Impact of streamflow regulation on two fish species through 2D simulations

A numerical investigation on the effects of streamflow regulation on two fish species is presented. The study reach (Ticino River, Italy) is 1.5 km long, placed downstream of the diversion Panperduto Dam. Composite Suitability Index (CSI) and Weighted Usable Area (WUA) variations were examined during a real flood event. A 2D unsteady flow model and the habitat suitability index method were used for hydraulic and habitat simulation, respectively. Brown trout and common barbel were selected as target species. For brown trout, the novel Stranding Risk Index (SRI) has been proposed. For both species, the main channel exhibits high CSI for low flows, while it becomes unsuitable for high flows. A secondary channel is instead suitable for both species during floods. The WUA decreases with increasing discharge, showing its maximum for Minimum Flow (MF). The stranding risk mainly concerns the secondary channel, concurrently to rapid flow decrease forced by upstream regulation.