Lonsdale Bight Investigations Review and Options Overview

A part of BMT in Energy and Environment

Reference: R.B22316.001.03.docx Date: January 2017 Draft

Lonsdale Bight Investigations Review and Options Overview

Lonsdale Bight Investigations Review and Recommendations Lonsdale Bight Investigations Review and Recommendations

Prepared for: Department of Environment, Land, Water and Planning

Prepared by: BMT WBM Pty Ltd (Member of the BMT group of companies)

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Document Control Sheet

Document: R.B22316.001.03.docx BMT WBM Pty Ltd Level 8, 200 Creek Street Title: Lonsdale Bight Investigations Review and Brisbane Qld 4000 Options Overview Australia PO Box 203, Spring Hill 4004 Project Manager: Craig Witt

Tel: +61 7 3831 6744 Author: Craig Witt Fax: + 61 7 3832 3627 Client: Department of Environment, Land, Water ABN 54 010 830 421 and Planning

www.bmtwbm.com.au Client Contact: Louise Hanigan Client Reference: Contract No: 332261 Synopsis: An independent review of reports and investigations of coastal processes and management strategies for Lonsdale Bight with an overview of suitable options for short and long term sand management (retention).

REVISION/CHECKING HISTORY Revision Number Date Checked by Issued by 0 24th Oct 2016 IAT CLW 1 7th Nov 2016 IAT CLW 2 25th Nov 2016 IAT CLW 3 5th Jan 2017 IAT CLW

DISTRIBUTION Destination Revision 0 1 2 3 4 5 6 7 8 Department of Word Word Word Word Environment, Land, Water & pdf & pdf & pdf & pdf and Planning BMT WBM File Word Word Word Word BMT WBM Library & pdf & pdf & pdf & pdf

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Summary Report

Background

The Lonsdale Bight foreshore is an important recreational asset for the region. It is also partly within the Port Phillip Heads Marine National Park which extends to High Water Mark and is recognised for its state-wide environmental, cultural and recreational values. The embayment is at the entrance to Port Phillip Bay and is therefore exposed to complex and varying coastal processes which cause shoreline erosion and fluctuations in beach levels. Seawalls and groynes of different types have been constructed over many years aimed at protecting the foreshore and as an attempt to retain a sandy beach with varying degrees of success. There have also been numerous investigations and reports associated with the processes and works.

Community concerns about the low beach level in front of the shopping precinct at Point Lonsdale Front Beach have amplified in recent months. There are also other sections of the foreshore which have experienced erosion and concerns have been raised about potential future risks, particularly in response to climate change influences including sea level rise.

The Department of Environment, Land, Water and Planning (DELWP), the Borough of Queenscliffe (BoQ) and Parks Victoria (PV), all of whom have responsibilities in management of the area, recognise the importance of understanding the coastal hazards and associated risks as well as the consideration of future strategies and actions to manage and mitigate those risks where needed. Given the considerable body of knowledge already gained through the previous investigations and reports, DELWP has commissioned this independent review of those reports since 1997 as the next step in moving forward.

Review of those reports together with project stakeholder liaison and site inspections has allowed a broad understanding to be gained of the processes, values and key issues. Gaps in knowledge important to inform future coastal management decisions have been identified and an overview provided of options which may be considered to address specific issues. An overall approach to coastal zone management based on a risk management framework is also presented for consideration. Review of Reports

A total of 29 reports have been reviewed and summarised together with other readily available information including historical photographs as uploaded on community Facebook pages and Nearmap aerial imagery over recent years.

These reports date back to 1997 and generally cover one or more of the following broad topics:

 Geomorphology and historical changes

 Coastal processes and related hazards

 Environmental values

 Cliff stability and management

 Coastal management options and works

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 Seawall and groyne condition and structural stability.

