Planning site

Stormwater filtration unit pilot in Taivallahti, Helsinki, Finland


As the city structure becomes denser and the area of impermeable surfaces increases, the amount of stormwater increases. Stormwater is often contaminated by undesirable substances originating from air pollution, various surfaces, effluents, accidents, pipe ruptures and other events. The main sources of emissions include traffic, construction materials, energy production and the chemicalisation of the environment. Nutrient loadings originate from fertilizing fields and green areas, as well as from wastewater discharges. The quality of stormwater needs to be improved before releasing to the water system to prevent the pollution.


Stormwater from heavily trafficked nearby street called Mechelininkatu will be directed into stormwater pipe and released into Taivallahti Bay. In pilot phase, part of the stormwater is directed into the stormwater filtration unit before releasing it to the sea. The unit purifies road pollution and debris (microplastics, suspended solids and other pollutants) from the water while it passes through the coarse and fine filtration units.

Stormwater filtration unit is suitable for different kind of natural or man-made environments, ie. urban and green areas, parks, squares and streetscapes. It is specifically designed in to urban waterfront and to be integrated in green infrastructure. Outer structures of a pilot unit are made of concrete and inner structures of recycled plastic lumber, however filter concept can be engineered from many other material too.

The structure is simple and easy to manage. It fits in a limited space. Shape, site, size, and filter materials are all adjustable. The solution is suitable for stormwater and waste water overflows, at the”end-of-pipe”. In addition, upstream distributed applications are possible. It can be part of a pier, a marine platform, a small bridge or part of a waterfront wall. Depending of the need, it is possible to place several units in one site or adjust the size of the unit.

The solution is one part of the treatment train and it is advisable to use also other structures and green infrastructure in addition to stormwater filtration unit in stormwater management. Design of hydraulics anticipate rain event: in the first flush water has maximum contact time with filters, in basic flow design allows many flow channels and in peak flow maximum velocity is enabled.

Stormwater filtration unit will be implemented in Taivallahti, Helsinki in autumn 2018.