CC - Storm Drainage Calcs STORM DRAINAGE REPORT AND CALCULATIONS
FOR
EDINGTON COMMONS SUBDIVISION NO. 2
3610 N. LINDER ROAD
MERIDIAN, IDAHO
\o r_
v�GEN,3 PREPARED BY:
16970 CORINNE M GRAHAM, PE
August 1 1 , 2021
cSw
C I V I L S I T E
w o a is s
PO BOX 6059
BOISE, ID 83707
(208) 946-3874
cgraham@cswengineering.com
INTRODUCTION
The existing 5.75-acre site for the Edington Commons Subdivision No. 2 is currently vacant agricultural
ground.The proposed development includes 46 single family residential lots, 9 common lots, and
associated public roads, landscaping, and utilities.
HISTORIC DRAINAGE
The existing project site sits northeast of the intersection of N. Linder Road and W. Ustick Road in
Meridian.The Coleman lateral, an irrigation lateral owned by Settlers Irrigation District, lies in the
northern part of the site. Historically the site drains from south to north towards the Coleman Lateral.
Surficial soils are comprised of fat clays.At depths of 4-5 feet,free draining gravels with silt and sand
were encountered during geotechnical exploration. Groundwater was encountered at depths of 6.9 -8.7'
during geotechnical exploration and groundwater readings over the past year indicate groundwater
depths as shallow as 5.5'.
The shallow depth to groundwater limits the suitability of standard infiltration facilities.Therefore,
shallow infiltration facilities are proposed to store and treat stormwater runoff.
PROPOSED DRAINAGE
The storm drainage calculations and design for the proposed improvements are intended to meet the
requirements of ACHD's storm water policy. Storm water facilities are designed to store and treat runoff
from a 100-year storm event and to pretreat the water quality volume defined as the 80t" percentile
storm event. Storm water runoff from 45' behind the sidewalk, including residential driveways,will be
conveyed to the public stormwater system to be owned and maintained by ACHD. Remaining lot
drainage will be contained within individual lots.
Basin#3 storm water runoff is conveyed via curb and gutter to drain inlets within the roadway then
piped to a vertical sand filter.The water quality storm event (2-year) is conveyed through a sand and
grease trap to the treatment bed where it is filtered through the vertical sand filter.The 100-year storm
event bypasses the sand and grease trap and is conveyed directly to the percolation bed where it is
stored and infiltrated.
Storm water runoff for the remaining basins is conveyed via curb and gutter to shallow drain inlets
within the roadway then conveyed to two bioretention swales where it is stored and infiltrated.
APPENDICES
• Drainage Basin Map
• Storm Drainage Calculations
• Project Geotechnical Report
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C I V I L S I T F—
PO BOX 6069
EDINGTON COMMONS SUB NO. 2 50 0 50 100
BOISE,ID 83707 DRAINAGE BASIN MAP SCALE: 1• = 100'
Ph. (208)946-3874
cgraham@cswengineering.com
Prepared By: Corinne Graham, PE
CSw August 11, 2021
CIVIL SITE
Edington Commons Subdivision No. 2
Storm Drainage Calculations
ACHD Basin Characteristics
C Values
Impervious =0.90
Landscape =0.20
Basin#1 Basin#2 Basin#3
Total Area (SF) 33715 49622 40285
Roadway Area (SF) 9921 15800 11432
Sidewalk Area (SF) 3030 3949 3487
House/Driveway Area (SF) 12309 15768 15328
Landscape Area (SF) 8455 14105 10038
C Value: 0.72 0.70 0.73
Catch Basin Calculations
CB#3A CB#3B
Total Area (SF) 30152 10133
Roadway Area (SF) 8792 2640
Sidewalk Area (SF) 2736 751
House/Driveway Area (SF) 11796 3532
Landscape Area (SF) 6828 3210
C Value: 0.74 0.68
ACHD Calculation Sheet for Finding Peak Discharge/Volume-Rational Method
NOTE:This worksheet is intended to be a guideline to standardize ACHD checking of drainage calculations and shall not replace the Engineer's calculation methodology.These
calculations shall establish a minimum requirement.The Engineer's methodology must result in facilities that meet or exceed these calculations in order to be accepted.
