Recurrence of Extreme Coastal Erosion in SE Australia Beyond Historical Timescales Inferred From Beach Ridge Morphostratigraphy

Abstract

Extreme storms present a major risk to coasts. Increasing populations worldwide, together with sea level rise, exacerbate concerns for coastal settlements, but the low frequency of extreme storms makes an assessment of risk difficult. In southeast Australia, the severest beach retreat on record relates to a series of extratropical cyclones in the 1970s, but the relatively short observational record hinders assessment of how frequent these events are. At Moruya in New South Wales, four decades of beach monitoring has provided new insights into response of beaches to extreme storms. We augment this recorded history with morphostratigraphic analysis of beach ridge evolution by using ground‐penetrating radar and optically stimulated luminescence dating. We find an episode of extreme retreat over 550 years, proving that the 1970s extreme event is a recurrent phenomenon. Our high‐precision morphostratigraphic analysis provides evidence with which to better plan coastal adaptation.

Evaluation of UAV LiDAR for Mapping Coastal Environments

“…Obu et al [10] used airborne LiDAR datasets captured repetitively over a period of one year to study coastal erosion and volumetric change, together with the accompanying geomorphic process. Tamura et al [11] integrated topographic data obtained by airborne LiDAR and Real-Time Kinematic Global Navigation Satellite Systems (RTK-GNSS) survey along with stratigraphy data collected by ground-penetrating radar to conduct a high-precision morphostratigraphic analysis of beach ridge evolution. Other studies integrated LiDAR-based DSM with satellite images or aerial photos.…”

The turnaround from transgression to regression of Holocene barrier systems in south‐eastern Australia: Geomorphology, geological framework and geochronology

“…Recent reassessment of the ridge progradation rate using OSL has revised the view that the shoreline has built out at a decelerating rate, indicating instead that the progradation rate appears to have been relatively constant since the most landward ridge was formed around 7200 years ago. Tamura et al (2019) refined the depositional chronology of the seawardmost ridges and the anomalous higher foredune, indicating that ongoing progradation occurred, punctuated by storm cut.…”

“…Seaward of 40 m in the profile (Fig. 9A) is evidence of a series of seaward-dipping reflections that are typical of shoreline progradation and beachface cut and fill (see Dougherty et al, 2004;Tamura et al, 2019). The uppermost portion of the profile contains few clear reflections, and ringing precludes further interpretation of the sedimentary history.…”

“…Between 30 m and 60 m along the GPR profile and at 1 to 3 m AHD (Fig. 6A), typical beachface and dune reflections associated with a prograding shoreline are evident, with seaward-dipping concave-up beachfaces that represent storm lag deposits, interspersed with subhorizontal to gently seaward-dipping reflections, which represent fair-weather beach accretion (see Buynevich et al, 2004Buynevich et al, , 2007Tamura et al, 2019).…”

“…Use of ground-penetrating radar (GPR) to image subsurface reflections within sandy coastal facies has enabled researchers to distinguish seaward-dipping from landward-dipping reflections (Neal, 2004;Dougherty et al, 2004;Buynevich et al, 2009;Tamura, 2012). Recent advances in geochronology, specifically the availability and use of optically stimulated luminescence (OSL) dating, have constrained the timing of landform deposition (Murray-Wallace et al, 2002;Tamura et al, 2019;Fruergaard et al, 2020).…”