Chew Valley Lake

2008/9 Schools Wikipedia Selection. Related subjects: Geography of Great Britain

Chew Valley Lake
Governing body	Bristol Water
SSSI Ref	1001346
SPA Code	UK9010041

Map of the lake

Chew Valley Lake ( grid reference ST5659) is a large reservoir in the Chew Valley, Somerset, England, and the fifth-largest artificial lake in the United Kingdom (the largest in south-west England), with an area of 1,200  acres (4.9 km²). The lake, created in the early 1950s and opened by Queen Elizabeth II in 1956, provides much of the drinking water for the city of Bristol and surrounding area, taking its supply from the Mendip Hills. Some of the water from the lake is used to maintain the flow in the River Chew.

Before the lake was created, archaeological investigations were carried out that showed evidence of occupation since Neolithic times and included Roman artefacts. The lake is an important site for wildlife and has been dedicated as a Site of Special Scientific Interest (SSSI) and a Special Protection Area (SPA). It is a national centre for birdwatching, with over 260 species recorded, including some unusual sightings. The lake has indigenous and migrant water birds throughout the year, and two nature trails have been created. The flora (plants) and fauna provide a variety of habitats and include some less common plants and insects.

Some restricted use for recreational activities is permitted by the owner, Bristol Water, including dinghy sailing and fishing, primarily for trout.

Location

Chew Valley Lake in the Chew Valley at the northern edge of the Mendip Hills, surrounded by meadows and woods and close to the villages of Chew Stoke, Chew Magna and Bishop Sutton. When it was built in the 1950s, its 1,200 acres (4.9 km²) were flooded with 4,500 million imperial gallons (20,000,000 m³) of water from the Mendip hills, with a catchment area of 14,000 acres (57 km²). It is relatively shallow, with an average depth of only 14 ft (4 m) at top level and a maximum depth of just 37 ft (11 m). It is fed by several small rivers, and it flows into the River Chew for 17 miles (27 km) before it joins the Avon to head out to sea. The deepest part is near the dam and the outlet tower, where the steeply sloping shores of Walley Bank and the north shore result in depths of up to 20 ft (6 m). "Denny Island", above the surface throughout the year, is wooded and provides a habitat for wildlife.

The lake is owned and operated by Bristol Water, which created it in 1956 when the demand became too large for nearby Blagdon Lake. Working with the Avon Wildlife Trust, Somerset Wildlife Trust and other environmental groups, Bristol Water has encouraged various species of birds and plants, and created a venue for visitors.

It has two large landscaped picnic areas. Facilities include a tea shop, with indoor and outdoor seating areas with a view of the lake, and information centre. There are also a souvenir shop and small art gallery and two nature trails. The Grebe Trail is a hard-surfaced, all-weather path suitable for pedestrians, pushchairs and wheelchairs and covers a circuit 0.75 miles (1.2 km) long, starting and finishing at the wooded picnic area. The Bittern Trail is reached from the Grebe Trail by the footbridge over Hollow Brook. It is not a surfaced path. This trail runs along the east shore, visits an open bird hide and returns to the footbridge, making a 1-mile (1.5 km) circuit. Bristol Water impose conditions on visitors, particularly related to the areas where dogs are allowed.

Access and transportation

Access to the waterside is restricted at several points to reduce the disruption to wildlife. Paths around the lake are generally flat and, where paths are surfaced, wheelchair access is possible.

Visitors are officially invited to use public transport, but overwhelmingly arrive by private car, encouraged by the provision of parking spaces. The "Chew Valley Explorer" bus route 672/674 provides access.

In 2002 a 1.9-mile (3 km) safe cycle route, the Chew Lake West Green Route, was opened around the western part of the lake. It forms part of the Padstow to Bristol West Country Way, National Cycle Network Route 3. It has all-weather surfacing, providing a smooth off-road facility for ramblers, mobility-challenged visitors and cyclists of all abilities. It was funded by Bath and North East Somerset Council with the support of Sustrans and the Chew Valley Recreational Trail Association. Minor roads around the lake are also frequently used by cyclists.

Bristol International Airport is approximately 10 miles (15 km) away, and the nearest major road is the A368, which runs along the southern edge of the lake and provides access from Bath and Weston super Mare. The A37 and A38 are slightly further away, providing access from Bristol. Car parking is available at the visitor centre and Woodford Lodge, for which a charge is made, and a small amount of parking is available at various points around the lake; some of these are restricted to those with fishing permits.

History

Plaque unveiled by Queen Elizabeth II in 1956

The area the lake covers was once rich farmland. Several farms and houses had to be removed before the land was flooded, and old roads, hedgerows and tree stumps can reappear when dry summers cause the level of the lake to drop. Prior to the flooding of the reservoir, archaeological excavations were carried out by Philip Rahtz and Ernest Greenfield employed by the Ministry of Works, from 1953 to 1955. The excavations found evidence of people belonging to the consecutive periods known as Upper Palaeolithic, Mesolithic and Neolithic (Old, Middle and New Stone Age), Bronze Age and Iron Age, including implements such as stone knives, flint blades and the head of a mace, along with buildings and graves. The artefacts from this period are held at Bristol City Museum and Art Gallery. Further evidence of Neolithic and Bronze Age occupation is provided by the archaeological survey of the Mendip Hills Area of Outstanding Natural Beauty.