�Fps for Peak Dis
Calculate Post-Development Flows(for pre-development flows,increase number of storage facilities to create new tab)
User input in yellow cells.
1 Project Name ACHD Basin p1
2 Is area drainage basin map provided? YES
(map must be included with stormwater calculations)
3 Enter Design Storm(100-Year or 25-Year With 100-Year Flood Route) 100
4 Enter number of storage facilities(25 max) 1
Click to Show More Subbasins ❑
Subbasin Subbasin Subbasin Subbasin Subbasin Subbasin Subbasin Subbasin Subbasin
1 Subbasin 2 3 4 5 6 7 8 9 10
5 Area of Drainage Subbasin(SF or Acres) SF 9,921 3,030 12,309 8,455
Acres 0.77
6 Determine the Weighted Runoff Coefficient(C) 0.90 0.90 0.90 0.20
C=[(C1xA1)+(C2xA2)+(CnxAn)]/A Weighted Avg1 0.72
7 Calculate Overland Flow Time of Concentration in Minutes(Tc)or use default User calculate
10 min 10 Min. Estimated Runoff Coefficients for Various Surface
Type of Surface Runoff Coefficients"I
8 Determine the average rainfall intensity(i)from IDF Curve based on i RF 2.58 2.58 in hr Business
Downtown areas 0.70-0.95
9 Calculate the Post-Development peak discharge(QPeak) Qp-k 1.45 1.45 cfs Urban neighborhoods 0.50-0.70
Residential
Single Family 0.35-0.50
10 Calculate total runoff vol(V)(for sizing primary storage) V 1,938 1,938 ft Multi-family 0.60-0.75
V=CI(Tc=60)Ax3600 Residential(rural) 0.25-0.40
11 Calculate Volume of Runoff Reduction Vrr Apartment Dwelling Areas 0.70
Industrial and Commercial
Enter Percentile Storm I(95th percentile=0.60 in) 80th 0.34 in Light areas 0.80
Enter Runoff Reduction Vol(95th Percentile=0.60-in x Area x C) Vrr 686 686 ft' Heavy areas 0.90
12 Detention:Approved Discharge Rate to Surface Waters(if applicable) 0.00 cfs Parks,Cemeteries 0.10-0.25
Playgrounds 0.20-0.35
Railroad yard areas 0.20-0.40
13 Volume Summary Unimproved areas 0.10-0.30
Surface Storage:Basin Streets
Asphalt 0.95
Basin Forebay V 194 ft' Concrete 0.95
Primary Treatme nt/Sto rage Basin V 1,744 ft' Brick 0.95
Subsurface Storage Roofs 0.95
In Common Lot-No Sediment Factor Required V 1,938 1,938 ft' Gravel 0.75
Fields:Sandy soil Soil Type
Slope A B C
Flat:0-2% 0.04 0.07 0.11
Average:2-6% 0.09 0.12 0.15]
Steep:>6% 0.13 0.18 0.23
Adapted from ASCE
C:\Users\cgrah\Dropbox\Projects\21004 Edington Sub Ph2\Reports\Storm Drainage\ACHD_SD_CALCS 8/10/2021,8:19 PM
Version 9.0,December 2016
ACHD Calculation Sheet for Sizing Bioswales & Borrow Ditches
#REFI
#REF!
1 Project Name ACHD Basin#1
2 Enter number of Bioswales/Borrow Ditches(25 max) 1
3 Design Storm 100
Weighted Runoff Coefficient C 0.72 Link to: #REF!
4 Area A(Acres) 0.77 acres #REF!
#REF!
Approved discharge rate for the given storm(if applicable) 0.00 cfs #REF!
