CC - Storm Drainage Calcs STORM DRAINAGE REPORT AND CALCULATIONS
FOR
DELANO SUBDIVISION NO. 1
MERIDIAN, IDAHO
PREPARED BY:
a
16970 CORINNE M GRAHAM, PE
December 7, 2020
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 14.09-acre site for the proposed Delano Subdivision is currently three rural residential lots.
The proposed development includes 59 single family residential lots, 8 landscape common lots, and
associated public streets, landscaping, and utilities.
HISTORIC DRAINAGE
The existing project site sits west of Eagle Road between Ustick and McMillan Roads.The existing site is
relatively flat with the existing homes elevated and existing drainage flowing outward towards the
perimeter of the property.
Surficial soils are comprised of lean clays and sandy silts.At depths of 4-8 feet, free draining poorly
graded gravel with sand was encountered during geotechnical exploration. Groundwater was not
encountered at depths up to 14 feet below ground nor has groundwater been observed in piezometers
that were installed on site.
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 801h percentile
storm event. Storm water runoff from 40 feet 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. Drainage for the future multi-family site east of
Centrepoint Way will be responsible for on-site stormwater retention.
Storm water runoff is conveyed via curb and gutter to drain inlets within the roadway then piped to four
underground seepage beds where it is treated and finally infiltrated. Sand and grease traps will be
installed to provide pre-treatment for the water quality event.
APPENDICES
• Drainage Basin Map
• Storm Drainage Calculations
• Project Geotechnical Report
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PO BOX6059 DRAINAGE BASIN MAP
BOISE,ID 83707
Ph: (208)946-3874
cgraham@cswengineering.com
Prepared By: Corinne Graham, PE
CSW December 7, 2020
C I V I L SIT E
Delano Subdivision Phl
Storm Drainage Calculations
ACHD Basin Characteristics
C Values
Impervious=0.90
Landscape=0.20
Basin#1 Basin#2 Basin#3 Basin#4
Total Area (SF) 100526 49973 117978 10186
Roadway Area (SF) 33666 15809 32917 4397
Sidewalk Area (SF) 10520 4548 10601 1470
House/Driveway Area (SF) 20910 15901 39312 1128
Landscape Area (SF) 35430 13715 35148 3191
C Value: 0.65 0.71 0.69 0.68
Catch Basin Characteristics
CB#1A CB#113 CB#1C CB#11D CB#2A CB#213 CB#3A CB#313 CB MA CB#413
Total Area (SF) 12040 7416 42122 38948 35746 14227 53194 64784 5810 4376
Roadway Area (SF) 5708 3228 10614 14116 10406 5403 14299 18618 2454 1943
Sidewalk Area (SF) 1590 821 3671 4438 2628 1920 4082 6519 740 730
House/Driveway Area (SF) 0 0 15000 5910 13061 2840 19317 19995 128 1000
Landscape Area (SF) 4742 3367 12837 14484 9651 4064 15496 19652 2488 703
C Value: 0.62 0.58 0.69 0.64 0.71 0.70 0.70 0.69 0.60 0.79
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#1
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 33,666 10,520 20,910 35,430
Acres 2.31
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 Calculate Overland Flow Time of Concentration in Minutes(Tc)or use default 10 User Calculate
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 Tc i 2.58 2.58 in hr Business
Downtown areas 0.70-0.95
9 Calculate the Post-Development peak discharge(OPeak) OPeA 3.89 3.89 cfs Urban neighborhoods 0.50-0.70
Residential
50
10 Calculate total runoff vol V for sizing rims storage) V 5,210 5,210 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) Vr, 1,845 1,845 fY 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 521 ft' .
