Recent Trends in Suspended Sediment Loads across the River Rhine Basin (1997-2014)

Understanding the spatial and temporal transport of suspended sediment in rivers is of major relevance for sustainable sediment management in the Rhine basin. Suspended sediment concentration and discharge data was collected from 34 monitoring stations along the Rhine River and its four major tributaries Aare, Neckar, Main and Mosel. For each station, the annual suspended sediment loads were calculated using the rating curve method for the period 1997-2014. For fitting the rating curves, a 5-year moving window was applied. Generally, the calculated loads show an increase in downstream direction. The tributaries deliver large amounts of sediment to the Rhine River. However, the Rhine River encompasses sections where the changes in suspended sediment loads are negative. The loads decrease at the Lake Constance after the alpine section. Also, the impounded section between the Weil am Rhein and Karlsruhe stations shows a decline in suspended sediment load and in the most downstream lowland section a decrease in was observed too between the Bad Honnef and Lobith stations. Except for the headwaters of the Rhine River in Switzerland (high Rhine), the Aare River, and the upstream parts of the tributary rivers, the suspended sediment loads of the Rhine River and its major tributaries show a consistent decreasing trend over time. This negative trend becomes stronger in the downstream parts of the river sections. This suggests that the decline in suspended sediment load is mainly caused by engineering works in the river channel.