Question Bank • QB_SWCE_003 NAT • 2 Marks

Section 4: Soil and Water Conservation Engineering

Hydrology

Subtopic: Runoff estimation

Question Statement:

A watershed of area $2.5\text{ km}^2$ has a runoff coefficient $C = 0.40$. During a storm event, the design rainfall intensity is $36\text{ mm/h}$. Using the Rational formula $Q = \frac{C I A}{3.6}$, the peak runoff rate in $\text{m}^3\text{/s}$ is ________ (answer in integer).

Answer Key:

10

Step-by-Step Solution & Explanation

By the Rational method: $Q_p = \frac{C \cdot I \cdot A}{3.6}$ Where: • $C = 0.40$ • $I = 36\text{ mm/h}$ • $A = 2.5\text{ km}^2$ $Q_p = \frac{0.40 \times 36 \times 2.5}{3.6} = \frac{36}{3.6} \times (0.40 \times 2.5) = 10 \times 1.0 = 10\text{ m}^3\text{/s}$
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