Excavations have also uncovered Roman remains, indicating agricultural and industrial activity from the second half of the first century to third century AD. These finds included a moderately large villa, at Chew Park where wooden writing tablets (the first in the UK) with ink writing were found. The tablets were sent to the British Museum, but other Roman material is on display at the Bristol City Museum and Art Gallery with the lake's other historical artefacts.

Further excavations around the village of Moreton, which has now been totally submerged, found evidence of a thriving community in medieval times and possibly the remains of the Nunnery of Santa Cruz. During the Middle Ages farming was the most important activity supported in the area covered by the lake, supported by four flour mills powered by the River Chew. Stratford Mill was demolished and re-erected in the grounds of Blaise Castle Museum. The largest settlement was Moreton, which is listed in the Domesday Book and survived until the flooding of the lake, when the remains of the Moreton Cross were moved to Chew Stoke Parish Church. There is also evidence of lime kilns, which were used in the production of mortar for the construction of local churches. Farming, both arable and dairy, continued until the flooding of the lake, with most households also keeping pigs. There were also a variety of orchards for fruit production, including apples, pears and plums.

The reservoir

Chew Valley Lake dam

Pumping Station

Plans for the building of the reservoir were under discussion prior to the Second World War, and an Act of Parliament submitted by the Bristol Waterworks Company was passed in 1939. Following this several farms were bought by the company and farmed by the previous owners as tenancies. Farms and buildings still remaining in private hands were acquired by compulsory purchase. The sanction for construction was given in 1949 and the contract awarded to A.E. Farr & Co., who employed approximately 300 people on the site. The main dam was initially stabilised by injecting concrete into the cracks in the bedrock. The core of the dam was made of puddled clay mixed with sand. This was the first time the gain in strength brought about by the use of sand drains had been quantified. The lake was inaugurated by Queen Elizabeth II, accompanied by Prince Philip, with the unveiling of a commemoration stone and plaque, which can be seen from the dam, on 17 April 1956, although it was not full until 25 February 1958.

During the storm of 10 July 1968, the lake gained an extra 471 million imperial gallons (2,140,000 m³) and rose 19 inches (480 mm) in under 12 hours. At one point worried Bristol police issued a warning that the dam might not hold, prompting localised evacuation of populated valley areas downstream including Pensford and Keynsham.

Ecology

View of Chew Valley Lake showing Herriot's Bridge

The lake is designated a Site of Special Scientific Interest (SSSI) (Site Ref: 1001346) and a Special Protection Area (SPA) (Site Code: UK9010041) largely because of the variety of species and habitats. Providing further protection, much of the area around the lake also falls within the Mendip Hills Area of Outstanding Natural Beauty (AONB).

The lake appears to have a higher sedimentation rate than would be expected in other similar reservoirs, being in the region of 100–150 t.km^-2.yr^-1.

Geology

The main geological outcrops around the lake are mudstone, largely consisting of red siltstone resulting in the underlying characteristic of the gently rolling valley landscape. There are also bands of sandstone of the Triassic period that contribute to the undulating character of the area. There are also more recent alluvial deposits beside the course of the River Chew.

Birds

Over 260 species of birds have been recorded at Chew, the third most important site in Britain for wintering wildfowl. From late July to February, up to 4000 ducks (Anatidae) of twelve different species may be present, including internationally important numbers of shoveler (Anas clypeata) and gadwall (Anas strepera). Some 400 great crested grebes (Podiceps cristatus) gather on the lake in autumn. A wide range of data on bird species and their numbers on the lake, dating back to the first " ringing" in 1964, is available from the Chew Valley Ringing Station.

Numerous other birds can be seen, especially during the spring and autumn migrations. Sand martins (Riparia riparia) arrive early and can usually be seen hawking over the water for insects in the second or third week of March. Mixed flocks of tits (Paridae), swallows (Hirundinidae), terns (Sternidae) and little gulls (Larus minutus) can regularly be seen. A variety of waders, such as lapwings (Vanellus vanellus), dunlin (Calidris alpina) and common snipe (Gallinago gallinago), are attracted to the muddy shores as the water level drops in autumn. By midwinter up to 40,000 gulls, mostly black-headed (Larus ridibundus) and common (L. canus), may be roosting. Good numbers of reed (Acrocephalus scirpaceus) and sedge warblers (A. schoenobaenus) nest in the fringing reeds, along with grebes (Podicipedidae) and coots (Fulica atra).

