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: Helsinki sustainable storm water solution: Sedimentation and biofiltration basins placed in the Maunulanpuisto Park to purify storm water from a lively trafficked area before entering the Haaganpuro brook.

Reconstruction of a water course in Tallinn
In order to protect River Pirita a section of Lepiku water course situated in the Botanical Garden of Tallinn was renewed. The original construction had collapsed in, the bottom and the culverts were full of sediments and in many places the soil had eroded. Following the new construction, parts of the old construction were removed. All stumps on the right side of the water course were erased, while roots were left as a natural barrier for erosion. Secondly, all the sediments from the bottom were excavated and culverts were cleaned and replaced where needed. After that, elements for the new water course were built up: At first a fabric suitable for the purpose was placed on the bottom and sides of the water course and on top of it gravel as well as limestone were spread out to construct the right slope, width and high. On the upper side of the course, a geocell was placed and filled with soil to avoid erosion. Along the watercourse, width and depth are constructed to vary in order to retain the water flow thus improving sedimentation of suspended material. Further, plants will be added along the coarse both on the bottom and sides.

Additionally to the objective of purifying the storm water running through the Botanical Garden, an important part of the aim achieved with this project is to show citizens that a water course in their yard may be a privilege. Instead of directing water into a pipe system, water elements diversify nature and bring recreational values to the area.

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.

Pictures above: The storm water wetland in Turku. The site where the wetland will be constructed.

Study visit, expert meeting and storm water brochure

The aim of implementing storm water solutions will be reached by

Arranging a study visit for civil servants from the partner cities Tallinn, Turku and Helsinki. CITYWATER organized a study trip to Malmö, Sweden 14-16 August 2013, to learn more about different storm water solutions. During three fruitful days the participants got to know e.g. the housing exhibition area Bo01 and the Eco-city Augustenborg. The storm water techniques included solutions such as vegetated roofs, swales, ponds and permeable pavings. The group consisted of 30 civil servants from different departments at the City of Helsinki, Tallinnn City and City of Turku. Read more about the visit here.

Organizing an expert meeting for civil servants 
An expert meeting was organized in December 2014 in Turku. Here, general challenges for cities in the Baltic Sea Region was discussed relating to future climate change predictions, legislation and city level strategies. The work with sustainable storm water solutions within the CITYWATER project was also presented. Read more about the visit here.

• A brochure describing the sustainable storm water handling solutions and realized constructions within the project was compiled. Download the brochure here.



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Other CITYWATER actions:

Promoting the Baltic Sea Challenge,
read more

Environmental communication, read more
Cost-benefit analysis, read more
Toolbox, read more
Disseminating results, read more

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