The lake renovation had been planned and renovation trials had been done since the 1960’s. Gallträsk lake is the only lake in Kauniainen. Lake surface area is 11.7 hectares, average depth is about 1 m, and the lake volume is approximately 115,00 m3 prior the renovation.
The renovation was done in 2009-2011 and it was commissioned by the city of Kauniainen. Sito and Sito-rakennuttajat Oy were responsible for project management, design, water permit applications, geotube® deliveries, construction, and work supervision.
The goal was to remove approximately 22,000 m3 of loose bottom sediments from an area the size of 2 hectares. Removing the bottom sediments will improve the lake’s oxygen levels, water turnover rate. It also increases depth, decreases the amount of plants in the water, and increases the lake’s recreational value. Removing the nutritious sediment can affect the load on the lake. The goal was to complete the project according to budget, according to the specifications on the water permit, and according to good environmental policy.
The renovation was completed regionally in three stages during 2009-2011. The sludge was lead to the geotubes® in the treatment area. The sludge was treated and dried with geotubes® at 2 treatment areas. The water released from the sludge was lead back to the lake. To reach the goals, approximately 100,000 m3 of nutritious sludge was treated. The amount of treated sludge is greater than the amount of dredged sediment, because additional water is mixed into the sediment during suction dredging.
Approximately 7,700 m3 of reusable material was left after the treatment. The treated material was mainly used to landscape the ski slope in Kauniainen.
The treatment removed approximately 980 kg of phosphorus and 12,000 kg of nitrogen from the lake.
Reaching the goals
- The project was done within the schedule and under budget.
- 26,000 m3 of nutritious sediment was removed from the lake. The goal was exceeded by 20 %.
- 100,000 m3 of bottom sediment was treated during the project. The result was 7,700 m3 of reusable material.
The clean water from the treatment was released back to the lake.
- The dredging and sediment treatment did not cause any harm the lake or the environment.
- The project was executed successfully, despite the small treatment areas.