Field observations of tidal flow separation at a mega-scale beach nourishment

Large beach nourishments are often considered an efficient way to deal with coastal zone management issues, notably coastal erosion. Such large nourishments can act as a geometric perturbation, which might cause the tidal current to detach from the coastline. The Sand Motor is a mega-scale beach nourishment in the Netherlands. Field observations of the tidal flow field north of the Sand Motor are presented, showing evidence of flow separation and eddy formation during the flood phase of the tide. GPS-tracked drifters are transported offshore upon deployment near the tip of the nourishment. Flow convergence measured with nearshore current profilers is indicative of flow reversal at the lee side. Images of the temporal development of coherent patterns in time-averaged X-band radar backscatter align with in-situ observations of the flow field. Tidal flow separation at such large nourishments might have an impact on morphological development of the nourishment, as well as on swimmer safety.