Salt marsh - Natural flood defence and wildlife haven?

Article by Graeme Hazard 19 December 2017

Once seen as coastal wasteland salt marshes are the upper vegetated section of coastal mudflats which are flooded and drained by the tides and can be found all around our low lying shorelines in estuaries and bays.


Salt marshes are formed in the upper tidal zone and can be identified by plants which are able to withstand regular submersion in seawater.  In areas where tides emit low wave energy fine sediments from rivers and the sea settle and allow algae and plants such as Samphire, Sea Aster and more common Glassworts (plants that thrive in saline habitats) and grasses to grow.


Where suitable, the maintenance of salt marshes can provide a cost effective sustainable way to prevent the erosion of our coastline and help protect properties at risk of flooding. There is also the added benefit of conserving our shores natural ecosystems and habitats. Salt marshes can contribute to our natural flood and coastal defences as they dissipate wave energy, studies show that these natural flood defences can reduce the height of waves in storm surge conditions by almost 20% helping to decrease the effects of flooding and coastal erosion. The stabilized ground on which the salt marshes grow also reduces scour and the ability of waves to undermine hard engineered coastal flood defences, although overtime and with rising sea levels coastal defences can stop the natural migration of the salt marsh and its vegetation (coastal squeeze).


One approach to encouraging new salt marsh creation is the managed retreat of manmade coastal defences which allows space to be created on the shoreline for the marsh to become established. In August 2017 the Environment Agency and the Royal Society for the Protection of Birds saw the completion of the Hesketh Out Marsh East Managed Realignment Scheme become the largest scheme of its kind in the UK. The project involved restoring 160 hectares of land which was reclaimed from the estuary for growing crops in the 1980’s, back to marshland by reinstating manmade embankments in shore, sections of earlier flood embankments were then removed allowing tides in to flood and drain the land. Not only does the scheme help to protect 140 properties and nearby infrastructure by dissipating tidal energy but it also provides an environment in which fish, migrating birds and marine life can now thrive.


Under the right conditions there may be a natural solution to help limit coastal erosion while protecting properties and conserving wildlife; it may not always be the case that hard engineering is the only answer to protecting our shoreline.


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