Stormwater Management Calculations Treatment

Stormwater Management Calculations Treatment
Stormwater Management Calculations
Treatment Design
THE EXTRA GARAGE III
Chatham County, NC
WET POND DESIGN: NCDENR METHOD, July 2007
Step 1: Compute Water Quality Volume
INPUT VALUES:
CALCULATED DATA:
Drainage Area:
Impervious Area:
Design Rainfall:
3.93 ac
2.68 ac
1.43 in
Percent Impervious Area:
Volumetric Runoff Coeff (Rv):
Water Quality Volume :
68.2 %
0.66
13540 cf
Step 2: Pond Characteristics
Surface Area INPUT VALUES:
CALCULATED DATA:
Assumed Pond Depth
Ratio Required of 85% TSS
3 ft
2.88
Ratio Req'd for 90% TSS
SA of Permanent Pool
4
14268 sf
Min. SA Req'd for 85% TSS
Minimum Surface Area Req'd
Min. SA Req'd for 90% TSS
Minimum Surface Area Req'd
Surface Area Acceptable
0.113184
4930
0.1572
6848
YES
ac
sf
ac
sf
Note: Ponds designed for removal of 90% TSS do not require vegetated filter strips.
Average Depth Calculation
INPUT VALUES:
Option 1
SA of Permanent Pool
Volume of Perm. Pool
CALCULATED DATA:
14268 sf
45276 sf
Average Depth (Option 1)
Average Depth (Option 2)
Average Depth > Assumed Depth
3.17 ft
3.69 ft
Yes
Temporary Pool Calculations
INPUT VALUES:
SA of Permanent Pool
Depth of Temp Pool
Volume per ACAD
CALCULATED DATA:
14268 sf
0.85 ft
13801 cf
Approx Depth of WQV
0.95 ft
WQV contained?
Yes
Step 3: Drawdown Calculations
Volume to Drawdown
Min Time of Drawdown
Max Time of Drawdown
Orifice Sizing
Trials
1
2
3
4
5
6
13801 cf
2 days
5 days
Test Diameters
1
in
1.25
in
1.5
in
1.75
in
2
in
2.25
in
Maximum Flow Rate
Minimum Flow Rate
Ave. Head (h/2)
0.425
ft
0.017
cfs
0.027
cfs
0.039
cfs
0.052
cfs
0.068
cfs
0.087
cfs
0.080 cfs
0.032 cfs
Driving Head (H/3)
0.283
ft
0.014
cfs
0.022
cfs
0.031
cfs
0.043
cfs
0.056
cfs
0.071
cfs
Note: State Manual recommends using H/3 for computation of flow through Orifice.
Size chosen
X
A B
C
D
E
F
G
H I J K
L
M
N
O
P
Q
R
S
T
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
Watershed Characteristics Ver2.0
Clear All Values
Clear All Values
Return to Instructions
to Instructions
Return
Proceedto BMP Characteristics
to BMP Characteristics
Proceed
Skip to Development Summary
Skip to Development Summary
Instructions
1. Select your physiographic/geologic region. (see map on 'instructions' page)
2. Enter the area of the entire development in square feet (ft2).
3. Select the location that is most representative of the site's precipitation characteristics. (see map on 'instructions' page)
4. For each applicable land use, enter the total area of that land use that lies within the development under pre‐development conditions.
5. For each applicable land use, enter the total area of that land use that lies within the development under post‐development conditions, before BMP implementation.
6. Ensure that the sum of pre‐ and post‐development areas entered equal the orginal development area. 7. Continue to "BMP Characteristics" tab.
Additional Guidelines
‐ For non‐residential watersheds, indicate acreages of each land use type in Column 1 for both pre‐ and post‐development conditions.
‐ For residential watersheds, complete the required information in Column 2 for both pre‐ and post‐development conditions. ‐ If a given land use is not present in the given watershed, leave the cell blank or enter a zero.
‐ Ensure that land use areas entered for both pre‐ and post‐development conditions match the total development area entered in cell O21.
‐ Residential areas may be entered by average lot size (column, part A), or may be separated into individual land uses (column 2, part B) ‐‐ do NOT list out individual land uses within an area already described by lot size. ‐ Unless runoff flowing onto the development from offsite is routed separately around or through the site, the offsite catchment area draining in must be included in the acreage
values of the appropriate land use(s) and treated.
