Before the flood: protecting London’s future

Thames barrier
The Thames Barrier

Grantham Affiliate Dr Ana Mijic examines London’s vulnerability to flooding, and the infrastructure projects safeguarding the city’s future.

This month saw the launch of Flood Re, a new UK government-backed scheme intended to lower the cost of insuring homes in high-risk areas against flood . Whilst the scheme will benefit thousands, as always, prevention – in the form of well though-out adaptation plans – is the best medicine.

For the UK capital, flooding is an issue of great importance. The Association of British Insurers has predicted that a major flooding event in London could have economic consequences comparable to the 2009 recession, causing damage to property, loss or disruption in the public service, and potentially endangering human lives. The Environment Agency estimates that the staff time lost due to a flooding event in the capital could cost as much as £10 million per day.

Keeping tidal floods at bay

Beautiful river views and strolls on the South Bank are integral to London life, but these perks come at a cost. Our location and high level of urbanisation mean London is at risk of flooding from various sources, including coastal, river, and surface water. But by far the most dangerous threat comes from the sea. A tidal wave moving up from the North Sea would have the potential to inundate swathes of Greater London along the Thames, affecting more than 1.25 million people and £200 billion worth of property. Moreover, this risk is increasing due to effects of climate change, including sea level rise and changes in rainfall patterns.

Fortunately, Londoners sleep easy for now. The Thames Barrier, fully operational since 1982, presently protects the city. In addition, the barrier also protects upstream areas from flooding that could be caused by high iupstream flows coming down the Thames. This dual function, however, has brought the barrier very close to its full operating capacity in recent years, indicating significant changes in the natural processes influencing the tidal cycle and river flows. To address this, the Thames Estuary 2100 project was put in place to plan for tidal flood risks to the end of the 21st century. This project is one of the world’s first examples of infrastructure planning taking into account for a range of different climate change scenarios, and developing options to adapt our cities by introducing a set of proposed interventions, such as additional flood storage, raising the existing defences and building a new barrier. The timescale for each of these steps will be adjusted depending on the rate of climate change.

Rainy days

London rain
London’s infrastructure may struggle to cope with extreme rainfall in future

While a dramatic tidal wave might not be out of place in a Hollywood film, our capital also faces a growing threat from a far more familiar phenomenon: rain. London’s aging water infrastructure and intensive urbanisation pose a new, and very important, question – for how long can the city cope with intensive rainfall events before facing significant consequences?

If London were to receive a comparable amount of rainfall to that which caused floods in central England in recent years, the consequences are expected to be much more significant, resulting in tens of billions of pounds of damage to property and infrastructure, and high probability of a severe effect on human health and lives.

As any Londoner knows, space comes at a premium, and measures to protect our city from flooding are constrained by the space available for  new or upgraded water infrastructure. Capital  projects, such as Thames Tideway Tunnel, are one possible solution to partially address this issue. Without this tunnel, intensive precipitation and the insufficient sewerage capacity mean an average of 20 million tonnes of water severely contaminated with untreated sewage are currently discharged each year into the Thames.

Future-proofing cities

However, innovative approaches to urban planning and engineering can enhance the flood resilience of mega-cities such as London, and improve quality of life of people living in urban environments. This philosophy underpins the work undertaken in the Civil and Environmental Engineering Department at Imperial College London through the EPSRC Centre for Doctoral Training in Sustainable Civil Engineering and related research projects. In the context of urban flooding this idea was explored in the Blue Green Dream project. The approach maximises multiple uses for infrastructure, in particular through the use of urban green spaces to reduce the amount of water runoff from the surface, at the same time providing wide-ranging benefits from reduced air pollution to enhanced biodiversity levels.

Investment in improving cities’ resilience to flooding is essential, and people should be aware of both the potential impacts of extreme weather events and the range of response options. Although London does face a significant flood risk, there are already multiple initiatives and plans underway at all levels to mitigate this risk– scientific, policy, governmental and business – these should mean that Londoners can still enjoy stress-free city-living for many decades to come.

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