GATE 2018 CE (CE2) – Question 57
A 1000 km² catchment receives 19 cm of rain in a 6 h storm. Its triangular direct-runoff hydrograph gives runoff volume $10^8$ m³. The φ-index, to one decimal, is ______ cm/h.
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Correct answer: 1.50 to 1.50
Explanation
Runoff depth is $10^8/10^9=0.1$ m = 10 cm. Loss depth is $19-10=9$ cm over 6 h, so $\phi=9/6=1.5$ cm/h, under the conventional constant-loss assumption for the contributing storm.