Copenhagen City Council signed off on its master plan for cloudburst management in November to be gradually implemented over the next 20 years. Jonathan Andrews explains what the US$1.4 billion plan entails and whether it can become a benchmark for other cities
The infamous cloudburst that struck Copenhagen in 2011 inundated the city with 15 centimetres of rain in less than three hours, flooding basements, train stations and key arterial roads. The flooding, according to the city, caused 6 billion Danish kroner (US$863 million) worth of damage, not including direct costs of repairing municipal infrastructure or indirect costs such as loss of earnings.
City officials, in the same year, released its now renowned climate adaptation strategy that set the Danish capital along the path of becoming the first city in the world to be carbon neutral by 2025. Although a cloudburst plan had been part of this ambitious strategy, the floods of 2011 pushed it to the top of the agenda.
“The impact of events like that [the 2011 cloudburst] created much more of a political focus,” explains Lykke Leonardsen, head of Climate Unit, Copenhagen City Council. “We had thought we would have a cloudburst management plan that only needed to cover about a third of the city which would be the most affected part, but what happened in 2011 meant we had to do a city-wide plan.”
This plan now incorporates both traditional measures that drain water away through an expansion of the sewer network underground, and–more remarkably–300 surface solutions to be rolled out across the city at a rate of 15 a year. Stormwater roads will transport water to lakes and the harbour, detention roads and detention areas will detain and store water, green roads will detain and hold back the water locally–typically in smaller side streets–and capacity will be increased in traditional stormwater pipes to carry excess water underground to lakes and to the harbour.
“We are trying to keep as much water as possible out of the sewer system,” explains Leonardsen. “We want to control its [the water’s] way through the city and slow it down via cloudburst boulevards, and prevent it from going to low-lying areas like Copenhagen Central Station, which was severely hit by floods in the past.”
At the forefront of the 300 surface solutions thinking is to incorporate dual usages and help create new urban spaces.
“From the very beginning we said that we don’t want to look at this as only solving problems, but as a way of creating opportunities for urban development, for improving the quality of life in the city,” says Leonardsen.
Leonardsen and her team set about working with local communities to create areas for water detention and temporary storage solutions, and to incorporate recreational and social purposes for them.
“Just reserving a space to be only used maybe once every 10 years is not the wisest thing to do,” she adds.
Dual function
This thinking is a common thread across Denmark. Anne-Mette Gjeraa, head of projects, Realdania, a private philanthropic organisation, has been instrumental in the development of WATER PLUS, a Realdania project that combines the handling of rainwater and urban development.
“It is this added-value thinking that we have behind WATER PLUS,” says Gjeraa. “As a society we have to invest a lot of money to climate adapt our cities to handle the new amounts of rainwater, and it is essential that we use the money as intelligently as possible so that we both take care of the rainwater and, at the same time, contribute to making better and more liveable and active cities.”
WATER PLUS has installed four projects, including one on the outskirts of Copenhagen in Gladsaxe and one in Frederiksberg, an autonomous enclave in the middle of Copenhagen City.
“In Denmark we haven’t got these vacant spaces either,” explains Gjeraa. “So we have to find a way to deal with rainwater in a place where there is also another function.”
In Gladsaxe, Realdania worked alongside the local municipality and Gladsaxe Sports Centre to incorporate water detention pools within the playing fields and traditional sports facilities. By diverting and collecting the rain through a series of ponds and canals, the water becomes visible during periods of rainfall. The three main pools flood during heavy rainfalls but during drier periods with small amounts of rain, the pools act as a paddle tennis court, a skate park and recreational area.
The addition of new facilities and activities has transformed the centre into a multifunctional sports area with wide user appeal and a stronger connection to the surrounding residential area.
Leonardsen and her team set about working with local communities to create areas for water detention and temporary storage solutions, and to incorporate recreational and social purposes for them
Long-term savings
By choosing surface solutions with a dual purpose, Gjeraa reveals that the project has saved approximately US$4.3 million, by comparing the traditional model that doesn’t add any recreational value.
