The European Soil Erosion Model (EUROSEM

The European Soil Erosion Model (EUROSEM
i
The European Soil Erosion Model
(EUROSEM):
documentation and user guide
Morgan, R.P.C., Quinton, J.N., Smith, R.E., Govers, G.,
Poesen, J.W.A., Auerswald, K., Chisci, G., Torri, D.,
Styczen, M.E., Folly, A.J.V.
Silsoe College
Cranfield University
Silsoe, Bedford MK45 4DT
United Kingdom
Version 3.6
July 1998
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G., POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
ii
Table of contents
CHAPTER 1 INTRODUCTION
1
1.1 GENERAL INTRODUCTION
1.2 CONCEPT OF A EUROPEAN SOIL EROSION MODEL
1.2.1 OBJECTIVES
1.2.2 STRATEGIES FOR MODELLING OVER TIME
1.2.3 STRATEGIES FOR MODELLING OVER SPACE
1
2
2
2
3
CHAPTER 2 MODEL DESCRIPTION
4
2.1 GUIDE TO SYMBOLS
2.2 BASIC CONCEPTS OF DYNAMIC SIMULATION MODELS
2.3 RAINFALL INTERCEPTION
2.4 INFILTRATION
2.5 SOIL SURFACE CONDITION
2.6 SURFACE RUNOFF PROCESSES
2.6.1 FLOW ROUTING
Interrill Flow
Rill Flow
Rill geometry
2.7 EROSION PROCESSES
2.7.1 SOIL DETACHMENT BY RAINDROP IMPACT
2.7.2 SOIL DETACHMENT BY RUNOFF
2.7.3 TRANSPORT CAPACITY OF THE FLOW
Rill Transport Capacity
Interrill Transport Capacity
2.8 CALCULATION OF HILLSLOPE SOIL EROSION
2.8.1 TREATMENT OF RILL FLOW
2.8.2 CHANNEL EROSION
5
6
8
10
13
13
14
15
15
15
17
17
18
19
19
20
20
21
22
CHAPTER 3 DESCRIPTION OF VARIABLES
23
3.1 RAINFALL DATA FILE
3.2 CATCHMENT CHARACTERISTICS FILE
3.2.1 SYSTEM
3.2.2 OPTIONS
3.2.3 COMPUTATION ORDER
3.2.4 ELEMENT-WISE INFO
23
24
24
25
25
25
CHAPTER 4 USING EUROSEM
35
4.1 GETTING STARTED
4.2 SYSTEM REQUIREMENTS
4.3 INSTALLATION
4.4 FILE CHARACTERISTICS
4.4.1 RAINFALL DATA FILE
35
35
35
40
40
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,ii POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
iii
4.4.2 CATCHMENT CHARACTERISTICS FILE
4.4.3 OUTPUT FILES
4.5 RUNNING EUROSEM
43
58
65
CHAPTER 5 SIMULATION TECHNIQUES
70
5.1 HOW TO SIMULATE….
5.1.1 HOW TO SIMULATE DIFFERENT SOIL TYPES
5.1.2 HOW TO SIMULATE THE EFFECT OF PLANTS
5.2 MODEL CALIBRATION
5.2.1 FIELD DATA QUALITY ANALYSIS
5.2.2 ORDER OF CALIBRATION
5.2.3 INFILTRATION PARAMETERS
5.2.4 HYDRAULIC ROUGHNESS
5.2.5 EFFECT OF PARAMETERS RECS
5.2.6 COMPARATIVE SENSITIVITY
70
70
72
73
74
76
76
77
78
81
CHAPTER 6 REFERENCES
82
CHAPTER 7 RELEVANT LITERATURE
88
APPENDIX 1 - DETERMINATION OF TIME-DEPTH PAIRS
1
APPENDIX 2 - DETERMINATION OF SLOPE
3
APPENDIX 3 - ESTIMATION OF MANNING'S 'N'
5
APPENDIX 4 - HYDROLOGICAL PROPERTIES OF SOILS
8
APPENDIX 5 - ROCK FRAGMENTS
12
APPENDIX 6 - SURFACE ROUGHNESS
15
APPENDIX 7 - VEGETATION PROPERTIES
17
APPENDIX 8 - RILL (CONCENTRATED FLOW PATH) MEASUREMENTS
23
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
iii POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
iv
APPENDIX 9 - SOIL ERODIBILITY
26
APPENDIX 10 - CHANNEL DIMENSIONS
30
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
iv POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
v
Forward to the 1998 EUROSEM user guide
This EUROSEM user guide replaces the guide produced in 1994 and represents the 3rd
edition. The guide is, however rather different in that we have incorporated model
documentation and examples of how to set the model up for different land use practices.
Since the 1994 user guide was produced EUROSEM’s use has become more widespread. It is
certainly no longer just a European model! We know of scientists using the model in many
parts of the world, including Australia, Malaysia, Kenya, and Bolivia. The model is also being
increasingly applied to catchment scale studies, with studies completed in the Netherlands and
Austria, and ongoing projects in Costa Rica, Mexico, Nicaragua and South Africa. We would
encourage those of you who are working with the model to let us know of your results. Give
us the address of your web site so we can link it to ours or send it some text to include on
ours.
The version of the model described in this user guide will be the last to run under DOS. We
are currently working on a graphical interface for EUROSEM that will enable it to be run from
Windows 95 or NT. This will also make the model more user-friendly. Other developments
being carried out at present include adding particle size selectivity and a more flexible
watershed representation and linkages with GIS software.
The European Soil Erosion Model (EUROSEM) is a joint effort of many European scientists.
Those who have worked on or assisted with the development of EURSOSEM are:
J. Albaladejo Montoro, V. Andreu, K. Auerswald, W. Blum, Boiffin, H.R. Bork, P. J.
Botterweg, V. Castillo, J.A. Catt, G. Chisci, B. Diekkrüger, W. Everaert, A.Folly, S.
Giakoumakis, G. Govers, B. Hasholt, A.J. Johnston, E. Klaghofer, Y. Le Bissonnais, G.
Monnier, R.P.C. Morgan, T. Panini, J.W.A. Poesen, J.N. Quinton, R.J. Rickson, J.L. Rubio,
V. Sardo, , R.E. Smith P. Strauss, M.E. Styczen, D. Torri, G. Tsakiris, R. Webster, M.
Vauclin and H. Vereeken,.
Financial support has been from Directorate General XII of the Commission of the European
Communities under the Third Environment Programme (Research Grant EV41*1591) and the
STEP Programme (Research Grant PL 900247).
Continued support for work on EUROSEM comes from the Commission of the European
Communities INCO programme (ERBIC18CT960096) and the Environment and Climate
Research Programme (ENV 4-CT97-0697).
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,v POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
1
Chapter 1 INTRODUCTION
1.1 GENERAL INTRODUCTION
The last decade has seen an increasing awareness by scientists, governments and the general
public of the problem of soil erosion within the countries of the European Community. Five
workshops on the topic have been organised and funded by the Commission of European
Communities: at Firenze, 19-21 October 1982 (Prendergast, 1983); Cesena, 9-11 October
1985 (Chisci and Morgan, 1986); Brussels, 2-3 December 1986 (Morgan and Rickson, 1988);
Valencia, 7-9 July 1987 (Rubio and Rickson, 1990); and Freising-Weihenstephan, 24-26 May
1988 (Schwertmann, Rickson and Auerswald, 1989). From the information presented at these
workshops, it is clear that erosion rates on agricultural land in the hilly areas of the
Mediterranean and on sandy, loamy and chalky soils in northern Europe can reach 10-100 t/ha
annually. Such rates often cause pollution and sedimentation downstream as well as reducing
the depth of soil available for future agricultural production. These rates should be compared
with a value of 1 t/ha which is generally considered the maximum allowable for control of
pollution and preservation of the soil resource (Evans, 1981). Some form of soil conservation
or soil protection policy is clearly needed within Europe (Morgan and Rickson, 1990) in which
management decisions are based on physical principles and sound scientific concepts.
The development of policies to control erosion is, at present, hindered because there is no
satisfactory system in Europe for assessing the risk of erosion, predicting erosion rates under
existing conditions or designing and evaluating different soil protection strategies. Methods of
erosion assessment based on scoring systems for rainfall erosivity, soil erodibility, slope and
land use (Auerswald and Schmidt, 1986; Rubio, 1988; Briggs and Giordano, 1992; Jäger,
1994) provide good information on the spatial distribution of erosion risk but only limited data
on erosion rates which cannot be easily validated. Also, they do not produce the information
necessary to design soil conservation measures or evaluate their effect. These deficiencies can
only be overcome by combining erosion risk assessments with predictions from erosion
models.
American scientists developed the Universal Soil Loss Equation (USLE) (Wischmeier and
Smith, 1978) as a technique for assessing erosion and evaluating the likely effects of different
soil conservation practices. Several studies have been carried out to test the applicability of the
USLE to European conditions. They show that great care is required in the selection of input
values for the rainfall (R) (Chisci and Zanchi, 1981; Richter, 1983) and soil erodibilty (K)
(Richter, 1980; De Ploey, 1986; Schwertmann, 1986) factors. Even if the equation could be
transferred successfully to Europe, there is considerable doubt as to whether it would provide
the information that policy makers need. The design of strategies to control pollution
associated with runoff and erosion on agricultural land requires knowledge of what happens in
individual rain storms, often on a minute-by-minute basis, in order to predict the size and
timing of peak discharges of water and sediment from hillslopes to rivers. The USLE cannot
provide this because it predicts only mean annual soil loss.
Another weakness of the USLE is that it predicts erosion by multiplying together values of
factors expressing rainfall, soil, slope, land cover and conservation practice, whereas, in
reality, erosion cannot be represented in this simplistic way (Kirkby, 1980). In order to
provide a better representation of erosion processes, American scientists have concentrated in
recent years on developing more physically-based erosion models such as those used in
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G., POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
2
CREAMS (Knisel, 1980; Foster et al, 1981); ANSWERS (Beasley, Huggins and Monke,
1980) and WEPP (Nearing et al, 1989). Similar models are also being developed in Australia
(Rose et al, 1983; Misra and Rose, 1992).
Soil erosion modelling was discussed at the European Community Workshop held in Brussels,
1986, when Chisci and Morgan (1988) proposed a framework for a European model to be
based on the best European research into erosion processes and their control. One of the
recommendations of the Workshop was that European scientists should "try to develop a new
general erosion model for use in the EC countries for erosion risk evaluation and the design of
erosion control measures" (Chisci, 1988). At the end of the meeting, twelve of the attending
scientists came together for an informal discussion and agreed to form a group dedicated to
the development of such a model. The group obtained funding for the work from Directorate
General XII of the Commission of European Communities, first, under the Fourth
Environmental Programme (1986-1990) and, subsequently, under the STEP Programme
(1989-1992). To date, the work has involved more than 40 scientists from ten European
Community countries, two other European countries and collaboration with the USDA
Agricultural Engineering Research Service, Fort Collins, Colorado, USA. This document
describes the resulting model, known as the European Soil Erosion Model or EUROSEM and
provides a guide to using the model.
1.2 CONCEPT OF A EUROPEAN SOIL EROSION MODEL
1.2.1 Objectives
Given the above background, the following objectives were set for a European soil erosion
model (Chisci and Morgan, 1988). It should
(1) enable the risk of erosion to be assessed;
(2) be applicable to fields and small catchments;
(3) operate on an event basis; and
(4) be useful as a tool for selecting soil protection measures.
In order to meet these requirements, a strategy was needed for modelling erosion in time and
space.
1.2.2 Strategies for modelling over time
Since soil erosion by water is closely related to rainfall and runoff, erosion modelling cannot
be separated from the procedures used to model the generation of runoff and its routing down
a hillside and through the river channel network. American models such as CREAMS and
WEPP are based on a continuous simulation approach in which changing soil moisture
conditions are modelled from daily calculations of the soil water balance. In this way, the
conditions at the start of each rainstorm are predicted. The problems with continuous
simulation models are that they require a large amount of input data on changing climatic and
land use conditions over a year, they are highly sensitive to the modelling of evapotranspiration and dynamic properties of the soils and they yield predictions for a large number
of events that produce only small amounts of runoff and soil loss.
Since measurements of soil erosion on hillside plots and in small watersheds in Europe show
that most erosion takes place in two or three storms each year (Sfalanga and Franchi, 1978;
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,2 POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
3
Boschi and Chisci, 1978; Richter, 1979; Raglione, Sfalanga and Torri, 1980; Boschi, Chisci
and Ghelfi, 1984; Tropeano, 1984; Chisci, Boschi and Ghelfi, 1985), it was considered more
important to develop a model which could be applied to these events. This approach requires
the starting conditions for each storm to be specified as data inputs.
Although both CREAMS and WEPP can be run for individual storms, they simulate only total
storm soil loss, and assume a steady flow profile along the surface. They do not model peak
sediment discharge or treat the pattern of events within a storm, or provide a sediment graph
showing the pattern of sediment discharge over time, information which is useful for looking
at potential pollution loadings from sediment fluxes into water courses. Especially for
catchments where one or two events define most of the annual soil loss, steady flow is rarely
achieved, and the WEPP methodology will be inappropriate. Given the significance of the offsite effects of erosion within Europe, it was decided that within-storm modelling of erosion for
selected storms was a more important objective than the between-storm modelling required for
continuous simulation. Within-storm modelling is also more compatible with the equations
used in process-based models to describe the mechanics of erosion. These equations are
strictly applicable to instantaneous conditions and they cannot be applied to average conditions
without loss of accuracy. Applying them to conditions averaged over one minute is thus more
acceptable than using them for conditions averaged over one hour or more.
1.2.3 Strategies for modelling over space
Many of the factors that influence erosion, particularly soil, slope and land use, have
considerable spatial variability and cannot be described by a single average value, even over
areas as small as one field. Lumped models, which treat an area as a single unit of uniform
characteristics, are not appropriate. If this spatial variability is to be taken into account, a
distributed model must be used. In such a model, an area is divided into sub-units, each having
uniform characteristics of slope, soil and land cover. These sub-units are then arranged in
sequence to form a cascade through which water and sediment movement can be routed from
top to bottom of the hillsides and from upstream to downstream along the river channels. Such
a distributed approach is adopted for EUROSEM, based on the KINEROS model structure
(Woolhiser, et al., 1990).
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,3 POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
4
Chapter 2 MODEL DESCRIPTION
EUROSEM is developed as a distributed event-based model that, in addition to predicting
total runoff and soil loss, produces hydrographs and sediment graphs for each event. The flow
chart for EUROSEM is presented in Figure 2.1.
Soil surface
conditions
Rainfall
Interception
Vegetation
Storage
Surface
depression
storage
Throughfall
Leaf Drainage
Detachment by
raindrop impact
Stemflow
Net Rainfall
Surface water
depth
Infiltration
Hortonian overland
flow
Flow transport
capacity
Detachment
by flow
Sediment
transport/
deposition
Total detachment
Figure 2.1. Flow chart of the European Soil Erosion Model
EUROSEM has a modular structure with each module being developed in as much detail as
the existing level of knowledge permits. This structure will enable continuous improvements to
be made in the light of new research. The model deals with:
•
the interception of rainfall by the plant cover;
•
the volume and kinetic energy of the rainfall reaching the ground surface as direct
throughfall and leaf drainage;
•
the volume of stemflow;
•
the volume of surface depression storage;
•
the detachment of soil particles by raindrop impact and by runoff;
•
sediment deposition; and
•
the transport capacity of the runoff.
Algorithms also deal with frozen soils and stoniness.
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,4 POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
5
2.1 GUIDE TO SYMBOLS
A
a
B
b
cross-sectional area of flow
coefficient in flow rating equation
saturation deficit of the soil
exponent in relationship between soil detachment rate and depth of
surface water layer
BW
bottom width of channel
C
sediment concentration
c
coefficient in relationship between transport capacity of flow and unit
stream power
COH
cohesion of the soil at saturation as measured with a torvane
COV
percentage vegetation cover
D
depth between average height of an interrill surface and the base of an
adjacent rill
D50
median particle diameter of the soil
DEPNO number of depressions along transect of roughness measurement
DET
rate of soil particle detachment by raindrop impact
DETpave rate of soil particle detachment by raindrop impact allowing for nonerodible (paved) surfaces
DF
net rate of soil particle detachment by flow
DS
depth of surface depression storage
DT
direct throughfall depth
Eq
erosive ability of flow
e
net rate of erosion of the soil bed per unit length
F
rainfall depth infiltrated by the soil
f
infiltration rate
fc
maximum rate of infiltration
G
effective net capillary drive
h
depth of surface water
IC
depth of rainfall intercepted by the vegetation
ICmax
maximum depth of interception storage
ICstore
depth of interception storage
j
exponent in equation describing the profile of a rill side wall and adjacent
interrill area
k
soil detachability per unit of rainfall energy
Ks
saturated hydraulic conductivity
Ksroc
saturated hydraulic conductivity allowing for rock fragments in the soil
Ksveg
saturated hydraulic conductivity allowing for effects of vegetation cover
KE
kinetic energy of rainfall
LD
depth of leaf drainage
m
exponent in flow rating equation
n
Manning‘s roughness coefficient
NR
net rainfall depth at the ground surface
P
wetted perimeter
PA
average acute angle of plant stems to ground surface
PAVE
proportion of the surface area occupied by non-erodible (paved) surfaces
PBASE
proportion of the surface area occupied by basal area of the plant stems
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,5 POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
6
PH
Q
q
qc
qs
R
Rcum
Ri
r
RD
RECS
ROC
RR
S
Si
Smax
SF
Su
Sucrit
TC
t
tp
TIF
u
ugcrit
ugmin
vs
w
wir
x
z
β
η
φ
ψ
effective height of the plant canopy
discharge
rate of lateral inflow of discharge per unit length
rate of lateral inflow of discharge per unit length of channel
rate of lateral sediment inflow per unit length
rainfall depth
cumulative rainfall depth during the storm
rainfall rate or rainfall intensity
hydraulic radius
rill depth
infiltration recession factor
proportion of the soil by volume occupied by rock fragments
roughness ratio
slope
initial value of relative saturation of the soil
maximum relative saturation of the soil
depth of stemflow
unit stream power
critical value of unit stream power
sediment concentration of flow at transport capacity
time
time to ponding
depth of temporarily intercepted throughfall
flow velocity
value of critical grain shear velocity of flow for rill initiation
minimum value of critical grain shear velocity necessary to detach soil
particle by flow
settling velocity of soil particles in the flow
flow width
width between centre line of a rill and centre line of the interrill area
distance
value of z when the side slope of a rill is expressed as a gradient, i.e. 1:z
efficiency coefficient for detachment of soil particles by flow
exponent in relationship between transport capacity of flow and unit
stream power
soil porosity
soil matric potential
2.2 BASIC CONCEPTS OF DYNAMIC SIMULATION MODELS
The model computes soil loss as a sediment discharge, defined as the product of the rate of
runoff (m3 s-1) and the sediment concentration in the flow (m3 m-3), to give a volume (or
mass) of sediment passing a given point in a given time. The computation is based on the
dynamic mass balance equation (Bennett, 1974; Kirkby, 1980; Woolhiser, Smith and
Goodrich, 1990):
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,6 POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
7
∂
( AC) ∂ (QC )
∂t
+
∂x
− e ( x, t ) = q s ( x, t )
(1)
in which C = sediment concentration (m3 m-3),
A = cross sectional area of the flow (m2),
Q = discharge (m3 s-1),
qs = external input or extraction of sediment per unit length of flow (m3 s-1 cm-1),
e = net detachment rate or rate of erosion of the bed per unit length of flow
(m3 s-1 cm-1),
x = horizontal distance, and
t = time.
This equation is illustrated in Figure 2.2 with respect to channel flow where qs represents
lateral inflows of sediment from the base of adjacent hillsides. When applied to overland flow
over hillslopes, qs becomes zero.
q
qs
water surface
A +δ A
A
Q
e
Q +δ Q
flow
depth
soil surface
δx
Figure 2.2. Representation of the mass balance equation for erosion (equation 1)
The term, e, in equation (1) is defined by two major components:
e = DET + DF
where
(2)
DET = the rate of soil particle detachment by raindrop impact, and
DF = the balance between the rate of soil particle detachment by the flow and the
particle deposition rate.
Since EUROSEM is an erosion model, it must be attached to a hydrological model from which
values of surface runoff Q(x,t) and A(x,t) can be generated. These are obtained by numerical
solution of the dynamic mass balance equation for water, analogous to Eq. (1):
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,7 POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
8
∂A ∂ Q
+
= r( t ) − f ( t )
∂t ∂ x
(3)
where r(t) is the rainfall rate less the interception
f(t) is the local infiltration rate.
EUROSEM is linked to the KINEROS model (Woolhiser, Smith and Goodrich, 1990) which
is an event-oriented, physically-based distributed model that numerically solves Eq. (3) using a
kinematic wave assumption for a fixed relation Q(A) (Woolhiser and Liggett, 1967;
Woolhiser, 1969). It has also been linked with the MIKE SHE model (Danish Hydraulic
Institute, 1993) which is a continuous simulation model and an extension of the original
Systéme Hydrologigue Européen (SHE) model (Danish Hydraulic Institute, 1985; Abbott et
al., 1986).
KINEROS generates runoff as infiltration-excess using the infiltration model of Smith and
Parlange (1978) . The combined EUROSEM-KINEROS model simulates soil erosion by
raindrop impact and infiltration-excess overland flow at a field and small catchment scale on a
minute-by-minute basis. It does not simulate saturation excess runoff from perched aquifers,
which is inherently a longer term process.
The catchment modelling approach, based on KINEROS, is to take a small watershed and,
using information on slope, soils and land cover, divide it into a series of units or elements
which are, more or less, homogeneous. These units can be planes, representing sub-divisions
of the hillslopes, or channels, representing separate channel segments. The units are then
linked as a series of cascading planes and channels. For numerical solution, each unit is also
divided into a series of computational nodes. The model then calculates the amount of runoff
and sediment produced at each node in each time step and routes them over the land surface of
each unit and then from one unit to another over the cascade and through the channel network
to the catchment outlet. An example of how to represent a catchment in this way is contained
in chapter 4.
The various components of the model are now described in turn, beginning with the rainfall
input.
2.3 RAINFALL INTERCEPTION
Rainfall input to the model is in the form of a depth R(mm) for each time step during a storm.
From this input, rainfall intensity Ri (mm hr-1) and rainfall volume (m3) (i.e. depth x area) are
calculated. Account is also kept of the cumulative rainfall (m) received during the storm.
On reaching the canopy of the vegetation, the rainfall is divided into two parts. These are that
reaching the soil surface as direct throughfall (DT), falling either on open ground or passing
through gaps in the canopy, and that which strikes the vegetation cover. The division is based
on the simple relationship:
IC = R * COV
where
IC
(4)
= the depth of rainfall intercepted by the vegetation, and
COV = the percentage cover of the vegetation.
An initial proportion of the intercepted rainfall is stored on the leaves and branches of the
vegetation. This is termed the interception store. The rainfall held in this store does not reach
the soil surface and therefore is unavailable for infiltration or runoff. In many erosion models,
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,8 POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
9
this interception store is either ignored, as in CREAMS, or is considered as a depth which has
to be filled before rain is allowed to pass from the vegetation canopy to the ground, as in
KINEROS. This last approach means that no rain reaches the soil surface from the canopy
until the interception store is full. EUROSEM adopts a more dynamic approach which allows
rainfall to pass from the canopy to the ground at the same time as the interception store is
being filled. This means that some transfer of water from the canopy will take place right from
the start of the storm. The volume of the interception store (ICstore) for a time step (t) is
modelled as a function of the cumulative rainfall (Rcum) from the start of the storm, using the
exponential relationship proposed by Merriam (1973):
ICstore = ICmax [1 − exp( Rcum / ICmax )]
(5)
where ICmax = the maximum volume of the interception store for the given crop or
vegetation cover.
This approach is shown diagrammatically in Figure 2.3.
