calculation of flow characteristics in overflow routes in the standard and obsolete basic hydraulic models.
Table 5.20 Qualitative Indication of the Accuracy of the HEC22 Procedures
(Inlet Capacities from HEC22 Procedure relative to Laboratory Results)
Inlet Type
Flow Range
Approximate Length of On-Grade Inlet
1 m or Shorter
Between 1 & 3 m
3 m and Longer
Grate Only
< 0.15 m /s
Grate Only
0.15 to 0.5 m /s
Grate Only
> 0.5 m /s
Underestimates by
about 25%
Kerb Inlet Only
< 0.15 m3/s
25% over for undepressed inlet,
50% under for
Kerb Inlet Only
0.15 to 0.5 m3/s
Kerb Inlet Only
> 0.5 m3/s
Combination with
1 m Grate
< 0.15 m3/s
Combination with
1 m Grate
0.15 to 0.5 m3/s
5% overestimate
Combination with
1 m Grate
> 0.5 m3/s
20% overestimate
DRAINS User Manual
November 2014
Velocities, depths and other characteristics are obtained from normal depth calculations using the
specified cross-section (from the overflow route cross-section data base), slope and roughness.
The HGL calculations associated with rational method in the urban stormwater drainage chapter of
Australian Rainfall and Runoff, and those in steady state hydraulics programs such as HEC-2 and HECRAS, are at the second level. Several programs, mostly proprietary ones, offer full hydrodynamic
modelling options using complex finite difference calculations. These can give the most accurate results
with an experienced, hydraulically-knowledgeable operator, but can be subject to stability problems.
Pipe Design Calculations
In a design run, DRAINS determines pipe sizes and invert level positions by calculating the peak flows of
hydrographs entering a pipe system and designing for these in a downwards pass, making certain
assumptions. The method considers both minor and major storms of different average recurrence
intervals. Pit sizes are also designed to keep overflows within safe limits defined in the overflow route
data base.
The design procedure must be followed by analysis runs using the same design storms to simulate and
display the performance of the system in detail. The designer can than assess whether this is
satisfactory, and make further changes and re-runs to refine the system.
Basic Hydraulic Calculations
In DRAINS, the now obsolete basic hydraulic model provided a conservative procedure for tracing
hydraulic grade lines through drainage systems, working upwards from tailwater levels at the outlet at
each calculation time step. At each time step in an analysis, this model made a pass downwards through
the drainage system, determining flows into pits, possible bypass flows and the flows along pipes. It then
retraced this path from a specified tailwater level at the system’s outfall, determining hydraulic grade lines
and water levels in pits. Allowance was made for pipe friction and pit pressure changes, and both part-full
and full-pipe flows were modelled. The possibility of water upwelling from pits due to the flow capacity of
the downstream pipe system being exceeded was also considered. With this model, DRAINS used a
hydraulic engine from the PIPES program to model pressurised flows. It switched to this when pipes
surcharged, going from part-full to full pipe flow, and handled the complex timing and flow volume
transitions involved in transferring between calculation methods.
Unsteady Flow Calculations in Standard and Premium Hydraulic Models
As noted in Section 4.2.7, the unsteady hydraulic method applied in the standard and premium hydraulic
models is quite different to method used by the basic hydraulic model. The unsteady model in DRAINS
solves the full St. Venant equations of momentum and continuity using an implicit finite difference scheme
with a staggered H, Q grid. This solution scheme is widely used in other software such as SWMM. Links
are divided into an odd number of reaches (1, 3, 5, etc.) with DRAINS automatically determining a
suitable number to use. When DRAINS reports the flow in a link it is referring to the flow calculated at this
central grid point.
The method applies the Saint Venant Equations for conservation of mass and momentum in unsteady
∂ A ∂Q
= 0
(Continuity or Mass)
... (Equation 5.17)
1 ∂Q
gA ( ∂t + ∂ x ( /A) ) + ∂x + Sf = 0
Q is flow,
H is water surface level,
x is distance along a channel,
Sf is friction slope
... (Equation 5.18)
A is cross-sectional area,
t is time,
g is gravitational acceleration,
The calculation procedure applied in DRAINS involves the solution of these equations to determine H and
Q at all points in a system at each time step of the simulation. Equations are gathered into a matrix and
solved, allowing for different types of boundary conditions imposed by flows entering pipe and channel
systems, downstream tailwater levels and the hydraulic features at on-grade and sag pits, headwalls and
other features.
DRAINS User Manual
November 2014
In the premium hydraulic model, pipes, open channels and overflow routes are all modelled by the same
procedures, based on open channels. Closed pipes can be treated as being open by using a Priessmann
slot (Figure 5.28). Each link has a representative cross-section, so it is necessary to divide open
channels and overflow routes into separate links where their geometric characteristics change.
Slot, a few mm wide
Full-Pipe Pressurised Flow
Part-full Flow
Figure 5.28 Priessmann Slot for Modelling Pipes as Open Channels
At sag pits there will be two HGL levels, one describing the water level in the ponded runoff at the surface
and the other describing the pipe HGL.
Calculations for outlet weirs from sag pits, detention basins, headwalls, and culverts use tables of
elevation vs. discharge. To cover the situation where tailwater levels below these controls are high, in
the premium hydraulic model, DRAINS uses the Villemonte equation to modify the table if the
downstream water level is above the weir crest (the level in the table at which Q=0). The Villemonte
equation allows for submergence of the weir:
Q = Cdf . Cd . 2/3 (2g)0.5. b . h1.5
…(Equation 5.19)
where Q is the flowrate (m3/s),
Cd is the discharge coefficient (dimensionless),
g is acceleration due to gravity (9.80 m/s2),
b is the effective width of the weir (m),
h is the effective head (m), and
Cdf is a drowning factor, equal to Cdf = A (1 – (h2/h1)1.5)n
where A and n are coefficients,
h1 is the upstream measured water level above the weir, and
h2 is the downstream measured water level below the weir.
At headwalls and culverts the flow capacity is often limited by inlet control. All flow models in DRAINS
use the equations for culverts and headwalls presented in this manual to check for inlet control at these
structures. DRAINS also allows for the specified inlet capacity relationships at on-grade pits as long as
these are not submerged.
For sag pits a truncated inverted pyramid shape is assumed, with the base length at the gutter invert level
being half that at the overflow level. Alternatively, the user can specify a table of elevation versus surface
area. With the premium hydraulic model, users must provide a weir control specification in the Overflow
Route property sheet and water can rise above the maximum ponded level. With the standard and basic
hydraulic models water does not rise above the maximum ponded level, rather any water above this level
is assumed to immediately spill into the overflow route.
Pipe Friction Equations
For circular pipes, you have a choice of the Colebrook-White Equation or Manning's Formula.
The Colebrook-White Equation employs the formula:
⎛ k
2.51 ⋅ υ
⎜ 3.7 ⋅ D D ⋅ 2g ⋅ D ⋅ S ⎟
V = -0.87. 2g ⋅ D ⋅ S ⋅ loge ⎜
.... (Equation 5.20)
g is gravitational acceleration (m/s2), generally 9.80 m/s2 at sea level,
D is diameter (m),
S is energy line slope (m/m),
k is pipe wall roughness (mm), sometimes termed e, and
DRAINS User Manual
November 2014
υ is the kinematic viscosity (taken as 1.14 x 10-6 m2/s at 15oC).
The pipe wall roughness values in Table 5.21 are recommended by Hydraulics Research (1983) and the
Standards Association of Australia (1978). Values for other materials are also given in these publications.
Table 5.21 Recommended Colebrook-White Roughnesses, k
SAA Recommendations: for
concentricallyjointed, clean
Hydraulics Research
values (mm)
pipe condition:
Pipe Material
Precast, with 'O' Ring Joints
Spun precast, with 'O' Rings
Monolithic construction, against
steel forms
Monolithic construction, against
rough forms
0.03 to 0.15
0.015 to 0.06
Chemically-cemented joints
0.003 to 0.015
Spigot and Socket Joint
Asbestos Cement
Manning's Equation is
V =
in which
1 0.667 0.5
.... (Equation 5.21)
V is velocity (m/s),
n is a roughness coefficient
R is the cross-section hydraulic radius (m) (= area / wetted perimeter, A/P ), and
S is longitudinal slope (m/m).
Pit Pressure Changes
(a) General
The head losses and changes to the energy grade line and hydraulic grade line at pits and junctions are
extremely important in determining pipe system behaviour accurately. Figure 5.29 shows how these are
represented by two functions of the pit outlet velocity Vo, for full-pipe flow.
Grate Flow
k LV0
k uV0
Figure 5.29 Pit Energy Losses and Pressure Changes
The TEL will drop by the amount of the head loss for the pit, which can be expressed as:
DRAINS User Manual
November 2014
hL = kL ⋅
…(Equation 5.22)
where hL is head loss (m),
kL is the head loss coefficient (dimensionless),
Vo is the full-pipe velocity in the outlet pipe from the pit (m/s), and
g is acceleration due to gravity (9.80 m/s2).
More importantly for design, the pressure change is given by:
hu = k u ⋅
… (Equation 5.23)
where h is head loss (m), and
ku is the head loss coefficient (dimensionless, also expressed as Ku).
Generally ku is positive, with the HGL dropping down, but it is sometimes negative, with the line rising due
to the downstream pipe having a larger diameter and slower velocity than the upper one. This has been
termed 'static regain'.
It is assumed that head losses and pressure changes take place at the centre of the pit, while actual
losses occur mainly in the outlet pipe just downstream of the pit. Where significant turbulence occurs in
the pit, the water level may be higher than the incoming HGL. A higher factor kw may be used in place of
ku to establish water levels where information on these factors is available. A different factor to the main
branch ku may also be applied to side branches.
There are an infinite number of combinations of factors affecting the magnitudes of kL and ku. These
include relative flows in upstream flows, the local inlet and the downstream pipe, the relative diameters of
upstream and downstream pipes, the angles of the pipes and the positions of their obverts and inverts,
the presence of benching in a pit, the degree of submergence of the pit, and the pit shape. The 'Missouri
Charts' (Sangster et al., 1958) are the primary source of information on pressure changes, with the paper
by Hare (1983) being useful. However, there are many cases that are not covered by these and other
references. The Queensland Urban Drainage Manual (Queensland Department of Natural Resources
and Water, 2008) provides a good coverage of available information on this topic, together with a rather
complex procedure for selecting pressure change coefficients using selected Missouri and Hare Charts.
There are theoretical relationships for pressure changes based on conservation of momentum
calculations (Hare and O’Loughlin, 1991), but these do not cover all cases. 1.5 is given as a default value
for ku in the DRAINS’ Drainage Pit property sheet.
A review of pit pressure changes and head losses (O'Loughlin and Stack (2002) discussed possible
algorithms or methods that might be used to determine pressure changes. Two procedures, the Mills
equation and the QUDM Method described below have been implemented.
(b) Mills Equation
In the DRAINS Run menu, there is the option named Revise Pit Loss Coefficients. This alters the
coefficients using an adaptation of an approximate method devised by Mills (Mills and O’Loughlin, 198298). Basically, this is
⎛ Qm ⎞
⎛Q ⎞
⎟⎟ + 4. ⎜⎜ g ⎟⎟
⎝ Qo ⎠
⎝ Qo ⎠
ku = 0.5 + 2. ⎜⎜
…(Equation 5.24)
where Qm is the inflow from upstream pipes that are misaligned,
Qa is the aligned flow,
Qg is the grate inflow, and
Qo is the outflow, equal to Qm + Qa + Qg
DRAINS assumes that pipes at angles of 45o or more to the outlet pipe are misaligned. A value of 0.5 is
subtracted if the outlet pipe diameter is larger than that of any of the inlet pipes. For a drop pit, the
incoming flow from a pipe may be classed as grate flow if the inlet pipe’s invert is located above the pit
water level. Mill’s assessment of misalignment of incoming pipes cannot be judged automatically by
DRAINS User Manual
November 2014
This procedure is implemented by performing a Design run, and then choosing the option Revise Pit
Loss Coefficients in the Run menu. This changes the original coefficients, using the flows determined
in the previous design run, thus overcoming the difficulty of having to estimate ku factors roughly in
advance when exact flows are not known. The procedure can also be implemented after an Analysis run.
This may lead to somewhat different coefficients because the relative values of Qm, Qo and Qg may be
different. The process can be repeated to refine the result. It must be noted that this procedure is
approximate and may give poor estimates for some situations. The estimated coefficients need to be
checked and corrected where necessary.
(c) The QUDM Method
As noted above, the Queensland Urban Drainage Manual (Queensland Department of Natural
Resources and Water, 2008) contains a procedure that guides a designer through a set of Missouri and
Hare Charts, enabling ku, and if appropriate water level factor kw and branch pipe factor kl to be
determined. This procedure has been outlined in Section 3.4.4, with the related spreadsheet outputs for
rational method calculations being set out in Section 3.5.4. It involves a search through several graphs
based on criteria set out in Appendix 4 in QUDM Volume 2. In complex cases where there is no
appropriate chart, an estimate from the momentum equations described by Hare and O’Loughlin (1991) is
The procedure in DRAINS allows ku coefficients to be determined automatically, without consideration of
all circumstances. It is therefore important to carry out checks using the appropriate charts.
(d) Part-Full Pipe Pressure Changes
Information on part-full pit pressure changes is sketchy, because researchers have concentrated on the
full-pipe flow case that is more likely to occur at peak flows through pipe systems. The treatment of partfull pressure changes has varied in DRAINS, as additional information has become available, and the
needs of the hydraulic modelling procedures have changed.
Currently, in the standard and premium unsteady flow models, a constant pit pressure change coefficient
ku is assumed to apply to both full-pipe and part-full flows. This is assumed in the interests of stability of
calculations, and is likely to conservatively overestimate changes.
Tailwater Levels
DRAINS calculations require a downstream boundary condition, with the levels of the receiving water
being specified in advance. This can be a level specified by the user in the Outlet Node property sheet,
or one assumed from conditions at the outlet. For steep pipe slopes (supercritical flow), it will be
assumed to be the normal depth, and for mild pipe slopes (subcritical flow), it will be assumed to be the
critical depth in the standard and premium hydraulic models.
Setting an appropriate tailwater level can be difficult. The For a pipe system discharging to a free water
body such as a lake, large stream or the sea, the tailwater will be the water level occurring in this body at
the time that the storm passing through the drainage system occurs. Using DRAINS, you must determine
the most likely level coinciding with the storm for normal design or analysis, and high values such as high
tide levels in marine waters for modelling of extreme conditions. The DRAINS Utility Spreadsheet
includes a procedures for modelling a tailwater level that changes with time during a storm event.
Where the drainage system catchment is significantly smaller than the catchment of the larger, receiving
water body, it is likely that the rainfalls over the two catchments will differ in intensity and timing. The
estimation of appropriate events to define critical conditions requires some statistical skill and knowledge
of local storms. Where the system being analysed is a pipe system discharging into a larger pipe or trunk
drain, the level to be selected should be the higher of the receiving pipe’s HGL or receiving open
channel’s water surface level at the junction. Hydraulic calculations may be necessary to establish these
levels, but valid results cannot be obtained unless appropriate tailwater levels are used.
