# Surface infiltration formula (Water Overlay)

Surface infiltration is calculated per cell.

First, the infiltration capacities are calculated:

$C_{water}=W_{surface}$ $C_{top}=max(I_{con},I_{surf})$ $I_{surf}=0$ if a construction is present

$I_{con}=0$ if no construction is present

Then the actual infiltration:

$\Delta w=min(C_{water},\Delta t\cdot C_{top})$ Where:

• $\Delta w$ = The surface infiltration which takes place.
• $\Delta t$ = Computational timestep.
• $C_{water}$ = The amount of infiltration that can take place based on the amount of water on the surface.
• $C_{top}$ = The amount of infiltration that can take place based on the infiltration values present.
• $W_{surface}$ = The amount of water (the water column) on the surface.
• $I_{con}$ = The GROUND_INFILTRATION_MD of a construction on a specific cell (if present).
• $I_{surf}$ = The GROUND_INFILTRATION_MD of the surface terrain type. This value should be interpreted as the vertical conductivity (Kv) of the sub-soil.

## 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
Substance flow model