When Slussen is rebuilt, it presents an opportunity to expand Mälaren area drainage capacity – that is, to enable the discharge of larger volumes of water from Mälaren to the Baltic Sea. This, in turn, reduces the risk of flooding across the Mälaren region and secures drinking water for approximately two million people in the area.
New regulation of Mälaren
Since the 1940s, the water level of Mälaren has been regulated through canals and sluice gates in Stockholm and Södertälje. The water level is adjusted by opening or closing the gates when it falls or rises to a certain level.
Stockholm City, in collaboration with, among others, the Swedish Meteorological and Hydrological Institute (SMHI), has developed a proposal for new regulation of Mälarens water level along with an expanded drainage capacity. The aim of the new regulation is to reduce the risk of flooding around Mälaren, lower the risk of low water levels, and prevent saltwater intrusion.
On August 20, 2015, the city received new permits under the Environmental Code to rebuild Slussen and regulate Mälaren. These permits cover works and new installations in the water, as well as groundwater diversion in connection with these projects.
Slussen is adapted for its entire lifespan
The new Slussen is designed to last for about 100 years, which is typical for this type of construction. The facility is planned to withstand the sea level rise that is likely to occur over its lifetime.
A key component in planning the redevelopment of Slussen is the work to reduce flood risks in both Stockholm and the Mälaren region. The project accounts for a global sea level rise of approximately 1 meter, which, when combined with post-glacial rebound, translates to a sea level roughly 0.5 meters higher than today in the Stockholm area. This means that the new Slussen is adapted to the sea level rise that SMHI considers likely within the facility’s 100-year lifespan.
While climate adaptation is an important aspect, the new facility must also be designed to function in today’s climate and account for the existing urban environment—not least the culturally and historically sensitive setting of the Old Town. Adapting Slussen to levels far beyond the likely sea level rise would negatively impact the cityscape and cultural environment.