Hydraulics of Open Channels
The basic hydraulic method, now obsolete, projected water surface upstream along open channels using
the standard step method (Chow, 1959, Henderson, 1966 and other texts) for subcritical flows, For
supercritical flows, the critical depth line is traced, and water depths are assumed not to fall below this,
providing a conservative estimate of depths.
DRAINS User Manual
November 2014
The unsteady flow procedures applied to open channels in the standard and premium model are the
same as those for pipes, outlined in Section 0, solving the mass and momentum flow equations.
Manning's equation is used to define channel friction. Suggested roughness values for channels are
given in Table 5.22. More comprehensive lists are given in texts and manuals on open channel flow and
in Chapter 4 of Australian Rainfall and Runoff, 1987.
Table 5.22 Manning's Roughness Coefficients, n
Surface Type
Suggested n Values
Concrete Pipes or Box Sections
Concrete (trowel finish)
0.012 - 0.015
Concrete (formed, without finishing)
0.013 - 0.018
Concrete (gunite)
0.016 - 0.020
0.014 - 0.016
Pitchers or Dressed Stone in Mortar
0.015 - 0.017
Random Stones in Mortar or Rubble Masonry
0.020 - 0.035
Rock Lining or Rip-Rap
0.025 - 0.030
Earth (clear)
0.018 - 0.025
Earth (with weeds or gravel)
0.025 - 0.035
Rock Cut
0.035 - 0.040
Short Grass
0.030 - 0.035
Long Grass
0.035 - 0.050
Various energy losses can occur at changes or transitions in channel sections. These are covered by
contraction and expansion losses, typically 0.1 and 0.3, respectively. These factors allow for energy
losses due to changes in cross-sections and velocities through these. If the velocity increases or
decreases between two cross-sections, the HGL is lowered by a coefficient multiplied by the difference in
velocity heads at the two sections. For example, if the upper and lower sections are labelled 1 and 2, the
losses for the two cases will be:
⎛ V22 V12 ⎞
⎝ 2g 2g ⎠
… (Equation 5.25)
⎛ V12 V22 ⎞
⎝ 2g 2g ⎠
… (Equation 5.26)
Contraction coefficient . ⎜⎜
Expansion coefficient . ⎜⎜
Table 5.23, taken from the HEC.RAS Version 3.1 Hydraulic Reference Manual (2002), Chapter 3, gives
values of coefficients.
Table 5.23 Contraction and Expansion Coefficients for Open Channel Flows
No transition Loss
Gradual Transitions
Typical Bridge Sections
Abrupt Transitions
Contraction Coefficient
Expansion Coefficient
Detention Basin Hydraulics
DRAINS performs accurate reservoir routing calculations for detention storages, employing the heightstorage-outflow relationship and initial storage supplied by the user. The method used is an extension of
the Modified Puls Method, based on the continuity equation applied over a time step, Δt,
Ii + Ii +1
Average of Inflow rates
at the start of a period, Ii
and at the end, Ii+1
DRAINS User Manual
Qi + Qi +1
Average outflow
rate over the
Si +1 − Si
... (Equation 5.27)
Rate of change
of storage
November 2014
together with a relationship linking outflow rates with corresponding storages for various water levels in a
reservoir or basin.
Reservoir routing procedures work on a finite-difference step-by-step procedure, working through the time
periods from the start of a known inflow hydrograph. Conditions at the beginning of each time step are
known, and relationships are used to derive conditions at the end. There are many ways of setting up
these calculations, both direct and iterative, but the following way, used in ILSAX, is probably the
Equation 6.32 can be rearranged so that the known terms are placed on the left hand side (LHS):
Ii + Ii+1
Qi +
Qi+1 +
2 Si + 1
… (Equation 5.28)
Inflow values Ii, Ii+1, etc. are known in advance, and outflow Qi and storage Si at the beginning of each
period are known. Routing procedures estimate values for Qi+1 and Si+1 by various methods of graphical
or numerical interpolation.
DRAINS applies this procedure at each time step, but also allows for tailwater effects that might alter the
elevation-discharge (or height-outflow) relationship.
A height-storage-outflow relationship can be developed from:
(a) a height-storage relation, derived from contour information on the topography of the storage area,
(b) a height-outflow relation, constructed from the hydraulic relationships for the outlet structures for the
reservoir, which can be orifices, pipe systems, weirs, or combinations of these.
DRAINS allows for separate height-outflow relationships for low- and high-level outlets of the type shown
in Figure 5.30. Routing is performed with a combined relationship, but outflows via high-level outlets,
such as diversion weirs, can be directed out of the system or to reaches other than the one immediately
Figure 5.30 Detention Basin Outlets
DRAINS User Manual
November 2014
Overflows from Basins
Low-level outlets from basins consist of culvert or drop pit pipe systems. The outflow rate for these is
dependent on the headwater and tailwater levels, and energy losses through the pipe system. Heightoutflow (or depth-discharge) relationships for various kinds of outlets are given in textbooks and manuals
on hydraulics. The equations shown in the box below are used for calculating height-outflow relationships
in DRAINS for detention basins, culverts and headwalls.
Equations for Determining Height-Outflow Relations used in the
Detention Basin, Culvert and Headwall Calculations
Outlets with Circular Cross-Sections
These depend on the threshold level, TH, which is usually the invert level at the upstream end of the
outlet pipe or culvert (m AHD), and pipe diameter D (m).
For (HW - TH) < 0.8 D, the flowrate for Inlet Control is:
Qi = Nc . 1.50 . (Sc/40)0.05 . (HW - TH)1.9 . D0.6
(inlet control, unsubmerged inlet, Henderson, 1966)
... (Equation 5.29)
For 0.8 D < (HW - TH) < 1.2 D,
Qi = Nc . 1.38 . (Sc/40)0.05 . (HW - TH)1.5 . D
… (Equation 5.30)
(inlet control, unsubmerged inlet, Henderson, 1966), and
For (HW - TH) > 1.2 D,
Qi = Nc . 1.62 . (HW - TH)0.63 . D1.87
(inlet control, submerged inlet, Boyd, 1986)
… (Equation 5.31)
The flowrate for Outlet Control is:
Qo = Nc .
π 2
.D . ((HW - TW) . 2g / (ke + kb + Factor + 1))0.5
…(Equation 5.32)
(outlet control, full pipe flow)
The outflow rate, Q (m3/s), corresponding to level in the basin or headwater level, HW (m AHD), is the
lesser of the calculated Qi and Qo values. Parameters used in the four equations are:
Nc is the number of parallel conduits,
Lc and Sc are the conduit length (m) and slope (%),
g is acceleration due to gravity, taken as 9.80 m/s2,
TW is the higher of :
(a) the tailwater level downstream of the outlet (m AHD), and
(b) a level half way between the outlet obvert level, equal to (TH - Sc . Lc + D)
and the level of the critical depth of the flow at the pipe outlet, calculated from:
⎟ 0.287 for c >= 0.82
⎝ 4.038 ⋅ D ⎠
… (Equation 5.33)
⎟ 0.510 for c < 0.82.
… (Equation 5.34)
dc = D . ⎜
dc = D . ⎜
Since Q is not known exactly when the tailwater level is being established, an
iterative procedure must be used In the above equations.
ke is the entrance loss factor,
kb is the total of other loss factors, e.g. at bends, and
Factor is a friction factor. If Manning's Equation is used with a roughness n, it is
⎛ D ⎞ /3
n2 . Lc . 2g . ⎜
DRAINS User Manual
… (Equation 5.4)
November 2014
If the Colebrook-White Equation is used, the Factor is f.
Lc , where f is the Darcy-Weisbach friction
factor. This can be obtained using an initial value given by the Swamee-Jain equation:
f = 1.325 / (loge(k/(3700 . D) + 5.74 / NR0.9))2
… (Equation 5.35)
and iterations using the Colebrook-White Equation:
f = 1.325 / (loge(k/(3700 . D) + 2.51 / (NR.f0.5 ))) 2
… (Equation 5.5)
in which,
k is the Colebrook-White wall roughness height (mm),
NR is the Reynolds Number of the flow (This is unknown when calculations
are performed, but it can be estimated roughly as:
V ⋅D
Qi D
π 2 υ
… (Equation 5.37)
V is the velocity of flow (m/s), and υ is the kinematic viscosity of water (1.14 x 10-6 m2/s at 15oC). Note
that the flowrate is assumed to be to be the inlet flow estimate and the pipe is assumed to be flowing full.
This is not exact, and an iterative procedure should be used. However, the value of f is insensitive to the
NR used, and this approximation should be adequate.)
Outlets with Rectangular Cross-Sections
These are based on the threshold level TH (m AHD), usually the invert at the upstream end of the culvert,
and the height of the culvert, H (m).
If (HW - TH) < 1.35 H, the flowrate for Inlet Control is:
Qi = Nc . 1.70 . (HW- TH )1.50 . B
(inlet control, submerged inlet, Boyd, 1986)
… (Equation 5.38)
If (HW - TH) ≥ 1.35 Height of Culvert:
Qi = Nc . 2.20. (HW- TH)0.61 . H0.89 . B
(inlet control, submerged inlet, Boyd, 1986)
… (Equation 5.39)
The flowrate for Outlet Control is:
Qo = Nc . H . B . ((HW - TW) . 2g / (ke + kb + Factor + 1))0.5
(outlet control, full pipe flow)
… (Equation 5.40)
As for circular pipes, the outflow rate, Q (m3/s), corresponding to level, HW, is the lesser of the calculated
Qi and Qo values. B is its breadth or width of the conduit (m), and the other factors are as described
In the calculations concerning tailwater, the critical depth is determined as:
⎛ Q2 ⎞ 0.333
dc = ⎜⎜
⎝ g⋅B ⎠
… (Equation 5.41)
In the equations for finding the friction factor, diameter D is taken to be 4 times the hydraulic radius (m),
equal to:
Area / Wetted Perimeter =
2(H + B)
… (Equation 5.42)
In most cases, inlet control will govern, with the greatest restriction on flow capacity occurring at the
culvert entrance. However, in some cases outlet control will apply, with the cause being high tailwater
levels, or friction in relatively long and flat culverts.
DRAINS User Manual
November 2014
High-level outlets such as weirs and slots are usually governed by the weir equation:
Q = C . w . hw1.5
.... (Equation 5.6)
Q is the outflow rate (m3/s),
C is a weir coefficient, depending on the weir shape, roughness
and length of the weir crest in the direction of flow,
w is the width of the weir (m), at right angles to the flow direction, and
hw is the depth of water in the basin above the weir sill or crest.
Laurenson and Mein (1990) provide the weir coefficients shown in Figure 5.31. Further information can
be obtained in the US Federal Highway Administration HDS-5 manual (Normann et al., 2005).
Figure 5.31 Weir Coefficients
On-Site Stormwater Detention
DRAINS is set up to model on-site stormwater detention (OSD) storages of the type shown in Figure
5.32, including high-early discharge (HED) systems, as shown in Figure 5.33. These can provide a
considerable reduction of the storage needed to limit outflows to a prescribed limit.
Speed Hump
Storage on Driveway
(acts as a weir)
Above-Ground Storage
Underground Tank
Figure 5.32 On-Site Detention (OSD) Storages
DRAINS User Manual
November 2014
Main Storage
HED Pit Components
State 1: The HED Pit Fills
State 2: The Larger Storage Fills
State 3: Both Storages are Full, and Act Together.
State 4: The Storages Empty
Figure 5.33 A High Early Discharge (HED) Pit
OSD storages are usually controlled by circular orifices with the discharge equation being:
Q = Cc .
π 2
d . (2gh)0.5
… (Equation 5.7)
where Cc is a contraction coefficient, taken as a constant of 0.6 in DRAINS,
d is the orifice diameter (m),
g is the acceleration due to gravity (m/s2), and
h is the height from the water surface to the centre of the orifice (m).
The second panel on the detention basin property sheet (Figure 2.37) displays data that can be used to
model stormwater infiltration out of a storage that has a permeable base and/or permeable sides. The
calculations involved are simple; the exposed surface of the storage at any time is multiplied by the
hydraulic conductivity to define an outflow. The greater the depth in the storage, the larger the infiltration
rate. Allowance is made for storages having permeable or impermeable floors and walls.
Infiltration procedures are discussed in detail in Argue, J.R. (editor) (2004) WSUD: Basic Procedures for
'Source Control' of Stormwater, University of South Australia Water Resources Centre,
Adelaide. Indicative values of hydraulic conductivity (p. 44) are given in Table 5.24. Specific values for a
site can be obtained from on-site tests and modified using factors provided in the above publication.
Table 5.24 Hydraulic Conductivities for Infiltration Calculations
Soil Type
Hydraulic Conductivity
Sandy soil
> 5 x 10-5 m/s
Sandy clay
between 1 x 10-5 and 5 x 10-5 m/s
Medium clay and some rock
between 1 x 10-6 and 1 x 10-5 m/s
Heavy clay
between 1 x 10-8 and 1 x 10-6 m/s
Constructed clay
< 1 x 10-8 m/s
DRAINS User Manual
November 2014
Culvert and Bridge Hydraulics
There are two meanings to the word, culvert. The first is a long pipe; the second is a pipe, usually short,
constructed to allow flows in streams and artificial open channels to pass under road and railway
embankments. The culvert component in DRAINS models the latter case. The first type of conduit
should be modelled as a channel, or if storage and overflows are important, as a detention basin.
Culverts convey flows in pipes or rectangular conduits that through road embankments, usually
obstructing flows by reducing the available waterway areas. Upstream water levels are raised, creating a
headwater level higher than the water levels occurring under unobstructed flows. Downstream levels are
lower, since flow emerges rapidly from the culvert, creating supercritical flow conditions until a hydraulic
jump occurs. Several procedures are available for the design of culverts and analysis of their behaviour.
In DRAINS the sets of equations presented by Henderson (1966) and Boyd (1986) given in Section 5.7
are used to determine the headwater levels occurring with a given flowrate and downstream tailwater
level at each calculation time step. These equations allow for inlet control, where the constriction at the
opening of the culvert is the determining factor, and for outlet control, where a high tailwater level and
significant head losses make the conduit flow full.
In DRAINS, the flowrate and the downstream water level at each time step are established, and the
corresponding headwater level is determined using the above equations. When either of two equations
can be used because there are two possible states of flow, the equation giving the highest headwater
level is selected.
A considerable amount of information on road culverts is available from the US Federal Highway
Administration in manuals and software available at www.fhwa.dot.gov/bridge/hyd.htm. Mays (2001) also
provides considerable information on culverts.
Bridge hydraulics is particularly complicated because it is necessary to allow for the transitions from a
broad channel cross-section to a constricted bridge cross-section and back to a channel section. The
bridge abutments, piers and possibly the deck can all obstruct flows. Hydraulic expertise is required to
interpret results.
