The Impact of Extreme Storm Events on Foredune Morphodynamics Along the Illawarra Coastline, NSW, Australia

Extreme storms drive much of the morphological change in coastal settings. This can result in dune degradation, scarping and sometimes destruction of important foredune features that protect and buffer coastal populations. The majority of beaches found along the Illawarra coast are embayed beach systems that have been classified within the intermediate morphodynamic beach type. They are highly dynamic and are prone to frequent change in response to storms associated with intense East Coast Low (ECL) storm systems.

Recently, community pressure has been focused around the amount of vegetation found on the Illawarra foredunes. The vegetation has extended seaward, reducing beach width and promoting atypically steep dune scarps following storm activity. As a consequence, the local councils have enacted various management initiatives. For example, in Woonona and Towradgi, the Wollongong City Council has preferentially removed selected dune vegetation and reshaped the backshore, leaving an almost bare foredune-beach in its place. This provides an unique opportunity to examine the importance of vegetation on such systems.

Due to the strong community concern regarding Illawarra foredune vegetation, and the lack of local research in this field, a re-examination of the role this vegetation plays in such environments is required, particularly during periods of sudden short-term change (i.e. storm activity). This study attempts to improve understanding of the eco-morphologic interactions between foredune vegetation and dune morphology occurring on Illawarra foredunes, and investigate how these systems have responded to recent storm activity as well as to infer how similar settings will respond to future storm events.

In particular, RTK GPS survey and Terrestrial Laser Scan data from several extreme storm events (esp. 4-5th June, 2016) impacting four ecologically diverse, but morphological similar foredune settings are studied to quantify storm impact and foredune recovery. These dune changes are compared in terms of: a) storm characteristics, to identify variability in dune response, and b) vegetation assemblages, to assess whether native versus exotic species influence storm impact severity and subsequent dune recovery rates (i.e. speed and style of recovery). Preliminary results reveal that the storm impacted the central to southern ends of beach-dune sites within the Illawarra. Where almost all of the incipient foredunes had been removed from the system, producing 0.7 - 3m high scarps along the front of established foredunes. Highly urbanised dunes appeared to have been impacted more severely than those that retain more “natural” vegetation assemblages across both younger incipient and older established foredunes. Evidence for differing rates of recovery will be discussed to gain a better understanding of the longer-term role of various foredune plants. This will not only help further our understanding in ecomorphodynamics, but aid in forming more accurate storm impact modelling along this coastline.