Cloudburst protection, Østerbro, Copenhagen

Sweco is designing a cloudburst tunnel under Strandboulevarden to protect the Østerbro district against cloudbursts. The project is part of the City of Copenhagen’s Cloudburst Management Plan, which also includes improvements of urban spaces.


Customer: HOFOR

Period: 2015–2019

Location: Østerbro, Copenhagen

Expected tunnel budget: DKK 130 million


The 1.1-kilometre-long cloudburst tunnel – which will run under Strandboulevarden and Gl. Kalkbrænderi Vej to the harbour basin – is well on its way through the design phase. The tunnel's inner diameter is 2.0 and 2.5 metres respectively and it is expected to be ready for use in 2019.

The overall requirement of the City of Copenhagen is that the project maintains the level of flooding with a maximum of 10 cm for a one-hundred-year cloudburst event in 2110. Finally, it should be possible for the tunnel to cut off everyday precipitation from the existing combined sewer system.

Sweco's project manager, Bo Bonnerup, manages the project along with Jesper H. Thyme, Project Manager, HOFOR. One of the challenges is the forthcoming cloudburst park – on top of the tunnel – being planned by the City of Copenhagen.

This very interaction between the cloudburst park and the transport capacity through the tunnel is interesting, because it involves factors such as how to ensure that we can achieve the hydraulic targets during extreme rain events and how to establish shafts and tunnelling in a densely populated urban area. Tunnelling is a complex construction method where precision in the preliminary studies and planning is crucial. This is because changes during the construction phase can lead to high additional costs and inconvenience. For this reason, comprehensive geotechnical and hydro-geological studies were carried out to minimise surprises wherever possible.


"The tunnel enables us to protect large areas of Østerbro against cloudbursts. In a densely populated urban area, it is very difficult to establish other solutions, as every inch of space is being used, and because of the sheer enormity of the volume of rainwater that needs to be managed. For this reason, HOFOR will establish a number of tunnels in the years ahead which, together with ground-level solutions, will protect the city against cloudbursts."