The U.S. Federal Highway Administration has published methods by Bradley (1970) which have been
used in the AUSTROADS waterway manual (1994). More extensive procedures are incorporated in the
HEC-RAS computer program (Hydrologic Engineering Center, 1997). You are referred to these
references for further details. DRAINS covers relatively simple bridge layouts. Use of HEC-RAS is
recommended for complex arrangements involving multiple openings and broad channel cross-sections.
DRAINS uses the AUSTROADS procedures to define the afflux or rise in upstream water level caused by
a bridge constriction. It does this at each calculation time step, for the current flowrate and downstream
water level. As with culverts, allowance is made for possible overtopping and submergence of the bridge
deck, treating this as a weir. Any overflows are added to the flows through the bridge opening occurring
at the same time.
5.10 File Formats
5.10.1 General
This section provides some notes on file formats, as a guide to persons exchanging data between
DRAINS and other programs.
5.10.2 Drawing File Formats
DRAINS can import and export graphical data in DXF format. As shown in Figure 5.34, this is an ASCII
format, which can be edited on a text editor.
DRAINS User Manual
November 2014
5.10.3 GIS File Formats
(a) GIS Systems
Geographic Information System (GIS) programs combine a mapping facility with a data base of
information on the spatial position of components, such as drainage pits and pipes, and on their other
attributes, such as pipe diameters. Objects displayed in different ways, according to one or more of their
attributes. Maps can be produced on paper or can be inspected electronically.
The most common products used in Australia are ArcView (produced by ESRI (www.esri.com) and
MapInfo (produced by MapInfo Corporation (www.mapinfo.com), but Autodesk Map (www.autodesk.com)
and Intergraph (www.intergraph.com). There are also a number of companies that provide systems
based on the main types of software. GIS file structures can be complex. In MapInfo, two file types, with
suffixes MID and MIF, are required, so that 12 files are generated in a transfer from DRAINS.
Figure 5.34 ASCII File in an Editor
(b) ESRI (ArcView) Formats
ArcView stores spatial information in various formats. The data imported or exported by DRAINS are in a
set of three binary files, all having the same initial part of their name:
a SHP file, the main file defining a number of records for shapes (points, lines, poly-lines or
polygons), defined by the coordinates of their vertices,
a SHX file acting as an index to the records in the main file,
a DBF file containing a DBASE table of attributes associated with each record.
To specify an object such as a pipe fully, a set of these three files is established. The transfers to and
from DRAINS involve files for up to six objects - pits, sub-catchments, pipes, overflow routes, survey data
on ground levels along pipe routes and positions of other services, a total of 18 files, plus a DXF file
containing the background to the drainage system, which can be transferred at the same time.
For nodes, a table with the following 13 headers for columns or 'fields' are required:
DRAINS User Manual
November 2014
the nature of the object (point)
any name up to 10 characters
an internal number used by DRAINS to connect nodes and link this
must be kept blank
type of node: 'OnGrade', 'Sag' or 'Node'
the pit family, corresponding to a family in the pit data base in the
DRAINS model to which the data is being transferred, or 'N/A'
a pit size within the nominated pit family, or 'N/A'
the volume of water that can pond over a sag pit (m3)
the pit pressure change coefficient (Use 'N/A' for simple nodes)
the surface elevation at the node (m)
a Colebrook-White or Manning's roughness coefficient
any constant baseflow (m3/s) originating at the node
a blocking factor to be applied at pits ('N/A' is used for nodes),
a 'Yes', 'No' or 'N/A' as to whether there is a bolt down lid
In a shapefile exported from DRAINS, there may also be:
- optionally, one or more HGL levels taken from a series of runs for.
Different storms. 'XXXXX' takes different values.
For pipes, a table with the following 12 headers for columns or 'fields' are required:
the nature of the object (line or poly-line),
any name up to 10 characters
an internal number used by DRAINS to connect nodes and links - this
must be kept blank
the pipe length (m),
the invert level at the upstream end of the pipe (m),
the downstream invert level (m),
the pipe slope (%),
the pipe type, which must correspond to a type in the pipe database of
the DRAINS model to which the data is being transferred
the nominal pipe diameter (mm) corresponding to diameters in the pipe
type nominated
a Colebrook-White or Manning's roughness coefficient
'New' or 'NewFixed’ or ‘Existing’
the number of parallel pipes, usually 1
In a shapefile exported from DRAINS, there may also be:
Flow_XXXXX - optionally, one or more flowrates from different storms, designated by XXXXX,
- optionally, one or more velocities from different storms, for example'50Yr'.
For information on the other four components, you can refer to the formats of exported ESRI files in the
MIF files. Note that all numbers are exported as text and not as numbers. They will need to be converted
in an ESRI program if the attributes are to be used as the basis for colour-coded thematic mapping.
(c) MapInfo Formats
MapInfo stores spatial information in a set of two ASCII files, both having the same initial part of their
a MIF (MapInfo Interchange File) is the main file defining a format for data records associated with
objects (points, lines or polygons) and the coordinates of the vertices of objects,
a MID file containing the contents of a table of attributes associated with each object.
The data for nodes (pits) in the MID file is in a table with the following 12 headers:
DRAINS User Manual
November 2014
any name up to 11 characters
an internal number used by DRAINS to connect nodes and links - this
must be kept blank
type of node: 'OnGrade', 'Sag' or 'Node'
the pit family, corresponding to a family in the pit data base in the
DRAINS model to which the data is being transferred, or 'N/A',
a pit size within the nominated pit family, or 'N/A',
the volume of water that can pond over a sag pit (m3)
the pit pressure change coefficient (Use 'N/A' for simple nodes),
the surface elevation at the node (m),
a Colebrook-White or Manning's roughness coefficient
any constant baseflow (m3/s) originating at the node
a blocking factor to be applied at pits ('N/A' is used for nodes)
a 'Yes', 'No' or 'N/A' as to whether there is a bolt down lid
In a MID file exported from DRAINS, there may also be:
- optionally, one or more HGL levels taken from a series of runs for.
Different storms. 'XXXXX' takes different values, for example, '5 Yr'.
For pipes, the table includes the following 11 or more headers:
any name up to 11 characters
an internal number used by DRAINS to connect nodes and links - this must
be kept blank
the pipe length (m),
the invert level at the upstream end of the pipe (m),
the downstream invert level (m),
the pipe slope (%),
the pipe type, which must correspond to a type in the pipe database of the
DRAINS model to which the data is being transferred
the nominal pipe diameter (mm) corresponding to diameters in the pipe type
a Colebrook-White or Manning's roughness coefficient
'New' or 'NewFixed’ or ‘Existing’
the number of parallel pipes, usually 1
In a MID file exported from DRAINS, there may also be:
- optionally, one or more flowrates from different storms, designated by XXXXX,
- optionally, one or more velocities from different storms.
For information on the other four components, you can refer to the formats of exported MapInfo files,
reading the MIF file with a text editor.
Note that all numbers are exported as text and not as numbers. They will need to be converted in
MapInfo if attributes are to be used as the basis for colour-coded plotting.
5.10.4 Spreadsheet File Formats
DRAINS transfers data to spreadsheet programs in the space-delimited ASCII format shown in Figure
5.35. This appears in cells when opened in a spreadsheet program, as shown in Figure 1.33.
DRAINS User Manual
November 2014
Figure 5.35 DRAINS Spreadsheet Output displayed in an Editor
5.10.5 TUFLOW TS1 File Formats
Using the File → Export → Tuflow TS1 Files… option described in Section 3.5.6, DRAINS can transfer
calculated hydrographs to TUFLOW and other programs in the format shown in Figure 5.36, which can
readily be imported into spreadsheet programs.
Figure 5.36 TUFLOW TS1 Output Displayed in an Editor
DRAINS User Manual
November 2014
A.1 Introduction
Written in a simpler style than the main manual, this appendix describes how to use of the DRAINS
Viewer, which allows a checker to examine any DRAINS model submitted to them. It has been prepared
for persons checking or reviewing DRAINS models, either internally within a design organisation, or as a
council officer or private assessor. It also provides guidance to designers on choices to be made when
setting up models and on information to be submitted for review.
Use of the free Viewer relieves reviewers of the need to check manually for numerical errors in tables or
spreadsheets submitted for approval. A DRAINS model can be submitted to the reviewer as a .drn file
with included results. The reviewer can then inspect the model using the Viewer and concentrate on the
suitability of the selected inputs and the resulting flows and flood levels, knowing that results have been
reliably calculated by DRAINS.
A.2 Setting Up and Running the Viewer
The free installation file named DrainsViewerSetup.execan be obtained from Bob Stack on (02)
6649 8005 or [email protected] To install the Viewer on any PC running Microsoft Windows,
run the file exe and follow the instructions that appear.
Once installed, the DRAINS Viewer can then be opened from the Start menu by selecting Programs and
then DrainsViewer. The Main Window will then open, and after you have closed the introductory
message, will appear as shown in Figure A.1. If needed, Help can be called from the Help menu, or by
pressing the F1 button. Options in the View menu can be used to alter the look of the model.
Space for displaying
drainage system
Figure A.1 Main Window of the DRAINS Viewer
If you are familiar with DRAINS you will find that the Viewer operates in the same way except that the
model cannot be altered or run.
Initially the Viewer will display a blank space. As in DRAINS, the operations of the Viewer are controlled
from menus. Drainage systems are constructed from a set of named components (pits, sub-catchments,
pipes, overflow routes, channels, etc. that are joined together as shown in Figure A.2. The information for
each component is set out in a property sheet that can be opened by right clicking on the component and
selecting Edit Data from the pop-up menu.
DRAINS User Manual
November 2014
Sheet for
and Names
Figure A.2 Gymea Pipe Drainage Example, before a DRAINS Run
Running DRAINS requires suitable data bases for hydrology, rainfall data, pipes, pits and overflow routes
that can be viewed using options in the Project menu. After a run, the component names change to
colour-coded values of peak flowrates and the levels of hydraulic grade lines (HGLs) at pits and nodes,
as shown in Figure A.3. Models can be saved with data and results intact, as a DRAINS .drn file.
Pipe LongSection
Figure A.3 Results from a Design Run and Standard Hydraulic Analysis of the Gymea Example
To understand this more completely, you can view one of the demonstration examples that are installed
with DRAINS in C:\Program Files\Drains\StandardExamples. This file, named Gymea ILSAX
Example - Standard.drn, can be opened using the Open… option in the DRAINS File menu. (Note
that if a blank screen appears when a model is loaded, the model can be located using the Index Sheet
option in the View menu.)
The Gymea system, located in suburban Sydney, includes a background showing street and property
boundaries imported from a CAD file. Components can be inspected by opening the property sheets for
the components, as shown in Figure A.2. If Property Balloons is switched on in the View menu
properties of components can also be seen in balloons that appear as the mouse pointer runs over them.
DRAINS User Manual
November 2014
Data can also be inspected by exporting tables to a spreadsheet via the Windows clipboard, using
options in the Edit menu. Part of a table is shown in Figure A.4. The facility of viewing long sections of
pipelines and transferring them to CAD programs is not available in the Viewer.
Pit and
Node Data
Sub-Catchment Data
Pipe Data
Figure A.4 Spreadsheet Output of Data for the Gymea Model
Usually, similar names are given to a pit, the sub-catchment draining to it, and the pipe and overflow route
carrying water away from it. Overflow routes are an essential part of the model, being used to check that
surface flow widths, depths and velocities are not excessive. Even where overflows are required to be
zero, a route should be included to demonstrate that this is so.
You will not be able to run this model with the Viewer, but you can open another Gymea model named
Gymea Piped Drainage Model with Results.drn from the demonstration examples. This
displays the run results shown in Figure A.3. More detailed explanations are provided in the main body of
this DRAINS User Manual and in the Help system.
A.3 Information Required for Checking
This section spells out, in checklists, the basic information required to assess DRAINS models for various
purposes. The pertinent information is:
• The physical nature of the system, shown in design plans or system diagrams.
• The assumptions made in the design or analysis – these should be reasonable and conform to council
requirements, or else be supported by references to manuals or other documents when they differ
from council guidelines.
• The extent to which the design meets stated design requirements – systems should convey or store
runoff so that flooding of properties and hazards to persons are avoided, at appropriate levels
specified by average recurrence intervals (ARIs).
Where a submission accompanies a development application to a municipal council, the design needs to
comply with council guidelines that are specified in a number of forms (codes, manuals, development
control plans) and are usually available on council or drainage authority websites. It may be reasonable
to submit a design that does not meet some requirements, provided that is accompanied by evidence that
the submitted design meets the overall purpose.
Property Drainage Systems
For stormwater drainage systems on private properties, DRAINS can be used to design gravity and
pumped pipework and simulate the behaviour of detention and retention storages. Table A.1 notes the
DRAINS User Manual
November 2014
required and optional information that is normally needed by reviewers. The optional items may be
required for assessment if (a) systems are complex, (b) consequences of failure are significant, or (c)
precise, documented design is needed.
Table A.1 Typical Requirements for Assessing Property Drainage Systems
Required Items
Plan view of stormwater drainage system,
showing locations of downpipes, above- and
below-ground pipelines, storages and other
A concept plan, drawn to scale but not in
detail, should be sufficient for most purposes
Plan and section views of on-site detention
tanks and surface storages, showing positions
and levels of inflow and outflow pipes and
discharge control pits
The storage volume provided and sizes of
outlet controls such as orifice plates should be
Results of on-site detention calculations,
including rainwater tanks where these are
integrated with OSD storages and allowance
for stormwater infiltration where this is
The amount of information required depends
on the requirement of the council or approving
authority. If the method used requires storage
routing, DRAINS outputs provide the
necessary results.
Optional Items
Pipe long-sections, Table of quantities
Outputs from DRAINS may be provided.
Roof gutter and downpipe calculations
Generally only required where consequences
of failure are significant.
Pipe design calculations.
Tables of results from DRAINS may be
Roof gutters and downpipes are sized to prevent water for storms of a specified ARI overflowing the
edges of gutters. The commonly-used design chart from AS/NZS2500.3 is based on hydraulic theory and
testing, but methods also incorporate factors of safety such as freeboards (differences between peak
water levels and edges of gutters).
ARIs of 20 years are commonly used for eaves gutters on the perimeters of buildings, and 100 years for
'box gutters' that span buildings. Pipe systems should be sized according to the consequences of failure
in case of overflows, although some councils specify required ARIs. The usual range is from 5 to 20 year
ARI. The ARIs for surface drainage can be smaller than those used for roof design, depending on the
relative consequences of failure.
Pipe design methods for property and inter-allotment pipe systems are generally simpler than for street
drainage networks, partly because the specification of minimum pipe sizes to prevent blockages leads to
overdesign of smaller systems. Typically, requirements are less strict for small developments, or for
single dwelling developments compared to multi-unit residential, commercial and industrial developments.
In some cases, reviewers may only require a statement or certification that a certain requirement has
been met, for example that a roof drainage system has been designed according to AS/NZS2500.3.
