Intertidal Mudflats & Sandflats
Intertidal mudflats and sandflats are submerged at high tide and exposed at low tide. They form a major component of estuaries and large shallow inlets and bays in the UK but also occur extensively along the open coast and in lagoonal inlets. The physical structure of the intertidal flats ranges from mobile, coarse-sand beaches on wave-exposed coasts to stable, fine-sediment mudflats in estuaries and other marine inlets. This habitat type can be divided into three broad categories- clean sands, muddy sands and muds – although in practice there is a continuous gradation between them. Within this range, the flora and faunal communities vary according to the type of sediment, its stability and the salinity of the water.
The intertidal part of the Severn Estuary supports extensive mudflats and sandflats. These cover an area of approximately 20,300 ha – the fourth largest area in a UK estuary. It represents approximately 7% of the total UK resource of intertidal mudflats and sandflats and approximately 10% of the UK Natura 2000 resource, by area. There are extensive mudflats fronting the Welsh shore and Bridgwater Bay, and large banks of clean sands in the more central parts of the Estuary at Middle and Welsh Grounds.
The high biomass of invertebrates in the mudflats of the Severn provide an important food source for a diverse range and large number of fish and benthic predators. These intertidal areas are therefore important in supporting the fish assemblage sub-feature of the SAC and Ramsar Site.
Mudflats also provide a valuable feeding, roosting and resting area for a wide range of species of wading birds and waterfowl and are therefore important supporting habitats for the wintering and passage bird features of the SPA and Ramsar Site. The type of sediment, its stability and the salinity of the water have a large influence on the wildlife species present.
For more information, please see the Severn Estuary EMS Regulation 33 Conservation Advice Package.