Foredune Response to Storm Erosion and the Role of Vegetation in Recovery

Erosional scarping of beaches as a result of the June 6th 2016 storm event provided an opportunity for coastal managers to increase knowledge regarding the impacts of large storm events on beach-dune systems. The recovery of scarps through slumping has not been widely investigated, with previous studies focused on beach response to storm events as an overview. The Illawarra and south coast region was examined during the course of beach recovery to determine whether erosional scarp height recovery is influenced by scarping height. The study also considered whether vegetation influences the recovery process through slumping. This study aims to determine whether scarp height influences the length of time taken for scarps to recover through slumping on a short term scale, whilst longer term recovery processes such as berm accretion occur. Therefore the study investigated to whether higher scarps took longer to recover than smaller scarps. Scarping was investigating through visual examination of immediate post-storm LiDAR obtained by the University of New South Wales for the office of Environment and Heritage. Further, a recovery LiDAR capture was undertaken in November with scarping visually examined. The two LiDAR sets were then compared through production of LiDAR derived profiles, to determine differences in scarp shape and height through time. RTK GPS surveying was also utilised to examine scarp recovery through showing monthly change for a 5 month recovery period and supplemented photographic visual comparison to examine this aim. This was complemented with vegetation assessment to determine if a trend exist between vegetation present on scarping and the rate of recovery. The results of this investigation showed that higher scarps did retain a vertical cut and higher height for a longer period of time during the recovery process. Moreover a possible trend was identified that shrubs including Acacia var. sophorae and Leptospermum laevigatum influenced scarp shape, with a higher vertical cut retained for a longer period. This study showed that investigation of scarp height, a major erosional impact of storms, has been largely understudied. LiDAR derived profiles and Digital Elevation Model maps provide an accurate and detailed morphological view of storm impacts and subsequent recovery. LiDAR is costly to acquire, however coastal managers should utilise this emerging technique to investigate large storm events to generate a catalogue of accurate spatial data to allow a standard when examining highly erosive event impacts to be tracked and future impacts to be predicted with storm frequency increasing due to climate change