Controlling sediment flushing to mitigate downstream environmental impacts

This work reports on the downstream environmental effects of ten sediment flushing operations from four hydropower reservoirs in the Italian Alps. The sediment concentration of the sluiced water was controlled to mitigate the downstream impacts that were quantified through monitoring of benthic macroinvertebrates and brown trout (Salmo trutta trutta). Benthic communities were severely impaired by all of the monitored flushing operations, in terms of both density and richness, but they usually recovered to pre-flushing values within a year if the riverbed alteration due to sediment deposition was low. As expected, impacts on trout were heavier on juveniles. Evidences provided by the monitored flushing activities can support the planning phase of analogous operations at comparable sites.