Figure 2.3. Representation of rainfall interception pattern by plant canopy. (a) interception store must be filled
before rain is allowed to reach ground surface; (b) in EUROSEM, rainfall reaches the ground while the
interception store fills exponentially.
Values of ICmax depend upon the plant species, which affects the size, shape and roughness
of the leaves, as well as on the plant density, the growth stage of the vegetation and the wind
velocity.
The rainfall which is intercepted by the canopy and not held in the interception store becomes
temporarily intercepted throughfall (TIF) and reaches the ground surface as either stemflow
(SF) or leaf drainage (LD). The volume of stemflow (m3) is modelled as a function of the
average acute angle (PA; degrees) of the plant stems to the ground surface, using equations
developed in laboratory experiments by van Elewijck (1989a; 1989b). These equations have
been modified by assuming that a maximum of half the volume of temporarily intercepted
throughfall is available for stemflow, to give:
SF = 0.5 TIF (cos PA . sin2 PA)
(6)
for grasses, and
SF = 0.5 TIF .cos (PA)
(7)
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,9 POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
10
for other plant species.
Conceptually, equations (6) and (7) describe the relationship between the diameter of the
catching surface (stems and leaves) and the median volume drop diameter of the raindrops.
Where, as with grasses, the mean diameter of the catching surface is less than the drop
diameter, gravity, expressed by sin PA, plays an important role in determining the volume of
stemflow. With thicker catching surfaces, stemflow volume depends only on the projected
length of the stems or leaves, as expressed by cos (PA).
The difference between the volume of the temporarily intercepted throughfall and the volume
of stemflow comprises leaf drainage, i.e. that component of the rainfall which reaches the soil
surface as individual drips from the leaves. The net rainfall at the ground surface (NR), which
is therefore available for infiltration, is the summation of the direct throughfall, stemflow and
leaf drainage. These relationships are summarised as follows:
LD = TIF - SF
(8)
NR = DT + LD + SF = R - Icstor
(9)
2.4 INFILTRATION
Infiltration is accounted for in the KINEROS part of the model. A detailed description can be
found in Woolhiser, Smith and Goodrich (1990), so only a brief account of the procedure is
given here. The infiltration equation used (Smith and Parlange, 1978) is:
fc = Ks
exp( F / B )
exp( F / B ) − 1
(10)
where fc = the maximum rate at which water can enter the soil, which is known as the
infiltration capacity (cm min-1),
Ks = the saturated hydraulic conductivity of the soil (cm min-1),
F = the amount of rain already absorbed by the soil (cm), and
B = an integral capillary and water deficit parameter of the soil.
The term B is obtained from:
B = G (θs - θi)
where G
(11)
= the effective net capillary drive,
θs = the maximum value of water content of the soil, and
θi = the initial value of soil water content (cm3 cm-3).
The term G is a conductivity-weighted integral of the capillary head of the soil, defined as:
1
G=
Ks
in which
ψ
0
∫ K (ψ )dψ
(12)
−∞
= the soil matric potential (-), and
K(ψ) = a hydraulic conductivity function.
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
10POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
11
G is essentially a property of the soil with units of length and is conceptually equivalent to a
value of effective capillary head. Typical values for G, Ks and θs are given in appendix 4 for
a range of soil types.
KINEROS models infiltration through a single soil layer. The process comprises three stages.
Initially, infiltration is limited by the rainfall intensity and F is accumulated at the rainfall rate;
in this stage, the infiltration rate (f) at time t equals the rainfall rate (r), i.e.
f(t) = ri(t)
(13)
From the time that infiltration capacity is reached which is equivalent to the time of ponding,
equation (10) determines the infiltration rate, so that:
f(t) = fc
(14)
The relationships for the first two stages are illustrated in Figure 2.4. The third stage begins
when the rain ceases or the rainfall intensity falls below the infiltration capacity. Infiltration is
then modelled as fc times the proportion of the soil surface covered by (flowing) water. This is
achieved through the use of the parameter, RECS, which describes the roughness of the soil
surface and represents, conceptually, the local maximum average depth of flow (h) when the
surface is just completely covered by water. A high value of RECS represents a rough surface,
such as one recently ploughed with a mouldboard, and a low value represents a smooth
surface, such as a recently-prepared seed bed. The procedure assumes that the proportion of
the soil surface covered by flowing water decreases in direct proportion to the decline in mean
flow depth below RECS:
f ( t ) = f ( t −1 )
h
RECS
(15)
in which h is the mean flow depth (cm).
Where Ks is based on measurements made in the field with an infiltrometer, its value will take
account of the effects of rock fragments or stones within the soil profile and the effect of any
crop or vegetation cover on the surface. Where this is not the case, the values for bare soil Ks
are modified within the model. Rock fragments effect infiltration in two ways. The first is that
they reduces the effective overall storage in porosity (θs - θi). The KINEROS model modifies
the parameter B in equation (10) to account for the presence of rock fragments (ROC) using
the relationship (Woolhiser, Smith and Goodrich, 1990):
Broc = B (1.-ROC)
where Broc = the parameter B modified for rock fragments, and
(16)
ROC = the fraction of the soil composed of rock fragments, expressed as a volume
between 0 and 1.
The second way in which rock fragments effect infiltration into soils is through their position
on the surface of the soil (Poesen and Ingelmo-Sanchez, 1992; Poesen et al., 1994). Those
rocks which are embedded into a surface seal (i.e. a top layer with pore spaces due to the
packing of primary particles) will reduce infiltration. Those which sit on the surface will
protect surface structure, and promote infiltration. EUROSEM models the first case using the
equation:
Ksroc = Ks (1-PAVE)
(17)
and the second using the equation:
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
11POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
12
Ksroc = Ks (1+PAVE)
(18)
where Ksroc = a modified value of saturated hydraulic conductivity (cm/min), and
PAVE = aerial rock fragment cover.
Figure 2.4. Representation of the infiltration model (equation 9) used in KINEROS and EUROSEM. The
infiltration rate (f) equals the rainfall rate (r) until ponding occurs (Fp). After ponding, the infiltration rate is
controlled by the infiltration curve and is asymptotic to a final rate which is equal to the effective saturated
hydraulic conductivity.
The infiltration capacity of a given soil is affected by the type and density of the vegetation
cover, as demonstrated by the numerous studies reviewed by Dunne (1978) and Faulkner
(1990). The effect is not dealt with explicitly within KINEROS and the research base for
modelling it is rather sparse. Thornes (1990) proposes that infiltration capacity increases
exponentially with increasing percentage vegetation cover as a function of increases in organic
matter and decreases in the bulk density of the soil. Such a relationship is similar to that
developed by Holtan (1961) to express the saturated hydraulic conductivity of the soil as a
function of the percentage basal area of the vegetation. Based on his work, the following
equation is used in EUROSEM to modify the saturated hydraulic conductivity value of the
soil:
Ksveg = K s
1
1 − PBASE
(19)
where Ksveg is the saturated hydraulic conductivity of the soil with the vegetation,
Ks is the saturated hydraulic conductivity of the bare soil, and
PBASE is the total area of the base of the plant stems expressed as a proportion
(between 0 and 1) of the total area of the plane.
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
12POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
13
2.5 SOIL SURFACE CONDITION
The roughness of the soil surface, including roughness brought about by tillage, affects runoff
and erosion, and determines the volume of water that can be held on the surface as depression
storage. The basis for modelling depression storage is extremely limited with only a few
studies available to quantify the depths of water likely to be involved (e.g. Reid, 1979; Evans,
1980). Depression storage is not modelled in KINEROS and is ignored in most hydrological
models. However, it is included in EUROSEM where it can be used to describe one of the
effects of tillage.
Boiffin (1984) categorises four grades of surface roughness (0 - 1.2 cm; 1.2 - 2.0 cm; 2.0 - 3.0
cm; and > 3 cm micro-relief) in relation to tillage practices on loamy soils. This is part of a
classification of the state of the soil surface for predicting the likelihood of erosion (Boiffin,
Papy and Monnier, 1988; Auzet et al., 1990). These values cannot be used directly as
indicators of depression storage, however, because the shallower depressions on any surface
will fill, overflow and produce interconnecting runoff paths whilst the deeper depressions are
still filling. Thus only a proportion of the depression depth constitutes effective depression
storage. Few studies exist as a basis for estimating what that proportion might be.
The roughness of the soil surface is expressed in EUROSEM by a roughness measure (RFR)
defined with respect to the ratio of the straight line distance between two points on the ground
(X) to the actual distance measured over all the microtopographic irregularities (Y):
RFR =
Y−X
* 100.
Y
(20)
This is illustrated in figure 2.5 and the procedure for measurement is described in Appendix 6.
This mean height is converted into a surface storage depth, D, using a regression equation
from Auerswald (1992):
D = exp( − 6.66 + 0.27 * RFR)
(21)
X
Y
Figure 2.5. Illustration of the parameterisation of surface roughness in EUROSEM.
2.6 SURFACE RUNOFF PROCESSES
The basis for describing flow velocity within an erosion model is rather limited. Savat (1980)
proposes algorithms for obtaining best estimates of mean velocity for four different flow
conditions: smooth laminar, rough laminar, smooth turbulent and rough turbulent. The
KINEROS model also allows transition between early laminar flow and turbulent flow at
larger discharges. However, because of the disturbance by raindrops and the difficulty in
experimentally detecting the early laminar flow regime, EUROSEM uses equations for
turbulent flow only. This is the type of flow most likely to occur in the storms for which
EUROSEM is designed. The mean velocity of this type of flow without sediment is described
by the Manning equation as indicated below. Several studies (Emmett, 1970; Pearce, 1976;
Morgan, 1980) indicate that values of Manning‘s n for overland flow are about an order of
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
13POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
14
magnitude higher than those pertaining to channel flows because most of the vegetation and
rock fragments project rigidly above the flow. Although the boundary resistance is similar to
that observed in open channel flow, the form resistance is much higher (Thornes, 1980). This
should result in increasing flow depth and decreasing velocity. Sometimes this can be offset,
however, by surges in velocity between the roughness elements and vortex erosion upslope
and downslope of the elements (Babaji, 1987) which may, in turn, increase erosion (De Ploey,
Savat and Moeyersons, 1976). If sediment in the flow also increases the velocity (Govers,
1989; 1990), actual flow velocity will be determined by the relative balance between this
velocity increase and the retarding effects of roughness. It is not possible from present
knowledge to model this balance.
Considering all the above points, it would seem that the best estimate of flow velocity is
obtained using normally accepted values of Manning‘s n, i.e. without any increase in value for
shallow overland flow. If this leads to an overestimation of velocity for clear flow, it may, at
the same time, allow for likely increases in velocity due to surges and the presence of sediment
in the flow. The Manning equation is therefore used in EUROSEM to calculate flow velocity
for shallow overland flow. Tables for estimating Manning n values are found in appendix 3.
Use of Manning's equation for channel flow is perhaps less controversial because of its wide
use by engineers. Also, the sediment concentrations are much lower than in overland flow so
their effect on velocity will be much less. Alternatives would be to use equations involving the
Chezy or Darcy-Weisbach friction coefficients but values of these for a range of soil,
microtopographic and vegetation conditions are not so readily available as values of
Manning‘s n. A model based on these alternatives would therefore suffer from a lack of
suitable input data.
2.6.1 Flow Routing
When the net rainfall intensity at the ground surface exceeds the infiltration rate and surface
depression storage is satisfied, the excess comprises surface runoff. In the KINEROS model,
runoff along a slope for a plane element, a rill, or a channel is viewed as a one-dimensional
surface flux in which discharge (Q) is related to the hydraulic radius (r). Hydraulic radius is
defined as the area A divided by the wetted perimeter, p. The rating equation is based on the
normal flow equation, which in general may be written:
u = α r m−1
(22)
where, based on the Manning equation for flow velocity,
r = hydraulic radius,
α = (s)0.5/n,
n = Manning roughness value, and
m = 5/3.
In terms of discharge Q, with Q = uA, the general rating equation can be written
Q = uA = α pr m
(23)
This equation is combined with the continuity equation (3) to give:
p∂ r α p m−1 ∂ r
+
ρ
= q ( x ,t )
∂t
m
∂x
(24)
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
14POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
15
Interrill Flow
For shallow flow surface flow, a unit width is used for computations, so p = 1 and r = depth
h, so that the discharge rating Eq. (23) becomes
Q = α hm
(25)
In this case Eq. (24) becomes, for a unit width (p = 1):
∂ h α m−1 ∂ h
+ h
= q( x , t )
∂t m
∂x
(26)
where for interrill areas, q = Ri - f is the lateral inflow rate, or "rainfall excess." In
KINEROS, the kinematic wave equations (23) or (26) are solved numerically for a finite
difference grid by a four-point implicit method using the Newton-Raphson technique (Pearson,
1983; Woolhiser, Smith and Goodrich, 1990). The upslope boundary condition for the depth
of flow (h) at x = 0 and t = 0 is either 0 or is equal to the depth of runoff from an upslope
contributing plane.
Rill Flow
A similar procedure is adopted for routing flow in rills or channels, where the relevant rating
equation is Eq. (24). The term q(x,t) in Eq. (24) becomes the unit discharge into the rills
from interrill contributions. There are 3 cases for the surface topography of a surface element:
a. The surface may contain no rills, but have some surface irregularities.
b. The surface may be rilled, with interrill flows routed toward the rills as described by
Eq. (26)
c. The surface may be furrowed, or have very dense rills, such that interrill routing is
illogical due to the short distance traversed by interrill flows.
For case (a), interrill flow is assumed over the entire element, and the flow direction is directly
down the plane. Interrill splash and transport relations are used. Figure 2.6 illustrates the
abstracted geometry used to describe a rilled surface [option (b), above]. Flow must slope
toward the rills, and for any element their spacing is assumed to be uniform. Interrill slope is
taken as the vector sum of the slope along the rills and the slope of the surface in a direction
normal to the rills. When distance of interrill flow is less than 1 m, interrill routing is
abandoned, and rain flow transport concentrations are used for interrill sediment
concentrations. Runoff is not routed, but rill input rate q is taken as the rainfall excess rate
times the interrill flow distance. The reader is referred to the KINEROS manual (Woolhiser,
Smith and Goodrich, 1990) for further details of the surface flow equations.
Rill geometry
Figure 2.7 is a general definition equation for the geometry of a rill. The rill is essentially a
trapezoid, with side walls having slopes of 0 (vertical) or greater. The interrill area must have
a slope toward the rill. For the furrow case, the rill spacing is equal to furrow spacing, and the
general furrow depth and sideslope may be specified.
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
15POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
16
Figure 2.6. Geometric abstraction for flow on a rilled surface element.
W
L
w
r
W
d
When furrows are overtopped, the flow in the rill area and the overflow area are treated as
having equal water elevation, but different velocities owing to the different hydraulic radii of
the rill and the overbank areas.
Figure 2.7. Representation of the hydraulic geometry in the rill profile : wir = the width between the centre
line of the rill and the centre line of the interrill area, d = the depth between the base of the rill and the
average height of the interrill surface, z = the side slope of the rill, expressed as the ratio of horizontal to
vertical component
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
16POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
17
2.7 EROSION PROCESSES
2.7.1 Soil detachment by raindrop impact
Soil detachment by raindrop impact is considered for both direct throughfall and leaf drainage.
In the present version of EUROSEM, soil detachment is related to the kinetic energy of the
rain. If this proves unsatisfactory, trials will be conducted to see whether relating detachment
to the sum of the squared momentum of each raindrop, as proposed by Styczen and HøghSchmidt (1988), gives better results.
The rainfall energy reaching the ground surface as direct throughfall (KE(DT); J m-2 mm-1) is
assumed to be the same as that of the natural rainfall. It is estimated as a function of rainfall
intensity (Ri , mm hr-1) from the equation derived by Brandt (1989), assuming that the
raindrop size distribution follows that described by Marshall and Palmer (1948):
KE(DT) = 8.95 + (8.44 log r)
(27)
The energy of the leaf drainage (KE(LD); J m-2 mm-1) is estimated from the following
relationship developed experimentally by Brandt (1990):
KE(LD) = (15.8 . PH0.5) - 5.87
(28)
where PH = the effective height of the plant canopy (m).
This relationship is considered valid because the drop-size distribution of leaf drainage has
been shown to have a consistent median drop diameter of about 4.8 mm, regardless of the type
of plant (Brandt, 1989), which means that the mass of a unit of leaf drainage can be taken as
constant. Variations in the energy of leaf drainage are therefore a function of the impact
velocity of the raindrops which depends on the height of fall. The model sets the kinetic
energy of leaf drainage to zero when the canopy height is less than 14 cm to avoid the negative
values predicted by equation (28).
The total kinetic energy of the rainfall can be calculated by multiplying the energies obtained
from equations (27) and (28) by the respective depths of direct throughfall and leaf drainage
received and summing the two values. This calculation is made in EUROSEM for every
increment of the rainstorm.
Soil detachment by raindrop impact (DET; g m-2) is calculated from the equation:
DET = k (KE) e-bh
where
(29)
an index of the detachability of the soil (g J-1),
KE
=
total
kinetic
energy
of
the
rain
(J
m-2),
b
=
an
exponent,
and
h = the depth of the surface water layer (mm).
k
=
the
Soil detachability depends on soil texture. Values for the detachability index, k, are given in
appendix 9. They are taken from graphs and tables presented by Poesen (1985), Govers
(1991) and Everaert (1992), and corrected according to the procedure proposed by Poesen
and Torri (1988) to allow for differences in the size of the measuring plots used by the various
researchers.
Although Torri, Sfalanga and Del Sette (1987) show that the value of the exponent, b,
depends on soil texture, insufficient experimental work is available to define the relationship
over a wide range of soils. A working value of 2.0 is therefore proposed as representative of a
range of values between 0.9 and 3.1. The relationship assumes that soil detachment by
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
17POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
18
raindrop impact decreases exponentially as the water depth increases. This occurs because the
raindrop energy is absorbed by the water surface instead of the soil and because the water
layer resists the development of lateral water jets set up within the splash crater.
Where non-erodible surfaces, such as rock outcrops, desert pavements, concrete and tarmac,
occur within the element, the detachment rate is modified by:
DETpav = DET (1 - PAVE)
where
(30)
DETpav = the detachment rate allowing for the non-erodible surfaces, and
PAVE = the proportion (between 0 and 1) of the element covered by non-erodible
surfaces
Initial Condition for Sediment Concentration
Even before runoff commences, surface soil is being disturbed by the energy of raindrops, so
that there are soil particles in the very first runoff water. Moreover, even if the flow is below
the threshold of transporting capacity, rainsplash can cause a concentration to remain in the
flowing water, as discussed below.
Since during a rainstorm, splash erosion will already be taking place when runoff begins, the
initial sediment concentration in the runoff cannot be taken as zero. Based on an analysis of
Eq (1) at the time of ponding (tp) or x=0 and A=0, the sediment concentration (C) at tp is
calculated from:
C( t p ) =
DET
q + vs
(31)
where vs is the particle settling velocity (m s-1).
This equation is also used to determine the boundary condition at the upper end of a slope
plane when there is no input of runoff or sediment from above.
The influence of slope on soil particle detachment is neglected in EUROSEM because of the
difficulty in characterising the ‘effective slope’ which needs to be measured over distances of
several drop diameters from the point of raindrop impact. It is not the same as the general
surface slope, which is generally smaller. Further work is required on how to determine the
‘effective slope’ parameter, which will need to take account of surface roughness and the
angle of internal friction of the soil (Torri and Poesen, 1992).
2.7.2 Soil Detachment by Runoff
Soil detachment by runoff is modelled in terms of a generalised erosion-deposition theory
proposed by Smith et al (1994). This assumes that the transport capacity concentration of the
runoff (TC) reflects a balance between the two continuous counteracting processes of erosion
and deposition. It implies that the ability of flowing water to erode its bed is independent of
the amount of material it carries and is only a function of the energy expended by the flow,
particularly the shear between the water and the bed, and the turbulent energy in the water.
The implication seems entirely reasonable in the light of work by Rauws and Govers (1988)
which shows that sediment detachment by overland flow is related to the grain shear velocity
of the flow, and studies by Govers (1987) which indicate that the initiation of soil particle
movement is associated with turbulent perturbations within the flow. The erosion rate of the
flow (Eq) is continually accompanied by deposition at a rate equal to wCvs, where w is the
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
18POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
19
width of flow, C is the sediment concentration in the flow and vs is the settling velocity of the
particles. This condition can be expressed as:
DF = Eq - w C
(32)
where DF = the net detachment rate of soil particles by the flow (equation 2).
According to the generalised theory, the transport capacity concentration (TC) represents the
sediment concentration at which the rate of erosion by the flow and accompanying rate of
deposition are in balance. In this condition, DF, is zero and Eq equates to the deposition rate
(w.TC.vs). A general equation for soil detachment by flow and deposition during flow,
expressed in terms of settling velocity and transport capacity, then becomes:
DF = w vs (TC - C)
(33)
This equation, however, assumes that the soil particles are loose so that processes are
reversible, whereas, in reality, detachment will be limited by the cohesion of the soil material.
The pick-up rate for cohesive soil therefore needs to be reduced by a coefficient whenever C is
less than TC. This coefficient is equivalent to the efficiency functions proposed by Rose et al
(1983) and Styczen and Nielsen (1989) in their modelling of soil detachment by flow.
Equation (33) becomes:
DF = β w vs (TC - C)
(34)
where β = a flow detachment efficiency coefficient. By definition, β is 1 when DF is negative
(deposition is occurring), and β is less than one for cohesive soils when DF is positive (TC
greater than C). To calculate β for cohesive soils, the concentration capacity deficit is first
expressed in relative terms: C* = (Cmx - C)/Cmx. Cohesion as measured by a Torvane in kPa
under saturated conditions may be represented by J. For J less than 1, β is assumed = 0.335.
For larger values of J, β is reduced exponentially:
β = 0.79e −0.85 J
(35)
When TC is zero and DET has a value due to rainfall energy, there will be a value of C
obtained such that, using Eq (2) with e = 0, DET = wvsC. The concentration in flow will be
C = DET/wvs . This has been termed "rain flow transportation" (Moss et al. 1979).
2.7.3 Transport Capacity of the Flow
The capacity of runoff to transport detached soil particles is expressed in terms of a
concentration, TC. For flow in rills, it is modelled as a function of unit stream power, using a
relationship based on the work of Govers (1990) which showed that the transporting capacity
of overland flow could be predicted from simple hydraulic parameters. For interrill flow, TC
is modelled as a function of modified stream power, based on the experimental work of
Everaert (1991).
Rill Transport Capacity
Simple stream power is the hydraulic variable on which rill TC is based, and is defined as:
ω= u S
(36)
Based on this variable, Govers(1990) found that TC could be expressed for any particle size
(ranging from 50 to 150 µm) as follows:
TC = c (ω - ωcr)η
(37)
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
19POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
20
where S
=
slope,
u
=
mean
flow
velocity
(cm/s),
ωcr = critical value of unit stream power (= 0.4 cm/s), and
c,η = experimentally-derived coefficients depending on particle size.
Further analysis has shown that one can estimate c and η as follows:
c = [(d50 + 5)/0.32]-0.6
(38)
η = [(d50 + 5)/300] 0.25
These relationships were derived from experiments carried out on a range of materials with a
median grain size (d50) from silt to coarse sand, slopes from 1 to 12 per cent and discharges
from 2 to 100 cm3 cm-1 s-1. They are valid for sediment concentrations up to 0.32 which
seemed to be an upper limit obtained in the experiments beyond which further increases in
stream power caused no further increase in sediment concentration. The need to insert a
critical value for unit stream power of 0.4 cm/s means that the equations cannot be used at
very low unit stream powers and they are probably not valid when the unit stream power falls
below 0.7 cm/s.
