Sedimentation in the Reservoir of the Altenwoerth Hydropower Plant

This paper addresses two objectives. The first objective is to describe the sedimentation process in the reservoir of the hydropower scheme Altenwoerth. It is located on the Austrian part of the Danube about 60 km upstream from Vienna. Starting in 1976 the aggradation of the river bed has been monitored annually to estimate the sedimentation rate along a longitudinal section in the reservoir. Further, cores were taken over the whole sediment layer to analyse the grain size distribution, the bulk density, the mineralogic structure of the sediment and the heavy metal concentrations in the layer. It was found that the annual average sedimentation of suspended material amounts to 390 000 m3/a. The grain size of the samples vary from well sorted sands to poorly sorted, clay rich sediments. The heavy metal concentrations refer to the fraction less than 20 µ m. In comparison to the guidelines for sewage sludge disposal the observed heavy metal content of zn and Pb is slightly above the respective limits. The second objective is to demonstrate the application of a one dimensional sedimentation model which describes the accumulation over the operation period from 1976 to 1985. The model is related to the unit stream power concept and is based on the transport capacity equation of Engelund and Hansen. The model yields satisfying results for both the quantity of the sediment and also its gradation.