Question

1. Our site is located in Orange County, in the non-mountainous area. The following table summarizes the land cover and our site information: L(ft) 1000 500 250 slope % 2.3 Area (acres) Land cover Parking Residential Lots (1/4 acres) Open Space Soil Group 42.4 Determine the runoff for a 25 year storm

Answer 1

Here, we can use the rational method to determine the runoff for the given 25 year storm data.

Return period, T = 25 years

The rational method formula is given by-

Q=c.i.A

where

Q - discharge

c - runoff coefficient

i - rainfall intensity

A - drainage area

To determine runoff coefficient 'c':

Runoff Coefficient, C Soil Group C Soil Group D Slope: <2% 2-6% > 6%. < 2% 2-6% -6% Forest Meadow Pasture Farmland 0.12 0,16 0.20 0,15 0.20 0.25 0.26 0.35 0.44 0.30 0.40 0.50 0.30 0.42 0.52 0.37 0.50 0.62 0.20 0.25 0.34 0.24 0.29 0.41 0.28 0.32 0.40 0.31 0.35 0.46 Res. 1/2 acre 0.31 0.35 0.42 0.34 0.38 0.46 Res. 1/3 acre 0.33 0.38 0.45 0.36 0.40 0.50 Res. 1/4 acre 0.36 0.40 0.47 0.38 0.42 0.52 Res. 1/8 acre 0.38 0.42 0.49 0.41 0.45 0.54 Res. 1 acre 0.86 0.86 0.87 0.86 0.86 0.88 0.89 0.89 0.90 0.89 0.89 0.90 Streets: ROW 0.84 0.85 0.89 0.89 0.91 0.95 0.95 0.96 0.97 0.95 0.96 0.97 Disturbed Area 0.68 0.70 0.72 0.69 0.72 0.75 Industrial Commercial Parking

Also, from Kirpich equation, we have, time of concentration 'tc' in minutes,

0.01947し0.77 S0.385 tc

where

L - length of flow in metre

S- slope

Area (acres)	Land cover	Soil Group	c	tc (min)	i (inch/hr)
1	Parking	C	0.96	6.804	2.83
9	Residential Lots (1/4 acres)	C	0.36	5.498	2.50
5	Open Space	D	0.96	1.735	2.83

0.96 × 1 +0.36 × 9 +0.96 × 5 1 95

c = 0.6

i = 2.72 in/hr

A = 10 acres

Q = c.i.A

Q = 24.48 cfs