Processes acting on the formation of surface runoff

Mechanisms of runoff generation (1 infiltration-excess overland flow, 2 saturation overland flow, 3 rapid through flow in macropores, 4 displacement flow in saturated macropores, 5 ground water flow)

Long time Hortonís concept(*1) was used to explain the surface runoff purely on the basis of precipitation water that was exceeding the infiltration capacity of the topsoil layer (infiltration-excess water). The infiltrated water was only contributing to the evapotranspiration and groundwater recharge.

In the meantime our knowledge could be extended to an almost complete understanding of the contributing processes of surface runoff generation. The surface runoff is not only generated by infiltration excess flow but also on saturated topsoil layers, water bodies (lakes, rivers and streams) which Dunne(*2) named saturation flow. The subsurface runoff can be generated by rapid throughflow of new infiltrated storm water within macropores and soil pipes draining at the end directly into the stream flow. In case of saturation of the soil matrix (micropores) and the macropores prestorm soil water returns to the surface through the additional water pressure created by the blocked runoff within the macropores at the depression zones. Thus this return runoff mainly occurs close to rivers and is rather important in hillsides with concave shape and in wide flat river valleys(*3).

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Hydrology of Floods



*1 Horton (1933)

*2 Dunne (1978)

*3 Dunne et al (1975)

Tanaka et al (1988)



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