HomeMy WebLinkAboutCC - Storm Drain Report Signed 3-7-25 STORM DRAINAGE REPORT AND CALCULATIONS
FOR
SKYBREAK SUBDIVISION NO. 4
MERIDIAN, IDAHO
\oar_
PREPARED BY:
16970 CORINNE M GRAHAM, PE
cos�g �P,o�P�. March 7, 2025
OF1
��tiNE M.GAP
Csw
C 1N/I L S ITE
W O R K S
PO BOX 6059
BOISE, ID 83707
(208) 946-3874
cgraham@cswengineering.com
INTRODUCTION
The existing 8.52-acre site for the proposed Skybreak Subdivision No. 4 is currently vacant row crop
ground.The proposed development includes 48 single family residential lots, 6 landscape common lots,
2 common drives, and associated public streets, landscaping, and utilities.
HISTORIC DRAINAGE
The existing project site sits southeast of the intersection of E. Lake Hazel Road and S. Eagle Road in
Meridian.The eastern portion of the site that was developed in Phase 1 lies along Meridian's southern
rim.
Surficial soils are comprised of sandy silts and silty sands.At depths of 3-6 feet,free draining poorly
graded gravel with sand was encountered during geotechnical exploration. Groundwater was not
encountered at depths up to 15.2 feet and is not anticipated to reach levels higher than 20 feet below
existing ground.
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 801" percentile
storm event. Storm water runoff from half of the residential lots, 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.
Four temporary swales will be installed at the end of the two stub streets to collect runoff until
permanent facilities are constructed in Phase 5.
APPENDICES
• Drainage Basin Map
• Storm Drainage Calculations
• Project Geotechnical Report
N
0 30 60 120 180
SCALE: 1" = 60'
— � — — � — � —� � — - - — - - - - - - — — — — — — — — — — — — —
I /
I
I
TEMP
M BASIN #2 BASIN #4A
I
/ /^ TEMP
..:::::.:.:........:...
EP
r
\ / /
�' ♦ J/ BASIN #413
II
_ TEMP
BASIN #3A
m
— — ♦ \ M \ d3 I
\ \ ♦ --1 I I
I
� \ ♦ � ♦ TEMP
' BASIN #313
M \
� ♦ BASIN # 1
I I
I �
I \
I
C IVI II— S IT E
SKYBREAK SUBDIVISION NO. 4PO W o R K !a
DRAINAGE BASIN MAP BOIISBOID 83 07
Ph: (208) 946-3874
cgraham@cswengineering.com
Prepared By: Corinne Graham, PE
CSw March 7, 2025
CIVIL SITE
Skybreak Subdivision No. 4
Storm Drainage Calculations
Drainage Basin Characteristics
C Values
Impervious =0.90
Landscape =0.20
ACHD ACHD Temp Temp Temp Temp
Basin#1 Basin#2 Basin#3A Basin#3113 Basin#4A Basin#4113
Total Area (SF) 81395 105894 5009 20534 4605 4883
Roadway Area (SF) 20949 23793 2031 2317 1818 1818
Sidewalk Area (SF) 6288 7256 670 931 666 790
House/Driveway Area (SF) 27183 33868 0 7979 0 0
Landscape Area (SF) 26975 40977 2308 9307 2121 2275
C Value: 0.67 0.63 0.58 0.58 0.58 0.57
Catch Basin Calculations
CB#1A CB#1B CB#1C CB#2A CB#2B
Total Area (SF) 40172 33078 8144 58734 47160
Roadway Area (SF) 9909 7885 3155 12692 11101
Sidewalk Area (SF) 3182 2444 662 3923 3333
House/Driveway Area (SF) 13716 13467 0 22672 11196
Landscape Area (SF) 13365 9282 4328 19447 21530
C Value: 0.67 0.70 0.53 0.67 0.58
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 20,949 6,288 27,183 26,975
Acres 1.87
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 2.58 2.58 in hr Business
Downtown areas 0.70-0.95
9 Calculate the Post-Development peak discharge(ClPeak) peak 3.22 3.22 cfs Urban neighborhoods 0.50-0.70
Residential
50
10 Calculate total runoff vol V for sizing rims storage) V 4,314 4,314 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, 1,528 1,528 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 431 ft' .
