Question Bank • QB_EXP_IDE_DRN_019 NAT • 2 Marks

Section 5: Irrigation and Drainage Engineering

Agricultural Drainage: Surface Drainage & Runoff Removal

Subtopic: Drainage coefficient discharge computation

Question Statement:

An agricultural drainage basin of area $A = 230\text{ ha}$ is designed with a drainage coefficient of $DC = 3.5\text{ cm/day}$. The required design capacity of the main surface drainage ditch is ________ $\text{m}^3/\text{s}$ (round off to two decimal places).

Answer Key:

0.93

Step-by-Step Solution & Explanation

The drainage discharge is calculated as: $Q = \frac{A \times DC}{864}$ where $A$ is in $\text{ha}$ and $DC$ is in $\text{cm/day}$, giving $Q$ in $\text{m}^3/\text{s}$: $Q = \frac{230 \times 3.5}{864} = \frac{805.0}{864} = 0.932\text{ m}^3/\text{s}$ Rounding to two decimal places: $0.93\text{ m}^3/\text{s}$.
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