Cloudburst mitigation will prevent cities from drowning

After three massive cloudbursts in recent years, Copenhagen is preparing for climate change and the impact of future extreme weather. Over the next 30 years, Copenhagen will implement an ambitious cloudburst masterplan and a number of concretisation plans to protect the entire city against the damages of heavy rain.

St. Jørgens sø in Copenhagen

The world is facing severe issues as a result of climate changes. Cities all over the world are increasingly plagued by flooding causing large damages to private and public space. From August 2010 to August 2011 Copenhagen was hit by three devastating cloudbursts, flooding major roads and other infrastructure facilities. Total damage from the most destructive of the three events left the City of Copenhagen with expenses of more than EUR 800 million.

Protecting Copenhagen from flooding

As a consequence of the disastrous 12 months, the municipality of Copenhagen decided to protect the city against future cloudbursts by implementing a cloudburst masterplan and its concretisation plans. Eight concretisation plans covering the whole city of Copenhagen have been published, with Ramboll creating four of them covering more than half of the area.

- Research connected to cloudburst planning shows that investments and improvements pay off. The events in Copenhagen have taught us that if cities don't take proper action, expenses will rise. Cities must be passable, even during large cloudbursts, says Martin Vilhelmsen, Senior Project Manager at Ramboll Water.

When fully implemented 30 years from now, the cloudburst concretisation plans will protect Copenhagen from severe storms and will take climate change into account as well. The concretisation plans aim at decoupling 30-40% of the storm water from sewer system in order to level out the effects of climate change predicted to cause 40% more extreme rainfall over a period of 100 years.

Managing wastewater over ground

The cloudburst concretisation plans are based on a few simple principles. The main principle is to keep the water on the surface and control it rather than installing large, expensive pipes underground. Instead, cloudburst streets will collect and transport the water away from the vulnerable, low-lying areas.

Adjacent to the cloudburst streets, secondary streets will be transformed into green streets that retain the water. In areas where the water simply cannot be managed over ground, large underground cloudburst tunnels up to three metre in diameter will be built instead of cloudburst streets.

The cloudburst concretisation plans intend to create synergy for the city as a whole through visionary solutions. This is achieved by using water-sensitive, blue-green solutions to increase the overall liveability of the city. The water on the terrain will serve as a resource in the city space. Benefits include increased recreational value from upgrading of parks and meeting places.

Cloudburst planning will increase liveability

The design of the concretisation plans visualises how cloudburst streets, retention streets and green streets will support the overall goal of increasing the liveability of the city of Copenhagen.

- When we think about liveable cities, we consider the big picture. Everything you build or upgrade must have one primary function – to support general quality of life in the city, says Martin Vilhelmsen.

Multi-functional spaces are key elements in the plan, such as parks and playgrounds that can be flooded during heavy rainfall but in dry weather serve as recreational spaces for the citizens. One of the more radical suggestions in one of the cloudburst concretisation plans is to transform one of Copenhagen's three inner-city lakes, Sankt Jørgens Lake, into a beach park by lowering the water level in the lake. This creates a vast area for the collection of rainwater while improving Copenhagen's recreational value. At the same time, the park can be flooded during cloudbursts.

Global need for holistic urban planning

Copenhagen was named the world's most liveable city by Monocle magazine in 2014, and the cloudburst concretisation plans will help consolidate this position. The plans highlight the importance of long-term urban planning with a focus on holistic and sustainable solutions. It also serves as a showcase for other cities facing the same issues around the world.

- Other cities can learn a lot from Copenhagen in terms of becoming greener and more liveable, even much larger cities with more imminent challenges. Maintaining a holistic mindset is of vital importance, both in the short and long run, says Martin Vilhelmsen.

- Urbanisation is increasing, particularly in Asia where more and more people are moving to the cities. Meanwhile, they are shifting from low to middle income and demanding better standards of living. This puts enormous pressure on urban development and infrastructure, creating an urgent need for holistic urban planning and city solutions, he concludes.

Ramboll Group A/S

Ramboll Group A/S
Hannemanns Allé 53
DK-2300 Copenhagen S
Tel:+45 5161 1000
Fax:+45 5161 1001


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