Case study:Ennerdale Mill Weir Removal

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Location: 54° 28' 31.05" N, 3° 31' 33.80" W

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Project overview

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Status	Complete
Project web site	http://westcumbriariverstrust.org/projects/ennerdale-mill-weir-removal
Themes	Environmental flows and water resources, Fisheries, Habitat and biodiversity, Hydromorphology, Urban
Country	England
Main contact forename	Luke
Main contact surname	Bryant
Main contact user ID	User:WCRT
Contact organisation	West Cumbria Rivers Trust
Contact organisation web site	http://www.westcumbriariverstrust.org
Partner organisations	Natural England & Environment Agency
Parent multi-site project
This is a parent project encompassing the following projects	No

The weir at Ennerdale Mill, on the River Ehen in Egremont, prior to removal, showing significant damage to the structure and face of the weir

Project summary

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Ennerdale Mill Weir, located on the River Ehen in Egremont (Grid Ref NY 012099) dates back over 250 years and was constructed to power the Ennerdale Paper Mill. The Weir has not been used as it was intended for many years and has been proven to be a barrier to migratory species of fish in the Ehen catchment, as well as a crucial site for Freshwater Mussels.

A consortium of funders- WCRT, the Environment Agency, Natural England, the European Maritime and Fisheries Fund and James Fisher Nuclear- have combined resources to enable this weir removal project to take place over the summer of 2018. The project was delivered as part of the Cumbria River Restoration Strategy, a partnership between the EA, NE and WCRT.

In June 2018, we mobilized to site to begin the delicate task of removing the weir, without causing ecological damage through the uncontrolled release of silt and sediment into the river system. A specialized contractor, Ebsford Environmental, were chosen to deliver the works, ensuring silt control measures were installed downstream of the weir. In addition, prior to the works, WCRT and Natural England conducted a translocation of freshwater mussels from within the work site, re-locating 48 mussels upstream of Egremont.

The working methodology, developed by WCRT and AECOM, involved river bank re-profiling, berm lowering, re-grading of the existing riverbed & installation of toe protection (boulders that reinforce the river bank to provide protection against erosion), all conducted in a specific order to minimise sediment disturbance. Once the preparation was complete (approx. 4 weeks) we were ready to ‘notch’ the weir which lowered the water levels upstream, allowing the sediment & gravels that had built up over decades to be removed in the dry. Removing the weir structure itself took one week, and throughout that process Durham University were conducting heritage recording of the site so that we have a historic record of the structure of the weir.

With the weir structure removed, the final tasks were to re-profile the riverbed and rapids upstream and downstream, and further strengthen the river banks with stone protection.

Works completely finished on 31st July 2018, meaning the whole project was delivered in around 7 weeks.

The Rivers Trust and the Environment Agency, supported by other partners, have been working with the Marine Management Organisation and Defra to develop a coordinated and funded programme of projects for 2018/19 with the aim of freeing migration routes of barriers to fish.This project is part of that programme funded by over £1.6 million of European Maritime and Fisheries Funds, which is matched by more than £1 million of Agency/Defra funding and £300,000 of other funds.

Monitoring surveys and results

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Durham University undertook Archaeological Monitoring in 2017 and during the removal in 2018

Immediately post-removal WCRT have been conducting regular fixed-point photography across the site, to highlight how the river adapts and responds to being re-naturalised.

Drone-captured aerial imagery has also been recorded post-removal; once collated this can be contrasted with the footage captured pre-removal for before-and-after analysis

Lessons learnt

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Image gallery

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View from below the weir, highlighting the extent of the drop in water levels

Installing sediment-trapping mats downstream of the weir, prior to removal

Removing the actual structure, 6th July 2018

Site of the former weir, 3 weeks after removal

Gravel & cobble deposition is evident as the river is rapidly re-naturalising and responding to natural processes (December 2018)

Catchment and subcatchment Select a catchment/subcatchment Edit the catchment and subcatchment details (affects all case studies in this subcatchment) Catchment River basin district North West River basin South West Lakes Subcatchment River name River Ehen (lower) Area category 100 - 1000 km² Area (km2) Maximum altitude category 200 - 500 m Maximum altitude (m) 387387 m <br />0.387 km <br />38,700 cm <br /> Dominant geology Siliceous Ecoregion Great Britain Dominant land cover Improved grassland Waterbody ID GB112074069980 Site Edit site Name River Ehen WFD water body codes WFD (national) typology WFD water body name Pre-project morphology Reference morphology Desired post project morphology Heavily modified water body No National/international site designation Local/regional site designations Protected species present Yes Invasive species present No Species of interest Freshwater pearl mussel (Margaritifera margaritifera), Atlantic salmon (Salmo salar), Brown trout (Salmo trutta) Dominant hydrology Dominant substrate River corridor land use Average bankfull channel width category 10 - 50 m Average bankfull channel width (m) Average bankfull channel depth category 0.5 - 2 m Average bankfull channel depth (m) Mean discharge category Mean annual discharge (m3/s) Average channel gradient category Average channel gradient Average unit stream power (W/m2) Project background Edit project background Reach length directly affected (m) Project started 2018/06/01 Works started 2018/07/31 Works completed Project completed Total cost category Total cost (k€) Benefit to cost ratio Funding sources Cost for project phases Phase cost category cost exact (k€) Lead organisation Contact forename Contact surname Investigation and design Stakeholder engagement and communication Works and works supervision Post-project management and maintenance Monitoring Reasons for river restoration Edit reasons for restoration Mitigation of a pressure Barriers to fish migration Hydromorphology Biology Physico-chemical Other reasons for the project Measures Edit Measures Structural measures Bank/bed modifications Weir removal Floodplain / River corridor Planform / Channel pattern Other Non-structural measures Management interventions Social measures (incl. engagement) Other Monitoring Hydromorphological quality elements Edit Hydromorphological quality elements Element When monitored Type of monitoring Control site used Result Before measures After measures Qualitative Quantitative Biological quality elements Edit biological quality elements Element When monitored Type of monitoring Control site used Result Before measures After measures Qualitative Quantitative Physico-chemical quality elements Edit Physico-chemical quality elements Element When monitored Type of monitoring Control site used Result Before measures After measures Qualitative Quantitative Any other monitoring, e.g. social, economic Edit Other responses Element When monitored Type of monitoring Control site used Result Before measures After measures Qualitative Quantitative Monitoring documents Upload monitoring documents Additional documents and videos Upload additional documents Additional links and references Edit links and references Link Description Supplementary Information Edit Supplementary Information