Impact of Climate and Land Use Change on River Discharge and the Production, Transport and Deposition of Fine Sediment in the Rhine basin - a summary of recent results

Abstract

Over the past decennia, the palaeogeographic development of the Rhine-Meuse delta in the Netherlands has been extensively studied and an extremely detailed database of the Holocene delta architecture has been established. The delta offers a unique palaeo-environment to study both palaeogeography and avulsions on a timescale of millenia, because of the relatively complete geological record, as a result of rapid aggradation during the Holocene, governed by relative sealevel rise and land subsidence. The palaeogeographic reconstruction provided many new insights in the characteristics of the fluvial system, such as period of existence of individual channel belts, avulsion frequency and the factors influencing these characteristics over time scales of centuries to millennia. In recent years, research attention also became focused on the Rhine basin, which is the main source area of the water and sediment for the delta. These studies considered a decadal to century time scale, and aimed at assessing the potential impacts of future changes in climate and land use on the river Rhine discharge regime as well as on the production of fine sediment and the net transport of wash load from the upstream basin to the lower Rhine delta. For this purpose, a suite of GIS-embedded models has been developed that simulates this sequence of processes. The results indicate that climate change may accelerate erosion rates. However, land use changes, that foresee a reduction in arable land, lead to a net reduction of erosion in the German part of the basin. Due to inefficient sediment delivery, increasing erosion in the Alps has little effect on the sediment load farther downstream. Suspended sediment loads transported into the lower delta are expected to decrease by 13 %. Due to the combined effect of increased peak flows, discharge-dependent sediment transport and trapping efficiencies of floodplains, long-term average sedimentation rates at low floodplain may decrease, while sedimentation rates at high floodplains may accelerate.