Tidal range is the difference in height between high tide and low tide . Tides are the rise and fall of sea levels caused by gravitational forces exerted by the Moon and Sun , by Earth's rotation and by centrifugal force caused by Earth's progression around the Earth-Moon barycenter . Tidal range depends on time and location.
36-626: Severn Area Rescue Association ( SARA ) or Severn Rescue is an independent, marine and land based, search and rescue organisation covering the Severn Estuary and upper reaches of the River Severn . SARA is the largest independent lifeboat service in the UK, second only to the RNLI , with 22 operational inshore lifeboats , 20 vehicles and approximately 200 personnel. They receive no funding from
72-624: A registered charity , all funding is raised by way of donations. All SARA stations are members of Mountain Rescue England and Wales and SARA is part of the South West England Rescue Association (SWERA). SARA Beachley is a recognised Mountain Rescue Post, and operates an assistance capacity to the fire brigade for cliff rescues. SARA is also heavily involved in land searches, which are becoming
108-445: A lake of 185 square miles (479 km ) with a potential energy depth of 14 metres (46 ft). Tidal power only runs for around ten hours a day, but by using the enclosed lake as a reservoir of potential energy more hours of operation could be achieved. Other energy sources, such as wind and solar power, also create electricity at times that do not always match when it is needed. Excess power could be stored by pumping water uphill , as
144-435: A more frequent requirement. The need for SARA is increasing with more callouts evident year on year. The variety and range of callouts is also increasing. Typical incidents involve boats or persons in difficulty in one of the rivers SARA cover, but also the search for missing persons, animal rescue and flood relief are becoming common. SARA has become a Royal Yachting Association (RYA) recognised teaching establishment. With
180-789: A new station was opened at Upper Arley in the Wyre Forest. SARA Wyre Forest is currently based in Kidderminster and operates in the largest geographical area of the four stations covering Shropshire , Worcestershire and parts of Herefordshire and the West Midlands county . SARA Wyre Forest operates three rescue boats, one 4x4 and one road ambulance, as well as housing and maintaining one of SARA's Incident Support Units. SARA currently operates from six stations, Beachley , Newport, Sharpness , Tewkesbury (Gloucestershire Water Rescue Centre), Upton on Severn and Wyre Forest and
216-712: A number of certified instructors SARA is able to teach and certify its own members to RYA Powerboat Levels 1 & 2 and RYA Safety Boat. This service is also offered to the public to help bring awareness and funding to the organisation. Severn Estuary The Severn Estuary ( Welsh : Aber Hafren ) is the estuary of the River Severn , flowing into the Bristol Channel between South West England (from North Somerset, Bristol and South Gloucestershire) and South Wales (from Cardiff, Newport to Monmouthshire). Its very high tidal range , approximately 50 feet (15 m), creates valuable intertidal habitats and has led to
252-595: Is To bring together all those involved in the development, management and use of the Estuary within a framework which encourages the integration of their interests and responsibilities to achieve common objectives . In 2001 SEP published the Strategy for the Severn Estuary , which sets out a plan for the management of the estuary. SEP uses a geographically extended definition of the Severn Estuary, beginning at
288-424: Is a small rocky island of 0.24 hectares (0.6 acres), with scrub vegetation, approximately three miles north of Portishead. Its rocky southern foreshore marks the boundary between England and Wales, but the island itself is reckoned administratively to Monmouthshire , Wales. The estuary is about 2 miles (3.2 km) wide at Aust, and about 9 miles (14 km) wide between Cardiff and Weston-super-Mare. It has one of
324-554: Is already done at a variety of other installations in the UK. The UK Government shelved the plans in the late 1980s due largely to cost issues and local environmental concerns. However, this was before recent huge rises in the price of energy, and before global warming had started to be taken seriously. In April 2006 the Welsh Assembly approved the idea of utilising the tidal power, but the RSPB has raised serious concerns about
360-415: Is calculated as the difference between mean high water (i.e., the average high tide level) and mean low water (the average low tide level). The typical tidal range in the open ocean is about 1 metre (3 feet) – mapped in blue and green at right. Mean ranges near coasts vary from near zero to 11.7 metres (38.4 feet), with the range depending on the volume of water adjacent to the coast, and the geography of
396-577: Is designated as a Ramsar site . The estuary is recognised as a Special Protection Area (SPA) under the EC Directive on the conservation of Wild Birds. The estuary is recognised as a Special Area of Conservation (SAC) under the EU Habitats Directive. Parts of the estuary have also been designated a Site of Special Scientific Interest . The SSSI includes most of the foreshore upstream from Cardiff and Brean Down and most of
