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eng.rational-method-peak-flow2 Calculator
Calculates peak runoff flow using the Rational Method from catchment area, runoff coefficient, and design rainfall intensity. The Rational Method is the most widely used small catchment design tool — it's accepted by most drainage codes for areas below 80 ha.
Inputs
Rainfall Intensity Mm Hr
Reference formula or conversion factor shown for context.
Catchment Area Ha
Two-dimensional surface extent (m²). For complex shapes, break into simpler sub-shapes and sum.
Runoff Coeff
Reference formula or conversion factor shown for context.
Time Of Conc Min
Amount of solute per unit volume. Higher concentration = more solute dissolved.
Results
peak flow Q (m³/s)
Reference formula or conversion factor shown for context.
peak flow (L/s)
Reference formula or conversion factor shown for context.
runoff volume (m³)
The computed three-dimensional volume.
Q = C·i·A
Reference formula or conversion factor shown for context.
runoff coeff C range
The difference between the maximum and minimum values.
validity
Reference formula or conversion factor shown for context.