Question Bank • QB_EXP_IDE_002 NAT • 2 Marks

Section 5: Irrigation and Drainage Engineering

Agricultural Drainage

Subtopic: Drainage coefficient

Question Statement:

An agricultural drainage system removes excess water from an agricultural command area of 120 hectares. The drainage outlet discharges water at a constant rate of 0.35 m³/s. The drainage coefficient of the watershed in mm/day is ________ (rounded off to 2 decimal places).

Answer Key:

25.20

Step-by-Step Solution & Explanation

1. Watershed area $A = 120\text{ ha} = 120 \times 10^4\text{ m}^2 = 1.2 \times 10^6\text{ m}^2$. 2. Daily discharge volume $V = Q \times 86400\text{ s/day}$: $V = 0.35\text{ m}^3/\text{s} \times 86400\text{ s} = 30240\text{ m}^3/\text{day}$ 3. Drainage depth per day (Drainage Coefficient): $DC = \frac{V}{A} = \frac{30240}{1.2 \times 10^6} = 0.0252\text{ m/day} = 25.20\text{ mm/day}$.
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