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Estuaries

Estuaries, including harbours and flooded river valleys (known as rias), are the places where the regions great rivers meet the sea. They are tidal and are mixtures of freshwater washed down from the hills and seawater coming in from the oceans.

Estuaries are complex places. They encompass many different `sub’ habitats such as mudflats, saltmarshes and rocky and sandy shores. The water quality itself also varies, with different amounts of salt present in the water as the river approaches the sea. All of these have a bearing on the diversity of wildlife present on our estuaries.

The estuaries of the South West are a very varied and valuable resource. They range from the Severn, one of the country's largest estuaries with the second largest tidal range in the world, through smaller estuaries such as the Hayle, and rias such as the Salcombe–Kingsbridge estuary, to semi-enclosed lagoon-like sites such as Poole Harbour.

Whilst not supporting the vast numbers of waterfowl supported on estuaries elsewhere in the country, South West estuaries support relatively large populations of many nationally rare species, and act as vital refuge areas in periods of severe weather. The range of habitats associated with the variety of estuary types is reflected in the diversity of invertebrate life, with several estuaries supporting rare crustaceans, hydroids and algae.

The estuaries of the South West of England are extremely valuable. They have not, on the whole, experienced the large-scale loss of habitat through building development that has affected other sites in the country.

The South West is estimated to contain c16,700 ha of mud and sandflats, representing 8% of the UK total (c200,000 ha), and c2,900 ha of saltmarsh, representing 6% of the UK total (c40-45,000 ha). The folowing table lists examples of important sites in the region.

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The following are examples of species that depend on coastal and floodplain grazing marsh, some of which are of conservation concern:

Historically our estuaries have be damaged largely through building development. Other problems include pollution from industrial discharges and sewage and over exploitation of shellfisheries.

Notable historic losses of habitat have occurred in Poole Harbour (harbour construction mid 1980s, marinas in 1980s–90s) and on the Exe (loss of intertidal mud and saltmarsh, and grazing marsh due to construction of the railways in mid 19th Century), Tamar (naval dockyards and other developments over several centuries), Plym (reclamation in 1800s and 1970s), Camel (flood defence), Taw Torridge (agriculture over last 200 years, marinas and flood defence in 1980s and 1990s), Hayle (post 1945 infilling of Copperhouse, building development south of causeway) and the Severn (Avonmouth and Portbury docks, Cardiff Bay barrage on the Welsh shore in 1990s).

A future problem will result from sea level rise, as our existing estuaries face being submerged.

Many different organisations are currently working together drawing different plans which, if successful, will provide a safe future for our estuaries. These plans aim to get everyone`s agreement on the limits of development on estuaries, the quality of water and the safety of wildlife that depends on estuaries.

Alongside these plans, many of our estuaries contain nature reserves managed for conservation. For instance the RSPB has reserves on the Exe, Taw Torridge, Poole, Hayle and the National Trust is currently targeting estuaries in the Enterprise Neptune programme; there are also Voluntary Marine Conservation Areas on the Helford and at Polzeath, St Mawes, Looe.

It may also be possible to recreate estuary habitats such as saltmarsh.