Question Bank • QB_SWCE_HYD_003 NAT • 2 Marks

Section 4: Soil and Water Conservation Engineering

Hydrology

Subtopic: Hydrograph analysis, unit hydrograph theory and application

Question Statement:

A 4-hour Unit Hydrograph (UH) of a catchment has a peak discharge ordinate of $35\text{ m}^3\text{/s}$. A storm of 4-hour duration produces a total rainfall of $6.5\text{ cm}$. The average infiltration loss during the storm is $1.5\text{ cm}$ and the base flow is constant at $10\text{ m}^3\text{/s}$. The peak flood discharge of the total streamflow hydrograph in $\text{m}^3\text{/s}$ is ________ (answer in integer).

Answer Key:

185

Step-by-Step Solution & Explanation

1. Effective rainfall depth ($P_e$): $P_e = P - \text{Losses} = 6.5\text{ cm} - 1.5\text{ cm} = 5.0\text{ cm}$ 2. Direct Runoff Hydrograph peak ($Q_{DRH, peak}$): $Q_{DRH, peak} = P_e \times Q_{UH, peak} = 5.0 \times 35\text{ m}^3\text{/s} = 175\text{ m}^3\text{/s}$ 3. Total peak discharge: $Q_{total, peak} = Q_{DRH, peak} + \text{Baseflow} = 175 + 10 = 185\text{ m}^3\text{/s}$
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