Multiple choice

The average rainfall for a 3 hour duration storm is 2.7 cm and the loss rate is 0.3 cm/h. The flood hydrograph has a base flow of 20 m3/s and produces a peak flow of 210 m3/s. The peak of a 3-h unit hydrograph is

  1. 125.50 m3/s

  2. 105.50 m3/s

  3. 77.77 m3/s

  4. 70.37 m3/s
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The effective rainfall is calculated as (2.7 - 0.3 * 3) = 1.8 cm. The peak flow of the unit hydrograph is (Peak Flow - Base Flow) / Effective Rainfall = (210 - 20) / 1.8 = 190 / 1.8 = 105.55 m^3/s.

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