Weather & Calamities

Intermediate

Rational Method (Peak Runoff)

Estimates peak stormwater discharge from a catchment.

Formula

Q = C\,i\,A

Variables

QPeak discharge

CRunoff coefficient (0–1)

iRainfall intensity

ACatchment area

Example

C=0.7, i=50 mm/h over 2 ha gives a large peak flow

Did You Know?

Cities have high runoff coefficients (~0.9) because pavement absorbs almost no rain.

flood hydrology drainage urban

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