Long-time impact of a large dam on its downstream river’s morphology: determined by sediment characteristics, pollutants as a marker, and numerical modelling

Abstract

Many river systems are regulated by dams, which causes an altered flow regime and sediment deficit in the downstream reach. The Rur dam (North Rhine-Westphalia, Germany), constructed from 1900 to 1959, serves as a model example of the impact of a large dam in a European low mountain area on downstream morphology. Today, a new equilibrium incorporates flow regulations, a deficit in suspended sediment supply, and an increased mean sediment diameter downstream of the dam. A hybrid examination of field measurements and numerical modelling shows that the sediment deficit and increased mean sediment diameters downstream of the Rur dam are superimposed by the lithostratigraphy and the sediment supply of tributaries. However, the discharge regulations lead to floodplain decoupling downstream of the dam. Furthermore, the Rur dam functions as a pollutant trap. Overall, more studies on the impact of damming on downstream reaches are needed to classify the impact depending on the river type for sustainable water management.