# Surface infiltration formula (Water Overlay)

Surface infiltration is calculated per cell. First, the infiltration capacities are calculated:

Then the actual infiltration:

Where:

- = The average infiltration capacity based on constructions on top of the surface, based on GROUND_INFILTRATION_MD defined in either the building or function.
- = The average infiltration capacity based on the surface terrain, defined by GROUND_INFILTRATION_MD. This value should be interpreted as the vertical conductivity (Kv) of the sub-soil.

- = The average infiltration capacity on top of the surface.
- = The average infiltration capacity below the surface.
- = The infiltration capacity from surface to the unsaturated zone.

- = The surface infiltration which takes place.
- = The amount of water on the surface. Also known as the water column.
- = Computational timestep.

## Related

The following topics are related to this formula.

- Formulas
- Surface water level formula
- Groundwater level formula
- Underground infiltration formula
- Models
- Surface model
- Underground model
- Infiltration model
- Tracer flow model