// multi-utility computation suite · offline · instant · precise
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sci.SCS-CN-runoff Calculator
Calculates storm runoff volume from the SCS curve number method, accounting for antecedent moisture conditions (AMC I/II/III). AMC III (wet antecedent conditions) raises effective CN — after 5 days of rain, CN increases by 5–15 units relative to AMC II.
Inputs
Cn
Count of items or occurrences.
P Mm
Reference formula or conversion factor shown for context.
Ia Factor
A multiplier applied in the calculation.
Results
direct runoff depth Q (mm)
The computed depth.
potential retention S (mm)
Sample size or count used in the calculation.
initial abstraction Ia (mm)
Sample size or count used in the calculation.
runoff fraction Q/P
Sample size or count used in the calculation.
Q = (P − Ia)² / (P − Ia + S)
Reference formula or conversion factor shown for context.