OSD is a particularly complex issue, and many methods can be applied, some involving reservoir routing,
others employing simple calculations based on factors such as permissible site discharges and site
storage requirements specified by the council or drainage authority.
Specified ARIs for on-site detention (OSD) systems vary from council to council, and designers must
address stated local regulations. The current trend appears to be to analyse OSD systems for two levels:
a low ARI such as 2 years and a high 100 year ARI. The low ARI requirement is likely to have the
greatest influence on the storage required. Another trend is to specify double outlets, in series or parallel,
which are difficult to analyse. DRAINS can accomplish this and allow for high early discharge pits.
Stormwater detention systems are discussed further in Section A.5.
Inter-Allotment Drainage Systems
Also known as easement drainage systems, these are pipe and flow path draining through lower
properties to a street. As well as (a) a pipe, they involve (b) an overland flow path to carry flows
exceeding the pipe capacity, and (c) legal documentation defining the easement, rights of access and
prohibitions against obstructions. The usual requirements are:
DRAINS User Manual
November 2014
Table A.2 Typical Requirements for Assessing Inter-Allotment Drainage Systems
Required Items
Plan view of piped drainage system, showing
locations of pipes and pits, and extents of flow
Optionally, the sub-catchments leading to
each pit should be displayed with their areas,
and possibly land-uses.
Cross-section of flow path, and sections of any
special features such as flow-through fencing
Optional Items
Pipe long-sections
Long-sections exported from DRAINS can be
Drainage calculations
These can be the relatively simple calculations
employed with property drains. DRAINS
provides these
Table of quantities
Table from DRAINS may be presented.
Pipe design ARIs are usually in the range 5 to 20 years, with overflow paths needing to be assessed for
100 year ARI flows.
Street Drainage Systems
Piped drainage systems are required for subdivisions and occasionally for property developments that
need to connect to council drainage systems along streets. They may also be required for infrastructure
developments such as motorways, airports and port works. The usual documentation required for
checking is described in Table A.3. Much of this will be included in subdivision plans, along with drawings
of roadworks and other infrastructure.
Table A.3
Typical Requirements for Assessing Street Drainage Systems
Required Items
Plan view of piped stormwater drainage
system, showing locations of pipes, pits and
other features
On this, or a separate plan, the subcatchments leading to each pit should be
displayed with their areas, and possibly landuses.
Pipe long-sections
Long-sections exported from DRAINS can be
Plans and sections of any special pits,
junctions or chambers
Drainage calculations
These are usually set out in tables, following
examples in Australian Rainfall and Runoff,
1987 and other manuals. DRAINS provides
comprehensive tabular results. DRAINS also
produces a plan drawing of the design model.
Optional Items
Table of quantities, Pit schedule
A table from DRAINS may be presented.
Street drainage systems are commonly designed with the major/minor system, for minor ARIs
from 5 to 20 year ARI, with 2 year ARI applied in some tropical areas where rainfalls are very
high. Most design methods also include a check for fail-safe behaviour in major rainfalls, usually
at 100 year ARI. Most calculation software is based on the rational method procedures in
Australian Rainfall and Runoff 1987 (ARR87) which was developed before use of spreadsheets
became common and most calculations were made by hand. The formats of calculations sheets
associated with later manuals, such as the Queensland Urban Drainage Manual (QUDM), have
followed this model.
DRAINS relies on computer computations that go significantly beyond earlier hand calculations, and its
tabular outputs do not reproduce simple calculations such as the multiplication of numbers set out in
columns. While DRAINS data and results are set out in formats similar to the ARR87 calculations, their
purpose is to display significant results from the computer calculations, rather than to implement or show
any specific calculations.
DRAINS User Manual
November 2014
Design procedures consider surface flows as well as the flows through the pipe system, with the main
objectives being:
• preventing flows in street gutters or channels from being too wide (2 to 2.5 m) or deep (kerb height);
• keeping (velocity x depth) products below a limit (typically 0.4 m2/s) for pedestrian and vehicle safety;
• ensuring that flow levels do not come within a freeboard limit of habitable floor levels in adjoining
buildings (generally 0.30 to 0.50 m); and
• within pits, allowing an appropriate freeboard between the pit water level and the surface (generally
0.15 m) to ensure that flows can easily enter pits.
The ways that these can be inspected in DRAINS are described in Section 5. Names of pits and pipes
should follow a systematic pattern, with each component having a unique name. The names used in
DRAINS and those displayed on drawings should be consistent.
Trunk Drainage Systems
Runoff from individual pipe systems is collected in open channels located in dedicated flow path or
stream corridors. Designs are developed by setting up possible systems in a computer model such as
HEC-RAS or DRAINS, and then running the model to obtain a satisfactory profile at a design average
recurrence interval (ARI) such as 100 years. The arrangement and sizes of channel segments needs to
be refined by trial and error to achieve the best result. The required checking documents are set out in
Table A.4.
Table A.4 Typical Requirements for Assessing Trunk Drainage Systems
Required Items
Plan view of trunk drainage system, showing
locations of channels, entry points of pipes
along the channel and features such as drops
and culverts.
Survey set-out information is often included.
Channel long-section profiles and crosssections.
100 year ARI water surface profiles might be
Plans and sections of special features, such
as bends, junctions and culverts
Design report
Detailed calculations are not provided
because computer models are used, but
results in the report show water surface
profiles and indicators such as velocities and
Optional Items
Table of quantities
General practice for subdivision design is to prepare an initial trunk drainage master plan defining the
sizes of channels and detention facilities that need to be provided and the land area required to
accommodate these. As detailed design proceeds, these estimates are modified. Design ARIs are 100
year ARI, with probable maximum precipitation (PMP) estimates required where the potential
consequences of failure are severe.
Localised Flood Studies
Where developments or re-developments are located along flow paths, or in areas that may be flooded
due to water ponding downstream obstructions such as road embankments or existing buildings, a flood
study may be required, even for small projects. Councils determine whether such studies are required,
relying on reports of past flooding and area-wide modelling that reveals likely riverine and local overland
flooding situations.
The extent of the work required can vary considerably with the situation. Where stormwater runoff can
flow freely through or beside a development, it may be relatively simple to define a design flowrate and
flow path geometry, and to determine flow characteristics such as depths and velocities. However,
complex situations may require careful assessment of areas upstream and downstream of the
development site, and involve extensive hydraulic modelling.
DRAINS User Manual
November 2014
As shown in Table A.5, study report is usually required, setting out the pre- and post-development
situations, the methods applied and the results.
Table A.5 Typical Requirements for Assessing Localised Flood Studies
Required Items
Flood study report describing the effects of
flooding on the proposed development, and
measures taken, or needing to be taken, to
prevent damage.
The report must be consistent with
construction plans of the development
It will be necessary to demonstrate that the new development does not increase the flood hazard
affecting future occupants of the development, adjoining and downstream property owners and the public.
The results will usually focus upon 100 year ARI floods, but PMP may need to be considered in
developments where occupants are vulnerable, such as child care centres or nursing homes.
A.4 Assessing Models and Inputs
One of the first issues for the reviewer is to determine whether the model applied is adequate for the task.
Guidance can be obtained from Australian Rainfall and Runoff (1987) and other manuals, but these are
often out of date. Thirty years ago, calculations were generally performed by hand on calculations pads.
Now, computer models are now likely to be used in all but a few cases. These can perform such a
volume of computations that checking the arithmetic is impossible, so reviewers must consider matters
'external' to the actual calculation process, such as:
• the capabilities of a method or program,
• its suitability for modelling the situation to which it is to be applied, and
• the validity of the parameters used in the model.
DRAINS offers a choice of four types of hydrological model to generate flowrates, and two types of
hydraulic model, to calculate flow characteristics. These cover most of the tasks required in urban
stormwater practice.
Rainfall Inputs
(a) General
The main input to hydrological models is the design rainfall information provided by the Bureau of
Meteorology. This is based on older records, and is being renewed as part of the current revision of
Australian Rainfall and Runoff. For the present, the design rainfall information from ARR87 is the
definitive form of information for general design.
(b) Hydrograph Methods
DRAINS makes rainfall information available through procedures set out in its Project menu. The rainfall
data is the same for all the hydrological models in DRAINS (ILSAX, Extended Rational Method, RORB,
RAFTS and WBNM) except the rational method. For the Gymea model introduced in Section 2, which
uses the ILSAX model, the Rainfall Data option opens the window shown in Figure A.5. This displays a
design storm pattern or hyetograph taken from ARR87, which is included in a rainfall data base. Many
storms can be included in this base and selected as Minor and Major storms for design calculations.
The intensities used can be viewed and checked against intensity-frequency-duration
(I-F-D) charts included in council documents or obtained from the Commonwealth Bureau of Meteorology.
The rainfall patterns selected for a run can be reviewed by looking at the Select Major Storms and
Select Minor Storms options in the Project menu, as shown in Figure A.6.
In the Gymea example, only two storms are considered, but designers would normally use 4 to 8
patterns, with durations covering the range where the highest peak flows occur. (Generally, shorter storm
durations produce the highest flows in small catchments, but as catchment size increases, the critical
duration also increases. Thus, designers might use durations up to 1 or 2 hours for piped drainage
systems, and durations from 15 minutes to 3 hours for trunk drainage studies.)
DRAINS User Manual
November 2014
Figure A.5 Rainfall Data Sheet for Hydrograph-Producing Models
Figure A.6 Window for Selection of Design Storms
(c) Data for the Rational Method
The rational method procedure available in DRAINS does not employ rainfall patterns, but instead works
from I-F-D information based on the eight rainfall intensities shown in Figure A.7, which appear when the
Rainfall Data option in the Project menu is selected. (You can see this in the Gymea model by changing
the hydrological model to a rational method in the drop-down menu in the window that appears when
Hydrological Model is selected from the Project menu.)
(d) Other Rainfall Inputs
Most Australian projects will employ the ARR87 design rainfall data. For specialised studies, actual
recorded storms or other required patterns can be imported into DRAINS from spreadsheets, or simply
typed in. PMP data from the Bureau of Meteorology and special data for the Gold Coast City Council
area can be obtained from the DRAINS Utility Spreadsheet located on the CD accompanying this Guide.
If required, these spreadsheets can be submitted to reviewers.
A.4.3.1 General
All the designs or analyses described in the previous section require the estimation of design flows,
otherwise the use of hydraulic calculations is a case of 'garbage in – garbage out'. Designers rely on
methods set out in authoritative manuals such as Australian Rainfall and Runoff (1987) and the
DRAINS User Manual
November 2014
Queensland Urban Drainage Manual (1992, 2007), but these are far from perfect, due mainly to the
dearth of available data for calibrating and testing models.
Figure A.7 Rainfall Data Used with the Rational Method in DRAINS
The models that are commonly used in urban stormwater practice in Australia are shown in Table A.6.
These are only a few of the many models available, but they are the ones that are sanctioned by manuals
or have achieved wide use through promotion and recognition of their advantages. Although DRAINS
offers 'event' models that run with rational method and ILSAX hydrology, and emulate the RORB, RAFTS
and WBNM programs, it does not perform continuous modelling of the type carried out by MUSIC.
Table A.6 Urban Hydrological Models Commonly-Used in Australia
Implemented in:
Manual pipe design method in
ARR 1887 and software derived
from this, manual rural runoff
methods (e.g. QUDM); NSW
and Victorian probabilistic
rational methods (really regional
flood frequency procedures)
Loss Model
Routing Model
Both loss and routing effects are incorporated in
the selected runoff coefficient C and the time of
concentration; generation of hydrographs
requires additional assumptions about volumes
DRAINS (similar models are
applied in xpswmm)
Depression storages and
Horton infiltration for
pervious areas
Time-area method
Initial and continuing
Non-linear storage
Initial and continuing
Non-linear storage
routing (also
contains continuous
ARBM model)
Initial and continuing
Non-linear storage
Daily Rainfall
Relatively simple
continuous daily rainfall
model with disaggregation
for shorter time steps
routing between
The revision of Australian Rainfall and Runoff (see www.arr.org.au) is likely to change the preferred
hydrological models, with some of the methods in Table A.6 being superseded. DRAINS will adjust to
accommodate any new methods recommended by Australian Rainfall and Runoff.
The Extended Rational Method is not included in the above table because it is not yet widely used in
Australia. Now available in DRAINS, it provides the capability of a hydrograph-producing model using
rational method runoff coefficients to practitioners who prefer the rational method.
DRAINS User Manual
November 2014
In many situations, two or more of these models can be validly applied to a catchment, but they are likely
to provide different estimates of flowrates. A particular model can also give widely-varying results when
applied with different loss and routing parameters. In routine applications, such as the design of a
subdivision drainage system, guidance can be obtained from manuals, but for more difficult applications,
experience and judgement are needed to select an appropriate model and its parameters.
(b) The ILSAX Model
The ILSAX model will be considered first. To inspect the models in DRAINS, choose the Hydrological
Models option from the Project menu to open the window shown Figure A.8. The buttons on the right
allow models to be inspected, created or deleted, while the drop-down menu on the left allows alternative
models to be selected. The program will apply the selected model when the OK button is pressed. If the
Edit Default Model button is pressed, the window shown in Figure A.9 appears, displaying the model
characteristics. This comes from the model in file Gymea Piped Drain Model.drn, using the
hydrological model in the ILSAX program from which DRAINS was developed.
The parameters shown are (a) depression storages, which represent depths of water retained in puddles
over the whole sub-catchment area, and (b) the soil type, which relates to sets of numbers that control the
infiltration rate of water into the soil.
The depression storages apply to the three types of land-use used in ILSAX models:
paved, representing the impervious areas directly connected to a drainage system,
supplementary, representing impervious areas that are not directly-connected, where runoff must
flow over an infiltrating surface before reaching the drainage system, and
grassed areas, representing pervious surfaces of various kinds.
Typical values for depression storages are 1 mm for paved and supplementary impervious surfaces, and
5 mm for grassed surfaces. The higher these storages are, the lower the resulting runoff flowrates will
be. Values exceeding 2 mm for impervious surfaces and 10 mm for grassed surfaces should be justified.
Figure A.8 Hydrological Model Window Specifying an ILSAX Model
DRAINS User Manual
November 2014
Figure A.9 An ILSAX Model Property Sheet
The soil parameter relates to a system developed by the US Soil Conservation Service. Values from 1 to
4 are commonly selected, based on the following descriptions:
Table A.7 ILSAX Soil Types
Soil Type
1 (or A)
low runoff potential, high infiltration rates (consists of sand and gravel)
2 (or B)
moderate infiltration rates and moderately well-drained
3 (or C)
slow infiltration rates (may have layers that impede downward movement of water)
4 (or D)
high runoff potential, very slow infiltration rates (consists of clays with a permanent
high water table and a high swelling potential)
There is a third parameter affecting the infiltration into soils that appears in the rainfall data base. The
antecedent moisture condition (AMC) is a number with the same range as the soil type (1 to 4) that
indicates the wetness of the soil in the sub-catchment. This is specified for individual storm patterns in
the Rainfall Data sheet shown in Figure A.5.