Interrill Transport Capacity
Experimental work was also done on shallow interrill flow by Everaert (1991), who used a
modified stream power based on work of Bagnold (1966):
Ω = ω1.5/h2/3
(39)
Everaert also used a range of particle sizes, from 33 to 390 µ. Fitted to this data, EUROSEM
uses the following interrill flow equations:
TC =
(
)
b
0.7 / n
Ω − Ωc )
−1
(
ρs q
n
(40)
where n is 5 and b is a function of particle size:
b = (19 - d50/30.)/104
(41)
Ω c is a critical Bagnold stream power, defined as
Ωc
(0.5u u )
=
2 3/ 2
*c
2/3
h
(42)
using critical stream power,
u*c =
yc (ρ s − 1)gd50
(43)
in which yc is the modified Shields' critical shear velocity (White, 1970) based on particle
Reynolds number.
2.8 CALCULATION OF HILLSLOPE SOIL EROSION
The numerical solution of Eq. (24) or (26) provides an array of values of Q, A, u, at each
finite difference node point, and these values, along with the array of values of C at each node
[Ci ; i=1, N] plus the upstream condition Ci=0, allows explicit solution of a finite difference
formulation of Eq. (1).
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
20POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
21
For each time step and each node along the slope plane, the net rate of erosion (e) and the
sediment discharge (product QC) are calculated. Combining equations (2) and (34), e is
obtained as:
e = DET + y w vs (TC - C)
(44)
When rates of soil detachment by raindrop impact are sufficiently small and the sediment
concentration in the flow exceeds the transport capacity, e becomes negative and represents a
net deposition rate. This situation will arise when DET is very low or when runoff and
sediment are routed from one slope plane to another of lower gradient. Since, effectively,
excess sediment concentration will be deposited at a rate dependent upon the settling velocity
of the particles, there may be short time periods and short distances along the slope plane over
which sediment will continue to be transported in excess of transport capacity until the pick-up
rate and transport capacity come into equilibrium. Although, as pointed out by Kirkby (1980),
this approach to modelling the interaction between erosion and deposition has not been
exhaustively tested, it has the advantage of smoothing out the processes over time and space.
An alternative approach, allowing all the excess material to be dumped immediately (Meyer
and Wischmeier, 1969) causes large discontinuities in erosion and deposition rates to occur
along a slope plane.
2.8.1 Treatment of Rill Flow
When equation (1) and (44) are applied to a relatively smooth slope plane, i.e. one without any
rills or plough furrows, the model simulates interrill erosion with a high proportion of the soil
surface covered by shallow overland flow. When rills or other defined channels exist on the
slope plane, the model can simulate both shallow flow between rills dominated by rainsplash
erosion, and downslope flow with much larger carrying capacities.
When flow depth is sufficient to overtop the rills, the "overbank" flow is assigned a velocity
determined by the hydraulic geometry of that portion of the flow, independent of the velocity
of the portion in and above the rill. The two areas are linked by having equal surface
elevations, as is done for routing in overtopped river reaches.
The unified rill profile model can also be used to describe the profiles of furrows produced by
agricultural implements. Since a furrowed surface will generally have a larger depth and
smaller width than a rill, the solution of equation (1) is more stable because overtopping of the
furrows by flow is less common than that of shallow rills. By using the unified rill model with
furrows, EUROSEM can simulate plough-rill erosion.
An option available within EUROSEM is to specify whether the rills are of uniform depth over
the whole length of a plane or whether the depth increases downslope. If the second option is
chosen, the model estimates rill depth (d) at a given node (k) on the plane from (Smith,
personal communication):
 x + dx 

d k = D j  k −1
 L j + dx 
where D(j)
0.5
(45)
= the depth of the rill at the bottom of the element, j,
x(k-1) = the horizontal distance from top of element, j, to previous node,
dx
= the horizontal distance between node, k, and previous node, and
x(j)
= the horizontal distance of element, j.
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
21POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
22
2.8.2 Channel Erosion
As in the KINEROS model, channel erosion is simulated in EUROSEM using the same
general approach as adopted for hillslope erosion. The main differences are that soil
detachment by raindrop impact within the channel is neglected and that lateral inflows of
sediment from the hillsides (qs in equation 1) become important. Equation (1) is solved for
sediment concentration (C) at distance (x) and time (t) beginning at the first node below the
upstream boundary. If there is no input of runoff at the upper end of the channel, the transport
capacity at the first node is zero and the boundary condition is set as:
C ( o, t ) =
qs
Q + v s BW
(46)
where BW = the bottom width of the channel.
Otherwise, procedures are precisely the same as for calculation of rill sediment transport. Bank
collapse is not simulated.
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
22POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
23
Chapter 3 DESCRIPTION OF VARIABLES
Table 3.1 lists the input variables and parameters in alphabetical order and gives brief
definitions. A more detailed description is presented below with the listings in the order in
which the user will come across them in the input files. The two input files are considered
separately.
When entering into data files, care should be taken to follow the style of the template files
provided. It is important to distinguish between values which are integers and those which are
real numbers; the latter must be entered with a decimal point.
3.1 RAINFALL DATA FILE
NGAGES
The number of rain gauges for which data are presented in the file. A number
between 1 and 20 is accepted.
MAXND
The maximum number of time-depth pairs used to describe the pattern of
accumulated rainfall during the storm. Where different time-depth pairs are
used for each gauge, the number refers to gauge with the highest number of
such pairs. The procedure for determining the number of time-depth pairs
using data from a recording rain gauge is described in Appendix 1.
The number of time-depth pairs must be sufficient to take the cumulative
rainfall record beyond the total computational time (TFIN) for which it is
proposed to operate the model.
ELE.NUM.(J) Each catchment is represented by a number of elements (slope planes or
channels) which are identified and numbered separately.
RAINGAUGE The number of the rain gauge to which the element number is matched.
WEIGHT
A proportional weighting factor for the rain gauge used where an element is
matched to two or more rain gauges. The weighting factor describes the
relative importance attached to each gauge in describing the rainfall
characteristics on that element.
ALPHA-NUMERIC GAGE IDENTIFICATION
This is the name you assign to each rain gauge to aid its identification. The
name must be kept short and must not extend on to an extra line of text.
GAGE NUM. The identification number of the rain gauge.
NUM. OF DATA PAIRS (ND)
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
23POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
24
The number of time-depth pairs for which data are entered for the identified
rain gauge.
TIME
The starting time from the beginning of the storm of each time-depth pair.
Units: min
ACCUM.DEPTH
The accumulated depth of rain at the beginning of each time-depth pair.
Units: mm
3.2 CATCHMENT CHARACTERISTICS FILE
The input data are organised in four sections headed: SYSTEM,OPTIONS,
COMPUTATION ORDER and ELEMENT WISE.INFO.
3.2.1 System
NELE
The total number of elements in the catchment. The value must be the same as
the number of elements entered under ELE.NUM.(J) in the Rainfall Data File.
NPART
This relates to a component within KINEROS which describes the settling of
sediment in ponds. It is not used in the present version of EUROSEM. A
value of 0 should always be used.
CLEN
The characteristic length of overland flow. It represents the longest possible
length of flow in the catchment through a series of cascading planes and
channel elements. Use maximum lengths of cascading planes or longest channel.
Units: m
TFIN
The total computation time for which the simulation is to be run. Its value
must be less than the end-time of the last time-depth pair in the Rainfall Data
File.
The value of TFIN will depend upon the duration of the storm and the response
time of the catchment. It should be sufficient to contain the hydrograph of
surface runoff and should therefore extend from the start of the rainfall to the
time that surface runoff on the hillslopes ceases.
Units: min
DELT
The time increment used in the simulations. Ideally this should be as short as
possible. However, the total number of time steps, defined as TFIN/DELT
should not exceed 1000. A warning message will appear if the model is run
with a time step which is too large. Generally, values between 0.5 and 1.0
minutes are appropriate.
Units: min
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
24POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
25
THETA
The weighting factor used in the finite difference equations in KINEROS for
routing overland flow and channel flow. A value between 0.5 and 1.0 should
be used.
TEMP
The air temperature at the start of the storm. It is used in the model to
compute the kinematic viscosity of water.
Units: º C
3.2.2 Options
The values of the entries under this heading must always have values of 2, otherwise
EUROSEM will not operate.
NTIME
The code for the time units used in KINEROS. NTIME = 1 for seconds and
NTIME = 2 for minutes. A value of 2 should always be used with the present
version of EUROSEM.
NEROS
This allows the user to call or reject the erosion option within KINEROS. With
values of 0 and 1, the option is not called. A value of 2 calls the erosion option
which, in this case is EUROSEM.
3.2.3 Computation Order
This heading describes the order in which the plane and channel elements comprising the
catchment must be organised to provide the correct cascading sequence for the movement of
runoff and sediment over the land surface.
NLOG
This denotes the order of calculation.
numerical sequence.
Each entry must therefore be in
NUM.(J)
This defines the corresponding element number for each entry in the sequence.
The element numbers need not be in numerical order. The total number of
elements listed here must be the same as the total number entered under
ELE.NUM.(J) in the Rainfall Data File and the same as that entered under
NELE above.
3.2.4 Element-Wise Info
This heading gives the data on the catchment characteristics of each element. The number by
which each element is known must be the same as that listed above under NUM.(J), where the
computational order is defined, and also that listed under ELE.NUM.(J) in the Rainfall Data
File.
J
The identification number of the element.
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
25POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
26
NU
The number of the element which contributes runoff and sediment to the
upslope boundary.
NR
This entry applies only to channel elements. It identifies the number of the
plane (hillslope) element contributing runoff to the channel from the right-hand
side when viewed in the direction of the flow (i.e. downstream). For plane
elements, a value of 0 should be entered.
NL
This entry applies only to channel elements. It identifies the number of the
plane element (hillslope) contributing runoff to the channel from the left-hand
side when viewed in the direction of the flow (i.e. downstream). For plane
elements, a value of 0 should be entered.
NC1
This entry applies only to channel elements. It identifies the number of the first
channel element contributing flow from upstream. For plane (hillslope)
elements, a value of 0 should be entered.
NC2
This entry applies only to channel elements. It identifies the number of the
second channel element contributing flow from upstream. It is relevant for
channels downstream of a confluence so that there are two contributing channel
elements at the upstream end. For plane (hillslope) elements, a value of 0
should be entered.
NPRINT
This controls the amount of information provided in the auxiliary output file.
The value should normally be set to 1.
XL
The length of the element.
Units: m
W
The width of the element. The entry applies to plane (hillslope) elements only.
A value of 0.0 should be used for channel elements.
Units: m
S
The average slope of any rills on the element, measured in the direction of
maximum slope, i.e. at right angles to the contour. For unrilled plane elements,
enter a value of 0.0 and for channel elements, enter a value of 0.01. Further
information on slope measurement is contained in Appendix 2.
Units: m/m
ZR
The side slope of the right-hand side of the channel, assuming a trapezoidal
cross-section and expressing slope as 1:ZR. For plane (hillslope) elements,
enter a value of 0.0.
ZL
The side slope of the left-hand side of the channel, assuming a trapezoidal
cross-section and expressing slope as 1:ZL. For plane (hillslope) elements,
enter a value of 0.0.
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
26POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
27
BW
The bottom width of the channel, assuming a trapezoidal cross-section. For
plane (hillslope) elements, enter a value of 0.0.
Units: m
MANN(RL) The value of surface roughness, expressed by Manning's n, for the rill channels
on a plane (hillslope) element. The value should take account of the effects of
soil particle roughness, surface microtopography and land cover. They should
also be modified to take account of rock fragments on the surface of the soil.
The procedure for estimating the value is described in Appendix 3 where Tables
of guide values are also found. A value of 0.0 can be set when no rills are
simulated.
Units: m1/6
MANN(IR)
The value of surface roughness, expressed by Manning's n, for a plane(hillslope)
element without rills, for the interrill area of an element with rills or for a
channel element. The value should take account of the effects of soil particle
roughness, surface microtopography and land cover. They should also be
modified to take account of rock fragments on the surface of the soil. The
procedure for estimating the value is described in Appendix 3 where Tables of
guide values are also found.
Units: m1/6
FMIN
The saturated hydraulic conductivity of the soil. The value entered should be
that for the soil itself and need not be adjusted for plant cover or rock
fragments. These adjustments are made within EUROSEM, as functions of
PBASE, ROC and PAVE. However, if the values of FMIN have been obtained
for soils with a vegetation or rock fragment cover, the measured values should
be used; the input values of PBASE, ROC and PAVE should then be set to 0.0
so that no automatic adjustment is made to the FMIN value within the model.
For further information and guide values for soils of different textures, see
Appendix 4.
Units: mm/h
G
Effective net capillary drive of the soil (see equation 12, Section 2.3). For
guide values for soils of different textures, see Appendix 4.
Units: mm
POR
The porosity of the soil.
areprovided in Appendix 4.
Guide values for soils of different textures
Units: % v/v
THI
The initial volumetric moisture content of the soil, i.e. at the start of the storm.
Where this is estimated, rather than measured, the value must lie between
THMAX and the residual moisture content (THR) at permanent wilting point.
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
27POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
28
For further information and guide values of THMAX and THR for soils of
different textures, see Appendix 4.
Units: % v/v
THMAX
The maximum moisture content of the soil.
For further information and guide values for soils of different textures, see
Appendix 4.
Units: % v/v
ROC
The fraction of the soil, expressed between 0 and 1 occupied by rock
fragments.
Conceptually, ROC represents the relative volume of the soil which does not
act as a porous medium. Its effect is to reduce the value of FMIN (see
equation 17, Section 2.3). A value of 0.0 should be used if the FMIN value is
a measured one which already takes account of the rock fragments. The
procedure for obtaining values of ROC from field samples is described in
Appendix 5.
RECS
The infiltration recession factor, defined as the average maximum local
difference in microrelief of the soil surface.
RECS is used to drive the infiltration process after rain ceases and infiltration is
controlled by the depth of water lying on the surface. Conceptually, RECS
represents the local average surface depth of water when the surface is
completely covered by water. The procedure for measuring RECS in the field
is described in Appendix 6.
Units: mm
DINT
The maximum interception storage of the plant cover.
Guide values are presented in Appendix 7 for a range of cover types.
Units: mm
DEPNO
The average number of rills (concentrated flow paths) across the width of the
plane (hillslope) element. The procedure for determining DEPNO in the field is
described in Appendix 8. Flow paths may range in size from small continuous
depressions of millimetre-sized depths and widths to clearly-defined rills and
plough furrows, provided they are aligned downslope. For an unrilled plane, a
value of 0.0 should be entered. For a channel element, a value of 0.0 should be
used.
RILLW
The average bottom width of the concentrated flow paths or rills (see Appendix
8). An option exists within EUROSEM to specify whether the rills are of
uniform width over the length of the plane element or whether the width
increases downslope (see RS below). If the second option is chosen, the width
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
28POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
29
should be specified as at the bottom of the plane and scaling is automatically
applied within the model. For a channel element, a value of 0.0 should be used.
Units: m
RILLD
The average depth of the concentrated flow paths or rills (see Appendix 8). An
option exists within EUROSEM to specify whether the rills are of uniform
depth over the length of the plane element or whether the depth increases
downslope (see RS below). If the second option is chosen, the depth should be
specified as at the bottom of the plane and scaling is automatically applied
within the model. For a channel element, a value of 0.0 should be used.
Units: m
ZLR
The average side slope of the concentrated flow paths or rills expressed
as1:ZLR (see Appendix 8). For a channel element, a value of 0.0 should be
used.
RS
This sets the option for specifying whether the width and depth of the
concentrated flow paths or rills is uniform or increases downslope. If RS = 1,
the model assumes that the values of RILLW and RILLD apply to the whole
length of the element. If RS = 0, the model assumes that the values of RILLW
and RILLD apply to the bottom end of the element and scales the values to
smaller dimensions with distance upslope.
RFR
The roughness of the surface determined downslope, i.e. in the direction of
flow, and expressed as a ratio, defined in Appendix 6. The ratio is used in
EUROSEM to express the effects of tillage as well as naturally-occurring
variations in microtopography.
Appendix 6 describes the methods
recommended for obtaining the ratio from field measurement. It also contains a
Table of guide values related to different tillage practices and procedures for
modifying the values according to soil type and to change over time as
roughness levels decline through raindrop impact.
SIR
The interrill slope. For unrilled plane elements, this is the average slope of the
plane. For channel elements, this is the average slope of the channel. For a
plane element with rills, SIR is defined as the average ground slope followed by
overland flow as it passes over the interrill area into the rills (see Appendix 2).
The average slope of the rills should be entered under S.
Units: m/m
COVER
The effective percentage canopy cover of the vegetation. Strictly it refers to
the proportion (between 0 and 1) of the ground surface obscured by the
vegetation when viewed vertically from above. The value should take account
of ground vegetation, mulches and any litter layer as well as trees and bushes
(see Appendix 7).
SHAPE
An indicator of the shape of the leaves of the vegetation cover. A value of 1.0
is used to denote bladed leaves (e.g. those found on grasses and cereal crops)
and needle leaves. A value of 2.0 is used to denote broad leaves. Conceptually
QUINTON, J.N., SMITH, R.E., GOVERS, G.,
29POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
MORGAN, R.P.C,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
30
the SHAPE factor describes, in a simplified way, the relationship between the
size of the leaves and the median volume drop diameter of the rainfall. A value
of 0.0, to be entered when there is no vegetation cover, will cause stemflow to
be set zero.
PLANGLE
The average acute angle between the plant stems and the ground surface. Guide
values for mature plants are given in Appendix 7.
Units: degrees
PBASE
The percentage basal area of the vegetation cover expressed as a fraction
between 0 and 1. Details of field measurement and a table of guide values are
found in Appendix 7.
PLANTH
The average height of the plant canopy above the ground surface. Since the
purpose is to describe the fall height of intercepted raindrops, any ground
vegetation, mulches and litter layer should be considered. Guide values for
mature plants are given in Appendix 7 where further information of methods of
field assessment is provided,
Units: cm
DERO
The depth of any resistant or non-erodible layer (e.g. plough pan or
concretionary horizon) below the soil surface. Once erosion reaches this depth,
the model prevents further downcutting by rills; from then on the rills are only
able to erode by widening their channels.
Units: m
ISTONE
D50
An indicator of the effect of rock fragments on the surface of the soil on the
saturated hydraulic conductivity (see Appendix 5). A value of +1 should be
used where the rock fragments sit on the surface and protect the soil from
structural breakdown due to raindrop impact; or where the rocks either sit on
or are fully embedded in a soil with high macroporosity, e.g. due to recent
tillage. In this instance, the rock fragments will enhance infiltration. A value of
-1 should be used where the rocks are partially embedded within or sit on top
of a sealed surface which will reduce infiltration.
The median particle size of the soil as obtained from standard particle-size
analysis using the USDA system to define textural classes (i.e. clay: < 0.002
mm; silt: 0.002 - 0.05 mm; sand 0.05 - 2.00 mm).
Units: µm
EROD
The detachability of the soil particles by raindrop impact. Appendix 9 describes
a method for determining detachability using field measurement and also gives a
table of guide values for use where measured data are not available.
Units: g/J
SPLTEX
The value of the exponent relating detachment of soil particles by raindrop
impact to the depth of water on the soil surface. The current version of
EUROSEM uses a constant value of 2.0 for this exponent. As further
QUINTON, J.N., SMITH, R.E., GOVERS, G.,
30POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
MORGAN, R.P.C,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
31
information becomes available, future versions of EUROSEM may allow the
value to be varied according to soil texture.
COH
The cohesion of the soil as measured in the field with a torvane (Soil Test CL600) after the soil has been saturated (see Appendix 9). Guide values for soils
of different textures are given in Appendix 9 for use when measured data are
not available. These values should be adjusted where a vegetation cover is
present to allow for additions to cohesion brought about by root reinforcement.
Units: kPa
RHOS
The specific gravity of the sediment particles. This is normally set at 2.65
Mg/m3.
Units: Mg/m3
PAVE
The fraction of the surface occupied by non-erodible material, e.g. rock
fragments, concrete, tarmac. It is used in EUROSEM to reduce the rate of soil
detachment by raindrop impact in direct proportion to the area occupied by
non-erodible surfaces and also to influence the way rock fragments affect the
saturated hydraulic conductivity of the soil (see ISTONE above).
SIGMAS
The standard deviation of the mean sediment particle diameter (µm) for any
element upslope of a pond. It is used within KINEROS for modelling
sedimentation within ponds or reservoirs. It is not required in the present
version of EUROSEM which does not deal with ponds. A value of 0.0 can
therefore be entered.
MCODE
The value chosen for MCODE allows the user to choose the equations used in
EUROSEM to simulate sediment transport by interrill flow.
MCODE = 1 selects the equations proposed by Everaert (1992) which relate
specifically to interrill flow. MCODE = 0 selects the equations proposed by
Govers (1990) for rill flow and applies them to both interrill and rill flow.
In the first version of EUROSEM, Govers's equations were used for all flows.
Later, Everaert's equations were included in the model but, in certain situations,
their use gave very high values of transport capacity so that, where the interrill
flow contributed to rills, the transport capacity of the rill flow was often filled
by sediment from the interrill areas. The detachment of soil particles by flow in
the rills was then reduced to zero and the rills did not enlarge during the storm.
The result was an overall high rate of predicted erosion but with no rill erosion.
The ability to use Govers's equations was therefore maintained as an option
where such results were considered by the user to be unrealistic. Although, in
the current version of EUROSEM, this problem of overprediction has been
overcome, the two options are retained to allow the user to choose.
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
31POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
32
Table 3.1 Definitions of input variables and parameters used in EUROSEM identified by the
labels in the computer code.
Variable
Symbol
Definition
Units
ACCUM.DEPTH
Accumulated depth of rain
mm
BW
Width of channel bottom
m
CLEN
Characteristic length of catchment. Use maximum
lengths of cascading planes or longest channel
m
COH
J
Cohesion of the soil or soil-root matrix as measured
at saturation using a torvane
kPa
COVER
COV
Percentage canopy cover
%
D50
d50
Median particle diameter of the soil
µm
DELT
Time increment number used in calculations,
usually 1 minute
min
DEPNO
Average number of concentrated flow paths (rills)
across the width of the plane
DERO
Maximum depth to which erosion can occur because
of a non-erodible layer in the soil
m
Maximum interception storage of the vegetation
cover
mm
DINT
ICmax
ELE.NUM.(J)
Element number
EROD
Detachability of the soil particles by raindrop impact
g/J
FMIN
ksat
Saturated hydraulic conductivity of the soil
mm/h
G
G
Effective net capillary drive of the soil
mm
GAGE.NUM
Rain gauge number
ISTONE
Governs effect of rock fragments on saturated
hydraulic conductivity (+1 = increase in hydraulic
conductivity; -1 = decrease in hydraulic
conductivity)
J
Element number
MANN(IR)
n
MANN(RL)
MAXND
MCODE
Value of Manning’s n for the interrill area, allowing
for roughness effects of soil particles, rock
fragments, surface microtopography and vegetation
cover (also used for non-rilled elements and channel
elements)
m1/6
m1/6
Value of Manning’s n for the rills, allowing for
roughness effects of soil particles, rock fragments,
surface microtopography and vegetation cover
Maximum number of time-depth pairs for all rain
gauges
Governs selection of sediment transport equations
for interrill flow (0 = Govers; 1 = Everaert)
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
32POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
33
Table 3 (continued)
Variable
Symbol
Definition
NC1
Element number of first channel contributing at
upstream boundary of a channel element
NC2
Element number of second channel contributing at
upstream boundary of a channel element
NELE
Total number of plane and channel elements
NEROS
Allows user to call or reject erosion option within
KINEROS. Set = 2 for EUROSEM
NGAGES
Number of rain gauges (1-20)
NL
Element number contributing flow to left-hand side
of channel (when facing downstream)
NLOG
Governs computation order
NPRINT
Controls amount of information provided in the
auxiliary output file. Normally set at 1 (other options
are 2 and 7).
