Question Statement:
A subsurface relief pipe drainage system is installed in a homogeneous agricultural soil overlying an impermeable horizontal floor. The hydraulic conductivity of the soil is $K = 1.50\text{ m/day}$. The depth of the impermeable floor below the drain centers is $D = 6.0\text{ m}$, yielding an equivalent depth of $d = 3.20\text{ m}$. The steady design drainage recharge rate is $q = 0.0040\text{ m/day}$ ($4.0\text{ mm/day}$) and the maximum permissible water table rise midway between drains above drain level is $h = 1.00\text{ m}$. Using Hooghoudt's equation, $q = \frac{8 K d h + 4 K h^2}{L^2}$, the required drain spacing $L$ in meters is ________ (round off to two decimal places).
```
Ground Surface ─────────────────────────────────────────────────────────────
| |
| Water Table |
| _--~~~~~~~~~--_ |
| / h \ | h = 1.0 m
Drain Pipe (O)─────────' / \ `─────────(O) Drain Pipe
| |
| d = 3.2 m (Equivalent depth) | L (Drain spacing)
| |
═════════════╧═════════════════════════════════════════════════════════╧════════════ Impermeable Floor
```