Ground infiltration formula (Water Overlay)

Underground infiltration (from the unsaturated zone to the saturated zone) is calculated per cell.

First the height of the unsaturated zone is calculated.

H_unsat = H_surface - WL_underground

Then the ratio of water amount to unsaturated height is calculated.

S = W_unsat/H_unsat

Then calculate the distance of the unsaturated zone which can infiltrate.

C_inf = min( H_unsat , Δt * I_und )

Finally, calculate the amount of actual amount of water infiltrating.

Δw = C_inf * S

Where:

• Δw = The underground infiltration which takes place.
• Δt = Computational timestep.

• H_unsat = The height of the unsaturated zone.
• S = Ratio of water to height in the unsaturated zone.
• C_inf = The height in the unsaturated zone which can be subject to infiltration to the saturated zone.

• W_unset = The amount of water in the unsaturated zone. The height of the water column if the equivalent amount of water was placed on the surface.
• WL_underground = The groundwater level, relative to datum.
• H_surface = The terrain height in the cell, relative to datum.
• I_und = The GROUND_INFILTRATION_MD of the underground terrain type.