Canvey Island - Geography

Geography

Canvey Island lies off the south coast of Essex 30 miles (48 km) east of London, and 15 miles (24 km) west of Southend-on-sea. The island is separated from the mainland to the north and west by Benfleet, East Haven and Vange creeks, and faces the Thames Estuary to the east and south. Along with neighbouring Two Tree Island, Lower Horse, and Upper Horse, Canvey is an alluvial island formed in the Holocene period from silt in the River Thames and material entering the estuary on the tides of the North Sea from the coast of Norfolk. An unsuccessful search for coal beneath the island in 1953 revealed that the alluvium rests upon layers of London Clay, Lower London Tertiaries, Chalk, Lower Greensand and Gault Clay, with the basement rocks at a depth of 1,300 feet (400 m) consisting of hard Old Red Sandstone of Devonian age.

The island is extremely flat, lying 10 feet (3 m) below mean high water level and consequently is at risk of flooding. Before reclamation, the surrounding area contained a number of islands separated by tidal creeks. Flood defences have been constructed since the Middle Ages, and the first sea wall to completely surround the island was built as part of the island's reclamation in 1622. The island suffered extensive flooding in 1731, 1736, 1791, 1881, and 1897, and substantial loss of life in the North Sea Flood of 1953. As of 2008, the flood defences consisted of a concrete seawall, flood sirens and an internal surface storm water drainage system. The sea wall was completed in 1982, is 15 miles (24 km) long and surrounds 75% of the island's perimeter terminating with flood barriers spanning Benfleet Creek to the north and East Haven Creek in the west. The drainage system consists of sewers, culverts, natural and artificial dykes and lakes which feed seven pumping stations and gravity sluices that discharge the water into the Thames and creeks. Four of the discharge sites are "high flow" stations capable of discharging 600 litres of water per second at any tide level. The levels within the system are managed by a further five "low flow" pumping stations. The Environment Agency's Thames Estuary 2100 flood defence plan includes Canvey Island as one site for alleviating the flood risks to London and the Thames estuary area. It is proposed that the western side of Canvey is developed as a site which is either temporarily flooded at times of risk, or transformed into a permanent wetland.

Developments in the 20th century have produced a marked contrast between the environments in the east and west of the island. The eastern half of the island is allocated to residential areas, the main public amenities, and a small holiday camp and seafront, while the western half of the island is mainly farmland, marshes, and industrial areas. The marshes in the west include the 30 hectares known as West Canvey marshes, acquired by the RSPB in 2007, and the Canvey Wick nature reserve. Canvey Wick is a designated Site of Special Scientific Interest (SSSI) at the site of the abandoned and incomplete oil refinery. The foundations of the 100 hectare (0.4 sq mile) site were prepared in the 1970s by laying thousands of tonnes of silt dredged from the Thames; the abandoned and undisturbed area has flourished as a haven for around 1,300 species of wildlife, many of which are endangered or were thought to be extinct; including the shrill carder bee, the emerald damselfly and the weevil hunting wasp. It has been said that the site may have one of the highest levels of biodiversity in western Europe. Other areas of natural interest include the eight hectares (20 acres) of Canvey Lake Local Nature Reserve owned by Castle Point Borough Council. The lake was used for salt-making during the Roman settlement of the island, and is also thought to have functioned as an oyster bed. At the eastern point of the island is the 36-acre (150,000 m2) Canvey Heights Country Park which was reclaimed from the Newlands landfill site that operated there between 1954-89. The park is the highest land elevation on the island and thus has wide views across the creeks and marshes and along the Thames. The environment supports an array of wildfowl such as skylarks, dark-bellied brent geese, and grey plover.