5 Design Vol With 0%Sed for Swales V 1,938 1938 ft' #REF!
6 Length of Swale 150 ft
7 Infiltration Window?(Note:infiltration required if Longitudinal Slope<1%)
Design Infiltration Rate 8.00 in/hr
8 Infiltration Window Width 2.00 ft
9 Set Swale Bottom Width b 2.00 ft
10 Set Swale Top Width 14.00 ft
11 Set Swale Depth y 2.00 ft
12 Swale Side Slopes H:1 Sxs 3.00
13 Calculate cross-sectional area Axs 16.00 16.00 ft2
2
Axs=y z+by
14 Total Swale Capacity Without Driveways 2,400 2400.00 ft'
15 Does it Have Capacity? OK
16 Time to Drain 9.7 9.69 hr
90%volume in 48-hours minimum OK
Check Swale With Driveways
17 Avg.Driveway Fill Slope in Swale (H/V) ft/ft
18 Enter Total Number of Driveways ea 0.0 ft3 Deduct driveway slope
19 Enter Total Length of all Driveways ft 0.0 ft3 Deduct driveway length
20 Lost Swale Length From Trees,etc. ft 0.0 ft3 Deduct other
21 Adjusted Length of Infiltration Area 0.0 ft
22 Excess Capacity=Storage-Deductions-Runoff Volume (1,937.9) ft3
23 Is Capacity Good?
24 Time to Drain 0.0 hr
90%volume in 48-hours minimum OK
C:\Users\cgrah\Dropbox\Projects\21004 Edington Sub Ph2\Reports\Storm Drainage\ACHD_SD_CALCS 8/10/2021,8:19 PM
Version 9.0,December 2016
ACHD Calculation Sheet for Finding Peak Discharge/Volume-Rational Method
NOTE:This worksheet is intended to be a guideline to standardize ACHD checking of drainage calculations and shall not replace the Engineer's calculation methodology.These
calculations shall establish a minimum requirement.The Engineer's methodology must result in facilities that meet or exceed these calculations in order to be accepted.
�Fps for Peak Dis
Calculate Post-Development Flows(for pre-development flows,increase number of storage facilities to create new tab)
User input in yellow cells.
1 Project Name ACHD Basin p2
2 Is area drainage basin map provided? YES
(map must be included with stormwater calculations)
3 Enter Design Storm(100-Year or 25-Year With 100-Year Flood Route) 100
4 Enter number of storage facilities(25 max) 1
Click to Show More Subbasins ❑
Subbasin Subbasin Subbasin Subbasin Subbasin Subbasin Subbasin Subbasin Subbasin
1 Subbasin 2 3 4 5 6 7 8 9 10
5 Area of Drainage Subbasin(SF or Acres) SF 15,800 3,949 15,768 14,105
Acres 1.14
6 Determine the Weighted Runoff Coefficient(C) 0.90 0.90 0.90 0.20
C=[(C1xA1)+(C2xA2)+(CnxAn)]/A Weighted Avgl 0.70
7 Calculate Overland Flow Time of Concentration in Minutes(Tc)or use default User calculate
10 min 10 Min. Estimated Runoff Coefficients for Various Surface
Type of Surface Runoff Coefficients"I
8 Determine the average rainfall intensity(i)from IDF Curve based on i 2.58 2.58 in hr Business
Downtown areas 0.70-0.95
9 Calculate the Post-Development peak discharge(QPeak) Qp-k 2.06 2.06 cfs Urban neighborhoods 0.50-0.70
Residential
Single Family 0.35-0.50
10 Calculate total runoff vol(V)(for sizing primary storage) V 2,760 2,760 ft Multi-family 0.60-0.75
V=CI(Tc=60)Ax3600 Residential(rural) 0.25-0.40
11 Calculate Volume of Runoff Reduction Vrr Apartment Dwelling Areas 0.70
Industrial and Commercial
Enter Percentile Storm I(95th percentile=0.60 in) 80th 0.34 in Light areas 0.80
Enter Runoff Reduction Vol(95th Percentile=0.60-in x Area x C) Vrr 977 977 ff' Heavy areas 0.90
12 Detention:Approved Discharge Rate to Surface Waters(if applicable) 0.00 cfs Parks,Cemeteries 0.10-0.25
Playgrounds 0.20-0.35
Railroad yard areas 0.20-0.40
13 Volume Summary Unimproved areas 0.10-0.30
Surface Storage:Basin Streets
Basin Forebay V 276 f Asphalt 0.95
t'
Concrete 0.95
Primary Treatme nt/Sto rage Basin V 2,484 ft' Brick 0.95
Subsurface Storage Roofs 0.95
In Common Lot-No Sediment Factor Required V 2,760 2,760 ft' Gravel 0.75
Fields:Sandy soil Soil Type
Slope A B C
Flat:0-2% 0.04 0.07 0.11
Average:2-6% 0.09 0.12 0.15]
Steep:>6% 0.13 0.18 0.23
Adapted from ASCE
C:\Users\cgrah\Dropbox\Projects\21004 Edington Sub Ph2\Reports\Storm Drainage\ACHD_SD_CALCS 8/10/2021,8:19 PM
Version 9.0,December 2016
ACHD Calculation Sheet for Sizing Bioswales & Borrow Ditches
#REFI
#REF!