20
21
22
23
2
Total Development Area (ft ): Development Name:
Model Prepared By: Piedmont
C
Raleigh
Physiographic/Geologic Region:
Soil Hydrologic Group
Precipitation location:
486,565
The Extra Garage III
Charles P Koch
24
25
26
COLUMN 1 -- NON-RESIDENTIAL LAND USES
COLUMN 2 -- RESIDENTIAL LAND USES
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
COMMERCIAL
Parking lot
Roof
Open/Landscaped
INDUSTRIAL
Parking lot
Roof
Open/Landscaped
TRANSPORTATION
High Density (interstate, main)
Low Density (secondary, feeder)
Rural
Sidewalk
PERVIOUS
Managed pervious
Unmanaged (pasture)
Forest
JURISDICTIONAL LANDS*
Natural wetland
Riparian buffer
Open water
LAND TAKEN UP BY BMPs
TN EMC
(mg/L)
TP EMC
(mg/L)
1.44
1.08
2.24
0.16
0.15
0.44
1.44
1.08
2.24
0.39
0.15
0.44
3.67
1.4
1.14
1.4
0.43
0.52
0.47
1.16
3.06
3.61
1.47
0.59
1.56
0.25
‐‐
‐‐
‐‐
1.08
‐‐
‐‐
‐‐
0.15
Pre‐
Development
(ft2)
Post‐
Development
(ft2)
71,975
44,800
164,553
205,237
Custom Lot Size (ac)
PART A
⅛‐ac lots
¼‐ac lots ½‐ac lots
1‐ac lots
2‐ac lots
Multi‐family
Townhomes
Custom Lot Size
PART B
Roadway
Driveway
Parking lot
Roof
Sidewalk/Patio
Lawn
Managed pervious
Forest
Natural wetland*
Riparian buffer*
Open water*
LAND TAKEN UP BY BMPs
Age
(yrs)
TN EMC TP EMC
(mg/L) (mg/L)
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
1.0
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
1.4
1.44
1.44
1.08
1.4
2.24
3.06
1.47
‐‐
‐‐
‐‐
1.08
0.52
0.39
0.39
0.15
1.16
0.44
0.59
0.25
‐‐
‐‐
‐‐
0.15
Pre‐
Development
(ft2)
Post‐
Development
(ft2)
4,352
4,230
10,000
467,983
*Jurisdictional land uses are not included in nutrient/flow calculations.
LAND USE AREA CHECK
Total Development Area Entered (ft2):
486,565
Total Pre‐Development Calculated Area (ft2):
2
Total Post‐Development Calculated Area (ft ):
486,565
486,565
U
BMP Characteristics Ver2.0
Clear All Values
Return to Watershed Characteristics
Return to Instructions
BMP DETAILS
Proceed to Development Summary
BMP
Instructions
1. Select the type of BMP for each catchment.
2. Enter the area of each land use type in the contributing drainage area for each BMP. 3. Continue to "Development Summary" tab.
Additional Guidelines
‐ This spreadsheet allows the development to be divided into as many as 6 smaller catchments. ‐ BMPs 1, 2, and 3 for a given catchment are assumed to operate in series, with the outflow from 1 serving as the inflow to 2, etc. ‐ If the outflow from an entire catchment (including outflow from selected BMPs) drains to another BMP, indicate this in the drop down menu below the BMP type and leave all cells for individual land uses blank. ‐ Not all BMP or catchments must be utilized. Simply leave fields blank in the columns not needed.
‐ Leave cells blank or insert zeroes if a land use is not present in the area draining to the BMP.
‐ For water harvesting BMPs, be sure to enter the percent volume reduction that will be achieved by your system. Volume detention (catch‐and‐release mechanisms) will not be considered ‐ only proven volume reductions are valid inputs. ‐ The BMP undersizing option should only be used for existing development or retrofit sites.
‐ Volume reduction efficiencies for undersized BMPs are calculated based on a 1:1 ratio (a BMP that is 60% smaller than the required design size is assigned a removal efficiency equal to 60% of the standard efficiency
value). Effluent concentrations remain the same as full‐sized BMPs.
‐ IMPORTANT: for the land area calculation checks to occur, you MUST press enter after entering a value for area to be treated by a BMP (not just click on the next cell).
‐ See User's Manual for instructions on modeling oversized BMPs.
‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐ CATCHMENT 1 ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐
BMP #1
BMP #2
BMP #3
‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐ CATCHMENT 2 ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐
BMP #1
BMP #2
BMP #3
Volume Reduction (%)
TN Effluent Concen. (mg/L)
Bioretention with IWS
50%
Bioretention without IWS
35%
Dry Detention Pond
0%
Grassed Swale
0%
Green Roof
50%
Level Spreader, Filter Strip
40%
0%
Permeable Pavement*
5%
Sand Filter
Water Harvesting
user defined
Wet Detention Pond
10%
Wetland
20%
*if treating commercial parking lot, TP effluent concentration = 0.16 mg/L
‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐ CATCHMENT 3 ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐
BMP #1
BMP #2
BMP #3
‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐ CATCHMENT 4 ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐
BMP #1
BMP #2
BMP #3
‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐ CATCHMENT 5 ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐
BMP #1
BMP #2
BMP #3
0.95
1.00
1.20
1.21
1.08
1.20
1.44
0.92
1.08
1.01
1.08
TP Effluent Concen. (mg/L)
0.12
0.12
0.20
0.26
0.15
0.15
0.39
0.14
0.15
0.11
0.12
‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐ CATCHMENT 6 ‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐‐
BMP #1
BMP #2
BMP #3
Wet Detention Pond
Type of BMP:
If BMP is undersized, indicate the BMP's size relative to the design size required to capture the designated water quality depth (i.e. 0.75 = BMP is 75% of required design size):
*For water harvesting BMP, enter percent volume reduction in decimal form.
Does BMP accept the outflow from another Catchment? If so, indicate which one(s). (Land use areas entered below are in addition to the watershed areas treated by contributing catchment(s).)
Catchment 1:
‐‐
‐‐
‐‐
no
no
no
no
no
no
no
no
no
no
no
no
no
no
no
Catchment 2:
no
no
no
‐‐
‐‐
‐‐
no
no
no
no
no
no
no
no
no
no
no
no
Catchment 3:
no
no
no
no
no
no
‐‐
‐‐
‐‐
no
no
no
no
no
no
no
no
no
Catchment 4:
no
no
no
no
no
no
no
no
no
‐‐
‐‐
‐‐
no
no
no
no
no
no
Catchment 5:
no
no
no
no
no
no
no
no
no
no
no
no
‐‐
‐‐
‐‐
no
no
no
Catchment 6:
no
no
no
no
no
no
no
no
no
no
no
no
no
no
no
‐‐
‐‐
‐‐
Drainage Area Land Use
Area Treated
by BMP
2
(ft )
COMMERCIAL
Parking lot
Roof
Open/Landscaped
INDUSTRIAL
Parking lot
Roof
Open/Landscaped
TRANSPORTATION
High Density (interstate, main)
Low Density (secondary, feeder)
Rural
Sidewalk
MISC. PERVIOUS
Managed pervious
Unmanaged (pasture)
Forest
RESIDENTIAL
2‐ac lots (New)
2‐ac lots (Built after 1995)
2‐ac lots (Built before 1995)
1‐ac lots (New)
1‐ac lots (Built after 1995)
1‐ac lots (Built before 1995)
½‐ac lots (New)
½‐ac lots (Built after 1995)
½‐ac lots (Built before 1995)
¼‐ac lots (New)
¼‐ac lots (Built after 1995)
¼‐ac lots (Built before 1995)
⅛‐ac lots (New)
⅛‐ac lots (Built a er 1995)
⅛‐ac lots (Built before 1995)
Townhomes (New)
Townhomes (Built after 1995)
Townhomes (Built before 1995)
Multi‐family (New)
Multi‐family (Built after 1995)
Multi‐family (Built before 1995)
Custom Lot Size (New)
Custom Lot Size (Built after 1995)
Custom Lot Size (Built before 1995)
Roadway
Driveway
Parking lot
Roof
Sidewalk
Lawn
Managed pervious
Forest
LAND TAKEN UP BY BMP
Area treated
Area treated
by BMP #2 that is by BMP #3 that is not treated by BMP not treated by BMPs #1
#1 or #2
2
2
(ft )
(ft )
Area Treated
by BMP
2
(ft )
Area treated
Area treated
by BMP #2 that is by BMP #3 that is not treated by BMP not treated by BMPs #1
#1 or #2
2
2
(ft )
(ft )
Area Treated
by BMP
2
(ft )
Area treated
Area treated
by BMP #3 that is by BMP #2 that is not treated by BMP not treated by BMPs #1 or #2
#1
2
2
(ft )
(ft )
Area Treated
by BMP
2
(ft )
Area treated
Area treated
by BMP #3 that is by BMP #2 that is not treated by BMP not treated by BMPs #1 or #2
#1
2
2
(ft )
(ft )
Area Treated
by BMP
2
(ft )
Area treated
Area treated
by BMP #3 that is by BMP #2 that is not treated by BMP not treated by BMPs #1 or #2
#1
2
2
(ft )
(ft )
Area Treated
by BMP
2
(ft )
Area treated
Area treated
by BMP #3 that is by BMP #2 that is not treated by BMP not treated by BMPs #1 or #2
#1
2
2
(ft )
(ft )
71,975
44,800
54,433
2
TOTAL AREA TREATED BY BMP (ft ):
2
TOTAL AREA TREATED BY SERIES (ft ):
171,208
0
171,208
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
Total Land Use Area Treated By All BMPs
2
(ft )
Allowable Total Land Use Area to be Treated Based on Post‐Dev. Areas
2
(ft )
71,975
44,800
54,433
71,975
44,800
164,553
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
205,237
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
3. Development Summary
Development:
Prepared By:
Date:
The Extra Garage III
Charles P Koch
January 2, 2014
WATERSHED SUMMARY Ver2.0
BMP VOLUME REDUCTIONS/EFFLUENT CONCENTRATIONS
REGION:
TOTAL DEVELOPMENT AREA (ft2):
Piedmont
486,565
Pre‐Development Conditions
Post‐Development Conditions
Post‐Development w/ BMPs
1.8%
24.0%
24.0%
Percent Impervious
(%)
Volume Reduction TN Effluent Concen. TP Effluent Concen. (mg/L)
(%)
(mg/L)
Bioretention with IWS
50%
0.95
0.12
Bioretention without IWS
35%
1.00
0.12
Annual Runoff Volume (c.f.)
