Stocksbridge Weir, England

Removal of the Stocksbridge Weir will support the restoration of ecological connectivity of the River Don allowing species to move through the river and forage, breed and find shelter more effectively.

Introduction

The Don Catchment in northern England covers about 1700 km2 and includes the uplands of the Pennines in the west and lowlands in the east. At the downstream end, the River Don flows into the River Ouse shortly before it discharges into the North Sea through the Humber Estuary.

The region’s historical importance as a centre of metal working has resulted in the impoundment of the catchment’s rivers by over 200 weirs which were mainly built to divert river water to water mills. These structures are typically 1–3 m tall, with the incline of the downstream facing slope ranging from vertical to moderately steep. By the 18th century impoundments and severe water pollution caused the extirpation of the formerly abundant salmon population.

The catchment’s weirs are now thought to be inhibiting the return of diadromous migratory fish such as Atlantic salmon (Salmo salar) and sea trout (Salmo trutta morpha trutta), European eel, and sea lamprey (Petromyzon marinus), all of which must travel between marine and freshwater ecosystems to complete their lifecycles

As the water quality of the River Don has improved, so ambition has grown to address barriers on the river to restore ecological connectivity to facilitate the re-establishment of salmon and to increase the stability, abundance and distribution of populations of fish currently resident.

At a glance

Project typeDam removal (demolition)
Project statusComplete
Removal dateOctober 2023
CountryEngland
RiverDon
Km opened200m
Focal speciesAtlantic salmon, brown trout, grayling, and bullhead
Websitehttps://dcrt.org.uk/

Project context and opportunity

Efforts to address barriers on the Don began in 2001, when a bypass channel containing a rock ramp was built by the UK Environment Agency to enable fish to circumvent Crimpsall Sluice, just upstream of Doncaster. Since then, many more fish passes have been built by a number of organisations. Unfortunately, it has often not been possible to remove many weirs as some still retain an important function, so fish pass installation has been the most common intervention type, which is an imperfect way of restoring ecological connectivity. Nevertheless, the work has resulted in sightings of salmon in the city of Sheffield for the first time in over 200 years.

Most of the best salmon spawning habitat on the River Don occurs upstream of Sheffield, and this length of river is now the focus of our attention. We plan to remove Stocksbridge Weir. Currently, nearly all of the weirs downstream of Stocksbridge Weir have been addressed, and there are plans in motion to deal with the two that haven’t. Stocksbridge Weir is 50 – 100 cm high depending on point along crest and about 20 m wide. While it isn’t a very tall structure, the shallow depth of water at the foot of the weir makes it a significant barrier to fish.

Project aims

Through the removal of this weir, it is hoped that Atlantic salmon will benefit from the project, but other fish that will immediately benefit include brown trout (Salmo trutta), grayling (Thymallus thymallus), and bullhead (Cottus perifretum). The restoration of ecological connectivity will enable these species to move through the river and forage, breed and find shelter more effectively. It will also confer much greater protection against local extinction of unique and locally-adapted genetic diversity due to improved prospects for gene flow between artificially-fragmented populations.

Furthermore, the weir removal will restore 250 m of river which currently is degraded by the impounding effect of the weir. This section of the Don should naturally be swift-flowing but instead is canal-like.

It is anticipated that the weir removal will have a major positive impact on fish populations and the wider riverine ecosystem. Research has shown that the restoration of ecological connectivity in another heavily impounded and formerly industrial catchment comparable to the Don Catchment resulted in a large increase in the abundance of brown trout and bullhead.

Project achievements

By removing a section of the weir, natural flows have once again been restored to a 200m section of river immediately upstream of the weir. This will also clear away fine sediment, leaving gravels, spawning habitats, and diverse riffle and pool habitats – essential for upland fish species to fully complete their lifecycle.

Partners

Don Catchment Rivers Trust

Environment Agency

Yorkshire Water