NR
Element number contributing flow to right-hand side
of channel (when facing downstream)
NU
Element number of plane contributing to upslope
boundary
NUM.OF DATA
PAIRS (ND)
Number of time-depth pairs for rainfall data
NUM.(J)
Number of element corresponding to NLOG.
Governs order in which elements are treated in
computation.
PAVE
PBASE
PLANGLE
PAVE
PBASE
PA
RECS
RFR
Identification number assigned to the rain gauge
m
% v/v
Specific gravity of the sediment particles
RILLD
Average depth of concentrated flow paths (rills)
RILLW
ROC
mm
Infiltration recession factor
Downslope roughness
RHOS
ROC
degrees
Soil porosity
RAINGAGE
RFR
Percentage of basal area of vegetation expressed as a
proportion between 0 and 1
Effective canopy height
POR
RECS
Fraction of surface covered by non-erodible material,
e.g. rock fragments, concrete, tarmac
Average acute angle of the plant stems to the soil
surface
PLANTH
Units
mg/m3
m
m
Average width of concentrated flow paths (rills)
Proportion of rock fragments in the soil by volume
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
33POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
34
Table 3 (continued)
Variable
Symbol
RS
S
Definition
Units
Governs the option of whether the width and depth
of rills are uniform over the length of the element or
whether they increase downslope
s
Average slope of the rills or concentrated flow paths
on a plane element
SHAPE
Plant leaf shape factor, 1 = bladed leaves; 2 = broad
leaves. A value of 0 = no vegetation and sets
stemflow to zero
SIGMAS
Standard deviation of sediment diameter (not used in
present version of EUROSEM)
SIR
s
Interrill slope (also used for slope of plane elements
without rills and for channel elements)
SPLTEX
b
Water depth exponent affecting soil detachment by
raindrop impact (set to 2.0 in present version of
EUROSEM)
m/m
m/m
TEMP
Air temperature at time of rainfall
°C
TFIN
Duration of model simulation. Value must be less
than the end-time of the last time-depth pair of the
rainfall data
min
THETA
Weighting factor in finite difference equations,
usually set between 0.5 and 1.0
THI
θI
Initial volumetric moisture content of the soil
% v/v
THMAX
θs
Maximum volumetric moisture content of the soil
% v/v
TIME
Accumulated time from start of storm
min
W
Width of plane element (set to 0.0 for channels)
m
WEIGHT
Multiplication factor for weighting of RAINGAGE
XL
Length of plane or channel element
m
ZL
Side slope of left side of trapezoidal channel
1:x
ZLR
Side slope of concentrated flow paths (rills)
1:x
ZR
Side slope of right side of trapezoidal channel
1:x
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
34POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
35
Chapter 4 USING EUROSEM
4.1 GETTING STARTED
The following instructions are intended to be foolproof but if you have problems,
e.g. error messages, please write or fax the authors, stating exactly what happens.
Use of the computer’s ‘print-screen’ facility is often helpful in these situations.
4.2 SYSTEM REQUIREMENTS
To run EUROSEM you will need the following:
• An IBM compatible PC with at least 2MB of free hard disk space
• MS DOS 3 or higher
• 8086 or higher processor
• A VGA monitor to run the graphics option.
4.3 INSTALLATION
To install EUROSEM on to your computers hard disk
1. go to the C:\ prompt;
2. insert the floppy disk into drive A;
3. type install.
EUROSEM will be copied onto your hard drive and installed in the directory
C:\EUROSEM. Any additional information on EUROSEM which has arisen after
the production of this manual will be displayed on the screen. Alternatively you
can copy the files yourself into a directory of you choosing and display the latest
information on EUROSEM by typing the file READ.ME.
4.4 Describing A Catchment For Eurosem
EUROSEM describes catchments by decomposition into elements which are
either planes or channels. The method is taken from the KINEROS, and more
details and examples can be found in the KINEROS manual (Woolhiser et al,
1990). Figure 4.1 illustrates several aspects of the topographic decomposition of
a catchment into elements. The plan of a simple catchment is shown in Fig. 4.1a,
with the elevation countours and channel locations. Flow moves always normal
to the contour lines, and the catchment can be divided into flow elements along
flow lines as indicated in Figure 4.1b. Channel segments are lettered A through
D, and there are 11 numbered surface elements. The catchment could be divided
into fewer or into many more elements.
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
35POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
36
Each surface element is represented by a rectangle whose length should be equal
to the average flow path length through that element, and whose area matches
the area of the element as measured from the plan, Figure 4.1b. Each catchment
should be sub-divided into elements based on the vegetation and the topography.
The slope of each element is the mean slope of the area it represents and
elements which have significant breaks in
b
a
6
8
3
7
C
4
9
2
D
1
5
B
11
10
A
12
c
6
7
8
3
9
C
4
11
D
B
2
1
A
10
12
5
Figure 4.1 Illustration of the decomposition of natural topography into elements
for modelling a catchment.
slope should be represented by several cascading elements, each element
representing a locally dominant slope. Likewise, as shown in this figure by
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
36POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
37
elements 1-2 and 3-4, surfaces with significant convergence or divergence can be
represented by a succession of elements with increasing or decreasing width.
Care should be taken in agricultural catchments that the specified slope (and
other geometry) refers to the actual slope of the flowing water: furrows may
direct the flow in contradiction to the overall land surface slope. Figure 4.2
illustrates a case where a paddock surface flow is directed by furrows in a
direction (indicated by dotted lines) which is not the same as the flow direction
when that paddock is unfurrowed (white arrow). In the latter case, the same area
might better be represented by a cascade of successively narrower surfaces in
order to represent the flow convergence toward the near corner.
When an area contributing to the side of a channel has significantly nonuniform
length, the channel can be divided into segments and each segment assigned a
contributing surface of different length, as shown by elements 9-11 or 10-12
contributing to sequential channel segments B and A in Figure 4.1.
The width of an element is found by dividing the area by the length. For the case
of an element which is actually a parallelogram, as for element 5 in Figure 4.1,
the length of the channel into which the element flows will be significantly longer
than the surface width. Such a parallelogram is correctly modeled in
EUROSEM, with the surface outflow distributed uniformly along the receiving
channel length.
A surface element may receive input at its upper boundary from another surface
element, and may flow into a downslope surface element or into the head end or
the side of a channel. A channel may receive input either from its upper end, and
from a surface element on either one or both sides, or only one of those options.
A channel cannot flow onto a surface. At the upper end of a channel, there may
be either a plane (in figure 4.1c, element 2 flows into channel D) or one or two
channels providing input.
Several kinds of variability or topographic complexity can be represented in this
scheme, many of which have been referred to above:
Variations in Slope. A runoff surface with significant changes in slope along the
flow path can be represented by a sequence of planes which flow onto one
another.
Convergent and Divergent Flow. When a hillslope which feeds runoff into a
channel exhibits significant widening or narrowing along the direction of flow,
several elements of increasing or decreasing width may be cascaded to represent
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
37POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
38
the hillslope. The joining of cascading elements of different widths is
accomplished by matching total discharge and sediment concentrations at the
shared boundary.
Changes in Rill Density. Like the other geometric changes, if it is desired to
model a hillslope with downslope changes in rill density, a cascading set of
surfaces can be used. At each boundary, total discharge will be matched, while
upstream flows and sediment concentrations will be redistributed into the
assigned rill geometry. Note that parameter RS will have to be 0 for all but the
uppermost surface.
Other Variations Likewise, any other parameter variations can be simulated
along a hillslope by use of cascading planes, including changes in hydraulic
roughness, infiltration parameters, plant type or cover conditions, initial wetness,
or soil rockiness. The soil particle size, D50, however, needs realistically to be
kept constant, since there is no facility in EUROSEM to treat the implications of
a changing D50. That requires a model with the ability to transport some particle
sizes at the same time that others are being deposited, and other differentiating
processes which arise when there are a variety of soil particle sizes.
Parameterisation. The parameter input file is organised into elements, which
need not be numbered in input order. They should, however, be input in a
computational order, so that for any element, those providing input values will
have been simulated before the element is simulated. The numbers in Figure
4.1b and c are in such a computational order, for example, except that in this
example, for illustrative purposes, channels were given letters rather than
numbers. In the model, all elements must have a unique number. The element
number is an identifier which is used by other elements to indicate where outflow
is directed, or from which elements inflow is received. Channels are not
assigned any significant surface area, and the sum of all surface elements should
match the surface area of the catchment.
The model admits a total of 60 elements of all kinds. The code parameters NU,
NL, NR, NC1, and NC2 are used to indicate the flow connections of an element.
NU is the element number, if any, whose flows provide the upper boundary
condition of an element. NU=0 designates an upstream element. NL and NR are
the elements flowing into the left and right sides of a channel, and only apply to
channel elements. NC1 and NC2 indicate, if positive, the element numbers for
channels which flow into the upstream end of a channel. If the element is a
channel, NU is the surface element which flows directly into its upper end. For
the example in Figure 4.4.1b and c, channels D and C would have NU=2 and 6,
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
38POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
39
respectively.
Figure 4.2 Flow and appropriate slope may follow topography, or may be
directed by mechanically formed furrows.
4.5 Creating And Editing Input Files
The two data files supplied can be used as templates for creating input files for
the area to which the model is being applied. Appropriate names should be
chosen for the input files. It is recommended that the files are known by the name
or location of the area. For example, the files on the templates have been created
to simulate erosion for the storm on 26 January 1990 on erosion plot number 6 of
the experimental plots operated by Silsoe College and Rothamsted Experimental
Station at Woburn, Bedfordshire, UK. They have therefore been titled
WOBR1.DAT for the rainfall data file and WOBC1.DAT for the catchment
characteristics file.
When creating new data input files, the new files should be created by copying
and renaming the template files. This is done by typing:
COPY WOBR1.DAT [ new file name ]
to create a new rainfall data file, and
COPY WOBC1.DAT [ new file name ]
to create a new catchment data file.
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
39POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
40
Before the new files can be used, they must be edited so that they contain the
data specific to the study area. This can be done using the MS-DOS editor,
'EDIT' or another full screen editor.
You should enter the editing system and practise editing and saving your new
files. If you are using the full-screen type you will see the files displayed as in
Figures 4.3 and 4.4.
You should only edit the data input values. Any other changes will alter the way
in which EUROSEM reads the input files and will cause the programme to abort.
You should make sure that you do not delete any of the marker signs, # and *, or
add extra lines of text to the file. The name labels for each item of data are only
for guidance but they should not be changed or deleted.
4.4 FILE CHARACTERISTICS
4.4.1 Rainfall data file
To illustrate how a rainfall data file is produced, we will describe the procedure
we followed to create the rainfall data file (WOBR1.DAT) provided as the
template. You should follow a similar procedure when creating your own file. It
is recommended that you print out your copy of the template file WOBR1.DAT
and refer to it alongside the description which follows.
NGAGES
NGAGES refers to the number of rain gauges in the study area. Since, in
this example, rainfall data were available from only one gauge, the value of
NGAGES was set to 1.
MAXND
This refers to the maximum number of time-depth pairs used to describe
the pattern of accumulated rainfall during the storm. It can be determined
by the procedure described in appendix 1.
Figure A1.1 shows the trace for storm rainfall obtained from a recording
rain gauge. Based on changes in the slope of the line on this plot, the storm
can be divided into discrete time periods within which the rainfall is of
more or less uniform intensity.
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
40POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
41
This information is then used to describe the storm by defining the time (T;
mins) of the start of each period of the storm and the cumulative rainfall
(D; mm) received in the storm up to that time, as shown in Table A1.1.
Each entry in Table A1.1 is termed a time-depth pair. The number of timedepth pairs must be sufficient to take the cumulative rainfall record past
the total computational time (TFIN) for which it is proposed to operate the
model. The value for TFIN will depend upon the duration of the rainfall
and the response time of the catchment. It should be sufficient to contain
the hydrograph of surface runoff and should therefore extend from the start
of the rainfall to the time that surface runoff on the hillslope ceases.
For the one storm and one gauge being considered, the number of timedepth pairs was 9 (Table A1.1). Therefore, we entered MAXND = 9.
ELE.NUM.(J)
Each catchment is represented by a number of elements which need to be
identified here and numbered. Since we were considering one erosion plot
and this is represented by a single plane, the number of elements = 1.
Therefore, we entered ELE.NUM.(J) = 1.
RAINGAUGE
Each element in the catchment must be assigned to a rain gauge. In this
instance, since there was only one gauge, element 1 was assigned to
RAINGAUGE 1.
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
41POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
42
EUROSEM Rainfall Input Data
#
***************************
Gage Network Data
****************************
#
NUM. OF RAINGAGES MAX. NUM. OF TIME-DEPTH DATA PAIRS FOR ALL GAGES
(NGAGES)
(MAXND)
-------------1
9
#
There must be NELE pairs of (GAGE WEIGHT) data
*
ELE. NUM. (J) RAINGAGE
WEIGHT
------------------------1
1
1.0
#
*****************************
Rainfall Data
*****************************
There must be NGAGES sets of rainfall data. Repeat lines from * to * for each gage inserting a variable
number of TIME-DEPTH data pairs (see example in User Manual).
#
* ALPHA-NUMERIC GAGE ID: WOBURN EROSION PLOTS - FARM GAUGE
#
GAGE NUM.
NUM. OF DATA PAIRS (ND)
------------------------------1
9
#
There must be ND pairs of time-depth (TD) data: NOTE: The last time must be greater than TFIN (the total
computational time).
#
TIME(min)
ACCUM. DEPTH(mm)
----------------0.0
0.0
45.0
0.2
60.0
0.4
70.0
1.0
85.0
1.5
89.0
2.9
90.0
2.2
125.0
3.0
160.0
3.0
*
Figure 4.3. Example of EUROSEM Rainfall Data File (WOBR1.DAT)
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
42POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
43
WEIGHT
This allows the opportunity of weighting the rainfall recorded at a given
gauge by a multiplier to provide a better estimate of the rainfall on a given
element. For example, if the element was located one quarter of the way
between gauge A, which received a storm rainfall of 36 mm, and gauge B,
which received 20 mm, we could estimate that the rainfall on the element
would be 32 mm. We could then assign the element to gauge A but weight
rainfall received at gauge A by 32/36 or 0.88.
In this instance, since there was only one element and one gauge, we
entered WEIGHT = 1
ALPHA-NUMERIC IDENTIFICATION
This is the name that you wish to assign to the raingauge. For the alphanumeric identification for Woburn we chose ”Woburn erosion plots - farm
gauge•. You should keep this identification tag quite short and make
certain that it does not extend on to an extra line of text.
TIME-ACCUM.DEPTH PAIRS
For GAGE 1, the number of time-depth pairs (ND) was 9 in this example.
The data for each time-depth pair were entered, starting at time 0 and the
accumulated rainfall (ACCUM.DEPTH) for the first time period. We
checked that the starting time of the last time-depth period was equal to or
greater than the intended total computational time (TFIN).
The rainfall data file was then complete.
When you have completed your new rainfall data file, we recommend that
it should be saved immediately to avoid any chance of losing the data. The
file should be saved under its new name, using the appropriate command
under the computer editing system for saving the current edited file.
4.4.2 Catchment characteristics file
The template file WOBC1.DAT was created using the following
procedure. We recommend that you print out your copy of the template
file and refer to it alongside the description given below.
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
43POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
44
The file arranges the input data in four sections. These are headed
SYSTEMS, OPTIONS, COMPUTATION ORDER and ELEMENT
WISE INFO.
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
44POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
45
EUROSEM V. 3/93 Parameter Input File Woburn plots
#
**********************************
*********** S Y S T E M ********
**********************************
* NELE NPART CLEN(M) TFIN(min)DELT(min)
THETA TEMP
1 0
100.
150.
0.5
0.7
10.0
#
***********************************
********* O P T I O N S ***********
***********************************
NTIME
NEROS
2
2
#
***********************************************
**** C O M P U T A T I O N O R D E R ****
***********************************************
There must be NELE elements in the list. NLOG
must be sequential. ELEMENT NUM. need not be.
#
COMP. ORDER
ELEMENT
(NLOG)
NUM. (J)
------------1
1
#
***********************************************
****** E L E M E N T - W I S E I N F O ***
***********************************************
There must be NELE sets of the ELEMENT-WISE prompts and data
records; duplicate records from * to * for each element. The
elements may be entered in any order.
*
J
NU
NR
NL
NC1
NC2
NPRINT
1
0
0
0
0
0
1
XL(M)
W(M)
S
ZR
ZL
BW(
RLMAN
M)
N
35.0
25.0
0.11
0.0
0.0
0.0
0.04
FMIN(mm G(mm)
POR
THI
THMX
ROC
RECS(m
/h)
m)
2.6
240
0.453
0.4
0.42
0.00
10.0
DEPNO
RILLW( RILLD(
ZLR
RS
RFR
m)
m)
10.0
0.08
0.05
1.0
0.
1.0
COVER
SHAPE
PLANG
PLANTBA PLANTH( DERO
LE
SE
cm)
0.1
1
55.0
0.03
15.0
3.0
D50(µ)
EROD
SPLTEX COH
RHOS
PAV
SIGMAS
E
250.
1.6
2.
2.65
2.65
0.0
1.00
*
IRMAN
N
0.04
DINT(m
m)
3.0
SIR
0.07
ISTONE(+/)
-1
MCODE
0
Figure 4.4. Example of EUROSEM Catchment Characteristics File (WOBC1.DAT)
(1) SYSTEMS
The following entries are made under this heading:
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
45POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
46
NELE
This defines the total number of elements in the catchment. Its value
should agree with the number of elements entered under ELEMENT
NUM. (J) in the Rainfall Data File. Since, in this example, only one slope
plane was being considered, we entered NELE = 1.
NPAR
This relates to a component of the KINEROS model which describes the
settling of sediment in ponds. At present, it is not used in EUROSEM. A
value of 0 should always be set here.
CLEN
This is the characteristic length of overland flow and represents the longest
length in a series of cascading planes or channels. Since the erosion plot
was being treated as one slope element, CLEN was set here as equal to the
downslope length of the plot, i.e. 35 m.
TFIN
This is the total computational time (min) for which the model is to be run.
Its value must be less than the end-time of the last time-depth pair in the
Rainfall Data File. For the storm considered here, the last time-depth pair
ends at 160 minutes, so we set TFIN = 150 min.
DELT
This defines the time increment used in the calculations. Ideally, this
should be as short as possible. However, the total number of time steps,
defined as TFIN/DELT should not exceed 1000 in which case the model
will pause and a warning message will appear. We chose a value of DELT
= 0.5.
THETA
This is a weighting factor used in the finite difference equations in
KINEROS for routing overland flow and channel flow. It should have a
value between 0.5 and 1.0. A value of 0.7 is recommended and this was
the value we chose.
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
46POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
47
TEMP
The air temperature (° Celsius) at the start of the storm should be set here.
(2) OPTIONS
No changes should be made to the entries under this heading. EUROSEM
is designed to operate with values of 2 under both entries.
NTIME
This is the code for the time units used in the model. NTIME = 1 for
seconds and NTIME = 2 for minutes.
NEROS
This allows the user to call or reject the erosion option in the model. With
values set at 0 or 1, the erosion option is not called and only the
hydrological calculations are made. A value of 2 calls the erosion option.
(3) COMPUTATION ORDER
This heading describes the order in which the elements must be organised
to provide the correct cascading sequence for the movement of runoff and
sediment downslope and downstream.
NLOG
This denotes the order of calculation. Each entry must therefore be in
numerical sequence.
ELEMENT NUM.(J)
This defines the corresponding element number for each entry in the
sequence.
The element numbers need not be in numerical order. The total number of
elements listed here should be the same as the total number entered under
ELE. NUM. (J) in the Rainfall Data File and correspond to the number
entered under NELE above.
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
47POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
48
Since only one slope plane was being considered at Woburn, NLOG was
set to 1 and ELEMENT NUM. was therefore also equal to 1.
(4) ELEMENT WISE INFO
This heading gives the data on the catchment characteristics of each
element. The number by which each element is known must be the same as
that listed above under ELEMENT NUM, where the computational order
is defined, and also under ELE. NUM. (J) in the Rainfall Data File.
J
This represents the number of the element. J = 1 for the first element, J = 2
for the second element, and so on. In the example being used here, there
was only one element, so J = 1.
NU
This denotes the number of the element which contributes runoff and
sediment to the upslope boundary. Since there was only one element, there
were no upslope contributing elements, so NU = 0.
NR
This entry applies to elements which are channels and denotes the number
of the hillslope elements contributing flow to the channel from the righthand side when viewed in the direction of flow, i.e. facing downstream.
For hillslope elements, as here, NR = 0.
NL
This entry similarly applies to channels and denotes the number of the
hillslope element contributing flow to the channel from the left-hand side.
For hillslope elements, as here, NL = 0.
NC1
This entry also applies to channels and denotes the number of the first
channel element contributing flow to the channel from upstream. For
hillslope elements, NC1 = 0.
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
48POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
49
NC2
This entry denotes the number of the second channel element contributing
flow to the channel from upstream. It is relevant for channels downstream
of a confluence so that there are two contributing channel elements at the
upstream end. For hillslope elements, NC2 = 0.
NPRINT
This controls the amount of information provided in the auxilary output
file. In our case it is set to 1.
XL
This is the length of the element (meters). Since the erosion plot was 35 m
long, XL = 35.0.
W
This is the width of the element (m). Since the erosion plot was 25 m wide,
W = 25.0. It should be noted that W = 0.0 if the element being described
is a channel.
S
This is the average slope of any rills on the element (m/m), measured in the
direction of maximum slope, i.e. at right angles to the contour. Since the
average slope of the rills was measured in the field at 11 per cent, we
entered S = 0.11.
ZR
This is the side slope of the right-hand side of the channel, assuming a
trapezoidal shape and expressing the slope as 1:ZR. Since we were dealing
with a plane element, there were no channels, so ZR = 0.
ZL
This is the side slope of the left-hand side of the channel, assuming a
trapezoidal shape and expressing the slope as 1:ZL. Since we were dealing
with a plane element, there were no channels, so ZL = 0.
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
49POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
50
BW
This is the bottom width (m) of the channel, assuming a trapezoidal shape.
Since we were dealing with a plane element, there were no channels, so
BW = 0.0.
RLMANN
This is the value of Manning‘s n for the rill channels (concentrated flow
paths) on the element, taking account of the combined effects of soil
particle roughness, surface microtopography and plant cover on the
element. For the sandy loam soil in a smooth seed-bed, a typical value
would be n = 0.015. For wheat, n ranges from 0.01 to 0.30, depending on
the percentage cover and planting density. For the smooth seedbed and 10
per cent cover prevailing at the time of the storm, we estimated a value at
the lower end of the range, e.g. 0.04.
The value for Manning's n should be further adjusted to take account of
rock fragments or stones in the surface soil, using equation A3.2 in
appendix 3. Since the soil at Woburn is not stony, no adjustment was
necessary here.
IRMANN
This is the value of Manning's n for the interrill area of the element, again
taking into account soil particle roughness, surface microtopography and
plant cover. For the smooth surface and cover of the element in question,
the same value was chosen as for Manning's n in the rills. We therefore
entered IRMANN = 0.04.
As with the case above, the Manning's n value should be adjusted, if
necessary, for rock fragments or stones in the surface soil, using equation
A3.2 in appendix 3. No such adjustment was needed for Woburn. You
should note that the model will further adjust the value of IRMANN to
take account of the level of roughness on the interrill area, as expressed by
the downslope roughness ratio, RFR (Appendix 6).
FMIN
This is the saturated hydraulic conductivity of the soil (mm/h). This should
be the value for the soil itself and should not be adjusted for plant cover or
stoniness. These adjustments are made within the model itself, as functions
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
50POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
51
of input data on PBASE and ROC respectively. From Table A4.2, we
could have selected a value of 26 mm/h but this would be for an
uncompacted soil. Allowing for the fact that the soil had been exposed to
raindrop impact for four months and compacted by farm machinery during
drilling before the storm took place, it was decided to reduce the value by
an order of magnitude, giving a value similar to that of a clay loam. The
value of FMIN = 2.6 was therefore entered.
