Last update:

1st May 2008

Quick links:

What are estuaries?

Monitoring estuary quality

Estuaries in the South West

Estuary quality in the South West

Regional estuary water quality

Data agreement

Severn Estuary

Dart Estuary

SW estuary modelling projects

Pressures on estuaries

Pollution and estuaries

Development and estuaries

Estuarine habitat loss

Bathing waters

Shellfish waters

Rivers

Groundwater

Drinking water

Discharges & releases

Diffuse pollution

Useful websites:

South West Biodiversity Partnership

SW Habitat Action Plan for estuaries

Local Biodiversity Action Plan in North Devon

Environment Agency - estuaries

Water Framework Directive

Severn Estuary Partnership

Camborne School of Mines - mining and estuaries in Cornwall

Estuaries

New on this page...

• Estuaries update - including information on the water framework directive
• Cleaner Coasts, Healthier Seas - state of the marine environment in England and Wales
• Defra launches consultation on draft Marine Bill and Shoreline Management Plans

The South West Biodiversity Audit published in 1998 found that the region had 8% of the UK’s total of mud and sandflats, and 6% of saltmarsh, are be found in the region.

What are estuaries and rias?

Estuaries are tidal basins where the rivers meet the sea. They are characterised by wide inlets subject to tidal incursion and a salinity range in the water decreasing towards the head of the estuary from the mouth. In this context, estuaries will also include the fringing vegetation such as saltmarshes of all types through to brackish marshes.

Estuaries are haven's for wildlife, recreation areas and can be important industrial corridors.

Estuaries provide a complex of habitats, including:

• tidal waters
• intertidal mudflats
• saltmarshes
• rocky and sandy substrates (see Habitat Action Plan for rocky seabeds and sand dunes)
• subtidal habitats
• water column and surface

Rias are drowned river valleys created by land subsidence, a rise in sea level, or a combination of both, forming deep narrow, well defined channels which have a large marine influence, such as high salinity

Source: South West Biodiversity Partnership.

Due to the large range of habitats found in estuaries many contain designated conservation areas such as Special Areas of Conservation (SACs) and RAMSAR sites. For further information see the biodiversity page.

Estuaries in the South West

The South West is estimated to contain around 16,700 hectares of mud and sandflats, representing 8% of the UK total (c200,000 ha) and around 2,900 hectares of salt marsh, representing 6% of the UK total (c40-45 000 ha)
The South West’s estuaries include the Severn, one of the country’s largest (with one of the highest tidal ranges in the world).

The South West’s estuaries include the Severn, one of the country’s largest (with one of the highest tidal ranges in the world). Important estuaries in the South West also include:

• Severn Estuary
• Fal, Helford, Looe, Fowey (Cornwall)
• Tamar complex (Cornwall / Devon)
• Exe, Salcombe-Kingsbridge, Yealm, Dart, Taw - Torridge (Devon)
• Poole Bay / Harbour, Portland Harbours (Dorset)
• Bridgwater Bay (Somerset)

There is a Habitat Action Plan for estuaries in the South West as well as a Local Biodiversity Action Plan in North Devon.

Many of the Estuaries in the South West contain designated areas for conservation these include;

Monitoring estuary quality

Estuaries are included in the Water Framework Directive (WFD) as transitional water bodies. The WFD main aims are to improve and protect water quality in inland and coastal waters while reducing any danger a water body poses, such as flooding. It's also designed to stop the deterioration of wetlands and improve aquatic habitats for wildlife and will concentrate even more on biological quality, including plants and fish.

The Water Framework Directive requires a large range of pressures to be assessed and will provide a more complete assessment of the ecological quality of transitional waters. Data will be collected between 2006 to 2008, the classification of these water bodies will be released in River Basin Plans in 2009.

Transitional Waters identified under the WFD in the South West of England

A range of monitoring elements will be collected in transitional waters including Phytoplankton, Chlorophyll, Nutrients, water chemistry samples, transitional fish, macroalgae, fucoid extent, saltmarsh and sea grass. Varying amounts of monitoring will take place in some of these water bodies depending on their size and characteristics.

More information about the Water Framework Directive is available from the Environment Agency.

A more local perspective

The Severn Estuary

The Severn estuary is one of Britain's largest estuaries spanning English and Welsh coastlines and, with the second highest tidal range in the world, is one of the most dynamic. It runs from just above Gloucester to Hurlstone point near Minehead on the English coast and Nash Point (West of Barry) on the Welsh coast.

A large proportion of the Estuary is designated under the International Ramsar Convention and is a SPA (Special Protection Area) under European Conservation Directives. A description of the SPA is available from the Joint Nature Conservation Committee.

The Severn Estuary Partnership (SEP) was established in 1995 and aims to:

• Improve communication, understanding and co-operation between agencies, users and local people.
• Provide opportunities for wide ranging community involvement.
• Co-ordinate and monitor implementation of plans within the Estuary.
• Establish a permanent management group to include and interact with local, regional and national policy process.

The Severn Estuary Gateway website details Estuary Management Groups on the Severn Estuary.

The Dart Estuary

The River Dart forms an estuarine system of immense natural beauty with national and international importance. It contains a rich and diverse wildlife, landscape and historic heritage valued greatly by those who live in, work or visit the area. It is also a source of livelihood for the local population whether through tourism, fishing or any one of a host of different activities taking place in, or around the river.

