Changing climate conditions will imply heavier rainfall in Denmark putting a growing pressure on wastewater treatment and sewer systems. Paved surfaces in urban areas prevent infiltration, and instead the rainwater is led to the sewers, which have limited capacity, resulting in overflow and outlet to lakes and harbours with the risk of potential water contamination of vital natural habitats. Rainwater from urban areas is not clean and must not be discharged directly into our lakes, streams and the sea. The rainwater contains large amounts of sand and nutrients, which bind to particles in the rainwater.

The Municipality of Viborg
Energi Viborg
LYTT Architecture
Svend E. Madsen
The Danish Foundation for Culture and Sports Facilities
The Danish Nature Agency

Carsten Ingemann


The Municipality and Utility of Viborg, Denmark, created the recreational area sØnæs to expand the treatment facilities of the urban area with a multifunctional wastewater treatment park. The cleaning pond is cleaning rainwater from rooftops and roads from separate sewer systems in Viborg, before the rainwater is discharged to Sønder Lake. The discharged rainwater derives from an area of 50 ha. corresponding to 100 football fields. The water surface in the cleaning pond is approximately 2.6 ha. The team combined the need for climate adaptation, wastewater treatment, recreational facilities, climate-change education and improvement of nature and environment in one. The area facilitates water-related sports and playgrounds, and puts the treatment techniques, water circulation and natural resources on display. Parts of the park have a permanent water surface, while other parts are designed to be resistant to flooding. The cleaning process in the cleaning pond is carried out by sedimentation. The water in the large cleaning pond is almost stagnant, which will cause sand, particles and impurities to seek to the bottom. In this way, the water is purified and can be discharged to the lake. In case of an extreme rain event, the water will flow from the treatment basin to several overflow basins ensuring that the water is always clean before reaching the lake.

Location of sØnæs


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