Runoff Coefficient

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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

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