Coastal Hazard Study

The coastal hazard component of the study will investigate and quantify a range of coastal processes including:-

Beach Erosion and Recession

Beach erosion and shoreline changes are influenced by a range of factors including wave climate, beach sediment composition, under lying rock, soundness of shoreline structures ans sea level rise. A range of investigative techniques will be adopted to quantify the erosion and shoreline change processes, including modelling and analysis of historical shoreline change data.

Long-term shoreline change data is available for many beaches in the Illawarra region since the 1950's. The data can be used to define the historical shoreline changes. The figure below shows an example of the shoreline position at Thirroul Beach at selected times since the 1960's.

Figure 1 - Examples of the shoreline position at Thirroul Beach at selected times since the 1960's. Each coloured line indicates the shore line position for a given year.

A range of empirical and numerical models will be applied to define various components of shoreline change.

Wave Conditions

Defining the nearshore wave climate will be a critical component of the coastal zone study. A detailed wave climate study is being undertaken using the SWAN wave model system which is one of the world's most advanced numerical wave models. The figure below shows an example of the modelled wave conditions near North Beach, Wollongong for a severe ocean storm.

Figure 2 - An example of modelled wave conditions near North Beach, Wollongong for a severe ocean storm. Red indicates regions of high wave height and blue indicates regions of low wave height.

Ocean Inundation

In addition to wave modelling, outcomes from the wave climate study will also be used to define coastal inundation extents. The coastal inundation component will address a range of processes including ocean inundation, wave run-up levels and overtopping volumes for coastal structures. A range of the latest numerical and empirical models will be used to define these parameters.

Climate Change

The consequences of sea level rise and other effects of climate change on coastal hazards in the Wollongong region will be assessed on the basis of recent data and publications such as those from CSIRO, Australian Greenhouse Office and the IPCC (2007). Assessment of climate change effects on coastal physical processes will include:-

• Sea level rise and shoreline recession.
• Rainfall, catchment run-off and stormwater inflows.
• Wave climate and shoreline erosion.

Calculations including numerical modelling of climate change scenarios will be undertaken to define the impact of climate change on such factors as storm erosion and recession and coastal inundation. Climate change scenarios will be developed in conjunction with the recently awarded study to assess the impact of climate change on the Wollongong coastline to enhance the consistency between future estuarine and coastal policies in the Wollongong region.

Defining Hazard Extents

Results from these investigations will be used to define the 50-year and 100-year coastal hazard extents for current and future climate conditions. The figure below shows an example of the erosion hazard extents recently calculated for North Wollongong Beach.

Figure 3 - An example of the erosion hazard extents recently calculated for North Wollongong beach. The red line indicates the extent of erosion hazard and the orange line indicates the region of geotechnical instability.

A range of other factors will be considered in the coastal hazard study including:-

• Ecological factors.
• Economic, Social and Cultural Issues and Values of the Coastal Zone.