The floodplains built along Mustapuro will help protect Helsinki’s important infrastructure located in Myllypuro, such as Itäväylä, the metro track and the Jokeri Light Rail route. Floodplains are meadows a few dozen metres wide, onto which stream water is diverted during heavy rain. Bridges and culverts along Mustapuro were also overhauled. A small pedestrian bridge was demolished on the south-east side of the Kajaaninlinnantie site of Daycare Puotila.
The floodplains improve biodiversity in the stream ecosystem
Meadows were sown on the new floodplains to increase biodiversity along the stream. The floodplains are wetter than their surroundings, and some of them have been deliberately shaped into depressions that are always wet. This creates habitats for insects and wetland, aquatic and meadow plants that thrive in a variety of conditions.
The overhaul was carried out with as few trees felled as possible. The floodplains were placed in areas where trees would have had to be removed every few years anyway for the safety of the power line going through the area. Finnish tree species were planted to replace the removed trees, keeping the requirements of the power line in mind. Trunks of the removed trees were left in place as decaying wood to provide habitats for fungi, lichens and insects.
Mustapuro was restored with respect for nature – new spawning grounds for fish
The restoration of Mustapuro also took into account the underwater life of the area. Gravel and shingle were added to flow areas in the stream to provide shelter and diversity. These spots serve as spawning grounds for trout. Water mosses were planted underwater to improve the quality of the stream habitat and provide food for the stream’s biota, from bottom-dwelling animals to fish. The work on the stream was timed so as not to disturb the protected spawning season of trout.
During construction, solids were removed from the worksite water through sedimentation and filtration to prevent the sensitive aquatic ecosystem from being stressed by the excavation work. The culverts, bridges and flow regulation structures were designed with the fish of the stream in mind.
The completed section is located between Itäväylä and Ring Road I. The plan is to build one more floodplain next year on the east side of Ring Road I, in Mustapuronpuisto Park. Work on restoring the stream section on the south side of Itäväylä will also start next year. The streambed will be widened and deepened at the Marjaniemi allotment garden and new, larger culverts will be built under Tulisuontie. The bridges in the allotment garden will be overhauled and restored. The aim is to reduce the risk of flooding both in the allotment garden and upstream.
