Storms, Cloudbursts and flooding – learning from Copenhagen


In Denmark the State of Green reports on how city of Copenhagen is rethinking its strategy to sudden storms and the increased risk of flooding exacerbated by the impact of climate change. This work particularly follows from severe storms in 2011 which caused massive local flooding costing a billion euros in property damage and recovery. A report  concludes that the cost of adaptation and mitigation would be money much better spent than on recovery even from infrequent major floods – a conclusion which is significant to the UK given recent flood events.

With the support of its Mayor Copenhagen is developing its new ‘Cloudburst Management Plan‘ which takes a long-term, 20-year development perspective which sees water as an asset, rather than as a problem. Instead of taking a conventional approach that sees storm water as being an issue to be addressed with greater channelization and sewer development, it is instead looking to develop a much more holistic response using blue-green solutions wherever possible. The city’s climate adaption strategy gives significant emphasis on revising existing water management to separate its sewage management from rain and flood water drainage. While Copenhagen does need to improve its sewage systems because of the city’s growth and handling larger volumes; this is a different, though related question to responding to sudden weather events. Its related particularly because better containment and separation of sewage makes it safer and more hygienic to address flood water at ground level.

The Cloudburst Management Plan takes a much wider socio-economic perspective. It includes proposals to develop new bicycle transport routes which also serve as storm-water channels. There is increased emphasis on street trees and planting alongside open storm channels (swales); in these systems water can be diverted to temporary storage and taken up by the living plants to slow water progression. This approach helps create an environment where people also benefit from the aesthetic improvements which are a side benefit of the adaptation measures. Needless to say it is an approach which also benfits urban biodiversity by creating more habitat and extending connectivity.

The report highlights that its it far cheaper and easier to implement these sort of surface/near surface improvements than developing harder, deeper grey infrastructure solutions but points to limitations in the denser areas of the city where these solutions are physically difficult to develop and far harder to combine with amenity and recreational advantages.

Another significant point of the report is its recognition of wider catchment issues and that water is not contained within political administrative boundaries; so that the plan is being developed with neighboring municipalities to be coherent. Additionally, given the long scale of strategic development to deliver the responses across the city, it identifies priority flood risk areas which need to be initial targets for improvement.

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