Beneficial use of dredged sediment
Coarse sediment barrier protecting saltmarshes
Climate Change (Sea Level Rise) Mitigation
Flood Risk Management
This project involved the placement of dredged material (sand and gravel) to protect the islands, saltmarshes and harbour around west Mersea (Blackwater Estuary, Essex). In total around of 98,000 m³ of sand and gravel was deposited at four separate sites in Mersea Harbour (Cobmarsh Island, Old Hall Marsh, Tollesbury Wick and Packing Marsh Island).
The material was dredged from the deepening of a navigation channel at the Port of Harwich. The dredger deposited at high water as close as possible to the disposal areas. Disposal was done either by direct pumping of material over the bow (rainbowing) or via a floating pipeline. Part of the site also needed fencing to retain the sediments (see Exo Environmental Video on this page)
This initiative (called the ‘Mersea Harbour and Tollesbury Wick Climate Change Adaptation Recharge Project’) was overseen by the Mersea Harbour Protection Trust. It was planned well in advance so that it deliberately coincided with capital dredging work at Harwich.
This project is, therefore, a valuable example of how it is possible for consent for a beneficial use project to be achieved in advance of the need to undertake the dredging work itself. This required independent vision from, and advance communications between, the provider and the user of the sediment resource.
The project also highlighted regulatory challenges and timescales. After a relatively long and costly process, permissions were obtained from the Marine Management Organisation (MMO) in March 2018. The work was then carried out at the end of 2021 and early 2022.
This project is accompanied by a relatively detailed monitoring programme (notably drone work – see images from Jim Pullen Surveys on this page) which will describe the effects of the work during its implementation as well as the behaviour of the deposited sediments and how they ecological develop over time. It is expected that valuable lessons will be learned for future projects as a result of this work.