Download Rational Equation Calculator (Excel file)
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The Rational equation is the simplest method to determine peak discharge from drainage basin runoff.
Rational Equation:  Q=ciA The Rational equation requires the following units: Q = Peak discharge, cubic meter/second c = Rational method runoff coefficient i = Rainfall intensity, mm/hour A = Drainage area, ha
The Rational method runoff coefficient (c) is a function of the landuse, soil type and drainage basin slope. (Check Table here for calculating c, Rational method runoff coefficient) Source: Batelaan and Woldeamlak  (2007)