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Bristol Floating Harbour

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Dec 2017

Float your Boat

It doesn’t take a civil engineer to know how engineering projects generally go. Someone gets a good idea. Then 40 years later someone else thinks they should start doing something about it. Then unforeseen ‘teething’ problems arise that escalate the costs. The project runs out of money and has to be rescued by the tax payer. Then someone gets an even better idea which makes the whole project obsolete. Thus goes the story of Bristol Floating Harbour, as told by Peter Malpass to the December gathering of Thornbury History and Archaeological Society.

From medieval times Bristol was an important commercial centre and trading port. In 1240 the ‘Great Trench’ was dug to create a deep water channel between the rivers Frome and Avon, now known as St. Augustine’s Reach, and this became the beating heart of the bustling port. By the late 17th century Bristol had 6, 000 tons of shipping, half of which was importing tobacco from America. But there was a problem. The estuaries of the river Severn have the second highest tidal range in the world. Vessels could be stranded in the mud for up to 1 or 2 weeks during neap tide periods. Time is money, and deep water coastal ports could handle vessels in all tidal conditions. In the 18th century Liverpool began to take over Bristol’s trade. Something had to be done.

The engineer John Smeaton proposed building a non-tidal harbour in 1765, and in 1802 (for the situation was urgent) another engineer, William Jessop, was engaged to carry out a scheme. The Bristol Dock Company was set up by Act of Parliament to raise private capital, execute the works and levy dues. The river Avon was dammed below Bristol to create 80 acres of floating harbour with entrance locks at Cumberland Basin. From here a new Avon channel was hand-dug by hundreds of navvies to join the natural river above Bristol at Totterdown.

Then what? Oh yes, the teething problems. Basically, they found they had created the largest open sewer in the country. Silt carried along the Frome and the feeder canal settled to the bottom of the stagnant waters of the harbour, along with the effluent from the burgeoning city of Bristol. At regular intervals the docks had to be drained and the silt dug out by hand. For well-heeled Bristol merchants this was perhaps a good time for a short holiday in fragrant Bath. To solve the problem the Dock Company had to head-hunt the famous Mr. Brunel. Along with other improvements Brunel changed the harbour outflow from an ‘overfall’ weir into a deep water ‘underfall’ sluice that would carry the silt with it. Hence this area had the name of Underfall Yard.

The cost of building and maintaining the harbour was so great that the Dock Company had to charge very high dues and this only helped to drive more trade to Liverpool. By 1848 the town council (i.e. the tax payer) had to step in and take over the Dock Company in order to save the commercial viability of the docks. Perhaps one casualty of the takeover was Brunel, who parted company with the docks in 1849. Throughout the 19th century they thrived, importing huge amounts of timber to the area known as Baltic Wharf and vast loads of grain which were stored in new giant warehouses.

But Bristol would always be at a disadvantage. It was 6 miles from the Severn estuary up a winding muddy river, and the Severn estuary itself is not the easiest navigation in the world. By strange coincidence, Brunel was perhaps both the saviour and the nemesis of Bristol’s Floating Harbour. His S.S. Great Western and S.S. Great Britain, built in Bristol in the 1830s and 40s, heralded a new era of large iron steamships that were too big to manoeuvre up the Avon and into the harbour. It was the beginning of the end. By 1908 the Royal Edward Dock was built at Avonmouth and Bristol’s Floating Harbour waned through the rest of the 20th century.

Perhaps we have the Avonmouth docks to thank for the 80 acres of now pleasant and interesting waterways in the centre of Bristol, and we also have to thank Peter Malpass for his interesting talk.


The Thornbury Local History and Archaeology Society always welcomes new and occasional members. Details of our programme can be found on this website, the library or the Town Hall. Our meetings are on the second Tuesday of the month, held at St Mary's Church Hall beginning at 7.30pm. Visitors are always welcome at the society for the small charge of £2.50.

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