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Biofiltration areas for storm waters are tested along the Tikkurilantie road in Vantaa

Natural storm water management areas were constructed along the Tikkurilantie road extension in the city of Vantaa in the summer of 2013. These biofiltration areas, or biofilters, filter the rain water runoff from the road and the bicycle and pedestrian route. At the same time they also slow down the water flow into the Vantaa River (Vantaanjoki), thus reducing the flood risk.

© Vantaan kaupunki

Basic information

Institution in Charge: Water supply and sewerage authority of the city of Vantaa. Construction: infrastructure and construction service company Destia Ltd. Planning and research: Finnish Environment Institute.
Location: City of Vantaa, Tikkurilantie road

New traffic routes increase storm water runoff

The annual precipitation in Finland is projected to increase due to climate change. At the same time, the area covered by buildings and impervious surfaces is also expanding. Because of these factors, it is more important than ever to prevent floods caused by storm water runoff and to develop flood prevention techniques.

An extension to the Tikkurilantie road is being built in North-West Vantaa between the Katriinantie and Riipiläntie roads north of Ring Road III. The storm water runoff from the new street section will be directed to the roadside biofiltration areas which slow down the storm water runoff into the Vantaa River (Vantaanjoki). Due to the anticipated heavy traffic volume, the storm water runoff from the road contains large amounts of pollutants. It is thus important to filter the water before conveying it into the Vantaa River. Another aim of the project is to examine and compare the functionality and effectiveness of the different biofilter structures.

Structural differences help determine the most effective biofilter structure

In order to determine the most efficient filtration system and ground vegetation species, seven biofiltration areas were constructed. They differ slightly from each other. Variables in the research are the different substrates, vegetation, and types of wood mulch. The quality and flow of the storm water runoff are measured before it reaches a biofilters and after it has passed through it. This process provides information about how effectively the different biofilters remove pollutants from storm water runoff and how much they can temporarily store and absorb water after rainfall. The research process began in the autumn of 2013./p>

The Tikkurilantie biofiltration areas are elongated depressions built parallel to the road (measurements circa 2 x 60 metres). They are 1.5 metres deep and consist of multiple layers. The uppermost layer consists of substrate which lies atop a sand-filled filter layer. The next layer is a transition layer filled with fine gravel followed by the lowermost drainage layer that consists of drainage gravel and a drain pipe. The whole structure is surrounded by filtration fabric.

A biofilter area can be further divided into three parts based on its different conditions: the wet and the dry sections and the middle section that has to endure both conditions. It is important to choose the plants for each section based on its moisture conditions. One biofiltration strip filters the storm water runoff from an approximately 60 – 80 m long stretch of the road. The contour of the road is slightly slanted to allow the water to run into the biofilters. The filtered water is then directed through subsurface drainage pipes to ditches which run into the Vantaa River.

Biofilters reduce storm water discharge but demand maintenance

The biofiltration areas reduce the local storm water discharge caused by the new road extension. At the same time it also protects the Vantaa River by removing pollutants from the storm water runoff. The research done in the area also provides information about the functionality of the different filtration systems, and this information can be utilised in similar projects in the future.

However, the biofiltration areas need regular maintenance.  Road verges in urban areas fall into category A3 of the Finnish green area maintenance classification. According to the classification, these areas have a two-year guarantee period, during which the constructor is responsible for replacing dead plants, while the street maintenance division of the Vantaa Utility Services Centre sees to the maintenance. After this period the city of Vantaa is solely responsible for the maintenance of the biofilters. The maintenance duties include keeping the biofilters clean and in good condition. This means removing litter, replacing dead plants with new ones and weeding the areas three times during the growing season. If need be, the plants will also be irrigated.


11.7.2013 (This article was translated in the Climate-Proof City (ILKKA) - Tools for planning project co-financed by the ERDF)

More info

Komulainen, Elina. 2012. Hulevesien biosuodatuksen soveltuvuus Suomen ilmasto-oloihin. Diplomityö. Aalto-yliopistot, Insinööritieteiden korkeakoulu, Espoo. 118 + 11 s.

More information about the research arrangements of the Tikkurilantie road biofiltration area: Ms Pinja Kasvio, Researcher, Finnish Environment Institute, Freshwater Centre, tel.: +358 400 148 885

Contact Info

Name: Ms Tiina Okkonen, Project engineer, City of Vantaa
Phone: +358 9 8392 6085