NIRAS employee in tunnel
Two large-scale cloudburst projects on the way in Copenhagen. NIRAS is consultant on the new tunnels for rainwater.
Tunnel expertise

HOFOR starts large-scale tunnel projects in Copenhagen with NIRAS as consultant

Two new 'highways for rainwater' will be drilled in the Copenhagen underground. Denmark's largest utility company, HOFOR, has hired an international team of consultants with NIRAS in the lead to solve the complicated cloudburst projects.

04. Jun 2018

Not only one – but two cloudburst tunnels are now being established in the Copenhagen underground by HOFOR and Frederiksberg Kloak (sewer utility). These large-scale projects will be constructed as two independent tunnels through the calcareous underground beneath the districts Valby, and from Vesterbro to Kalvebod Brygge.

The tunnels will cost 300 million DKK and 320 million DKK, respectively, and the main purpose is to prepare the city for rare extreme rainfall events – defined as 15 millimeters of rain (about 0.6 inches) in a 30-minute period. At the same time, the two tunnels will also have a climate protection effect on the increased amounts of everyday rain, says Project manager Morten Elton Jensen from HOFOR.

"When constructing this kind of 'highway for water', we kill two birds with one stone. We need to do something about torrential rain – which is the main purpose of the tunnels. But the tunnels can also be used for the increased amounts of everyday rain, thus ensuring that the capacity of the sewage system is sufficient for the future," says Morten Elton Jensen.

2,860 meters of tunnel

The two tunnels will be up to three meters in diameter and drilled at a depth of 12-20 meters below sea level – in the same way the Copenhagen metro is constructed. The Kalvebod Brygge tunnel will extend over 1,360 meters while the Valby tunnel will have a stretch of 1,500 meters.

"We expect that it will rain 30 percent more in the future. Therefore, it will be necessary to disconnect 30 percent of surface water falling on streets and straits. Instead of expanding the capacity of the sewers, we think differently and divert the water into cloudburst tunnels", says Lene Nørgård Rasmussen, HOFOR's Project manager for the cloudburst tunnels.

Heavy technical challenges

The two tunnel projects may seem almost identical, but there is a world of difference. Project manager Lene Nørgaard Rasmussen explains that HOFOR does not expect the residents of Valby to even notice that the tunnel is being constructed in the underground, but the Kalvebod Brygge tunnel, however, will become an extremely demanding construction task.

"On the Kalvebod Brygge tunnel, we will be confronted with some very difficult technical challenges. We will have to cross the new metro city line, while at the same time working above the stable limestone layers in the underground. Here, there is not much room. We will have to work in contaminated soil under the buildings in Copenhagens Meatpacking District, and at the same time we must avoid to disturb the city", says Lene Nørgård Rasmussen.

For the Kalvebod Brygge tunnel, a temporary tunnel shaft with secant piling will be established in the harbor. Therefore, the Kalvebod Brygge project will be visible in the urban landscape for several years contrary to the Valby tunnel, which is not expected to attract attention, as this tunnel is situated far from neighbors and with ample space around the construction site.

International Consultancy Team

A very strong team of Danish and international competencies and partners has been assembled for this task. The builders, HOFOR and Frederiksberg Kloak A/S (sewer utility), have engaged NIRAS as consultant. NIRAS has composed an international team of consultants, in which experts from the Danish GEO and tunnel specialists from Germany and England together with NIRAS shall lift this very complicated project.

"NIRAS is a listening consultant, who makes an effort to understand the client’s wishes - a very good quality. On this project, a team of foreign specialists and a Danish sub-consultant have been selected, and in our point of view, this is the optimal team for this particular task”, says Morten Elton Jensen from HOFOR.

Experience from the Damhus tunnel

In NIRAS, climate adaptation is an area that has developed enormously for the last 5-7 years. Compared to that time, NIRAS currently employs twice as many engineers and specialists within climate adaptation and drainage systems.

As a consultant, NIRAS is at the forefront with creative projects on the edge of the city. But this also applies to urban climate adaptation above ground level and under ground level as is the case with the two new cloudburst tunnels, and before them, the Damhus tunnel in Copenhagen, says Vice President for Water and Utilities in NIRAS, Jens Brandt Bering.

"When we talk about urban climate adaptation, our successful cooperation with HOFOR on the Damhus cloudburst tunnel has been a game changer for NIRAS. Due to the 3,400 meters of cloudburst tunnel in the park of Vigerslev, we have gained valuable experience, which has resulted in several and more projects concerning urban climate adaptation,” says Jens Brandt Bering.