Brunel's swing bridge alongside north entrance lock, Hotwells and Harbourside, City of Bristol

Summary

A swing bridge of 1849-1850 by IK Brunel constructed of wrought iron and moved to its current position in 1873. It was de-commissioned in 1968.

Description

Swing bridge of 1849-1850 by IK Brunel, moved to its current location with alterations in 1873, and with C21 repairs.

MATERIALS: constructed of wrought and cast iron with repairs in cast iron and steel.

DESCRIPTION: the bridge stands in its open position, parallel to the south side of Howard’s Lock, and is 33.7m in length. A balloon flange girder type, it is formed by tubular section long members with wrought-iron tie bars, side panels and flanged plate girders (transverse to the ends and turntable beams to the centre) providing the deck support. The timber deck covering has been removed. The transverse beams are set diagonally. The turntable beams are engaged with a pivot pin set in a wheel pit with an iron ring. Four iron wheels, one a C21 replacement, are sat in plummer blocks in the pit. These wheels help turn the bridge via a turntable ring with C21 steel track. Outer wheels are carried in a sunken iron rail, which terminates at a timber bollard. Inspection panels in the ground extending from below the bridge cover the machinery used to drive the swing bridge and are lined with riven stone setts.

History

Bristol’s Floating Harbour was designed and built in the early C19 to improve the function of the City’s port, and thereby its competitiveness in international trade. Access to the port was hampered by the extreme tidal range of the River Avon and by the mid- C18 Bristol was superseded by Liverpool as the principal English port linked to the transatlantic slave trade. In 1802, after much delay, the City’s merchants finally agreed a scheme to dam and bypass the river to create a floating harbour of around 70 acres that could function irrespective of the tide height. Ships would enter an open area of water called Cumberland Basin via one of two locks at Rownham and pass into the harbour via another lock at Hotwells. The River Avon was diverted into a ‘New Cut’ on a route to the south of the City with overfall dams to scour the harbour of silt.

William Jessop designed the scheme and was employed as Chief Engineer under the newly formed Bristol Dock Company (BDC); work started in 1803 following Parliamentary approval. The works were completed in 1809 and the basin and Floating Harbour are shown on the 1828 map by Plumley and Ashmead, along with bridges across both entrance locks. The Floating Harbour reputedly provided Bristol with the largest area of impounded water for shipping in the world and the two Entrance Locks into the Cumberland Basin from the River Avon were the largest structures of their kind yet built.

In 1832, BDC commissioned IK Brunel who designed and installed a new underfall dam to scour the basin and proposed changes to the entrance locks, which had fallen into disrepair and could no longer accommodate the increasing size of steamships. Work started in 1842 to increase the length and width of the South Entrance Lock (Brunel’s Lock, listed at Grade II*). Brunel’s pioneering wrought-iron caisson design, with single-leaf gates, maximised the operating length of the lock. Brunel intended to span the lock with a retractable rolling bridge, but instead in early 1849 he designed an innovative wrought-iron swing bridge, which his staff nick-named the ‘Swivel Bridge’, and was completed in the autumn of 1850. The unusual ‘tubular’ top flanges on the side girders gave rise to the term ‘balloon topped bridge’ and were part of a new design type required to reach across the lock when closed. Brunel fixed wrought-iron tie-bars within the top flanges to counter deflections caused by the long length of the side girders. The lock opened in 1849 and is shown with bridges across both entrance locks on Ashmead’s Map of 1855.

In 1863 the Bristol City Docks Engineer, Thomas Howard, designed and installed a three-quarter length ‘replica’ bridge over Jessop’s North Entrance Lock, which was eventually moved to Bathurst Basin following the closure and infilling of the lock and the creation of a new lock to the north as part of Howard’s plans to improve the function of Cumberland Basin. Brunel’s Lock was recommended for closure to create a graving dock and Brunel’s original swing bridge was transferred to the newly built North Entrance Lock (Howard’s Lock) in 1873. The bridge was shortened to 33.7m as part of its installation across Howard’s Lock. The plan for a graving dock was subsequently dropped and in 1875-1876 another replica swing bridge was built and installed on Brunel’s Lock.

The new arrangement of locks and bridges is shown on the First Edition Ordnance Survey Map of 1886 and the 1870s hydraulic machinery of the bridge was renewed in 1901-1902 and manufactured by Sir W.G. Armstrong, Whitworth and Co Ltd of Newcastle upon Tyne. The swing bridge was de-commissioned in 1968 following the construction of the Plimsoll Bridge as part of a new road system, and narrowly avoided being removed. Repairs have taken place in the C21 and various parts of the structure have been strengthened. It stands in the open position on the lockside (Grade II) under the Plimsoll Bridge (not listed).

Reasons for Listing

Brunel’s swing bridge alongside north entrance lock is listed at Grade II* for the following principal reasons:

Architectural Interest:

* as an innovative bridge design that utilised new technology to serve the specific requirements of Brunel’s South Entrance Lock (separately listed at Grade II*);
* as the subject of a successful relocation to its current position across a new North Entrance Lock in around 1873 through skilled engineering it is an example of high quality of adaptation to the evolved waterway ensemble at Cumberland Basin;

Historic Interest:

* the work of I.K. Brunel as an engineer and as a designer is widely regarded as exemplary and often of national and international significance;
* non-railway designs associated with Brunel are rare and this is an early example of his ‘balloon topped’ bridge that would prove influential in the development of bridge design and foreshadowed his Royal Albert Bridge at Saltash (Grade I);
* Cumberland Basin itself is a rare example of a tidal basin design and a critical part of Bristol’s Floating Harbour, which in the early C19 was a bold constructional achievement.

Group Value:

* the bridge forms a distinct grouping with the south entrance lock and swing bridge (Grade II*) and the walls to Cumberland Basin (Grade II), with which it formerly shared raised road sections and fixtures that allowed for passage across the two locks and land between.

External Links

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