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15/09/2017

Flood prevention: A universal problem with a toolkit of solutions

Words: Anthony Guay
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Flooding is on the increase, globally as well as locally – and its impact can be calamitous. Planning, engineering and landscaping provide solutions, but we need to learn from good practice being developed around the world, says Anthony Guay of environmental, engineering and design consultancy Ramboll.

Recent extreme storm events in Texas, Florida and the Caribbean provide a stark reminder of how the impacts of climate change may be felt with increasing frequency over time. In 2016 Houston was hit with 45cm of rainfall in one day, whilst in August this year Hurricane Harvey dropped over 120cm of rain in a five-day period. This compares with 90cm as the average UK annual rainfall. At least 60 lives were lost as a result of Hurricane Harvey and estimates for the total financial cost could be as high as $100bn (£77bn).  Much of the area that flooded in Houston was known to be at risk of flooding but had been developed due to ever-increasing pressures on urban expansion.

We are also seeing more extreme weather in the UK. This summer has seen flooding in Cornwall, and flood warnings issued in London and Yorkshire in early August. Instances of extreme rainfall are overwhelming drainage systems in our cities, and cleaning up after these events has deep economic ramifications.

"Extensive urbanisation has disrupted the natural water cycle, contributing to flooding and disconnecting our citizens from the water environment"

Extensive urbanisation has disrupted the natural water cycle, contributing to flooding and disconnecting our citizens from the water environment. The Intergovernmental Panel on Climate Change has produced models suggesting that extremes of flooding will become more common this century, and we face the major challenge of making our national infrastructure more resilient to this changing climate. Innovative responses to such international events are being implemented around the world, providing lessons for the UK.

The international perspective

In 2011 Copenhagen received 150mm of rainfall in just two hours, with parts of the city left under up to a metre of water. The Danish describe this as a “Cloudburst” event, from their archaic word ‘Skybrud’, and it seems a fitting term for the devastating event. It resulted in insurance claims totalling over €800m, and overall socio-economic losses are believed to have been twice this amount. In response, the city produced a Cloudburst mitigation plan. The plan, prepared by Ramboll among others, designates the areas of the city most at risk from future Cloudburst events, and proposes a toolkit of solutions to improve Copenhagen’s resilience to flooding. These include:

  • Green streets, on which road profiles and cambers are adapted to provide surface level water storage, whilst also keeping a ‘dry lane’ to maintain movement across the city.
  • In St Jorgen’s Lake in the city centre, it is proposed that the water level will be lowered to provide a storage area for flood waters, alongside designated city squares which will also provide surface level storage.

In Copenhagen, the goal is to pair water management with pleasant public spaces, featuring greenery and smart design. Parks can be extensive and beautiful, while also reverting to floodplains and reservoirs in moments of extreme need.

"Bishan Park can accommodate the sort of severe rainfall that Singapore receives while remaining a traversable route and pleasant environment"

Similarly, fluctuating water levels led Singapore’s city planners to rethink the use of one of the city’s main drainage canals, eventually transforming it into a sinuous natural river couched in 62 hectares of parkland. Bishan Park, as it is now known, can accommodate the sort of severe rainfall that Singapore receives while remaining a traversable route and pleasant environment for citizens.

Finally, Portland, Oregon’s ageing sewer systems have led the city to implement blue-green systems to avert flooding issues. Water absorption will be generally improved by schemes such as ‘eco-roofs’, vegetated roofing systems that provide wildlife habitats and increase efficiency. Green streets pair standard drainage with planting and greenery in a similar manner to Copenhagen’s. Meanwhile the planting of some 40,000 trees will aid water retention across the city.

On the home front

Are such attractive and sometimes expensive measures easily applied in the UK, though? Well, perhaps more readily than we may think. In Calderdale, Yorkshire, we are working with the local council to aid decision-making for the implementation of a number of ‘toolkit’ techniques, some of which were explored in Copenhagen to avert serious flooding issues. Sustainable drainage systems (SuDS) are also developing into the UK mainstream, although uptake has been held back whilst waiting for the relevant parts of the 2010 Flood and Water Management Act to be implemented. Nonetheless, SuDS are now an essential and material planning consideration for major applications.

More challenging is finding a willingness to implement more integrated catchment solutions like the Cloudburst approach taken by the city of Copenhagen. Surface water management plans undertaken by lead local flood authorities have gone part of the way to creating a more holistic approach, but it’s questionable how much change these have brought – especially with reductions in government spending and council budgets in recent years.

"With cooperation between various arms of councils, from parks departments to town planning and developers, these techniques can and should be hugely effective"

Despite this, there are examples of proactive and successful work in the UK. The Queen Caroline Estate in central London, has been remodelled to include green roofs on bin stores, alongside rain gardens and detention basins with raised walkways. These additions are practical but also attractive for local residents compared with asphalt spaces and concrete materials, and have proven hugely popular. A significant number of our own projects in the UK have for more than 20 years embraced SuDS, including permeable paving, swales and surface water features to create spaces that welcome and encourage wildlife while helping to reduce the number of localised instances of flooding.

Moving forward

These projects, paired with the international picture, show that Copenhagen’s toolkit approach is a valuable one – with a variety of tools available to planners, including among others:

  • Green streets
  • Urban tree planting
  • Rain gardens
  • Permeable paving
  • Swales
  • Living, green or blue roofs

With cooperation between various arms of councils, from parks departments to town planning and developers, these techniques can and should be hugely effective in combating flooding in the UK. The economic costs of doing nothing are mounting, and our cities ought to learn from the good practice and innovative approaches to be found within pockets of the UK and from abroad.

Flood risk can be mitigated by a combined approach of appropriate planning, clever engineering and sensitive landscaping, which will aid in combating the global impacts of climate change. As a result of the recent extreme weather events in India, Bangladesh, the Caribbean and America it will be interesting to see if world leaders act further on the threat of climate change.

Anthony Guay is a director of Ramboll Environment & Health 

Photo | iStock

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