With a doubling of flood risk by 2050, we need new policy for development on floodplains sooner rather than later Between 2000 and 2004, floods killed 185 people within the EU and affected half a million. When you think of it the amount of damage that a flood does to a house, the amount of disruption and human distress that it will cause, the amount of waste that it generates then you quickly get the idea that it is best avoided. So why didn’t we figure this out earlier? Well of course we did and then we forgot about it. The traditional way of dealing with flood prone areas was to avoid significant development in them. For example, the original city of London was built on a hill and only started developing lower lying areas from the 18th century onwards. The second line strategy was generally to provide civil works to drain or divert floods away from particularly important properties (great houses and the like). There was always a final option to design the buildings so that the clean up afterwards was quick and effective (ordinary people’s homes). Had we bothered to adopt any of these approaches in our planning and building then the damage of the past month would be much less severe. Historical approaches to deal with flooding might provide a good starting point for a new policy for living with floodplains. We might also bear in mind that climate change is expected to result in elevated rainfall and flood risks in the future. As a rule of thumb British Insurers reckon that peak winter river flows in the UK will increase by 20% by 2050. This works out as a doubling of flood risk by 2050. So while Met Eireann say November 2009 is the wettest on record, we might do well not to dismiss this flood as a one off event. I think that building in a flood plain should not be banned, just strongly discouraged. To ban all development in areas where there is a risk of flooding would be to condemn existing communities and development to potential blight. However when development is allowed in areas of elevated flood risk it should be on the basis that the consequences of a flood are much reduced and that the development does nothing to increase the risk of flooding locally or elsewhere. Strategies of providing flood resilience (easy to repair and clean after the flood) and flood resistance (ability to keep flood waters out) are both sensible ways to manage and mitigate the risk. Indeed research is showing that there are ways in which new developments can combine sustainable practices with ecological flood mitigation measures to reduce flood risks. So adopting practices where surface run off is directed to sustainable urban drainage schemes, permeable paving and in general not putting water into pipes when we can help it will also help alleviate local flooding risks. It is estimated that on undeveloped land that 15 to 20% of rain ends up as run-off, whereas this rises to 80% or above on developed land. Not only is the amount of surface water increased by traditional development but the peak flow increases 10 fold as the vegetation and landscape which store water and block its flow are missing from developed areas. So what do we need to protect us from the floods and all the misery and waste they bring? An effective planning system is a prerequisite. Without a clear strategy and effective control of development then flooding on this scale may well be a far more common occurrence. As a society we need to get some control on where and what we build. We need to do it quickly, and not just for avoiding flooding either. 1.“The LifE report: Long-term initiatives for flood-risk environments”, Baca Architects & BRE, 208 pp. ISBN: 978-1-84806-101-9 This article was written exclusively for irishconstruction.com by Éanna Nolan, head of BRE Ireland. |
