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• Written by John Gillett

Bristol's flood defences

This year the City Council is completing a 4-year, £11miliion programme of improvements to the city’s flood control systems.  On the 21^st July, at the Friends Meeting House in Hampton Road, Steven Sodek, who manages the department that looks after Bristol’s flood planning and management strategies, described the work of his department.

Steve has two main concerns: flooding in the City caused by an extra high tide and flooding arising from heaving rain and the flooding of the Frome and/or Avon.  Tidal damage is the dominant risk.

This year two sets of lock gates were installed at the entrance to the Floating Harbour, the first line of defense against tidal surges.  These huge gates replace the 1870 wooden gates (some of this wood has been recyled to make public seating) which were still operated by Brunel's water-powered pistons and hand-pulled chains.  The new Dutch-built steel gates, 50 tons each, and designed to last over 100 years, are operated by state-of-the art hydraulic rams.

Brunel's hydraulic rams and the pumps that powered the hydraulic power network will be on display in the MShed where they are being prepared for display.

Whereas the original gates required a team of workers to operate the gates, the new gates are semi-automatic and one person in a new, modern control room can control the gates and monitor the water level and any problems in the lock itself.  More pictures here.

The new control rooms aroused some comment: some thought the corrugated stainless steel cladding was a monstrous intrusion in an historic dock landsape while others thought it an exciting modern and practical innovation. 

 Entering a control room requires one to climb some stairs becase the floor is nearly 1 metre higher than the dock.  The reason for this is that a tidal surge may be higher than the top of the docks.   To accommodate a tidal surge at the time of the Spring high tides say, the level of water in the Floating Harbour is lowered by 30cm.

Defending against flooding is expensive but not as expensive as repairing flood damage.  It cost more than £1bn to repair the damage from the Gloucester floods in 2007 - flood engineers calculate that a pound spent on flood defence should save £8. Currently Steve is planning to protect Bristol from rising sea levels due to global warming for the next 100 years.  Steve's department is one of the few to get increased funding and an increased staff allocation (currently 5 members) which will him re-enforce our defences against storm water in the Fome and Avon valleys. 

The final phase of the improvements is the replacement of the locks at Netham.  For the next few months these engineering works will provide a worthwhile spectacle.

In summary Steve told an interesting story and those members of the audience who live in low-lying area (Hotwells, Coronation Road) can now sleep more soundly.