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The potential to influence runoff processes by changes in land use


Presented at the European Conference on Advances in Flood Research
Potsdam, Germany, 2000.






Storm runoff in catchments is produced either by Hortonian overland flow (HOF), saturation overland flow (SOF) or fast subsurface flow (SSF). HOF reacts rapidly to precipitation, SOF producing areas first have to be saturated and show therefore a delayed reaction. Even more delayed is SSF, although it is faster than usually assumed due to preferential flow. Areas with high infiltration rates and storage capacity or percolation into the bedrock do not contribute to storm runoff.
Based on geo-information of soils, geology, topography and land use as well as rainfall and infiltration experiments combined with tracer techniques, areas in a catchment were identified where different types of runoff processes can be expected during precipitation events. The interrelation of runoff processes on hillslopes was also considered. With these evaluations, maps of dominant runoff processes in a catchment were set-up. In order to study effects of land use changes on storm runoff, this methodology was applied to three different meso-scale catchments in the Nahe basin, which consist of different land use composition.
In areas with delayed runoff contribution, a change in land use has little effect. A reduction of storm runoff is only possible on areas where fast reacting runoff processes can be transformed into slower ones by a change of land use as well as land use management practices. Based on the knowledge of the spatial distribution of the dominant runoff processes and of the land use, the potential for influencing storm runoff characteristics (e.g. runoff peak, runoff volume) for different rainfall events in the three catchments was assessed by model simulations.