Surface Runoff

Depiction of two types of surface runoff: infiltration excess and saturation excess overland flows.

There are two types of surface runoff that occur during rainfall or snowmelt.

Infiltration excess overland flow occurs with soil that is not saturated. In fact, the soil can be quite dry, but soil properties or land cover do not allow for infiltration to keep up with high rainfall or snowmelt rates.

Saturation excess overland flow occurs when the soil becomes saturated and there is no longer any space for water to infiltrate. This can occur even with soil that would typically allow for large amounts of infiltration in sub-saturated conditions.