Eric Wright Civil Engineering has helped to safeguard one of England’s rarest animals thanks to a complex design and build project in the Lake District at Ennerdale Water.
The scheme involved re-routing Ben Gill, a tributary of the River Ehen, to its original course in order to restore the delicate habitat in which protected species like freshwater mussels and salmon can thrive.
The lower part of Ben Gill was originally diverted in the 1970s to enable a greater flow of water to be stored for abstraction at Ennerdale Water. However, the piped water also stopped sediment supply to the upper reaches of the Ehen – a designated Special Area of Conservation (SAC) and Special Site of Scientific Interest (SSSI). Now, due to a recent review of abstraction licences by the Environment Agency, the decision was taken to revoke abstraction consent, obliging United Utilities to recreate the original Ben Gill channel to enable sediment and water to enter the River Ehen as it would have done naturally.
Restoring the natural supply of stones and gravel will improve habitats for young mussels and spawning Atlantic salmon in the River Ehen and the Environment Agency have already seen some natural habitats start to return.
Explains Gavin Hulme from EWCE: “The diversion of Ben Gill had reduced the volume of sediment entering the river and altered its hydrological regime, which affected flow and geomorphic conditions to cause degradation of the mussels’ habitat. As a result, the population was ageing and declining so urgent action was needed to protect it.
“Our task, working closely with United Utilities and the Environment Agency, was to ensure that the restoration works were designed and constructed in a manner that was both sympathetic to the local environment and would provide a robust solution for restoring the local eco system.”
The project involved deconstruction of the existing intake structure at the head of the diversion pipeline to enable re-grading of the new Ben Gill channel. The 900mm abstraction pipe was then plugged and modifications were made to the existing pipe outlet headwall structure at Ennerdale Water.
EWCE was then able to construct a replacement lower Ben Gill watercourse channel using only materials won from the site, and a new confluence of lower Ben Gill channel and the River Ehen, including the formation of a ‘seed’ gravel confluence bar.
Sections of reinforced concrete ‘training’ walls were built as part of the project and EWCE constructed a light vehicle bridge over the newly formed channel along with a new ford crossing at the upstream end of the works.
The scheme was also designed to avoid any environmental impact from the works and changes to the landscape, including re-profiling of the field through which the reinstated water course runs, using surplus excavated material where possible.
“Overall the project has now benefitted the complex eco system of the River Ehen and will afford the mussels and other sensitive wildlife populations every opportunity to flourish in the future. Our success in delivering the project demonstrates our experience of environmentally-sensitive water sector projects and is testament to effective collaborative working between our team, United Utilities and the Environment Agency.”
Simon Povey, United Utilities Project Manager, commented “Eric Wright Civil Engineering worked tirelessly to ensure the work they undertook on Ben Gill did not impact the highly designated River Ehen. The site team were really focused on the environmental impact their work could have had, and worked in partnership with us the Environment Agency and Natural England to complete the project.”
Michelle Donoghue from the Environment Agency said: “It’s exciting news that we have worked together to undertake restoration in such a wild, beautiful part of the Lake District. This project is a fantastic example of how we can balance the needs of people and nature and secure the future of one of Cumbria’s great wild spaces.
“Ben Gill has been given back to nature and once again helps provide vital habitats for spawning Atlantic salmon, fresh water mussels and other local species.”
