Kuninkaantammi residential district is the Pilot of the Helsinki Storm Water Strategy

Kuninkaantammi, located in the Kaarela city district in northwestern Helsinki, is the pilot target of the Helsinki storm water strategy introduced in 2008. The ecologically sustainable urban residential area will be built on an old industrial zone, and the management of storm waters in the area will be carried out through natural methods.

When planning the Kuninkaantammi residential area, various solutions will be presented for utilising, absorbing and delaying storm waters, before leading them to the two rivers through ditches. Helsinki City Council has already approved the first zoning plan for the area. Construction in the area will start during 2014 and 2015.

Rain gardens, green rooftops and vegetation dells

The natural storm water management methods will be visible in the area as technical solutions integrated with the urban landscape, such as various pools and stone streams along the streets, vegetation dents, large trees, green rooftops on the buildings and rain gardens on the plots. The most important goals of the various methods are to 1) utilize flow peaks, 2) decrease the total run-off and 3) potentially improve the water quality.

Green roofs reduce storm water run-off. (Photo: Saara Pellikka 2013)

The storm water solutions planned to the Kuninkaantammi area are quite new in Helsinki: Open water features have previously not been used much in residential areas or parks as they are often seen as being problematic, i.e. because of prejudiced smells or safety risk. Furthermore a compact, traditional sewer system has been a convenient solution in the dense urban environment due to restrictions of space. Since 2008, the Helsinki storm water strategy has determined the priorities of the storm water management, which means that combined sewers are not built anymore. Today the storm water solutions are mostly determined based on the limitations of the area. Systems to absorb or delay the waters are implemented if there are green areas nearby to where dents can be built.

Zoning plan regulations control storm water management

Among others, the following regulations concerning the storm water management have been included to the zoning plan of Kuninkaantammi:

• The minimum demand of storm waters to be delayed in districts is 0,5m3/100m2 of each hard, impermeable surface.
• Delaying the storm waters should primarily be arranged through rain gardens shared by the plots.
• Green rooftops should be built on all one-storey building parts, outbuildings, bike sheds, etc.

The delay volume of storm waters has already been a zoning regulation in several plans in various cities, but the regulation concerning the rain gardens is yet only applied Kuninkaantammi. The Kuninkaantammi zoning regulation concerning green roofs of one-storey building parts and the green roofs of a school building is among the first in Helsinki regarding delaying storm waters. Some zoning plans have had regulations concerning green roofs, but these have mostly been due to urban landscape related reasons.

Cost comparisons of storm water solutions in a wetland park supports natural methods

The storm waters of Kuninkaantammi are led to a wetland park, Helene Schjerfbeck Park, which is constructed next to the residential area. Based on the cost comparisons made of the storm water management options for the park, a natural method of storm water management would be up to three times more economical to implement compared to the traditional pipe methods.

17.3.2014