HomeMy WebLinkAboutConnections Credit Union Fall Storm Drainage Calculations Connections Credit Union
Ten Mile Road Branch - Meridian, Idaho
Storm Drainage
Calculations
(Addendum 10-14-14)
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Basin-5
Pretreatment: 1000 gallon sand and grease trap
Storage: Infiltration Gallery #1
C-Value
Roof 2115 Sq. Ft. 0.95
Concrete&Asphalt 13007 Sq. Ft. 0.95
Landscape 1169 Sq. Ft. 0.15
Not Used 0 Sq. Ft. 0
Total Area 16,291 Sq. Ft.
Run Off Coefficient 0.89
Basin Length: 133 feet
Delta Z: 1.65 ft
Average Basin Slope: 1.24 %
Time of Concentration: 10.00 min
Intensity(WQ Event) 0.34 in/hr Qp(WQ): 0.11 cfs
Intensity(2-year): 1.0 in/hr Qp (2-year): 0.34 cfs
Intensity(25-year): 2.5 in/hr Qp (25-year): 0.83 cfs
Intensity(50-year): 2.8 in/hr Qp (50-year): 0.92 cfs
Intensity(100-year): 3.2 in/hr Qp(100-yr): 1.06 cfs
Sand & Grease Trap Throat Velocity
The target throat velocity design value is 0.5 ft/sec through the baffles of the S&G trap for the
2-year water quality design storm.
1000 GAL AREA= 8 SF
Baffle/Box Width = 48 inches
Throat Width = 24 inches
1500 GAL AREA= 10.42 SF DB-350
Baffle/Box Width = 62.5 inches 41 inches
Baffle Spacing = 24 inches 5 inches
2-Year WQ EVENT(0.34") 100-Year
Throat Qp Throat Vel Qp Throat Vel Throat Vel
SIZE Structure Area SF CFS ft/sec CFS ft/sec Qp ft/sec
1000 SG-1 8.00 0.34 0.04 0.11 1.06 0.13
All of the S&G trap throat velocities are near or below the 0.5 ft/sec guideline.
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(Basin#5) Infiltration Gallery No. 1
CONNECTIONS CREDIT UNION TEN MILE ROAD BRANCH
Storm Drain Infiltration Trench Sizing
100-Year Recurrance Interval
Using ITD Zone A Chart Interpolated For A 100 Year Storm
C-Value
Roof 2115 Sq.Ft. 0.95
Concrete&Asphalt 13007 Sq. Ft. 0.95
Landscape 1169 Sq.Ft. 0.2
NOT USED 0 Sq.Ft. 0
Total Area 16291 Sq.Ft.
Run Off Coefficient 0.90
Bed Length*** 62 Ft.
Bed Width 14 Ft.
Bed Depth 3 Ft.
Percolation Rate 8 In./Hr.
Include Percolation Credit for Desig y (Y/N)
Predevelopment Discharge Rate 0 CFS(for 1-hour storm)
Storm Storm Run Off Run Off Percolation Storage
Duration Intensity Rate Volume Volume Required
in/hr cfs ft3 ft3 ft3)
5 Min. 4.38 1.46801 440 17 424
30 = 1.73 0.57983 1,044 101 942
1 Hr. 1.06 0.35527 1,279 203 1,076
2 = 0.61 0.20445 1,472 405 1,067
6 Hr. 0.26-_- 0.08714 1,882 1,216 666
12 Hr. 0.150 0.05027 2,172 2,432 260
24 Hr. 0.081 0.02715 2,346 4,864 (2;518
Drain Bed Voids 40 %
18"Pipe Volume 1.77 Cu. Ft./Ft.
Bed Storage Volume 17.86 Cu. Ft./Ft.
Stormwater Volume 1,076 Cu. Ft.
Required Seepage Bed Volume 1,076 Cu.Ft.
Increase 0% 0 Cu.Ft.
Total 1,076
Seepage Bed Storage Volume 1,107 Cu.Ft.
Swale Storage Volume 0 Cu. Ft.
Pre-Development Discharge Volume 0 Cu. Ft.
Total Storage Available 1,107 Cu.Ft.
Perc Volume Per Hour 202.7 cuft/hr
Time to infiltrate 90%of the design storm= 5.3 hours
* Rational Formula Q=CiA
** Percolation Area=2/3 of trench wall height along bed perimeter(excluding freeboard)
INFILTRATION GALLERY-1.xls
7/31/2014