BRISTOL CITY DOCKS
BY DAVID NEALE (BRISTOL CITY DOCKS ENGINEER) RETD.
& ROSS FLOYD
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The Approach to the City Docks - looking seaward from the New Cut - about 1880
THE CREATION OF BRISTOL CITY DOCKS
With a huge tidal range, one of the highest in the World, the Avon is only navigable for a few hours either side of high water and many vessels have been wrecked because they missed the tide or were carried onto the mud banks by the fast current. The current can reach 5 knots on a spring tide.
In 1802 Engineer William Jessop was commissioned by the newly formed Bristol Dock Company to carry out long-overdue improvements. He dammed the Avon in three places and diverted the river to create the 70 acre City Docks, which were officially opened on May 1st 1809. Prior to this Bristol Harbour had been a tidal river with banks of mud and stone but now ships could remain afloat in the harbour, upright and not 'take the ground' on each ebb tide. This speeded loading and manoeuvring and dramatically improved efficiency.
However, the new scheme required a way to equalise the levels inside and outside the Dock for the passage of vessels to and from the Avon, and bridges to cross the water. Jessop built Cumberland Basin with two entrance locks from the tidal Avon , of width 45 feet and 35 feet respectively, and a junction lock (width 45 feet) between the Basin and what became known as the Floating Harbour. This arrangement provided flexibility of operation with the Basin being used as a lock when there were large numbers of arrivals and sailings.
A panoramic view of the original locks. Jessop's first lock in the foreground, now filled in, and Brunel's behind.
The New Cut is behind the tongue of mud. The current working lock is out of sight to the left.
After 35 years the Dock Company resolved to construct a larger lock to replace the smaller of Jessopís two entrance locks. Brunel was commissioned and designed the new lock with floating hinged gates known as ship-caissoons (local spelling). Despite this innovation the lock was not a great success. Ballast chambers were prone to silting up because of the silt-laden tidal water and the lock was only 54 feet wide, a modest increase having regard to the ever-increasing size of ships. The lock was opened in 1850.
Brunel's lock - now unused. The main swing bridge of the Cumberland Flyover takes traffic over the locks.
Brunel had previously (c.1835) designed a system for compartmentalising and scouring mud from the Floating Harbour at low tide with shipping being moved to allow compartments to be emptied and scoured in turn through a system of sluices. Jessopís overfall dam at Redcliffe, a masonry structure with a kind of letterbox arrangement to let off flood water, was replaced by a low-level wooden Ďtrunkí and sluice, known as the Underfall.
It is not known how long Brunelís scouring regime remained in operation, but his dragboat, for scraping mud away from the sides of the harbour was eventually scrapped in 1961. ( The machinery and engine are preserved by the Industrial Museum ). Dredging replaced scouring in the Floating Harbour, with a system of four Underfall Sluices (now electrified and computer-controlled) to regulate the Float Level and to release into the River Avon, mud dumped in the sluice forebay from bottom-opening hopper barges. Because of the smell occasioned by the release of mud, the Clifton & Hotwells Improvement Society (CHIS) successfully petitioned the Docks Committee of Bristol Corporation to convey the mud to sea. Two steam mud hoppers, the AVON and FROME, were built and ran the river for sixty or more years until the mid-1960s. The smell was not abated and the removal of mud to the Bristol Channel did not reduce the dredging task at the City Docks. The smell eventually went away with the development of Bristolís sewage treatment works and foul-water interceptor system. The Docks Committee quietly resumed the release of mud at the Underfalls!
It was in Jessopís 45-foot lock that Brunel's 48-foot beam SS Great Britain almost came to grief before she ever went to sea in 1841. She was being towed away from her builders to have her engines and interior fitted out on the Thames but unfortunately was fractionally too big to go through.
The ship was moored in the Floating Harbour for a year or more before proceeding into Cumberland Basin, in an orderly fashion, with coping stones and lock gate platforms removed from the Junction Lock. They tried but failed to sail on an evening spring tide - over the top of the copings and lock gate platforms - the ship was pulled back into Cumberland Basin, either because they were too late or because the tide had 'cut'. Coping stones and platforms were removed over-night and the ship sailed the following morning. Because it is unsafe to navigate the river on a falling tide, there was a pre-planned beaching of the ship off Cumberland Basin followed by final sailing, under tow, on the evening tide.
Brunel's lock was finally closed in the 1930's and the heavy wooden timbers that filled the unusual step on the Northern side were removed after World War II. The step must have been included in Brunelís design to prevent a repetition of the Great Britain fiasco. It has been used in recent years for the careening of small boats. There is a much more substantial facility for ship repair, known as Ďthe gridironí in the entrance channel to the former Jessop 45 ft lock. This can be kept clear of mud by sluicing from the Howard lock, but is currently completely silted-up and out of use.
The remains of Brunel's lock, showing
the 'shelf' and the 'replica' bridge.
In former years there were smaller entrances from the tidal Avon at Bathurst, Totterdown and Netham. At Netham, the original course of the Avon is impounded by Netham Ďdamí, which is really a weir. The Feeder Lock controls the flow of water into the Docks and enables barge traffic to proceed upstream to the Bath River Navigation.
THE HOWARD LOCK 1873
Brunel's lock was for the most part superseded by the present entrance lock designed by Docks Engineer Thomas Howard and opened in July 1873. This has a 62 foot width and is the only entrance lock now in use at the City Docks.
The Howard lock - entrance to the City Docks from the tidal River Avon. Looking seaward.
Looking towards the City.
In the background and almost out of sight is the old swing bridge, powered by water pressure from the Underfall Yard hydraulic engine house at 750 pounds per square inch (psi). In the foreground, the new Plimsoll Bridge, completed in 1965, has a more modern electro-hydraulic system using oil at a pressure of 4,480 psi. When last resurfaced Farvis equipment was much in evidence !
The ill fated 'Prince Ivanhoe' in the lock circa 1981.