The flowrates calculated by DRAINS are sensitive to the AMC selected. The lower the AMC, the higher
the infiltration loss into the soil will be, and the lower the runoff. The following table is used to set an AMC
based on the expected rainfall in the 5 days prior to a storm
Table A.8 Antecedent Moisture Conditions
Total rainfall in 5 days
preceding the storm (mm)
Completely dry
Rather dry
0 to 12.5
Rather wet
12.5 to 25
Over 25
In a design situation, the AMC should reflect the expected conditions prior to a representative future
rainfall event. This can be determined by examining records of previous rainfalls near the site. For
example, daily rainfalls can be ranked and the 5-day rainfalls prior to the largest rainfall events can be
identified. Examples for two locations are shown Figure A.10.
In Section A.4.4, the large variability of model results with AMC is demonstrated. Similar variations can
occur with different soil types. Reviewers need to be satisfied that the parameters selected reflect the soil
types and wetness occurring at the project site.
An issue that sometimes arises is the application of the ILSAX model to rural catchments. This is
uncertain because the ILSAX model has not been calibrated using rural data. The calibrations made to
urban data described in Chapter 5 of the DRAINS User Manual give confidence that the model will work
well where a catchment has a significant impervious portion, say 20% or more, and a man-made drainage
system. However, for largely-rural catchments with natural drainage systems, the results are uncertain.
DRAINS User Manual
November 2014
AMC Values
AMC Values
Toowoomba, Queensland (Mean AMC = 3.5)
Perth, WA (Mean AMC = 2.8)
Figure A.10 Histograms of AMCs for Daily Rainfalls 5 Days prior to the 100 Highest Daily Rainfalls
on Record
This may be overcome by calibrating the model to peak flow estimates from Chapter 5 of ARR87 (Book 4,
Section 1 in the 1998 version) such as the NSW Probabilistic Rational Method. The main DRAINS
parameter that can be changed to alter flows is the time of concentration for pervious areas, but other
parameters such as the AMC and depression storages may also be changed. It will be necessary to
analyse a number of storm durations to obtain a worst-case flowrate.
Where DRAINS is applied in rural conditions, the procedure should be outlined and the assumptions
regarding parameters and results made clear in reports submitted to reviewers.
(c) The Rational Method and the Extended Rational Method
DRAINS also offers a procedure that carries out rational method calculations. This can be viewed in the
Gymea model by choosing the Hydrological Model… option in the File menu, and selecting the Gymea
Rational Method model shown below:
This can then be viewed by clicking the Edit Default Model button. The model that appears is likely to
be an ARR87 model using the procedures from Australian Rainfall and Runoff, 1987, as shown in Figure
DRAINS User Manual
November 2014
Figure A.11 Property Sheet for a Rational Method Model
This model uses two runoff coefficients, 0.9 for impervious areas and 0.51 for pervious areas. The latter
is based on the 10 year ARI, 1 hour duration design rainfall intensity for Gymea, as described in Section
14.5.5 of ARR87 (Section 1.5.5. of Book 8 of the 1998 version). The rational method averages these
runoff coefficients according the specified impervious and pervious areas using a much simpler procedure
than that applied in the ILSAX model.
The run results are similar to those from the ILSAX model, except that peak flowrates are produced but
no hydrographs of flow, so the results cannot be used to model detention storages, as ILSAX and other
hydrograph-producing models can.
To meet the needs of users wanting to apply the rational method to detention basin calculations, an
extended rational method (ERM) has been provided in DRAINS. This can be selected from the
Hydrological Models… property sheet as shown below:
The parameters required are shown in Figure A.12. The ERM determines a runoff volume based on the
runoff coefficients supplied and then uses the same time-area routing procedure as the ILSAX model to
produce hydrographs. Consequently hydrographs can be produced from ARR87 rainfall patterns, but
because of the different infiltration assumptions, these will differ from ILSAX hydrographs produced from
the same rainfall patterns.
Figure A.12 Property Sheet for an Extended Rational Method Model
The ERM peak flowrates will also differ from the rational method flowrates unless the following actions
are taken:
the Total sub-catchment area option is selected in the box shown at the bottom-left of Figure A.12;
a synthetic rainfall pattern based on the I-F-D relationship for the site is applied, instead of the
ARR87 storm patterns, which are not used by the rational method.
These issues are described in detail in the DRAINS User Manual and Help system.
The rational method is suited to basic pipe system design without storage effects, but is a poor analysis
model. Assumptions about timing of peak flowrates must be made to estimate what happens in larger
flood events and this becomes a more complicated task than running a hydrograph-producing model.
The ERM provides a hydrograph model based on rational method principles. This is unique to DRAINS
and is not covered in manuals, but the principles used are similar to methods commonly applied in the UK
and US.
DRAINS User Manual
November 2014
Comparison of Hydrological Methods for Piped Drainage Systems
This section provides comparative information on the three models provided by for use with piped
drainage systems. An example based on the Gymea model is shown in Figure A.13 and the subcatchment characteristics relevant to the ILSAX and rational method models are shown in Table A.9. The
focus is on the runoff produced by the sub-catchments and flows in pipes are not considered in this
assessment. An additional sub-catchment has been added at the outlet to model a sub-catchment that is
mainly pervious.
Table A.10 sets out the results of a series of runs made with the modified Gymea model. . Four ILSAX
models apply a typical Soil Type of 3 and AMC values of 1, 2, 3 and 4. The rational method uses a 10
year ARI pervious area runoff coefficient of C10 = 0.51, based on a 10 year ARI, 1 hour intensity of 56
mm/h to develop 5 and 100 year ARI coefficients of C5 = 0.48 and C100 = 0.61. The extended rational
method (ERM) uses the same coefficients, but is applied in three ways, with ARR87 and synthetic storms
being used, and impervious and pervious runoff being calculated separately or on a total basis. Times of
concentration are consistent for all models.
Figure A.13 Gymea Model used for Comparisons
Peak flowrates for 5 and 100 year ARI are shown for each sub-catchment. Those from the ILSAX models
and the ERM with ARR87 storms are the highest values out of twelve storm patterns with durations from
5 minutes to 4.5 hours.
DRAINS User Manual
November 2014
Table A.9 Characteristics of Comparative Gymea Model Sub-Catchments
Hydrological Model
Cat A.1
Rational Method and ERM
& Grassed %
& Grassed tc
& Pervious
& Pervious.
tc (minutes)
30, 5, 65
5, 1, 12
35, 65
5, 12
Cat A.2
80, 0, 20
2.5, 0, 3
80, 20
2.5, 3
Cat A.3
80, 0, 20
2.5, 0, 3
80, 20
2.5, 3
Cat A.4
10, 0, 90
6, 0, 18
10, 90
6, 18
Cat B.1
50, 5, 45
8, 1, 13
55, 45
8, 13
Cat C.1
55, 5, 40
6, 1, 10
60, 40
6, 10
Table A.10 Comparison of Flowrates and Volumes Generated by
Gymea, New South Wales Pipe System Models
Hydrological Model
ILSAX with Soil Type of 3 and AMC of
ERM* with:
5 Year ARI Flowrates (m3/s)
Cat A.1
Cat A.2
Cat A.3
Cat A.4
Cat B.1
Cat C.1
100 Year ARI Flowrates (m /s)
Cat A.1
Cat A.2
Cat A.3
Cat A.4
Cat B.1
Cat C.1
5 Year ARI Runoff Volumes from the Whole Catchment (% of Rainfall)
Design Storm
5 minute
25 minute
4.5 hour
100 Year ARI Runoff Volumes from the Whole Catchment (% of Rainfall)
5 minute
25 minute
4.5 hour
* The ERM dies not run with the total area assumption and ARR87 storms
DRAINS User Manual
November 2014
Relative results vary with the proportions of impervious and pervious areas, but the rational method and
ERM generally specify lower flowrates than the ILSAX models, specially where an AMC or 3 or 4 is used,
which will be the usual situation at Gymea.
The reasons for the rational method providing lower flowrates than ILSAX are:
• ILSAX uses ARR87 patterns such as that shown in Figure A.5, which contain higher peak intensities
than the rational method, which assumes that rainfall occurs as a rectangular block.
• The ILSAX hydrological model gives different runoff volumes to the rational method and applies
different routing procedures. It only applies a depression storage loss of 1 mm for impervious areas
while the rational method and ERM apply C5 = 0.86 and C100 = 1.0.
The three alternative ERM combinations demonstrate how this model produces different peak flows
depending on the assumptions and rainfall inputs applied. The last of the three variations provides peak
flowrates that are the same as the rational method estimates.
Table A.10 also displays the volumes of hydrographs generated for selected storm patterns. These are
expressed as a percentage of the total rainfall in these patterns. The ILSAX models show a spread of
volumes depending on AMCs and storm durations, while the ERM results show consistent volumes of
65% for 5 year ARI and 78% for 100 year ARI. These percentages are the weighted average C values
obtained from the impervious and pervious coefficients. The ERM assumes that the volumetric coefficient
(ratio of total runoff to total rainfall) is the same as the runoff coefficient used to define peak flowrates.
A designer at Gymea using a (Soil Type, AMC) combination of (3, 3) or (3, 4) would generally generate
greater volumes than from the ERM. If the results were applied to a detention basin design, a larger
storage would be required when the ILSAX mode is used.
Similar variations in ILSAX model results to those caused by AMC occur when Soil Types are changed,
although the extent of variations is not as great.
To check whether these results apply in other parts of Australia, the analysis has been applied using
rainfall and parameter values applying at a location with higher rainfalls, the suburb of Manly in Brisbane,
and a site with lower rainfall – Port Adelaide, South Australia. Results from models adapted from the
Gymea model are shown in Table A.11 and Table A.12.
At Manly, the 10 year ARI, 1 hour rainfall intensity of 68 mm/h leads to pervious area runoff coefficients of
C10 = 0.67, C5 = 0.64 and C100 = 0.80. An AMC of 3 is used for comparisons. The impervious area
coefficients are the same as at Gymea, and the comparative results are similar to those at Gymea, with
the ILSAX models giving higher peak flows and volumes.
At Port Adelaide, the 10 year ARI, 1 hour rainfall intensity of 24.5 mm/h defines pervious area runoff
coefficients of C10 = 0.10, C5 = 0.095 and C100 = 0.12. The Soil Type is assumed to be 2, reflecting sandy
soils, and combined with the lower rainfall intensities, runoff can be assumed to be much lower than at
Gymea and Manly. The ILSAX estimates in Table A.12 are generally below the rational method peaks
and volumes. Even if the AMC is set at 3, the rational method estimates are still slightly higher, although
the differences in flows and volumes are small.
These comparisons are provided as information for designers and reviewers. It is beyond the scope of
this Guide to argue the merits of the individual models.
Other Hydrological Models in DRAINS
DRAINS can also apply runoff routing or storage routing models emulating the RORB, RAFTS and
WBNM programs described in Chapter 5 of this manual. These can be viewed using the Hydrological
Models…option in the Project menu, which appears as shown in Figure A.14.
Runoff routing model can be run together with an ILSAX model in DRAINS. This is convenient where the
tailwater affecting a small urban drainage system is created by flows from a larger urban rural catchment.
A number of storm events can be modelled without having to transfer data and results between models.
Further information on the DRAINS implementation of these models is provided in the DRAINS Manual
and the Help system. The models and their results can be inspected using the Viewer in the same way
as the ILSAX and rational method models.
DRAINS User Manual
November 2014
Table A.11 Comparison of Flowrates and Volumes Generated by
Manly, Queensland Pipe System Models
Hydrological Model
ILSAX with Soil Type of 3 and AMC of
ERM* with:
5 Year ARI Flowrates (m3/s)
Cat A.1
Cat A.2
Cat A.3
Cat A.4
Cat B.1
Cat C.1
100 Year ARI Flowrates (m /s)
Cat A.1
Cat A.2
Cat A.3
Cat A.4
Cat B.1
Cat C.1
5 Year ARI Runoff Volumes from the Whole Catchment (% of Rainfall)
Design Storm
5 minute
25 minute
4.5 hour
100 Year ARI Runoff Volumes from the Whole Catchment (% of Rainfall)
5 minute
25 minute
4.5 hour
These three established models were made available in DRAINS to model rural or largely-rural
catchments. The time-area procedure used by ILSAX has not been calibrated to rural catchment data,
while the other three have been extensively tested and used in rural environments, and are supported in
Australian Rainfall and Runoff, 1987.
The emulations of the models will give similar answers to the original RORB, RAFTS and WBNM models,
but there may be differences in flowrates due to different computational procedures and the many
different features in the operation of these models. For example, the RAFTS model in DRAINS is simpler
and has less features that the xprafts program provided by xpsoftware. Designers and reviewers will
need to ensure that the correct parameters for a location are applied. These may come from published
relationships such as those in Chapter 9 of ARR87 (Book 5, Section 3 of the 1998 version), or by
calibrating the storage routing model to rural model peak flow estimates from Chapter 5 of ARR87 (Book
4, Section 1 in the 1998 version).
DRAINS User Manual
November 2014
Table A.12 Comparison of Flowrates and Volumes Generated by
Port Adelaide Pipe System Models
Hydrological Model
ILSAX with Soil Type of 2 and AMC of
ERM* with:
5 Year ARI Flowrates (m3/s)
Cat A.1
Cat A.2
Cat A.3
Cat A.4
Cat B.1
Cat C.1
100 Year ARI Flowrates (m /s)
Cat A.1
Cat A.2
Cat A.3
Cat A.4
Cat B.1
Cat C.1
5 Year ARI Runoff Volumes from the Whole Catchment (% of Rainfall)
Design Storm
5 minute
25 minute
4.5 hour
100 Year ARI Runoff Volumes from the Whole Catchment (% of Rainfall)
5 minute
25 minute
4.5 hour
Pipe, Pit and Overflow Route Data Bases
When DRAINS runs it refers to data bases describing the
hydrological model, rainfall data and details of the pipe, pit and
overflow routes specified in the property sheets for various
components. This information can be seen in the Viewer by
(a) opening the property sheets for components, (b) using the
property balloons (see Figure A.16), or (c) transferring data to
a spreadsheet. The transfer options are shown to the right.
The data bases can also be viewed using options from the
Project menu. Details are covered in the Manual and Help
DRAINS User Manual
November 2014
Figure A.14 Model Property Sheet for a RORB Model
The data bases selected should obviously reflect the conditions at the site. Users can create their own
pipes, pits or overflow routes by adding information to the data bases. In analysing existing systems, this
may be necessary because a pit may be an obsolete type for which no inlet capacity information is
available. A Generic Spreadsheet for Pit Inlet Capacities, provided on the accompanying CD, can be
used to establish relationships for these pits. Where inlet capacity is an important consideration, details
should be provided with any design or analysis documentation.
Designers apply hydraulic methods to determine flow characteristics corresponding to hydrological flow
estimates. These characteristics – water levels, depths, widths, velocities and products of depths and
velocities, are used to decide whether the flow is being conveyed safely along a pipe or channel.
