Section 4: Soil and Water Conservation Engineering
Hydrology
Subtopic: Hydrograph analysis, unit hydrograph theory and application
Question Statement:
A triangular 5-hour unit hydrograph (UH1) of a catchment area of 400 km² has a peak discharge of 60 m³ s⁻¹. Another triangular 5-hour unit hydrograph (UH2) having the same base width as UH1 has a peak flow of 90 m³ s⁻¹. The catchment area corresponding to UH2 in km² is
Options:
(A) 267
(B) 600
(C) 750
(D) 867
Official Answer Key:
B
Step-by-Step Solution & Explanation
For a triangular unit hydrograph, the volume under the hydrograph (which represents 1 cm of direct runoff over the catchment) equals ½ × base × peak. Since both UH1 and UH2 share the same base width, this volume — and hence the catchment area (Volume = Area × 1 cm) — is directly proportional to the peak discharge:
Area₂/Area₁ = Peak₂/Peak₁ = 90/60 = 1.5
Area₂ = 400 × 1.5 = 600 km². Answer: (B).
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