If FMIN has been measured for soils with a vegetation or stone cover, the
measured value should be used. The input values for PBASE and ROC
should then be set to zero so that no further adjustment is made to the
FMIN value within the model.
G
This is the effective net capillary drive of the soil (mm), as described in
Section 3.3.1. From Table A4.1, a value of 240 was chosen for a sandy
loam soil, so here G = 240.
POR
This is the porosity of the soil (% v/v). From Table A4.1, a value of 0.453
was chosen for a sandy loam soil and we entered POR = 0.453.
THI
This is the volumetric moisture content of the soil at the start of the storm.
This has to be estimated in relation to the time since it last rained and the
speed with which the soil dries out. As explained in Appendix 4, THI will
take a value between the maximum moisture content of the soil (THMX)
and the moisture content at wilting point. Since the storm occurred in the
middle of a wet spell of weather, the soil had had little opportunity to dry
out between storms. A rather high value of THI = 0.4 was therefore
chosen.
THMX
This is the maximum moisture content of the soil. From Table A4.1, we
chose a value of THMX = 0.42.
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
51POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
52
ROC
This is the proportion (% v/v) of the soil occupied by stones and rocks.
Since the sandy loam soil at Woburn is not stony, we entered ROC = 0.0.
A value of ROC = 0.0 should also be used if the input value for FMIN is a
measured one which already takes account of the presence of rock
fragments or stones.
RECS
This is the infiltration recession factor and is defined as the average
maximum local difference in microrelief (mm). Based on field
measurements of surface roughness (Appendix 6), a value of RECS = 10.0
was selected.
It should be noted that a value of RECS > 0 must always be entered.
DINTR
This is the maximum interception storage of the plant cover (mm). From
Table A7.1, for winter-sown wheat, a value of DINTR = 3.0 was chosen.
DEPNO
This denotes the average number of rills (concentrated flow paths) across
the width of the slope plane. Since the erosion plot is ploughed up-anddown slope, the plough furrows act as concentrated flow paths. Based on
field observations, an average of ten paths was recorded, using the
procedure shown in Appendix 8. A value of DEPNO = 10.0 was therefore
entered.
RILLW
This is the average bottom width (m) of a concentrated flow path or rill.
Based on field measurement, the average furrow width was 8 cm, so a
value of RILLW = 0.08 was entered.
A flat surface would be assigned a value of RILLW = 0.0.
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
52POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
53
RILLD
This is the average depth (m) of a concentrated flow path or rill. Based on
field measurement, the average furrow depth was 5 cm, so a value of
RILLD = 0.05 was entered.
ZLR
This denotes the average side slope of a concentrated flow path (rill),
expressed as 1:ZLR. Based on field measurement, a typical side slope was
1:1. Therefore a value of ZLR = 1.0 was entered.
RS
If RS = 0, the model assumes that the values of RILLW and RILLD
entered above apply for the whole length of the element. If RS = 1, the
model assumes the values apply to the rill at the lower end of the element
and scales the values to smaller dimensions with distance upslope. In this
case, the scaling option was not selected, so we entered RS = 0.
RFR
This is the downslope roughness ratio. Based on field measurements, using
the procedure described in Appendix 6 and illustrated in Figure A6.1, a
value of RFR = 1.0 was obtained and entered.
Although this value is much lower than those listed in Table A6.1, it is a
typical value for a relatively smooth surface. As stated earlier when
choosing a value for Manning’s n, the condition of the ground at the time
of the storm was a smooth seed-bed flattened by several months of
raindrop impact.
SIR
This is the interrill slope, defined as the average ground slope followed by
overland flow as it passes from the interrill area into the rills. Field
measurements along the overland flow paths observed during storms, gave
a slope of 7 per cent. A value of SIR = 0.7 was therefore entered.
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
53POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
54
COVER
This is the effective percentage canopy cover of the vegetation. Since, at
the time of the storm, this was estimated at 10 per cent, a value of COVER
= 0.1 was entered.
SHAPE
This refers to the shape of the leaves. SHAPE = 1 for bladed leaves and
needle leaves. SHAPE = 2 for broad leaves. Since the crop was wheat, we
entered SHAPE = 1.
PLANGLE
This is the average acute angle (degrees) between the plant stems and the
ground surface. Based on field measurement, a value of PLANGLE = 55°
was entered.
PBASE
This is the percentage basal area of the vegetation cover. From Table
A7.3, we can see that the value for small grains (wheat, barley, rice)
ranges from 0.2 to 0.3, depending on the planting density. As this may be
assumed to be high, a value of 0.3 is chosen. Since the percentage plant
cover was only 10 per cent, the value was reduced accordingly and we
entered PBASE = 0.03.
It should be noted that if the value entered for FMIN has been determined
in the field for vegetated conditions, PBASE should be set to 0.0. This
avoids further adjustment of the FMIN value within the model to allow for
the effect of the vegetation cover.
PLANTH
This is the average height of the plant canopy (cm). From field
measurements, a value of PLANTH = 15.0 cm was entered.
DERO
This is the maximum depth (m) to which erosion can proceed before a
resistant or non-erodible layer (e.g. hard pan) in the soil is reached. Since
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
54POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
55
there are no inhibiting layers in the soil at Woburn, a relatively high value
was chosen. We entered DERO = 3.0.
ISTONE
An indicator of the effect of rock fragments on the surface of the soil on
the saturated hydraulic conductivity. Since there are no rock fragments on
the soil surface, the model will not be using this parameter and either + or
- can be entered.
D50
This is the median particle size of the soil (µm). From textural
determinations of the sandy loam soil on the plot, a value of D50 = 250
µm was entered.
EROD
This is the detachability of the soil particles by raindrop impact (g/J). From
Table A9.1, for a sandy loam soil, a value of EROD = 1.6 was selected.
SPLTEX
This is the value of the exponent relating detachment of soil particles by
raindrop impact to the depth of water on the soil surface. A value of 2.0 is
used in EUROSEM.
COH
This is the cohesion of the soil (kPa). The value should take account of the
effects of the root system of the vegetation. From field measurements with
a torvane on the bare saturated soil, cohesion is very low at about 2.0 kPa.
From Table A9.2, assuming that wheat has a similar effect to barley, an
increase in cohesion of between 0.6 and 2.6 kPa may be expected as a
result of root reinforcement. For a crop at the stage of 10 per cent cover,
we might estimate an increase at the lower end of the range, say 0.65 kPa.
If this is added to the cohesion value for the bare soil, we get a total
cohesion of 2.0 + 0.65 kPa = 2.65 kPa. A value of COH = 2.65 was
therefore entered.
RHOS
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
55POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
56
This is the specific gravity of the sediment particles. This is normally set at
2.65 Mg/m3.
PAVE
This is the proportion of the surface occupied by non-erodible material,
e.g. concrete, tarmac, desert pavement. For the erosion plot at Woburn,
we entered PAVE = 0.0.
SIGMAS
This is the standard deviation of the sediment particle diameter (µm) for
any element immediately upslope of a pond. It is used within KINEROS
for modelling the process of sedimentation in a pond or reservoir. Since
EUROSEM does not deal with ponds, SIGMAS was set = 0.0.
MCODE
This allows the user to choose the sediment transport capacity equations
for the interrill flow. MCODE = 0 selects the equations proposed by
Govers (1990). MCODE = 1 selects the equations proposed by Everaert
(1992).
Interrill sediment transport capacity controls the rate at which sediment
from the interrill areas is delivered to the concentrated flow paths or rills.
Everaert's (1992) equations give much higher values of interrill sediment
transport capacity with the result that the transport capacity in the rills can
often be filled by material from the interrill areas. The detachment of soil
particles by flow in the rills is then reduced to zero and the rate of erosion
becomes controlled by the detachability of the soil and the effects of
vegetation on the interrill areas and not by the cohesion of the soil and the
roughness imparted by vegetation in the rills. We chose to use the
equations of Govers (1990) and therefore entered MCODE = 0.
The Catchment Characteristics File was then complete.
To avoid losing any data, it is recommended that, when complete, the
catchment characteristics file is immediately saved.
Observed data file
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
56POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
57
EUROSEM 3.0 allows the possibility of displaying the simulated
hydrographs and sediment graphs graphically. The graphs can also be
compared with observed data. In order to use this facility, which is
particularly useful for calibration and validation work, an observed data
file must be created. Figure 4.5 shows the observed data file for the event
at Woburn. The data file must be given a name; we chose to call ours
OBSERVE.DAT.
The file consists of three columns, showing time, runoff (mm/h) and
sediment discharge as a volumetric concentration. The relevant data
should be entered under these headings. EUROSEM does not require
information for each time step used in the model simulation. Only the time
steps on which the observations were made are required. It is not
necessary to have both runoff and sediment concentration values for each
time step but, if a value is missing, you should enter a negative number.
Checking the data files
A large amount of data has now been placed in the two input files and it
would be surprising if there were not some errors. The two input data files
and the observed data file (if used) should now be checked.
Although checking can be done on the monitor screen, it is better to check
the data on print-outs of the files. After correction, the files must be saved.
Checking and correcting the data files in this systematic way generally
produces fewer errors than working directly on the file as displayed on the
monitor screen.
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
57POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
58
********EUROSEM V3 OBSERVED DATA FILE**********
TIME(MIN)
Q(MM/H)
.00
.0
21.00
.0
21.50
.0
22.00
.0081
22.50
.0636
23.00
.2619
23.50
.7521
24.00
1.6945
24.50
3.1316
25.00
4.9729
25.50
7.0957
26.00
9.3023
26.50
11.3030
27.00
12.8613
27.50
13.9506
28.00
14.9752
28.50
15.5398
29.00
15.9054
29.50
16.1392
30.00
16.3341
30.50
16.2235
31.00
15.5284
31.50
14.1153
32.00
12.1616
32.50
10.1129
33.00
8.2561
33.50
6.6692
34.00
5.3545
34.50
4.2887
35.00
3.4391
35.50
2.7694
36.00
2.2439
36.50
1.8312
37.00
1.5056
37.50
1.2469
38.00
1.0395
38.50
.8720
39.00
.7360
39.50
.6246
40.00
.5325
40.50
.4559
60.00
.00000000
QS(KG/MIN)
.0000
.0000
.2588E-0
.1855E-07
.3332E-06
.3200
-10.
7.525
18.34
35.10
57.13
82.18
106.0
124.4
136.3
149.0
154.9
158.0
159.8
161.0
160.7
155.6
140.9
117.5
92.26
70.23
52.45
38.72
28.37
20.75
15.20
11.18
8.10
6.156
4.608
3.465
2.615
1.980
1.502
1.140
.8629
.0000
Figure 4.5. Example of a EUROSEM observed data file (OBSERVE.DAT)
4.4.3 Output Files
Version 3.0 and higher allow the option of three output files. These are:
Dynamic output file
Static output file
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
58POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
59
Auxiliary output file
All output files are provided automatically. However, they must be given file
names. We chose to call them respectively:
WOBC1.DYN
WOBC1.STA
WOBC1.AUX
DYNAMIC OUTPUT FILE
Figure 4.6 shows the dynamic output file for the sample storm on the erosion plot
at Woburn. The file contains the information that was entered for identifying the
study area, the names of the input files used, the total sediment removed from the
element, the area of the element, data on runoff volume, runoff depth, sediment
concentration and total sediment removed from the element for each time step in
the simulation, the time to peak flow rate and the rate of flow at the peak, and a
water balance calculation for the storm.
We see that the total erosion simulated from the plane was 163.8 kg and that the
simulated peak runoff of 60 mm/h and peak sediment discharge of 139.8 kg/min
occurred 90 minutes after the start of the storm. The total runoff was 1.198 mm
which, for a storm of 5.7 mm, represents a runoff coefficient of 21 per cent. The
volume balance error was very small at less than 1 per cent.
STATIC OUTPUT FILE
Figure 4.7 shows the static output file. The file gives information identifying the
study area and a list of the input data used in the simulation. The derived
parameter is the modified value of Manning's n for the interrill area calculated
within the model, taking account of the input value for IRMANN and the value
of RFR. The file follows with a summary of the total erosion or deposition
simulated for the storm with separate accounting for the rill and interrill areas,
hydrological and sediment discharge characteristics of the simulated storm,
changes in the dimensions of the rills arising from erosion or deposition, and a
water balance calculation. We can see that the total erosion amounts to 1.87 t/ha
and that whilst rill depth increased downslope, rill width attained a maximum at
17.5 m down the slope.
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
59POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
60
INPUT PARAMETER FILE:
INPUT RAINFALL FILE:
ELE #
----1
wobc1.dat
wobr1.dat
=== DESCRIPTIVE RUN TITLE ===
VOL. BAL.
TYPE
ERROR %
------------PLANE
.453E-01
SED. TOTAL
(KGS.)
---------163.774
.0017 mm Inactive Storage Capacity on plane
HYDROGRAPH FOR ELEMENT 1
CONTRIBUTING
AREA=
875.00 SQ. METER OR
HECTARES
TIME(MIN)
Q(M3/Min)
Q(MM/H)
CONC.
.00
.50
1.00
1.50
89.00
89.50
90.00
90.50
91.00
91.50
92.00
92.50
93.00
93.50
94.00
94.50
95.00
95.50
96.00
96.50
149.00
149.50
150.00
.000000
.000000
.000000
.000000
.000000
.370911
.874920
.490726
.216932
.086407
.029550
.013895
.007116
.003629
.001955
.000626
.000170
.000002
.000000
.000000
.000000
.000000
.000000
.0000
.0000
.0000
.0000
.0000
25.4339
59.9945
33.6498
14.8753
5.9251
2.0263
.9528
.4880
.2488
.1341
.0429
.0116
.0002
.0000
.0000
.0000
.0000
.0000
.00000000
.00000000
.00000000
.00000000
.00000000
.04710156
.06029553
.07414180
.05721624
.04008070
.02542549
.01754890
.01221337
.00791453
.00478878
.00049014
.00000763
.00000924
.00000000
.00000000
.00000000
.00000000
.00000000
TIME TO PEAK FLOW RATE = 90.000
.0088
QS(KG/MI
N)
.0000
.0000
.0000
.0000
.0000
46.30
139.8
96.42
32.89
9.178
1.991
.6462
.2303
.7611E-01
.2481E-01
.8127E-03
.3437E-05
.5990E-07
.0000
.0000
.0000
.0000
.0000
(MIN)
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
60POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
61
PEAK FLOW RATE =
59.995 (MM/H)
------------------------------------------------------------------------TOTAL RAINFALL DEPTH = 5.701 (MM)
**** EVENT SUMMARY ****
----- ------GLOBAL VOLUME BALANCE
VALUES ARE IN UNITS OF LENGTH (VOL./BASIN AREA)
BASIN AREA =
875.00000
(M**2)
STORAGE REMAINING ON ALL PLANES
=
.00000
(MM)
STORAGE REMAINING IN CHANNELS+CONDUITS
=
.00000
(MM)
STORAGE REMAINING IN PONDS
=
.00000 (MM)
TOTAL INFILTRATION FROM ALL PLANES
=
4.45074
(MM)
TOTAL INFILTRATION FROM ALL CHANNELS
=
.00000 (MM)
TOTAL BASIN RUNOFF
=
1.19819 (MM) 1.0484
CU.M.
--------TOTAL OF STOR., INFIL. AND RUNOFF TERMS
=
5.64893 (MM)
*** GLOBAL VOL. ERROR =
.9088 PERCENT ***
Figure 4.6. Example of EUROSEM Dynamic Output File (WOBC1.DYN) (To
save space some timesteps in the hydrograph output have been omitted)
AUXILARY OUTPUT FILE
Figure 4.8 shows the auxiliary output file. The file gives information on the
depths of total rain (RAIN), direct throughfall (TFALL), leaf drainage (DRIP),
stemflow (STEM) and interception storage (VEGSTORE), rainfall intensity, and
the kinetic energy of both the direct throughfall and the leaf drainage, for each
time-depth pair of the storm; the amount of rainfall intercepted by the plant cover
and the capacity interception storage (stocap). Details are provided of the rill
spacing and dimensions of the rill at the top and bottom of the element at the start
of the storm. A sediment budget is given comprising the volume of material
eroded on the element (eros), the input of sediment from the element above, if
any (susp), the volume of sediment removed from the element (sedout) and the
overall sediment balance. This information is provided separately for the interrill
and rill areas.
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
61POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
62
Also given are the final spacings and dimensions of the rills or concentrated flow
paths; the values of selected hydrological and erosion input data; the total surface
erosion or deposition within the storm for each node on the element for which
simulations were made; and a water balance at the end of the element. Additional
information, provided when relevant, includes a recalculation of the volumetric
moisture content of the soil after periods in the storm when rainfall ceases and
the surface is free of water; and the relationships between flow depth, crosssectional area of the flow and wetted perimeter used in routing flow across the
interrill area and along the rills. Interrill flow is only routed explicitly by the
model when the interrill flow paths are extremely long.
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
62POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
63
-----------------------------------------------------------------|
|
*
EUROSEM 3 STATIC SUMMARY FILE
*
|
|
-----------------------------------------------------------------RUN TITLE:
INPUT DATA FOR ELEMENT 1
=========================
NU:
0
W:
25.00 M
XL:
MANN:
.04
FMIN:
POR:
.45
THI:
ROC:
.01
RECS:
DEPNO:
10.00
RS:
ZLR:
1.00
RILLW:
COVER:
.10
SHAPE:
PBASE:.03
PHEIG:
.15 M
EROD:
1.60 G/J
SPLTX:
RHOS:
2.65kgm3
PAVE:
SIR:
.154
DERO:
Derived parameter:
MN(IR): .039
EROSION SUMMARY
--------------TOTAL RILL EROSION
TOTAL INTERRILL EROSION
TOTAL EROSION/DEPOSITION
(a minus denotes deposition)
35.00 M
2.60 MM/HR
.40
5.00 MM
.0
.08 M
1
D50:
2.00
.00
3.00 m
159.322 kg
1.122 kg
1.821 t/ha
.013 t/ha
163.774 kg
1.872 t/ha
HYDROLOGY SUMMARY, ELEMENT 1
==============================
NET RAINFALL
PEAK RAINFALL RATE
TIME TO RUNOFF
DURATION OF RUNOFF
TIME TO PEAK FLOW RATE
PEAK FLOW RATE
=
TIME TO PEAK SEDIMENT DISCHARGE=
PEAK SEDIMENT DISCHARGE
=
=
=
=
=
=
59.995
90.000
139.80
5.7007
119.14
89.500
6.5000
90.000
(MM/H)
(MIN)
(kg/MIN)
RILL DIMENSION SPATIAL SUMMARY, ELEMENT 1
------------------------------------------DISTANCE
RILL DEPTH
RILL WIDTH
DOWNSLOPE
M
mm
mm
.00
22.36
80.00
8.75
32.64
84.99
17.50
40.46
85.41
26.25
46.84
84.72
35.00
52.16
84.35
GLOBAL VOLUME BALANCE
=====================
TOTAL RAINFALL DEPTH
=
STORAGE REMAINING ON ALL PLANES
=
STORAGE REMAINING IN CHANNELS+CONDUITS
=
STORAGE REMAINING IN PONDS
=
TOTAL INFILTRATION FROM ALL PLANES
=
TOTAL INFILTRATION FROM ALL CHANNELS
=
TOTAL BASIN RUNOFF
=
1.19819 (MM)
--------TOTAL OF STOR., INFIL. AND RUNOFF TERMS
=
*** GLOBAL VOL. ERROR
=
S:
G:
THMX:
DINTR:
RFR:
RILLD:
PANG:
250.00 um
COH:
SIGMA:
.11
240.00 M
.4
3.00 MM
1.000
.05 M
55.01 o
2.65 KPA
1.00
(MM)
(MM/H)
(MIN)
(MIN)
(MIN)
DEPTH
INCREASE
mm
.00
1.02
1.73
2.12
2.16
WIDTH
INCREASE
mm
.00
4.99
5.41
4.72
4.35
5.701 (MM)
.00000 (MM)
.00000 (MM)
.00000 (MM)
4.45074 (MM)
.00000 (MM)
1.0484 CU.M
5.64893 (MM)
.9088 PERCENT ***
Figure 4.7. Example of EUROSEM Static Output File (WOBC1.STA)
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
63POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
64
INPUT PARAMETER FILE:
wobc1.dat
INPUT RAINFALL FILE:
wobr1.dat
=== DESCRIPTIVE RUN TITLE ===
INTERCEPTION DATA FOR ELEMENT 1
ALL DATA EXPRESSED AS MM PER TIME DEPTH PAIR
TIME
RAIN
TFALL
DRIP
MIN
MM
MM
MM
45.
.200
.180
-.021
60.
.200
.180
-.015
70.
.600
.540
-.019
85.
.500
.450
.004
89.
1.400
1.260
.055
90.
2.000
1.800
.114
125.
1.100
.990
.067
160.
.000
.000
.000
0.
.000
.000
.000
*** PLANE NO. 1 DIAGNOSTIC INFORMATION ***
stocap(m): .000002
STEM
MM
-.013
-.009
-.012
.003
.034
.071
.042
.000
.000
RAINFALL HYETOGRAPH FOR PLANE NO. 1
(AFTER INTERCEPTION REMOVED)
TIME (MIN)
INTENSITY(MM/HR)
.0
.19
45.0
.62
60.0
3.06
70.0
1.83
85.0
20.24
89.0
119.14
90.0
1.88
125.0
.00
160.0
.00
VEGSTORE
MM
.05438
.04452
.09073
.04342
.05043
.01427
.00149
.00000
.00000
ERROR
%
.00000
.00000
.00000
.00000
.00000
.00000
.00000
.00000
.00000
Kinetic Energy (J/m2)
Rain
.000
6.360
17.785
13.320
31.181
44.421
12.873
.000
.000.000
Leaf Drip
.000
.000
.000
.002
.010
.014
.015
.000
THE RAIN GAGE FOR PLANE 1 IS GAGE NO. 1
PPCT. WEIGHT IS 1.00 INTERCEPTION IS .30 (MM)
Short Interrill flow length: not explicitly routed
Every 2.50 m there is a rill with sideslope
Width(m) and Depth(m) at Top of slope:
.08000
Width and Depth at Bottom:
1.00
.02236
.08000
.05000
INITIAL SATS. AFTER HIATUS:
.31230480 .31230480 .31230480 .31230480 .31230480
Large NC -.00001
At I= 2, depth -.00001
Large NC -.00010
At I= 3, depth -.00010
Large NC -.00005
At I= 4, depth -.00005
Large NC -.00004
At I= 5, depth -.00004
INtRill eros, susp, sedout, and Bal. (m*3):
-.00042 .00000 .00042 .00000
Rill eros, susp, sedout, and Bal. (m*3):
-.06012 .00000 .06180 .00168
GEOM. PARAMETERS ARE L= 35.0 W= 25.0 S= .1100
Every 2.50 m there is a rill with sideslope 1.00
Width(m) and Depth(m) at Top of slope:
.08000 .02236
Width and Depth at Bottom:
.08435 .05216
ROUGHNESS COEF. IS MANNINGS N= .040
INFILT. PARAMETERS ARE FMIN= 2.68041 mm/h; G= 240.000 mm
POR= .4000 SMAX= .4530 SI= .4200 ROC= .010 RECS= .00 mm
EROSION PARAMETERS ARE --D50= 250. RHOS= 2.65 POR= .45 PAVE.FAC.= .000
ACCUMUL. SURFACE DEPOSIT. OR EROSION (NEG.)
AT EACH NODE (m.)
