What can we learn from Copenhagen’s Cloudburst Strategy?
Can some flood mitigation measures in Copenhagen be implemented to cities.
With the rapid changing of climate, people are often looking for the best respond to defend their properties against flooding and improve their infrastructure at every level in between. Due to extensive urbanisation in the past two decades, we have disrupted our natural water cycle, contributing to intense flooding from the water environment. What I’ve found, however, is that our ageing infrastructure isn’t as robust as we think when faced with increasing weather extremes, and when the drainage systems are overwhelmed and flood waters erupt from the subterranean networks, the damage and consequences are severe.
It is evident that Europeans are facing more extremes weather. Reports of river, coastal, groundwater and urban flooding across Denmark are increasingly in the news. Extreme rainfall events deluge cities and overwhelm the drainage systems, with subsequent economic consequences.
IPCC suggests that extremes of flood and drought will become more common in the future, and cities are facing major challenges of making their national infrastructure more resilient to this changing climate. And in this post, I would like to take some successful examples of flood mitigation measures in Denmark.
What happened in Copenhagen?
In 2010 and 2011 the city of Copenhagen had suffered from extremely heavy downpours. Streets and parks were flooded all over the city. However, the administration was a little bit prepared. There was a new Wastewater Plan, a new Strategy for Biodiversity and a Green Structure Plan. Together they were the base of the “Climate Adaption Plan” — accepted in 2011.
The city described this as a “cloudburst” event, from the Old Danish word Skybrud, and it seems a fitting term for the extremely intense storms that are becoming more frequent across Europe. Insurance claims from this flood exceeded over €800 million and the total socio-economic loss has been estimated to be double this figure. In recognition of the significant impact on society and the economy, the city produced a Cloudburst Mitigation Plan. This plan, identifies the parts of the city most at risk from future cloudburst events, and proposed solutions to increase the city’s resilience to flooding.
The overall principles of the strategy implemented in Denmark are
- To retain rainwater in the upper catchment
- To provide robust and adaptable drainage of lower lying areas
- To focus on implementing green and blue solutions in existing projects
Green spaces within streets
Copenhagen has an approach towards public realm solutions, including the cloudburst-adapted streets and retention streets mentioned above, as well as the provision of other green streets and central areas of retention in existing squares and lakes. Road profiles and cambers have been adapted to provide surface level storage in cross-section, whilst also keeping a “dry lane” to maintain movement across the city. These solutions reflect the hierarchy of streets across the city. Where wider streets such as Tåsinge Plads in Østerbro, a grassed channel can be incorporated for storage, treatment and conveyance. Narrower streets such as the Hans Tavsens Park in Korsgade has additional channels installed in the existing paving, and benefit more from adaption of the camber to facilitate storage. There are a lot of streets in Copenhagen that implemented a mix of hard and soft water strategies in proportion to their width and use.
Sankt Jørgens Sø, an existing lake sprawls across Østerport/ Nørrebro/ Frederiksberg and Vesterbro, is proposed to provide a central storage area for flood waters, along with designated city squares which will also provide surface level storage. This network of blue-green infrastructure aims to replicate the natural water cycle that has been disrupted through modern urban development. A by-product is that water is increasingly brought to the surface where it is more visible, blockages can be more easily identified and managed, and the overall consequences of failure are reduced. As well as the flood relief and water management functions, I found theses solutions have been contributing to the amenity and liveability of the city by increasing planted areas.
How is this relevant to other places
So some may ask the question, how transferable are these kinds of solutions in urbanised and developing cities? Well, perhaps they are more transferable than we may think. For example the Sustainable Drainage Systems (SuDS) have become increasingly mainstream. In the UK, the NPPF has been strengthened in this area and SuDS are now a material planning consideration for major applications.
My experience working in a project in Copenhagen with NIRAS suggests that SuDS have been most successfully implemented on a smaller project by project basis rather a catchment basis, perhaps due to funding pressures. The range of solutions in Copenhagen have identified could just as easily be applied in some post-industrial cities. The Surface Water Management Plans in UK is undertaken by Lead Local Flood Authorities and it has gone part of the way to 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.
In response to flood events, public spending on flood defence schemes and watercourse maintenance is increasing. However, the impression is that cities are still too reactive to flood events rather than taking pro-active measures to make our towns and cities more flood resilient, enjoying the economic, amenity and liveability benefits at the same time.
Some practices have been made in the UK
Cities like Sheffield and London already have established Blue and Green city plans, aiming to capitalise on the existing water networks and green spaces for the amenity and health benefits of their citizens. Hard and soft SuDS, blue/green spaces, retrofit SuDS and resilient buildings are all becoming more common and should become ever more so as Lead Local Flood Authorities work out the finer detail of their strengthened position with regard to SuDS and urban flooding. Making communities and national infrastructure more resilient to extreme weather and flooding for the future.
A lesson from Copenhagen is that as well as funding, the key issue is cross-department co-operation between the roads, water, parks and environment authorities. The responsibility for water in UK is spread unevenly between local authorities, water, landscape and transport departments. However the implementation for SuDS in the NPPF is definitely a step in the right direction. But in the face of a changing climate, the economic costs of doing nothing are mounting, and cities should learn from the good practice and reform its cloudburst approach like Copenhagen. When disaster strikes, as it did in Copenhagen, the hidden costs of not taking proactive action are painfully realised. This is a valuable lesson cities should be taken into account.
