Direction: A four hour unit hydrograph of a catchment is traingular in shape with base of 80 hours. The area of the catchment is 720 km². The base flow and f-index are 30 m³/s and 1 mm/h, respectively. A storm of a 4 cm occurs uniformly in 4 hours over the catchment.
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The peak flood discharge due to the storm is
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- 210 m³/s
- 230 m³/s
- 260 m³/s
- 720 m³/s
Correct Option: A
Rainfall excess, R = P – φt
= 4 – 0.1 × 4 = 3.6 cm
Peak of DRH = Peak of UH × R
= 50 × 3.6 = 180 m³/s
Peak of flood hydrograph = Peak of DRH + Base flow
= 180 + 30 = 210