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#1732780639516432-618: Is the international importance for wintering and wading birds of passage, and of estuarine habits of outstanding ornithological significance. It is stated that the estuary supports over 10% of the British wintering population and is the single most important wintering ground for dunlin , and for significant numbers of Bewick's swans , European white-fronted geese and wigeon . Nationally important wintering populations are supported such as gadwall , shoveller and pochard . There are notably seven species of migratory fish which pass through
468-654: The Bristol Channel , between England and Wales. The highest predicted extreme (not mean) range is 17.0 metres (55.8 feet), in the Bay of Fundy. The maximum range in the Bristol Channel is 15 metres (49 feet). The fifty coastal locations with the largest ranges worldwide are listed by the National Oceanic and Atmospheric Administration of the United States. Some of the smallest tidal ranges occur in
504-658: The International Hydrographic Organization places the boundary between the estuary and the open sea of the Bristol Channel at a line between Sand Point, North Somerset (north of Weston-super-Mare ) and Lavernock Point (south of Penarth in south Wales), at which point it is over 8 miles (13 km) wide. This definition is used by the Severn Estuary Partnership and Visit England. A narrower definition adopted for navigation purposes by some charts includes only
540-518: The Mouth of the Severn . The tidal range results in the estuary having one of the most extensive intertidal wildlife habitats in the UK, comprising mudflats, sandflats, rocky platforms and islands. These form a basis for plant and animal communities typical of extreme physical conditions of liquid mud and tide-swept sand and rock. The estuary is recognised as a wetland area of international importance and
576-595: The River Avon joins at Avonmouth . West of the Wye, the estuary forms the boundary between Wales and England . On the northern side of the estuary are the Caldicot and Wentloog Levels which are on either side of the city of Newport ; and, to the west, the city of Cardiff together with the resort of Penarth . On the southern, English, side, are Avonmouth , Portishead , Clevedon , and Weston-super-Mare. Denny Island
612-509: The English side is available to view and download from the reference link. Tidal range Larger tidal range occur during spring tides ( spring range ), when the gravitational forces of both the Moon and Sun are aligned (at syzygy ), reinforcing each other in the same direction ( new moon ) or in opposite directions ( full moon ). The largest annual tidal range can be expected around
648-502: The RNLI. SARA currently operates from six stations. Four are operated by the charity at Beachley , near the Welsh border at Chepstow , Newport, Sharpness and Upton upon Severn . Two stations are based at a local fire station, one at Tewkesbury and the other Wyre Forest fire station near Kidderminster . SARA was founded in 1973, with its then headquarters at Tutshill , which is near
684-528: The Severn Estuary and Bristol Channel a focus for tidal energy schemes and ideas. Plans for a Severn Barrage — running 16 km (9.9 mi) across the Bristol Channel from Lavernock Point near to and south west of Cardiff to Brean Down near and just south west of Weston-super-Mare in Somerset — would generate a massive 8640 MW when the tide flows, and have been discussed for several decades now. The power generated would come from
720-465: The UK's electricity, contributing significantly to UK climate change goals. The proposal for a hydro-electric barrier to generate 8.6 GW and meet five percent of Britain's power needs, is being opposed by some environmental groups. The Severn Estuary Partnership (SEP) was set up in 1995 as an independent initiative to focus the activities of local government, statutory authorities and interested parties such as farmers and fisherman. Its stated aim
756-788: The area being at the centre of discussions in the UK regarding renewable tidal energy. Definitions of the limits of the Severn Estuary vary. In pre-modern times the area was commonly referred to as the River Severn, or the Severn Sea. Today, at the upstream boundary, the normal tidal limit of the river is at Maisemore weir (on the West Channel) and Llanthony Weir (on the East Channel), close to Gloucester Docks , although exceptionally high tides can overtop these weirs. Downstream,
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#1732780639516792-535: The area downstream of the Second Severn Crossing near Severn Beach , South Gloucestershire . The definition used on Admiralty Chart SC1179 and the Bristol Channel and Severn Cruising Guide is that the estuary extends upstream to Aust , the site of the Severn Bridge . On the north-west (Welsh) side, the rivers Wye and Usk flow into the estuary, and on the south-east (English) side,
828-538: The basin the water sits in. Larger bodies of water have higher ranges, and the geography can act as a funnel amplifying or dispersing the tide. The world's largest mean tidal range of 11.7 metres (38.4 feet) occurs in the Bay of Fundy , Canada (more specificially, at Burntcoat Head, Nova Scotia ). The next highest, of 9.75 metres (32.0 feet), is at Ungava Bay , also in Canada, and the next, of 9.60 metres (31.5 feet), in
864-593: The current Beachley station. In 1976, SARA became a registered charity and purchased its first boat in 1977. In 1985, SARA became an official Mountain Rescue Team in the role of cliff rescue for the Wye Valley . A year later in 1986, a second station was opened at Sharpness. This was primarily in response to a tragic loss of life in the Sharpness area. Five boats are now stationed at Sharpness In June 2005,
