Planning for a cloudburst: how places adapt to extreme weather

Extreme weather is becoming the norm. There is much the UK can learn from international examples to mitigate the impact, as Anthony Guay explains

Weather in the UK is getting more extreme – this is not up for debate. This summer alone has seen devastating floods 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.

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. The UK is, however, not alone in experiencing such issues, and we are able to learn from innovative responses that are being implemented around the world.

Planning for a ‘cloudburst’ in Copenhagen
In 2011 Copenhagen experienced 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, a term derived from their archaic word ‘skybrud’, which 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, which 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, while also keeping a ‘dry lane’ to maintain movement across the city
• A proposed lowered water level in St Jorgen’s Lake, a lake in the city centre, 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.

Green streets and new rivers
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 residents.

Finally, Portland, Oregon’s ageing sewer systems have led the city to implement blue-green systems to avert flooding issues. Water absorption will generally be improved by schemes such as ‘ecoroofs’, vegetated roofing systems which provide wildlife habitats as well as offering efficiency bonuses. 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.

Toolkit approach in the UK
Are such attractive and sometimes expensive measures easily applied in the UK, though? Well, perhaps more readily than we may think.

In Calderdale, Yorkshire, Ramboll is 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 becoming mainstream in the UK, although the government has held back on implementing the relevant parts of the 2010 flood and water management act. Nonetheless, SuDS are now an essential and material planning consideration for major applications.

‘The economic costs of

doing nothing are mounting’

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 some way towards 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.

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 projects over more than 20 years have embraced porous paving and water management to create spaces that welcome wildlife while helping to prevent local instances of flooding.

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 abroad.