GATE 2025 CE (CE2) – Question 59
The peak of flood hydrograph due to a 3-hour duration storm in a catchment is 180 m$^3$/s. The total rainfall depth is 6.6 cm. It can be assumed that the average infiltration loss is 0.2 cm/h. There are no other losses. The base flow is constant at a value of 30 m$^3$/s.
The peak value of the 3-hour unit hydrograph for this catchment (in m$^3$/s) is ______ (round off to the nearest integer).
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Correct answer: 25
Explanation
The peak of the direct runoff hydrograph is $180 - 30 = 150$ m³/s. The infiltration loss over the 3-hour storm is $0.2 \times 3 = 0.6$ cm, so the effective rainfall is $6.6 - 0.6 = 6.0$ cm. A unit hydrograph is for 1 cm of effective rainfall, so its peak is $\frac{150}{6.0} = 25$ m³/s.