The extensive document list provides a good overview of the processes, values and issues at hand with respect to management of the Lonsdale Bight foreshore. There is general agreement throughout the reports with respect to the broad coastal processes although there are some gaps in knowledge of relevance to future coastal management decisions. Overview of Coastal Processes

Beaches are subject to natural fluctuations in level and alignment in response to how sand moves along and across the foreshore. This movement is driven by the changing forces of waves, currents and water levels that the foreshore is exposed to particularly during storm events with elevated water levels and high waves. Natural controlling features such as rocky headlands and reefs as well as man-made structures such as seawalls and groynes can also affect the processes.

The driving forces and shoreline response are subject to variability seasonally throughout the year and over longer annual and decadal cycles associated with meteorological phases as well as over geological time scales and with future climate change. Knowledge and understanding of contemporary and longer term processes are essential in developing appropriate coastal management strategies to address hazards associated with the processes. Dealing with natural variability and uncertainty with respect to the nature, timing and extent of future changes are key considerations.

There is a broad understanding and agreement of the coastal processes influencing Lonsdale Bight as interpreted from the documents reviewed. Sand is transported along the Bass Straight foreshore from west to east to Point Lonsdale under the influence of the dominant SSW – SW waves. At Point Lonsdale, it has been estimated that about half of this sand is transported offshore or into deeper parts of the entrance during the ebb tide. The remainder is transported around the headland and into Port Phillip Bay under the combined and complex interactions of waves and flood tide currents. This supply of sand is noted as being intermittent and dependent on weather conditions typically occurring in pulses predominantly during storms and varying from year to year.

There are strong tidal currents in the entrance to Port Phillip Bay and along parts of the foreshore. Ocean waves also penetrate in through the entrance and gradually reduce in height as they propagate further into Lonsdale Bight and approach the shoreline. The waves are also influenced by the strong tidal currents.

About half of the sand that enters around Point Lonsdale continues to be moved into the Bay across the seabed of Lonsdale Bight under the influence of the waves and tidal currents. The presence of exposed reefs and a thin veneer of sand indicate that the potential to transport the sand exceeds the supply. The remainder of the sand is moved along the coast from south-west to north-east in a narrow band primarily under the influence of the waves approaching the shoreline at an angle. At Point Lonsdale Front Beach, the waves approach at a steep angle and therefore the potential to move the sand along the coast is high.

The key coastal processes of relevance to ongoing management of the Lonsdale Bight foreshore is this dominant wave induced longshore transport of sand along the coast coupled with offshore transport during storm events, both of which are subject to seasonal, inter-annual and decadal

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variations. These variations lead to fluctuations in the volumes of sand, levels of the beaches and alignment of the foreshore. In addition to this, the intermittent and potentially reducing supply of sand around Point Lonsdale and into the compartment adds further variability and uncertainty with respect to fluctuations in the volumes of sand along the foreshore.

With future climate change influences including a rise in mean sea level and increased storminess, it can be expected that enhanced wave energy will impact on the beaches and structures at a higher level. This will have associated implications for beach erosion, overtopping and potential damage to structures. Such processes will be gradual and necessitate ongoing and potentially increased maintenance of structures and associated adaptation strategies. Summary of Historical Changes and Works

Numerous works have been undertaken over many decades including the construction of seawalls and groynes of various types and characteristics aimed at managing the threat of erosion and low levels of sand. These works have been subject to damage and modified and have had varying degrees of success. They in turn have also influenced the prevailing sediment transport processes with associated implications for shoreline alignments and sand levels/volumes.

Construction of a masonry seawall first commenced at Point Lonsdale Front Beach in 1900. Severe erosion occurred in 1934 and timber groynes were initially constructed in 1935 in an attempt to retain sand and halt the erosion. The masonry wall was extended between 1939 and 1947 to address back shore erosion. Erosion continued to the north of the masonry wall and a rock revetment seawall was progressively constructed as the erosion advanced, with the final section to Dog Beach being complete in 1977.

The original timber groynes became dilapidated and were replaced with further timber groynes of a different design. These early timber groynes were typically short and low crested with some being of a slatted permeable design to allow sand to pass through. These groynes reportedly had varying levels of success in retaining a sandy beach. Nevertheless, there are historical photos that show the beach with both high and low levels of sand indicating periods of fluctuations.