1 Project Name ACHD Basin#2
2 Enter number of Bioswales/Borrow Ditches(25 max) 1
3 Design Storm 100
Weighted Runoff Coefficient C 0.70 Link to: #REF!
4 Area A(Acres) 1.14 acres #REF!
#REF!
Approved discharge rate for the given storm(if applicable) 0.00 cfs #REF!
5 Design Vol With 0%Sed for Swales V 2,760 2760 ft' #REF!
6 Length of Swale 173 ft
7 Infiltration Window?(Note:infiltration required if Longitudinal Slope<1%)
Design Infiltration Rate 8.00 in/hr
8 Infiltration Window Width 2.00 ft
9 Set Swale Bottom Width b 2.00 ft
10 Set Swale Top Width 14.00 ft
11 Set Swale Depth y 2.00 ft
12 Swale Side Slopes H:1 Sxs 3.00
13 Calculate cross-sectional area Axs 16.00 16.00 ft2
2
Axs=y z+by
14 Total Swale Capacity Without Driveways 2,768 2768.00 ft3
15 Does it Have Capacity? OK
16 Time to Drain 12.0 11.96 hr
90%volume in 48-hours minimum OK
Check Swale With Driveways
17 Avg.Driveway Fill Slope in Swale (H/V) ft/ft
18 Enter Total Number of Driveways ea 0.0 ft3 Deduct driveway slope
19 Enter Total Length of all Driveways ft 0.0 ft3 Deduct driveway length
20 Lost Swale Length From Trees,etc. ft 0.0 ft3 Deduct other
21 Adjusted Length of Infiltration Area 0.0 ft
22 Excess Capacity=Storage-Deductions-Runoff Volume (2,759.9) ft3
23 Is Capacity Good?
24 Time to Drain 0.0 hr
90%volume in 48-hours minimum OK
C:\Users\cgrah\Dropbox\Projects\21004 Edington Sub Ph2\Reports\Storm Drainage\ACHD_SD_CALCS 8/10/2021,8:19 PM
Version 9.0,December 2016
ACHD Calculation Sheet for Finding Peak Discharge/Volume-Rational Method
NOTE:This worksheet is intended to be a guideline to standardize ACHD checking of drainage calculations and shall not replace the Engineer's calculation methodology. These
calculations shall establish a minimum requirement.The Engineer's methodology must result in facilities that meet or exceed these calculations in order to be accepted.
Calculate Post-Development Flows(for pre-development flows,increase number of storage facilities to create new tab)
User input in yellow cells.
