Drainage Hooghoudt's equation


A drainage equation is an equation describing the relation between depth and spacing of parallel subsurface drains, depth of the watertable, depth and hydraulic conductivity of the soils. It is used in drainage design.
A well known steady-state drainage equation is the Hooghoudt drain spacing equation. Its original publication is in Dutch. The equation was introduced in the USA by van Schilfgaarde.

In steady state, the level of the water table remains constant and the discharge rate (Q) equals the rate of groundwater recharge®, i.e. the amount of water entering the groundwater through the watertable per unit of time. By considering a long-term (e.g. seasonal) average depth of the water table (Dw) in combination with the long-term average recharge rate®, the net storage of water in that period of time is negligibly small and the steady state condition is satisfied: one obtains a dynamic equilibrium.

Related formulas


Qsteady state drainage discharge rate (m/day)
Kbhydraulic conductivity of the soil below drain level (m/day)
dequivalent depth, a function of L, (Di-Dd), and radius r (dimensionless)
Didepth of the impermeable layer below drain level (m)
Dddepth of the drains (m)
Dwsteady state depth of the watertable midway between the drains (m)
Kahydraulic conductivity of the soil above drain level (m/day)
Lspacing between the drains (m)