GATE 2025 AR — Planning – Question 40

Infrastructure, Services and Utilities · Surface water runoff estimate, Discharge from streams and rivers · 2 marks · Numerical answer

A 12 ha site has 6 buildings, each covering 3% of site area. Landscape covers 40%; roads occupy the rest. Runoff coefficients are 0.15 for landscape and 0.6 for roads. Ignore roofs and outside inflow. At 70 mm/hour rainfall, find peak runoff in m³/s to two decimals.

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Correct answer: 0.70 to 0.74

Explanation

Buildings cover 18%, leaving roads 42% and landscape 40%. Runoff-weighted area is 120000(0.40×0.15+0.42×0.60)=37440 m². Rainfall intensity is 0.070/3600 m/s. The rational balance gives Q=37440×0.070/3600=0.728 m³/s, or 0.73. Roof runoff is excluded rather than assigned a coefficient of one.

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