.00000 -.19038E-03 -.30781E-03 -.36887E-03 -.38907E-03
**** WATER BALANCE AT END OF PLANE ****
<INFLOW BASED ON (PPT*GAGE WT) - INTER. + RUNON>
INFLOW= .499E+01 OUTFLOW= .494E+01 STOR.=.000E+00 ERROR=.453E-01 %
-------------------------------------------------------------------------
Figure 4.8. Example of a EUROSEM Auxiliary Output File (WOBC1.AUX)
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
64POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
65
The message, Large NC, followed by calculations of negative depths at various
nodes on the element indicates instability in the numerical solutions of the
infiltration sub-routine. These arise when there is insufficient surface water to
satisfy the infiltration requirement. They are not important in terms of the overall
simulation of erosion by EUROSEM, however, and can be ignored.
We can see that the peak rainfall intensity of 119 mm/h occurred 89 minutes after
the start of the storm. The timing of the peak flow and sediment discharge thus
represent an almost immediate response to this. By comparing the dynamic and
auxiliary output files, we can also see that runoff ceased only five minutes after
the end of the storm. By summing the data in the interception table, we find that
direct throughfall accounted for 4.86 mm of the 5.7 mm of rain. This is not
surprising. With a crop cover of only 10 per cent, the effect of vegetation in
intercepting the rain and reducing its energy would be expected to be small.
If we multiply the value for rill sediment leaving the plane (sedout = 0.00168 m3)
by the specific gravity of the sediment particles, we get the value for total erosion
as given in the static output file. If we examine the value for erosion at each
node we can see how erosion has increased from zero at the top of the slope
plane to a maximum at the bottom.
4.5 RUNNING EUROSEM
Now that the two input data files have been prepared and a decision made on the
names of the output, EUROSEM is ready for use.
Assuming you are operating from the hard disk, you should now change to the
directory which contains the EUROSEM program by typing:
C:\ CD EUROSEM
The screen will then display
C:\EUROSEM\
You should then type:
EURO
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
65POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
66
and hit the carriage return. The following will appear on the screen:
EUROSEM
RUNNING WITH PROGRAM KINEROS/ Metric LAHEY VERSION
OF 11/97
VERSION 3.2L 11-97 FOR LAHEY LISK GRAPH LIBRARY. THIS
VERSION
REPLACES ALL PREVIOUS VERSIONS. USE WITH CARE!!!
Hit Carriage Return to Continue:
On hitting the return key, the following will appear:
PLEASE REPORT ALL BUGS/PROBLEMS TO:
DR J.N.QUINTON
SILSOE COLLEGE
SILSOE
BEDFORD
MK45 4DT
UNITED KINGDOM
TEL + 44 - (0)1525 - 863294
FAX + 44 - (0)1525 -863300
EMAIL [email protected]
Enter a 1 to 80 char. title for the output file:
This entry is merely for purposes of description. For the example being used
here, we entered the place and date of the storm:
woburn jan 26 1990
After this entry has been made, a series of questions appears on the screen.
Do you want screen graph of output hydrograph?
If your computer can display the graphic outputs contained within EUROSEM
and you wish to view them, type Y. Otherwise type N.
After this entry, the following dialogue will appear:
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
66POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
67
File name Assignments in Memory:
INPUT PARAMETER FILE: WOBC1.DAT
INPUT RAINFALL FILE: WOBR1.DAT
Recorded Data File: OBSERV.DAT
Static Output File: WOBC1.STA
Dynamic Output File: WOBC1.DYN
Output Auxiliary File: WOBC1.AUX
Use These I/O FILES? (Y or N)
This provides the option of using input data files and output files whose names
have been stored by the program from a previous application of the model. It is
useful when you have completed one simulation with EUROSEM and want to
make some changes to the input data before running another simulation.
Answering Y (YES) to this question saves you having to specify the names of the
input and output files over again.
If you answer Y, you skip the next seven questions.
If you answer N, you pass to the following questions:
NAME OF INPUT PARAMETER FILE (UP TO 12 CHAR):
You should now enter the name you wish to use for the catchment characteristics
file. This can be up to twelve characters in length. The name should be split
between part of the label which relates to the site and part which relates to the
data contained in the file. The section of the label relating to the data should be
three characters in length and separated from the first part of the label by a fullstop.
NAME OF INPUT RAINFALL FILE (UP TO 12 CHAR):
You should now enter the name of the rainfall file.
NAME OF STATIC OUTPUT FILE (UP TO 12 CHAR):
You should now enter the name of the static output file.
NAME OF DYNAMIC OUTPUT FILE (UP TO 12 CHAR):
You should now enter the name of the dynamic output file.
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
67POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
68
NAME OF AUXILIARY OUTPUT FILE (UP TO 12 CHAR):
You should now enter the name of the auxiliary output file.
ARE ANY ELEMENTS PONDS? (Y OR NO)
This question is not relevant to EUROSEM Version 3.0, so type N.
Name of Recorded Data File: (if any)
You should now either enter the name of the observed data file. If you do not
have an observed data file, you should leave the entry blank (i.e. not type
anything at all) and press the carriage return
The model will then run.
Whilst the model is running, the word Working will appear on the screen.
Completion may take from a few seconds to several minutes depending upon the
computer being used, the length of the storm and the amounts of runoff and
erosion being predicted.
If a graphical output has been requested, this will appear on the screen on
successful completion of the simulation. At present it is not possible to save the
graph to a file and it cannot, therefore, be printed. The graph is, however, useful
for immediate visual comparison of the shapes of the hydrographs and sediment
graphs with observed data and with the output of previous simulations. When
you have viewed the graph, hit the carriage return to return the screen to the DOS
prompt.
If a graphical output was not selected, the words
NORMAL COMPLETION
will appear on the screen, if the programme has run successfully, and you will be
returned to the DOS prompt.
Any other message indicates an error has occurred within the program. If this is
the case, you should first check the input files closely for any faults. If this does
not solve the problem, it should be reported to the authors.
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
68POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
69
After a run has been completed successfully, the individual output files can be
called by name in turn and displayed on the screen. They can also be printed out
if required.
It should be stressed that this version of EUROSEM is intended for users to try
out and comment on. It is not intended for practical applications, although later
versions will be.
NO LIABILITY MAY BE CLAIMED FOR DIRECT OR CONSEQUENTIAL
DAMAGE ARISING FROM USE OF THE PROGRAM.
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
69POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
70
Chapter 5 SIMULATION TECHNIQUES
5.1 HOW TO SIMULATE….
This section describes in detail how to simulate different soil types and the effect of plant
parameters on model output.
5.1.1 How To Simulate Different Soil Types
Soil properties have a significant effect on both runoff and erosion. When simulating the
effect of different soil types and soil conditions, the User needs to set appropriate input values
for the following parameters which influence (a) the hydrological behaviour of the soil and (b)
the resistance of the soil to erosion. Hydrological behaviour is influenced by FMIN, G, POR,
THI, THMAX, IRMANN and RLMANN; the resistance of the soil is influenced by EROD
and COH.
The User should always remember that erosion cannot be properly or even accurately
simulated for a catchment unless the runoff is first well simulated. Predictions of erosion are
moderately sensitive to FMIN, G, IRMANN and RLMANN and highly sensitive to THMAX
and THI (Quinton, 1994). The User therefore needs to pay particular attention to those
parameters which relate to infiltration and runoff generation. This is especially true if the
parameter values have to be selected without the benefit of a measurement on which
calibration may be performed, or if the measurement does not allow a distinction to be drawn
between interactive parameters. The use of hydrologically-sensitive parameters for calibration
is described in Section 5.2.
The two most important infiltration parameters are FMIN and G to which predictions of the
volume of storm runoff and the peak flow are moderately sensitive (Quinton, 1994). Values
for each can be chosen in a general way in relation to soil type, but there is no consistent trend
and the presence of organic matter and the condition of the soil can modify any general
relation. Tables A.4.1 and A.4.2 (Appendix 4) give an indication of how the parameter values
can change with soil texture. The values are based on a compilation of data on soil hydraulic
properties from Rawls et al (1982) and include ranges based on the standard deviation of the
data on which they are based. The overall trend is that FMIN declines and G increases in
value as the soil becomes finer. Further, the sensitivity of each parameter is increased as
values of the other parameter also increase. In detail, the values of both parameters depend
much more on the particle-size distribution than on the median particle size of the soil. The
general inverse relationship of FMIN decreasing as G increases also holds when the parameter
values are adjusted for changes in soil condition due to compaction, loosening by tillage, or
surface seal formation. Measurements indicate that the range in values of FMIN is
significantly larger than that in G.
Next to FMIN and G in importance is the maximum water content THMAX to which
predictions of runoff volume and peak are highly sensitive (Quinton, 1994). This value can
change easily with soil condition and management. Whilst tillage will consistently tend to
increase THMAX, the compaction of the soil by tractor wheels and the sealing of the surface
due to rainfall will create a shallow surface layer with significantly reduced FMIN, reduced
THMAX and a somewhat increased G. Usually, changes in FMIN are more dramatic than
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
70POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
71
changes in G. It should be noted that the values of THMAX and THI should represent net
conditions for the overall wetted soil depth during infiltration and not just the surface layer.
For these reasons, a shallow surface seal should not have undue influence over parameter
values, except for the value of FMIN. Catchment behaviour will be far more sensitive to
conditions in the immediate soil surface in storms of very high intensity, as compared with
lower intensity storms which wet the soil to a greater depth prior to the start of runoff.
Not surprisingly, predictions of runoff volumes and peaks are highly sensitive to THI
(Quinton, 1994) and, in the absence of measured data, the value of this parameter needs to be
set very carefully. The value of residual water content (THR; Table A.4.1) may be used as a
guide in determining a realistic lower limit for the value of THI. This limiting value should be
approached, however, only for very dry conditions. Furthermore, soil profile drying is initially
rapid following wetting, and much slower later on, so that estimates of very high THI (close to
THMAX) should also be avoided, except immediately after rainfall.
The User can set values of IRMANN and RLMANN in relation to the median particle size of
the soil (equation A.3.1; Appendix 3). Since the values, however, represent only a smooth
bare surface, they have to be increased to take account of microtopographic roughness and the
presence of a vegetation or crop cover. Generally, these latter factors will outweigh the
effects of soil texture choosing an appropriate value. Nevertheless, where a range of values is
available from which to choose (Table A.3.1), a value at the upper end of the range should be
selected for coarse-textured soils and a value at the lower end for fine-textured soils.
Although predictions of runoff volumes and peaks have a low sensitivity to the Manning's n
(Quinton, 1994), its value should still be chosen with some care since it will have an effect on
the shape of the rising limb of the hydrograph and, in short-duration storms, the peak flow
rate. The effect is sufficiently important for Manning's n to be useful for calibration purposes
(see Section 5.2).
As would be expected, the predictions of erosion are moderately sensitive to changes in the
values of both EROD and COH (Quinton, 1994). The User can select a value of EROD from
Table A.9.1 according to the texture of the soil. The values are highest for soils with a high
silt and very fine sand content, which are the most detachable (Poesen, 1985) and decrease
with both increasing clay and increasing sand contents. A range of values is given. Generally,
the mean values should be used for a sealed or compacted soil, the high values for loose and
moist soils, and the low values for loose and dry soils. However, account should also be taken
of the aggregate stability of the soil. This particularly applies to clay soils. Low values should
be used for soils with high aggregate stability and, therefore, for soils with high organic
contents and low plastic limits (Chisci et al, 1989) and high values for soils with less stable
aggregates.
EROD can also be used as a calibration factor (Section 5.2).Wherever possible, measured
values should be used for COH. The User can, however, select a guide value, depending on
soil texture, from Table A.9.2. Here two sets of values are given, one for compacted soils and
one for uncompacted. Particular care is needed in choosing a value if rill slopes are high or
the interrill Manning's n value is low since the sensitivity of model outputs to COH is increased
under these conditions (Quinton, 1994). The aggregate stability of the soil should again be
considered, with higher values being used for soils with strongly stable aggregates, high
organic content and low plastic limits. Account should also be taken of the initial soil
moisture condition; dry loamy soils (Govers, 1991) and soils with high contents of illite and
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smectite (Grissinger, 1966) are often highly erodible. The importance of initial soil moisture
content will be greater for short-duration storms than for long-duration storms during which
soils will be saturated for a considerable period of time.
Low values of cohesion should therefore be used if the initial moisture content is close to
saturation or if the surface soil layer is extremely dry (say THI < 0.1), but somewhat higher
values if the initial soil condition could be described as moist. Given the above, it is not
surprising that the range of values from which the User can choose is much greater for clay
soils. The User should select a value only after having taken a detailed account of the soil
conditions.
5.1.2 How To Simulate The Effect Of Plants
Generally, a plant cover will reduce erosion by protecting the soil against raindrop impact,
decreasing the volume of runoff (through increasing interception storage and infiltration of
rain water into the soil), imparting roughness to flow (lowering flow velocity) and increasing
the cohesion of the soil. In addition, the plant cover will influence the volume and energy of
the rainfall at the ground surface.
Where a plant cover is present, the User should take account of these effects by choosing
appropriate input values for COVER, PLANTH, DINTR, SHAPE, PLANGLE, PBASE,
MANN and COH. Particular attention should be given to PBASE to which all model outputs
are highly sensitive because of its effect on FMIN (Quinton, 1994).
Ideally, the User should obtain values of COVER, PLANTH and PLANGLE by measurement
(see Appendix 7 for techniques). The measurement of COVER must be based on any
vegetative material which will intercept the rainfall before it reaches the soil surface. Account
should be taken of litter layers, mulches, surface-laid geotextiles and ground vegetation, as
well as the canopies of bush, shrub and tree layers.
In contrast, PLANTH must reflect the height of the lowest vegetation layer. For instance, in
forest with a good litter layer and ground vegetation, effective PLANTH may be zero or a few
centimetres; where such surface protection does not exist beneath the trees, PLANTH will be
the height of the canopy (or the lowest canopy level in multi-storey vegetation) which may be
tens of metres. On arable land, PLANTH may be zero in minimum tillage systems where a
residue cover or mulch is retained but will be the height of the crop canopy where such cover
is absent. PLANTH does not need to be determined very accurately for contact covers and
low-growing vegetation because the model is insensitive to changes in PLANTH when it is
below 14 cm. Greatest accuracy is required for PLANTH between 14 and 50 cm because the
erosion predictions are most sensitive to values in this range. When PLANTH exceeds 50 cm,
its value also needs to be determined accurately when COV > 70 per cent (Quinton, 1994).
Although it is sometimes possible to obtain measured data for DINTR, PLANGLE and
PBASE, it is tedious to do so. The User should make use of the Guide values (Tables A7.1,
A7.2 and A7.3) contained for these parameters and also for PLANTH in Appendix 7. Since
these values are for mature plants, the User should adjust the values to take account of the age
of the plants or crop growth stage. PLANTH will also vary if the plant growth is retarded for
any reason, e.g. a period of drought, infertile soil, high groundwater table. For DINTR, the
effective value for a given stage of growth will reflect the percentage cover; the Guide value
should therefore be weighted by the ratio of actual percentage cover to percentage cover at
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maturity. Generally, greater accuracy is required in determining DINTR when COV and
PBASE are high. A similar weighting procedure could be adopted for determining PBASE
values at different stages of plant growth, although care should be taken to stay within the
recommended range of values. It should be stressed that the Guide values given for poor and
good covers, both represent conditions at maturity. The value for poor cover should not
therefore be used to represent a crop or vegetation with potentially good cover but in an early
stage of growth.
Where Guide values are adopted for PLANGLE, the User should use general and local
knowledge of the appearance of the vegetation or crop at the appropriate stage of growth.
Depending on the type of vegetation, both measured and Guide values of PLANGLE can
show a high level of variability. The User should follow the protocol described in Appendix 7
to deal with this. It should be kept in mind, however, that model outputs are rather insensitive
to changes in PLANGLE so it may not be worthwhile spending a lot of time in determining its
value very accurately.
SHAPE is relatively easy to categorise and can be done by observation of the plant or by
choosing from the Guide values listed in Appendix 7.
The User must modify the values used for RLMANN and IRMANN to allow for the effects of
vegetation. The procedure described in Appendix 3 should be followed in interpreting the
Guide values contained in Table A3.1. Model outputs on erosion are more sensitive to the
chosen value when it is < 0.25. Since this will generally be the case, some care is required in
selecting an appropriate value. When the model is calibrated on Manning's n (see Section
5.2), the calibrated value should be checked to see that it falls within a realistic range. When
rills are present in the landscape, they are more likely to be cut in bare soil, so that different
values will generally be required for RLMANN and IRMANN.
Although it is generally recognised that plant roots contribute to the overall cohesion of the
soil, it is difficult to obtain adequate measurements of the cohesion of the soil-root matrix in
the field. If the cohesion is measured with a torvane, as required by EUROSEM for
measurements on bare soil, roots become entrapped within the vane and it is their resistance
that determines the measured value. Although the cohesion of the soil-root matrix depends
upon the tensile strength of the roots, it is the tensile resistance of the root system which is
important rather than the strength of an individual segment of root (Wu, 1995). Thus, the
values obtained from torvane measurements cannot be directly applied. The User should
therefore take the cohesion values for bare soil and modify them according to the Guide
Values found in Appendix 9 (Table A9.3). Generally, a 10-20 per cent increase in the value of
cohesion can be expected depending on the plant density and the vegetation type.
The dynamic nature of vegetation must be recognised. Thus, where a User is simulating
erosion over a succession of storms during the growing period, the vegetation parameters in
the Catchment Characteristics File must be regularly updated.
5.2 MODEL CALIBRATION
Model parameters for any system may be determined from measured input and output data by
running a model and changing parameter values until the model and the measurements agree.
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
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This is called parameter calibration. It is especially useful when parameters are not physically
measurable, or when the parameter represents the effective mean of a spatially variable value.
Calibration may be used to estimate several EUROSEM parameter values when an
experimental plot or well defined small catchment provides reliable rainfall and runoff data to
which results from EUROSEM may be compared. Good calibration requires good data, not
only having accurate rates of rainfall and runoff, but also having coincidence of timing of both
records. It is also desirable to have a calibration event covering a relatively long period of
runoff. Calibration with a variety of types of storms is often desirable, because it is often
impossible to fit all results equally well with the same parameters. In practical terms, storms
used for model calibration would have to be subdivided based upon their storm pattern which
in some cases vary according to the season. For the purpose of model evaluation, rainstorms
for the calibration and validation should exhibit similar characteristics.
5.2.1 Field data quality analysis
There are several important points to consider in judging whether experimental data is likely to
lead to a good calibration. Large catchments inherently will contain much water in storage
during runoff, and using such data to calibrate for infiltration parameters is very difficult. Even
using small plot data for infiltration calibration requires understanding that there may be on the
order of a minute delay between the actual onset of runoff and the appearance of water in a
measuring flume record. A minute may be significant if the time to ponding is only a few
minutes from the start of rainfall. This could lead to parameter errors of 20% or more.
If runoff is measured by a flume or weir, there may also be a significant backwater storage
involved. For each discharge rate through the measuring device, there is an associated depth of
water which is measured, called a control depth, and for each control depth, there is a volume
of storage behind the device. This storage may be referred to as backwater storage. During
any time interval when flow is increasing, some of the water that flows to the device, such as a
weir, will be used to increase the storage, and some will flow through the device. Accounting
for that storage increase during hydrograph rise, and storage loss during recession, is called
derouting. Derouting must be undertaken if the rate of inflow to the weir is to be estimated.
Derouting can be accomplished if necessary by solution through time of a linear differential
equation which can relate inflow rate, storage change and measured outflow, and thus derive
the time of pattern of inflow. The actual method of performing derouting will not be discussed
here.
The importance of timing coincidence of rainfall and runoff records cannot be
overemphasized. Figure 5.1 illustrates a clear case of this problem. The sharp peak in runoff
physically must be associated with a significant drop in the rate of rainfall excess, yet it comes
about one minute before this could have occurred for the rainfall hyetograph shown. Many
other such errors in hydrograph-runoff data would not be so obvious. Fitting infiltration and
soil roughness parameters to this data without recognizing the inherent error in timing would
inevitably result in extremely biased calibrated parameters.
Many of the parameters required by EUROSEM are measurable, and some can be estimated
by sampling, but a few are not physically measurable, and must be estimated from tabulations
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
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Figure 5.1 Example of a data timing error.
based on experimental experience or by fitting to plot rainfall/runoff data. Table 5.1 illustrates
in general how the basic hydrologic and erosion parameters of EUROSEM may be classed
according to measurability for storms/events.
Table 5.1 Parameter measurability
Parameter source
Parameter type
Hydrology
Measurable overall
XL
W
S, SIR
RILLW, RILLD,
ZRL
PAVE
Measurable by sample
ROC
FMIN
G
THI
THMX
RECS
RFR
Erosion
D50
COVER
SHAPE
COH
PLANTH, PLANGLE
PBASE
Practically
unmeasurable
RLMANN,
IRMANN
EROD
SPLTX
The following discussion will assume that a user of EUROSEM has rainfall and runoff data for
a particular experimental catchment for which best fit parameters listed above are to be found
for storms or events. Emphasis will be placed on calibrating to obtain best estimates of plot or
experimental parameters by comparing a measured and simulated runoff hydrograph or
hydrographs.
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The first items listed as measurable are unmistakably parameters that can be found from a field
investigation or a detailed map, in some cases. Most of the other parameters, while physically
related and physically measurable, may have significant temporal and spatial variation, and
values can be obtained only in a statistical sense by measurements. Even rill dimensions should
be considered only measurable by sampling, except for the common case of regular ‘rills’
which are furrows formed by farm implements. It might also be more correct to list the mean
particle size, D50, and plant cover ,COVER, as sampled parameters as well.
Although FMIN and G can be estimated by performing infiltrometer tests at a sample point,
they cannot be found for a catchment as a whole, and usually need to be found by calibration.
Infiltrometer tests to find values for these parameters are tedious at best. Measurement of
Manning n is possible in special cases with special plot design, but is usually very difficult, and
it should be considered normally unmeasurable. These 3 parameters will be the focus of much
of the discussion in this section. Not only are they the most difficult to measure or estimate,
but the results of EUROSEM are sensitive to their values.
5.2.2 Order of Calibration
It is quite important to calibrate the runoff hydrology before attempting to calibrate the
sediment transport parameters. The sediment transport simulation of EUROSEM cannot
logically be better than the quality of the hydrologic simulation.
5.2.3 Infiltration parameters
It is best to obtain a good estimate of the plot mean infiltration parameters G and FMIN, and
then to fit a value for Manning’s n, but depending on the length and size of the storm, there
are some inherent parameter interactions to be dealt with in finding these parameters.
Parameter interaction is used here to describe the condition where two different parameters
can be used interchangeably to effect a similar change in the shape of a hydrograph. Very short
storms lend themselves to the greatest problems of parameter interactions.
The general definition diagram for infiltration shows that, for the early part of the infiltration
capacity curve, the relation is linear in log-log space. During this early period, in fact, the
infiltration relation is effectively independent of gravity, and the asymptote of the ƒc curve at
small I can be simply described (Smith, 1990), using the parameters defined in chapter 2:
ƒc =
BK s
I
(5.1)
Thus for short storms during which this relation holds, the time to start of runoff can as easily
be fitted by an adjustment of B (containing G) as by adjustment of Ks. For a longer storm
which carries the infiltration capacity relation as far into the asymptotic region (the start of the
curve) as possible it is necessary to fit both G and Ks. For such an event, Ks, will have the most
significant effect on runoff amount and rate later in the storm, and G (B) may be independently
adjusted to match the time of inception of runoff. These parameter characteristics are
illustrated in Figures 5.2 and 5.3. Parameters G and FMIN have very similar effects even for
these long steady rains. Care must be taken to look independently at both timing and volume
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
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of runoff, because there are more than one combination of these two parameters which will
match a given amount of runoff. This can be easily seen by reference
Figure 5.2 Effect of FMIN on longer hydrograph.
Figure 5.3 Effect of Parameter G on longer hydrograph.
to figure 5.4; the volume of runoff for this storm, shown as the unshaded area below the
dotted line, could be conserved by increasing the level of Ks and reducing G appropriately.
Figure 5.4 illustrates the parameter interaction indicated by equation 5.1, for the short storm.
