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GATE 2021 AG – Question 44

Soil and Water Conservation Engineering · Hydrology · 2 marks · Multiple choice

A catchment IUH is an isosceles triangle with peak60 m³/s at 3 h. Constant baseflow7.5 m³/s. Find the peak of its3-hour unit hydrograph in m³/s.

  1. 43.33
  2. 50.83
  3. 52.50
  4. 60.00

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Show answer and explanation

Correct answer: (A) 43.33

Explanation

A duration-D unit hydrograph is the moving average of the IUH over D. For the stated symmetric triangle, the maximum3-hour window is 1.5–4.5 h;its area is 135 (m³/s)h and mean45 m³/s. A unit hydrograph excludes baseflow;including it gives 52.5 m³/s. The official key nevertheless selects **A,43.33**. Neither standard interpretation reproduces43.33 from the supplied triangle, so the source/key discrepancy is stated rather than assigning an unsupported derivation.

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