CC - Storm Drainage CalcsPO BOX 6059
BOISE, ID 83707
(208) 946-3874
cgraham@cswengineering.com
STORM DRAINAGE REPORT AND CALCULATIONS
FOR
EDINGTON COMMONS SUBDIVISION NO. 1
3610 N. LINDER ROAD
MERIDIAN, IDAHO
PREPARED BY:
CORINNE M GRAHAM, PE
September 14, 2020
INTRODUCTION
The existing 7.73-acre site for the Edington Commons Subdivision No. 1 is currently vacant agricultural
ground. The proposed development includes 45 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 80th 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 #1 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 is conveyed through a sand and grease trap
to the treatment bed where it is filtered through the vertical sand filter. The 25-year storm event
bypasses the sand and grease trap and is conveyed directly to the percolation bed. The 100-year storm
event is designed to overflow into the large open park space then recede back into the percolation bed
for infiltration.
Storm water runoff for the remaining basins is conveyed via curb and gutter to shallow drain inlets
within the roadway then conveyed to three bioretention swales where it is stored and infiltrated.
APPENDICES
• Drainage Basin Map
• Storm Drainage Calculations
• Project Geotechnical Report
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M(D,1*721&2MM21SS8%12
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PO BOX 6059
BOISE, ID 83707
Ph: (208) 946-3874
cgraham@cswengineering.com
Prepared By: Corinne Graham, PE
September 14, 2020
ACHD Basin Characteristics
C Values
Impervious = 0.90
Landscape = 0.20
Basin #1 Basin #2 Basin #3 Basin #4
Total Area (SF) 56736 28330 45870 48256
Roadway Area (SF) 17236 9505 16502 14506
Sidewalk Area (SF) 4656 2926 3671 3583
House/Driveway Area (SF) 14940 8986 13119 17880
Landscape Area (SF) 19904 6913 12578 12287
C Value: 0.65 0.73 0.71 0.72
Catch Basin Calculations
CB #1A CB #1B
Total Area (SF) 39076 17660
Roadway Area (SF) 10074 7162
Sidewalk Area (SF) 2369 2287
House/Driveway Area (SF) 14940 0
Landscape Area (SF) 11693 8211
C Value: 0.69 0.57
Edington Commons Subdivision Ph1
Storm Drainage Calculations
Steps for Peak Discharge Rate using the Rational Method calculated for post‐development
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
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
1 Subbasin 2
Subbasin
3
Subbasin
4
Subbasin
5
Subbasin
6
Subbasin
7
Subbasin
8
Subbasin
9
Subbasin
10
5 Area of Drainage Subbasin (SF or Acres)SF 17,236 4,656 14,940 19,904
Acres 1.30
6 Determine the Weighted Runoff Coefficient (C) 0.90 0.90 0.90 0.20
C=[(C1xA1)+(C2xA2)+(CnxAn)]/A Weighted Avg 0.65
7
I100, TC<=60
8 i 2.58 2.58 in/hr
9 Qpeak 2.20 2.20 cfs
10 V 2,946 2,946
ft3
V = Ci (Tc=60)Ax3600
11
Enter Percentile Storm I (95th percentile = 0.60 in)80th 0.34 in
Enter Runoff Reduction Vol (95th Percentile=0.60‐in x Area x C)Vrr 1,043 1,043
ft3
12 Detention: Approved Discharge Rate to Surface Waters (if applicable)0.00 cfs
13 Volume Summary
Surface Storage: Basin
Basin Forebay V 295 ft3
Primary Treatment/Storage Basin V 2,651 ft3
Subsurface Storage
In Common Lot ‐ No Sediment Factor Required V 2,946 2,946
ft3
Determine the average rainfall intensity (i) from IDF Curve based on
Calculate the Post‐Development peak discharge (QPeak)
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.
