Introduction

Cardno was commissioned by the City of Greater Geelong (CoGG), the Department of Sustainability and Environment (DSE) (now the Department of Environment and Primary industries (DELWP), the Corangamite Catchment Management Authority (CCMA), the Department of Planning and Community Development (now part of DELWP) and the Borough of Queenscliffe (BoQ) to undertake the Bellarine Peninsula - Corio Bay Local Coastal Hazard Assessment (Bellarine Peninsula – Corio Bay LCHA). These organisations make up the Project Control Group (PCG). This study is one of four Local Coastal Hazard Assessments undertaken in Victoria through collaborative partnerships with local stakeholder agencies and was initiated through the DSE (now DELWP) Future Coasts Program. 

The Bellarine Peninsula – Corio Bay LCHA study area includes the entire Bellarine Peninsula and the northern side of Corio Bay, from Point Wilson in the north, to Breamlea in the south. The key aim of this study is to provide a comprehensive understanding of the extent of coastal hazards and the impacts on the coastal environments within the study area. This was done by addressing coastal, estuarine/riverine and climate-change challenges by defining the possible magnitudes and extents of the hazards in a considered and robust manner. This provides information for local land managers regarding their sections of the coast, and provides a basis to identify additional studies to be carried out in the future. This will ensure councils and land managers are prepared for future hazard and climate-change related challenges, and to inform strategic planning and decision making.

It is intended that this study will inform subsequent risk and mitigation assessments, which will guide the prioritisation and implementation of management actions. This will ensure best use of existing coastal management budgets, and also provide information to gain external funding where possible.

Study Area

The study area consists of a variety of coastal environments. The Bass Strait open coast section of the study area is generally a high-energy environment with a relatively consistent wave climate, shallow nearshore bathymetries, consolidated dunes/cliffs and unconsolidated dunes ranging in elevation from 2 to 30 m AHD. Headlands and rocky foreshores have fixed the ends of the local beaches, and characteristic arc and zeta curve shaped beaches lie between the fixed points. The key hazard along the open coast is erosion. Inland at Breamlea and Barwon Heads there are low-lying land areas vulnerable to inundation.

The entrance to Port Phillip Bay is a complex environment dominated by swells and strong currents. Within the bay the tidal range is lower than that in Bass Strait.  The influence of swell decreases with distance from the bay entrance and the resulting environment is quite different. The wave climate is dictated by wind, meaning wave heights are fetch-limited. Due to sedimentation, water depths on the western side of the bay are shallow near the Great Sands, resulting in lower (depth-limited) wave heights.

In the vicinity of the entrance, the Lonsdale Bight coastline consists of high cliffs, long sections of protection structures (seawall and revetment) and dunes. The key hazards are erosion, overtopping of the protection structures and inundation of the low-lying areas around Queenscliff and Swan Bay. Further north along the St. Leonards and Portarlington coast the shoreline elevation is low, leaving some discrete areas vulnerable to inundation and erosion during storm events. The Clifton Springs coast from Portarlington to Geelong consists of cliffs with narrow beach widths at the base. The hazards here are mostly slope stability related, with some low‑lying areas vulnerable to inundation. The coastal processes are dominated by wind, wind-waves and currents. The Corio Bay area is very low energy in comparison to the rest of the study area. Wave heights are more significant during north easterly wind events, due to the greater fetch from this sector. The northern Corio Bay area is also low energy, the energy increases slightly towards Point Wilson, due to the exposure to the wider bay. The shoreline is mostly rocky with a low-lying hinterland behind.  

Methodology

A site visit and review of all relevant data sets and previous studies was undertaken early in the study. After consultation with the Project Control Group (PCG) and technical reviewers, the methodology was refined to ensure the most appropriate methods were undertaken to deliver the desired project outcomes. Due to differing landscapes and levels of hazard and potential risk, the appropriate scale and resolution of the modelling was determined for each study compartment.

The initial modelling considered waves and water levels throughout the study area, which enabled the determination of design conditions for subsequent inundation modelling. Inundation hazards were determined using hydrodynamic and static modelling (for less complex areas).  Due to the nature of the differing coastal environments there were some limitations within the inundation assessments of this study, and these were considered and reported on within the findings

Key Findings

The results and findings of the inundation assessments, as well as the hazard maps are presented for the study compartments where necessary. The study findings show that the level of hazard is markedly different between locations. The following sections provide commentary of the key findings for each compartment. Figure ES 1 shows the locations of study compartments, with the boundaries of the hydrodynamic models. 

Compartment 1: Breamlea to Blue Rocks

The present day inundation vulnerability to a 1% annual exceedance probability event (AEP) with 0.0 m sea-level rise (SLR) is low. Under this and the 0.2 m SLR scenario, the areas of inundation are mostly low-lying floodplain areas, therefore the impacts to habitat are potentially of significance. It is not until the events with the higher sea-level rise scenarios that infrastructure and assets are impacted.

The local habitat resilience to saline inundation should be assessed, and areas of appropriately elevated land mapped for future areas. 

