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UtILItY WEEK | 21st - 27th March 2014 | 23 Operations & Assets Market view T he Thames Barrier earned its keep this winter, keeping the flood waters at bay more than twice as oen as it ever had before. That has led some – including London mayor Boris Johnson – to wonder whether the current plans to protect London from flood risk are enough. Environment Agency data shows the bar- rier has been closed 173 times to prevent flooding in its history, with more than 50 of the closures in the winter of 2013/14. The graph gives an idea of quite how extraordi- nary this winter has been. The Environment Agency predicts that the flooding risk in this country is likely to increase in the next few decades as a result of climate change. That is concerning, because the Environment Agency says that if the barrier is closed 50 times a year on aver- age or more, new defences will need to be put in place. The agency's Thames Estuary 2100 Plan sets out a range of options the government can choose to implement if it is concerned about the increased risk of flooding. The accompanying technical document identifies three thresholds that would trigger a deci- sion on new defences. Threshold 1 is the level at which the cur- rent flood defences can no longer cope. Threshold 2 would be passed if the current Thames Barrier and improved defences upriver of the barrier look like they could get overwhelmed. Threshold 3 is set at a point where an improved Thames Barrier com- bined with increased flood storage and bet- ter defences upriver and down river are no longer enough to keep the floods at bay. The point at which the Environment Agency decides each threshold is passed is based on monitoring three things. The first is rises in sea level rise. The existing system should be able to withstand around 0.5 metres of sea level rise, accord- ing to the Environment Agency's report. Anything above that level would make flood defence improvements necessary, with a new set of improvements needed for a rise of around 1 metre (threshold 2) and approxi- mately 1.5 metres (threshold 3). The second is tidal surge. The Thames is particularly vulnerable to surges of water. When they are generated in the Atlantic, they can funnel down the North Sea, into the English Channel, and up the Thames Estuary toward London. When such surges coincide with high tides, they can raise the sea level in eastern England by more than 2 metres. Sea level rise as a consequence of climate change could contribute to higher storm surges, further increasing the risk of flooding. The third area it monitors is operational capacity. The Environment Agency says the Thames Barrier reaches its limit of effective- ness when it is being used 50 times a year on average (and is part of threshold 1's crite- ria). Other barriers have similar restrictions. The more the Thames' flood defences get used, the more maintenance they need, and the greater the urgency for improving the defences. If the current flood defences get used more oen than expected, and degrade more quickly as a consequence, then the thresholds get passed sooner. But pinning down precisely when the thresholds are likely to be passed is a chal- lenge because of the complexity of the UK's flood defences. For instance, improving one part of the UK's flood defence system may allow another part to operate effectively for longer, delaying when the next threshold will be passed. For example, raising the upriver defences may mean the Thames Barrier can be closed less oen, allowing it to be used for longer with- out technological improvements (increas- ing the amount of time between threshold 1 being passed, and hitting threshold 2). Furthermore, while scientists warn that climate change increases the risk of flood- ing due to sea level rise and more intense rainfall, the rate at which this may occur is uncertain. So, zeroing in on exactly when the gov- ernment will have to make decisions about the future of the Thames' flood defences is difficult. The UK has just experienced an excep- tionally wet and stormy winter, but this year's weather may be a one-off. And the Environment Agency is keen to stress that this year, the Thames Barrier has done its job. It told Carbon Brief the barrier "continues to operate exceptionally well thanks to day- to-day maintenance, replacing parts and reg- ular inspections." So there's no suggestion the barrier is in trouble. The agency also says the figures in the strategy "should be taken as an average over time". This means closing the barrier 50 times in any one year does not itself increase the chance of it failing to unacceptable levels. While its plan suggests a new barrier would be able to withstand even the worst expected impacts of climate change, it would cost billions of pounds and take decades to build This article by Mat Hope, Ros Donald and Robin Webster first appeared on Carbon Brief, a website dedicated to climate and energy news and analysis (www.carbonbrief.org) Barriers to change? The Thames Barrier has had an extraordinary year, called into action dozens of times to see off flooding. Carbon Brief asks whether it's time to reconsider long-term flood plans for the capital. 1982/83 1983/84 1984/85 1985/86 1986/87 1987/88 1988/89 1989/90 1990/91 1991/92 1992/93 1993/94 1994/95 1995/96 1996/97 1997/98 1998/99 1999/00 2000/01 2001/02 2002/03 2003/04 2004/05 2005/06 2006/07 2007/08 2008/09 2009/10 2010/11 2011/12 2012/13 2013/14 50 40 30 20 10 0 Number of closures Tidal Combined tidal and fluvial Limit Number of Thames Barrier called into action