The 'SCS Curve Number' (CN) method for estimating runoff uses CN values that depend on:
Choose the correct answer
Only the slope of the watershed
Soil hydrological group (A–D), land use/cover type, and antecedent moisture condition (AMC) — governs runoff potential
Only total annual rainfall
River channel roughness (Manning n)
Correct Answer
B. Soil hydrological group (A–D), land use/cover type, and antecedent moisture condition (AMC) — governs runoff potential
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SCS (now NRCS) Curve Number method: Q = (P-0.2S)²/(P+0.8S) for P > 0.2S, where S = (25400/CN)-254 (mm). CN (0–100) depends on: (1) Soil hydrological group (A = sandy, B, C, D = clay — infiltration capacity); (2) Land use/cover (impervious, cultivation type, row crops vs meadow); (3) Antecedent Moisture Condition (AMC I, II, III — dry, normal, wet). Higher CN = more runoff. Used worldwide for small watershed design.
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