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Haaganpuro brook in Helsinki was restored to prevent flooding

Climate change will increase heavy precipitation events which will, in turn, increase storm water runoff as well as urban floods. To prepare for the increasing floods, the bottom of the Haaganpuro brook in Helsinki was restored by placing submerged weirs and boulders to slow down the flow velocity and to decrease the flood risk downstream.

Basic information

Institution in Charge: Stara (Construction Services of the City of Helsinki)
Location: Helsinki, Haaganpuro brook

Regulating the flow rate reduces flood risk

The Haaganpuro brook (previously known as Mätäpuro brook) is an 11.6 km long urban brook in the city of Helsinki. There are ecologically valuable sites in the catchment area of the brook which provide habitat for birds and other organisms, while the brook itself is important due to its urban sea trout population.

The aim of the brook restoration process was to slow down the flow velocity. Flooding of the brook can be prevented when the water downstream has a chance to discharge before more water flows in from the upper reaches of the brook. In addition, suspended sediments carried in the slowly flowing water are able to settle to the bottom of the sedimentation basins where they are dredged up. This reduces the discharge of nutrients into the Baltic Sea.

Structural solutions control storm water

Storm water runoff that flows into the brook increases the brook’s flow rate and flood risk, which can both be reduced by placing boulders in the brook bed and building flood plains. Instead of installing piping, storm water runoff should be diverted to ditches where landscaping stones and sills restrain and direct the water flow. Flood plains, sedimentation basins and wetlands balance the peak flow and thus prevent flooding and damages to public and private property. Submerged sills were placed on the river bed to steer and slow down the water flow which decreases the flood risk downstream.

Unfortunately, Helsingin pienvesiohjelma (Small Water Action Plan for Helsinki, a programme to improve the conditions of brooks, ponds, wetlands and springs in Helsinki), faced deep budget cuts during the economic recession. Consequently, the restoration of the brook is now mainly taken care of by volunteers and the Centre for Economic Development, Transport and the Environment of the region of Uusimaa. The city of Helsinki, however, attempts to support the programme for example by providing the stones needed in flow control. The volunteers of the Virtavesien hoitoyhdistys ry (the flowing water management association) have had a remarkable role in restoring the brook.

Restoring the brook improves biodiversity and urban landscape

According to the representative of the Construction Services of the City of Helsinki (Stara), the brook restoration programme has received extremely positive feedback. In addition to improving flood control, the restoration measures have also increased biodiversity. Successful attempts to control the changes in the water flow caused by storm water runoff reduce erosion and improve the habitat of the brook biota (living organisms). In addition, the brook is a green corridor and a migration route used by different insects and other life forms. The restored brook also increases the aesthetical value of its surroundings and creates a pleasant sound environment in the middle of the buzzing city.

Although the process to restore the Haagapuro brook has been successful, the delicate balance of the brook could easily be shaken. The sea trout population, for example, occasionally suffers from sewage and pollutants that run into the brook with storm water runoff.  Even so, the efforts to conserve the original sea trout population of the brook have been successful.

 

1.7.2013 (This article was translated in the Climate-Proof City (ILKKA) - Tools for planning project co-financed by the ERDF)

More info

Helsinki rakentaa luonnonmukaisen hulevesirakenteen Pohjois-Pasilaan - Helsingin kaupungin ympäristökeskuksen tiedote 25.3.2015

Lehtoranta, V., Sarvilinna, A. & Hjerppe, T. 2012. Purojen merkitys helsinkiläisille - Helsingin pienvesiohjelman yhteiskunnallinen kannattavuus. (The significance of streams for the residents of the City of Helsinki. (Contingent Valuation Study for the feasibility of the Small Water Action Plan. Abstract in English.) Suomen ympäristökeskus, Helsinki. Suomen ympäristö 5/2012, Luonnonvarat. 66 s.

Lintinen, O., Orava, M., Loukkaanhuhta, U., Järvinen, M., Kärki, T. Nuotio, A.-K., Vasama, K., Koskela, V.-P. & Järvelä, J. 2007. Helsingin pienvesiohjelma. Helsingin kaupunki rakennusvirasto & Ramboll Oy, Helsinki. Helsingin kaupungin rakennusviraston julkaisut 2007:3/Katu- ja puisto-osasto. 168 s.

Sarvilinna, A., Hjerppe, T., Arola, M., Hämäläinen, L. & Jormola, J. 2012. Kaupunkipuron kunnostaminen. (Restoring urban brooks. Abstract in English.) Suomen ympäristökeskus, Helsinki. Ympäristöopas 2012. 76 s.

Virtavesien hoitoyhdistys ry. Mätäpuro

Contact Info

Name: Tomi Silander, foreman (group supervisor), Helsingin pienvesiohjelma (Small Water Action Plan for Helsinki) ), Stara - Construction Services of the City of Helsinki
Phone: +358 50 383 6132