Case study:Ennerdale Mill Weir Removal

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Location: 54° 28' 31", -3° 31' 34"
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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


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)
3 days after notching - weir structure exposed
After removal, showing the river bank vegetation recovering
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Catchment and 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) 387
387 m
0.387 km
38,700 cm
Dominant geology Siliceous
Ecoregion Great Britain
Dominant land cover Improved grassland
Waterbody ID GB112074069980



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

Reach length directly affected (m) 400
400 m
0.4 km
40,000 cm
Project started 01/04/2017
Works started 2018/06/01
Works completed 2018/07/31
Project completed 2019/07/31
Total cost category 100 - 500 k€
Total cost (k€)
Benefit to cost ratio
Funding sources Environment Agency, Marine Management Organisation, James Fisher Nuclear, Natural England

Cost for project phases

Phase cost category cost exact (k€) Lead organisation Contact forename Contact surname
Investigation and design 10 - 50 k€ West Cumbria Rivers Trust
Stakeholder engagement and communication 10 - 50 k€ West Cumbria Rivers Trust
Works and works supervision 100 - 500 k€ Ebsford Environmental
Post-project management and maintenance 1 - 10 k€ West Cumbria Rivers Trust
Monitoring 1 - 10 k€ West Cumbria Rivers Trust



Reasons for river restoration

Mitigation of a pressure Barriers to fish migration
Hydromorphology
Biology
Physico-chemical
Other reasons for the project


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

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative

Biological quality elements

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative

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

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative


Monitoring documents





Additional documents and videos


Additional links and references

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Supplementary Information

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