Supporting the return of salmon to the River Don
A major part of our project is reconnecting isolated river habitats with fish passes on weirs to allow fish to move freely. The outcome will be the return of salmon to Sheffield for the first time in 200 years. Tighter environmental regulation and investment in water quality by the water companies has resulted in river water quality being sufficiently good to once again support all river life. This includes migratory fish, particularly salmon, but they cannot return to historic upstream spawning gravels because the remaining weirs obstruct the free passage of fish along the river.
Five weirs in the centre of Sheffield will have fish passage solutions – Brightside, Norfolk Bridge (Burton’s Weir), Lady’s Bridge, Kelham Island and Steelbank.
Two of the larger weirs will have technical fish passes installed. These are called Larinier passes after the man who invented the type of baffles that sit on the base of the pass. The pass works by slowing the flow of water through the pass. Larger fish are then able to swim up the pass allowing fish to make their way up the pass with smaller fish being able to rest behind the baffles before they jump over the next one. The passes at Brightside and Steelbank will be two flight (see schematic below) with each flight having baffles with a resting pool in the middle.
The other three weirs will have easements. Some of our weirs have listed status and easements are a less invasive way of helping fish to ascend the weirs and a lower cost option. An easement consists of a baulk or beam usually made of wood or concrete being fixed across the face of the weir sloping downwards to the apron. Where the baulk meets the weir crest a notch is cut. In combination the notch and baulk create a channel of water across and over the weir through which fish can swim. (See schematic below).