The “Afsluitdijk”, built in 1932, is an icon of civil engineering that has brought security and economic development to the Netherlands. However, the construction of this dyke has caused a great deal of disruption to nature. The Zuiderzee and the Waddenzee were separated from each other and an almost insurmountable barrier was erected for migrating fish. Nowadays the fish are waiting in de Wadden Sea in front of the sluices in the dyke. When these sluices open the current is too strong for the fish to pass the dyke and the transition between fresh and salt water is to abrupt.

Therefore, a number of organisations, including the Province of Friesland, have taken the initiative to realise a fish migration river. This is not just a hole in the dyke. The river is situated in a natural sand bed with tidal channels and resting places.  Enclosed by breakwaters, water is given the opportunity to flow naturally into and out of the river. The tender for the construction of this project is scheduled for 2020. In anticipation of the work to be carried out, the so-called  “Westdam” will be constructed in 2020.  The “Westdam” is located on the IJsselmeer side. The location is now permanently below the water level.  Both the soil level and the structure of the soil vary significantly at the location.  De seabed is characterised on the one hand by silt deposits (deposited as a result of low flow velocities) and on the other hand a deep erosion channel is present near the existing breakwater.

For the construction of the “Westdam”, Geobest assessed the existing geotechnical advice regarding the expected settlements of the embankments to be constructed and the stability of these embankments and provided additional advice. In addition to the known subsoil conditions, the nature and  composition of the fill material also plays an important role. IJsselmeer sand from the shipping channel Kornwerderzand - Workum is the most likely source of raw materials for the execution of this Westdam.

Geobest is involved as a specialist geotechnical consultant.