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Sunday 1st April 2012
Sustainable Urban Drainage and Flood Resilience
Cities Contributor: Samir Jeraj

Editor’s Note: Defra’s recently released Climate Change Risk Assessment for the UK cited flooding as the single biggest threat that climate change poses to the country. Despite this flood management at a local level has left a lot to be desired. Flood protection measures have frequently focussed on ‘hard’ adaptation measures such as flood barriers and raising sections of road. Such actions can have the effect of simply moving the problem to other parts of the drainage system, creating problems for previously unaffected areas. Perversely urban drainage and flood protection measures have not always complemented each other. ‘Storm drains’, combined flood and sewer systems, and runoff channels have all been employed to manage the flow of rainwater. But these measures all have the effect of channelling rainwater into sewers and rivers extremely quickly, and can actually increase the likelihood of pluvial flooding. But, you’ll be pleased to hear, there is another way. As Samir Jeraj explains, employing sustainable urban drainage (SUD) techniques and taking a holistic approach to urban drainage systems can lead to flood-resilient cities that are more pleasant places in which to live.

 

The idea that an entire town in a developed, western country could be swept away by rain is something that seems almost mythical – more the stuff of local folklore than a potential reality for today’s urban planners.

However, pluvial flooding from heavy rainfall is a major hazard in the UK and is something that will only increase as climate change disrupts weather patterns and exacerbates extreme events. It will be a major challenge for UK flood resilience in the coming years. After the 2009 floods in Cockermouth, the government was forced to recognise that pluvial flooding was a particular and separate issue to ‘normal’ flooding from rivers and the sea. The reports and policy papers emerging in the aftermath of the floods have huge implications for the areas where people in the UK live and work.

The Joseph Rowntree Foundation assessed the scale of the problem in a report published at the end of last year. They calculated that 2 million people live in areas at risk of pluvial flooding; a figure that could rise to 3.2 million in 2050 due to the combined impact of climate change and population growth. The areas at highest risk are low-lying inner-city neighbourhoods, which are generally more deprived and hence more vulnerable. Insurance is a specific issue that is highlighted by the report, as many people living in council-owned property and privately rented housing do not have adequate cover; a problem identified alongside access to bank accounts as a key factor in increasing financial exclusion . The problem is likely to be further exacerbated as many people will now face rising premiums as a result of increasing flood risk.

The Cockermouth example illuminated some of the factors and planning decisions that have eroded resilience and made the towns more vulnerable to pluvial flooding. The town’s website, www.cockermouth.org, notes that, “Heavy rainfall was the main cause [of flooding] but rivers had been under-edged for years and a relief archway at Gote Bridge (added after an earlier traumatic flood) was partially silted up when the floods struck.”

With careful planning it should be possible for the Environment Agency and other authorities to ensure that high-risk areas are provided with the services that reduce the risk from pluvial flooding. New developments can be required to provide ‘Sustainable Urban Drainage’ measures such as grey water systems, green roofs, water butts and permeable pavements. However, many high risk areas were built on in the Victorian era, in dry valleys, which have come under further pressure as towns and cities have expanded and reduced the area into which rain can be absorbed. Implementing successful retrospective adaptation measures in these existing vulnerable areas is a major challenge when seeking to increase resilience to pluvial flooding.

There are a number of ways that existing urban areas can be improved to mitigate risk, and simultaneously provide a more pleasant local environment. A recent report conducted by the London Wildlife Trust highlighted the loss of front gardens to parking spaces in an increasingly crowded city environment as a contributing factor to urban pluvial flooding. Preserving such spaces would also have a positive impact on biodiversity, mental and physical health, adaptation to climate change, and economic benefits. Providing more green spaces and urban gardens would also provide more protection from infill development and would reduce the likelihood that derelict land was simply paved over.

In addition to protecting existing gardens and green space, we can further increase resilience by greening urban areas. Community gardens and allotments have thrived in recent years, meeting the growing desire of people in the UK to grow their own food and to clean up derelict sites in cities – examples of such schemes can be seen in cities across the UK from Norwich to Northumbria. Nation-wide the Federation of City Farms and Community Gardens now represents hundreds of school and city farms, allotments, and community gardens – employing around 550 people and with a turnover of £40million a year.

Another idea nascent in the UK, but well established in Nordic countries, are ‘green roofs’ – having living plants covering the roof of a property (remembering to take appropriate measures to stop damage of course!). Green roofs have the advantage of absorbing water, insulating homes, improving biodiversity, and reducing the impacts of summer heat in urban areas.

Local councils should take action to integrate sustainable urban drainage measures into planning decisions. Simple, cost-effective measures such as altering pavements to provide extra drainage, not simply by installing more drains, but by constructing pavements from porous materials, would considerably reduce flood risk. Councils must also promote the use of water butts in the same way that many councils have encouraged composting. Water butts not only store rainwater runoff that could otherwise contribute to pluvial flooding, but are also an essential part of water conservation in an increasingly dry environment.

One of the principal obstacles to such measures becoming reality is accountability within local governance structures. Drainage systems are governed by a wide range of stakeholders including councils, highways agencies and water companies. Communities must ask local authorities to identify who is responsible for the drainage system and whether they have a credible plan for reducing pluvial flood risk? Finding holistic solutions to drainage problems will not just make city environments safer and more resilient, they will make our cities greener better, more pleasant places to live and work.

 

Samir Jeraj is a Green Party City Councillor in Norwich where he is currently the deputy leader of the opposition. He has worked in local government and the voluntary sector, and recently completed an MA in Development Studies focusing on the rise of the far right in India.

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