Depth–area–duration analysis gives maximum average rainfall depth 80 mm over a 103\,km2 catchment during a six-hour storm. For that same storm, how does maximum average depth over 104\,km2 compare?

GATE 2026 AG – Question 25

Soil and Water Conservation Engineering · Hydrology · 1 mark · Multiple choice

Depth–area–duration analysis gives maximum average rainfall depth 80 mm over a $10^3\,\mathrm{km^2}$ catchment during a six-hour storm. For that same storm, how does maximum average depth over $10^4\,\mathrm{km^2}$ compare?

Greater than 88 mm
Less than 80 mm
Equal to 80 mm
Between 81 and 88 mm

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Correct answer: (B) Less than 80 mm

Explanation

A storm’s highest intensities are spatially concentrated. Averaging over a larger area incorporates surrounding lower-rainfall regions, so the depth–area curve decreases as area increases for fixed duration. The intended comparison is therefore **less than 80 mm, B**. Strict decrease assumes a spatially nonuniform storm rather than an ideal uniform field.

GATE 2026 AG – Question 25

Explanation

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