Controls of Variability in Berm and Dune Storm Erosion

Abstract

The erosion impact of large coastal storm events typically occurs across broad (100s of km) sections of coastline and may include significant variability both alongshore and vertically between the berm and dunes. Identifying controls of variability in storm erosion is critical to understanding the response of coastlines to present and changing storminess. This contribution analyses immediate pre‐ and post‐storm Lidar data of over 1700 cross‐shore profile transects, determined at every 100 m alongshore and spanning 400km of the southeast Australian coastline. This unique dataset allowed for a data‐driven Bayesian network analysis of the key relationships between the measured storm erosion response and a range of variables describing the antecedent morphology and hydrodynamic forcing at the coastline. It was found that while erosion of the dune and berm was observed to increase with increased exposure of the local profile to incident storm waves, additional erosion controls were found to be different for these two different sections of the beach. Erosion of the berm was specifically linked to the pre‐storm berm volume, with more accreted berms experiencing a greater proportion of erosion of the overall berm, regardless of variability in forcing conditions. In contrast, dune erosion was equally controlled by the exceedance of wave runup above the antecedent dune toe elevation and the width of the beach immediately fronting the dune, with wider beaches resulting in reduced dune erosion. The results of this large, data‐driven analysis provide important affirmation and insights into the primary controls of berm and dune storm erosion.

A rules-based shoreface translation and sediment budgeting tool for estimating coastal change: ShoreTrans

“…This results in offshore transport (erosion) from the sub-aerial beach and dunes, to the lower active profile. The berm is initially eroded and, if water levels and waves are sufficiently high, significant dune erosion may occur [14,41,42].…”

“…10). For beaches backed by infrastructure, such as where houses are built within the active profile (e.g., Narrabeen, Australia [42]), there is risk of losing beach width if the infrastructure is defended ("Hold the line" policy in the UK [39]), but the beach will survive if infrastructure is abandoned ("Managed retreat"), or alternatively if the beach is sufficiently nourished (e.g., [3]). Accordingly, the next report on the future of the world's beaches should focus on beach width, as well as shoreline recession, and the methods described here provide a means with which to address this question of vital public interest.…”

Spatial Variation in Coastal Dune Evolution in a High Tidal Range Environment

“…Dune vegetation helps to trap dune directed aeolian sediment supply [15,16] and also stabilizes the dune from erosion by wind [17] and waves [18]. Waves are typically considered from an erosive perspective in relation to dune systems e.g., [19][20][21][22][23][24][25]; however, there is a recognition that wave-driven onshore transport can provide sediment reservoirs that subsequently can nourish dunes through aeolian transport [26][27][28]. Spatial variation in foredune evolution has been noted over a range of scales [29][30][31][32].…”

Citizen science for monitoring seasonal-scale beach erosion and behaviour with aerial drones

“…Alternatively, the closest comparable topographic monitoring methods are repetitive airborne light detection and ranging (LiDAR) surveys or fixed coastal imaging stations (ARGUS). Coastal LiDAR is often used for quantifying wide-scale shoreline spatial variability of single-event post-storm erosion 19 , 64 , 65 , however, high operational costs have traditionally limited its temporal resolution within geoscientific research 66 , often missing the fine seasonal dynamics that our approach provides. ARGUS stations on the other hand can typically provide hourly shoreline images of key sites, which are then processed to obtain shoreline elevations and later used to monitor erosion/accretion patterns in a relatively cost effective way.…”