Similarly, Copenhagen outlines that its combined approach of traditional and dual-purpose stormwater measures will create a socio-economic surplus over 100 years of 5 billion Danish kroner (US$722 million) in comparison to a situation in which the city does nothing. If a solely traditional sewer-based approach were taken, according to city officials, there would be a deficit for society of 4 billion Danish kroner over 100 years.
Although the plan is a giant step change in stormwater management, the plan has come under criticism with some calling for a greater emphasis on sustainable urban drainage systems (SUDS) and less reliance on traditional floodwater systems.
“In the first place this was very much the idea, to see stormwater not as something to be gotten rid of but as something to use,” says Marina Bergen Jensen, Professor at the Department of Geosciences and Natural Resource Management, University of Copenhagen and who has worked closely with the city since 2007. “In 2011 when we had the cloudburst they [the city council] then got a little scared of all that water. They still wanted the added value but were not sure to what extent they could rely exclusively on SUDS, so they decided to enlarge the conventional capacity.”
Jensen says a bigger emphasis should be placed on road swales and permeable pavings, and more at the individual building level through initiatives such as rain gardens and green walls. These are based on green infrastructure, and enable households, businesses and streets to disconnect from the sewer and stormwater systems.
“To develop SUDS with cloudburst capacity takes time, especially in the denser part of the city, both from a technical point of view and from an administrative point of view,” says Jensen. “It is not that easy to disconnect a street or a building from the sewer system and it is still a cumbersome process but there is awareness popping up.”
By choosing surface solutions with a dual purpose, Gjeraa reveals that the project has saved approximately US$4.3 million, by comparing the traditional model that doesn’t add any recreational value
Jenson highlights one example in Nørrebro, a Copenhagen neighbourhood, where residents in three buildings renovated their shared courtyard and, at the same time, disconnected the rooftops from the city’s stormwater system and installed rain gardens. She admits however that in the past she would be inspired by other cities’ stormwater approaches but now looks closer to home.
“Two years ago we started taking students to Danish sites to show them how to manage stormwater. Previously we took them to Sweden,” she reveals. “Now, we have some really interesting projects here.”
Technological challenges still remain in the plan with further development needed in areas like filtration. These include stormwater that is washed off roads and houses, the so-called ‘first flush’, which can contain and accumulate particles with substances alien to the water environment where they end up. Roads that are salted in winter also add a problem as the new infrastructure provides a potential risk of harming ecosystems and lakes by increasing salt levels.
“The technology sector will be much more active once we begin implementing the solutions,” says Leonardsen, from Copenhagen City Council. “We have to show them that there is a market for developing the answers first, a lot of people are working on them now.”
Who pays?
As stormwater does not follow municipal boundaries or divisions between private and public land, Leonardsen says that the city has worked and will work closely with adjacent municipalities during the roll out. Copenhagen has also been instrumental in changing the national legislation to adapt financing models.
Cities within Denmark and abroad have also shown an interest in implementing their own versions, including Washington DC and New York City
“Most of the measures will be financed by the water rates,” explains Leonardsen. “Where a clear water feature exists, that will be paid by the utility. As soon as we go above ground then it becomes a little more complicated because a cloudburst boulevard is a street 95 percent of the time. In those cases we have to get the projects approved by a national secretariat, that will determine what the city pays and what will be paid by the utility.”
The city, recognised as one of the most liveable in the world, has already received plaudits for its cloudburst plan, including the INDEX 2013 Award in the community category.
Cities within Denmark and abroad have also shown an interest in implementing their own versions, including Washington DC and New York City in the US, the latter signing a collaboration agreement with Copenhagen.
“The idea of creating a cloudburst management programme for the entire New York City is a little bit daunting,” adds Leonardsen. “It’s crazy enough doing it in Copenhagen! But I think we are the only ones that have taken this city-wide approach. Although there are a lot of cities that have been inspired, each city has to find its own approach.”
The new approach taken by Copenhagen in stormwater management is, however, a work in progress of which Leonardsen is fully aware. “I’m sure in 20 years time I will look back at some of the plan’s aspects and ask ‘What was I thinking?’ It is still very much a learning curve.”
