Back to Planning Tools
Stormwater Runoff Calculator
Calculate peak flow and total volume using the Modified Rational Method
Input Parameters
Results
0 cfs
0.02 cf
Recommended Pipe Size
About the Modified Rational Method
The Modified Rational Method is used to estimate peak discharge and runoff volume from small drainage areas. It extends the traditional Rational Method by incorporating storm duration to calculate total volume.
Formula:
Q = CIA
- Q = Peak flow rate (cubic feet per second)
- C = Runoff coefficient (dimensionless)
- I = Rainfall intensity (inches per hour)
- A = Drainage area (acres)