There has been rapid development of hydraulic models recently, particularly 2-dimensional models of
surface flows. Table A.13 and Table A.14 provide a classification of models, with examples of the
software used in Australia. The first two types in Table A.13 are procedures that can be implemented
with a calculator, while the others are packages that organise large amounts of data describing the
geometry and characteristics of pipes, channels and flow paths.
Table A.13 Pipe System Hydraulic Models
Implemented in:
Estimation of velocities and flow capacities for pipe-full
'but not under pressure' conditions
Manual calculations using Manning’s
equation or a similar relationship
Normal depth calculations estimating flow depths,
velocities and other characteristics for a given flowrate
(involving simple iterative procedures)
Manual or spreadsheet calculations, or
simple overflow route calculations in
programs such as DRAINS
Projection of hydraulic grade lines through pipe
systems, allowing for full- and part-full flow, pipe
friction and pit pressure losses
DRAINS basic hydraulics model (now
1-D unsteady water surface profile calculations
through pipes using Priessmann slot or similar
methods to model full-pipe flows
DRAINS, SWMM, xpswmm, Mouse,
The basic hydraulics procedure was the first model implemented in DRAINS. It is now obsolete, and only
available in models developed with pre-2011 versions of DRAINS. The current standard and premium
hydraulic models both apply unsteady flow hydraulic calculations in pipes and channels. They differ in
the hydraulic calculations for overflow routes. The standard model assumes uniform flows, providing
information based on normal depth calculations for the peak calculated flows at a nominated point along
DRAINS User Manual
November 2014
the overflow route. The premium model calculates a full water surface profile along overflow routes,
allowing for tailwater levels. Because it allows for stored surface water at pits and in along flow paths, it
usually specifies lower flowrates and water levels than the standard model. Thus, the standard model
can be considered to give results that are conservatively high.
Table A.14 Hydraulic Models applicable to Open Channels and Overflow Routes
Implemented in:
Estimation of flow capacities and velocities for a given
flow depth (channel-full levels)
Manual calculations using Manning’s
equation or a similar relationship
Normal depth calculations estimating flow depths,
velocities and other characteristics for a given flowrate
(involving simple iterative procedures)
Manual or spreadsheet calculations, or
simple models in programs such as
HEC-RAS or DRAINS (overflow routes
only in basic hydraulic model)
1-dimensional (1D) steady water surface profile
calculations - sub-critical, supercritical or mixed (both)
HEC-RAS, DRAINS basic hydraulic
model (now obsolete)
1-D quasi-unsteady water surface profile (a series of
steady state calculations)
DRAINS basic hydraulics model
1-D unsteady water surface profile calculations
Quasi-2-dimensional surface flow models created by
linking 1-D unsteady flows in a network with suitable
overflow controls
CELLS (obsolete), MIKE11, xpswmm,
2-dimensional (2-D) surface flow models
RMA-2 (using finite elements), MIKE 21,
Sobek and TUFLOW (finite differences,
finite volume), Info works 2D (boundary
elements), ANUGA (finite volume)
Integrated 1-D - 2-D surface flow models
MIKE Flood (MIKE11 + MIKE21), Sobek,
TUFLOW, xp2d (xpswmm + TUFLOW)
Integrated 1-D - 2-D surface flow models combined
with unsteady pipe flow models
MIKE Flood + MOUSE, Sobek, TUFLOW,
xp2d (xpswmm + TUFLOW)
Reviewers can tell which hydraulic model has been used to produce a set of results from the status bar at
bottom left of screen.
Information on the working of the models and their data requirements are given in the DRAINS User
Manual and Help system. Reviewers will mainly be concerned with the results, particularly with the water
levels estimated. Methods of checking these are described in the following section.
In pipe system calculations, peak flowrates are assumed to occur simultaneously in the rational method,
but in hydrograph models such as the ERM and ILSAX, allowance is mode for the peaks occurring at
different times due to varying times of concentration. The calculation and checking procedure set out in
ARR87 (Tables 14.14 and 14.16, or Tables 1.14 and 1.16 in the 1998 version).does not properly describe
the processes in hydrograph models which usually specify lower HGLs.
An important issue in modelling, beyond the scope of this Guide, is the selection of a model that is
adequate for the task. Judgements on this require theoretical knowledge of hydraulics as well as
experience with models. The DRAINS pipe models have been tested and can be applied by relatively
inexperienced designers. Open channel calculations may require knowledgeable interpretation and any
modelling of large or critical systems should be done by experienced engineers.
DRAINS models allow flows to be reversed, for example, when high water levels or pressures in a
pipeline force water back through side branches. This may not be obvious from the initial display of peak
flows, because DRAINS only displays the peak positive pipe flowrate, so it will be necessary to explore
results and property sheets. Both DRAINS hydraulic models can sometimes display instabilities (rapidly
fluctuating water surfaces) or spikes (sudden rises and falls in water level and flowrates). These are
typically caused by overshooting of interpolation and extrapolation calculations, and can usually be
ignored after checking the model. If instabilities are present in any models submitted to a reviewer,
explanations or interpretations should also be provided, indicating that these will not invalidate the results.
DRAINS User Manual
November 2014
A.5 Checking Model Components, Flowrates and Water Levels
Viewing Pipe System Components
Components can be inspected by opening property sheets (Figure A.15), property balloons (Figure A.16)
or transferring data to a spreadsheet via the Windows Clipboard using options in the Edit menu (Figure
A.17). The spreadsheet data output is the only easy way of detecting baseflows and user-provided
Figure A.15 Pipe Property Sheet
Pipes and pits can be inspected using long section window called from the pop-up menu for a pipe
(Figure A.18) and from the multi-pipe long sections that can be created in the Export option in the File
menu by specifying a route between pits (Figure A.19).
Figure A.16 Balloon Showing Pipe Data
Figure A.17 Part of Spreadsheet Output
DRAINS User Manual
November 2014
Figure A.18 Long Section Plot for a Pipe, Showing Pipe and Flow Characteristics
Figure A.19 Pipeline Long Section Plot, displayed prior to Transfer to a CAD Program
Viewing Pipe System Results
If a model loaded into the Viewer contains run results, you
will see these straight away as coloured numbers, as
shown in Figure A.20. Since the overflow routes will
probably be the most critical they are displayed in red.
If this result comes from an ILSAX or ERM hydrological
model, it will probably be the maximum flowrate out of a
series of analyses of storm patterns. You can view
individual patterns by selecting them from the drop-down
menu at the top-left of the Main Window, shown to the right.
DRAINS User Manual
November 2014
Pipe Flowrates
Overflow Route
Flowrates (m3/s)
Flowrates (m3/s)
HGL Level
(m AHD)
Figure A.20 Displayed Flowrates and HGL Levels
Note that flowrates in and out of a pit or node will not necessarily add to zero, as they may represent
conditions at different times, or come from different storm events. More accurate checks involving
hydrograph volumes are provided in the spreadsheet output of results.
It is worthwhile to check the run report by selecting the Last Run Report option in the View menu. This
produces a report such as that shown in Figure A.21. This shows a warning that water is being lost from
this system, which occurs when a pit overflows but no overflow route is provided to convey this overflow.
In such situations the model should be amended. The message also indicates that there are no
overflows from the pipe system and that freeboard is adequate, that is, the peak pit water level is more
than the minimum freeboard allowed, normally 150 mm, to meet a requirement mentioned in Section 3.4.
Figure A.21 Run Report
In designs there should be no upwelling or other problems at the Minor flowrate, but these can be
permitted under major flow conditions, usually 100 year ARI storm events. It is also possible to view
other characteristics using the Customise Text… option in the View menu. This changes the display to
the form shown below.
Figure A.22 Displayed Surface and Pipe Invert Levels
DRAINS User Manual
November 2014
Results can be viewed in more detail using options in the pop-up menu displayed by right-clicking on
components. These can display hydrographs and HGL plots as shown in Figure A.23 and long-sections
of pipes (Figure A.18). Tables of results can also be displayed and exported to a spreadsheet via the
Windows Clipboard.
Figure A.23 Display of Hydrographs and Hydraulic Grade Lines (HGLs)
The most critical output will probably be the flow characteristics in overflow routes, which can be
displayed by opening the property sheet for an overflow route, and going to the second page tagged
Cross Section Data. As shown in Figure A.12, a picture of the section is shown, together with flow
widths, depths, velocities and velocity-depth products. This can be used to check the critical
characteristics for street drainage systems detailed in Section 3.5 – the allowable width and velocitydepth product. It can also be used to assess flood depths to be related to floor levels of existing or
planned buildings.
The flow that is displayed in Figure A.24 may be greater than the rate displayed in the Main Window, due
to an additional flow being specified to allow for overflows combining with flows from the sub-catchment
through which they flow. This occurs when the number in the box labelled % of downstream catchment
flow carried by this channel in Figure A.24 is greater than zero. Refer to the Manual and Help system
for more information.
Reviewers should note that when the basic or standard hydraulic model (see Section 4.4) is used in
DRAINS the flow characteristics in overflow routes are calculated by assuming uniform flow conditions
along the overflow route. In fact, the flowrate will vary along the route. If the premium hydraulic model is
applied, the water surface will be determined more accurately and it will be possible to display a long
section as shown in Figure A.25. Therefore, when the standard or basic hydraulics are used, the flow
characteristics should be considered as an indicator, rather than as an accurate estimate. Overflow route
characteristics are also questionable for short routes and those running round corners.
Using additional spreadsheets included on the CD accompanying this guide, the DRAINS spreadsheet
outputs can be converted to tables of the form shown in Figure A.26. This is from the Gymea ILSAX
example. There is another that converts rational method results to tables employed by Queensland
councils. These outputs present pit pressure change coefficients ('k values') developed by a procedure
that looks up the tables presented in the Queensland Urban Drainage Manual. Details are provided in the
DRAINS User Manual and Help system.
DRAINS User Manual
November 2014
Figure A.24 Display of Overflow Route Flow Characteristics
Figure A.25 Overflow Route Long Section from Premium Hydraulics Model
DRAINS User Manual
November 2014
Figure A.26 Table for Gymea Design Example
Reviewing Stormwater Detention and Retention Systems
Detention basins in DRAINS usually involve three parts arranged as shown in Figure A.27 – a basin
component, a pipe outlet and one or more overflow routes that represent 'high-level' outlets such as a
weir overflow,. A sub-catchment can be attached directly to a basin, and channels and pipes can be
directed into it.
The basin property sheet, shown in Figure A.28, specifies the type of 'low-level' outlet (pipe, orifice, sump,
etc.) and a relationship defining storages, either an elevation-surface area table or an elevation-storage
table. In the second page tagged Infiltration Data information can be added that will allow stormwater
infiltration to occur through the floor and walls of the basin.
Peak water levels
upstream and just
downstream of the
low-level basin
outlet (m AHD)
Overflow over
weir (m3/s)
Pipe Outflow (m3/s)
Figure A.27 Detention Basin Layout and Results
DRAINS User Manual
November 2014
Figure A.28 Detention Basin Property Sheet
The pipe property sheet is the same as the usual sheet shown in Figure A.15, while the overflow route
has three pages describing the weir control of the high-level outlet (Figure A.29) and the geometric
properties of the overflow route carrying flows from this.
Figure A.29 Part of the Overflow Route Property Sheet for a Detention Basin
When a run is made, the results shown in the lower part of Figure A.27 are obtained, and the reservoir
routing calculations can be viewed from the pop-up menu for the basin and the components connecting to
it. Figure A.30 shows routed hydrographs.
Basins can take many configurations and multiple high-level outlets can be specified.
Reviewers should check that volumes in and out are consistent. There can be differences between these
due to infiltration, to DRAINS cutting long drawn-out outflows short, and to basins being drawn down
below the outlets at the start of a storm event. Inspection of the hydrographs and other plots will enable
reviewers to trace the behaviour of the detention basin.
Some issues that arise with basins are:
• Use of multiple low-level outlets in parallel or series – The DRAINS User Manual describes methods
for dealing with these. If tailwater levels are not high, overflow routes can model these accurately.
DRAINS User Manual
November 2014
Figure A.30 Routed Inflow and Outflow Hydrographs for a Detention Basin
• Modelling of sumps or infiltration basins – It is possible to model basins without outlets, where water is
disposed of by infiltration. DRAINS models the entry of inflow hydrographs and the slow draining of
the basin, monitoring storage levels and enabling the storage volumes required to be defined.
One matter that frequently arises is how to model a requirement that post-development flows must not
exceed pre-development flows. This can be difficult because many ARIs and storm durations must be
When on-site detention systems were first introduced most authorities required only that 100 year ARI
flowrates to meet this requirement, with some applying a more rigorous requirement such as ensuring
that 100 year ARI post-development flows to be no greater than 10 year ARI pre-development flows. This
was sometimes justified on the basis that the downstream pipe capacity was limited to, say, 10 year ARI,
but was also a means of limiting flows at ARIs lower than 100 years to pre-development levels.
It has now become common to limit post-development flows to two levels, typically 2 and 100 year ARI,
often justifying the lower level on environmental grounds, as a way of preventing erosion in natural
streams carrying runoff from developments. Compared to only having to implement this requirement at
the 100 year ARI level, this requires either (a) a more restrictive outlet and a larger storage volume or (b)
double low-level outlets.
Since DRAINS can easily model multiple storm events, it is feasible to analyse all relevant design storms.
For example, Table A.15 and Figure A.31 show results from the Sydney OSD Example with
Results.drn model in which three storms have been analysed. (In practice, 6 to 8 storms would
usually be required.
Table A.15 OSD Model Results
Storm Duration
Outflow (m3/s)
Outflow (m3/s)
This model contains both the pre-and post-development systems, so that they can be analysed together
and the total outflows compared. Inspecting the results, it is possible to develop the following table of
results from 100 year ARI storms.
DRAINS User Manual
November 2014
Figure A.31 On-Site Detention Model Results
Thus, it is possible to ensure that post-development flows peaks are held to pre-development levels for all
storms analysed.
When modelling pre- and post-development conditions, it is important that the same hydrological model is
applied to both cases, with adjustments to allow for increased development and imperviousness.
Reviewing Open Channel Systems
Open channel systems can be set up in DRAINS by specifying a number of reaches with appropriate
cross-sections and parameters. Different procedures are applied for the basic calculations and the
unsteady flow (standard and premium hydraulic model) calculations.
The Toowoomba Estate Example with Results.drn file on the CD defines a system containing both
pipes and open channels, shown in Figure A.32. HGL and water surface levels at nodes and plots of
longitudinal and cross-sections can be inspected.
If it is required to find a surface water level at a location along a channel, perhaps at the site of a
proposed development, then a node should be located at this point. DRAINS will than specify calculated
flow levels at this exact point.
A.6 Analyses
One of the main uses of DRAINS is the analysis of localised flood problems. It is difficult to define precise
rules for this, as there are many variations in development projects and drainage systems, particularly in
established urban areas.
The level of detail required and the handling of upstream and downstream drainage systems require
judgement, balancing the accuracy required against the resources available, such as funding, information
and time.
