Climate-adapted urban space retains water

10.02.2021

The legendary Copenhagen oasis Enghaveparken was updated and geared to handle future extreme rainfall. In January, the successful integration of climate-adaptation measures and cultural history received the architecture award Årets Arne, named after architect Arne Jacobsen, who designed the characteristic features of the park.

For almost a century, Enghaveparken has served as a green breathing space for Copenhageners, located at the heart of the old workers’ neighbourhood in the Danish capital. In the future, the park will also play a key role in boosting the city’s resilience to cloudbursts and flooding.

An impressive 22,600 m³ of water can be stored in the park’s new multifunctional cloudburst basins located behind a 550-metre bank, which hugs the park as part of the last and largest of four cloudburst storage areas.

Updating the preservation-worthy park is part of the City of Copenhagen’s cloudburst management plan. Indeed, analyses of catchment areas and the existing terrain showed that water naturally gathers in Enghaveparken during cloudbursts. As a result, the task at hand was to create cloudburst infrastructure, while preserving the green oasis for the benefit of the city residents.

Together with architectural firm TREDJE NATUR, Platant and constructor contractor Hoffmann, COWI was in charge of equipping the park to handle future challenges. Priority was given to preserving the recreational and architectural values of the park, which is known for its clam-shaped stage as well as the pavilions at the entrance, which were designed by world-famous architect Arne Jacobsen.

Thanks to the successful combination of modern technology and regard for citizens’ experiences, biodiversity and the architectural qualities, the project was awarded Årets Arne by the Danish Architects Association in January 2021.

Among other things, the jury stated that the project succeeded in integrating a technologically complex program with the cultural history that the park carries.

Photo: Allan Budolf. COWI

NATURAL ADVANTAGES

The many recreational features of the park include a petanque court, ice rink, the clam-shaped stage – and soon the water, which can be used for play, water art, watering and water for sweepers.
“We utilised the park’s existing terrain, which allowed for simple delay and retention of large volumes of water, while preserving and improving the protected main lines and function of the park,” says Leading Project Manager in COWI’s department of Water and Nature Management.

The new features include a three metre deep, lowered pitch, which will serve as stormwater basin in case of heavy cloudbursts.

“The design of the cloudburst infrastructure intends to make the park accessible for as long as possible – even during heavy rainfall – and to render operation as easy as possible. From the initial idea generation phase, it was decided to establish four basins, which will fill hierarchically. The underground basin below Rosenhaven (established by Greater Copenhagen Utility (HOFOR)) only receives so-called daily stormwater from roof surfaces, thereby relieving the main sewer system in the area, which is then able to hold more water during heavy rainfall. At the same time, water can be used for the new, recreational water elements in the park,” she explains.

Photo: Allan Budolf. COWI

URBAN CHALLENGES

It was not straight-forward to transform a protected park at the heart of a city into cloudburst infrastructure. Architect Flemming Rafn with TREDJE NATUR calls it a true catch-22:

”The park is loved by many – each year, one million Copenhageners visit it. How were we to preserve the masterpiece that is the park, while making room for 22,600 m³ of water?”

Part of the answer was to lower the ground level in sections of the park to create basins, install large, underground pipelines between the basins, while preserving trees in the park and minimising the visual impact of the technical components.

Annie, who headed COWI's role as main consultant on the design and tendering of the construction work contract, says: “Take, for instance, the largest pipeline for transporting cloudburst water between the park basins – it measures 1.4 metres in diameter and is made of concrete. You can’t just make it wind smoothly between trees, so it took a lot of planning to design and install the pipelines and wells in a way that does not hit you in the eye.”

The biggest giveaway of the climate protection function is the new, lowered multi-purpose pitch. Surrounded by concrete, this will be the first above-ground basin to fill when the main sewer can no longer convey the large volumes of water and overflows.

“However, we don’t expect water to flow from the multi-purpose pitch to the lake and onwards to Rosenhaven, where the ground level is lowered to form a basin, more often than once every ten years. From Rosenhaven, water is expected to spill over the basin edges every 15 years,” says Annie. Most of the time, the park will be fit for use. That was also one of the requirements set by the City of Copenhagen, when the assignment was defined.

Photo: Allan Budolf. COWI

INTERNATIONAL ATTENTION

The climate-adapted park was inaugurated in 2019, and hopefully, the answer to how to protect a densely populated part of the city against the consequences of cloudbursts may serve as inspiration for other parts of the world.

“We already saw a lot of attention during the process. We hope this project can serve as a source of inspiration for how architects and engineers can join creative forces to safeguard existing urban space against cloudburst in a beautiful and harmonic way, while considering the unique features of the area,” says Annie.

“These are elements that may inspire other municipalities, utility companies and countries. For instance, when working to integrate the UN sustainable development goals in the construction and renovation of stormwater and cloudburst infrastructure, or incorporate a story, play and learning into the end infrastructure.”