121,290
489,769
446,759
Total Nitrogen EMC (mg/L)
1.43
1.37
1.14
Dry Detention Pond
0%
1.20
0.20
Total Nitrogen Loading (lb/ac/yr)
0.97
3.76
2.84
Grassed Swale
0%
1.21
0.26
Total Phosphorus EMC
(mg/L)
0.26
0.18
0.14
Green Roof
50%
1.08
0.15
Total Phosphorus Loading
(lb/ac/yr)
0.18
0.50
0.36
Level Spdr, Filter Strip
40%
1.20
0.15
Permeable Pavement*
0%
1.44
0.39
Sand Filter
5%
0.92
0.14 user defined
1.08
0.15
Wet Detention Pond
10%
1.01
0.11
Wetland
20%
1.08
0.12
Percent Difference Between:
Pre‐Dev. &
Post‐Dev. without BMPs
Post‐Dev without BMPs &
Post‐Dev with BMPs
Percent Impervious (%)
22%
Pre‐Development &
Post‐Development with BMPs
22%
Annual Runoff Volume (c.f.)
304%
268%
‐9%
Total Nitrogen EMC (mg/L)
‐4%
‐20%
‐17%
Total Nitrogen Loading (lb/ac/yr)
288%
193%
‐25%
0%
Total Phosphorus EMC (mg/L)
‐30%
‐44%
‐20%
Total Phosphorus Loading (lb/ac/yr)
184%
106%
‐27%
Water Harvesting
Return to Instructions
Return to Watershed Characteristics
Return to BMP Characteristics
Print Summary
*if treating commercial parking lot, TP effluent concentration = 0.16 mg/L
*Negative percent difference values indicate a decrease in runoff volume, pollutant concentration or pollutant loading. Positive values indicate an increase. BMP SUMMARY Ver2.0
CATCHMENT 1
CATCHMENT 2
CATCHMENT 3
CATCHMENT 6
CATCHMENT 5
CATCHMENT 4
BMP 1
BMP 2
BMP 3
BMP 1
BMP 2
BMP 3
BMP 1
BMP 2
BMP 3
BMP 1
BMP 2
BMP 3
BMP 1
BMP 2
BMP 3
BMP 1
BMP 2
BMP 3
Wet Detention Pond
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
Total Area Treated
(ac)
3.93
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
Total Inflow Volume
(c.f.)
430,100
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
Percent Volume Reduced
(%)
10%
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
Inflow Nitrogen EMC
(mg/L)
1.32
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
Total Inflow Nitrogen
(lb/ac/yr)
9.05
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
Inflow Phosphorus EMC
(mg/L)
0.163
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
Total Inflow Phosphorus
(lb/ac/yr)
1.11
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
BMP Outflow
Nitrogen (lbs/ac/yr)
6.41
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
BMP Outflow
Phosphorus (lbs/ac/yr)
0.73
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
‐‐
Catchment Outflow Nitrogen EMC (mg/L)
1.04
‐‐
‐‐
‐‐
‐‐
‐‐
Catchment Outflow
Total Nitrogen (lb/ac/yr)
6.41
‐‐
‐‐
‐‐
‐‐
‐‐
Percent Reduction in Nitrogen Load (%)
29%
‐‐
‐‐
‐‐
‐‐
‐‐
Catchment Outflow Phosphorus EMC (mg/L)
0.119
‐‐
‐‐
‐‐
‐‐
‐‐
Catchment Outflow
Total Phosphorus (lb/ac/yr)
0.727
‐‐
‐‐
‐‐
‐‐
‐‐
Percent Reduction in Phosphorus Load (%)
35%
‐‐
‐‐
‐‐
‐‐
‐‐
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