ACHD Basin #1
Calculate Overland Flow Time of Concentration in Minutes (Tc) or use default
10 min
Calculate total runoff vol (V) (for sizing primary storage)
Calculate Volume of Runoff Reduction Vrr
C:\Users\cgrah\Dropbox\Projects\18049 Edington Subdivision\Reports\Storm Drainage\ACHD_SD_CALCS
Version 9.0, December 2016
9/14/2020, 9:51 AM
Steps for Seepage Beds
#REF!
#REF!
1 Project Name
2 Enter number of Seepage Beds (25 max)1
3 Design Storm 100 #REF!
4 Weighted Runoff Coefficient C 0.65 Link to:
5 Area A (Acres)1.30 acres
6 Approved discharge rate (if applicable)0.00 cfs
7 Design Volume V
1,043 1,043 ft3
Water Quality Runoff
8 Set Total Design Width of All Drain Rock W
8.0 ft
9Set Total Design Depth of All Drain Rock D
3.5 ft
Rock Only, Do Not Include Filter Sand Depth or Cover
10 Void Ratio of Drain Rock Voids
0.4
0.4 for 1.5"‐2" drain rock and 3/4" Chips
11 Design Infiltration Rate (8 in/hr max) Perc 8.00 in/hr
12 Size of WQ Perf Pipe (Perf 180⁰)Dia pipe 18 in 0.9
13 Size of Overflow Perf Pipe (Perfs 360⁰), REQD if Q100>3.3 cfs in
14 Calculate Total Storage per Foot Spf
11.4 ft3/ft
Spf=Apf=WxD‐APerf_PipexVoids+1/2 Perf_Area
15 Calculate Design Length L
93 96 ft 0
Override Value Required for Chambers
16 Variable Infiltration Window LSWL96 ft
17 Variable Infiltration Window WSWW8.0 ft
18 Time to Drain 1.8 hours
90% volume in 48‐hours minimum OK
19 Length of WQ & Overflow Perf Pipes 96 ft
20 Perf Pipe Checks. Qperf >= Qpeak; #REF!
where Qperf=CdxAx√(2xgxH)d 0.0313 ft
Optional Storage Chambers
Note: This assumes chambers are organized in a rectangular layout.
1Type of Chambers
1‐StormTech,
SC740
2Volume to Store V
0 ft3
3 Installed Chamber Width Cw
4.25 ft
Installed Chamber Depth Cd
2.50 ft
Installed Chamber Height Ch
7.12 ft
4Chamber Void Factor
5Chamber Storage Volume, Without Rock, Per Manuf 45.90 ft3/Unit
6Chamber Storage Volume, With Rock, Per Manuf 74.90 ft3/Unit
7Total Number of Units Required 0ea
8Area of Infiltration Aperc
ft2
9Volume Infiltration Vperc
0 ft3/hr
10 Time to Drain #DIV/0!hours
90% volume in 48‐hours minimum #DIV/0!
ACHD Calculation Sheet for Sizing Seepage Bed With Optional Chambers
#REF!
Note this spreadsheet pulls information from the "Peak Q,V" tab
ACHD Basin #1 ‐ Percolation Bed (WQ Volume)
C:\Users\cgrah\Dropbox\Projects\18049 Edington Subdivision\Reports\Storm Drainage\ACHD_SD_CALCS
Version 9.0, December 2016
9/14/2020, 9:54 AM
Steps for Seepage Beds
#REF!
#REF!
