Understanding the dynamics of erosion and deposition of cohesive and contaminated sediment is an important requirement to assess the risk of erosion and to manage mud-dominated ecosystems. Here, we present data on the erodibility of cohesive sediments from the impounded Upper Rhine River and develop a modelling concept to understand the sediment dynamics at large spatial scale (∼164 km) and long time scale (∼30 years). The conceptual framework includes ten reservoirs of the Upper Rhine between Basel and Iffezheim, which serve as long-term sinks of cohesive sediment. Each reservoir is represented by a 1D sediment budget model, which is coupled to its upstream and downstream neighbour. In this paper, we focus on the uncertainty associated with the measurement of the erodibility of cohesive sediments and on the implications to model the risk of erosion. Therefore, preliminary model results of the bed changes of the Iffezheim reservoir are presented and evaluated with empirical evidences from quarterly echo-soundings of the reservoir. The probabilistic approach that is based on Monte Carlo simulations allows to assess the uncertainty related to our limited knowledge i) of the dynamics of contaminated sediments and ii) of the environmental conditions in the reservoir that control the risk of erosion of contaminated sediments.