Finland: Lake Galltrask Dredging Project Makes Progress

Lake Gallträsk, situated 15km west of Helsinki, used to be a popular recreational area with beaches and clear water. Unfortunately, it has suffered from major strain caused by habitation and industry.

The biggest damage to the area was done between the 1920s and 1970s, when wastewater was released into the lake causing silting up and eutrophication. The water capacity of the lake reduced and its current depth is only 1m on average. As a consequence, the recreational value of the area has declined drastically.

Different rehabilitation projects have been planned and attempted since the 1960s, but they were all unsuccessful due to the lack of proper equipment. The organic sediment in Lake Gallträsk was simply too lightweight to be removed with traditional machinery.

Environmental dredging

Traditional dredgers are mostly designed for industrial use and work in deep waters, but they are often not suitable for environmental needs. Lake Gallträsk is an excellent example of a case requiring specifically environmental dredging.

Environmental dredging means removing harmful or contaminated sediment and vegetation to improve the conditions of the water environment. An environmental dredger should be lightweight and have the ability to float and work in shallow waters. It needs to have good mobility and the right tools for environmental tasks.


The Watermaster environmental dredger was chosen as the most suitable product to complete the work. It is a serially produced machine that exceeds all of the requirements set for an environmental dredger; its mobility and versatility sets it apart from other machines.

Multipurpose capabilities allow it to complete many kinds of works at a site. The Watermaster had already been used at Gallträsk to remove vegetation and trash, with a rake to clean the lake’s bottom.

In most cases, the silt is pumped into settling ponds. However, the area of Lake Gallträsk is densely populated so building such settling ponds was not an option. The pumped sediment would have required two big ponds and, as the sediment is so lightweight, the settling process would have taken too long.

For these reasons, it was decided that the silt would be treated with the Geotube method. Watermaster would pump the silt up to a maximum distance of 1km into Geotube containers, which let the excess water drain through the small pores in the geotextiles resulting in effective dewatering. Geotubes do not need nearly as much space as settling ponds; they can even be piled on top of each other.

The first part of the dredging work was completed in the spring and autumn of 2009. The Geotubes and dried-up silt will be removed from the area for the next spring and summer, and in autumn 2010 the dredging work will continue. The whole renovation project is due to be done by 2014.

All together, 26,000m3 of silt will be sucked from an area of about 2 hectares. The Watermaster will pump the silt into 12 Geotubes placed in two separate areas, about 550m from the worksite. The goal is to dredge 300–500 hours per year.


The effects of the dredging project are positive. The lake’s oxygen content and nutrient balance will recover and the habitat of the fish will improve. As a result of deepening the lake, the growth of reeds will reduce. Overall the ecology of the lake will recover close to its original state, and once again people can enjoy using the lake as a recreational area.



Source: porttechnology, August 27, 2010;