Sediment flushing downstream dams: a study on the clogging by fine sediments

Water reservoirs used to produce electricity have an impact on the environment and durability by : • stopping the natural sediment flux • changing the flow regime downstream of the reservoirs • storing (fine) sediments that reduce the storage volume Those 3 issues have been leading to the development of strategies in order to improve the equilibrium of the ecosystem downstream such structures, with solution such as sediment flushing and simple water flushing reproducing flood events. Those operations produce excessive sediment inflow on certain river sections, which can lead to the clogging of the gravel bed. River construction work, soil erosion, emergency actions and natural river bank erosion can also bring similar problematic. For example, a dramatic event happened in 2013 on the Spöl River in Eastern Switzerland. Due to some operations on a Punt dal Gall dam, important amountsof fine sediments were flushed downstream the reservoir and resulted in significant damages to the river ecosystem1. A strong clogging of the river bed was noted. A clean water flushing a few months later led to a cleaning of the clogged areas.