Ketelmeer, a lake in the Netherlands with a length of some 10 kilometers and a width varying from two to three kilometers, separates the North Eastern and Southern Polders constructed during the late 1960s and early 1970s. It is a major example of the problem of 'historic pollution'. Lake Ketelmeer receives the waters of the Rijn and IJssel and over a period of three or more decades, tens of millions of cubic meters of highly contaminated sediments entered Ketelmeer from hundreds of upstream locations. The bottom was covered by polluted sediments to an average depth of 50 cm. A significant proportion of this material had to be removed, or capped by the cleaner sediments of recent years, if a normal aquatic environment was to be restored.
The strategy for Ketelmeer was based on selective removal, in areas such as the main shipping channels, together with the construction of a permanent and fully isolated repository for contaminated dredged material. This facility, the IJsseloog, will serve both Ketelmeer and the entire northern region of The Netherlands and has a capacity of 23 million m3. When the facility is full, it is likely to be capped and developed as a recreational area within a rejuvenated Ketelmeer. This new island, with its adjacent wetland habitats, has the potential to become a significant nature reserve in its own right. The Boskalis system deployed at Ketelmeer had a capacity of 500 cu m/hr and had the ability to strip very thin layers (0.05 m to 0.60 m). The system featured on an environmental disc cutter (a horizontal rotating disc) with a visor on the dredge side. Boskalis contributed to two key objectives. The first was to achieve a significant reduction in the re-suspension of sediments, due to vessel traffic in the main channels and movements in the many small harbors around Ketelmeer. The second was to deepen the shipping channel from the IJssel to Lake IJsselmeer.