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ABPmer
Quayside Suite
Medina Chambers
Town Quay
Southampton
SO14 2AQ
2023
Managed realignment
United Kingdom
Blackwater Estuary
0.71650654
51.720276
Saltmarsh
4.2 Hectares
Biodiversity Enhancement
Create a More Natural Shoreline
Habitat Enhancement
From around 2015/16 onwards the National Trust (who own and manage Northey Island) has been carrying out several new coastal adaptation and habitat enhancement initiatives on the island. These all follow on from the first ever managed realignment in the UK which was carried out on this island back in 1991
These projects (past and present) are captured across his OMReg database and include the beneficial use of dredge sediment on the West side of the island and another new managed realignment of an embankment to the south.
As one major component of this integrated mix of initiatives, a new 4 hectare managed realignment was carried out the south east side of the island. This was done from 2021 to 2023.
In 2021 a new counter wall (closing embankment) was constructed first (to allow time for settlement of the soils and establishment of vegetation). This new embankment replaced one that was in a poor condition and had failed. However, the alignment of the new bank was carefully designed to adopt a sinuous alignment (rather than linear) for aesthetics and to protect a badger sett in an adjacent hedgerow and ditch system.
Around 3,000 Essex Blocks (removed from the south embankment prior to its breaching in 2019) were re-used on the landward face of this new bank. they were buried just beneath the final surface layer to prevent badgers forming setts in the new structure. The topsoil within the footprint of the banks (including any vegetation) was stripped and placed in a temporary stockpile until it could be replaced onto the newly formed (bare) surface of these banks. Behind the main embankment a freshwater pond and a feeder ditch (with pools) was also created.
The central bank was also constructed with a raised clay platform at its eastern end, on which a bird hide was constructed. This was designed to have views overlooking the freshwater pond (to west), the managed realignment area (to south), and the existing saltmarsh (to east). Information boards about the saltmarsh creation through managed realignment were prepared by the National Trust and included inside the hide.
During 2022, preparatory excavations were made into the land surface to create a main creek and ‘starter creeks’ that would (after sea wall breaching) allow for efficient tidal water ingress/egress across the site (to help deliver sediment, nutrients and seeds to the new intertidal area after the embankment lowering and breaching).
During 2023, the embankment was lowered and breached in a controlled manner (in advance of its otherwise likely imminent uncontrolled failure). This was undertaken along two sections of embankment, one approximately 200m section was to the rear of the 1991 managed realignment site and the other, approximately 50m section, further to the north.
The work at Northey Island is possible thanks to National Trust Neptune Funding and EU funding under the LIFE on the Edge Project.
ABPmer
Quayside Suite
Medina Chambers
Town Quay
Southampton
SO14 2AQ