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ABPmer
Quayside Suite
Medina Chambers
Town Quay
Southampton
SO14 2AQ
2024
Beneficial use of dredged sediment
United Kingdom
Lymington Estuary
-1.5051484
50.750169
Saltmarsh
0.06 Hectares
Biodiversity Enhancement
Climate Change (Greenhouse Gas) Mitigation
Demonstration or Pilot Project
Habitat Enhancement
Other
To enhance saltmarshes at the entrance to Limington Harbour, several projects have been undertaken since 2011 which involve beneficially using dredge sediment. These projects are captured elsewhere on the OMREg site.
This project was the most recent one. It was started in 2024 under MMO marine licence L/2023/00294/1. Under which, Lymington Harbour Commissioners are working with Land and Water Services Ltd (LAWS), the Hampshire and Isle of Wight Wildlife Trust (HIWWT) and other stakeholders to raise the bed elevation of an ecologically deteriorating central part of the island.
This restoration area (10 ha in total) was once covered in saltmarsh plants but is now unvegetated and in an ecologically poor condition. To return vegetation to this area, dredged sediment is being used to raise the intertidal bed level so that it matches, or even exceeds, the height of the surrounding healthier marsh. The intention is to expand the healthier vegetated marsh and provide much needed habitat for breeding seabirds as well as help delay the loss of this large eroding marsh island.
The approach being taken is unique in the UK and possibly globally. It involves using dredged sediment that has already been, and will be, placed in front of Boiler Marsh. This sediment is deposited at a licenced deposit ground at the lower lying seaward edges of Boiler Marsh using a ‘bottom placement’ approach. For this approach, sediment is dropped directly from split hopper barges that can access upper mudflat at high water on larger spring tides.
For the first campaign this sediment movement was done using a new Saltmarsh Restoration Drag Box (SRDB) technique. This involves drawing a steel ‘drag box’ with load bearing skis along a winch line from the low to the high shore. The winch line is held between pulleys on a spud barge moored temporarily to seaward of the dredge sediment placement area and an excavator positioned on the landward side of the receiving/restoration site.
A drag box was also used at the West Itchenor site (see separate OMReg page). However the first trial of his approach (in September 2024) here was challenging and not successful. The distance of transit was too large and there were technical difficulties with applying this technique at this site. There were also adverse weather conditions that had to be contended with.
For this first campaign, the amount of sediment moved was a lot lower than planned. On completion, only two small raised mounds of sediment were created. The northernmost of these was high in elevation and is most likely, depending on how it settles, to be suitable for marsh plant growth. The lessons are captured in a report (ABPmer (2025) see link below) and the survey work will also continue during 2025 in accordance with the monitoring plan requirements. . This will provide further lessons of the 2024 campaign one year on which will then be reported at the end of this calendar year.
ABPmer
Quayside Suite
Medina Chambers
Town Quay
Southampton
SO14 2AQ