Y Concrete 0.95
Primary Treatment/StorageBasin V 3,883 ft' Brick 0.95
Subsurface Storage Roofs 0.95
Volume Without Sediment Factor(See BMP 20 Tab) V 4,314 4,314 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\23003 Skybreak Sub Ph4\Reports\Storm Drainage\ACHD_SD_CALCS_101023 3/7/2025,12:25 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
_ steps�Beds
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 0.67 Unkto: Q.V
QV TR55
5 Area A(Acres) 1.87 acres
6 Approved discharge rate(if applicable) 0.00 cfs
7 Is Seepage Bed in Common Lot? Yes V 4,314 4,314 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 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 180°) 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 58.6 ft3/ft
15 Calculate Design Length L 74 74 ft
Override Value Required for Chambers
16 Variable Infiltration Window L SWL 74 74.0 ft
17 Variable Infiltration Window W SWW 15.0 15.0 ft
18 Time to Drain 5.2 hours
90%volume in 48-hours minimum
19 Length of WQ&Overflow Perf Pipes 74 74 ft
20 Perf Pipe Checks.Qperf>=Qpeak;
where Qperf=CdxAxJ(2xgxH)
C:\Users\cgrah\Dropbox\Projects\23003 Skybreak Sub Ph4\Reports\Storm Drainage\ACHD_SD_CALCS_101023 3/7/2025,12:28 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.
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 23,793 7,256 33,868 40,977
Acres 2.43
6 Determine the Weighted Runoff Coefficient(C) 0.90 0.90 0.90 0.20
C=[(C1xA1)+(C2xA2)+(CnxAn)]/A Weighted Avg 0.63
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 2.58 2.58 in hr Business
Downtown areas 0.70-0.95
9 Calculate the Post-Development peak discharge(ClPeak) peak 3.95 3.95 cfs Urban neighborhoods 0.50-0.70
Residential
50
10 Calculate total runoff vol V for sizing rims storage) V 5,286 5,286 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, 1,872 1,872 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 529 ft' .
Y Concrete 0.95
Primary Treatment/StorageBasin V 4,757 ft' Brick 0.95
Subsurface Storage Roofs 0.95
Volume Without Sediment Factor(See BMP 20 Tab) V 5,286 5,286 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\23003 Skybreak Sub Ph4\Reports\Storm Drainage\ACHD_SD_CALCS_101023 3/7/2025,12:25 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
Steps�Beds
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 0.63 Unkto: Q.V
QV TR55
5 Area A(Acres) 2.43 acres
6 Approved discharge rate(if applicable) 0.00 cfs
7 Is Seepage Bed in Common Lot? Yes V 5,286 5,286 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 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 180°) 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 58.6 ft3/ft
15 Calculate Design Length L 90 90 ft
Override Value Required for Chambers
16 Variable Infiltration Window L SWL 90 90.0 ft
17 Variable Infiltration Window W SWW 15.0 15.0 ft
18 Time to Drain 5.3 hours
90%volume in 48-hours minimum
19 Length of WQ&Overflow Perf Pipes 90 90 ft
20 Perf Pipe Checks.Qperf>=Qpeak;
where Qperf=CdxAxJ(2xgxH)
C:\Users\cgrah\Dropbox\Projects\23003 Skybreak Sub Ph4\Reports\Storm Drainage\ACHD_SD_CALCS_101023 3/7/2025,12:28 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.
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#3A
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 2,031 670 2,308
Acres 0.11
6 Determine the Weighted Runoff Coefficient(C) 0.90 0.90 0.20
C=[(C1xA1)+(C2xA2)+(CnxAn)]/A Weighted Avg 0.58
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(QPeak) Qpe k 0.17 0.17 cfs Urban neighborhoods 0.50-0.70
Residential
50
10 Calculate total runoff vol V for sizing rims storage) V 229 229 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, 81 81 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 23 ft' .
Y Concrete 0.95
Primary Treatment/StorageBasin V 207 ft' Brick 0.95
Subsurface Storage Roofs 0.95
Volume Without Sediment Factor(See BMP 20 Tab) V 229 229 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\23003 Skybreak Sub Ph4\Reports\Storm Drainage\ACHD_SD_CALCS_101023 3/7/2025,12:25 PM
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#3A
2 Enter number of Bioswales/Borrow Ditches(25 max) 1
3 Design Storm 100
Weighted Runoff Coefficient C 0.58 Link to: LQv
4 Area A(Acres) 0.11 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 229 229.49 ft3
6 Length of Swale 22 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 2.00 ft
10 Set Swale Top Width 14.00 ft
11 Set Swale Depth y 1.50 ft
12 Swale Side Slopes H:1 Sxs 4.00
13 Calculate cross-sectional area Axs 12.00 12.00 ftz
Axs=Y zz+by
14 Total Swale Capacity Without Driveways 264 264.00 ft3
15 Does it Have Capacity? OK
16 Time to Drain 7.8 7.82 hr
90%volume in 48-hours minimum OK
C:\Users\cgrah\Dropbox\Projects\23003 Skybreak Sub Ph4\Reports\Storm Drainage\ACHD_SD_CALCS_101023 3/7/2025,12:26 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.
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#313
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 2,317 931 7,979 9,307
Acres 0.47
6 Determine the Weighted Runoff Coefficient(C) 0.90 0.90 0.90 0.20
C=[(C1xA1)+(C2xA2)+(CnxAn)]/A Weighted Avg 0.58
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(QPeak) Qpe k 0.71 0.71 cfs Urban neighborhoods 0.50-0.70
Residential
50
10 Calculate total runoff vol V for sizing rims storage) V 949 949 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, 336 336 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 95 ft' .
