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In the period 2011 - 2017, EcoShape conducted experiments with sand engines at two locations in Lake IJssel (IJsselmeer) at the Frisian IJsselmeer coast. The IJsselmeer is the largest fresh water lake in The Netherlands. The aim was to gain knowledge about the system in the IJsselmeer region and to determine the effectiveness of Building with Nature measures including sand motors for strengthening the Frisian IJsselmeer coast.

Water level increase

Tim van Hattum and colleague Ane Wiersma were responsible for the project. Van Hattum explains: 'The reason for this project was the future water level increase in the IJsselmeer area. A new water level management has been included in the 2015 Delta Plan to increase the buffer supply of fresh water in the IJsselmeer. The so-called flexible water level management requires extra protection for the areas outside the dykes. Ten centimeters of level rise means that more than 100 hectares of land are regularly flooded. Along the Frisian IJsselmeer coast there are vulnerable areas outside the dykes that can deteriorate due to this new water level management. We have investigated measures to compensate for the negative effects of the higher water level and water level fluctuations, even if the water level rises further in the future. '

A close look at sand engines

The research question was whether a sand motor is an effective, sustainable and ecologically robust measure for strengthening the Frisian IJsselmeer coast and whether the concept of sand motor can be scaled up to other locations along the Frisian IJsselmeer coast. Through practical research in the project, knowledge has been developed about the extent to which natural processes such as wind and sand transport can help sustainable coastal protection. At two pilot locations, the researchers applied sand nourishments: at Workumerwaard and Oudemirdum. A model study was carried out for the Hindeloopen location. An extensive monitoring program has been carried out to monitor the effects of the sand motors on the coast, to measure how the sand moves and to map how the ecology develops.

System knowledge

"We learned a lot about the system," says Tim. 'The scale of the pilots turned out to be too small to have an effect on coastal reinforcement. The scale of a sand nourishment must therefore be greater to have an effect and the choice of location is important. What we also saw is that the sand does not spread beyond the existing channels at the west coast of the IJsselmeer. As a result, measures with sand in this area have little potential. The south coast, on the other hand, is one continuous system, so that sand interventions are promising. "The most unexpected result? Tim: 'The sand nourishment at Oudemirdum slowly moved towards the coast, while the nourishment at Workumerwaard moved much more northward. So there appeared to be a stronger northward current here than we thought.

Established

The results were presented at the end of 2017 to the Frisian IJsselmeer Coast project group, which is working on a plan for the protection of the Frisian IJsselmeer coast. Tim: 'We have paid a lot of attention to this. We noticed that the province of Friesland and collaborating partners around the IJsselmeer region were particularly interested in how the system works. System knowledge is indispensable when planning measures for flood protection and water management. But perhaps the most important result is that the Building with Nature way of thinking has become established with the parties involved. It's really on the agenda.'