Old contaminated sediments in the Rhine basin during extreme situations

Sediments play an important role in water resources management. In the past, hazardous contaminants from municipal and industrial wastewater effluents and from agriculture were discharged in large quantities into the water bodies and accumulated within the bottom sediments. Today, relatively unpolluted recent sediment surface layers cover older contaminated sediments. Due to increasing water discharges associated with high precipitation and heavy rainfall events (climate change) and land use changes there is an increasing risk of the resuspension of old contaminated sediment layers and the transport of the particle-bound pollutants downstream in river systems over long.In this study we focus on the potential release of the old contaminated sediments in the Rhine basin during extremely high discharges and low flows. The main aims of this study are to make an overview of the relevant knowledge gaps and to identify advisable research directions on the basis of existing information (data) and models.The main conclusion of this study is that insight is missing in the expected remobilisation and recontamination levels of contaminated sediments during extreme situations. The focus not only has to go on the historical contamination but also on the present-day contaminations, and on the identification of actual and potential problems.Better sediment and water quality measurements (e.g. one hour samples during flooding events) and models (source location) will allow us to get a better understanding of the sediment dynamics in the Rhine basin during extreme situations. This will give us a deeper insight in the substance interactions with sediment and in the water column (geometry of the pollutants).