The Rhine naturally transports great amounts of detritus, sand and pebbles, the so called bed load. This is continually being moved. Smaller parts of the bed load are called sediments or suspended matter.
The quality of sediments/suspended matter transported by the Rhine has an effect on water quality.
Since insoluble substances – including pollutants – are taken up by sediments and later on released back to the water, sediments are considered to be the long term memory of former pollutions. This may influence the various activities using Rhine water. Therefore, the ICPR has drafted a sediment management plan. The actual situation of the implementation of the sediment management plan is described in the interactive maps and in the ICPR report 212.
The Alp Rhine carries great amounts of detritus and gravel into Lake Constance. Therefore, sand dredgers constantly remove gravel from the estuary. The effect of sedimentation in the mouth of the Alp Rhine is that the Rhine leaves Lake Constance without any glacial drift and sediment particles. The first sediment input of importance is that of the Aare with sediments from the Central Swiss Alps, the Swiss Plateau and the Jura. Even though only minor tributaries flow into the Rhine between the mouth of the Aare and Basel (70 km) (Rhine km 170), the amount of suspended matter transported by the Rhine rises from about 0,5 million tons to about 1.5 million tons.
Due to sedimentation, the southern Upper Rhine loses about 300 000 tons of its annual amount of suspended matter in the chain of barrages between Basel and Iffezheim. At the German-Dutch border at Bimmen/Lobith (Rhine-km 865), the Rhine transports about 3 million tons of suspended matter representing the charge transported by some 150 000 lorries.
that annually sand dredgers must remove 20 million m³ of sand from the port of Rotterdam in order to grant the depth required for navigation?
Sediments arrive from the Rhine-Maas delta, but also with tidal currents.