The use of sensitivity analyses, repeating calculations with different possible inputs, is probably the most
powerful tool for examining and reducing uncertainties. For example, if tailwater conditions are uncertain,
DRAINS runs can be made with different tailwater levels and the results assessed to come up with a
reasonable but conservative estimate.
DRAINS User Manual
November 2014
Figure A.32 Open Channel Model Results
Reviewers need to be satisfied that the analysis has been carried out correctly and will probably expect a
conservative estimate. Generally, the more uncertain the conditions and the less experienced the
modeller or designer, the more conservative the results should be.
Using the ILSAX model, DRAINS has been applied in detailed models of existing drainage systems of
2500 pits extending over 3 km2. This is reasonable as long as all parts of the system are modelled in
detail. However, a problem occurs when a point of interest such as a re-development site is located well
downstream in a catchment. The drainage system near the site can be modelled in detail, but the
difficulty lies in determining to what accuracy the upper part of the catchment drainage system should be
If all of the upper flow arrives as surface or open channel flows, or if all arrives in a pipeline, then it would
be reasonable to apply a broad-brush method, such as modelling the entire upstream area as a single
sub-catchment. But when upstream flows can arrive both on the surface and in pipes, it is necessary to
provide further detail upstream. This may require all upstream pits and pipes to be included, although this
can be done in a rough manner at locations away from the site. For example, getting pit surface levels
and pipe lengths exactly right will not be important, but pit inlet capacities need to be described more
accurately as these will define the proportion of upstream flows that enter the pipe system.
A.7 Conclusion
This Guide, originally issued with the DRAINS Viewer, aims to provide useful advice for reviewers and
designers that will make checking and assessment processes more efficient. Further guidance is given in
the publications on flood estimation in the reference list.
If you require more information, or have comments on the contents of the Guide, please contact the
developers of DRAINS:
Bob Stack
Watercom Pty Ltd
15 Little River Close
Wooli NSW 2462
phone/fax: (02) 6649 8005
[email protected]
DRAINS User Manual
Geoffrey O’Loughlin
Anstad Pty Limited
72 Laycock Road
Penshurst NSW 2222
(02) 9570 6119, fax (02) 9570 6111, 0438 383 841
[email protected]
November 2014
ACADS (1981) (The Association for Computer-Aided Design) Backwater Programs, Publication M6,
Aitken, A.P. (1975) Hydrologic investigation and design of urban stormwater drainage systems,
Australian Water Resources Council Technical Paper No. 10, Australian Government Publishing
Service, Canberra
Argue, J.R. (editor) (2004) WSUD: Basic Procedures for 'Source Control' of Stormwater, University of
South Australia Water Resources Centre, Adelaide
Australia, Bureau of Meteorology (2003) The Estimation of Probable Maximum Precipitation in Australia:
Generalised Short – Duration Method, (www.bom.gov.au/has/gsdm_document.shtml)
ACT Government, Urban Services (undated) Urban Stormwater, Standard Engineering Practices, Edition
1, www.act.gov.au/storm/
AUSTROADS (1994) Waterway Design Manual, Sydney
Austroads (2013) Guide to Road Design, Part 5: Drainage, General and Hydrology Considerations,
(Armistead, A. et al.), Sydney
BMT WBM (2010) TUFLOW User Manual, GIS Based 1D/2D Hydrodynamic Model, Brisbane
Boyd, M.J., Pilgrim, D.H. and Cordery, I. (1979) An improved runoff routing model based on
geomorphological relations,. Institution of Engineers Australia, Hydrology and Water Resources
Boyd, M.J., Rigby, E.H., VanDrie, R. and Schymitzek, I. (2005) Watershed Bounded Network Model,
WBNM2003 User Guide, University of Wollongong, Wollongong (download from
Boyd, M. (1986) Head-Discharge Relations for Culverts, Monier Rocla Technical Journal, November
Bradley, J.N. (1970) Hydraulics of Bridge Waterways, Hydraulic Design Series No. 1, Federal Highway
Administration, U.S. Department of Transport, Washington, DC
Cartwright, A.P. (1983) The Application of ILLUDAS to an Urban Drainage Catchment in Sydney,
Australia, Master of Engineering Science Project, School of Civil Engineering, University of NSW
Chan, A. (1998) Retrieval, Processing and Analysis of Rainfall Data from the Hewitt Gauging Station
(1998-1999), Undergraduate Project, Faculty of Engineering, University of Technology, Sydney
Chaudhry, M.H. (1993) Open-Channel Flow, Prentice Hall, NJ
Chen, J.J.J. (1985) Systematic explicit solutions of the Prandtl and Colebrook-White equations for pipe
flow, Proceedings, I.C.E., Part 2, Vol. 79, June
Chow, V.T. (1958) Open Channel Hydraulics, McGraw-Hill, New York
Dayaratne, S.T. (1997) Quantification of the Errors in Urban Catchment Rainfall-Runoff Models – A
Review, 24th Hydrology & Water Resources Symposium, Auckland, 1997
Dayaratne, S.T. (2000) Modelling of Urban Stormwater Drainage Systems Using ILSAX, PhD Thesis,
School of the Built Environment, Victoria University of Technology, Melbourne
Engman, E.T. (1986) Roughness Coefficients for Routing Surface Runoff, Journal of Irrigation and
Drainage Engineering, ASCE, Vol. 112, No. 1, February
Goyen, A.G. and Aitken, A.P. (1976) A Regional Stormwater Drainage Model, Hydrology Symposium,
Institution of Engineers, Australia, Canberra
Goyen, A.G. and O’Loughlin, G.G. (1999) Examining the Basic Building Blocks of Urban Drainage,
Proceedings of the 8th International Conference on Urban Storm Drainage (edited by I.B. Joliffe and J.E.
Ball), Sydney
Guo, J.C.Y. (1996) Street Hydraulics and Inlet Sizing Using the Computer Model UDINET, Water
Resources Publications, Highlands Ranch, CO (with program)
Hare, C.M. (1983) Magnitude of Hydraulic Losses at Junctions in Piped Drainage Systems, Civil
Engineering Transactions, Institution of Engineers, Australia, Vol. CE25
Hare, C. and O'Loughlin, G.G. (1991) An Algorithm for Pressure Head Changes at Pits and Junctions,
Urban Drainage and New Technologies (UDT '91), Dubrovnik, 1991
DRAINS User Manual
November 2014
Heeps, D.P. and Mein, R.G. (1973) An independent evaluation of three urban stormwater models,
Research Report 4, Department of Civil Engineering, Monash University
Henderson, F.M. (1966) Open Channel Flow, Macmillan, New York
Huber, W.C. and Dickinson, R.E. (1998) Storm Water Management Model Version 4: User's Manual,
University of Florida for U.S. Environmental Protection Agency, Athens, Georgia
Hydraulics Research (1990) Charts for the hydraulic design of channels and pipes, 6th Edition, Thomas
Telford Ltd., London
Hydrologic Engineering Center, U.S. Army Corps of Engineers (1997) HEC-RAS River Analysis System,
Hydraulic Reference Manual, Version 2.0, (written by G.W. Brunner), Davis, California
Institution of Engineers, Australia (1987) Australian Rainfall and Runoff, a Guide to Design Flood
Estimation, 2 volumes (edited by D.H. Pilgrim and R.P. Canterford), Canberra (loose leaf version
produced in 1997)
Izzard, C.F. (1946) Hydraulics of Runoff from Developed Surfaces, U.S. National Research Council,
Highway Research Board, Proceedings, Vol. 26, p.129-150 (with discussion)
Neville Jones & Associates Pty Ltd and Australian Water Engineering (1992) Queensland Urban
Drainage Manual, 2 volumes, prepared for the Queensland Water Resources Commission, the Local
Government Engineers' Association of Queensland and Brisbane City Council, Brisbane
Laurenson, E.M. and Mein, R.G. (1990) RORB - Version 4 Runoff Routing Program User Manual,
Monash University Department of Civil Engineering with Association for Computer Aided Design
(ACADS) and Montech Pty Ltd, Melbourne
Mays, L.W. (2001) (editor) Stormwater Collection Systems Design Handbook, McGraw-Hill, New York
Mein, R.G. and O'Loughlin, G.G. (1985) Application of ILLUDAS-SA to Gauged Urban Catchments,
I.E.Aust. Hydrology and Water Resources Symposium, Sydney
Mills, S.J. and O'Loughlin, G.G. (1982-98) Workshop on Piped Urban Drainage Systems, Swinburne
Institute of Technology and University of Technology, Sydney (first version 1982, latest 1998)
New South Wales, Department of Housing (1987) Road Manual, Sydney
New South Wales, Department of Main Roads (1979) Model Analysis to Determine Hydraulic Capacities
of Kerb Inlets and Gully Pit Gratings, Sydney, 1979
Normann, J.M., Houghtalen, R.J. and Johnston, W.J. (2005) Hydraulic Design of Highway Culverts,
Hydraulic Design Series HDS 5, 2nd Edition, Federal Highway Administration, Washington, DC
O'Loughlin, G. (1993) The ILSAX Program for Urban Stormwater Drainage Design and Analysis (User's
Manual for Microcomputer Version V2.13), Civil Engineering Monograph 93/1, University of
Technology, Sydney (fifth printing, first version 1986)
O'Loughlin, G.G., Darlington, D. and House, D. (1992) Mathematical Description of Pit Entry Capacities,
I.E.Aust. International Symposium on Urban Stormwater Management, Sydney
O'Loughlin, G.G., Haig, R.C., Attwater, K.B. and Clare, G.R. (1991) Calibration of Stormwater RainfallRunoff Models, Hydrology and Water Resources Symposium, I.E.Aust, Perth
O’Loughlin, G. and Stack, B. (2002) Algorithms for Pit Pressure Changes and Head Losses in
Stormwater Drainage Systems, 9th International Conference on Storm Drainage, ASCE, Portland,
Pereira, J. (1998) Gauged Urban Catchment Study at Jamison Park, Penrith, Undergraduate Project,
Faculty of Engineering, University of Technology, Sydney
Pezzaniti, D., O’Loughlin, G.G. and Argue, J.R. (2005) General Characteristics of Pit Inlet Capacity
Relationships, poster paper, 10th International Conference on Urban Drainage, Copenhagen
Poertner, H.G. (editor)(1981) Urban Stormwater Management, American Public Works Association,
Queensland Department of Main Roads (2002) Road Drainage Design Manual, Part C Hydraulic Design,
Brisbane (Available for download - search for this title on the internet - the URL is too long to quote)
Queensland Department of Energy and Water Resources (2013) Queensland Urban Drainage Manual,
3rd Edition, Brisbane
Ragan R.M. and Duru, J.O. (1972) Kinematic Wave Nomograph for Times of Concentration, Journal of
Hydraulics Division, ASCE, Vol. 98, No. HY10, October
DRAINS User Manual
November 2014
Rigby, E.H., Boyd, M.J. and VanDrie, R. (1999 ) Experiences in developing the hydrology model WBNM,
8th International Conference on Urban Storm Drainage, Sydney Australia
Ross, C.N. (1921) The calculation of the flood discharge by the use of time contour plan, Transactions,
Institution of Engineers Australia, Volume 2, pp. 85-92
Ryan, C. (2005) CatchmentSIM, A stand-alone GIS based terrain analysis system, CRC for Catchment
Hydrology, Melbourne (wwww.toolkit.net.au/catchmentsim)
Sangster, W.M., Wood, H.W., Smerdon, E.T. and Bossy, H.G. (1958) Pressure Changes at Storm Drain
Junctions, Engineering Series Bulletin No.41, Engineering Experiment Station, University of Missouri
Shek, J. and Lao, J. (1998) Urban Rainfall-Runoff Modelling at Hewitt, Penrith, Undergraduate Project,
Faculty of Engineering, University of Technology, Sydney
Siriwardini, N.R., Cheung, B.P.M. and Perera, B.J.C. (2003) Estimation of Soil Infiltration Rates of Urban
Catchments, 28th International Hydrology and Water Resources Symposium, Institution of Engineers,
Australia, Wollongong
Standards Australia/Standards New Zealand (2003) AS/NZS 3500.3.2:2003, Plumbing and drainage,
Part 3: Stormwater drainage, Sydney
Stephens, M.L. and Kuczera, G. (1999) Testing the time-area urban runoff model at the allotment scale,
Proceedings of the 8th International Conference on Urban Storm Drainage (edited by I.B. Joliffe and J.E.
Ball), Sydney
Streeter, V.L. and Wylie, E.B. (1981) Fluid Mechanics, 8th Edition, McGraw-Hill, New York
Terstriep, M.L. and Stall, J.B. (1969) Urban runoff by road research laboratory method, Journal of
Hydraulics Division, ASCE, Vol. 95, No. HY6, November
Terstriep, M.L. and Stall, J.B. (1974) The Illinois Urban Drainage Area Simulator ILLUDAS, Bulletin 58,
Illinois State Water Survey, Urbana
Tran, L (1998) Operation of Urban Gauging Station and Analysis of Cranebrook Catchment,
Undergraduate Project, Faculty of Engineering, University of Technology, Sydney
U.K. National Water Council (1981) Design and Analysis of Urban Storm Drainage - The Wallingford
Procedure, 5 volumes, London
U.K. Transport and Road Research Laboratory (1976) A Guide for Engineers to the Design of Storm
Sewer Systems, Road Note 35, 2nd Edition (1st Edition 1963), HMSO, London
U.S. Department of Transportation, Federal Highway Administration (1984) Drainage of Highway
Pavements, Hydraulic Engineering Circular No. 12, (Authors: Johnson, F.L. and Chang, F.F. M.), Office
of Engineering, Office of Technology Applications, Washington, DC
U.S. Federal Highway Administration (2009) Urban Drainage Design Manual, Hydraulic Engineering
Circular No. 22, 3rd Edition, (S. A. Brown, J.D. Schall, J.L. Morris, C.L. Doherty, S. M Stein and J.C.
