Suspended sediment and bed load problems of the Upper Rhine

Abstract

Summary The regulation of the southern Upper Rhine by dams down to Iffezheim has considerably changed the sediment balance of the stream. In the impounded sections fine-grained sediments are deposited, narrowing the cross section and thus impeding high-water discharge. Concluding from the high illite content of the suspended material, a considerable part of the settling sediment is derived from the waste waters of the Alsatian potassium mining. In the freely flowing Rhine downstream of Iffezheim, in turn, erosion occurs. Although the degradation of the riverbed downstream of the Iffezheim dam is prevented successfully by artificial addition of gravel, this has no positive influence on the erosion reaches farther northwards. This becomes apparent both in the petrographic composition of the bed load material as well as in its particle size distribution: Medium-grained to coarse gravel with high carbonate rock content are already deposited upstream of Speyer. Downstream of Speyer sand and fine gravel rich in crystalline components are taken up from the river bottom. This situation might probably be improved by appropriate addition of sand and fine gravel downstream of Iffezheim.