Boskalis CSR report 2017

Impact on the environment CSR 2017 – BOSKALIS 38 BUILDING WITH NATURE – THE MARKER WADDEN ISLANDS RESTORING THE ECOLOGICAL BALANCE With the completion of the 26-kilometer-long Houtrib dike between the Dutch lakeside cities of Enkhuizen and Lelystad in 1976, Markermeer lake was formed as sibling to the IJsselmeer. Since then, the Houtrib dike has had a substantial impact on the underwater environment of the lake. Fine sediment, that had previously been carried away by the wind-driven currents to the IJsselmeer, settled on the bottom of Markermeer, forming a silt blanket that stifles soil life. The resulting high levels of turbidity have resulted in a dramatic decline in the fish and bird populations in and around the Markermeer. In addition, natural banks and shallows have disappeared and with them the nesting grounds for many bird species. Looking to restore the ecological balance, whilst maintaining the natural beauty of the Markermeer lake area, the Dutch Society for the Preservation of Nature found a sustainable solution in the Building with Nature approach as used by Boskalis. Although a number of Building with Nature projects have already been executed by Boskalis, the Marker Wadden project is the first, both in the field of nature restoration and hydraulic engineering, to be carried out based wholly on this approach. The main challenge in this project was building with the soft cohesive clay taken from the bottom of Markermeer. In close collaboration with the client, Boskalis found the solution in an innovative idea based on the Building with Nature approach: using the soft clay from the lake to create natural islands on which marine, animal and plant life would be able to flourish.