Warner), National Highway Institute, Arlington, VA and FHWA Office of Bridges, Washington, DC
U.S. Natural Resources Conservation Service (2007) National Engineering Handbook, Chapter 7,
Hydrologic Soil Groups,
U.S. Soil Conservation Service, Department of Agriculture (1975) Urban hydrology for small watersheds,
Technical Release 55, Washington, DC
Upper Parramatta River Catchment Trust (2005) On-Site Detention Handbook, Version 4 Parramatta
(available for download on www.uprct.nsw.gov.au)
Vale, D.R., Attwater, K.B. and O'Loughlin, G.G. (1986) Application of SWMM to Two Urban Catchments
in Sydney, I.E.Aust. Hydrology and Water Resources Symposium, Brisbane
VicRoads (1994) Road Design Guidelines Part 7, Drainage, Melbourne
Watkins, L.H. (1962) The Design of Urban Sewer Systems Research into the Relation between Rate of
Rainfall and Rate of Flow in Sewers, Technical Paper No. 5, U.K. Department of Scientific and Industrial
Research, Road Research Laboratory
Watkins, L.H. and Fiddes, D. (1984) Highway and Urban Hydrology in the Tropics, Pentech Press,
Watson, M.D. (1981a) Application of ILLUDAS to Stormwater Drainage Design in South Africa, Report
1/81, Hydrological Research Unit, University of the Witwatersrand, Johannesburg
DRAINS User Manual
November 2014
Watson, M.D. (1981b) Time-Area Method of Flood Estimation for Small Catchments, Report 7/81,
Hydrological Research Unit, University of the Witwatersrand, Johannesburg
Wilkinson, A. (1995) Rainfall Variability Investigations at Hewitt, Penrith (1994-95), Undergraduate
Project, School of Civil Engineering, University of Technology, Sydney
XP Software (2000) XP-RAFTS User's Manual Version 5.1, Reference Manual, Canberra
DRAINS User Manual
November 2014
Computing aspects, 4.1
Continuing loss, 5.3
Continuity check, 3.28
Contraction coefficient, 2.29, 5.36
Copy data to spreadsheet, 3.25
Copy results to spreadsheet, 3.27
Culvert, 2.35, 4.7, 5.42
Customise DXF drawing, 3.24
Customise storms, 2.16
Customise text dialog box, 1.16, 3.13
Customising storms property sheet, 2.16
Data bases, 2.2, 2.38, A.18
Data entry, 3.1
Default data base, 1.9
Default Data Base, 3.12
Depression storage, 4.7, 5.3
Description, 1.22
Description property sheet, 3.16
Design method, 4.13
Design method, 4.10
Design mode, 1.18
Design procedures, 4.8
Design process, 4.12
Detention basin, 2.22
calculations, 4.7
continuity equation, 5.36
hydraulics, 5.36
Detention basin circular pipe outlet, 2.23
Detention basin elevation-discharge relationship,
Detention basin high level outlet, 2.26
Detention basin low level outlet, 2.22
Detention basin orifice outlet, 2.22
Detention basin property sheet, 2.22, 2.23
Detention basin rectangular pipe outlet, 2.23
Detention basin with no low-level outlet, 2.23
Dialog box, 1.12
Directly connected impervious area, 5.7
Dongle, 1.4
basic description, 1.1
data file, 1.22
demonstration version, 1.5
display options, 3.13
operations, 4.2
output options, 3.22
DRAINS development path, 5.1
DRAINS Utility Spreadsheet, 3.4
DRAINS Viewer, 4.1, 4.13, A.1
Draw menu, 2.2
drn file, 4.1
Drop pit, 4.6, 4.9
DXF exports, 3.23
DXF long-section, 3.25
Edit menu, 2.2
Enhanced design procedure, 4.8
ERM, 5.17
Error message, 3.19
ESRI file formats, 5.43
ESRI imports, 3.4
Established drainage systems, 4.14
’During Design runs’ options, 2.10
12d, 1.4, 3.35, 4.12
12d file transfers, 3.10
ACT pits, 5.24
Advanced Road Design, 1.4, 3.35
Alignment of pits, 1.12
Allowable connections of components, 2.37
Allowable ponding depth, 1.15
AMC, 4.7
Analysing established systems, 4.14
Analysis information, 4.14
Antecedent moisture condition, 1.8
Antecedent moisture condition (AMC), 5.10
Areally-varying rainfall intensities, 2.16
ARI, 1.7
ARR Wizard, 1.25
ARR2013 Rainfall procedures, 2.40
Assessing hydraulics, A.19
Assessing hydrology, A.8
Assessing models, A.7
Assessing rainfall inputs, A.7
Asset management, 4.17
Australian / New Zealand Standard AS/NZS
3500.3.2, 5.17
Australian height datum (AHD), 2.4
AUSTROADS Waterway Design manual, 5.42
Autodesk Land Desktop, 3.35
Average recurrence interval, 1.7
Background, 1.12, 2.3
Background colour, 3.2
Background replacement, 3.3
Baseflow, 2.7, 3.28
Basic hydraulic calculations, 5.35
Basin elevation-storage relationship, 2.22
Blocking factor, 5.25
Blocking theory
new, 2.6
Bolt down lid pit, 4.6
Branching pipes, 4.5
Bridge, 2.35, 4.7, 5.42
abutment, 2.35
pier, 2.35
Brisbane City Council chart format, 3.30
Bypass flow, 2.4
Calculation of inflows, 4.4
Calculation structure, 4.5
Calibration, 4.7
Catchment surface types, 5.6
Channel breakout, 2.28
Channel condition, 2.32
Channel cross-section, 2.28
Check HGL procedure, 3.28
Checking DRAINS models, 4.13
Checking requirements, A.3
Choke factor, 5.25
Colebrook-White equation, 5.32
Coloured number display, 1.20
Combination of hydrographs, 5.13
Combining components, 2.37
Comparing model results, A.14
Computer aspects, 1.4
DRAINS User Manual
November 2014
Infill developments, 4.13
Infiltration, 5.3
Initial loss, 5.3
Inlet control for culverts, 5.39
Input options, 3.1
Installation of DRAINS program, 1.5
Integrated linkages, 4.11
Inter-allotment requirements, A.4
Interception, 5.3
Intermediate levels, 3.18
Intermediate nodes, 2.9
Intermediate points, 2.11
Invert levels, 4.14
Irregular open channel, 2.29
bank, 2.29
chainage, 2.29
Junction, 2.4, 4.5
Kinematic wave, 5.3
Kinematic wave equation, 2.12
Kinematic wave routing, 1.29
Lag time, 1.15, 2.14
Land-use types, 1.15, 2.11
Links, 2.3
Localised study requirements, A.6
Long section display, 2.11
Looped pipes, 4.5
Loss model, 5.9
Loss models, 5.3
Main Window, 1.5
Major/minor design system, 1.20, 5.1
Manhole, 2.4
Manning equation, 5.33
Manning's coefficients, 5.36
MapInfo file formats, 5.44
MapInfo file imports, 3.7
Maximum ponded volume, 1.15
Menu, 1.12
Menu bar, 2.1
Menus, 1.5, 2.1
Merging DRAINS files, 3.35
Merging files, 3.9
MID/MIF files, 3.33
Mills pit coefficient equation, 5.34
Mills revision of Ku coefficients, 3.19
Misalignment of pits, 1.12
Missouri Charts, 5.34
Mixing of hydrological models, 2.39
Modelling aspects, 1.2
Modelling pits and pipes, 4.6
Modified Puls method, 5.36
Modified Rational Method, 5.17
Moving storm, 2.16
Multi-channel, 2.31
Multiple rainfall pattern entry, 2.40
Names of components, 1.15
New data bases, 3.12
New South Wales Pits, 5.23
Nodes, 2.3
Non-return valve, 2.11
On-grade pit, 5.23
On-site stormwater detention, 2.38
On-site stormwater detention system, 4.13
Open channel
cross-section, 2.29
Manning's roughness n, 2.29
Evaporation, 5.3
Existing drainage systems, 4.14
Existing service, 4.14
Expansion coefficient, 2.29, 5.36
Exporting ESRI files, 3.30
Exporting MapInfo files, 3.33
Extended Rational Method, 5.17
Extending the calculation period, 2.48
Fencing, 4.15
File formats, 5.42
File menu, 2.1
Flood studies, 4.18
problem locations, 4.17
remedial works, 4.17
Floodway (grassed), 2.31
Flow depth, 1.23
Frequency factors, 5.17
Full hydrodynamic model, 5.30
Gauged catchment data, 5.14
Gauging rainfalls and runoff, 4.15
Generic Pit Inlet Capacity Spreadsheet, 3.4
GIS file formats, 5.43
GIS file imports, 3.4
Grassed area, 1.15, 5.3
Greenfields drainage systems, 4.11
Gully pit, 2.4
Hardware lock, 1.4
head losses, 5.33
Headwall, 2.34
Headwall property sheet, 2.34
Headwater level, 2.34
HEC 22, 5.27
HEC-RAS, 2.35
Help, 1.7
Help system, 3.37
High early discharge pit, 2.23
Horton's infiltration equation, 1.4, 5.5, 5.9
Hydraulic analysis, 4.5
Hydraulic conductivity, 5.41
Hydraulic grade line (HGL), 1.20
Hydraulic models, A.19
Hydrograph, 2.8
translation, 1.29
Hydrograph attenuation, 5.18
Hydrograph translation, 5.18
Hydrograph-producing models, 5.2
Hydrographs, 1.21
Hydrological calculations, 4.3
Hydrological model specification, 1.7
Hydrological models, 1.6, 2.11
Hydrological models data base, 2.39
Hydrology, 5.2
Hyetograph, 1.7
Hyetograph data base, 2.40
ILLUDAS, 1.4, 5.1
ILSAX, 1.4, 5.1
ILSAX file imports, 3.9
ILSAX hydrological model, 5.3
ILSAX Hydrological Model, 1.2
Impervious area, 1.15
Impervious areas, 1.15
Import DB1 data base file, 2.48
Index sheet, 3.13
DRAINS User Manual
November 2014
routing equation, 5.19
RAFTS model property sheet, 1.30
RAFTS Model sub-catchment property sheet,
RAFTS reach property sheet, 1.30
RAFTS sub-catchment property sheet, 1.30
Rainfall data, 1.7, 1.24
Rainfall data property sheet, 1.8
Rainfall multiplier, 2.16
Rainfall pattern, 1.7
Rainfall pattern data base, 2.40
Rational Method, 1.2
Rational method frequency factors, 5.17
Rational method output converter, 3.30
Rational method runs, 1.23
Rational method sub-catchment property sheet,
Rational Method sub-catchments, 2.14
Rational Method theory, 5.16
Reviewing analyses, A.29
Reviewing results, 1.20
Revise pit loss coefficients, 3.19
RORB, 1.3, 5.19
RORB Model sub-catchment property sheet,
Roughness coefficients, 5.36
Routing models, 5.3
Run log, 3.18
Run menu, 2.3
Run options, 3.16
Running an ILSAX design model, 1.5
Running DRAINS, 1.18
Running storage routing models, 1.26, 1.28
Sag pit, 5.22
orifice flow, 5.22
weir flow, 5.21
Screen capture techniques, 3.22
Screen presentation options, 3.13
Sealed pit, 2.5, 4.6
Shapefiles, 3.31
Simple node, 2.8
Simulation models, 5.2
Soil type, 4.7, 5.10
South Australian pits, 5.26
Spreadsheet documentation, 4.17
Spreadsheet file formats, 5.45, 5.46
Spreadsheet imports, 3.4
Spreadsheet transfer, 1.20
Spreadsheet transfers, 3.25
St Venany equations, 5.31
Standard design method, 4.8
Standards Australia AS/NZS 3500.3, 2.15
Storage routing model theory, 5.18
Storage routing models, 1.3
Storage routing run results, 1.30
Storage routing sub-catchments, 2.15
Stormwater ponding, 4.15
Stream routing reach, 2.32
Street drainage requirements, A.5
Sub-catchment property sheet, 1.16
Sub-catchments, 2.11
Subdivision drainage systems, 4.11
Supplementary area, 1.15, 2.11, 5.3, 5.7
Support for DRAINS, 1.4
Surface elevation, 2.4
Options, 1.9
Ordinates, 2.8
Orifice (special) for basins, 2.27
Orifice equation, 5.41
Orifice flow, 5.21
OSD, 2.38
Other services, 2.11
Outlet control for culverts, 5.39
Outlet node property sheet, 2.9
Overbank flow areas, 2.28
Overflow path critical location, 2.21
Overflow path cross-section, 2.20
Overflow route, 2.17
Overflow route data base, 2.53
Overflow route property sheet, 2.17, 2.18, 2.19
Overflow routes, 4.10
Overland flow, 5.7
Part-full flow change, 4.6
Paste data from spreadsheet, 3.30
Paved area, 1.15, 5.3
Performing calculations, 4.2
Pervious area runoff coefficient, 5.17
Pine Rivers chart format, 3.30
friction equations, 5.32
Pipe data base, 2.48
Pipe Data property sheet, 1.17
Pipe property sheet, 2.9, 2.10, A.21
Pipe system hydraulics, 5.30
Pipes, 2.9
rectangular, 2.10
survey data, 2.10
blocking factor, 5.25
inlet capacity, 5.21
on-grade, 2.4
pressure change, 5.33
pressure change coefficient, 2.4
sag, 2.4
Pit blocking factors, 2.5
Pit data base, 2.50
Pit or sump outlet, 2.23
Pits, 2.4
Pits in swales, 5.29
Ponding, 4.15
Pop-up menus, 3.16
Print DRAINS diagram, 3.23
Prismatic open channel, 2.28
property sheet, 2.28
Programming of DRAINS, 4.1
Project menu, 1.6, 2.2
Property balloons, 1.18, 3.16
Property drainage requirements, A.3
Pump link, 2.28
Pump property sheet, 2.28
Quantities, 3.18, 3.21
QUDM design chart format, 3.30
QUDM pressure change coefficient method,
QUDM revision of Ku coefficients, 3.19
Queensland pits, 5.25
Queensland Urban Drainage Manual, 3.18, 4.10,
RAFTS, 5.19
BX parameter, 1.29
DRAINS User Manual
November 2014
Unsteady flow hydraulics, 5.31
Upwelling, 4.4
User-provided inflow hydrograph, 2.7, 3.28
Velocities, 3.28
Velocity-depth product, 1.23
Verification of DRAINS, 4.19, 5.14
Victorian pits, 5.24, 5.27
View menu, 2.2
Viewer setup, A.1
Viewing components and results, A.21
Villemonte equation, 5.32
Warning message, 3.19
Watercom Pty Ltd, 1.1
Watershed Bounded Network Model, 2.16, 5.19
WBNM, 1.3, 5.19
lag parameter, 5.20
stream lag factor, 5.20
Weir (special) for basins, 2.27
Weir coefficient, 2.35
Weir equation, 5.40
X-Y coordinates (cross-section), 2.35
X-Y coordinates (irregular channel), 2.29
X-Y coordinates (overflow route), 2.53
X-Y coordinates (pits and nodes), 3.26
Zoom extents, 3.16
Zoom factor, 3.13
Zoom window, 3.16
Surface overflows, 4.6
Surface roughness factors, 5.8
Surface types, 5.6
Survey data property sheet, 4.9
SWMM, 1.4
Synthetic storms for ERM, 2.44
Tab key operation, 1.13
Tailwater level, 4.6, 5.35
Template file, 3.37
Testing of DRAINS, 4.19, 5.14
Time lag, 2.16
Time of entry, 1.15
Time of flow, 5.7
Time step sensitivity, 4.3
Time steps, 4.3
Title block, 3.16
Toolbar, 1.11, 2.3
Trench widths, 3.22
TRRL method, 5.1
Trunk drainage requirements, A.6
TUFLOW TSI file export, 3.35
Uninstall DRAINS, 1.5
Units, 4.1
Unsteady flow calculations, 4.5
Animation, 1.29
Inputs, 2.17
Unsteady flow examples, 1.26
DRAINS User Manual
November 2014
Was this manual useful for you? yes no
Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Download PDF