Project Summary
Coffey delivered the Derwent Scour Remediation Project for Severn Trent Water. This project addressed scour damage at the Derwent Reservoir Dam, stabilising the scour hole and extending the spillway to ensure long-term resilience.
Project Description
Located at the Derwent Reservoir in the Upper Derwent Valley, the project involved filling a 4-5 m deep scour hole that was undermining the concrete structure of the spillway. Works included filling the scour hole with rock bags and gabion baskets, and constructing a new concrete wall as an extension to the existing spillway to prevent future scouring and erosion.
Scope of Works
The works included:
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Site mobilisation, including temporary closure of footpaths and access roads, and installation of welfare facilities
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Excavation and preparation of a crane platform, using recycled 6F5 to ensure stability
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Delivery, storage, and lifting of rock bags into the scour hole
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Installation of gabion baskets filled with local stone to create a robust stabilisation structure
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Construction of a stepped concrete wall tied into the existing spillway structure
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Removal of temporary works and reinstatement of the site, including biodiversity planting and footpath reinstatement
Technical Highlights
A spider excavator was used to excavate silty material and regulate the scour hole with rock infill. Over 210 m³ of rock bags were installed to stabilise the scour hole, complemented by pre-filled gabion baskets to form a new spillway extension. A new concrete wall was tied into the existing structure using L-shaped dowels, and additional works included installation of reno mattresses and chain-link mesh for slope stabilisation.
Environmental and Community Measures
Environmental protection was a priority due to the site’s location within the Peak District National Park. Local stone was used to fill the rock bags, reducing concrete use and minimising vehicle movements. A biodiversity net gain of 17% was achieved by replanting trees and shrubs at the crane platform location. Engagement with the local community and stakeholders, including the Forestry Commission, ensured safe access and minimal disruption to the popular visitor destination.
Added Value
Coffey added value through:
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Completing additional works to address an enlarged scour hole while the site team was mobilised
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Using local stone to reduce environmental impact and improve habitat creation within the gabions
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Providing constant stakeholder updates, clear communication with local residents, and effective traffic management during crane lifts and deliveries
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Achieving a merit award from the Institution of Civil Engineers East Midlands Merit Awards 2024
