Flow dynamics over a high, steep, erosional coastal dune slope

Abstract

Flow dynamics over a high, unvegetated, and steep scarp slope that fronts a severely eroded relict transgressive dunefield were investigated at Salmon Hole (also known as Post Office Rock), a small headland-bay beach located near Beachport, south east South Australia. The ~15-metre-high steep dune at Salmon Hole provided the opportunity to conduct a wind flow experiment on a larger, higher and longer stoss slope than previously studied. The scarp slope is comprised of segments of varying slope that have a significant impact on flow dynamics over the dune. Percentage speed up and a decrease in turbulence were recorded up the stoss slope due to streamline convergence and flow compression. However, flow expansion at a change in gradient on the upper stoss slope caused a significant drop in wind speed and an increase in turbulence, contrary to what has previously been found in the literature where maximum percentage speed up is primarily recorded at the crest. Topographic steering typically seen in wind flow over scarps and foredunes was observed at Salmon Hole along with flow separation and the formation of a reversing vortex on the lee slope. This study also demonstrates how a lack of sediment delivery back to the beach and thence to the dune between storm events results in the inability for dune recovery or translation. However, the Salmon Hole study shows that blowouts can still develop and grow through dune cannibalization regardless of the lack of sediment supply from the beach and the recession of the shoreline.