Drainage formula (Water Overlay)

Drainage passive: First the flow capacity is calculated

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

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

if $w_{w}>w_{g}$ then:

$Q_{max}=A_{w}\cdot (w_{w}-z_{w})$

else:

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

$Q_{d}=min(Q_{p,t},Q_{b},Q_{max})$

Drainage active:

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.

$A_{w}$ is the waterway area size in square meters.

$z_{w}$ is the max waterway height.

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

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

$Q_{max}$ is the amount available in the ground above the drainage.

$Q_{p_{t}}$ is the drainage capacity at time t

$Q_{d}$ is the actual drained volume at time t

Related

The following topics are related to this formula.

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