River Erosion at Chapel-en-le-Frith, Derbyshire

November 2020

The Challenge

Along the Warmbrook, Chapel en le Frith four sections of the channel side had been eroded and slipped, starting to encroach on the public footpath resulting in a serious public safety concern.

Key Facts

  • Main river, Environment Agency Permit required
  • Erosion protection
  • Man-made ground
  • Limited access
  • Japanese Knotweed
  • White Clawed Crayfish
  • Green solution

The Solution

We were commissioned to carry out a full site investigation to identify the failure mechanism of the bank and undertake a lifecycle costed feasibility study for suitable solutions. To undertake the options appraisal, we looked at options ranging from do nothing to hard engineered solutions. For each option we scored them against different economic, technical and environmental factors to put forward the preferred option. We undertook a cost estimate for both construction and maintenance requirements using CESMM and our knowledge and experience of contractor rates. This was presented to the Client Project Manager in the form of a technical report, along with a meeting to discuss the findings.

The site had limited access to the working areas and the footpath itself provided the only working area restricting the size of plant and materials that could be transported to site. The An additional complication to the access, was the unstable nature of the ground, this was spoil from the historic housing development to the rear.

In addition, Japanese Knotweed and White Clawed Crayfish were identified in the working area. The impact to both of these issues had to be mitigated within the contractor’s method statement. The measures included but were not limited to isolating areas, siltation control and plant/material inspections during excavation.

Our recommended solution was a vegetated geotextile bag system that provides an erosion protection function but is aesthetically and environmentally sensitive. To complete our detailed design we used a fluvial river model to assess river flows and procured topographic, geotechnical, ecological and utilities surveys.

As Principal Designer in line with CDM2015 we undertook both the required site and design risk assessments. We gained approval for the required Flood Risk Activity Permit from the Environment Agency and planning permission from the Local Authority.

We produced the tender documents including a detailed specification and Bill of quantities. During the tender period we replied to any technical clarifications and attended a day on site with the prospective contractors. Following tender completion, we reviewed the responses and recommended a preferred bidder together with a contractual risk register.

During the construction period, We worked under the NEC3 Short Contract as the clients representative and supervising engineer. We visited site at least twice a week to assess the progress of the contractor against their programme, to make sure they undertook the work in line with their Risk Assessment Method Statement and to make sure the build quality was to our specification. There were known difficulties on site due to the restricted access and unstable nature of the made ground covering the site. The contractor was not dealing with these issues adequately, resulting in unsafe working conditions and delays to the programme. In line with the contract, we issued an early warning to the contractor to bring the site back into a safe working condition before work continued. Numerous compensation events were claimed by the contractor for additional time and additional cost for this and other issues encountered. Each compensation event was assessed and accepted or challenged by us and considered in the monthly requests for payment. The final client account for the works came in under budget but the project was delayed due to contractor owned risks.


Our ‘cradle to grave’ approach allowed us to integrate all aspects of the project and to work on behalf of the client to ensure the project was delivered safely to specification and within budget.