Section 4: Soil and Water Conservation Engineering
Hydrology
Subtopic: Hydrograph analysis, unit hydrograph theory and application
Question Statement:
A catchment with an area of 756 km² has a 6 h unit hydrograph which is triangular with a base of 70 h. The peak discharge of direct runoff hydrograph due to 5 cm of rainfall excess in 6 h from the catchment is
Options:
(A) 60 m³ s⁻¹
(B) 535 m³ s⁻¹
(C) 300 m³ s⁻¹
(D) 756 m³ s⁻¹
Official Answer Key:
C
Step-by-Step Solution & Explanation
Volume of runoff for 1 cm over the catchment = Area×0.01 m = 756×10⁶×0.01 = 7.56×10⁶ m³. For a triangular UH, this volume = ½×base×peak, so peak (for 1 cm) = 2×Vol/Tb = 2×7.56×10⁶/(70×3600) = 60 m³/s. For 5 cm rainfall excess (linear scaling, principle of superposition), peak = 60×5 = 300 m³/s.
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