Soil and Water Conservation Engineering · Watershed Management · 2 marks · Numerical answer
A40 ha watershed has curve number80 under AMC-II. Initial abstraction is20% of maximum retention. Find direct runoff from40 mm rainfall in mm (two decimals).
SCS retention is S=25400/CN−254=63.5 mm, and Ia=0.2S=12.7 mm. Since P>Ia, runoff Q=(P−Ia)²/(P−Ia+S)=(27.3)²/(90.8)=8.21 mm. Watershed area affects runoff volume, not this depth.
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