A design and build project to undertake improvements to an existing debris screen complete with fish pass, which is located within Chester Burn. The debris screen forms part of a series of flood defence measures used to reduce the flood risk to residential properties, non-residential properties and infrastructure within Chester le Street town centre. Specifically, the works included the relocation of the debris screen, and the upgrade of access arrangements. The project will improve operational efficiency in the removal of debris from the burn, reducing the risk of blockages. The project was delivered in close co-ordination with the Environment Agency, and was programmed in accordance with the Salmon migratory season.
Prior to onsite construction, our project team were responsible for working with the Environment Agency to secure the necessary Food Risk Activity Permit. Initial works included the construction of a temporary dam consisting of sand bags and ducting, allowing the burn to continue to flow, whilst creating a dry area. This arrangement was constructed at both the existing screen location and the new downstream location. The debris screen was broken out from its existing location, complete with piers and ground slab. At a new location, approximately 4m downstream of the existing location, a new ground slab was constructed acting as the base for the debris screen. Temporary formwork was then erected, allowing the installation of reinforcement and pouring of concrete to form new pier structures. The existing debris screen and fish pass was then fixed to the piers using bolted brackets.
Following relocation of the debris screen, the existing access ramp was extended. This involved excavation of existing bedrock and concrete. Required drainage and ducting has been incorporated into the new section of ramp. At both an upstream and downstream location, existing vegetation was then stripped back to allow the excavation of a waterside trench, used to install erosion protection. Terram sheeting together with rock bags were then installed as a bank protection system to the burn. A new outfall pipe has been incorporated within the erosion protection measures. Rock bags have also been installed across the perimeter of the access ramp to prevent future under scour.
During the initial stages of the contract, the project team encountered high river flows as a result heavy rain. To mitigate against delay, weekend working was required to achieve the agreed programme. Due to the location of the works, significant consideration was given to access requirements with a bespoke traffic management plan produced. This involved co-ordinating plant movements and deliveries along a narrow single lane access road.