Storm water handling

Storm water is rain or melting water originating from precipitation. In urban areas storm water is collected from roads and roofs or from other non-permeable surfaces. Storm waters differ from other runoff in their origin, which is strongly linked to human activities.

More storm waters due to climate change 

Storm waters are of concern for two main reasons: for their quantity and quality.
Firstly, it is predicted that climate change will lead to more and heavier rainfall in Northern Europe. Simultaneously, urbanization is increasing which leads to more non-permeable surfaces. This means that there is a need for developing the capacity for storm water management. In this context, the interest for natural handling of rain and melting water is increasing. Examples of natural handling of storm waters include green roofs, wetlands and swales. Secondly, storm waters are of concern due to nutrients, harmful substances and contaminants that the water might be carrying. Awareness towards storm water management is arising, and the importance of proper management policies will be further emphasized due to climate change.

Storm water constructions in Helsinki, Tallinn and Turku

The CITYWATER project has planned and implemented sustainable storm water solutions in each partner city: Helsinki, Tallinn and Turku. The established good cooperation between the cities gives an additional advantage of learning together and sharing experiences of storm water handling in urban areas. Constructing these storm water solutions has given information about good practices and tips on how to manage storm waters even better in the future.

Biofiltration in Helsinki
In order to protect the Haaganpuro brook, a biofiltration area was constructed  in the northern parts of Pasila in Maunulanpuisto Park in Helsinki. Here, rain and meltwater from the Metsäläntie Road and the adjacent southern area are collected in storm water pipes and were previously led directly into a ditch feeding into the Haaganpuro Brook. As the drainage area is heavily trafficked and paved with asphalt, high sediment particle, nutrient and oil levels have occasionally been measured in the rainwater and meltwater entering the Haaganpuro Brook. Such contamination is harmful to the fish stocks (e.g. trout) and other organisms in the brook, which is why the storm water needs cleaning. A sedimentation basins and a biofiltration area was constructed in order to purify rainwater and meltwater originating from the central parts of the city and Metsäläntie Road. The basins, vegetation and sandy layers capture particles, bind nutrients and absorb harmful substances and thus improving the water quality in the Haaganpuro Brook. The construction was finished during the autumn 2015.

Pictures above: The storm water construction in Tallinn. Before; work underway and construction ready (July 2014).

Planning of a residential storm water wetland in Turku
The storm water solution consider a wetland to be built in the Hirvensalo area in Turku in order to clean and collect storm waters before they enter the already eutrophic Lake Illoistenjärvi. The location for the solution resembles a country side area at the moment, but will be turned to a residential area in the near future. Thus, when the wetland is planned and constructed already before the housing, it will be able to collect and purify storm water both during and after the construction phase of the residential area. Especially during construction of land areas, storm waters are impacted by heavy leakage of suspended solids, nutrients and possibly even heavy metals, which may be absorbed by the wetland. When the residential area is finished, the wetland will additionally function as a recreational water element for the residents.

During project time the construction plans were drawn for the wetland (2015). The wetland will be constructed in the Peippolanoja ditch in future years, parallell with the construction of local infrastructure.

Metsälän tie IMG_2860_web

The Metsäläntie street and surrounding areas form the drainage area for the purified storm waters.

First part of course IMG_2863_web

The first part of the original water course for storm water solution

Second part of course IMG_2874_web

The second part of the original water course.

Haaganpuro brook

Meeting with the constructor

Sedimentation basin

Meeting with constructor and guests

Sedimentation and biofiltration basins without vegetation

Sedimentation and biofiltration basin