Stormwater management in Stockholm city, Sweden
Solution to which problem
City of Stockholm in the past years had to deal with surface water and with flooding events due to high heavy rains.
Technical conditions
City of Stockholm decided to create good growing conditions for trees in order to take care of the surface water and to improve the air quality. They installed three different layers in the ground in order to allow the water to penetrate the soil: pavement, geotextile, layer of crush rock for infiltration of surface water and for airing the soil and granite stones. They also create a catchment chamber for infiltration of surface water and airing the structural soil. The geotextile connection acted against inlets, no fine materials could run into the airy base course.
Implementation
The project has developed a system for collecting water from pavements and conveying it to trees based on experiences. In this way it was possible to take water from roofs and pavements and lead it down to the structural soil by inlets. If the percolation layer is full the stormwater flows into the old street inlet.
Result
The establishment of infiltration channels has resulted in a lower burden on surface water receiving bodies and it has increased infiltration and cleaning of surface water in the existing environment. There has also been less damage to water and sewerage pipes and road paving from trees. Another good consequence of this implementation is lower air pollution in central Stockholm.
Rainfalls in Stockholm are about 600 mm/year, it is around 2,3 million liters of water per year that has to be treated. With this solution it was possible to save 2300 £/year for the treatment of stormwater. In addition, this implementation reduced the risk of flooding and reduced the presence of particles and carbon dioxide in the air. It also reduced the load on stormwater systems and thereby reduced pollution in lakes and in the Baltic Sea during torrential rains.