For pervious surfaces (e.g. unpaved surfaces), runoff is calculated as the difference between the surface water inputs and the sum of actual evaporation and the change in the soil water store.
Pervious runoff = surface inputs - evapotranspiration + change in pervious storage
Used to calculate: runoff into streams, stormwater drainage and floodwaters
Depends upon:
—Parameters: proportion of pervious water storage filled - initial conditions and proportion of wastewater piped
—Other metrics: ecosystem area, sewage from people, water used outside, rainfall and evapotranspiration