There is no single agency or organisation with responsibility for the estuary as a whole. A consortium of local agencies with responsibilities within the Dart Estuary have acknowledged the interrelationships of their activities and have agreed jointly to promote the development of an EMP for the Dart. The organisations concerned are:

• the Dart Harbour and Navigation Authority
• South Hams District Council
• Environment Agency
• South West Water Services Ltd.
• English Nature
• Duchy of Cornwall

These organisations have collaborated to develop the Dart Estuary Environmental Management Plan, which aims to integrate the diverse range of economic and leisure activities that take place so that they do not conflict or threaten the sustainability of the natural environment.

South West estuary modelling projects

Modelling projects have been undertaken on estuaries in the South West, details of which are available on the South West Environmental Modelling Group's web pages. These include:

• Fal estuary
• Truro estuary
• Fowey estuary
• Dart estuary
• Exe estuary
• Taw and Torridge estuary
• Axe estuary

Pressures on estuaries

The main pressures on South West estuaries are summarised in the SW Estuaries Habitat Action Plan as being:

• Pollution from industrial discharges
• Enrichment from run-off and sewage
• Recreation and disturbance
• Sea level rise and 'coastal squeeze'
• Potential over-exploitation of shell fisheries
• Lack of biological information and data concerning/marine/sub-tidal features.
• Development pressure (in the immediate future this will concentrate on the Severn, particularly on the Welsh side e.g. Cardiff Bay, Gwent levels)
  

Pollution

Due largely to geology and mining activities, some sediments in the Gannel, Hayle, Fal, Looe and Tamar have been identified as amongst the poorest quality in the country for each of the listed metals:

• Gannel     lead, tin, silver, arsenic
• Hayle       tin, zinc, silver, arsenic, copper
• Fal           lead, tin, zinc, silver, arsenic, copper
• Looe        lead, silver
• Tamar      lead, arsenic, copper

However, the sediments of the Erme and Avon Estuaries have been identified as the least metal-contaminated in England and Wales.

Research by the Camborne School of Mines has found localised contamination from tributyltin in the Fal estuary around Falmouth docks. Tributyltin was used extensively as an anti-fouling agent in shipping but is now recognised as being a toxic contaminant. Their research also found that the intensity and scale of the Cornish metal and china clay mining industry has had a very significant impact on the sediment chemistry in the estuary and also on the rate of sediment deposition in the estuary. The two main types of mine waste which have been discharged into the estuary are:

• Acid mine drainage - water discharged from local mines which may carry metals in solution
• Particulate mine waste tailings, comprising both the gangue minerals and also unrecovered grains of the ore minerals.

More details about this case study, the impacts of hard rock mining on estuary quality and the Wheal Jane pollution incident are available on the Camborne School of Mines website.

English Nature states that many important marine and estuarine wildlife sites are at risk from nutrient enrichment and toxic chemicals that are discharged from the land and waterways into the water column. Current research indicates that even subtle lowering of oxygen levels in seawater and increases in turbidity are sufficient to disrupt the behaviour, growth and survival of some fish species.

The Torrey Canyon oil spill in 1967 is the worst pollution incident off the Cornish coast., when 14,000 tonnes of oil, borne on the highest spring tides for half a century, were stranded on the Cornish coastline.

Diffuse pollution is a problem in the Dart Estuary, due to the very steep sided nature of the Dart Valley, which has what is known as a 'flashy' catchment - meaning that rain falling on the land surrounding is seen almost instantly in the river. Unlike rivers that have a large flood plain there is no time for pollutants, or excess nutrients, to be absorbed before they turn up in the river. There are also many examples of where farmland is used right down to the waters edge, meaning that there are not many buffer zones around the edges of the estuary where run-off can be naturally filtered before it reaches the river. There has been an increase in intensive methods of farming means more slurry is produced and stored on farms as well as an increase in the number of organic farms, which make greater use of natural fertilisers which, if not carefully applied, can produce run-off with lots of bacteria. See the Dart Estuary Environmental Management website for more information.

Development / unsustainable use

The South West Biodiversity Partnership identifies that, as natural harbours, estuaries have been the focus of development from the early ages of settlement and trading. They have always been the subject of human activity of some sort, either through water from development taking out estuary habitat directly or in time not allowing the estuary to respond naturally to sea level rise.

Coastal squeeze can occur when the construction of sea walls hastens the erosion of mudflats and marshes on their seaward side. If left to themselves, coastal habitats would naturally adjust to sea level rise, and move inland. Construction of a sea wall prevents such movement and, in the event of sea level rise, leads to drowning of the inter-tidal areas.

Habitat change

According to the SW Estuaries Habitat Action Plan, notable historic losses of habitat have occurred in:

• Poole Harbour (harbour construction mid 1980's, marinas in 1980s-1990s)
• Exe (loss of intertidal mud and salt marsh, 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 1990's)
• Hayle (post 1945 infilling of Copperhouse, land-claim south of causeway) and the
• Severn (Avonmouth and Portbury docks, Cardiff Bay barrage on the Welsh shore in 1990s).

NOTE:

All data & information used here that has been provided by the Environment Agency is covered by the Agency's standard data re-use licence. The licence conditions are viewable at http://www.environment-agency.gov.uk/other/help/196644/?version=1&lang=_e