Urban areas face increasing challenges with handling intense rainfall, or cloudbursts, which can overwhelm drainage systems, leading to flooding and environmental concerns. Traditional rainwater management systems often direct all rainwater, both from everyday rainfall and intense cloudbursts, directly into sewers, burdening wastewater treatment facilities and wasting valuable resources. Frederiksberg Municipality and Frederiksberg Forsyning recognized the need for a more sustainable approach that would relieve pressure on the sewer system while integrating rainwater into the natural water cycle wherever possible.

In 2023, Frederiksberg Forsyning completed an innovative cloudburst management system in a residential area of western Frederiksberg, marking a new generation in urban rainwater solutions. This system applies a dual approach to rainwater handling, carefully distinguishing between everyday rainfall and intense cloudburst events.

For routine rainfall, the system channels water through a local purification stage before directing it to an infiltration system, where it recharges the groundwater. By allowing most rainfall to remain within the natural water cycle, the system reduces the load on local sewers and treatment facilities, conserving both energy and resources.

Cloudburst water, however, is handled differently to address both capacity and environmental concerns. During cloudbursts, rainwater often mixes with wastewater due to sewer overflows, creating a contaminated runoff. To manage this, excess rainwater is directed to a large cloudburst basin with a 24,000 cubic meter capacity, located on a nearby sports field. Here, the water is temporarily stored until it can be safely discharged into the sewer system once capacity becomes available, preventing untreated, mixed water from entering the ground.

In line with the green objectives of the project, the streets in the area have been converted into “climate streets,” where residents are encouraged to avoid using road salt in winter, as this could seep into the groundwater and cause environmental harm. Instead, they use eco-friendly alternatives like sand or gravel to ensure road safety without compromising water quality.

By diverting routine rainwater back into the natural cycle and reserving sewer capacity for cloudburst events, the project significantly reduces stress on the municipal sewer infrastructure. In the process, it conserves energy and minimizes the environmental impact of heavy rain events.

Frederiksberg Forsyning actively collaborates with Frederiksberg Municipality to enhance the city’s climate resilience, and this project serves as a prime example of effective adaptation to intensifying weather patterns.