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.

d_{u}=B_{c}-w_{u}

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

r=\Delta w_{u}/d_{u}

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

d_{i}=min(d_{u},\Delta t\cdot I_{u})

Finally, calculate the actual amount of water infiltrating.

\Delta w_{i}=d_{i}\cdot r

Where:

\Delta w_{i}

= The underground infiltration which takes place.

\Delta t

= Computational timestep.

d_{u}

= The height of the unsaturated zone.

r

= Ratio of water to height in the unsaturated zone.

d_{i}

= The height distance in the unsaturated zone which can be subject to infiltration to the saturated zone.

\Delta w_{u}

= 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.

w_{u}

B_{c}

= the datum height of the surface of cell c, set by the elevation or a Terrain elevation prequel.

I_{u}

= The GROUND_INFILTRATION_MD of the underground terrain type.

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