// multi-utility computation suite · offline · instant · precise
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sci.rational-method-runoff Calculator
Calculates peak surface runoff rate from the Rational Method formula Q = CiA with US units (Q in cfs, A in acres, i in inches/hour). Runoff coefficient C: impervious pavement 0.85; lawn 0.35; woods 0.15 — C is the fraction of rainfall that becomes surface runoff.
Inputs
C Runoff
Reference formula or conversion factor shown for context.
I Mm Hr
Reference formula or conversion factor shown for context.
A 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.
estimated time of concentration tc (min)
The proportional relationship between two quantities.
runoff volume (m³)
The computed three-dimensional volume.
Q = C·i·A / 360
Reference formula or conversion factor shown for context.
C guide
Reference formula or conversion factor shown for context.