Subtopic: Hooghoudt spacing for drains on impermeable barrier
Question Statement:
Parallel subsurface relief drains are laid at a depth of $1.8\text{ m}$. The impermeable barrier lies at the drain level ($d = 0$). If $K = 1.0\text{ m/day}$, steady drainage rate $q = 0.004\text{ m/day}$, and maximum allowable water table height mid-spacing is $h = 0.6\text{ m}$, the drain spacing $S$ by Hooghoudt's equation ($S = \sqrt{4 K h^2 / q}$, in meters) is:
Answer Key:
18.97
Step-by-Step Solution & Explanation
When barrier is at drain level ($d = 0$):
$S^2 = \frac{4 K h^2}{q} = \frac{4 \times 1.0 \times (0.6)^2}{0.004} = \frac{1.44}{0.004} = 360\text{ m}^2$
$S = \sqrt{360} = 18.97\text{ m}$