1 Project Name ACHD Basin#3
2 Is area drainage basin map provided? YES
(map must be included with stormwater calculations)
3 Enter Design Storm(100-Year or 25-Year With 100-Year Flood Route) 100
4 Enter number of storage facilities(25 max)
Click to Show More Subbasins ❑
Subbasin Subbasin Subbasin Subbasin Subbasin Subbasin Subbasin Subbasin
1 Subbasin 2 3 4 5 Subbasin 6 7 8 9 10
5 Area of Drainage Subbasin(SF or Acres) SF 11,432 3,487 15,328 10,038
Acres 0.92
6 Determine the Weighted Runoff Coefficient(C) 0.90 0.90 0.90 0.20
C=[(C1xA1)+(C2xA2)+(CnxAn)]/A Weighted Avg 0.73
7 Calculate Overland Flow Time of Concentration in Minutes(Tc)or use default 10 Usercalculate
10 Min. - Estimated Runoff Coefficients for Various Surfac
8 Determine the average rainfall intensity(i)from OF Curve based on Tc i EW 2.58 2.58 in hr Type of Surface Runoff Coefficients"
Business
9 Calculate the Post-Development peak discharge(QPeak) Qpeak 1.73 1.73 cfs Downtown areas 0.70-0.95
Urban neighborhoods 0.50-0.70
10 Calculate total runoff vol(V)(for sizing primary storage) V 2,319 2,319 ft Residential
Single Family 0.35-0.50
V=Ci(Tc=60)Ax3600 Multi-family 0.60-0.75
11 Calculate Volume of Runoff Reduction Vrr Residential(rural) 0.25-0.40
Apartment Dwelling Areas 0.70
Enter Percentile Storm I(95th percentile=0.60 in) 80th 0.34 in Industrial and Commercial
Enter Runoff Reduction Vol(95th Percentile=0.60-in x Area x C) Vr, 821 821 ft' fight areas 0.80
12 Detention:Approved Discharge Rate to Surface Waters(if applicable) 0.00 cfs Heavy areas 0.90
Parks,Cemeteries 0.10-0.25
Playgrounds 0.20-0.35
13 Volume Summary Railroad yard areas 0.20-0.40
Surface Storage:Basin Unimproved areas 0.10-0.30
Basin Forebay V 232 ft' Streets
Asphalt 0.95
Primary Treatment/StorageBasin V 2,087 ft' Concrete 0.95
Subsurface Storage Brick 0.95
Volume Without Sediment Factor(See BMP 20 Tab) V 2,319 2,319 ft' Roofs 0.95
Gravel 0.75
Fields:Sandy soil Soil Type
Slope A B C fl' ..
Flat:O-2% 0.04 0.07Average:2-6% 0.09 0.12 0Steep:>6% 0.13 0.18 0
Adapted from ASCE
C:\Users\cgrah\Dropbox\Projects\21004 Edington Sub Ph2\Reports\Storm Drainage\Storm Drain Calc-Vertical Sand Filter 3 8/10/2021,8:20 PM
Version 10.5,November 2018
ACHD Calculation Sheet for Sizing Vertical Sand Filters
NOTE:This worksheet is intended to be a guideline to standardize ACHD checking of drainage calculations and shall not replace the Engineer's
calculation methodology. These calculations shall establish a minimum requirement.The Engineer's methodology must result in facilities that
meet or exceed these calculations in order to be accepted.
Note this spreadsheet pulls information from the"Peak QV"tab
Calculate Post-Development Flows(for pre-development flows,increase number of storage facilities to create new tab)
User input in yellow cells.
Project Name ACHD Basin#3
Enter number of Seepage Beds(25 max) 1
Design Storm Unlined Side 100'QV'
Design Storm Lined Side 2 LQ,v
QV TR55
Weighted Runoff Coefficient C 0.73 Link to:
Area A(Acres) 0.92 acres
Approved discharge rate(if applicable) 0.00 cfs
100 Year Storm Volume V 2,319 ftA3
2 Year Storm Volume V2 628 ftA3 '
Width of Unlined Side W 14.5 14.5 ft
Width of Lined Side W2 4.0 '
Depth of Unlined Side D 4.0 ft
Depth of Lined Side D2 4.0 ft
Void Ratio of Drain Rock Voids 0.4
0.4 for 1.5"-2"drain rock and 3/4"Chips
Design Infiltration Rate(8 in/hr max) Perc 8.00 in/hr
Size of Perf Pipe(Perf 360°) Dia pipe 18 in
Design Length of Unlined Side L 100 100
Design Length of Lined Side L 98 100 ft
Time to Drain Unlined Side 2.2 hours
90%volume in 48-hours minimum -
Length of WQ&Overflow Perf Pipes 98 117 ft
Perf Pipe Checks.Qperf>=Qpeak;
where Qperf=CdxAxV(2xgxH)