Drainage, Simple empirical equations on groundwater outflow

The simplest empirical approach (EmpiricalDrainEq) is based on a first-order recession equation. Unlike the case for the physically-based approach, this sink term will only be calculated in the layer where the ground water table, z_sat, is located and no account is taken of flow paths in the saturated part of the soil profile. When the ground-water level, z_sat, is above the bottom of the profile, a net horizontal water flow is given as a sum of ‘base flow’ and a more rapid ‘peak flow’:

                     (2.39)

where q₁, q₂, z₁, z₂ are parameters obtained by fitting techniques. See viewing function Empirical drainage equation.

z_sat is defined as the level where the matrix potential is zero and thus calculated from values on soil water content.