The evolution of river sediment deposits in reservoirs as a dynamic phenomenon - Application to the Kremasta reservoir

The depositional pattern and the temporal evolution of incoming sediments in the Kremasta reservoir is studied. To this aim, an hydrographic survey has been carried out using a differential Global Positioning System (GPS) technique and a typical fathometer. The evolution of the depositional pattern within the reservoir depends mainly on the incoming intense floods, the properties of the river sediments and the stage of the reservoir. Low reservoir stage allows erosion of deposited sediments which subsequently are carried further downstream. An illustration of this pattern is given in this paper. The spatial distribution of the sediment deposits in the reservoir suggests that at least for large reservoirs, the concept of designing the dead volume near the dam is under serious doubt. Specifically, for the reservoir under study, the deposits tend to occupy a significant (in absolute terms) part of the reservoir's useful volume whilst the nominal dead volume is almost empty of sediments.