Science Fair Project Encyclopedia
This article is about the British river. For other uses see Severn (disambiguation).
The Severn (known as Afon Hafren in Welsh) is the longest British river, at 354 kilometres (219 miles) long; it rises at an altitude of 610 metres on Plynlimon near Llanidloes, in the Cambrian Mountains, Mid Wales, and it passes through a number of English counties, with the county towns of Worcester, Gloucester and Shrewsbury located on its banks. The Severn becomes the Bristol Channel at its estuary, eventually discharging into the Irish Sea and the Atlantic Ocean.
The Severn Tunnel carries the Great Western Main Line under the estuary. The two Severn Bridges carrying roads (opened in 1966 and 1996) link Wales with the southern counties of England and are among the most important in Britain. The Severn is bridged at many places, and many of these bridges are notable in their own right, with several designed and built by the engineer Thomas Telford. (See List of Severn bridges for more).
A six mile stretch of the Severn valley in Shropshire, known as the Ironbridge Gorge, was designated a World Heritage Site by UNESCO in 1986. Its historic importance is due to its role as the centre of the iron industry in the early stages of Britain's Industrial Revolution. Ironbridge gets its name from the bridge across the Severn, built in 1779 which was the first cast iron bridge ever constructed.
According to some sources, the name "Severn" is derived from the name Sabrina (or "Sabern"), based on the mythical story of the drowning of a nymph in the river.
The port of Bristol is located at the mouth of the Severn, where another river River Avon flows into it. Between Gloucester and the Welsh border at Chepstow is the Forest of Dean flanking the north bank.
A curious phenomenon associated with the lower reaches of the Severn is the tidal phenomenon known as the bore. The river's estuary, part of the Bristol Channel, has the second largest tidal range in the world - about 15 metres — and at certain combinations of the tides, the rising water is funnelled up the estuary into a wave that travels rapidly upstream against the river current; enthusiasts even attempt to surf along on the wave. (Note that the Gloucester Harbour Trustees as competent harbour authority for this part of the river, explicitly advise against this pastime). The Severn Bore is a natural example of a self-reinforcing solitary wave or soliton.
The bore forms somewhat upstream of the Port of Sharpness, which is also the Southern terminus of the Gloucester and Sharpness Canal. The canal was built in the 1820s to enable safer passage of trading ships to Gloucester Just North of the Port are the remains of the Severn Railway Bridge, which bridged the river until it was badly damaged in a ship collision in 1960.
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