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Crossing the River Severn

There had been ferries across the turbulent Severn Estuary for centuries, but many preferred to travel via Gloucester rather than brave the ten troubled tides. By the 20th century, it became feasible to construct a road bridge, thus shortening the route between England and Wales considerably for road-users.

The first Severn Bridge was constructed in 1966, but by the 1980s it was becoming obvious that a second crossing was needed. In 1992 construction began on a bridge over the shortest and most treacherous section of the Severn Estuary, locally known as The Shoots. This area was well known for tidal streams that vary from 3 to 8 knots and a tidal range of 14.5m. Sailing through The Shoots in the days before powerful engines was especially dangerous, and called for very high level of seamanship. The area is fringed by rocks on each side of the river and known for tricky whirlpools. It was a hostile place to build, the company paid for two Met. Office staff during the period of the build so they had, in effect, their own weather station, and the decision was made to construct the sections on shore and convey them to their final positions to minimise the work done on and within the river. This approach required the conversion of several suitable large marine craft and appropriate special heavy lifting gear.

The design included a Cable Stayed Bridge over the navigable section, flanked by viaducts largely supported by the existing rocks. The sections of the bridge were constructed on shore and transported out to the river at low tide on crawler units across a specially built causeway to a purpose built barge. At high tide the barge transferred the sections to a fixed crane barge in the river (Lisa A) which lifted them into position when the tide receded. The whole operation of placing the sections of the bridge was guided by a sophisticated computer-operated satellite positioning system. The Lisa A was then floated to the next location and the operation repeated. The project, led by John Laing plc and GTM Entrepose, opened in June 1996, after a memorable fancy dress charity walk from the Welsh and English sides of the river!

Contributed by Dee Halliday, Bristol Channel member of the OGA

Dee Holladay, OGA Bristol Channel member