Defending Copenhagen from climate-driven flooding
How two advanced cloudburst tunnels will help Copenhagen weather the storm
All images courtesy of HOFOR
Climate change is driving more extreme weather worldwide, including heavy rainfall — defined as 0.6 inch (15 millimeters) or more in 30 minutes. Copenhagen faces a triple climate threat: The Danish Meteorological Institute predicts rainfall will increase by 30% to 70% by 2100; the sea is estimated to rise by 16.5 inches (42 centimeters); and the groundwater levels are rising. To protect the low-lying areas in Copenhagen and Frederiksberg and reinforce the city’s aging sewage infrastructure, a total of five cloudburst tunnels are being built in the capital.
Denmark’s largest utility, HOFOR, and the utility Frederiksberg Forsyning appointed Jacobs as part of a collaborative team working with NIRAS to provide engineering services for the construction of two of the cloudburst relief tunnels and a pumping station. Services include preliminary and detailed design, procurement support and construction oversight. Once complete, the tunnels will extend 3.8 kilometers (2.36 miles) beneath Valby, Vesterbro and Kalvebod Brygge, with the Kalvebod Brygge Tunnel ranging from 2 to 3 meters (6.6 to 9.8 feet) in diameter and the Valby Tunnel being 4 meters (13.1 feet) in diameter.
1.3 km
(0.81 mi) the length of the Kalvebod Brygge Cloudburst Tunnel
2.5 km
(1.55 mi) the length of the Valby Cloudburst Tunnel
110 tonnes
(121 tons) the weight of “Sigrid” one of the tunnel boring machines used
Building resilience beneath a historic city
In summer 2011, extreme rainfall overwhelmed Copenhagen’s drainage systems, flooding low-lying areas and the historic city center. The damage was estimated at $987 million (€940 million). In response, the city adopted the Copenhagen Cloudburst Management Plan in 2012, a 50-year initiative to strengthen infrastructure against future extreme weather. This plan identified new blue-green projects and drainage system upgrades. HOFOR works closely with the municipalities on a wide range of climate adaptation solutions, including everything from local rain gardens and urban parks to underground retention basins and tunnels.
Although tunnel construction isn’t new to the region, this project marked Scandinavia’s first storm tunnel system of this scale. It required global experience and innovative risk management to navigate the challenges of building in densely populated urban areas with existing metro lines, limited construction space — especially in the harbor — and complex geological conditions.
The primary topographical challenge was the flat, low-lying terrain, which lacks the natural gradient needed for a gravity-led drainage system. Additionally, tunneling in such an urbanized environment demanded meticulous planning to minimize disruptions while preserving historical infrastructure.
Supporting from design through construction
Jacobs was tasked with engineering two cloudburst relief tunnels and supporting the development of a pumping station to address the flow challenge. This scope included:
- Preliminary design using 3D modeling and computational fluid dynamic [CFD] modeling
- Detailed design for construction to ensure safe and efficient execution
- Procurement support for construction tendering
- Construction oversight to completion
CFD modeling was a key requirement in the original tender. This was essential for optimizing the design of drop shafts and the pumping station, helping to reduce operational risks. This skill, not widely available in NIRAS or Denmark, was a critical contribution by Jacobs to the project.
10,000m3
(353K ft 3) water capacity in the Kalvebod Brygge Cloudburst Tunnel
99.5%
Calculated reliability of the tunnels in handling cloudbursts, per NIRAS
20m3
(303 ft 3) water pumped into the harbor per second by the Kalvebod Brygge station
Accelerating progress with a new risk management approach
To ensure smooth execution, the team developed a five-factor, cross-discipline risk management framework aligned with local regulations and met the International Code of Practice to embed a risk-minimizing mindset across the program, considering:
- Health and safety
- Environmental impact
- Reputational risks
- Cost implications
- Time constraints
A custom risk register and modeling tool was created and hosted on a shared data platform, allowing continuous updates throughout the project. Regular workshops and training sessions helped discipline leads from the project partners and HOFOR implement this costed risk management approach, which included Monte Carlo cost simulations for cost estimates.
To overcome challenges relating to public and business impact, public acceptance, environmental constraints and obtaining permissions, the team used this risk management approach to develop design solutions and rigorously examine alternatives, including different routes and additional tunneled sections. This approach is constantly reviewed to incorporate the latest innovations and best practice.
For the Valby Tunnel, the team expanded this model to include a sixth impact factor: operation and maintenance and security of supply (system availability) — ensuring long-term functionality.
Driving collaboration with technology and new ways of working
The success of the tunnel project relied on seamless collaboration among multiple contractors and consultants. The team used federated 3D modeling and Revizto, a BIM-focused software that connected all stakeholders across design, engineering and construction in real time.
Another key to success was the “Blue Week” workshops, monthly in-person meetings in Copenhagen that strengthened relationships, improved teamwork and helped navigate regulatory and procedural differences across international project teams.
By leveraging cutting-edge technology, risk-based decision-making and a highly integrated approach, the Kalvebod Brygge and Valby tunnels are setting a new standard for climate resilience in urban flood management.
