A dream at the river mouth
Discharging into geotubes, which seperate the water and the sediments
THE CITY OF JOENSUU in the eastern part of Finland is transforming an old contaminated sawmill area near the city centre into a modern eco-friendly housing district.
Before the building can start, the whole area must be thoroughly restored after more than a century of heavy industrial usage.
Joensuu (which means, “mouth of a river”) is a lively city of about 75 000 people, located approximately 450 km northeast of Helsinki.
From 1871 until 1988, a sawmill operated on the banks of the river Pielis close to the city centre in an area called Penttilä. After a century of industrial use, the soil and storage bay at the Penttilä area had become severely contaminated with heavy metals and other toxic materials.
The city bought Penttilä in 2008, planning to turn the area into a modern, eco-friendly housing district for between 3-4,000 residents during the next 20 years - but first the area had to be thoroughly cleaned.
The total restoration cost rose to about 21m euros, one of the biggest restoration projects ever to be carried out in Finland. The name of the project became “a dream at the river mouth”.
Penttilä district is 40 hectares in size and more than 500 000 m3 of soil had to be cleaned.
The old storage bay right next to the river had been kept open during the winters by directing the flue gases from the near by plant to the bay. This inevitably caused the accumulation of vast amounts of heavy metals in the bottom sediments. The size of the bay is about three hectares and the depth varies from two to four metres. It was the most polluted spot in the whole sawmill area and the cleaning of the bay was considered to be the most challenging part of the whole restoration project.
The bay is shallow and hard to reach with traditional dredging machinery, so after thorough trials, the versatile Watermaster dredger was chosen to be the best solution for the site.
Watermaster is a Finnish-made serially produced versatile dredger, which can perform suction and backhoe dredging and even pile driving work. Watermaster can "walk" in and out of water without crane assistance and it moves independently in water as well, minimising the need of extra machinery and labour - it is thus very cost effective.
The contractor has operated all the previous Watermaster generations as well but is now using the latest model - Classic IV, the 4th generation of the original Watermaster concept. He is very happy with the new Classic IV as it offers more depth, greater boom and stabiliser forces and cabin LX.
Watermaster has suction dredged vast amounts of contaminated sediments from the bay between 2009 and 2011. The material is pumped into geotextile tubes to separate the sediments from the water. Sediments are left to dry for about a year and will then be transported for further processing to the nearby waste treatment plant. A small marina will be built on the storage bay area later on.
The building phase is set to begin in 2012. Penttilä should be receiving its first new residents in 2013, but more new buildings will be built during the next two decades.
By the end of the project, Penttilä will have been transformed from an industrial wasteland into a modern, verdant and desirable new residential area, which will undoubtedly attract new residents to live at the “mouth of the river”. So far, about 30 geotubes have been used at the site (size approximately 50m long and 9m wide).
Timeframe for the project
2009-2011 area restoration
2010-2012 building the infrastructure
2012 building of the apartments begins
2013 first new residents
2014 new bridge to the city for pedestrians
2015 the small marina will be completed
2030 the whole project will be completed.
The restoration has now been completed (early October 2011). The contaminated sediments have been transported to the waste treatment plants nearby. The city is now ready to start building the infrastructure and the apartments. The pond that Watermaster cleaned will be turned into a small marina - it should be completed by 2015.
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