Sediment retention in the floodplains of the river Elbe

The studies provide basic knowledge of sedimentation in active floodplains as part of large-scale sediment retention processes. It is pointed out that floodplains are regions of concern for the sediment management concept of the river Elbe. Therefore, floodplain characteristics such as vegetation pattern and inundation frequencies have been analysed for the active floodplains of the free-flowing Elbe river in Germany. The results reveal that floodplain vegetation and land-use types are heterogeneously distributed along the Elbe. The most important land-use units are grasslands (68 %), followed by croplands (12 %) and forests (11 %). Data are demonstrating that the Elbe river degradation until the confluence of the Saale river reduces inundation frequencies and sedimentation processes during smaller flood events. The evaluation of measured sediment inputs has revealed marked dependencies both on discharge depth and on the distance of the gauging points to the river. As a function of discharge, large-scale sediment retention was calculated, amounting to more than 40,000 t in the case of smaller floods (2MQ) up to more than 220,000 t in the event of extreme flooding in the German Elbe floodplains. These figures are in the range of 7 to 30% of the annual suspended sediment loads near Hitzacker, underlining the importance of floodplains for sediment retention and their meaning for a sediment management concept.