Controlled sediment flushing of Cancano reservoir

Sediment flushing at Cancano hydropower reservoir (120 Mm3 storage, 1900 m AMSL top of active pool) aimed to start removal of a silty deposit (over 0.2 Mm3) burying the lower outlet of the dam by more than 15 meters. Operations were performed on March and April 2010 to get minimum seasonal storage and low enough temperatures, to prevent significant snow-melting inflows. Silt was displaced both by excavators and mud-pumps and by-passed down-stream of the dam. The whole operation required almost fifty days. Attention was paid to the environmental sustainability of the flushing: limits for Suspended Solid Concentration (SSC) were fixed along the river below the dam, field surveys were carried out to quantify the impact on river habitats and biocenosis. Continuous turbidimeter measurements were employed to rule the works of mechanical means and the water diversion at high elevation intakes, achiev-ing satisfactory control of SSC.