In the years to come, HOFOR (Greater Copenhagen Utility) will construct a number of cloudburst tunnels in the undergrounds of Copenhagen, which will protect the Danish capital against floods. One of the tunnels is Kalvebod Brygge Clousburst Tunnel. In the event of massive cloudbursts, this underground tunnel will lead the rainwater to a large pumping station, which will subsequently pump the water into Copenhagen harbour.
In the test facilities at DHI A/S in Hoersholm, the clients HOFOR and Frederiksberg Utility, as well as an international team of consultants lead by NIRAS have executed a number of crucial and fascinating tests with a specially built model of the pumping station. With a 2½ meter tall plexiglass water tank, they have been able to create a true-to-nature model of the planned pumping station by Kalvebod Brygge in Copenhagen.
With this accurate model it is possible to test pumps’ dimensionality and function in the tunnel shaft with an aspect ratio of 1:11. It requires powerful pumps to lift the massive amounts of cloudburst water from the large tunnel shaft approx. 12 meters up and out into the dock. The pumping station will be equipped with six pumps, which will yield a capacity of 20 cubic meters of water per second – that is the equivalent to emptying an Olympic swimming pool in just two minutes.
Blue tracer liquids show the water’s movement
The exact subjects of testing at DHI are the pumps, the design of the tunnel shaft, as well as the way in which the water behaves inside the tunnel shaft. Through complicated calculations, the experts from the international consulting team have devised the unique solutions.
Those solutions have now been successfully tested in the model, where blue tracer liquids show the water’s way from the tunnel while it fills the shaft and is pumped up and out into the habour.
One of the essential results at DHI was that the project team realized that baffles had to be built into the bottom of the tunnel shaft. Baffles are vertical bricks made of concrete or steel, which control the stream of water passing through the tunnel and inside the tunnel shaft with great force.
Completely unique solutions
Nothing about Kalvebod Brygge Cloudburst Tunnel is standard. Everything is custom-made and unique – which is exactly why HOFOR and Frederiksberg Utility have chosen to test the solutions at DHI.
The cloudburst tunnel is expected to be needed around once every five years during particularly powerful cloudbursts. In that event, the cloudburst tunnel will prevent floods in Copenhagen, which would otherwise cost billions in damages. The solution consequently has to work perfectly.
The call for tenders is expected in August 2020. This means, that the construction will commence around August 2021, and finally the tunnel is expected to be commissioned in 2025.
The design of Kalvebod pumping station is extreme in many ways. Both in economic terms, when it comes to capacity as well as the framework in which the pumping station is built. Nothing in this project follows ‘standard procedures’, and we therefore have to ensure that it works as intended. That is the purpose of this model test.