4 minute read
Marker Wadden
Lake Marken, Flevoland, the Netherlands
Inventing a new engineering technique to bring a dead lake back to life. Lake Marken, or Markermeer, lies in the center of the Netherlands. The conditions of this lake became ecologically very poor because of plans to turn the lake into a polder. Though these plans were suspended in the 1990s, many dams and dikes were already built by then. So, the lake lacked natural shores. As a result a 30-centimeter layer of sediment on the lake bed turned the water increasingly murky, making life difficult for many aquatic species. As fish populations dropped, the birds also disappeared, leaving an area devoid of wildlife. In March 2016, Natuurmonumenten (a Dutch nongovernmental organization for nature conservation) and Rijkswaterstaat, with input from dredging experts, nature conservationists, engineering firms, universities, and landscape architects, began restoring an area in the northeastern portion of the lake. The project team added 1,000 hectares of new habitat, including islands constructed from sand, clay, and silt—an engineering first at this scale. The islands’ harbor opened in 2018; but from the start, the team has provided visitors and researchers many opportunities to visit these new islands. Remarkably, wildlife began returning to the site as soon as construction started; biodiversity has exploded.
Article cover: The new footpath through the marshes was created for recreational and educational use. (Photo by Peter Leenen, Straystonephoto)
Producing Efficiencies
The same fine sediment that caused the ecological problems in the lake has become the solution as the team constructed the islands by using dredged clay and fine sediment. Building with sediment on the soft lake surface had never been done before. Therefore, to address this new challenge, several universities and institutes, in addition to researchers from the dredging company, have monitored every step of the process. The innovative hydraulic engineering techniques used for this maritime construction will lead to an increased understanding of sediment processing.
Using Natural Processes
The Marker Wadden archipelago allows the lake and new marshland ecosystem to interact more fully. The islands are a mosaic of mudflats, marshland vegetation, creeks, and shallow isolated pools, surrounded by wide channels that provide additional sheltered shallow water. Further, gradual transitions from land to water, ideal for marsh and water vegetation, create areas that trap sediment and trigger biochemical processes, capturing phosphorus and stimulating nitrification and denitrification. Wind causes waves to enter the area and leave more sediment between the marshes, and specially created washovers stimulate these natural processes.
Broadening Benefits
With the creation of the islands and the improved water quality, many species, such as common terns (Sterna hirundo), avocets (Recurvirostra spp.), and black-headed gulls (Chroicocephalus ridibundus), have returned. The islands function as a living laboratory for both citizen-scientists and academic researchers. Many tourist companies have started offering special nature trips to the islands, and water recreation from the harbor island has become popular. The next phase’s visitor center will further foster the growth of this community hub for recreation, nature, and science.
Promoting Collaboration
With a goal of restoring 100 square kilometers, Marker Wadden represents one of the largest naturebased engineering projects in Europe. To succeed, the project brought together a broad range of complementary expertise and enabled mutual learning. Working together since 2013, Rijkswaterstaat and Natuurmonumenten have combined their nature restoration and public work experience. To this they added Boskalis’s innovative technology and the support of many partners and stakeholders. Because of this, Marker Wadden now serves as a testament to Dutch marine engineering.
