Dr Andrew McCowan

Managing Director, Water Technology

Coastal hazard studies for the Victorian coastline have recently been completed for Ninety Mile Beach and the Gippsland Lakes, Western Port Bay, and Phillip Island. The projects have assessed inundation and erosion hazards along the shoreline of each study area under both present mean sea level and also taking into consideration predicted increments of future sea level rise. While the determination of the extent of inundation hazards associated with sea level rise can be quantified accurately using available engineering modelling tools and approaches, the estimation of erosion hazard is more uncertain and brings together the more qualitative science of coastal geomorphology with the quantitative requirements of coastal engineering.

Each of the three study areas posed unique requirements when assessing coastal erosion;

• Ninety Mile Beach: is an elongate accumulation of sand initiated by waves, wind transport and vegetation growth. It is a highly dynamic landform which provides a barrier to the extent of the marine processes and influences that can impact the Gippsland Lakes and associated landforms in its lee.
• Western Port Bay: is characterised generally by relatively erosion resistant steep cliffs and embayments on western and southern shores, whilst the northern shorelines are typically lower relief comprising sediments more prone to erosion.
• Phillip Island: has distinctly different northern and southern shorelines, with the sandy spit landform of Silverleaves, the coastal wetlands of Rhyll Inlet, and the steep coast and sandy embayments from Cape Grant to the Woolamai isthmus.

In order to characterise the current and future likely extent of erosion hazard for each location a process based approach was developed. Detailed geologic and coastal geomorphic interpretation identified a range of different landforms and the physical drivers and processes that determine susceptibility to erosion from both marine and terrestrial influences. These drivers and processes were examined in detail, using a range of tools such as hydrodynamic models. The use of models allowed changes in the physical drivers and process, such as wave energy on the shoreline or extent and depth of inundation of a coastal wetland, to be quantified. Relationships were then developed between current erosion or shoreline variability and what this may look like with incremental increases in sea level.

The outcomes of the projects allow the estimation of shoreline erosion for a range of coastal geomorphologies which can inform the decision making process around adaption to future changes in such highly dynamic environments.