Abstract
Natural formations of rock and coral can support geologically controlled beaches, where the beach dynamics are significantly influenced by these structures. However, little is known about how alongshore variations in geological controls influence beach morphodynamics. Therefore, in this study we focus on the storm response of a beach (Yanchep in south Western Australia) that has strong alongshore variation in the level of geological control because of the heterogeneous calcarenite limestone reef. We used a modified version of XBeach to simulate the beach morphodynamics during a significant winter storm event. We find that the longshore variation in topography of the reef resulted in: (1) strong spatial difference in current distribution, including areas with strong currents jets; and (2) significant alongshore differences in sand flux, with larger fluxes in areas strongly geologically controlled by reefs. In particular, this resulted in enhanced beach erosion at the boundary of the reef where strong currents jet-exited the nearshore.
Highlights
Sandy beach morphodynamics are the result of complex interactions between sand, meteorological and oceanographic conditions, and in many cases, geological controls
The majority of the storm erosion occurred on the section of beach fronted by reefs, rather than the more exposed area to the north (Figure 8)
We explored the influence of alongshore variability of reefs on sand flux during a storm using XBeach
Summary
The inshore ridge coincides with the shoreline and has highly variable alongshore topography. This creates a diverse geological framework that supports a diverse range of beaches. The reef at Yanchep (Figure 1c), located 60 km north of the city of Perth, varies alongshore in elevation, continuity and distance seaward from the beach. This makes this relatively short, 3 km stretch of coastline an ideal location to investigate how rock topography influences beach morphodynamics. The limestone becomes patchier forming isolated submerged rock outcrops (“bommies”)
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