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ABPmer
Quayside Suite
Medina Chambers
Town Quay
Southampton
SO14 2AQ
2016
Unmanaged realignment
United Kingdom
Stour Estuary (Essex)
1.05821
51.95337
Mudflat
6.5 Hectares
Other
Cattawade North Marsh in the upper reach of the Stour Estuary (on the east coast of England) is a valuable example of a site where managed measures have been put in place in response to an unmanaged flood event. What happened here, and the decisions that were taken in response, illustrate the balance that needs to be struck, and can be struck, between achieving ecoligical value while also protecting important socio-economic assets (power lines and railway routes)
The site was was grazing marsh until 2013 when a tidal surge and then successive high tides overtopped and weakened the sea wall. With this hinterland flooding, 6.5 ha of intertidal mud was created. A secondary beach also developed in 2017/18 close to this location. This site is bounded on the west by the A120 road crossing, on the east by a railway embankment and river wall and by residential and commercial properties on the northern boundary.
Although not within the Stour estuary SSSI/SPA it was agreed that this extra mudflat was of value as functionally linked habitat with the SPA. It is expected to potentially provide an extra hour of feeding for birds on a rising tide within less than a kilometre of the high tide roost at Brantham (TM11146,32772)
Later Natural England and the Environment Agency, in discussions with Network Rail and UK Power Networks, secured an agreement that the breach could be sealed temporarily to allow access for maintenance operations, but that a flood control structure will be installed to allow the continued development of the new intertidal habitat at this location.
The flood control works are to be carried out in two phases, the first (in 2025) is to protect the existing tower which sits within the Network Rail land. This is to be done by capping the tower legs in concrete; the concrete is then likely to be clad to match the network rail bank. The second phase was to replace the overhead lines with underground cables, part of this was done using a directional drill within the new intertidal habitat.
In late June 2023 there were 11 Little Ringed Plovers (3 well-grown juveniles and 8 adults) on the site which might well have been 4 pairs. The birds were able to breed because of the bare muds and gravels created by the flooding and subsequent closure of the breach to permit works to proceed and were present until September. One of the pairs was seen displaying in July and on July 9th there were three chicks. In summary there were 14 individuals at the site over the period comprising 8 adult and 3 fledged juvs and a further 3 chicks of which 2 survived to fledging and 1 disappeared. The potential for Little Ringed Plover to breed on the site when dry in 2025 may mean that work is delayed while birds are nesting, or chicks are present.
When the works are completed, and tidal exchange is restored to the site there may be opportunities to create breeding sites for Ringed plover and Little Ringed Plover at the base of the power line poles and the edges of the railway and road embankments. Currently there are no agreed mechanisms for the creation of saltmarsh in the new inter-tidal, but this is something that may be discussed in future. There is some indication that saltmarsh may develop naturally, particularly around the bases of pylons.
ABPmer
Quayside Suite
Medina Chambers
Town Quay
Southampton
SO14 2AQ