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eng.rational-method-stormwater Calculator
Calculates peak storm runoff from a catchment using the Rational Method (Q = CiA) for stormwater design. The Rational Method is valid for catchments below 200 acres with concentration time under 20 minutes — larger catchments require continuous simulation methods.
Inputs
Runoff Coefficient C
Reference formula or conversion factor shown for context.
Rainfall Intensity Mm Hr
Reference formula or conversion factor shown for context.
Drainage Area Ha
Two-dimensional surface extent (m²). For complex shapes, break into simpler sub-shapes and sum.
Results
peak runoff Q (m³/s)
Sample size or count used in the calculation.
peak runoff Q (L/s)
Sample size or count used in the calculation.
Q = C·I·A
Reference formula or conversion factor shown for context.