A key location to note is the beach access at Bancoora Beach, which has the potential to become a breach location in future for inundation of the hinterland. The timing of this is uncertain. Regular monitoring of the beach is required to allow coastal managers to track any significant changes that would prompt a management response. The amenity use of this area is likely to increase in future also, therefore the formalisation of the access may be necessary to minimise future anthropogenic impacts. 

Compartment 2: Blue Rocks to Barwon Estuary

The inundation vulnerability to this section of coast is low due to the high dune/cliff elevations, however regular monitoring of the far western end of the beach (which is lower) will aid in tracking morphological change. This may be of significance to the inundation vulnerability in future.

Compartment 3: Barwon Heads, Barwon Estuary and Lake Connewarre

Riverine flood inundation has been investigated in the past, however focused solely on riverine inundation. This assessment considered the saline inundation primarily, and coincidence of this with riverine events. An assessment of the coincidence of these two factors was undertaken, it was found that storm-tide inundation and peak riverine flows due to high rainfall do not occur at the same time. The assessment therefore included two higher frequency flood events, an annual peak flow and a 10% AEP flood event, with the less frequent 1% AEP coastal event.

The saline inundation potential for Barwon Heads is less significant than previously assessed (Future Coast, 2011). In a 1% AEP event with a catchment baseflow the low-lying areas of the estuary shoreline are inundated. These are mostly areas of habitat. In events with sea-level rise above 0.2 m, the flood extents become more significant.  In a 1% AEP event with a 10% AEP catchment flow for the present day (i.e. 0.0 m SLR) the flood extent is greater than the equivalent baseflow case.  The inundation is likely to impact the eastern bank of the river, at Ocean Grove, where the low shore protection is likely to be overwashed. Note, the shore protection here is not forming a consistent barrier and appears to have been designed to minimise shoreline movement on the river bend, rather than flood protection. On the western bank of the river (Barwon Heads) the inundation potential increases with increases in sea-level rise. 

Compartment 4: Ocean Grove to Point Lonsdale

This section of coast is subject to erosion hazards and overtopping at the Ocean Grove seawall. This will have implications for future risk assessments. It is recommended that closer monitoring of the beach is undertaken to track coastal change and provide better background information for future assessments.

The seawall at Ocean Grove Main Beach is providing a high standard of protection to the hinterland presently. Overtopping volumes are generally low for the present day. Beach levels at the toe of the seawall are likely to decrease due to scour erosion, therefore increasing the depth of water at the toe of the structure during storm conditions. This in turn will allow larger waves to penetrate further inshore and increase overtopping. The rate of loss of beach volume is currently unknown, and should be monitored to inform future assessments.    

Compartment 5: Point Lonsdale to Point Edwards

This section of coast is subject to overtopping and inundation hazards. An assessment of the overtopping of the shore protection (seawall and revetments) was undertaken for Lonsdale Bight. This showed quite a significant hazard for the present day and in future with sea-level rise increases. The results are consistent with visual inspection of the area and information from the asset managers, the seawall is regularly repaired due to the effects of direct wave impact. Through time the incidence of damage due to wave impact is likely to increase, therefore continued maintenance and upkeep in this area is vital. The overtopping hazard decreases further around Lonsdale Bight due to the change from vertical seawall to revetment (which also increases in elevation from Lawrence Road) as well as a general decrease in wave energy with distance from the bay entrance.

Inundation is likely to be the overriding hazard for the Queenscliff area, more specifically, Fisherman’s Flats. The Fisherman’s Flats shoreline is significantly lower than the rest of the Queenscliff area; therefore any inundation is likely to originate from there. The shore protection is in very poor condition in some locations, and not forming a consistent barrier.  The newly upgraded marina shoreline is approximately 0.5 to 1 m higher.

The lowest areas of Fisherman’s Flats already pool runoff in high rainfall events, thus the inclusion of saline inundation will increase the vulnerability, although similarly to the Barwon Estuary the likelihood of the two hazards occurring together is low. The stormwater pumping infrastructure has been upgraded recently to address the runoff issues. It is recommended that investigation into management options to mitigate the effects of saline inundation in this location should occur in the near future.

At the southern end of Swan Bay, an assessment of the inundation of Lakers Cutting and the Lonsdale Lakes development was undertaken. The inundation vulnerability also extends to the Bellarine Highway and properties in the vicinity of Murray Road. The extent of inundation of this area becomes significant under a 1% AEP event with 0.2 m SLR. In this event, a low section of the railway embankment overtops west of the Marine Discovery Centre, possibly impacting a small number of properties along Murray Road. The timing and depth of inundation for this area during this event is likely to be low; this should be considered in subsequent risk and mitigation studies. In a 1% AEP event with 0.5 m SLR, the flood extents increase significantly. It is recommended that the railway embankment is further investigated, particularly the permeability, as with minor adaptation (e.g. valving of culverts and removal of drainage channels) this could aid in inundation mitigation during lower events. Under higher sea-level rise events, the embankment would likely be overwashed. This will impact the Bellarine Highway. 