1 Project Name
2 Enter number of Seepage Beds (25 max)1
3 Design Storm 100 #REF!
4 Weighted Runoff Coefficient C 0.65 Link to:
5 Area A (Acres)1.30 acres
6 Approved discharge rate (if applicable)0.00 cfs
7 Design Volume V
1,074 1,074 ft3
25‐year minus WQ
8 Set Total Design Width of All Drain Rock W
8.0 ft
9Set Total Design Depth of All Drain Rock D
3.5 ft
Rock Only, Do Not Include Filter Sand Depth or Cover
10 Void Ratio of Drain Rock Voids
0.4
0.4 for 1.5"‐2" drain rock and 3/4" Chips
11 Design Infiltration Rate (8 in/hr max) Perc 8.00 in/hr
12 Size of WQ Perf Pipe (Perf 180⁰)Dia pipe 18 in 0.9
13 Size of Overflow Perf Pipe (Perfs 360⁰), REQD if Q100>3.3 cfs in
14 Calculate Total Storage per Foot Spf
11.4 ft3/ft
Spf=Apf=WxD‐APerf_PipexVoids+1/2 Perf_Area
15 Calculate Design Length L
96 96 ft 0
Override Value Required for Chambers
16 Variable Infiltration Window LSWL96 ft
17 Variable Infiltration Window WSWW8.0 ft
18 Time to Drain 1.9 hours
90% volume in 48‐hours minimum OK
19 Length of WQ & Overflow Perf Pipes 96 ft
20 Perf Pipe Checks. Qperf >= Qpeak; #REF!
where Qperf=CdxAx√(2xgxH)d 0.0313 ft
Optional Storage Chambers
Note: This assumes chambers are organized in a rectangular layout.
1Type of Chambers
1‐StormTech,
SC740
2Volume to Store V
0 ft3
3 Installed Chamber Width Cw
4.25 ft
Installed Chamber Depth Cd
2.50 ft
Installed Chamber Height Ch
7.12 ft
4Chamber Void Factor
5Chamber Storage Volume, Without Rock, Per Manuf 45.90 ft3/Unit
6Chamber Storage Volume, With Rock, Per Manuf 74.90 ft3/Unit
7Total Number of Units Required 0ea
8Area of Infiltration Aperc
ft2
9Volume Infiltration Vperc
0 ft3/hr
10 Time to Drain #DIV/0!hours
90% volume in 48‐hours minimum #DIV/0!
ACHD Calculation Sheet for Sizing Seepage Bed With Optional Chambers
#REF!
Note this spreadsheet pulls information from the "Peak Q,V" tab
ACHD Basin #1 ‐ Percolation Bed (25‐year volume minus WQ)
C:\Users\cgrah\Dropbox\Projects\18049 Edington Subdivision\Reports\Storm Drainage\ACHD_SD_CALCS
Version 9.0, December 2016
9/14/2020, 9:54 AM
Steps for Peak Discharge Rate using the Rational Method calculated for post‐development
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
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
1 Subbasin 2
Subbasin
3
Subbasin
4
Subbasin
5
Subbasin
6
Subbasin
7
Subbasin
8
Subbasin
9
Subbasin
10
5 Area of Drainage Subbasin (SF or Acres)SF 9,505 2,926 8,986 6,913
Acres 0.65
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
I100, TC<=60
8 i 2.58 2.58 in/hr
9 Qpeak 1.22 1.22 cfs
10 V 1,639 1,639
ft3
V = Ci (Tc=60)Ax3600
11
Enter Percentile Storm I (95th percentile = 0.60 in)80th 0.34 in
Enter Runoff Reduction Vol (95th Percentile=0.60‐in x Area x C)Vrr 580 580
ft3
12 Detention: Approved Discharge Rate to Surface Waters (if applicable)0.00 cfs
13 Volume Summary
Surface Storage: Basin
Basin Forebay V 164 ft3
Primary Treatment/Storage Basin V 1,475 ft3
Subsurface Storage
In R/W ‐ 25% Sediment Factor Required V 2,049 1,639
ft3
Calculate total runoff vol (V) (for sizing primary storage)
Calculate Volume of Runoff Reduction Vrr
Determine the average rainfall intensity (i) from IDF Curve based on
Calculate the Post‐Development peak discharge (QPeak)
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.
ACHD Basin #2
Calculate Overland Flow Time of Concentration in Minutes (Tc) or use default
10 min
C:\Users\cgrah\Dropbox\Projects\18049 Edington Subdivision\Reports\Storm Drainage\ACHD_SD_CALCS
Version 9.0, December 2016
9/14/2020, 9:51 AM
Steps for Sizing Bioswale
#REF!
1 Project Name
2
2 Enter number of Bioswales/Borrow Ditches (25 max)1
3 Design Storm 100 #REF!
Weighted Runoff Coefficient C 0.73 Link to:
4Area A (Acres)0.65 acres
Approved discharge rate for the given storm (if applicable)0.00 cfs
5Design Vol With 0% Sed for Swales V
1,639 1639 ft3
6Length of Swale 180 ft
7 Infiltration Window? (Note: infiltration required if Longitudinal Slope<1%)
Design Infiltration Rate 8.00 in/hr
8 Infiltration Window Width 3.00 ft
9Set Swale Bottom Width b
3.00 ft
10 Set Swale Top Width 12.00 ft
11 Set Swale Depth y
1.50 ft
12 Swale Side Slopes H:1 SXS 3.00
13 Calculate cross‐sectional area AXS 11.25 11.25 ft2
AXS=y2z+by
14 Total Swale Capacity Without Driveways 2,025 2025.00 ft3
15 Does it Have Capacity?OK
16 Time to Drain 4.6 4.55 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 (1,639.0)ft3
23 Is Capacity Good?NO
24 Time to Drain 0.0 hr
90% volume in 48‐hours minimum OK
ACHD Calculation Sheet for Sizing Bioswales & Borrow Ditches
#REF!
ACHD Basin #2
C:\Users\cgrah\Dropbox\Projects\18049 Edington Subdivision\Reports\Storm Drainage\ACHD_SD_CALCS
Version 9.0, December 2016
9/14/2020, 9:54 AM
Steps for Peak Discharge Rate using the Rational Method calculated for post‐development
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
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
1 Subbasin 2
Subbasin
3
Subbasin
4
Subbasin
5
Subbasin
6
Subbasin
7
Subbasin
8
Subbasin
9
Subbasin
10
5 Area of Drainage Subbasin (SF or Acres)SF 16,502 3,671 13,119 12,578
Acres 1.05
6 Determine the Weighted Runoff Coefficient (C) 0.90 0.90 0.90 0.20
C=[(C1xA1)+(C2xA2)+(CnxAn)]/A Weighted Avg 0.71
7
I100, TC<=60
8 i 2.58 2.58 in/hr
9 Qpeak 1.92 1.92 cfs
10 V 2,577 2,577
ft3
V = Ci (Tc=60)Ax3600
11
Enter Percentile Storm I (95th percentile = 0.60 in)80th 0.34 in
Enter Runoff Reduction Vol (95th Percentile=0.60‐in x Area x C)Vrr 913 913
ft3
12 Detention: Approved Discharge Rate to Surface Waters (if applicable)0.00 cfs
13 Volume Summary
Surface Storage: Basin
Basin Forebay V 258 ft3
Primary Treatment/Storage Basin V 2,319 ft3
Subsurface Storage
In Common Lot ‐ No Sediment Factor Required V 2,577 2,577
ft3
Determine the average rainfall intensity (i) from IDF Curve based on
Calculate the Post‐Development peak discharge (QPeak)
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.
ACHD Basin #3
Calculate Overland Flow Time of Concentration in Minutes (Tc) or use default
10 min
Calculate total runoff vol (V) (for sizing primary storage)
Calculate Volume of Runoff Reduction Vrr
C:\Users\cgrah\Dropbox\Projects\18049 Edington Subdivision\Reports\Storm Drainage\ACHD_SD_CALCS
Version 9.0, December 2016
9/14/2020, 9:51 AM
Steps for Sizing Bioswale
#REF!
1 Project Name
2
2 Enter number of Bioswales/Borrow Ditches (25 max)1
3 Design Storm 100 #REF!
Weighted Runoff Coefficient C 0.71 Link to:
4Area A (Acres)1.05 acres
Approved discharge rate for the given storm (if applicable)0.00 cfs
5Design Vol With 0% Sed for Swales V
2,577 2577 ft3
6Length of Swale 162 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
9Set 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
AXS=y2z+by
14 Total Swale Capacity Without Driveways 2,592 2592.00 ft3
15 Does it Have Capacity?OK
16 Time to Drain 11.9 11.93 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 (2,576.8)ft3
23 Is Capacity Good?NO
24 Time to Drain 0.0 hr
90% volume in 48‐hours minimum OK
#REF!
ACHD Calculation Sheet for Sizing Bioswales & Borrow Ditches
ACHD Basin #3
C:\Users\cgrah\Dropbox\Projects\18049 Edington Subdivision\Reports\Storm Drainage\ACHD_SD_CALCS
Version 9.0, December 2016
9/14/2020, 9:54 AM
Steps for Peak Discharge Rate using the Rational Method calculated for post‐development
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
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
1 Subbasin 2
Subbasin
3
Subbasin
4
Subbasin
5
Subbasin
6
Subbasin
7
Subbasin
8
Subbasin
9
Subbasin
10
5 Area of Drainage Subbasin (SF or Acres)SF 14,506 3,583 17,880 12,287
Acres 1.11
6 Determine the Weighted Runoff Coefficient (C) 0.90 0.90 0.90 0.20
C=[(C1xA1)+(C2xA2)+(CnxAn)]/A Weighted Avg 0.72
7
I100, TC<=60
8 i 2.58 2.58 in/hr
9 Qpeak 2.06 2.06 cfs
10 V 2,763 2,763
ft3
V = Ci (Tc=60)Ax3600
11
Enter Percentile Storm I (95th percentile = 0.60 in)80th 0.34 in
Enter Runoff Reduction Vol (95th Percentile=0.60‐in x Area x C)Vrr 979 979
ft3
12 Detention: Approved Discharge Rate to Surface Waters (if applicable)0.00 cfs
13 Volume Summary
Surface Storage: Basin
Basin Forebay V 276 ft3
Primary Treatment/Storage Basin V 2,487 ft3
Subsurface Storage
In Common Lot ‐ No Sediment Factor Required V 2,763 2,763
ft3
Calculate total runoff vol (V) (for sizing primary storage)
Calculate Volume of Runoff Reduction Vrr
Determine the average rainfall intensity (i) from IDF Curve based on
Calculate the Post‐Development peak discharge (QPeak)
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.
ACHD Basin #4
Calculate Overland Flow Time of Concentration in Minutes (Tc) or use default
10 min
C:\Users\cgrah\Dropbox\Projects\18049 Edington Subdivision\Reports\Storm Drainage\ACHD_SD_CALCS
Version 9.0, December 2016
9/14/2020, 9:51 AM
Steps for Sizing Bioswale
#REF!
1 Project Name
2
2 Enter number of Bioswales/Borrow Ditches (25 max)1
3 Design Storm 100 #REF!
Weighted Runoff Coefficient C 0.72 Link to:
4Area A (Acres)1.11 acres
Approved discharge rate for the given storm (if applicable)0.00 cfs
5Design Vol With 0% Sed for Swales V
2,763 2763 ft3
6Length of Swale 174 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
9Set 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
AXS=y2z+by
14 Total Swale Capacity Without Driveways 2,784 2784.00 ft3
15 Does it Have Capacity?OK
16 Time to Drain 11.9 11.91 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 (2,763.3)ft3
23 Is Capacity Good?NO
24 Time to Drain 0.0 hr
90% volume in 48‐hours minimum OK
ACHD Calculation Sheet for Sizing Bioswales & Borrow Ditches
#REF!
ACHD Basin #4
C:\Users\cgrah\Dropbox\Projects\18049 Edington Subdivision\Reports\Storm Drainage\ACHD_SD_CALCS
Version 9.0, December 2016
9/14/2020, 9:54 AM