INTERVIEW-Managed flooding option for London sea defences
14 Feb 2007 17:37:28 GMT Source: Reuters
By Jeremy Lovell LONDON, Feb 14 (Reuters) - London's flood defences may be overwhelmed one day as global warming raises sea levels and worsens storms, so city planners are racing to find solutions. One option gaining favour with a government team tackling the problem is to allow vacant land away from the city to flood, instead of letting all the tidal water surge up the River Thames and endanger the heart of the city. By mid-year the team will shortlist options to make safer millions of people, thousands of homes and vital infrastructure that are protected by sea walls, raised riverbanks and the iconic Thames Barrier in the estuary between city and sea. "There are lots of combinations of possible options, but managed flooding has several appealing characteristics," Chris Burnham, policy director of the Department of the Environment's Thames Estuary 2100 project team, told Reuters. "It is flexible, relatively fast, and would give us much- needed breathing space to watch whether actual climate change does what it is predicted to do." It would also be a lot cheaper than building a new barrier downstream from the existing one at a cost of several tens of billions of pounds and which might not be needed for a century. Completed in 1984 in response to devastating floods in 1953, the Thames Barrier has been used about five times a year to protect London -- but the frequency is rising and it is expected to be being raised 30 times or more a year by 2030. "We are developing a flexible plan stretching in phases up to the end of the century and beyond," Burnham said. "As climate change progresses we can adapt the plans accordingly." VAST STAKES At stake is an estimated 160 billion pounds ($310 billion) worth of assets not just in London and its vital financial district but all along the banks of the river's estuary where vast new housing developments are still being planned. To build their plans Burnham and his colleagues are using models ranging from a sea level rise of half a metre (18 inches) with allowance for a 1.5 metre tidal surge to a sea level rise of three metres and a 1.5 metre tidal surge on top of that. Managed flooding of marshland and other areas east of the capital -- an idea also being tried across the English Channel in Belgium -- would not be the sole or even final solution to the problems caused by global warming this century, and would certainly not be simple. Flood defences upstream would still have to be maintained and possibly raised, and new defensive barriers would have to be built around the areas set aside for occasional flooding -- which may only happen once every 50 or 100 years. It would also have environmental impacts. But diverting surge tides away from the main river to land set aside for the purpose would extend the life of the Thames Barrier and mean flood defences upstream need not be raised so much. "People seem to think the Barrier will just fall apart in 2030 at the end of its design life. It will not. It can go on working for decades after that," Burnham said. "But the more often it is used the more the wear and tear." Behind the barrier lies the centre of London at risk of flooding -- with its 500,000 properties, 1.25 million people, 400 schools, 16 hospitals, eight power stations, City Airport, and about 100 rail stations. "The barrier can work up to 2080, but by then we expect it to be opening 60-80 times a year -- which it is not designed for," Burnham said. "Managed flooding would lessen that." The team's shortlist of options for the flood management of the whole estuary will go out for further consultation from mid-2007 to 2009 when it will make the final selection to be put to the Department of the Environment for approval.
