Quantification and Modeling of Fluvial Bedload Discharge from Hillslope Channels in two Alpine Catchments (Bavarian Alps, Germany)

Fluvial activity in hillslope channels play a major role for the geomorphic system in alpine catchments as they link sediment sources in the upper parts of the catchment to the channel network. Within the framework of the SEDAG Project (Sediment Cascades in Alpine Geosystems) it was the aim of the presented work to measure the fluvial bedload discharge from such hillslope channels in two catchments in the northern Alps between 2000 and 2006 using 33 sediment traps. In combination with geospatial and statistical analyses, these data made it possible to identify those parameters that influence the fluvial bedload discharge. The spatial variability of the mean annual fluvial bedload discharge can be statistically explained by the size of the sediment contributing area. This area is derived by a rule based approach which includes distance to channel, slope and vegetation cover. Based on these results, a statistical model for the Lahnenwiesgraben was developed to predict mean annual bed load using the regression between measured bedload discharge and the size of the sediment contributing area. The model was successfully validated using the measured bed load discharges in a second catchment (Reintal). Thus, by using the model it is possible to regionalize fluvial bedload discharge in the hillslope channels of both catchments and to identify those channels which have a very high sediment output. Furthermore it is possible to calculate the sum of mean annual fluvial bed load input to the main channel (torrent) from all coupled hillslope channels for both catchments.