ABSTRACT

The longitudinal continuity in sediment transport is responsible of the natural river conditions. Dams interrupt the sediment supply along the river since they trap sediment and store water in the upstream reservoir. Thus the river behaviour downstream the dam is highly impacted in terms of morphology and hydrodynamics. The lack of sediment supply induces several negative effects, such as riverbed incision, bank instability, loss of morphological variety and changes in channel width. Furthermore, a fish habitat depletion has been highlighted in such disturbed reaches. Sediment replenishment along the downstream reach of dams is an increasingly common technique to restore the sediment continuum. In order to provide guidelines for this method, a wider knowledge upon released discharge and quantity of material is desirable. Experimental work was performed on a flume facility to investigate the river replenishment technique at the Laboratory of Hydraulic Constructions (LCH) of the École Polytechnique Fédérale de Lausanne. The model reproduces the typical features of a straight armoured alpine gravel-bed river in terms of slope, cross section and bed grain size. The results show that the discharge, together with the geometrical placement of volumes, have a dominant influence on the erosion process. The pattern of the obtained morphological forms, created on the channel bed and related to the replenishment length, is presented and discussed.