Y Concrete 0.95
Primary Treatment/StorageBasin V 4,689 ft' Brick 0.95
Subsurface Storage Roofs 0.95
Volume Without Sediment Factor(See BMP 20 Tab) V 5,210 5,210 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\18010 Delano Subdivision\Reports\Storm Drainage\ACHD_SD_CALCS_112018 12/7/2020,1:03 PM
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 0.65 Link to: (I —
QV TR55
5 Area A(Acres) 2.31 acres
6 Approved discharge rate(if applicable) 0.00 cfs
7 Is Seepage Bed in Common Lot? Yes V 5,210 5,210 ft' 0%Sediment
8 Set Total Design Width of All Drain Rock W 13.0 ft
9 Set Total Design Depth of All Drain Rock D 10.0 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(Pert 1800) Dia pipe 18 in
13 Size of Overflow Perf Pipe(Perfs 3600),READ if Q100>3.3 cfs in
14 Calculate Total Storage per Foot Spf 60.8 ft3/ft
15 Calculate Design Length L 86 86 ft
Override Value Required for Chambers
16 Variable Infiltration Window L SWL 86 ft
17 Variable Infiltration Window W SWW 13.0 ft
18 Time to Drain 6.3 hours
90%volume in 48-hours minimum
19 Length of WQ&Overflow Perf Pipes 86 ft
20 Perf Pipe Checks.Qperf>=Qpeak;
where Qperf=CdxAxV(2xgxH)
Optional Storage Chambers W
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\18010 Delano Subdivision\Reports\Storm Drain age\ACH D_SD_CALCS_1 12018 12/7/2020,1:06 PM
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.
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 15,809 4,548 15,901 13,715
Acres 1.15
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 Calculate Overland Flow Time of Concentration in Minutes(Tc)or use default 10 User Calculate
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 Tc i 2.58 2.58 in hr Business
Downtown areas 0.70-0.95
9 Calculate the Post-Development peak discharge(OPeak) OPeA 2.10 2.10 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 2,807 2,807 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) Vr, 994 994 W 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 281 ft' .
Y Concrete 0.95
Primary Treatment/StorageBasin V 2,526 ft' Brick 0.95
Subsurface Storage Roofs 0.95
Volume Without Sediment Factor(See BMP 20 Tab) V 2,807 2,807 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\18010 Delano Subdivision\Reports\Storm Drainage\ACHD_SD_CALCS_112018 12/7/2020,1:03 PM
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 0.71 Link to: (I —
QV TR55
5 Area A(Acres) 1.15 acres
6 Approved discharge rate(if applicable) 0.00 cfs
7 Is Seepage Bed in Common Lot? Yes V 2,807 2,807 ft' 0%Sediment
8 Set Total Design Width of All Drain Rock W 10.0 ft
9 Set Total Design Depth of All Drain Rock D 10.0 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(Pert 1800) Dia pipe 18 in
13 Size of Overflow Perf Pipe(Perfs 3600),READ if Q100>3.3 cfs in
14 Calculate Total Storage per Foot Spf 46.8 ft3/ft
15 Calculate Design Length L 60 60 ft
Override Value Required for Chambers
16 Variable Infiltration Window L SWL 60 ft
17 Variable Infiltration Window W SWW 10.0 ft
18 Time to Drain 6.3 hours
90%volume in 48-hours minimum
19 Length of WQ&Overflow Perf Pipes 60 ft
20 Perf Pipe Checks.Qperf>=Qpeak;
where Qperf=CdxAxV(2xgxH)
Optional Storage Chambers W
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\18010 Delano Subdivision\Reports\Storm Drain age\ACH D_SD_CALCS_1 12018 12/7/2020,1:06 PM
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.
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 32,917 10,601 39,312 35,148
Acres 2.71
6 Determine the Weighted Runoff Coefficient(C) 0.90 0.90 0.90 0.20
C=[(C1xA1)+(C2xA2)+(CnxAn)]/A Weighted Avg 0.69
7 Calculate Overland Flow Time of Concentration in Minutes(Tc)or use default 10 User Calculate
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 Tc 2.58 2.58 in hr Business
Downtown areas 0.70-0.95
9 Calculate the Post-Development peak discharge(ClPeak) peak 4.83 4.83 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 6,472 6,472 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, 2,292 2,292 fY 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 647 ft' .
