# Surface infiltration formula (Water Overlay)

Surface infiltration is calculated per cell.

First, the infiltration capacities are calculated:

${\displaystyle C_{water}=W_{surface}}$

${\displaystyle C_{top}=max(I_{con},I_{surf})}$

${\displaystyle I_{surf}=0}$ if a construction is present

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

Then the actual infiltration:

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

Where:

• ${\displaystyle \Delta w}$ = The surface infiltration which takes place.
• ${\displaystyle \Delta t}$ = Computational timestep.
• ${\displaystyle C_{water}}$ = The amount of infiltration that can take place based on the amount of water on the surface.
• ${\displaystyle C_{top}}$ = The amount of infiltration that can take place based on the infiltration values present.
• ${\displaystyle W_{surface}}$ = The amount of water (the water column) on the surface.
• ${\displaystyle I_{con}}$ = The GROUND_INFILTRATION_MD of a construction on a specific cell (if present).
• ${\displaystyle I_{surf}}$ = 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