5.2.4 Hydraulic roughness
Figure 5.5 illustrates the basic effect that changing values of n will have on a simple plot
outflow with constant rainfall rate. The dotted line shows rainfall excess, the rate at which
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
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STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
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runoff is produced in place. The difference between this curve and the runoff rate measured at
the bottom of this hypothetical plot, is the rate at which water is going into storage. In fact
Figure 5.4 Interaction of parameters G and FMIN in short storms.
the area between the two curves up to any time T is the volume of storage V(T) on the plot
surface (assuming rainfall excess, r(t)-f(t), is uniform):
T
V(T) =
∫ [r (t ) − q (t )] dt
(5.2)
0
This volume must be equal to the volume of water on the surface at the end of the rainfall. If
infiltration rate could be assumed nearly constant, then it is not difficult to calculate this
volume, and it could be used to estimate the appropriate hydraulic roughness. In contrast to
the situation in figure 5.5, figure 5.6 shows that the hydraulic roughness is important for
estimating the peak runoff of short storms. Changing the amount of runoff which must go into
storage can have a significant effect on the peak for such short events. It can also be seen from
these figures that for short storms there is a subtle interaction between the infiltration curve,
which was assumed known in figure 5.2, and the roughness, since each can affect the shape of
the rising hydrograph and the peak runoff for a short storm.
This is another reason why a longer storm is far superior to a short one for purposes of
calibration. While changes in (Ks, G) or n both have an effect on the shape of the rising portion
of the hydrograph, later in the storm the effects of infiltration are significantly different from
the effects of roughness. Complexity of a long storm is not a problem, since the Ks (FMIN)
can be adjusted to match the volume, and roughness used to calibrate the peaks produced by
any later bursts of intense rain.
5.2.5 Effect of parameters RECS
The recession parameter RECS represents the effect of an idealised concept of
microtopography, which confines flow to an ever decreasing portion of the area as recession
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
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proceeds. This causes a reduction in gross infiltration, and lengthens the recession, as
illustrated in figure 5.7. While it is not as important as the infiltration parameters, RECS can
Figure 5.5 Effect of roughness in relation to surface storage.
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
79POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
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Figure 5. 6 Effect of roughness for short storm.
be used to achieve improved fits of recession, especially in runoff from quite rough or
undulating surfaces.
Figure 5.7 Calibration potential of the RECS parameter for recessions.
5.2.6 Calibrating erosion parameters
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
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EUROSEM provides the user with the ability to specify values for SPLTEX and EROD. The
former controls the effect that surface water depth has on damping the splash erosion of
raindrops, and should not require significant calibration. The latter, EROD, may be useful to
calibrate, since this parameter represents the relative rate of splash erosion for a particular soil.
Splash erosion is most significant in the early parts of a storm, when transport capacity is
relatively low, and depths of water are also relatively low. Thus, in calibrating EROD based on
measured sediment concentrations for a plot experiment, attention should be focused on the
concentrations during the rising portion of the runoff hydrograph. Figure 5.8 illustrates the
effect of EROD on runoff concentration early in a storm.
5.2.6 Comparative sensitivity
The results above indicate the interaction of parameters G and FMIN, and that runoff and
hydrograph shape is considerably more sensitive to the infiltration parameters than to hydraulic
roughness. Whatever combinations of G and FMIN are used, they should not be such that the
guidelines in Appendix 4 for these parameters are severely violated. A general guide should be
to calibrate parameters in the following order: FMIN, G, n, RECS for the hydrograph, and
then EROD to help match sediment concentration measurements.
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
81POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
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82
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MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
86POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
87
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erosion model: documentation and user manual. USDA Agricultural Research Service ARS77.
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87POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
88
Chapter 7 RELEVANT LITERATURE
Since the initial version of EUROSEM was developed, the model has been tested for a range
of conditions and extensive work on model uncertainty has been carried out. This chapter lists
some of the publications which have resulted from this work.
1. FAVIS-MORTLOCK, D., QUINTON, J.N., & DICKINSON, T. 1996. The GTCE
validation of soil erosion models for global change studies. Journal of Soil and Water
Conservation 51 (5), 397-403.
2. FOLLY, A.J.V., QUINTON, J.N. & SMITH, R.E. Evaluation of the EUROSEM model
for the Catsop Catchment. Accepted for publication in Catena.
3. MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G., POESEN, J.W.A.,
AUERSWALD, K., CHISCI, G., TORRI, D., & STYCZEN, M.E. 1998. The European
soil erosion model (EUROSEM) : a process-based approach for predicting sediment
transport from fields and small catchments. Earth Surface Processes and Landforms 23,
527-544.
4. MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G., POESEN, J.W.A.,
AUERSWALD, K., CHISCI, G., & TORRI, D. 1998. The EUROSEM model. In Global
Change: Modelling soil erosion by water (eds. J. Bordman & D. Favis-Mortlock), NATO
ASI series, Series 1: Global environmental change. Springer-Verlag, London. 373-382.
5. MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G., POESEN, J.W.A.,
AUERSWALD, K., CHISCI, G., TORRI, D., STYCZEN, M.E., FOLLY, A.J.V. 1998.
The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
6. MORGAN, R.P.C., QUINTON, J.N. & RICKSON, R.J. 1990. Structure of the Soil
erosion prediction model for the European Community. In Proceedings of the International
Symposium on Water Erosion, Sedimentation and Resource Conservation. pp.49-59.
Central Soil and Water Conservation Research and Training Institute. Dehradun, India
7. MORGAN, R.P.C., QUINTON, J.N. & RICKSON, R.J. 1991. EUROSEM a user guide.
Silsoe College, Silsoe, Bedford, UK., pp.56.
8. MORGAN, R.P.C., QUINTON, J.N. & RICKSON, R.J. 1992.
documentation manual. Silsoe College, Silsoe, Bedford, UK, pp. 34.
EUROSEM
9. MORGAN, R.P.C., QUINTON, J.N. & RICKSON, R.J. 1992. Soil erosion prediction
model for the European Community. In Erosion, Conservation and small scale
farming.(eds. Hurni, H. and Tato, K.). pp.151-162. GB-ISCO-WASWC.
10. MORGAN, R.P.C., QUINTON, J.N. & RICKSON, R.J. 1993. EUROSEM version 3.1 a
user guide. Silsoe College, Cranfield University, Silsoe, Bedford, UK., pp.83.
11. MORGAN, R.P.C., QUINTON, J.N. & RICKSON, R.J. 1994. Modelling methodology
for soil erosion assessment and soil conservation design: the EUROSEM approach.
Outlook on Agriculture 23, 5-9.
12. QUINTON, J.N. & MORGAN, R.P.C. 1996. Description of the European soil erosion
model (EUROSEM) and an example of its validation. In Soil erosion processes on steep
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
88POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
89
lands - evaluation and modelling, Proceedings of the international workshop on soil
erosion processes on steep lands - evaluation and modelling, Merida, Venezuela, 1993,
(eds. I. Pla Sentis, R. Lopez Falcon & D. Lobo Lujan), CIDIAT, Merida, Venezuela.
13. QUINTON, J.N. & MORGAN, R.P.C. 1998. EUROSEM: an evaluation with single event
data from the C5 Watershed, Oklahoma, USA. In Global Change: Modelling soil erosion
by water (eds. J. Bordman & D. Favis-Mortlock), NATO ASI series, Series 1: Global
environmental change. Springer-Verlag, London.
14. QUINTON, J.N. 1994. The validation of physically-based erosion models - with particular
reference to EUROSEM. In Conserving Soil Resources: European Perspectives (ed. R.J.
Rickson), CAB International, Wallingford.
15. QUINTON, J.N. 1994. The validation of physically-based erosion models - with particular
reference to EUROSEM. PhD thesis, Cranfield University.
16. QUINTON, J.N. 1996. Modelando el impacto de barreras vivas sobre la conservación de
Suelo y sgua: propósito y beneficios. p75 - 78. In Estrategias para prácticas mejoradas de
conservación se suelo y agua en los systemas de producción de ladera en los valles andinos
de Bolivia. Projecto Laderas and Silsoe Research Institute.
17. QUINTON, J.N. 1997. A physically-based approach to optimising barrier strip spacing in
the Andean Valleys of Bolivia. Annales Geophysicae. Part II, hydrology, Oceans,
Atmosphere and non-linear Geophysics C329:15(2). (Abstract only)
18. QUINTON, J.N. 1997. Efecto del modelando de barreras vivas en pastos sobbre
escurrimiento y la pérdida de suelo en laderas empinadas en Bolivia: Simulaciones
preliminares. In proceedings of workshop. Cochabamba, October 1997.
19. QUINTON, J.N. 1997. Reducing predictive uncertainty in model simulations: a
comparison of two methods using the European Soil Erosion Model. Catena 30, 101-117.
20. SMITH, R.E., GOODRICH, D.A. & J.N. QUINTON. 1995. Dynamic distributed
simulation of watershed erosion: KINEROS II and EUROSEM. Journal of Soil and Water
Conservation 50, 517-520.
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
89POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
1
APPENDIX 1 - DETERMINATION OF TIME-DEPTH PAIRS
Figure A1.1 shows a typical rainfall trace for a storm as obtained from a recording rain gauge.
Based on changes in the slope of the line defining the trace, the storm should be divided into
discrete time periods within which the rainfall is of more or less uniform intensity.
The storm is then described by defining the time (T; min) of the start of each discrete period
and the cumulative rainfall (D; mm) received up to that time, as shown in Table A1.1. Each
entry in Table A1.1 is termed a time-depth pair.
The number of time-depth pairs used to describe the storm must be sufficient to take the
cumulative rainfall record past the total computational time (TFIN) for which it is proposed to
run the model. The value for TFIN will depend upon the duration of the rainfall and the
response time of the catchment. It should be sufficient to contain the hydrograph of surface
runoff and should therefore extend from the start of the rainfall to the time that the
contribution of surface runoff from the hillslopes to the stream channel ceases.
For the storm shown here, the number of time-depth pairs (ND) is 9.
Cumulative rainfall depth (mm)
3
2.5
2
1.5
1
0.5
0
0
20
40
60
80
100
120
140
160
Time (min)
Figure A1.1. Trace for storm rainfall
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G., POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
2
Table A1.1. Time-depth pairs for the rainfall trace shown in Figure A1.1, based on periods of
equal rainfall intensity
Time (min)
Cumulative rainfall (mm)
0
0.0
45
0.2
60
0.4
70
1.0
85
1.5
89
1.9
90
2.2
125
3.0
160
3.0
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,2 POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
3
APPENDIX 2 - DETERMINATION OF SLOPE
EUROSEM uses two descriptors of slope steepness, SIR and S.
Definitions
SIR is the basic input parameter. On a simple uniform plane (hillslope) element without rills or
clearly-defined concentrated flow paths, SIR represents the average slope of the plane (m/m),
measured along the direction of maximum slope, i.e. at right angles to the contour. For a
channel element, SIR represents the average slope of the channel (m/m). In these two
situations, S is not used and a value of 0.0 may be entered for the plane and a value of 0.01 for
the channel parameter.
Where a hillslope plane contains rills or concentrated flow-paths, measurements of both SIR
and S are required. S represents the average slope along the rill channels. SIR represents the
interrill slope, i.e. the slope followed by the interrill flow as it moves from the interrill areas
into the rills. This will normally be at an angle to the rills. Field evidence of micro-rills,
sediment fans and vegetation streamlined by the flow should be used to determine the flow
direction. EUROSEM assumes that the interrill slope must be considerably steeper than the
rill slope, otherwise the flow would not concentrate into rills. At present the model defaults to
an interrill slope of 1.4 S, if a value of SIR E 1.4 is used as input.It should be noted that if
interrill flow is assumed to be nearly at right-angles to the rills, the interrill flow path will be
much shorted than if the flow is assumed almost parallel to the rills (Figure A2.1). The interrill
flow distance will affect the delivery of sediment from the interrill areas to the rills. Up until
such time as the sediment transport capacity of interrill flow is reached, a longer flow path will
increase the quantity of sediment delivered to the rills; if this is very high, the amount delivered
may even fill the transport capacity of the rills. However, once the interrill sediment transport
capacity is attained, a longer flow path will provide more opportunity for sedimentation to
occur and the proportion of sediment eroded on the interrill areas which is delivered to the rills
will fall. With interrill flow paths greater than 1 m, EUROSEM routes the movement of
runoff and sediment over the interrill areas. When interrill flow length is less than 1 m, explicit
interrill routing is abandoned (Section 2.5.1.2).
Measurement
The slopes of plane elements (rills and interrill) and channel elements should be measured in
the field with an Abney Level of clinometer. To check that the slope is reasonably uniform
over the length of the plane or channel, measurements should be made at 5 m intervals along
the profile. Judgement should be used in deciding whether an element can be reasonably
described by a single slope or whether it should be split into two or more elements.
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,3 POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
4
Rill (S)
Steeply sloping
interrill (SIR)
Gently sloping
interrill (SIR)
Figure A2.1. Rill (S) and interrill (SIR) slope paths on a plane (hillslope) element
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,4 POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
5
APPENDIX 3 - ESTIMATION OF MANNING'S 'N'
Manning's n is used in EUROSEM to describe the roughness imparted to flow. Strictly, the
value chosen should represent the summation of roughness (friction) effects as follows:
n = ng + nv + nm
where ng = grain roughness due to the soil particles,
nv = roughness imparted by vegetation, and
nm = microtopographic roughness of the surface, particularly that associated
with tillage practices and stoniness.
Since Manning's n cannot be measured directly, its value needs to be estimated. Alternatively,
Manning's n can be considered a calibration parameter (Section 5.2) but the calibrated value
should then be compared with commonly accepted values to see that it is physically realistic.
It is possible to estimated the grain roughness (ng) component of Manning's n, using the
Strickler formula:
ng = 0.041 D50 0.167
(A3.1)
where D50 is the median particle size of the soil (m). The estimated value could be used to
represent the total Manning's n value for smooth bare surfaces, i.e. conditions where no
vegetation or crop cover exists and where microtopographic relief is minimal. Since
procedures for estimating the nv and nm components have not been developed, there is no
way of modifying the ng value for a wider range of conditions. In most circumstances,
therefore, it is necessary to refer to published tables of experimentally determined values.
Table A3.1 gives Guide Values for Manning's n.
Table A3.1 shows a range of values for each condition. For example, for bare soil, four lines
of values are presented, each line representing a different level of microtopographic roughness.
Within each line, a value close to the upper end of the range should be chosen if the soil
particle (grain) roughness is high, and a value near the lower end of the range if the soil
particle roughness is low. Similarly, within the range of values presented for different crop
and mulch covers, a high value should be chosen for conditions of high grain roughness and
high microtopographic roughness, and a low value for conditions of low grain and
microtopographic roughness. Generally, the Manning's n value for bare soil is within the range
of 0.01 to 0.03. Where a vegetation or crop cover is present, the value of Manning's n should
never be less than that for bare soil.
The values given in Table A3.1 are derived from a range of experiments which include flows in
channels and shallow overland flow. It has been shown (Emmett, 1970; Pearce, 1976;
Morgan, 1980) that values of Manning's n for shallow flows on hillslopes are about an order of
magnitude higher than those relating to flow in channels because most of the vegetation and
rock fragments project rigidly above the flow. However, as seen in Section 2.5, other factors
may offset this effect. On balance, therefore, the tabulated values should be used for flows
both in channels and on hillslopes. Some distinction between the two types of flow can still be
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,5 POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
6
made, however, by chossing a value at the upper end of the listed range for interrill flow and a
value at the lower end for channel flow.
The values listed in Table A3.1 do not take account of the effects of rock fragments on the
surface. Where the soil surface has 10 per cent or more cover of rock fragments, the value
chosen for Manning's n should be modified as follows (Poesen, 1992):
nroc = n . e 0.018 ROC
(A3.2)
where nroc = the value of Manning's n with a rock fragment cover,
n = the value of Manning's n without a rock fragment cover, and
ROC = the fraction of the surface covered with rock fragments.
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,6 POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
7
Table A3.1. Guide values for Manning's n
Land use or cover
Bare soil: roughness depth
Bermuda grass: sparse to good cover
very short grass
short grass
medium grass
long grass
very long grass
Bermuda grass: dense cover
Other dense sod forming grasses
Dense bunch grasses
Annual grasses (e.g. Sudan grass)
Kudzu
Lespedeza (legumes)
Natural rangeland
Clipped range
Wheat straw mulch
Chopped maize stalks
Cotton
Wheat
Sorghum
Mouldboard plough
Chisel plough; residue rate
Disc/harrow residue rate
No tillage: residue rate
Coulter
< 25 mm
25-50 mm
50-100 mm
> 100 mm
> 50 mm
50-100 mm
150-200 mm
250-600 mm
> 600 mm
low
0.010
0.014
0.023
0.045
mean
0.020
0.025
0.030
0.047
high
0.030
0.033
0.038
0.049
0.015
0.030
0.030
0.040
0.060
0.300
0.390
0.023
0.046
0.074
0.100
0.150
0.410
0.450
0.150
0.200
0.150
0.100
0.130
0.150
0.055
0.100
0.150
0.180
0.020
0.040
0.070
0.080
0.125
0.090
0.060
0.070
0.180
0.300
0.400
0.080
0.160
0.250
0.300
0.040
0.070
0.300
0.100
0.040
0.060
0.085
0.150
0.200
0.480
0.630
0.070
2.5 t/ha
5.0 t/ha
7.5 t/ha
10.0 t/ha
2.5 t/ha
5.0 t/ha
10.0 t/ha
< 0.6 t/ha
0.6-2.5 t/ha
2.5-7.5 t/ha
> 7.5 t/ha
< 0.6 t/ha
0.6-2.5 t/ha
2.5-7.5 t/ha
> 7.5 t/ha
< 0.6 t/ha
0.6-2.5 t/ha
2.5-7.5 t/ha
0.100
0.020
0.050
0.075
0.100
0.130
0.012
0.020
0.023
0.070
0.100
0.040
0.020
0.010
0.070
0.190
0.340
0.010
0.100
0.140
0.030
0.010
0.160
0.050
0.230
0.320
0.240
0.080
0.150
0.200
0.250
0.050
0.075
0.130
0.090
0.300
0.110
0.100
0.170
0.340
0.470
0.460
0.410
0.250
0.530
0.070
0.130
0.470
0.130
After Petryk and Bosmajian (1975), Temple (1982) and Engman (1986)
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,7 POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
8
APPENDIX 4 - HYDROLOGICAL PROPERTIES OF SOILS
Input data are required on those soil properties which influence the generation of runoff. The
properties concerned are those used in the KINEROS model (Woolhiser et al, 1990) to
describe the infiltration of water into the soil. The maximum rate at which water can enter the
soil is known as the infiltration capacity. This rate depends upon the initial saturation deficit
(θmax-θ), the capillary drive and the saturated hydraulic conductivity of the soil (Section 3.3).
Information is required on the following parameters: saturation moisture content of the soil
(THMAX), initial moisture content of the soil (THI), soil porosity (POR), the effective net
capillary drive (G), and the effective saturated hydraulic conductivity of the soil (FMIN).
Saturation moisture content (THMAX)
The saturation moisture content of the soil (THMAX) is obtained by determining the
volumetric moisture content of the soil at zero tension, using a sand table. Guide values for
soils of different textures are given in Table A4.1.
Initial moisture content (THI)
The initial moisture content of the soil is obtained by determining the volumetric moisture
content of the soil in the field at the start of the storm. If the moisture content is determined
gravimetrically, the value can be converted by applying the equation:
θv = θm ρb / ρw
(A4.1)
where θv = the volumetric moisture content,
θm = the gravimetric moisture content,
ρb = the dry bulk density of the soil (Mg/m3), and
ρw = the density of water (= 1.0 Mg/m3).
Often it will be necessary to estimate the value of THI. The estimated value must lie between
THMAX and the residual saturation (THR), i.e. the relative saturation at permanent wilting
point. As a guide, it is helpful to determine the relative saturation values at both permanent
wilting point and field capacity, as defined by the measured volumetric moisture contents of
the soil at matric potentials of -150 m and -1 m respectively. With information on the relative
saturation values at permanent wilting point, field capacity and saturation, and local
knowledge of how quickly the soil drains after rainfall, a suitable estimate of THI can usually
be obtained. Guide values for residual saturation (THR) are given in Table A4.1.
Soil porosity (POR)
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,8 POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
9
Porosity (v/v) of the soil is calculated from:
POR = 1 - ρb / ρs
(A4.2)
where ρb = the bulk density of the soil (Mg/m3), and
ρs = the particle density of the soil (usually assumed = 2.65 Mg/m3).
Bulk density should be determined from soil cores taken in the field using density rings. A
minimum of three replications should be taken on each element. Guide values of porosity for
soils of different textures are listed in Table A4.1.
Effective net capillary drive (G)
Effective net capillary drive can be derived from the following equation relating unsaturated
hydraulic conductivity to the matric potential of the soil:
G =
1
k (ψ ) d (ψ )
ksat ∫
(A4.3)
where G = effective net capillary drive,
ksat = the saturated hydraulic conductivity, and
k = the unsaturated hydraulic conductivity at matric potential (ψ).
Since unsaturated hydraulic conductivity is rather difficult to measure, guide values for G, in
relation to soil texture, are given in Table A4.1.
Saturated hydraulic conductivity (FMIN)
EUROSEM requires an input value for the saturated hydraulic conductivity (ksat) of the bare
soil (fine earth component, i.e. < 2 mm). This should be determined either in the laboratory
from undisturbed soil core samples taken in the field or approximated by the terminal
infiltration rate, as measured in the field with a double-ring infiltrometer. Alternatively,
tension infiltrometers (disc permeameters) may be used.
Since the spatial variability of terminal infiltration rate is usually very high, ideally between 5
and 20 replications should be taken on each element. The mean value of these may then be
used or, alternatively, several simulations with the model may be undertaken, choosing values
randomly from within the measured range.
For most bare soil conditions, FMIN = ksat. Guide values are given in Table A4.2.
The input values for bare soil are adjusted within EUROSEM for the presence of rock
fragments and a plant cover, according to the input values of PAVE and PBASE respectively.
Where FMIN values have been measured in the field for samples containing both fine earth
and rock fragments and these values are used as input to EUROSEM, the value of PAVE
should be set to zero. It should be noted, however, that it will not then be possible to take
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,9 POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
10
account of the reduction in soil detachment by raindrop impact resulting from the rock
fragment cover, since this depends upon the value of PAVE (see Appendix 5). An alternative
procedure, which allows this problem to be overcome, is to set PAVE to its proper value. The
value of FMIN will then be modified within EUROSEM and its value will appear on the screen
as part of the interactive dialogue. At this point, the modified value can be rejected and the
model will operate with the input value of FMIN. Where FMIN has been measured in the
presence of a plant or crop cover, the values can be used as inputs to EUROSEM but the
value of PBASE should be set to zero. Since PBASE does not influence any other part of
EUROSEM, the rest of the simulation is unaffected by this procedure and the other
parameters describing the vegetation cover should be given their appropriate values.
Table A4.1. Guide values for soil hydraulic characteristics
Texture (*)
Porosity (POR) (v/v)
Residual
saturatio
n (THR)
(v/v)
mean
mean
low
high
Maximu
m
saturatio
n (THR)
(v/v)
mean
Sand
0.37
0.44
0.50
0.020
0.42
Loamy sand
0.37
0.44
0.51
0.035
0.41
Sandy loam
0.35
0.45
0.56
0.040
Loam
0.38
0.46
0.55
Silt loam
0.42
0.50
Sandy clay loam
0.33
Clay loam
Net capillary drive (G)
(mm)
low
high
22
mean
101
207
41
147
323
0.41
98
248
526
0.030
0.43
185
375
937
0.58
0.015
0.47
220
485
1043
0.40
0.46
0.070
0.33
220
617
1070
0.41
0.46
0.52
0.070
0.39
250
533
1174
Silty clay loam
0.42
0.47
0.52
0.380
0.43
370
720
1470
Sandy clay
0.37
0.43
0.49
0.110
0.32
373
768
1730
Silty clay
0.43
0.48
0.53
0.060
0.42
430
812
1700
Clay
0.43
0.48
0.53
0.090
0.39
460
890
1830
(*) Texture classes according to USDA classification
Values are those recommended by Woolhiser et al (1990) for use as inputs to
KINEROS.
