Interdecadal Foredune Changes along the Southeast Australian Coastline: 1942–2014

Abstract

Foredunes are important features within coastal landscapes, yet there are relatively few medium to long-term studies on how they evolve and change over time. This study of Australia's New South Wales (NSW) foredunes has used 70 years of aerial photographs (or photogrammetry) and recent Light Detection and Ranging (LiDAR) datasets to assess multi-decadal fluctuations in foredune morphology. It was shown that over the past 70 years NSW foredunes have exhibited considerable spatial variation, ranging from accretion/aggradation to recession. Those sites that accreted predominantly extended seaward as new incipient dunes, gaining a maximum of 235 m 3 m −1 in sand volume over the study period (for the entire dune system). These sites were commonly found in the north of the state, within closed sediment compartments, and with strong onshore (and alongshore) wind climates present (increasing the potential for aeolian sand transport). Stable foredunes were those that remained within +/− 50 m 3 m −1 of their initial volume and managed to recover from the various storm impacts over the study period. The majority of these sites were found within the central to southern half of the state, behind embayed beaches, and within leaky sediment compartments, or those that have estuarine sinks. Finally, those foredunes in recession have retreated landwards and/or have reduced in height or width, and lost up to 437 m 3 m −1 of sand volume over the study period. There was no clear spatial trend for these sites; however, generally they were found in compartments that had unusual orientations, had disruptions in longshore drift/cross shore sand delivery (i.e., rocky reefs), or were being impacted by humans (i.e., the installation of river training walls, sand bypassing systems, or coastal management programs). This study has shown that NSW foredunes have undergone substantial recent changes and, by understanding their past history, will provide better insight into how they can be managed into the future.

Mapping the Shoreface of Coastal Sediment Compartments to Improve Shoreline Change Forecasts in New South Wales, Australia

“…Sand supply from the lower shoreface to Perkins Beach is consistent with the long-term historical accretion of that shoreline (Doyle et al 2019b) and could represent a remnant process of shoreface lowering due to morphodynamic disequilibrium-stress, which would explain initial progradation of the Holocene Perkins-Windang barrier. That process has been shown to be the primary source of Holocene barrier progradation elsewhere in southeastern Australia (Kinsela et al 2016).…”

“…The result was similar, however, reflecting a previous study that identified the clockwise rotational trend (Cardno 2010). Doyle et al (2019b) found that Perkins-Windang Beach accreted by around 120 m 3 /m of shoreline on average during 1961-2014. The construction of the Lake Illawarra entrance training walls (2001)(2002)(2003)(2004)(2005)(2006)(2007) triggered scouring of sand shoals and channels within the tidal inlet, which appears to be driving progradation of the flood-tidal delta into the lake and aggradation of the ebb tidal delta outside the entrance, while increasing the tidal range within the lake (Young et al 2014;Wiecek et al 2016;Hart et al 2017).…”

“…The construction of the Lake Illawarra entrance training walls (2001)(2002)(2003)(2004)(2005)(2006)(2007) triggered scouring of sand shoals and channels within the tidal inlet, which appears to be driving progradation of the flood-tidal delta into the lake and aggradation of the ebb tidal delta outside the entrance, while increasing the tidal range within the lake (Young et al 2014;Wiecek et al 2016;Hart et al 2017). Although the long-term average trend found by Doyle et al (2019b) is likely influenced by human interventions, the beach is located on a prograded-stationary barrier and thus the Perkins-Windang shoreline is considered stable.…”

150 years of foredune initiation and evolution driven by human and natural processes

“…Arens et al, 2001;Jackson and Nordstrom, 2011;Bakker et al, 2012;Portz et al, 2015;Itzkin et al, 2020). Their impact on dune evolution on longer time-scales (decades to centuries) is less understood, as monitoring programs have been implemented too recently to cover these time scales (Bochev-van der Burgh et al, 2011;Doyle et al, 2019).…”

“…This holistic method illustrates the continuous evolution of around 250 m of the beach-dune system over the last 150 years including natural and anthropogenic evolutions (Figure 10c). This approach is complementary to information provided by the study of diachronic aerial (or satellite) photographs since the 1940s (Navaro-J o u r n a l P r e -p r o o f Journal Pre-proof Pons et al, 2016;Rader et al, 2018;Doyle et al, 2019;Jackson et al, 2019;Moulton et al, 2019) and makes it possible to extend the more recent 2DV database obtained using traditional topographic instruments and surveys (e.g. Bochev- Van der Burgh et al, 2011;Castelle et al, 2017b;Brodie et al, 2019;Nicolae Lerma et al, 2019).…”