The removal of the Scotton Weir opened up 18km of river to migratory fish such as salmon, sea trout and European eel. Moreover, its removal will help to restore natural processes to the river.
The Humber catchment is the largest in Britain at 26,100km2 and barrier removal is a critical element of the Humber River Basin Management Plan that aims to meet WFD targets for good ecological status for all waterbodies. Major tributaries like the River Nidd are failing for the lack of Atlantic salmon due to barriers to migration (like Scotton Weir) but other species with equal conservation status (eg European eel and lamprey spp.) are all similarly restricted.
The Wild Trout Trust has partnered with like-minded organisations within the Dales to Vales Rivers Network, and angling clubs like Nidderdale AC, Harrogate Flyfishers, Knaresborough Anglers upstream, and Harrogate AA downstream to improve habitat within the main Nidd channel and key tributaries for spawning, part of which involved smaller barrier / culvert removals. Nidderdale Area of Outstanding Natural Beauty has also just completed a series of weir removals on the Laver (Ure trib) for WFD reasons. However, to date, reconnection of the main River Nidd has been relatively slow, hence the importance of this project.
|Dam removal (demolition)
|Date of removal
|Atlantic salmon, brown trout, European eel, lamprey, grayling, chub
Extensive weir removal and fish easement projects have been carried out on other major rivers in the Humber River Basin. Salmon has returned to the R Don in Sheffield City centre and regularly caught on the Aire at Leeds, just downstream of a series of fish passes which were completed in 2022. Small numbers of salmon parr have been surveyed via electric-fishing from upstream of Hunsingore Weir (Dr A Nunn pers comm. 2021; Yorks Ouse Salmon Project), so modification of Hunsingore by the Environment Agency (2022/23) and removal of Scotton Weir in this project (the two main weirs identified as barriers to migration) should allow their rapid spread up through the Nidd system.
Yorkshire rivers have been subject to >5 ‘one in one hundred year’ events in the last 10 years and a number of Industrial Revolution era weirs have been structurally compromised as a direct result. Scotton weir was damaged and partially breached in December 2018 but impoundment and fish passage remained issues. Clearly, many more are now approaching the end of their ‘life-span’ and present flood risk / safety issues if they collapse during / after high rainfall events. The breach in Scotton Weir is a warning sign.
It is hoped that the project at Scotton Weir can be replicated and act as a local demonstration case study to catalyse further activity in the catchment. The Yorkshire Dales Rivers Trust and other partners within the Dales to Vales Rivers Network have expressed interest in using this project for knowledge exchange and best practice dissemination.
Scotton Weir is ~170km from the tidal limit in the upper Humber, but salmon already migrate from the Humber via the Ouse and into the lower Nidd ~75km downstream. It is one of two weirs severely impeding fish passage on the mid to lower Nidd, with potential to reconnect >50km of mainstem channel and >80km if key spawning tributaries are included. The structure at Scotton Weir was ~75m wide and ~4m high when fully intact and impounded the river upstream for ~800m masking the true character of the river channel. Removal of Scotton alone will reconnect ~18km of main channel and ~35km when considering access to tributaries.
There are expected benefits to the wider fishery in terms of reconnecting fragmented fish communities & increased resilience. At a local scale, two angling societies have the rights to fish and both envisage increased angling opportunities with the renaturalisation of the channel. A natural bank with native vegetation and availability of large woody material, instead of an impounded bank with limited vegetative cover, presents hydraulic roughness, habitat complexity and greater biodiversity as ecosystem benefits. From a geomorphological perspective, full removal will reinstate the natural transport of sediment down the channel.
The complete removal of Scotton Weir has successfully achieved the intended outcome of eliminating the impounded section. There has been a limited shift in sediments to date (March 2023), resulting in minimal impact on local invertebrate and fish communities. Ongoing monitoring, particularly after autumn and winter rainfall, will provide insights into potential changes.
Enhancements to angling opportunities have faced challenges due to low flows, compounded by the closure of the UK season for salmonids from September 30th to March 25th. Nevertheless, informal discussions with anglers and personal observations of fish and fish-eating birds indicate utilising the new free-flowing channel.
Theoretically, the reduction in flood risk has improved with decreased local stage height and removing the degrading structure. Notably, no adverse effects have been observed concerning bank readjustment.
Wild Trout Trust