Sheltered sandy beaches of southwestern Australia

Abstract

Four beach types were identified from field surveys of beach profiles on low-energy sandy beaches in Cockburn Sound, a micro-tidal, semi-enclosed basin in southwestern Australia. These were delineated by an exposure factor (Ef), which provided a surrogate for the relationship between incident wave energy and attenuation as a result of structures, banks and shoals. The four beach profiles identified were exponential, segmented, concave-curvilinear and convex-curvilinear in form. Whether the different profile shapes occurred in environments subject to different degrees of sheltering and protection under the same tidal regime was open to question. Beach profiles were examined for Como Beach and Princess Royal Harbour in Western Australia and compared with observations from Cockburn Sound to test this proposition. Cockburn Sound and Princess Royal Harbour are subject to minimal penetration of swell waves whereas Como Beach, in the Swan River Estuary, is wholly fetch limited. Profile forms identified in each environment were consistent with those described from Cockburn Sound. Similar profile types had similar exposure values for all sites such that Ef,1 was characteristic of exponential profiles, 1 -1.5 of segmented, 1.5-2 of concave-curvilinear, and Ef.2 of convex-curvilinear. Although this approach requires further testing in low-energy environments subject to different tidal ranges and fluctuations in sea level, use of the exposure factor for delineation of low-energy sheltered beach types appears to be a robust procedure.

Wave direction shift triggered severe erosion of beaches in estuaries and bays with limited post‐storm recovery

“…The subaerial beach profiles in this study were largely planar/slightly concave in the Pittwater Estuary, consistent with the findings of Hegge et al (1996) and Travers et al (2010) that more protected low-energy beaches sheltered by islands, reefs and headlands tend to have a concave shape. In Kamay, the beach closest to the entrance Figure A2) resulting in often a convex profile.…”

“…In Kamay, the beach closest to the entrance Figure A2) resulting in often a convex profile. It is notable that Yarra had a largely concave-curvilinear shape, which is indicative of more exposed conditions on sheltered beaches according to Travers et al (2010). Some of the profile changes are related to a small estuary/creek located near P2; preliminary wave measurements and anecdotic evidence suggest that this beach is strongly influenced by waves reflected off the adjacent port revetment (Figure 1c) that raise the hydrodynamic level of this beach.…”

“…Beaches in estuaries and bays (BEBs) are common but have been the subject of few studies. BEBs are sometimes also referred to as low-energy beaches (Jackson et al, 2002; Vila-Concejo et al, 2020), fetch-limited beaches (Jackson et al, 2002;Nordstrom and Jackson, 2012), bayside beaches (Nordstrom, 1980;Ekwurzel, 1990), sheltered beaches (Hegge et al, 1996;Travers et al, 2010) and tide-dominated beaches (Masselink and Short, 1993;Short, 2006). The lack of understanding of BEB morphodynamics is a critical issue with climate change, as it exacerbates uncertainties and vulnerability (Vila-Concejo et al, 2010;Nordstrom and Jackson, 2012;Harris et al, 2020).…”

“…Classifications and conceptual models that are routinely applied to sandy wave-dominated open coast beaches such as Wright and Short (1984) are based largely on features such as breaker bars and rip channels that generally do not occur on BEBs (Jackson et al, 2002). The works of Hegge et al (1996), Eliot et al (2006) and Travers et al (2010) provide an understanding of the morphology of low-energy microtidal beaches sheltered by reefs, islands and headlands in south-western Australia. Meanwhile, Nordstrom (1980), Nordstrom et al (1990), Jackson and Nordstrom (1992) and Nordstrom et al (1996), among other works such as Rosen (1977) and Rosen (1980), focused largely on beaches in estuaries and bays in north-eastern USA.…”

Sediment transport measurements with tracers in very low‐energy beaches

“…The importance of the above forcing mechanisms have been effectively discussed by several authors, who identify the foreshore as being the most active part of the profile (Nordstrom, ; Jackson and Nordstrom, ; Jackson, ). The slope and elevation of the fronting tidal flat, in the nearshore, affects wave energy by decreasing wave height by up to 70% (depending on wind conditions and terrace width; Travers et al ., ) and diminishes beach mobility (Jackson and Nordstrom, ; Eliot et al ., ). Geological inheritance can also be a dominant influence on profile shape where wave energy does not exceed the threshold for sediment mobilization or where the shoreline configuration limits sediment inputs or modifies wave activity (Nordstrom and Jackson, ; Kennedy, ).…”