Drainage formula (Water Overlay)

Drainage passive: First the flow capacity is calculated $Q_{p,t}=\Delta t*q_{t}$

The water head at the drainage area is calculated:

$h_{x,y}=(w_{g,x,y}-z_{d})\cdot f_{s}$

where:

$w_{g}$ is the ground water level in meters

$z_{d}$ is the drainage datum height in meters.

$A_{d}$ is the drainage area size in square meters.

$f_{s}$ is the average storage percentage of the ground above the drainage.