GATE 2022 AG – Question 56
Rainfall is 152.4 mm. Land uses: residential40%, soil C, CN83; good open space25%, soil D, CN80; commercial20%, soil C, CN94; industrial15%, soil D, CN93. Assume average antecedent moisture and initial abstraction .2S. Find runoff depth in mm, to two decimals.
Practise this question in The GATE Grind →
Show answer and explanation
Correct answer: 111.80 to 112.00
Explanation
Weighted curve number is $.40(83)+.25(80)+.20(94)+.15(93)=85.95$. Retention $S=25400/85.95-254=41.52065$ mm. Since P>.2S, $Q=(P-.2S)^2/(P+.8S)=\mathbf{111.86}$ mm. The composite CN is formed before applying the nonlinear runoff equation.