Flow and sediment transport with an innovative sand wing
Annually, sand nourishments with a total volume of approximately 12 million cubic meters strengthen the Dutch coastline. Projections indicate that this amount will be insufficient in the near future to ensure the safety of the Netherlands due to climate change and the related rise in sea levels. Within the program ‘Innovatie in de Kustlijnzorg’ (IKZ), WaterProof is collaborating with Waardenburg Ecology and the University of Groningen (RUG) on an innovation called ‘Sand Wing.’ Through scale experiments and numerical modelling, it is being investigated whether the Sand Wing can serve as an alternative solution to the conventional method of beach nourishment along the coast.
- Client: Rijkswaterstaat
- Location: Oosterschelde, Galgeplaat
Due to climate change and the related rise in sea levels, the Dutch coastline will need to be further reinforced in the near future, in addition to the current annual reinforcements already being carried out. In scenarios with accelerated sea level rise, the amount of sand needed for nourishment could increase to about 20 times the current volumes by 2100 (Deltares, 2018). This presents a challenge for Rijkswaterstaat (Dutch Directorate-General for Public Works and Water Management):
- Ensuring coastal safety with a rising sea level, meaning more sand is needed at the coast;
- Coastal nourishments must become more sustainable to counter further climate change and meet the set CO2 targets. In the current situation, sand is extracted from offshore pits and brought closer to the coast, where it is then naturally carried to the beach by currents, or it is directly sprayed onto the beach.
Method
As an alternative to the current method of nourishment, the Sand Wing has been devised. This wing is placed on a sandy seabed in a tidal or river current. The Sand Wing enhances the flow and changes its direction. The water carries sediment with it and transports it to the desired location due to the altered flow direction. This reduces the need for sand nourishments.
Through experiments with a scale model of the Sand Wing in a flume and sediment basin, the effects of the Sand Wing on flow and sediment transport have been mapped. Using measurement devices, the flow direction, flow strength, and degree of turbulence around the Sand Wing on a fixed bed were recorded. Thereafter, the Sand Wing was placed in a mobile sand bed, and the morphological effects were observed. In addition to the scale experiments in the flume and basin, modelling was also conducted to examine what effect a Sand Wing could have on a sandy shoal (Galgeplaat) in the Eastern Scheldt (Oosterschelde).
The experiments and modelling show that the Sand Wing influences water flow as expected. A sedimentation effect was observed, confirming the hypothesis that the Sand Wing can be used to guide sand transport in a preferred direction. Furthermore, the modelling studies indicated that multiple Sand Wings could be ‘linked’ together. By placing them in succession, sediment can be transported over large distances in a desired direction.
The next step in this study would be to test the Sand Wing in practice.
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