4 minute read
Kalkense Meersen Cluster
Scheldt River, Flanders, Belgium
The Scheldt River is a major waterway for inland navigation, connecting the Belgian ports of Ghent and Antwerp. The open delta towards the North Sea, however, poses serious inundation risks. The Belgian government’s Sigma Plan addresses these risks by strengthening the embankments and developing Flood Control Areas (FCA) to reduce flood risks along the Scheldt and its main tributaries. Climate change and associated projected sea level rise conditions were also factored into the plan. To create the FCAs, the original flood protection dikes along the Scheldt were lowered and new dikes were constructed deeper inland at a height suitable for providing flood protection (this is referred to as “the Sigma height”). With strict targets imposed by the European Union, enhancing nature is an equally important goal for the Sigma Plan. At the Kalkense Meersen Cluster, different solutions were devised—and the first completed in 2013— to enrich nature inside FCAs. The project was certified as a World Association for Waterborne Transport Infrastructure (PIANC) “Working with Nature” project in 2018.
Article cover: Bergenmeersen sluice. (Photo by Yves Adams / Vildaphoto.net)
Producing Efficiencies
Extensive modelling by the Flanders Hydraulics Laboratory optimized both the size and location of the FCAs. In order to create diverse forms of estuarine nature, or habitat, a number of innovative solutions were devised. The University of Antwerp provided the idea for the combination of FCAs with reduced tidal influence. The Institute for Nature and Forest Research provided valuable input for returning tracts of land that had been taken from the river and protected by dikes—usually for agricultural purposes—to the land’s original form (this is known as depoldering). The concept of non-tidal attachment was created by the project managers based on their combined experience in engineering and biology. The non-tidal attachment was created by making a small opening in an existing sluice to let water in at high tide. On the other side, a fish ladder was built to allow excess water to drain out. This refreshes part of the water at high tide, controls the water level, and allows for fish migration.
Using Natural Processes
At the Kalkense Meersen Cluster, the Scheldt River has a mean tidal amplitude of 3.5 meters. The tides and the tidal energy are used in different ways. After depoldering, the area is open to the Scheldt, and the natural processes of erosion and deposition will develop mudflats and tidal marshes. In the reduced tidal area, only a part of the tide is allowed in; hence, a slower rate of deposition will occur, leaving more capacity as a FCA. In the non-tidal attachment, an even smaller fraction of the tidal wave is used to replenish an artificial lake, while allowing for fish migration.
Broadening Benefits
The mudflats and marshes are of extreme importance as they are situated in the freshwater section of the Scheldt. This freshwater tidal habitat is critically endangered in Europe. In the absence of salt, willow trees will thrive and a form of temperate-climate mangrove forest will develop. Some iconic species, such as beaver and Twaite shad, are already making a comeback after more than 100 years. A total of more than 200 bird species have been counted by volunteers since the opening of the first areas in 2013. The project incorporates trails and wooden walkways inside the FCAs and asphalt bicycle routes on the embankments. As a result, tourism in the form of hiking, biking, and bird-watching is thriving.
Promoting Collaboration
The Sigma Plan was executed by De Vlaamse Waterweg nv and the Agentschap voor Natuur en Bos (the Agency for Nature and Forests). The Sigma Plan has a well-developed model for stakeholder consultation. Meetings are held on a national level with stakeholder groups; e.g., agricultural organizations and nongovernment organizations; as well as on the local level with municipalities, residents, and farmers. As a result, important adaptations were made to the project: using local soil for dike building, making several adaptions to the project perimeter, and contracting local farmers for nature maintenance tasks.
