SAMPLE CALCULATION
RETENTION BASIN PERCOLATION TIME
To determine the time necessary to drain a simple rectangular basin, the following equations may be used. (For the sake of simplicity in this example, the access ramp is not considered. All calculations submitted for review shall include suitable allowance for the access ramp in the volume calculations.)
Necessary information:
Length, width and depth of basin.
Side slope angle.
Absorption rate of soil.
A 1 = L 1 boldmath × W 1
(1)
A2 = L2 × W2
(2)
Basin Volume V = (h (A 1 + A 2 + sqrt A 1 × A 2))/3
(3)
The average wetted area is the surface area of the basin still underwater when half of the total volume is empty. Basin depth at half volume is given by:
h prime = (h)/4[4-((A 1+2sqrt A 1× A 2 +3 A 2))/((A 1+sqrt A 1× A 2 + A 2))]
(4)
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