Y Concrete 0.95
Primary Treatment/StorageBasin V 854 ft' Brick 0.95
Subsurface Storage Roofs 0.95
Volume Without Sediment Factor(See BMP 20 Tab) V 949 949 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\23003 Skybreak Sub Ph4\Reports\Storm Drainage\ACHD_SD_CALCS_101023 3/7/2025,12:25 PM
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#3B
2 Enter number of Bioswales/Borrow Ditches(25 max) 1
3 Design Storm 100
Weighted Runoff Coefficient C 0.58 Link to: LQv
4 Area A(Acres) 0.47 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 949 949.34 ft3
6 Length of Swale 75 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 1,125 1125.00 ft'
15 Does it Have Capacity? OK
16 Time to Drain 4.7 4.75 hr
90%volume in 48-hours minimum OK
C:\Users\cgrah\Dropbox\Projects\23003 Skybreak Sub Ph4\Reports\Storm Drainage\ACHD_SD_CALCS_101023 3/7/2025,12:26 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.
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#4A
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 1,818 666 2,121
Acres 0.11
6 Determine the Weighted Runoff Coefficient(C) 0.90 0.90 0.20
C=[(C1xA1)+(C2xA2)+(CnxAn)]/A Weighted Avg 0.58
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 0.16 0.16 cfs Urban neighborhoods 0.50-0.70
Residential
50
10 Calculate total runoff vol V for sizing rims storage) V 211 211 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, 75 75 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 21 ft' .
Y Concrete 0.95
Primary Treatment/StorageBasin V 190 ft' Brick 0.95
Subsurface Storage Roofs 0.95
Volume Without Sediment Factor(See BMP 20 Tab) V 211 211 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\23003 Skybreak Sub Ph4\Reports\Storm Drainage\ACHD_SD_CALCS_101023 3/7/2025,12:25 PM
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#4A
2 Enter number of Bioswales/Borrow Ditches(25 max) 1
3 Design Storm 100
Weighted Runoff Coefficient C 0.58 Link to:LQV
4 Area A(Acres) 0.11 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 211 211.03 ft3
6 Length of Swale 36 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 2.00 ft
10 Set Swale Top Width 10.00 ft
11 Set Swale Depth y 1.00 ft
12 Swale Side Slopes H:1 Sxs 4.00
13 Calculate cross-sectional area Axs 6.00 6.00 ftz
Axs=Y zz+by
14 Total Swale Capacity Without Driveways 216 216.00 ft'
15 Does it Have Capacity? OK
16 Time to Drain 4.4 4.40 hr
90%volume in 48-hours minimum OK
C:\Users\cgrah\Dropbox\Projects\23003 Skybreak Sub Ph4\Reports\Storm Drainage\ACHD_SD_CALCS_101023 3/7/2025,12:26 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.
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#413
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 1,818 790 2,275
Acres 0.11
6 Determine the Weighted Runoff Coefficient(C) 0.90 0.90 0.20
C=[(C1xA1)+(C2xA2)+(CnxAn)]/A Weighted Avg 0.57
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(QPeak) Qpe k 0.17 0.17 cfs Urban neighborhoods 0.50-0.70
Residential
50
10 Calculate total runoff vol V for sizing rims storage) V 222 222 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, 79 79 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 22 ft' .
Y Concrete 0.95
Primary Treatment/StorageBasin V 200 ft' Brick 0.95
Subsurface Storage Roofs 0.95
Volume Without Sediment Factor(See BMP 20 Tab) V 222 222 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\23003 Skybreak Sub Ph4\Reports\Storm Drainage\ACHD_SD_CALCS_101023 3/7/2025,12:25 PM
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#4B
2 Enter number of Bioswales/Borrow Ditches(25 max) 1
3 Design Storm 100
Weighted Runoff Coefficient C 0.57 Link to: LQv
4 Area A(Acres) 0.11 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 222 222.32 ft3
6 Length of Swale 28 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 2.00 ft
10 Set Swale Top Width 14.00 ft
11 Set Swale Depth y 1.50 ft
12 Swale Side Slopes H:1 Sxs 4.00
13 Calculate cross-sectional area Axs 12.00 12.00 ftz
Axs=Y zz+by
14 Total Swale Capacity Without Driveways 336 336.00 ft3
15 Does it Have Capacity? OK
16 Time to Drain 6.0 5.96 hr
90%volume in 48-hours minimum OK
C:\Users\cgrah\Dropbox\Projects\23003 Skybreak Sub Ph4\Reports\Storm Drainage\ACHD_SD_CALCS_101023 3/7/2025,12:26 PM
Version 10.0,May 2018