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.