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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
This project was started in 2024 under MMO marine licence L/2023/00294/1. It was undertaken by Lymington Harbour Commissioners and working with Land and Water Services Ltd (LAWS) with funding and support from the Environment Agency. The Crown Estate, the Hampshire and Isle of Wight Wildlife Trust (HIWWT) and other stakeholders.
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 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. It is dropped from split hopper barges that can access upper mudflat at high water on larger spring tides. In a novel move, this sediment, having been left to settle and stabilise, is now being moved up the shoreline to raise the bed elevation of a deteriorating part of the island.
For the first two annual campaigns (in 2024 an 2025) of this sediment relocation was done using a Saltmarsh Restoration Drag Box (SRDB) technique. This involves drawing a steel ‘drag box’ along a winch line. The winch line is held between pulleys on a spud barge moored to seaward of the dredge sediment placement area and an excavator positioned on the landward side of the receiving/restoration site.
The first trial of his approach (in September 2024) was challenging and the amount of sediment moved was a lot lower than planned. 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. The lessons are captured in a report (ABPmer (2025) see link below.
On completion, only two small raised mounds of sediment were created. The northernmost of these was high enough in elevation to be suitable for marsh plant growth. A year later it had a 60% cover of annual samphire and sea blite (see photo). This rapid rate of plant growth will be de to the rich seed source in this environment.
The drag box approach was trialled again in 2025 and involved working over shorter distances than in 2024. Monitoring and oversight of these campaigns is continuing.
ABPmer
Quayside Suite
Medina Chambers
Town Quay
Southampton
SO14 2AQ