Question Bank • QB_IDE_003 NAT • 2 Marks

Section 5: Irrigation and Drainage Engineering

Agricultural Drainage

Subtopic: Drainage coefficient

Question Statement:

An agricultural drainage basin has an area of $500\text{ ha}$. The design drainage coefficient is $12\text{ mm/day}$. The continuous design drainage discharge required to remove this excess water in $\text{m}^3\text{/s}$ is ________ (round off to 3 decimal places).

Answer Key:

0.694

Step-by-Step Solution & Explanation

1. Area $A = 500\text{ ha} = 500 \times 10^4\text{ m}^2 = 5 \times 10^6\text{ m}^2$. 2. Drainage coefficient $D_c = 12\text{ mm/day} = 0.012\text{ m/day}$. 3. Daily volume $V = A \times D_c = (5 \times 10^6) \times 0.012 = 60,000\text{ m}^3\text{/day}$. 4. Discharge in $\text{m}^3\text{/s}$: $Q = \frac{60,000}{24 \times 3600} = \frac{60,000}{86,400} = 0.6944\text{ m}^3\text{/s} \approx 0.694\text{ m}^3\text{/s}$
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