- On 24th November 2017
- In Dredging, Ecology, Engineering, Project Management, Sediment Management
- By William Coulet
The first phase of the Brightlingsea Dredging and Restoration Year 2 work package aimed to place accumulated sediments dredged from the South Channel within the St Osyth Borrow Pits. These twenty three (23) pits, approximately 30x30x1.5m in size, were originally excavated in the 1960’s along the seaward face of the local coastal flood defences following the 1953 floods, in order to strengthen the damaged structures and improve resilience of the area to future storm events.
To achieve this, a series of connecting excavations, dams and drop-board sluice gates were installed by subcontractors, Miles Water Engineering. Following the completion of the groundworks, Royal Smals were commissioned to employ their Cutter Suction Dredger (CSD) “Phoenix” to dredge approximately 12,000m3 and hydraulically pump the arising sediments up to 1.7km along the base of the flood wall to fill the borrow pits. During the pumping of this material, a series of y-unions and valves were used and operated to allow the close control of material flow. Once filled, dredged material within the pits was allowed to deposit out of suspension over the following 12hr period before the supernatant was subsequently drained through the careful operation of the drop-board timber sluice gates. Repeating this process over three successive neap tide periods allowed the maximum fill and storage volumes within the pits to be achieved, whilst mitigating for potential sediment losses due to erosion during spring tide high water flow. Overtopping of the pits during the final filling process, encouraged by Natural England, further maximised the fill achieved.
Throughout the operations, Exo provided site management services and expertise, including; coordination of works between the harbour, dredging and restoration teams, liaising with both contractors and members of the public to ensure understanding and encourage support of the project and to confirm all works and mitigation measures put in place were adhered to.
We’ll now keep an eye on the site, maintaining the infrastructure through the winter period whilst we eagerly await the arrival of spring to both warm up and to monitor vegetation colonisation across the restoration site. This will form part of our long-term research into the beneficial use of dredged material and its role in supporting habitat creation, restoration and enhancement applications.