Environmental Effects of Sediment Flushing from Artificial Reservoirs: Field Study on an Alpine Stream

The ecological response to sediment flushing from artificial reservoirs depends on a large number of parameters, often difficult to quantify because of their spatial and temporal variability: pre-flushing condition, sediment characteristics (size and chemical), release strategy, morphology of the effluent water bodies. The reliable prediction of the environmental effects of sediment flushing and thus the rational planning of the works are obstructed by the limited scientific information so far provided. This paper reports the main results of a monitoring campaign on the water courses downstream of a small alpine hydropower reservoir subjected to three consecutive flushing between 2006 and 2008. The focus is on the effects on fish fauna and macro-invertebrate community: on the former, lethal effects - particularly on the youngest individuals - were observed, the latter showed good recovery capacity. A simple model to predict sediment effects on fish fauna is evaluated, proving acceptable skill to delineate the magnitude of the impact.