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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 (east coast of England) is a good example of a site where management and site enhancement measures have been put in place retrospectively in response to an unmanaged flood event.
What happened here, and the decisions taken in response, illustrate the balance that can be struck, between achieving ecological value and protecting important socio-economic assets (in this case power lines and railway routes). At this site, these measures are being undertaken by Network Rail with advice and support from Natural England and the RSPB.
The site was was grazing marsh until 2013 when a tidal surge an 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 in the Stour estuary SSSI/SPA, it was agreed that this new mudflat was ecologically linked to the SPA because it was providing a feeding resource for SPA waterbird populations. Perhaps more significantly, due its elevation, it was providing an extra hour of feeding for birds on a rising tide in an area that is less than a kilometre from the high tide roost at Brantham (TM11146,32772).
After the first breach, Natural England and the Environment Agency, in discussions with Network Rail and UK Power Networks, secured an agreement that this breach could be sealed temporarily to allow access for maintenance operations. However, it was requested that flood control management be undertaken 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 phase (in 2025) involves protecting 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.
As part of this protective work, plans were developed to create individual island at the base of the power line poles and the edges of the railway and road embankment. These are designed to provide breeding and high-water roosting habitat for birds locally (including for species such as Ringed Plover and Little Ringed Plover) but also to further shield the railway foundations These islands were designed with a rounded and elevated profile on their wave-exposed sides and a shallower 'feathered' arrangement on their sheltered face. This morphology was designed to promote accretion between the islands and the railway line to further enhance the protection of the rail foundations.
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.
Valuable studies of waterbird responses during this whole process are being undertaken to inform management decisions. 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 juveniles 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 latest management works are completed, and tidal exchange is restored to the site, it is likely that the mudflat may increasingly become saltmarsh, particularly around the bases of pylons and the new island features.
ABPmer
Quayside Suite
Medina Chambers
Town Quay
Southampton
SO14 2AQ