Optimised Coanda screen for hydropower and fish

The water supply for hydropower plants in Switzerland, is predominantly sourced from gravel-rich mountain streams using Tyrolean weirs. However, to keep solids out of the turbine water system, a sand trap must be installed. Furthermore, the Tyrolean weir inhibits fish migration. For these reasons, Coanda screens are increasingly used as water catchment systems, although scientifically unsubstantiated facts on the degree of rejection of solids and fish-friendliness are still circulating. This article helps to clarify various assumptions about Coanda screens. Some are supported, others are discarded.