Drainage trenches spacing calculation

Calculation of the distance with steady-state groundwater (= constant flow); HOOGHOUDT‘s formula:

where:

L = distance between the drains in m;
K1 = hydraulic conductivity (in m d-1) of the soil above the drain level;
K2 = hydraulic conductivity of the soil below the drain level;
h = maximum acceptable height (in m) of the groundwater rise with respect to the drain plane at the midpoint between the two drains;
d = “equivalent depth” depending on the depth of the impermeable layer (D), the distance between the drains (L), and their radius (see following table);
q = amount of water to be removed daily (in m per day).

For further information see the Drainage document.