Free Runoff Coefficient Calculator
Calculate the peak stormwater runoff rate using the Rational Method from rainfall intensity, area, and runoff coefficient.
Peak Runoff Rate
0.833 m^3/s
Peak Runoff Rate vs Runoff Coefficient (C)
Rational Method for Stormwater Runoff
The Rational Method is the most widely used formula for estimating peak runoff from small catchments.
Formula
Q = C i A / 360
where Q is peak flow in m^3/s, C is the runoff coefficient (0 to 1), i is rainfall intensity in mm/h, and A is catchment area in hectares. The factor 360 converts units. This method assumes the entire catchment contributes to runoff when storm duration equals the time of concentration.
Example Calculation
5 hectare urban catchment, C=0.6, 100 mm/h intensity.
- 01Q = 0.6 x 100 x 5 / 360 = 300/360 = 0.833 m^3/s
- 02Q = 833 L/s
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