PPS 15: Planning and Flood Risk
Annex A: Overland Flow Flooding
A7 Sometimes referred to as overland sheet flow or pluvial flooding, overland flow flooding is characterised by water flowing over the ground surface where there is no drainage system to accept it. It is caused when the intensity of rainfall exceeds the infiltration capacity of the surface onto which it falls or when the soil is saturated and cannot accept more water. Overland flow may also occur where water flowing through the soil returns to the surface, for example in the saturated zone at the base of a slope. Ground conditions make overland flow a significant source of flooding in Northern Ireland.