900-426: The effect on the mud flats, that have European Environmental protection status, and the UK government Energy Review published later in the year did not endorse the scheme. Opinion is still divided on the benefits of a proposed barrage. John Hutton , Secretary of State for Business, Enterprise and Regulatory Reform , announced a further feasibility study on 25 September 2007. The Severn Tidal Power Feasibility Study
936-481: The estuary in both directions. These include significant numbers of Atlantic salmon and common eel . At Black Rock, Portskewett , a traditional method of fishing for salmon with lave nets is practised. The fishermen promote the fishery as a tourist attraction. In 2021, they reduced their activities in response to pressure from Natural Resources Wales to reduce their catch. A huge tidal range and high level of surrounding industry and population have long made
972-408: The estuary is under threat from natural processes such as coastal erosion , exacerbated by the high tidal range and strong tidal currents, and from threats such as ongoing development pressure along the shoreline, marine aggregates extraction and new coastal defensive and realignment measures as well as proposed major infrastructure projects. An archaeological aerial survey report of the archaeology on
1008-475: The highest tidal ranges in the world — about 50 feet (15 m). This funnel shape, large tidal range, and the underlying geology of rock, gravel and sand, produce strong tidal streams and high turbidity , giving the water a notably brown coloration. During the highest tides, rising water is funnelled up the estuary into the Severn bore , a self-reinforcing solitary wave that travels rapidly upstream against
1044-524: The lunar phases. Tidal data for coastal areas is published by national hydrographic offices . The data is based on astronomical phenomena and is predictable. Sustained storm-force winds blowing from one direction combined with low barometric pressure can increase the tidal range, particularly in narrow bays . Such weather-related effects on the tide can cause ranges in excess of predicted values and can cause localized flooding . These weather-related effects are not calculable in advance. Mean tidal range
1080-623: The major part of a larger area which includes the Taff / Ely Estuary and Bridgwater Bay (as well as the Upper Severn Estuary) The Upper Severn Estuary SSSI designation involves the English county of Gloucestershire. The site (Severn Estuary and Upper Severn Estuary) is listed in the 'Forest of Dean Local Plan Review' as a Key Wildlife Site (KWS). Both SSSI citations provide detail of the geological and biological interest and of particular note
1116-434: The operational areas for these stations include large parts of the rivers Severn, Wye, Bristol Avon and Usk. SARA are the designated rescue service for these areas, being called primarily via HM Coastguard , Police or Fire Brigade. During flooding and other events SARA has often operated away from its core area to provide rescue services when requested. The membership is made up entirely from volunteers, with no paid staff. As
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1152-479: The river current. West of the line between Lavernock Point and Sand Point is the Bristol Channel , which in turn discharges into the Celtic Sea and the wider Atlantic Ocean . The islands of Steep Holm and Flat Holm are located close to that line, in the middle of the estuary. The Ordnance Survey refers on its published mapping to a section of the estuary seaward of the two estuarine motorway crossings as
1188-525: The tidal limit of the River Severn in Gloucester and ending at a line drawn between Hurlestone Point near Minehead and Nash Point in the Vale of Glamorgan . The archaeology of the Severn Estuary is richly varied and of considerable importance, reflecting both the varied nature of the topography and the importance of the river for both fishing and as a maritime waterway. The archaeological resource within
1224-474: The time of the equinox if it coincides with a spring tide. Spring tides occur at the second and fourth (last) quarters of the lunar phases . By contrast, during neap tides , when the Moon and Sun's gravitational force vectors act in quadrature (making a right angle to the Earth's orbit ), the difference between high and low tides ( neap range ) is smallest. Neap tides occur at the first and third quarters of
1260-841: The upper estuary as far as Sharpness . The Upper Severn Estuary SSSI covers the tidal river between Purton and Frampton on Severn . The Severn Estuary SSSI original designation involves the then counties of Somerset, Avon and Gloucestershire in England, and Gwent and South Glamorgan in Wales. The Severn Estuary SSSI designation overlaps individual site designations for separate sites in Avon ( Spring Cove Cliffs , Middle Hope , Portishead Pier to Black Nore , Aust Cliff ), Gloucestershire ( Purton Passage ) and South Glamorgan ( Penarth Coast ). The 1976 designation includes two sites previously notified in 1952 ( Brean Down and Uphill Cliff ). The SSSI forms
1296-484: Was launched in January 2008 to assess all tidal range technologies (including barrages, lagoons and others). The study will look at the costs, benefits and impacts of a Severn tidal power scheme and will help Government decide whether it could or could not support such a scheme. The Severn Estuary has the potential to generate more renewable electricity than all other UK estuaries. If harnessed, it could create up to 5% of
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