For Swan Bay, the inundation hazards are less significant. There is little development around the bay, thus the key issues will likely be related to habitat resilience. The surrounding land areas rise gradually to higher land, therefore there appears to be nothing inhibiting any natural roll-back with sea-level rise.

Compartment 6: Point Edwards to Portarlington

The key inundation hazard area is at Salt Lake. There is a narrow section of shoreline between the lake and the coast, this is likely to overwash in a 1% AEP event with 0.0 m SLR via low sections in the road. In the higher sea-level rise scenarios, the shoreline is below the storm-tide level. It is recommended that risk and mitigation studies are undertaken in the near future for here.

From indented head to Portarlington the coast becomes more exposed to wave impacts, thus, erosion issues are more significant rather than inundation.

From Portarlington to Ramblers Road, the coast is vulnerable to inundation. Similar to the previous coastal section the exposure to the prevailing winds and waves is more significant here. The hinterland elevations at the Esplanade are low, and east of the pier are low, and decrease further moving west past the Bellarine Bayside foreshore to Ramblers Road. It is recommended that risk and mitigation studies are undertaken in the near future to address the inundation issues at Ramblers Road. 

Compartment 7: Portarlington to Point Henry

The inundation hazard along this section of coast is relatively low, the key location for inundation is near the Sands Caravan Park, however at the base of the cliffs around Clifton Springs there may be some impact to infrastructure in high water events.  

Compartment 8: Stingaree Bay to Geelong (South Corio)

The ground elevation in this area are very low, thus, inundation is a key hazard. In a 1% AEP event with 0.0 m SLR some fringe areas of the shoreline are impacted, mostly habitat around Point Henry. The salt pans are also likely to inundate, however this is of no consequence. In a 1% AEP event with 0.5 m SLR, the flood extents become more significant, potentially impacting some roads. Properties around Newcomb and Moolap are likely to be impacted by inundation in sea-level rise scenarios of 0.8 m and above. 

The inundation vulnerability around Geelong is low. The shoreline is heavily modified, protection structures exist from east of Eastern Beach to Western Beach, mostly vertical seawalls. An overtopping assessment was undertaken and the vulnerability is high, however the consequences of overtopping inundation are likely to be low as long as the ongoing maintenance of the structures and active management of the foreshore is continued. 

Compartment 9: North Corio Bay to Point Wilson

Beyond the Moorpanyal cliffs the ground elevation in this area is again very low, thus, inundation is likely to be the overriding hazard. Areas of foreshore are impacted in a 1% AEP event with 0.0 m SLR, these are mostly habitat areas. As sea-level rise increases, public infrastructure is also likely to be impacted, such as roads and storm water infrastructure.

The environmental value of this area is significant with large areas of rare habitat. Resilience studies and mapping of appropriate future habitat areas based on ground elevation and future inundation frequency should be undertaken. 

Area wide management recommendations

The following are general recommendations for the overall study area that may aid in reducing the uncertainty of the finding of this study, as well as aid coastal mangers in their future management undertakings:

Further Work to Fill Data Gaps

Each area’s results section gives some advice as to the data requirements for further studies. This will greatly aid in reducing the levels of uncertainty within this study. The reliability of the hazard studies stems from the quality and quantity of data available to carry out the coastal hazard assessment.

There are two overarching uncertainties related to these assessments, the lack of thorough and recent background data sets and the methods used in determining the present and future hazard extents. The following will aid in reducing uncertainty, and provide information to update the findings of this study in future.

Beach profiling

Beaches provide the primary protection against the erosive effects of the sea at many places in the study area.  The condition of beaches is thus an important factor in coastal hazards definition. There is lack of beach profile data available for the study area, as well as much of the Victorian coast. This will be vital in determining the short and long-term change of beaches, and better inform hazard studies in future.

Beach profile information will greatly reduce the uncertainty related to the profiles used in this study, and to monitor future change. Profiles were taken from LiDAR data flown in 2007 (DSE, 2007). The uncertainty associated with this relates to the following:

Beach profiling can be carried out using a number of methods e.g. surveyors, RTK GPS, photogrammetry (from regular aerial images, possibly collated by unmanned aerial vehicles, “drones”), profiles from high resolution LiDAR (potentially costly due to frequency required for thorough monitoring).

LiDAR & Bathymetry

The regularity of capture of airborne laser data sets is dictated by available funds to do so. Progressions in technology mean the costs associated with these technologies are coming down over time. Annual (ideally) or biennial capture and processing in future would provide essential information that would aid in baywide coastal management, as well as the wider Victorian coast, and this is recommended.

Aerial imagery

Aerial images are captured for the study area intermittently; it is recommended this is continued in future, preferably yearly. If a thorough program of beach monitoring, particularly beach profiling, is not undertaken, then photogrammetry methods using the aerial images may be useful to monitor shoreline change. This will be a less certain method; however in lieu of any others will be useful.

Further Coastal Management Studies

This study identified and informed about hazards in a wide context. The next step in the coastal management process for the Bellarine will be to investigate the most at risk areas in terms of assets, both built and natural and determine and prioritise mitigation actions. Future tasks will likely include: