HomeMy WebLinkAboutCC - Storm Drainage Calcs STORM DRAINAGE REPORT AND CALCULATIONS
FOR
WINDROW SUBDIVISION NO. 2
MERIDIAN, IDAHO
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PREPARED BY:
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16970 CORINNE M GRAHAM, PE
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PO BOX 6059
BOISE, ID 83707
(208) 946-3874
cgraham@cswengineering.com
INTRODUCTION
The existing 4.82-acre site for the proposed Windrow Subdivision No. 2 is currently vacant ground.The
proposed development includes 8 single family residential lots,4 landscape common lots, and
associated public streets, storm drainage, landscaping, and utilities.
HISTORIC DRAINAGE
The existing project site sits northeast of the intersection of W.Amity Road and S. Linder Road in
Meridian.The site is bisected from southwest to northeast by the Calkins Lateral, which is also the high
point along the property. The Calkins lateral was recently piped by the Boise Project Board of Control.
Surficial soils are comprised of silt and silty sands. At depths of 2-6 feet, free draining coarse sand was
encountered during geotechnical exploration. Groundwater was not encountered at depths up to 11
feet.
Because of the presence of free draining materials and the depth to groundwater,the site is suitable for
the use of infiltration facilities.
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 50' 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.
Stormwater runoff from the public streets is conveyed via curb and gutter to drain inlets within the
roadway then piped to one of two underground seepage beds where it is treated, stored, and finally
infiltrated. A sand and grease trap will be installed to provide pre-treatment for the water quality event.
A portion of the runoff from Routeburn Drive will be conveyed to a temporary swale for storage and
treatment. Extension of the public street in the future will include a permanent storm drain facility for
this runoff.
Runoff from Linder Road will be conveyed to a borrow ditch and sand windows along the street
frontage.
APPENDICES
• Drainage Basin Map
• Storm Drainage Calculations
• Project Geotechnical Report
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DRAINAGE BASIN MAP
SCALE: 1" = 60' PO BOX 6059
BOISE, ID 83707
Ph: (208) 946-3874
cgraham@cswengineering.com
Prepared By: Corinne Graham, PE
Date: March 10, 2026
CIVIL SITE
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Windrow Subdivision No. 2
Storm Drainage Calculations
C Values
Impervious=0.90
Landscape=0.20
ACHD ACHD ACHD Temp Linder Rd Linder Rd
Basin#1 Basin#2 Basin#3 #1A #113
Total Area (SF) 114899 37418 15174 18615 38543
Roadway Area (SF) 36920 9302 5652 5004 10726
Sidewalk Area (SF) 9733 2618 1682 2435 5294
House/Driveway Area (SF) 20563 13173 391 0 0
Landscape Area (SF) 47683 12325 7449 11176 22523
C Value: 0.61 0.67 0.56 0.48 0.49
Catch Basin Calculations
CB#1A CB#113
Total Area (SF) 22973 64323
Roadway Area (SF) 8148 19069
Sidewalk Area (SF) 2017 6009
House/Driveway Area (SF) 0 13526
Landscape Area (SF) 12808 25719
C Value: 1 0.51 0.62
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.
for Peak Discharge Rate using th r post-developm
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 k1
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 36,920 9,733 20,563 47,683
Acres 2.64
6 Determine the Weighted Runoff Coefficient(C) 0.90 0.90 0.90 0.20
C=[(C1xA1)+(C2xA2)+(CnxAn)]/A Weighted Avg 0.61
7 Calculate Overland Flow Time of Concentration in Minutes(Tc)or use default 10 User Calculate
min
10 Min. I Estimated Runoff Coefficients for Various Surface
Type of Surface Runoff Coefficients"I
8 Determine the average rainfall intensity(i)from IDF Curve based on Tc i 2.58 2.58 in hr Business
Downtown areas 0.70-0.95
9 Calculate the Post-Development peak discharge(ClPeak) DPeA 4.15 4.15 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 5,556 5,556 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, 1,968 1,968 ft' Heavy areas 0.90
12 Detention:Approved Discharge Rate to Surface Waters(if applicable) 0.00 cfs Parks,cemeteries 0.
Playgrounds 0.20-0.0-0.35
5
Railroad yard areas 0.20-0.40
13 Volume Summary Unimproved areas 0.10-0.30
Surface Storage:Basin Streets
Asphalt 095
Basin Foreba V 556 ft' .
Y Concrete 0.95
Primary Treatment/StorageBasin V 5,001 ft' Brick 0.95
Subsurface Storage Roofs 0.95
Volume Without Sediment Factor(See BMP 20 Tab) V 5,556 5,556 ft' Gravel 0.75
Fields:Sandy soil Soil Type
Slope A B C D
Flat:0-2% 0.04 0.07 0.11 0.
Average:2-6% 0.09 0.12 0.15 0.
Steep:>6% 0.13 0.18 0.23 0.
Adapted from ASCE
C:\Users\cgrah\Dropbox\Projects\24005 Windrow Sub Ph2\Reports\Storm Drainage\ACHD_SD_CALCS_Ph2 011425 3/10/2026,10:50 AM
Version 10.5,November 2018
ACHD Calculation Sheet for Sizing Seepage Bed With Optional Chambers
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.
1 Project Name ACHD Basin#1
2 Enter number of Seepage Beds(25 max) 1
3 Design Storm 100
4 Weighted Runoff Coefficient C 0.61 Unkto: —
QV TR55
5 Area A(Acres) 2.64 acres
6 Approved discharge rate(if applicable) 0.00 cfs
7 Is Seepage Bed in Common Lot? Yes V 5,556 5,556 ft' 0%Sediment
8 Set Total Design Width of All Drain Rock W 14.0 ft
9 Set Total Design Depth of All Drain Rock D 8.0 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
13 Size of Overflow Perf Pipe(Perfs 3601),READ if Q100>3.3 cfs 12 in
14 Calculate Total Storage per Foot Spf 54.8 ft3/ft
15 Calculate Design Length L 101 101 ft
Override Value Required for Chambers
16 Variable Infiltration Window L SWL 101 101.0 ft
17 Variable Infiltration Window W SWW 14.0 14.0 ft
18 Time to Drain 5.3 hours
90%volume in 48-hours minimum
19 Length of WQ&Overflow Perf Pipes 101 101 ft
20 Perf Pipe Checks.Qperf>=Qpeak;
where Qperf=CdxAxV(2xgxH)
Optional Storage Chambers
Note:This assumes chambers are organized in a rectangular layout.
1-StormTech,
1 Type of Chambers SC740
2 Volume 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
4 Chamber Void Factor
5 Chamber Storage Volume,Without Rock,Per Manuf 45.90 ft3/Unit
6 Chamber Storage Volume,With Rock,Per Manuf 74.90 ft3/Unit
7 Total Number of Units Required 0 ea
8 Area of Infiltration Aperc ftz
9 Volume Infiltration Vperc 0 ft3/hr
10 Time to Drain hours
90%volume in 48-hours minimum
C:\Users\cgrah\Dropbox\Projects\24005 Windrow Sub Ph2\Reports\Storm Drainage\ACHD_SD_CALCS_Ph2 011425 3/10/2026,10:51 AM
Version 10.0,May 2018
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.
for Peak Discharge Rate using th r post-developm
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#2
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 9,302 2,618 13,173 12,325
Acres 0.86
6 Determine the Weighted Runoff Coefficient(C) 0.90 0.90 0.90 0.20
C=[(C1xA1)+(C2xA2)+(CnxAn)]/A Weighted Avg 0.67
7 Calculate Overland Flow Time of Concentration in Minutes(Tc)or use default 10 User Calculate
min
10 Min. I Estimated Runoff Coefficients for Various Surface
Type of Surface Runoff Coefficients"I
8 Determine the average rainfall intensity(i)from IDF Curve based on Tc i 2.58 2.58 in hr Business
Downtown areas 0.70-0.95
9 Calculate the Post-Development peak discharge(ClPeak) Cip'A 1.48 1.48 cfs Urban neighborhoods 0.50-0.70
Residential
50
10 Calculate total runoff vol V for sizing rims storage) V 1,987 1,987 ft Single Family 0.60-0.75
( )( g primary g ) 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, 704 704 ft' Heavy areas 0.90
12 Detention:Approved Discharge Rate to Surface Waters(if applicable) 0.00 cfs Parks,cemeteries 0.10-0.
Playgrounds 0.20-0.35
5
Railroad yard areas 0.20-0.40
13 Volume Summary Unimproved areas 0.10-0.30
Surface Storage:Basin Streets
Asphalt 0.95
Basin Foreba V 199 ft'
Y concrete 0.95
Primary Treatment/StorageBasin V 1,789 ft' Brick 0.95
Subsurface Storage Roofs 0.95
Volume Without Sediment Factor See BMP 20 Tab V 1,987 1,987 ft' Gravel 0.75
( ) Fields:Sandy soil Soil Type
Slope A B C D
Flat:0-2% 0.04 0.07 0.11 0.
Average:2-6% 0.09 0.12 0.15 0.
Steep:>6% 0.13 0.18 0.23 0.
Adapted from ASCE
C:\Users\cgrah\Dropbox\Projects\24005 Windrow Sub Ph2\Reports\Storm Drainage\ACHD_SD_CALCS_Ph2 011425 3/10/2026,10:50 AM
Version 10.5,November 2018
ACHD Calculation Sheet for Sizing Seepage Bed With Optional Chambers
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.
1 Project Name ACHD Basin#2
2 Enter number of Seepage Beds(25 max) 1
3 Design Storm 100
4 Weighted Runoff Coefficient C 0.67 Unkto: —
QV TR55
5 Area A(Acres) 0.86 acres
6 Approved discharge rate(if applicable) 0.00 cfs
7 Is Seepage Bed in Common Lot? Yes V 1,987 1,987 ft' 0%Sediment
8 Set Total Design Width of All Drain Rock W 15.0 ft
9 Set Total Design Depth of All Drain Rock D 6.0 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
13 Size of Overflow Perf Pipe(Perfs 3601),READ if Q100>3.3 cfs in
14 Calculate Total Storage per Foot Spf 46.2 46.2 ft3/ft
15 Calculate Design Length L 43 43 ft
Override Value Required for Chambers
16 Variable Infiltration Window L SWL 43 43.0 ft
17 Variable Infiltration Window W SWW 15.0 15.0 ft
18 Time to Drain 47 hours
90%volume in 48-hours minimum
19 Length of WQ&Overflow Perf Pipes 43 43 ft
20 Perf Pipe Checks.Qperf>=Qpeak;
where Qperf=CdxAxV(2xgxH)
Optional Storage Chambers
Note:This assumes chambers are organized in a rectangular layout.
1-StormTech,
1 Type of Chambers SC740
2 Volume 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
4 Chamber Void Factor
5 Chamber Storage Volume,Without Rock,Per Manuf 45.90 ft3/Unit
6 Chamber Storage Volume,With Rock,Per Manuf 74.90 ft3/Unit
7 Total Number of Units Required 0 ea
8 Area of Infiltration Aperc ftz
9 Volume Infiltration Vperc 0 ft3/hr
10 Time to Drain hours
90%volume in 48-hours minimum
C:\Users\cgrah\Dropbox\Projects\24005 Windrow Sub Ph2\Reports\Storm Drainage\ACHD_SD_CALCS_Ph2 011425 3/10/2026,10:51 AM
Version 10.0,May 2018
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.
for Peak Discharge Rate using th r post-developm
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 Temp 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 5,652 1,682 391 7,449
Acres 0.35
6 Determine the Weighted Runoff Coefficient(C) 0.90 0.90 0.90 0.20
C=[(C1xA1)+(C2xA2)+(CnxAn)]/A Weighted Avg 0.56
7 Calculate Overland Flow Time of Concentration in Minutes(Tc)or use default 10 User Calculate
min
10 Min. I Estimated Runoff Coefficients for Various Surface
Type of Surface Runoff Coefficients"I
8 Determine the average rainfall intensity(i)from IDF Curve based on Tc i 2.58 2.58 in hr Business
Downtown areas 0.70-0.95
9 Calculate the Post-Development peak discharge(ClPeak) QpeA 0.50 0.50 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 670 670 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, 237 237 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 095
Basin Foreba V 67 ft' .
Y Concrete 0.95
Primary Treatment/StorageBasin V 603 ft' Brick 0.95
Subsurface Storage Roofs 0.95
Volume Without Sediment Factor(See BMP 20 Tab) V 670 670 ft' Gravel 0.75
Fields:Sandy soil Soil Type
Slope A B C D
Flat:0-2% 0.04 0.07 0.11 0.
Average:2-6% 0.09 0.12 0.15 0.
Steep:>6% 0.13 0.18 0.23 0.
Adapted from ASCE
C:\Users\cgrah\Dropbox\Projects\24005 Windrow Sub Ph2\Reports\Storm Drainage\ACHD_SD_CALCS_Ph2 011425 3/10/2026,10:50 AM
Version 10.5,November 2018
ACHD Calculation Sheet for Sizing Bioswales & Borrow Ditches
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.
User input in yellow cells.
1 Project Name ACHD Temp Basin#3
2 Enter number of Bioswales/Borrow Ditches(25 max) 1
3 Design Storm 100
Weighted Runoff Coefficient C 0.56 Link to: LQv(1)
4 Area A(Acres) 0.35 acres Q,V TRSS
Approved discharge rate for the given storm(if applicable) 0.00 cfs
5 Design Vol With 0%Sed for Swales V 670 669.80 ft3
6 Length of Swale 48 ft
7 Infiltration Window?(Note:infiltration required if Longitudinal Sloped%)
Design Infiltration Rate 8.00 in/hr
8 Infiltration Window Width 4.00 ft
9 Set Swale Bottom Width b 4.00 ft
10 Set Swale Top Width 16.00 ft
11 Set Swale Depth y 1.50 ft
12 Swale Side Slopes H:1 Sxs 4.00
13 Calculate cross-sectional area Axs 15.00 15.00 ftz
Axs=Y zz+by
14 Total Swale Capacity Without Driveways 720 720.00 ft'
15 Does it Have Capacity? OK
16 Time to Drain 5.2 5.23 hr
90%volume in 48-hours minimum OK
Check Borrow Ditch Infiltration Windows
17 Enter Infiltration Window Length 36.00 ft
18 Enter Infiltration Window Width 4 If
19 Time to Drain 7.8 7.8 hr
90%volume in 48-hours minimum OK
C:\Users\cgrah\Dropbox\Projects\24005 Windrow Sub Ph2\Reports\Storm Drainage\ACHD_SD_CALCS_Ph2 011425 3/10/2026,10:51 AM
Version 10.0,May 2018
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.
for Peak Discharge Rate using th r post-developm
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 Linder Road#1A
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 5,004 2,435 0 11,176
Acres 0.43
6 Determine the Weighted Runoff Coefficient(C) 0.90 0.90 0.90 0.20
C=[(C1xA1)+(C2xA2)+(CnxAn)]/A Weighted Avg 0.48
7 Calculate Overland Flow Time of Concentration in Minutes(Tc)or use default 10 User Calculate
min
10 Min. I Estimated Runoff Coefficients for Various Surface
Type of Surface Runoff Coefficients"I
8 Determine the average rainfall intensity(i)from IDF Curve based on Tc i 2.58 2.58 in hr Business
Downtown areas 0.70-0.95
9 Calculate the Post-Development peak discharge(ClPeak) QpeA 0.53 0.53 cfs Urban neighborhoods 0.50-0.70
Residential
50
10 Calculate total runoff vol V for sizing rims storage) V 709 709 ft Single Family 0.60-0.75
( )( g primary g ) 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, 251 251 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 095
Basin Foreba V 71 ft' .
Y Concrete 0.95
Primary Treatment/StorageBasin V 638 ft' Brick 0.95
Subsurface Storage Roofs 0.95
Volume Without Sediment Factor(See BMP 20 Tab) V 709 709 ft' Gravel 0.75
Fields:Sandy soil Soil Type
Slope A B C D
Flat:0-2% 0.04 0.07 0.11 0.
Average:2-6% 0.09 0.12 0.15 0.
Steep:>6% 0.13 0.18 0.23 0.
Adapted from ASCE
C:\Users\cgrah\Dropbox\Projects\24005 Windrow Sub Ph2\Reports\Storm Drainage\ACHD_SD_CALCS_Ph2 011425 3/10/2026,10:50 AM
Version 10.5,November 2018
ACHD Calculation Sheet for Sizing Bioswales & Borrow Ditches
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.
User input in yellow cells.
1 Project Name ACHD Linder Road#1A
2 Enter number of Bioswales/Borrow Ditches(25 max) 1
3 Design Storm 100
Weighted Runoff Coefficient C 0.48 Link to LQV rn
4 Area A(Acres) 0.43 acres Q,V TRSS
Approved discharge rate for the given storm(if applicable) 0.00 cfs
5 Design Vol With 0%Sed for Swales V 709 708.52 ft3
6 Length of Swale 277 ft
7 Infiltration Window?(Note:infiltration required if Longitudinal Sloped%)
Design Infiltration Rate 8.00 in/hr
8 Infiltration Window Width 2.00 ft
9 Set Swale Bottom Width b 0.00 ft
10 Set Swale Top Width 8.00 ft
11 Set Swale Depth y 1.00 ft
12 Swale Side Slopes H:1 Sxs 4.00
13 Calculate cross-sectional area Axs 4.00 4.00 ftz
Axs=Y zz+by
14 Total Swale Capacity Without Driveways 1,108 1108.00 ft'
15 Does it Have Capacity? OK
16 Time to Drain 1.9 1.92 hr
90%volume in 48-hours minimum OK
Check Borrow Ditch Infiltration Windows
17 Enter Infiltration Window Length 24.00 ft
18 Enter Infiltration Window Width 2 If
19 Time to Drain 24.6 24.6 hr
90%volume in 48-hours minimum OK
C:\Users\cgrah\Dropbox\Projects\24005 Windrow Sub Ph2\Reports\Storm Drainage\ACHD_SD_CALCS_Ph2 011425 3/10/2026,10:51 AM
Version 10.0,May 2018
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.
for Peak Discharge Rate using th r post-developm
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 Linder Road#16
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 10,726 5,294 0 22,523
Acres 0.88
6 Determine the Weighted Runoff Coefficient(C) 0.90 0.90 0.90 0.20
C=[(C1xA1)+(C2xA2)+(CnxAn)]/A Weighted Avg 0.49
7 Calculate Overland Flow Time of Concentration in Minutes(Tc)or use default 10 User Calculate
min
10 Min. I Estimated Runoff Coefficients for Various Surface
Type of Surface Runoff Coefficients"I
8 Determine the average rainfall intensity(i)from IDF Curve based on Tc i 2.58 2.58 in hr Business
Downtown areas 0.70-0.95
9 Calculate the Post-Development peak discharge(ClPeak) Qpe k 1.12 1.12 cfs Urban neighborhoods 0.50-0.70
Residential
50
10 Calculate total runoff vol V for sizing rims storage) V 1,501 1,501 ft Single Family 0.60-0.75
( )( g primary g ) 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, 532 532 ff' Heavy areas 0.90
12 Detention:Approved Discharge Rate to Surface Waters(if applicable) 0.00 cfs Parks,cemeteries 0.
Playgrounds 0.20-0.0-0.35
5
Railroad yard areas 0.20-0.40
13 Volume Summary Unimproved areas 0.10-0.30
Surface Storage:Basin Streets
Asphalt 095
Basin Foreba V 150 ft' .
Y Concrete 0.95
Primary Treatment/StorageBasin V 1,351 ft' Brick 0.95
Subsurface Storage Roofs 0.95
Volume Without Sediment Factor(See BMP 20 Tab) V 1,501 1,501 ft' Gravel 0.75
Fields:Sandy soil Soil Type
Slope A B C D
Flat:0-2% 0.04 0.07 0.11 0.
Average:2-6% 0.09 0.12 0.15 0.
Steep:>6% 0.13 0.18 0.23 0.
Adapted from ASCE
C:\Users\cgrah\Dropbox\Projects\24005 Windrow Sub Ph2\Reports\Storm Drainage\ACHD_SD_CALCS_Ph2 011425 3/10/2026,10:50 AM
Version 10.5,November 2018
ACHD Calculation Sheet for Sizing Bioswales & Borrow Ditches
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.
User input in yellow cells.
1 Project Name ACHD Linder Road#16
2 Enter number of Bioswales/Borrow Ditches(25 max) 1
3 Design Storm 100
Weighted Runoff Coefficient C 0.49 Link to: LQv(1)
4 Area A(Acres) 0.88 acres Q,V TRSS
Approved discharge rate for the given storm(if applicable) 0.00 cfs
5 Design Vol With 0%Sed for Swales V 1,501 1501.30 ft3
6 Length of Swale 527 ft
7 Infiltration Window?(Note:infiltration required if Longitudinal Sloped%)
Design Infiltration Rate 8.00 in/hr
8 Infiltration Window Width 2.00 ft
9 Set Swale Bottom Width b 0.00 ft
10 Set Swale Top Width 8.00 ft
11 Set Swale Depth y 1.00 ft
12 Swale Side Slopes H:1 Sxs 4.00
13 Calculate cross-sectional area Axs 4.00 4.00 ftz
Axs=Y zz+by
14 Total Swale Capacity Without Driveways 2,108 2108.00 ft'
15 Does it Have Capacity? OK
16 Time to Drain 2.1 2.14 hr
90%volume in 48-hours minimum OK
Check Borrow Ditch Infiltration Windows
17 Enter Infiltration Window Length 36.00 ft
18 Enter Infiltration Window Width 2 If
19 Time to Drain 34.8 34.8 hr
90%volume in 48-hours minimum OK
C:\Users\cgrah\Dropbox\Projects\24005 Windrow Sub Ph2\Reports\Storm Drainage\ACHD_SD_CALCS_Ph2 011425 3/10/2026,10:51 AM
Version 10.0,May 2018