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100 climate solutions from Danish Municipalities


In cooperation with a local utility company, Halsnæs Municipality has installed a new sluice to protect the City against rising water levels in Roskilde Fjord.

Situated between a large fjord and a lake, the old industrial city of Frederiksværk offers great cultural and natural experiences. Unfortunately, close proximity to water also means that rising water levels represent a major challenge and risk for the city’s operations, economy and cultural heritage. Therefore, in 2017 Halsnæs Municipality, together with a local utility company, constructed a high water sluice in Arresø Canal at the lake’s outlet to Roskilde Fjord.


When the water levels rise in Roskilde Fjord, the sluice now protects the city. Prior to the construction of the barrier, Frederiksværk city center, the city’s high school, historic buildings and the city’s campground were flooded by high water events of 1.2-1.4 meters. The new sluice can protect the city should water levels rise up to two meters.

In 2017, the sluice was challenged by Storm Ingolf and passed with flying colors.

In order to ensure effective water management, the municipality has installed two pumps within the sluice system which extract water from Arresø Canal, preventing water from accumulating inside the sluice when it is closed. The project has been undertaken by Halsnæs Municipality and a local utility company, who have also worked closely with the Nature Agency under the Danish Ministry of Environment and Food.

How the Global Goals are addressed

Sustainable Cities and Communities

With the new sluice, Halsnæs Municipality has taken an active step to protect the historic buildings of Frederiksværk for future generations.

Climate Action

The City of Frederiksværk is experiencing flooding caused by water level overflows with greater frequency. The sluice system makes the city more resilient and better adapted to climate change.

Life below Water

The sluice is a good example of how municipalities along the Danish coasts and fjords can manage and protect vulnerable areas in a manner that is both efficient and sustainable.