Agricultural Drainage and Salinity

Hooghoudt's steady-state equation for drain spacing $S$ with impermeable layer at depth $d$ below the drain level is:

Options:

• (A) $S^2 = \frac{4 K_1 m^2 + 8 K_2 d m}{q}$
• (B) $S = \frac{4 K m^2}{q}$
• (C) $S^2 = \frac{K d m}{q}$
• (D) $S = \sqrt{\frac{q}{4 K m}}$