Climate adaptation in sØnæs, Viborg

Viborg Forsyning is in the process of changing the sewer system to a separate sewer system in the city, and there was a need to clean the separated stormwater for e.g. phosphorus and nitrogen before it was discharged into Søndersø, east of sØnæs.

At the same time, there were major problems with overloading of the existing sewer system, and the low-lying buildings around sØnæs could get better protection against cloudbursts by building a stormwater basin.

A treatment basin was planned on an old bog area. The old bog area had served as a football field for a local club. The area was swampy and the football fields were bad.

The idea behind sØnæs is a climate project that combines a recreational park with facilities for cleaning and storing large amounts of stormwater during storms. The result is a city park with great recreational value in combination with a technical facility

sØnæs shows that climate adaptation can not only accommodate an important double function, but also a triple function, where, in addition to stormwater management and recreational functions, water purification for phosphorus and nitrogen is envisaged before discharge to Søndersø

The technical elements

The water comes via pipes from the stormwater catchment, where it flows into the treatment pond. The water stands there and sludge settles, after which the water is pumped out into Søndersø. When it rains, the water in the treatment pond rises and flows via two overflows into a series of flood areas, from where it flows back again as the water is pumped out into Søndersø.

The facility consists of:

  • Stormwater basin/purification pond with sedimentation with direct inlet
  • Retention basin, which consists of several smaller basins in series. They are fulfilled via overflow from the treatment pond by "feeding" a stream, which fulfills depressions at different levels
  • Recreational Park with elements for play and learning

Sketch of the basins for cleaning and storing stormwater.


sØnæs, Viborg (

Teknisk dokumentation af klimatilpasningsprojekter - Teknologisk Institut


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