The redundant Ennerdale Mill Weir on the River Ehen at Egremont was a major barrier to fish and badly impacted the movement of salmonids into the upper catchment where they are important for the river’s population of freshwater pearl mussels. We worked with the West Cumbria Rivers Trust to provide a more suitable option to enable better fish movement.
We analysed the watercourse around the current weir and modelled various channel responses to predict the reaction to various weir-replacement options. We also modelled options to help with the design of in-channel features to mitigate the impact of the weir’s removal.
It was clear from our findings that, following the release of 2m of head at the weir, the channel response would be significant if not controlled. Sediment release issues would be less impactful because the watercourse would integrate these into its flow, which was already receiving large volumes of sediment from natural erosion of glacial terrace deposits.
We delivered our results and options to key stakeholders and agreed on the final approach for improving the fish passage, which was taken to detailed design. With our help, funding was secured for the weir to be removed and for watercourse features to be created. The weir was successfully removed, restoring a natural river habitat for migratory fish, and providing better protection for freshwater mussels.