Runoff Coefficient
Runoff Coefficient
Runoff Coefficient is the ratio of between the peak runoff rate and intensity of rainfall.
The Rational Method is based upon following Two Assumptions:
1. Rainfall occurs at uniform intensity for duration at least equal to the time of concentration of watershed.
2. Rainfall occurs at a uniform intensity over the entire area of watershed.
The value of ‘C’ runoff coefficient in the rational formula should be taken from following table.
|
vegetative cover and land Slope |
Soil Texture |
||
|
|
Sand Loam |
Clay and Silt Loam |
Silty Clay |
|
1. Wood Land |
|
|
|
|
0 – 5 % slope |
0.10 |
0.30 |
0.40 |
|
5 – 10% slope |
0.25 |
0.35 |
0.60 |
|
10 – 30% slope |
0.30 |
0.50 |
0.60 |
|
2. Pasture land |
|
|
|
|
0 – 5 % slope |
0.10 |
0.30 |
0.40 |
|
5 – 10% slope |
0.16 |
0.36 |
0.55 |
|
10 – 30% slope |
0.22 |
0.42 |
0.60 |
|
3. Cultivated Land |
|
|
|
|
0 – 5 % slope |
0.30 |
0.50 |
0.60 |
|
5 – 10% slope |
0.40 |
0.60 |
0.70 |
|
10 – 30% slope |
0.52 |
0.72 |
0.82 |