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.