The Derwent Valley in Derbyshire is internationally famous for its industrial heritage, reliant upon many historic mills and weirs. These engineered structures put other beneficiaries of the Derwent’s might at risk. Salmon, trout, eel and other coarse fish species struggled to complete their life-cycles, as the speeding up of the industrial revolution meant more and more barriers for the fish. Darley Abbey weir, a key UNESCO-protected site outside of Derby, marks industrial progress and a permanent halt to fish migration journeys-until the Darley Abbey fish pass came along. A pioneering project, designed to prove that fish migration and industrial heritage can strike a compromise and that parts of our natural heritage can be restored.
Darley Abbey weir is a listed site, treasured and visited by thousands. As such, any modifications to the weir were a delicate act. In other words, the design needed to consider the historical value of the weir, preserve its character and function as a fish pass at the same time.
Watch how the project unfolded
After a comprehensive consultation, the parties involved agreed to a Larinier fish pass, as the most suitable option. A Larinier fish pass consists of a series of low, thin baffles using a herringbone design. The fish pass was fitted within a rectangular trough that blends into the weir. In Darley Abbey, the bespoke pass is 3m in width and 24.40m long, blending into the historical features.
The biggest challenge was a logistical one. The fish pass cuts through an island connecting the downstream with the upstream. Operating on an island, presented a range of complications to the construction of the fish pass, making the works one of the most complex endeavours for the engineering and construction teams on site. Concrete had to be mixed on the small island, installations to allow for the concrete to dry needed to be custom-built and a skilled hand at navigating heavy machinery within a watercourse was needed.
Back in 2013, the fish pass was one of the biggest projects completed by any Rivers Trust in the country. Its success encouraged long-term relationships between River Trusts, the Environment Agency and other public authorities.
Before Darley Abbey fish pass, fish were spotted at the foot of the weir as they were trying to cross the weir in their search for suitable spawning grounds. The Darley Abbey fish pass has changed this. Fish including migratory species such as Trout and Salmon can now complete their life-cycle further upstream. Moreover, coarse fish species such as barbel, chub, roach and perch can use the pass to access habitat that suits their life-stages.
While a fish pass only ever introduces part of the river function, failing to transport nutrients and sediments further downstream, or regulating the flow and temperature of a natural stream, this project’s success lies in its capacity to balance between weir and wild.
enquiries@trentriverstrust.org
The Trent Rivers Trust,
Middle Mill,
Darley Abbey Mills,Darley Abbey,DerbyDE22 1DZ
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