Mustapuro is one of the most significant urban streams in Helsinki, where even trout thrive. Preparations are being made for the flooding of the stream, as floods are estimated to increase due to increased rainfall resulting from climate change. The densification of urban areas also increases storm water and the risk of flooding. The Metrorata, Jokeri Light Rail route, Itäväylä and Varikkotie roads are located in the vicinity of the project area. This infrastructure is important for the City of Helsinki, which is why flood protection is being increased there. Flood protection is part of the City of Helsinki's efforts to adapt to climate change.
Flooding stream water is diverted to floodmeadows
The flood protection of Mustapuro will be improved by digging flood plains into the area between Kehä I and the Myllypuro Ice Hall. Floodplains are meadows a few dozen meters wide, where floodwater is directed during heavy rains. Floodwater is directed by means of dams built in the stream. In addition, bridges and culverts crossing Mustapuro will be replaced with more efficient structures for conveying water, and two unfit pedestrian bridges will be demolished. The access routes from Mustapuronpolku to the Puotila Kinderdarden and Myllypuro Ice Park will change.
Meadows will be sown on floodplains, which will improve biodiversity and recreational use at the urban area. The meadows are designed thematically so that habitats are created by the stream for various insects and plants that thrive in the meadows. This creates a flowering meadow, a low-growing coastal meadow with decaying trees and shrubs, and a wild and lush wetland landscape with duckboards and piers.
Floodplains are placed to preserve as many trees as possible. Trees growing on the banks of the brook will be preserved in locations where floodplains can be placed a few meters from the stream. However, trees must be removed from the floodplain areas to be excavated. The trees will be removed before April to ensure that birds can nest undisturbed.
Flood plains will primarily be placed in areas where trees would otherwise have to be removed for several years to ensure the safety of the power line. Finnish tree species will be planted to replace the removed trees, taking into account the requirements of the power line. The trunks of the removed trees will be left as decaying trees, providing habitats for fungi, lichens and insects.
Spawning gravels will be built in the Mustapuro stream by adding natural gravel to the stream points. Adding natural stones to the stream will create shelter and bring versatility to the stream environment. The new beach slopes will be landscaped to fit with the surrounding nature. Water moss will be planted in the stream to improve the quality of the stream habitat and provide food for biota from bottom fauna to fish. This will also serve to combat invasive alien species, such as Himalayan balsams and beach roses.
The principles of planning and building
Special precision will be observed during construction due to the natural values of the area. During construction, care will be taken that the water quality of the stream does not deteriorate due to construction. The waters discharged from the construction site to the stream will be clarified and the monitoring of their quality will be strictly guided.
Flow-regulating structures, culverts and bridges will take into account the passage of fish and other aquatic organisms. Calming the spawning time of trout will affect the work schedules.
Several river renovations have already been carried out in the Mustapuro stream, which have been taken into account while planning the project. A significant part of the stream that passes through the project area will remain untouched.
