GATE 2020 AG – Question 32
A watershed has rainfall erosivity 280 MJ mm/(ha h year), soil erodibility 0.38 ton ha h/(MJ mm), slope length 200 m, average slope 8%, slope-steepness factor 0.85, crop factor 0.35 and conservation factor 0.60. Find percentage reduction in soil loss if slope length is halved (two decimals).
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Correct answer: 29.10 to 29.50
Explanation
In USLE, with slope above 5%, length factor scales as L^m with m=0.5. All other factors remain fixed, so new/old soil loss=(1/2)^0.5. Reduction is 100(1−1/√2)=29.29%. The many unchanged multiplicative factors cancel.