Despite certain measures such as the construction of the Thames Barrier, London is still at risk from flooding. Climate change, increased demand on the capital’s drainage, increased building and expansion and the accompanying rise in hard surfaces mean measures need to be taken to reduce London’s flood risk.
What is the flood risk?
Various factors combine:
Climate and structural
Sea levels are rising and London has sunk by about one third of a metre since the second world war. The London Climate Change Partnership estimates that by the 2080’s winters will be some 30% wetter than now, and heavy rainfall could occur twice as often as it does at present.
The period mid-December 2013 to mid-February 2014 saw widespread flooding caused by a series of severe winter storms. This is the type of weather the UK is predicted to experience more of in the years to come.
Large parts of London are on a flood plain with some 1,250,000 people living and working on it. As the city expands, much of the new housing and other building work is being constructed on the flood plain itself thus adding to the flood risk.
The Thames Barrier has made a big difference – without it certain well-known buildings such as the O2 Arena, Tower Bridge and the Houses of Parliament would spend periods of time flooded. On average, the barrier has to be closed some three times a year to prevent flooding. It protects around 48 square miles of London and its infrastructure including a large part of the underground network.
Prevention: ideas under consideration include raising vulnerable homes on stilts, building roads on embankments above flood plains and using large swathes of Kent and Essex farmland as ‘escape areas’ for flood water during potential tidal surges to alleviate the pressure on London’s flood defences.
For new builds – and maybe even some existing properties – flood combating measures need to be incorporated such as lime based plaster to better cope with water, siting electrical connections higher up the walls, more waterproofing and solid concrete walls on ground floors.
London’s drains simply cannot cope with heavier demands such as periods of high rainfall. The capital’s expansion has meant an increased amount of land being covered with tarmac and concrete and thus more ‘hard surfaces’. Whereas some rainwater would have been absorbed into the ground previously, more of it now runs off the hard surface and into the drains – and if they can’t deal with it, the water stays on the surface and flooding can result.
Within the last ten years, significant floods in areas such as Cricklewood, Brent Cross, Bromley and Croydon have all been caused by excess surface water. Other areas of London including famous landmarks such as the Bank of England have been identified by these flood assessment experts as vulnerable to surface water flooding.
Prevention: a huge ‘super sewer’ – the Thames Tideway Tunnel – is due to start construction in 2016 and will alleviate the considerable strain on London’s sewers during periods of heavy rainfall. Instead of the overflow system depositing millions of tonnes of sewage into the river and contributing to the flood risk, the tunnel will carry it beneath the river and onto treatment works.
More localised measures such as sustainable urban drainage systems (SUDS) are being constructed in certain parts of the capital to help prepare for a time of more extreme weather conditions.
Poor drains maintenance
Many householders and other people responsible for property such as residential and commercial landlords are remiss in having drains inspected and cleared.
Part of the problem can stem from residents not being aware of when drains and water courses are their responsibility. Water authority websites usually explain using diagrams and graphics which drains are the property owner’s responsibility, but many are unaware.
Significant flooding on Canvey Island in Essex was caused by a number of residents simply not being aware of their responsibilities. In this case, it was people not knowing they were responsible for certain watercourses – and some not even being aware they existed in the first place.
Then there is improper drains use where inappropriate materials are disposed of via the drains. For example, there have been major blockages caused under city streets due to the buildup of fats – a problem that has taken a lot of man hours to deal with.
Prevention: a lot of this is trying to educate property owners and householders as to where their responsibilities lie with regard to their drains. Also, a programme of drains inspection and mapping would be required – in some cases, the location of water courses has been lost track of.
The threat of flooding to London is a very real one and, while some measures can be affected sooner rather than later, many of the significant ones will take many years to come to fruition. For example, the Thames Tideway Tunnel, discussed earlier, will take at least seven years to construct hence the need to identify the risks and plan for them as soon as possible.
About The Author
Fraser Ruthven is the Marketing Associate for London Drainage Facilities, one of London’s leading drainage companies. London Drainage provides a wide range of drainage diagnostic and repair services in and around London.