page_title: Portishead, Somerset
section_title: Physical geography
hierarchical_section_title: Portishead, Somerset / Geography / Physical geography
caption_attribution_description: Black Nore Seashore
context_page_description: Portishead is a coastal town on the Severn Estuary, close to Bristol - but within the unitary district of North Somerset, which falls within the ceremonial county of Somerset, England. It has a population of around 25,000, with a growth rate considerably in excess of surrounding towns.
  Portishead has a long history as a fishing port. As a Royal Manor it expanded rapidly during the early 19th century around the docks, with supporting transport infrastructure. A power station and chemical works were added in the 20th century, but the dock and industrial facilities have since closed and been redeveloped into a marina and residential areas. Portishead was also the telephone control centre used by British Telecom for non-direct dialled calls to maritime vessels, a service known as Portishead Radio.
  The town's population is expanding, and Portishead is now primarily a dormitory town for Bristol and its environs, although a range of service industries has grown up. The headquarters of both Avon and Somerset Constabulary and Avon Fire and Rescue Service are in Portishead.
context_section_description: Portishead is a coastal town on the Severn Estuary. It lies north east of Clevedon and immediately south west of Avonmouth just across the River Avon, which forms the boundary between Somerset and Bristol. The city of Bristol is 6 miles (9.7 km) to the east and Portishead is approximately 110 miles (180 km) west of London. On clear days, Wales can be seen across the Severn Estuary from the town. The Eastwood area has been designated as a local nature reserve. It consists broadleaf woodland on a coastal limestone ridge which leads to Battery Point which had a defensive gun position and Portishead Point Lighthouse is on the promontory. There is also geological interest in the fossils, folds and faults found in the area.
  The area immediately inland includes the Gordano Valley, which has been designated as a national nature reserve. The valley runs roughly north-east to south-west, between Carboniferous limestone ridges extending along the coastline between Clevedon and Portishead, and another ridge extending between Clevedon and Easton in Gordano. The area includes the villages of Clapton in Gordano, Weston in Gordano, Easton in Gordano, Walton in Gordano, Portbury and Sheepway.  The M5 motorway runs along the south side of the valley, splitting briefly into two levels – the south-west-bound level running above the north-east-bound carriageway.  The Gordano motorway service station is at the eastern end of the valley, near the Royal Portbury Dock and the Avonmouth Bridge.  There is no river Gordano – much of the valley is reclaimed land barely above sea level, drained by ditches (known locally as "rhynes"). The rhynes previously managed by the now amalgamated Gordano Valley Internal Drainage Board are now the responsibility of the North Somerset Internal Drainage Board. An area comprising a total of 400 acres (160 ha) has been designated as a biological and geological Site of Special Scientific Interest, for ornithological, entomological and stratigraphic interest, notification originally having taken place in 1971. Several sites in the valley are managed by the Avon Wildlife Trust as nature reserves. These include Weston Big Wood, Clapton Moor, Weston Moor and Walton Common. The name Gordano comes from Old English and is descriptive of the triangular shape of the whole valley from Clevedon to Portishead, being the ablative singular of the Latinised form of Gorden meaning muddy valley.
  Denny Island is a small rocky island of 0.6 acres (0.2 ha), 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 tidal rise and fall in the Severn Estuary and Bristol Channel can be as great as 49 ft (15 m), second only to Bay of Fundy in Eastern Canada. There has been concern about pollution levels from industrial areas in Wales and at the eastern end of the Bristol Channel; however, this tends to be diluted by the Atlantic waters. There are measurable levels of chemical pollutants, but little is known about their effects. Of particular concern are the levels of cadmium and to a lesser degree residual pesticides and hydrocarbons.
  Portishead Pier to Black Nore SSSI is a 177-acre (72 ha) geological Site of Special Scientific Interest notified in 1952. The Portishead Pier Section is made up of alluvial sandstones, the best exposure of Upper Carboniferous rocks in the Avonmouth Coalfield. The cliff and foreshore exposures around Portishead Point provide important exposures of geological structures formed during the Variscan mountain building episode in the Carboniferous Period of geological history. Also included are important exposures of the Devonian sequence that yield several species of fossil fish. Holoptychius scales are the most abundant fossils, but teeth scales of other species are also relatively common. Notably amongst the collection from this bed are plates of arthrodires, including Groenlandaspis. Eastwood and Battery Point Local Nature Reserve is a 9 hectares (22
caption: Black Nore
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