Coastal transgressive dunefield evolution as a response to multi-decadal shoreline erosion

Abstract

The Younghusband Peninsula coastal barrier extends ∼190 km and is predominantly comprised of a mix of active, semi-stabilised and stabilised (relict) transgressive and parabolic dunefields. Wave driven shoreline erosion has triggered the rapid development of a transgressive dunefield along a portion the peninsula. This study focuses on a ∼2 km region with the highest regional erosion rates (> −2.0 m/year since 1988), and which has experienced rapid destabilisation and subsequent landward translation of the dunefield. Aerial LIDAR derived datasets of the barrier system from 2008 and 2018 and eight drone photogrammetry surveys between August 2020 and April 2022 are used to compare the rates of change across the beach-dune system. The net and intra-survey changes are used to show the short- to medium-term system response and illustrate the relationship of sediment dynamics to the developing morphology and structure of the dunefield. Shoreline change rates (m/yr) are sourced from the Digital Earth Australia coastlines dataset which provides annual rates for continental Australia from a Landsat time series (1988–2021). When the rate of shoreline change is segmented from the total dataset to the study time-period (2008–2021), the average resulting rates show an increase from −2.2 m/yr to −3.3 m/yr, respectively. This coincides with a landward advance rate of >10 m/yr from 2008 of the dunefield edge, with the fastest eroding dune toes corresponding to regions with the highest rate of dunefield translation and transgression. Net volumetric totals and their ratios of gain to loss of sediments show that significant sediment is lost to offshore during the retrogradation of the dunefield as only a fraction of the stoss slope sediment is transferred landwards. All regions of the dunefield exhibit a net loss of sediments but the high-temporal resolution shows that the magnitude of 3D changes varies through time. An adapted model of erosional stoss slope evolution and dunefield development is advanced and a temporal model of transgressive dunefield evolution is synthesised.