Sand Engine – IJsselmeer Coast

Planning and design

This type of intervention was meant to have multiple benefits, such as: coastal reinforcement, dynamically evolving coastal fore-shores creating habitats for pioneer vegetation and cost reductions compared to traditional engineering.

The experiment was supported by national, provincial and water management authorities and by NGO’s, and each party framed the importance and the objectives according to their own interest. The Nature conservation NGO, for instance, stressed the importance of creating conditions for pioneer vegetation, because the salt water tidal estuarine habitats were replaced, after damming in 1933, by a stable water level, not allowing for ecological succession. The water authorities wanted innovation in flood prevention as an alternative to reinforcement of existing flood protection. The provincial authority aimed at improving the spatial quality of the Frisian coast. Lastly, the national government wanted to support adaptation of the Frisian coast after its decision to raise the IJsselmeer water level.

Selection of experiment locations had to consider processes of sand transport and sedimentation, ecosystem functioning, flood protection infrastructure, local recreational entrepreneurs and a governance system with multiple parties and interests.

To determine the best position of the nourishment, an advanced Unibest model (CROSSMOR) (van Rijn, 2006) was used to calculate sand transport and morphological changes perpendicular at the Workumerbuitenwaard (Folmer, 2010).  Using this model resulted in the placement of the nourishment in the dynamic zone at the edge of the shallow foreshore. For the design in Workum a long sand bar was chosen as it would create a long lee-side.

In Oudemirdum, the shape of a hook was chosen that stretched from close to the coast to the dynamic wave breaker zone to experiment with sand on the more shallow and less dynamical part of the foreshore.