Drainage formula (Water Overlay)

Drainage passive: First the flow capacity is calculated

$Q_{p,t}=\Delta t*q_{t}$

$Q_{b}=A_{d}\cdot f_{s}\cdot {\frac {(w_{g}-w_{w})\cdot A_{w}}{A_{d}\cdot f_{s}+A_{w}}}$

$Q_{max}=A_{d}*(w_{d}-z_{d})*f_{s}$

where:

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

$w_{w}$ is the water level in the waterway

$z_{d}$ 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.

$Q_{b}$ is the amount transfered for a balanced ground and surface water level

<math>Q_{max} is the amount available in the ground above the drainage.

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