Small-scale hydropower schemes and migratory fish passage

After a brief reminder of the reasons why migrating fish need to move freely up and down rivers, this article describes current techniques in the area of upstream fish passage facilities, emphasising the value and limitations of each type: poll-type fishways, fish locks and lifts, bypass channels and preliminary weirs. The authors then define what is meant by efficiency in this context, before going on to describe fishway monitoring methods. The second part of the article reviews current knowledge on downstream fish migration through hydropower stations, focusing on damage caused by fish passing through turbines or by spillways, and on the design of facilities (physical and behavioural barriers) used to prevent fish from entering water intakes. The study highlights surface bypasses which have been used successfully to guide migrating fish safely past existing water intakes. The authors conclude by emphasising that whatever the facilities used, small-scale hydropower stations virtually always have some impact on migratory fish populations, especially when a series of installations along their migratory route causes the impact to become cumulative.