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.

$C_{inf}=min(H_{unsat},\Delta t\cdot I_{und})$

Finally, calculate the actual amount of water infiltrating.

$\Delta w=C_{inf}\cdot S$

Where:

• $\Delta w$ = The underground infiltration which takes place.
• $\Delta t$ = 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.

Related

The following topics are related to this formula.

Formulas

Groundwater level formula

Surface infiltration formula

Underground seepage formula

Models

Underground model

Infiltration model

Tracer flow model

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