Data for THR and THMAX are taken from the SR and SMAX values respectively
in Woolhiser et al (1990) after dividing by soil porosity.
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
10POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
11
Table A4.2. Guide values for saturated hydraulic conductivity
Texture (*)
Sand
Saturated hydraulic conductivity
(mm/h)
low
mean
high
170
210
600
Loamy sand
18
61
800
Sandy loam
7
26
190
Loam
2
13
65
Silt loam
3
7
25
Sandy clay loam
1
4
50
Clay loam
0.4
2
38
Silty clay loam
0.6
1.5
12
Sandy clay
0.6
1.2
25
Silty clay
0.5
0.9
5
Clay
0.1
0.6
12
(*) Texture classes according to USDA classification
After Rijtema (1969), Li et al (1976), Brakensiek (1979), Brakensiek et al (1981), McCuen et al (1981), Cosby
et al (1984), Woolhiser et al (1990).
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
11POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
12
APPENDIX 5 - ROCK FRAGMENTS
EUROSEM simulates the following effects of rock fragments:
(1) a reduction in the relative volume of the soil not acting as a porous medium;
(2) a reduction in the area of fine earth exposed to raindrop impact; and
(3) a change in the effective saturated hydraulic conductivity of the soil.
These effects are expressed through the parameters ROC, PAVE and ISTONE respectively.
ROC
The parameter, ROC, represents the fraction of the soil composed of rock fragments,
expressed by volume. Its effect is to reduce the effective overall storage of water in the soil
(Section 2.3). The volume of rock fragments should be determined from field samples of
known volumes of the soil material (fine earth + rocks). The samples should be large enough
to include all stone sizes found in the area. A minimum of three samples should be taken on
each element. The stones should be separated by washing the soil from them and their volume
measured by displacement.
Where determinations of rock fragment content have been made on the basis of mass, the
nomograph shown in Figure A5.1 (Torri et al, 1994) can be used to convert to a volumetric
equivalent, provided that the bulk density of the rock fragment-free fine earth (ρb) and the bulk
density of the rock fragments (ρroc) are known.
PAVE
The parameter, PAVE, describes the fraction of the soil surface covered by non-erodible
material. For rock fragment covers, the simplest method of determination is to lay a
commercially available wire-mesh grid, 1 m2 in size with grid wires at 10 cm intervals, over
the surface. A photograph of the gridded area is then taken vertically from above. The
number of grid intersection points coinciding with rock fragments, expressed as a fraction
(between 0 and 1) of the total number of grid intersections, provides an estimate of the rock
fragment cover. Depending on the size of the element, between two and five replicate samples
should be used.
ISTONE
The parameter, ISTONE, determines whether the effect of PAVE is to decrease or increase
the saturated hydraulic conductivity of the soil (Section 2.3). The nature of the effect is
dependent upon the size of the element and the position of the rock fragments on the surface
of the soil (Poesen and Ingelmo-Sanchez, 1992; Poesen et al, 1994).
For elements which are smaller than 1 m2 or larger than 100 m2, the effect of rock fragments is
to reduce erosion. The value of ISTONE should therefore be set to +1.
For elements which are between 1 m2 and 100 m2 in size, rock fragments may act to either
decrease or increase erosion, depending on their effect on saturated hydraulic conductivity
(FMIN) and, therefore, runoff production. The effects may be simulated by setting ISTONE
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
12POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
13
to -1 (decreases FMIN, will increase erosion) or +1 (increases FMIN, will decrease erosion).
The following conditions, illustrated in Figure A5.2, may be used as a guide:
rock fragments embedded in a surface soil layer which shows structural
porosity (i.e. inter-aggregate pores, biopores and cracks) (Figure A5.2a) or a
porosity due to tillage - set ISTONE to +1;
rock fragments resting on the surface soil, which may be characterised by
either structural (Figure A5.2b) or textural porosity (Figure A5.2c) (i.e. pore
spaces due only to the packing of primary particles) - set ISTONE to +1.
rock fragments which are partially embedded in a soil layer with a surface
seal which has developed in a soil with essentially only textural porosity
(Figure A5.2d) set ISTONE to -1;
rock fragments embedded in a surface soil layer with structural porosity
(Figure A5.2e) - set ISTONE to -1.
Where porosity due to tillage outweighs either of the effects (3) and (4), ISTONE should be
set to +1.
Figure A5.1. Nomogram for converting rock fragment content measured by mass (Mr) to a by-volume (Vr)
basis (Torri et al, 1994).
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
13POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
14
ISTONE = +1
ISTONE = -1
LEGEND
(a)
(d)
TEXTURAL POROSITY
(b)
STRUCTURAL POROSITY
(e)
SURFACE SEAL
(c)
R
RUNOFF
Figure A5.2. Guides for setting value of ISTONE (after Poesen et al, 1994).
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
14POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
15
APPENDIX 6 - SURFACE ROUGHNESS
EUROSEM uses two measures of the roughness or microtopographic relief of the soil surface.
These are RFR and RECS.
RFR
The parameter, RFR, expresses the roughness of the soil surface as measured in the
downslope direction (i.e. the direction of surface water flow). It is used in EUROSEM to
estimate the surface depression storage (Section 4.3). The parameter is related to the ratio of
the straight-line distance between two points on the ground (X) to the actual distance
measured over all the microtopographic irregularities (Y).
The ratio can be obtained from field measurements using a 1-m long chain with 3-mm links, as
illustrated in Figure A6.1. Over smooth surfaces where the variation in roughness is less than
5 per cent, three downslope transects on each element should be sufficient but where the
variation in roughness exceeds 5 per cent, the number of transects should be increased to ten.
X
Y
soil
surface
Y = true surface length
X = straight-line surface length
Figure A6.1. Measurements required for calculating surface roughness ratio (RFR)
Guide values for RFR for a range of tillage practices are given in Table A6.1. These can be
used where measured data are unavailable but details of the tillage practice, soil texture and
rainfall are known. The values listed in the Table apply to the condition of the soil surface
immediately after tillage. They should be modified, using the following equations in turn, for
(1) the effect of soil type and (2) the decline in roughness over time as a result of raindrop
impact on the soil.
RFRsoil = RFRguideval . (0.4 + 0.025 CLAY)
RFR = RFR soil .e -0.7 CUMKE
(A6.1)
(A6.2)
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
15POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
16
where RFR = the roughness ratio,
RFRguideval = the guide value for the roughness ratio as given in Table A6.1,
the modified RFR value taking account of soil type,
CLAY = the percentage clay content of the soil, and
CUMKE = the accumulated kinetic energy of the rainfall (kJ/m2) since the time
RFRsoil =
of tillage.
RECS
The term, RECS, defines the average value of the maximum local difference in microrelief. It
is used to drive the infiltration process within the KINEROS model when, after the cessation
of rainfall, infiltration is controlled by the depth of water lying on the surface (Section 5.3).
The value of RECS can be obtained by measuring the absolute difference in height between
the highest and lowest point on each of the transects used to determine RFR, and taking the
average of the measurements.
Table A6.1. Guide values of the roughness ratio (RFR) for different tillage practices
Tillage implement
Roughness ratio (RFR; cm/m)
Mouldboard plough
30-33
Chisel plough
24-27
Cultivator
15-23
Tandem disc
25-28
Offset disc
32-35
Paraplow
32-35
Spike-tooth harrow
17-23
Spring-tooth harrow
25
Rotary hoe
21-22
Rototiller
23
Drill
20-21
Row planter
13-22
Data assembled by K.Auerswald from studies by Alberts et al (1989), Williams et al (1990) and Yoder et al
(1991).
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
16POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
17
APPENDIX 7 - VEGETATION PROPERTIES
EUROSEM requires data on six properties of the vegetation, namely COVER, DINTR,
PLANGLE, PLANTH, SHAPE and PBASE. In addition, the values of Manning's n and soil
cohesion should be adjusted to take account of plant cover effects (see Appendix 9).
COVER
The percentage canopy cover (COVER) refers to the proportion (between 0 and 1) of the
ground surface obscured by vegetation when viewed vertically from above. It varies with the
stage of growth of the plant or crop cover and therefore changes seasonally.
For most crops, bushes, shrubs and ground vegetation, COVER can be estimated in the field
by placing a 1 m2 quadrat, with a wire or string mesh grid at 10 cm intervals, over the top of
the canopy. A photograph of the gridded area is then taken vertically from above. The
number of grid intersection points coinciding with vegetation, expressed as a fraction of the
total number of grid intersections, gives an estimate of the canopy cover. Depending upon the
size of the element and the spatial variability in vegetation cover, between three and five
replicate samples should be used.
For taller vegetation, for example trees, it may be difficult to get above the canopy but
estimates can be made from photographs taken looking up through the canopy. Estimating
canopy cover is most difficult for vegetation between 1 and 3 m tall; here the only way is to
estimate by eye.
Since the purpose of measuring the percentage canopy cover is to determine the proportion of
the ground surface exposed to raindrop impact, the cover should include that of ground
vegetation, mulches and any litter layer, as well as that of trees and bushes.
DINTR
The maximum interception storage (DINTR; mm) of a vegetation cover depends upon its
canopy cover and the size, shape and roughness of its leaves. Since it is extremely difficult to
measure, guide values are presented in Table A7.1 for a range of vegetation types.
PLANGLE
The average angle of the stems (PLANGLE; degrees) of the vegetation cover is best
determined from photographs taken side on to the vegetation. The angle measured is the
acute angle between the ground surface and the stems or shoots. For some vegetation types,
there may be no dominant angle and the variation around the mean may be rather high. In
such cases, the user should carry out a sensitivity analysis for the application in question to
assess the impact of choosing different values on the model output. If the sensitivity is low,
the user should use the mean of the measured values. If the sensitivity is high, several
simulations should be made with different values chosen randomly from within the measured
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
17POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
18
range (see Section 9). Guide values for mature plants are given in Table A7.2.
PLANTH
The average height of the canopy (PLANTH; cm) should be measured in the field or
calculated from photographs taken from side on to the vegetation. Since the purpose of this
term is to describe the fall height of the intercepted raindrops, any ground vegetation, mulches
or litter layer should be considered. Thus, for a forested element, the effective plant height
could be zero if the soil is covered by dense ground flora or a continuous litter layer but it
would be the average height of the tree canopy if the soil is bare.
Guide values for mature plants are given in Table A7.2. Judgment should be used on varying
these values to take account of the stage of growth (age) of the vegetation, and the effects of
local soil and climatic conditions on plant growth.
SHAPE
EUROSEM uses a simple distinction for the plant shape factor (SHAPE) between thin bladed
vegetation such as grasses, cereals and needle-leaved trees (SHAPE =1) and broad-leaved
vegetation (SHAPE = 2). Guide values for mature plants are given in Table A7.2.
PBASE
Percentage basal area of the vegetation (PBASE) can be determined in the field by counting
the number of plant stems in a square metre, measuring the diameters of their stems and,
assuming the stems to be circular, calculating their cross-sectional areas. PBASE is the total
area of the plant stems expressed as a proportion (between 0 and 1) of the square metre. The
number of replicates required for a single element depends upon the complexity of the
vegetation. One sample may be sufficient for mono-cultures but four or five samples will be
needed where the vegetation cover is of mixed species. Some typical values of PBASE are
given in Table A7.3.
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
18POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
19
Table A7.1. Guide values of maximum interception storage for mature plants
Vegetation/Crop type
DINTR (mm)
Fescue grass
1.2
Molinia
0.2
Rye grass
2.5
Meadow grass, clover
2.3
Blue stem grass
2.3
Heather
1.5
Bracken
1.3
Tropical rain forest
2.5
Temperate deciduous woodland: winter
Temperate deciduous woodland: summer
1
2.5
Needleleaf forest: pines
1
Needleleaf forest: spruce, firs
1.5
Evergreen hardwood forest
0.8
Apple
0.5
Soya beans
0.7
Potatoes
0.9
Cabbage
0.5
Brussels sprouts
1
Sugar beet
0.6
Millet
0.3
Spring wheat
1.8
Winter wheat
3
Barley, rye, oats
1.2
Maize
0.8
Tobacco
1.8
Alfalfa
2.8
After Horton (1919), Zinke (1967), Rutter and Morton (1977) and Herwitz (1985)
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
19POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
20
Table A7.2. Guide values for canopy height, plant stem angle and plant shape factor for mature plants
Plant type
Height (m)
Stem angle (°)
Shape factor
Temperate deciduous forest
20-40
10-80
2
Coniferous forest: pine
30-40
10-80
1
Coniferous forest: spruce, fir
50-60
10-80
1
Apple
10-15
10-20
2
Peach, nectarine
6-7
40-60
2
Citrus
6-12
10-80
2
Olive
12-15
30-40
2
Banana
2-5
20-80
2
Grape
0.8-1
40-80
2
Fescue grass
0.05-0.06
60-90
1
Molinia
0.02-1.2
75-80
1
Rye grass
0.1-0.9
45-60
1
0.5-1
70-75
1
Oat grass
0.5-1.5
20-90
1
Bermuda grass
0.3-0.6
50-60
1
Kikuyu grass
0.2
40-70
1
Guinea grass
2-3
20-60
1
Napier grass
2-6
70-90
2
Rhodes grass
0.5-2
50-80
1
Vetiver grass
1-3
60-80
2
Prairie grass
0.8-1
40-80
1
Buffel grass
0.1-1
50-80
1
Elymus
0.3-0.5
50-90
1
Bent grass
0.4-0.5
60-80
1
Clover
0.3-0.6
10-60
2
Alfalfa, lucerne
0.3-0.9
50-70
2
Heather
0.5-0.6
0-90
2
Beans (Phaseolus, Vicia)
1-3
60-80
2
Mung bean, Black gram
0.3-1
60-80
2
0.1-0.2
20-40
2
3-4
20-40
2
Chick pea
0.4-0.5
60-70
2
Cotton
0.8-1.2
0-20
2
Groundnut
0.2-0.6
40-80
2
Hops
5-6
15-70
2
Maize
2-3
50-80
2
Timothy grass
Soya bean
Pigeon pea, Red gram
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
20POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
21
Millet, sorghum
1-2
50-80
2
1-1.4
25-60
2
0.8-1.6
60-90
2
Pineapple
0.5-1
70-90
2
Potato
0.6-1
30-50
2
Cassava
2.5-3
70-90
2
Rice
0.5-1
70-80
1
Sugar beet
0.8-1
70-80
2
Sugar cane
3-6
70-90
2
1.5-2
10-60
2
0.5-1.5
80-90
1
1-2
80-90
1
Rubber
18-30
20-80
2
Oil palm
9-10
0-90
2
Coffee
4-4.5
40-80
2
Tea
1-1.5
60-80
2
Cocoa
4.5-7
60-80
2
Coconut
18-30
0-90
2
Oilseed rape
Linseed
Tobacco
Wheat, barley, oats
Rye
After Cobley (1956), Bogdan (1977), Tindall (1983), Doorenbos and Kassam (1986), De Rougemont (1989)
and Langer and Hill (1991). These references should also be consulted for crops not listed.
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
21POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
22
Table A7.3. Basal area (PBASE) for different vegetation types
Land use or cover
Cover condition
Proportional
basal area (PBASE)
Fallow: after row crops
0.1
Fallow: after sod
0.3
Row crops
Small grain
Hay - legume
Hay - sod
Pasture or range (bunch grass)
Temporary pasture - sod
Permanent pasture or meadow
Woods and forest
poor
0.1
good
0.2
poor
0.2
good
0.3
poor
0.2
good
0.4
poor
0.4
good
0.6
excellent
0.8
poor
0.2
fair
0.3
good
0.4
poor
0.4
fair
0.5
good
0.6
poor
0.8
good
1.0
1.0
After Holtan (1961)
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
22POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
23
APPENDIX 8 - RILL (CONCENTRATED FLOW PATH)
MEASUREMENTS
For simplicity, EUROSEM treats all types of concentrated flow paths, e.g. rills, tractor
wheelings, plough furrows or other depressions which channel flow downslope on plane
elements, as rills. Their effect is expressed by four variables: width (RILLW), depth (RILLD),
side slope (ZLR) and frequency (DEPNO - defined as the average number of concentrated
flow paths across the width of the element). The User should also decide whether to model
the rills as uniform in their width and depth along the element or to scale them so that their
width and depth increase with distance downslope (parameter RS).
Where the flow paths are treated as uniform in their depth and width along the element, their
geometry and frequency should be measured on about ten cross-slope transects at regular
intervals downslope (Figure A8.1). Averages of the measured values should be used as input
data. Where a decision is taken to scale the rills, values should be based on measurements
made at the bottom of the element. Figure A8.2 shows the measurements of the geometry at a
rill cross-section.
Samplin
g transe
cts
Downs
lope di
stance
Where major changes occur along a slope in either the number or the size of the flow paths
(rills), new elements should be defined, even though the slope steepness and soil type may
remain the same over the whole length of the slope (Figure A8.3).
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
23POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
24
Figure A8.1. Measurement of the frequency of concentrated flow paths (rills).
Rill centre line
x
Rill
depth (h)
Side slope (ZLR) = x/h
Rill width
Downs
lope di
stance
Figure A8.2. EUROSEM rill geometry
Element 1
Element 2
Element 3
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
24POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
25
Figure A8.3. Division of slope into elements based on frequency of concentrated flow paths or rills.
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
25POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
26
APPENDIX 9 - SOIL ERODIBILITY
Soil erodibility is described in EUROSEM using two parameters: one is a measure of the
detachability of the soil by raindrop impact (EROD) and the other, used to express the
detachability of the soil by flow, is soil cohesion (COH).
EROD
The detachability of the soil by raindrop impact (EROD; g/J) is expressed as the weight of soil
particles detached per unit of rainfall energy. It can be measured in the field with splash cups
(Bollinne, 1980; Morgan, 1981), provided a correction factor is applied to allow for the effect
of cup size (Poesen and Torri, 1988):
MSR = MS e 0.054D
(A9.1)
where MSR = the real mass of splashed soil material per unit area (g cm-2),
MS = the measured splash per unit area (g cm-2), and
D = the diameter of the splash cup (cm).
Six replications are considered a suitable number for a single element with dimensions of tens
of metres. The number should be adjusted, however, according to the area of the element.
Determination of EROD also requires estimates of the kinetic energy of the rainfall which
caused the splash. The energy calculations can be made if the rainfall is recorded on an
automatic gauge since it is then possible to divide the rainfall rainfall into intensity classes,
estimate the energy of one millimetre of rain in that class using a suitable equation, determine
the total energy of the rain falling in that class by multiplying estimated energy for one
millimetre by the number of millimetres, and then summing the total energies for all the
intensity classes. The procedure is described more fully in Hudson (1995) and Morgan (1995)
where different energy-intensity equations are also presented.
EROD can now be calculated simply by dividing the total detachment (g/cm2) by the energy of
the rainfall (J/cm2).
Since it takes some time to obtain good replicated data on detachability, guide values for
EROD are given in Table A9.1 for different soil textures.
COH
Soil cohesion (COH; kPa) should be measured with a torvane (Soil Test CL-600) in the field
after the surface has been saturated. At least six replications should be made on a single
element; if the variability is greater than 15 per cent, the number of replicates should be
increased to 10.
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
26POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
27
Some typical values of cohesion for bare saturated soils of different textures are given as a
guide in Table A9.2. These should also be used to adjust measured values for changes in the
condition of the soil, e.g. if the measured values are for uncompacted soil and EUROSEM is
to be run to simulate a compacted soil.
Where a vegetation or crop cover is present, soil cohesion will normally be higher than on a
bare soil because of the reinforcement of the soil by plant roots. Ideally, the measurements of
cohesion should then be made in the rooted soil but sometimes this is difficult because the
torvane becomes entangled with the roots. Also, the cohesion values tend to reflect those
obtained when the roots break rather than those of the soil matrix. Arguably, however, these
measured values are the realistic ones since the increase in cohesion resulting from the roots is
a function of the tensile strength of the root material (Wu, 1995). Where measurements are
not possible in rooted soils, cohesion should be measured on bare soils and the value obtained
increased by a value selected from Table A9.3. Similarly, where guide values from Table A9.2
are used for soil cohesion, they should be increased by a value selected from Table A9.3 if a
vegetation cover is present.
Table A9.1. Guide values for soil detachability (EROD)
Texture (*)
low
Detachability (EROD; g/J)
mean
high
2.0
2.4
clay
1.7
clay loam
1.4
1.7
1.9
silt
0.8
1.2
1.6
silt loam
0.8
1.5
2.3
loam
1.0
2.0
2.7
sandy loam
1.7
2.6
3.1
loamy sand
1.9
3.0
4.0
fine sand
2.0
3.5
6.0
sand
1.0
1.9
3.0
(*) Soil texture classes according to the USDA system.
Minimum values should be used when the soil is in a loose and dry initial state. Maximum values should be
used when the soil is loose and moist. Mean values are for sealed or compacted top soil.
After Poesen (1985), Poesen and Torri (1988), Govers (1991) and Everaert (1992).
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
27POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
28
Table A9.2. Guide values of soil cohesion (COH; kPa) at saturation for compacted and
soils
Texture (*)
uncompacted
low
clay
mean
uncompacted
compacted
high
low
10
12
14
clay loam
9
10
14
silty clay
9
15
11
10
9
26
sandy clay loam
8
3
10
silt loam
2
3
loam
2
fine sandy loam
mean
high
29
33
44
5
6
9
17
3
4
7
7
8
2
3
3
5
6
8
sandy loam
2
2
4
4
7
10
loamy sand
2
2
3
6
8
9
sand
2
2
3
8
8
9
silty clay loam
(*) Soil texture classes according to the USDA system
After Vickers (1993)
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
28POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
29
Table A9.3. Guide values for increases in soil cohesion (COH) brought about by root reinforcement
Vegetation type
barley
Increase in soil cohesion
(COH; kPa)
0.2-0.6
grass
1-8
marram grass
1.5-15
chaparral, matorral
0.3-3
alfalfa
10
Alder
2-12
Sitka spruce
4-12
Hemlock
1-8
Willow
6
Poplar
2
Maple
4-6
Pines
4-10
Coniferous forest
1-17.5
Candlenut
15-35
Acacia
1-5
After Gray and Leiser (1982), Greenway (1987) and Wu (1995)
The values listed are for mature vegetation. Somewhat lower values should be used for plants
in earlier stages of growth.
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
29POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
30
APPENDIX 10 - CHANNEL DIMENSIONS
For channel elements, EUROSEM assumes a trapezoidal channel cross-section which is
described by three simple measurements: bottom width (BW), side slope of the left-hand side
(ZL) and side slope of the right-hand side (ZR). These are shown in Figure A10.1.
Measurements should be made at a number of cross-sections (transects) along the channel
element. Depending on the length of the element, between three and five transects should
suffice to obtain representative values. Where channel cross-sections are parabolic in shape,
an attempt should be made to fit a trapezoidal section based on the location of the breaks of
slope between the floor and the sides of the channel. The bottom width should be defined as
the distance between these two points. The side slope measurement should be based on a line
coincident with the greatest length of the bank slope.
Figure A10.1. EUROSEM/KINEROS channel geometry
MORGAN, R.P.C, QUINTON, J.N., SMITH, R.E., GOVERS, G.,
30POESEN, J.W.A., AUERSWALD, K., CHISCI, G., TORRI, D.,
STYCZEN, M.E., FOLLY, A.J.V. 1998. The European soil erosion model (EUROSEM): documentation and user guide. Silsoe
College, Cranfield University.
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