Y Concrete 0.95
Primary Treatment/StorageBasin V 5,825 ft' Brick 0.95
Subsurface Storage Roofs 0.95
Volume Without Sediment Factor(See BMP 20 Tab) V 6,472 6,472 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\18010 Delano Subdivision\Reports\Storm Drainage\ACHD_SD_CALCS_112018 12/7/2020,1:03 PM
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#3
2 Enter number of Seepage Beds(25 max) 1
3 Design Storm 100
4 Weighted Runoff Coefficient C 0.69 Link to: (I —
QV TR55
5 Area A(Acres) 2.71 acres
6 Approved discharge rate(if applicable) 0.00 cfs
7 Is Seepage Bed in Common Lot? Yes V 6,472 6,472 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 10.0 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(Pert 1800) Dia pipe 18 in
13 Size of Overflow Perf Pipe(Perfs 3600),READ if Q100>3.3 cfs in
14 Calculate Total Storage per Foot Spf 70.2 ft3/ft
15 Calculate Design Length L 92 92 ft
Override Value Required for Chambers
16 Variable Infiltration Window L SWL 92 ft
17 Variable Infiltration Window W SWW 15.0 ft
18 Time to Drain 6.3 hours
90%volume in 48-hours minimum
19 Length of WQ&Overflow Perf Pipes 92 ft
20 Perf Pipe Checks.Qperf>=Qpeak;
where Qperf=CdxAxV(2xgxH)
Optional Storage Chambers W
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\18010 Delano Subdivision\Reports\Storm Drain age\ACH D_SD_CALCS_1 12018 12/7/2020,1:06 PM
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.
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#4
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 4,397 1,470 1,128 3,191
Acres 0.23
6 Determine the Weighted Runoff Coefficient(C) 0.90 0.90 0.90 0.20
C=[(C1xA1)+(C2xA2)+(CnxAn)]/A Weighted Avg 0.68
7 Calculate Overland Flow Time of Concentration in Minutes(Tc)or use default 10 User Calculate
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 Tc i 2.58 2.58 in hr Business
Downtown areas 0.70-0.95
9 Calculate the Post-Development peak discharge(ClPeak) QpeA 0.41 0.41 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 550 550 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) Vr, 195 195 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 55 ft' .
Y Concrete 0.95
Primary Treatment/StorageBasin V 495 ft' Brick 0.95
Subsurface Storage Roofs 0.95
Volume Without Sediment Factor(See BMP 20 Tab) V 550 550 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\18010 Delano Subdivision\Reports\Storm Drainage\ACHD_SD_CALCS_112018 12/7/2020,1:03 PM
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#4
2 Enter number of Seepage Beds(25 max) 1
3 Design Storm 100
4 Weighted Runoff Coefficient C 0.68 Link to: (I —
QV TR55
5 Area A(Acres) 0.23 acres
6 Approved discharge rate(if applicable) 0.00 cfs
7 Is Seepage Bed in Common Lot? Yes V 550 550 ft' 0%Sediment
8 Set Total Design Width of All Drain Rock W 6.0 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(Pert 1800) Dia pipe 18 in
13 Size of Overflow Perf Pipe(Perfs 3600),READ if Q100>3.3 cfs in
14 Calculate Total Storage per Foot Spf 23.4 ft3/ft
15 Calculate Design Length L 24 24 ft
Override Value Required for Chambers
16 Variable Infiltration Window L SWL 24 ft
17 Variable Infiltration Window W SWW 6.0 ft
18 Time to Drain 5.2 hours
90%volume in 48-hours minimum
19 Length of WQ&Overflow Perf Pipes 24 ft
20 Perf Pipe Checks.Qperf>=Qpeak;
where Qperf=CdxAxV(2xgxH)
Optional Storage Chambers W
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\18010 Delano Subdivision\Reports\Storm Drain age\ACH D_SD_CALCS_1 12018 12/7/2020,1:06 PM
Version 10.0,May 2018