Quick and slow response to rainfall by an urban area

A rainstorm on an urban area causes a quick and a slow response. The quick one consists of the surface runoff from the covered area. The subsurface flow through the soil to the subsurface drainage system is low. The waterbalance of two different parts of an urban area shows that quantitatively the discharge of the subsurface drains can be of primary importance. Even for an almost completely paved area, the subsurface drainage system may discharge 40 percent of the precipitation. It is an important factor for the watermanagement because the water from the subsurface drains is of good quality. However from the point of view of floods, the discharge of the subsurface drains is slightly important. The data are from different urban catchment areas (flat roof, parking lot, housing area and shopping centre) in Lelystad.