Lake Mälaren is the 3rd largest lake in Sweden, and contains clear, clean water that attracts tourists and locals alike in the summer for camping, fishing, swimming and canoeing. In the winter, it freezes over and is popular for ice fishing and skating. In addition to recreation, it provides drinking water to a major portion of the capital, Stockholm. It is municipality owned and the drinking water treatment facilities are run by the Stockholm Water Company.
In the spring of 2016, a massive infrastructure project initiated development of a 21+ km long Stockholm bypass tunnel highway that would relieve arterial roads and the inner city traffic. One of the branches of the tunnel surfaces right outside the treatment plant Lovö.
As Dr. Niklas Strombeck, one of the consultants who worked with the City of Stockholm on this project explained, "during construction, the system will be used for dust after the blasting; meaning that numerous barges will pass the main water works. There is quite a risk that those barges will leak diesel, oil and dust to the water. Therefore they need a good warning system that also will let them choose the best water quality from three different depths.”
The main treatment facility has three intakes at different depths that allow them to choose where in the water column to pump in lake water. They partnered with Luode Consulting and Dr. Strombeck, who has a PhD in limnology and 20+ years of automated instrumentation experience. He and his colleagues Mikko Kiirikki, Mattias Ryman and Antti Lindfors recommended the YSI Vertical Profiler platform. Using this system, a YSI multiparameter sonde simultaneously measures water quality parameters such as temperature and conductivity at multiple depths, and transmits real-time data to their system as an early warning system to prevent intake of low-quality water.
While the Vertical Profiler is an extremely versatile water-monitoring platform, it is not necessarily designed for use in icy conditions as ice can damage the system’s platform, water quality sonde, or the profiling equipment. This was an obstacle for Stockholm Water because they needed to collect data year-round. So Dr. Strombeck and his colleagues came up with a solution.
In order to run the Profiler throughout the frozen winter, they were going to have to have a mechanism to keep the ice thawed permanently. Since the platform is fairly close to the treatment station, they were able to supply AC power to an automatic heating cable that keeps a constant temperature above freezing. By installing waterproof plywood under the electronics system, and adding an insulated “rain jacket” or “sweater” made out of PVC to the outside, this heating system keeps the electronics at a constant temperature, the Profiler ice-free, and allows them to monitor water quality all year.
The customization of the platform designed by Dr. Strombeck, Ryman, and Lindfors demonstrates expanded versatility into environments for which the Profiler is not normally designed. Further upgrades to the system include replacing the older sondes with YSI’s EXO2 multiparameter sondes. With these upgrades and additions to the Profiler, Stockholm Water will be monitoring Lake Mälaren and providing clean, high quality water for the residents of Stockholm for years to come.
Additional Blog Posts of Interest
Is a Vertical Water Quality Profiler Right for You?
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Monitoring Coral Reefs in the Caribbean: Protecting Our Rainforests of the Ocean
The Evolution of Water Quality Monitoring [free eBook]