Much of the management work carried out in the nature reserve is aimed at encouraging ducks to breed, and small numbers of tufted duck (Aythya fuligula), pochard (Aythya ferina), shelduck (Tadorna tadorna) and gadwall raise broods most years. Recent breeding successes also include water rail (Rallus aquaticus) and Cetti's warbler (Cettia cetti).

A new wetland reserve has been created at Herons Green on the opposite side of the causeway to the lake. A large shallow pool fringed with sedges (Cyperaceae), rushes (Juncaceae) and reedgrasses (Calamagrostis) and surrounded by lightly grazed, rough grassland may also prove attractive to snipe and Lapwings.

Fish

In late summer large shoals of roach (Rutilus rutilus) and perch (Osteichthyes) fry can congregate around the margins and weed beds, which are predated by the brown trout (Salmo trutta morpha fario) and rainbow trout (Oncorhynchus mykiss).

Insects

Aquatic midges (Chironomidae) provide the highest proportion of the fly life of the Lake. The trout (Salmonidae) will feed at the surface on these and water boatmen (Corixidae), and below the surface on the caddisfly (Trichoptera) larvae and pupae; they will also take the adult Caddisflies when they emerge. Many other aquatic fauna including daphnia and snails are also found in the lake. Near Herriot's Pool large populations of dragonflies including ruddy darters (Sympetrum sanguineum) and migrant hawker (Aeshna mixta) hunt over the water. Two scarce species of wainscot moth make their home in the reed beds.

Vegetation

Chew Valley Lake from Burledge Hill, showing Denny Island

The lake is surrounded with some fringing reedbeds, |carr woodland and grassland, which are managed by Bristol Water. The water conditions are eutrophic with some run off from local fields and streams. Open-water plant communities are rather sparse, largely comprising fennel pondweed (Potamogeton pectinatus), lesser pondweed (Potamogeton pusillus), opposite-leaved pondweed (Groenlandia densa) and water-crowfoot (Ranunculus spp.). On neutral soils around the reservoir, pepper-saxifrage (Silaum silaus), burnet-saxifrage (Pimpinella saxifraga) and devil's-bit scabious (Succisa pratensis) occur, and on calcareous soils fairy flax (Linum catharticum), dwarf thistle (Cirsium acaule) and salad burnet (Sanguisorba minor subspecies minor) are found.

The small and medium-sized fields around the lake are generally bounded by hedges and occasionally by tree belts and woodland, some of which date back to the most evident period of enclosure of earlier open fields which took place in the late medieval period. Hedgerows support the nationally rare bithynian vetch (Vicia bithynica). Mature oak (Quercus) and ash (Fraxinus excelsior) trees are characteristic of the area with occasional groups of scots pine (Pinus sylvestris) and Chestnuts (Castanea sativa). Many elm (Ulmus) trees have been lost in this area, and dead/dying elms are also evident in the surrounding landscape.

Leisure use

The lake is used for a wide variety of leisure pursuits.

Birdwatching

Birds on Chew Valley Lake taken from Herriot's Bridge

During 2005–2006 Bristol Water started restoring two artificial islands. These are intended to provide safe nesting and roosting sites for a range of wildfowl.

Permits to enter the reservoir enclosure and to use the access road, path and bird hides are available only to members of ornithological and naturalist societies recognised by Bristol Water. They can be obtained from Woodford Lodge and include conditions of use imposed by the owners.

Sailing

Chew Valley Lake Sailing Club has a large sailing area, approximately 1.9 miles (3 km) long, for dinghy sailing.

The lake is divided into two areas: a restricted summer area which is available during the fishing season (mid-March to mid-October), and the full area which can be used throughout the winter and on Sunday afternoons. The sailing area is marked out by lines of small white buoys. Racing marks are red buoys with flags, although large inflatable marks are used of open events.

The club can easily cater for fleets of over one hundred boats and it hosts many large national events. Normal club racing has fleet starts for the following dinghy classes: Flying Fifteen (keelboat), Laser (dinghy), Solo (dinghy) and Topper (dinghy) as well as a handicap fleet run under the Portsmouth yardstick scheme.

Five separate slipways enable easy launching. Off the water, the clubhouse facilities include large changing rooms, hot showers, hot food at the weekends, a bar and terrace overlooking the lake. The club also caters for disabled people with facilities on both floors and a lift.

The club is open for sailing to members on Wednesday and every weekend with racing held on Wednesday evenings and Sundays. Various Royal Yachting Association sailing courses are held at the club for members including race training, youth training, powerboat training, race officer training as well as more informal training run within each fleet. A selection of dinghies is also available for members to try.

The club is a private sailing club and so visitors should contact the Club prior to visiting.

Fishing

Day and afternoon bank fishing permits are available at Woodford Lodge. The restrictions imposed by Bristol Water mean that no fishing is allowed from the dams or stone embankments, the sailing club, in front of Stratford bird hide, in front of the picnic areas and in the nature reserve, and various other regulations are in force. There is a fleet of 32 motor boats for hire to fish.