With the beach in a depleted state and the timber groynes again deteriorating, the decision was made to remove them and construct two hybrid rock/timber groynes in 1999-2000. A third rubble mound (rock) seawall was constructed in 2005. These three groynes remain in place (2016) and have been effective in retaining some sand in the local vicinity although beach levels and extent continue to fluctuate. While past periods of substantial sand build up are evident, the areas of usable upper beach are presently limited to near the groynes with sand levels elsewhere in front of the masonry seawall being low and variable. It is reasonable to conclude that under low supply conditions, there would be very little usable beach in the absence of the existing groyne structures.

Sand levels in front of the rock seawall further to the north have fluctuated but have been typically low as at present with limited or no upper beach for most of its length. The groynes and exposed sections of all seawalls require regular maintenance to repair damage caused by waves during storm events, particularly with elevated water levels.

Further around the embayment to the north-east, terminal scour with a significant erosion scarp in the high dune is evident in the shoreline alignment at the end of the seawall at beach known as

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‘Dog Beach’. A stable sandy beach subject to natural variations extends eastwards to Shortland Bluff at Queenscliff. Port Phillip Heads Marine National Park Values

The Port Phillip Heads Marine National Park extends to High Water Mark and parts of the beach and nearshore areas of Lonsdale Bight are within the Point Lonsdale section of the Park. The Marine National Park (MNP) is recognised for its state-wide environmental, cultural and recreational values, including:

 Natural Values:

○ intertidal reef platforms that support the highest invertebrate diversity of any calcarenite reef in the State;

○ diverse and abundant algal assemblages on Lighthouse Reef;

○ deep undercuts in the Lonsdale Reef which are uncommon along Victoria’s open coast and which support algae communities more typical of deeper waters;

○ diverse fish and invertebrate assemblages on the Lonsdale Wall, including extensive encrusting communities such as ascidians, bryozoans and sponges;

○ calcarenite shore and reef platforms that are of regional and state significance for shorebird feeding; and

○ threatened marine mammals such as Australian Fur Seal (Arctocephalus pusillus), Southern Right Whale (Eubalaena australis) and Humpback Whale (Megaptera novaeangliae).

 Cultural Values:

○ heritage-listed shipwrecks and shipping history;

○ botanical and scientific survey sites of research and historical significance;

○ historical significance as one of the first marine reserves protected in Victoria;

 Tourism and Recreation Values:

○ swimming, surfing, walking, birdwatching, nature observation and passive recreation leisure activities

○ Internationally recognised subtidal reef dive sites

○ snorkelling sites between Lightning Reef and the Point Lonsdale Pier

○ recreational boating and sailing

○ opportunities for guided marine education and nature-based tourism

○ scenic landscapes.

The highly dynamic natural coastal processes involving natural accretion and attrition of beaches cause sand to cover and uncover the reefs and other nearshore habitats. These natural processes have contributed to the values of the MNP and have been influenced by the construction of the groynes and seawalls. Any modifications to these structures or other works to influence coastal

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processes will need to consider potential impacts on the environmental, cultural and recreational values recognised within the MNP. Furthermore, any such works will also need authorisation in writing from the relevant Minister as well as Coastal Management Act Consent. Interpretation of Key Issues

A detailed assessment of the hazards and risks associated with coastal processes and the related level of tolerance has not been undertaken. Nevertheless, the key coastal management issues for Lonsdale Bight as interpreted from available information relate primarily to:

 Fluctuations in beach levels and maintaining a sandy beach in front of the seawalls with associated potential risks to beach amenity, damage to structures and public safety during periods when sand levels are low;

 Potential for longer term recession and exacerbation of the above issues with future climate change influences including sea level rise and increased wave energy impinging on the coastline at a higher level; and

 The importance of the Marine National Park values and ensuring these are not compromised.

The foreshore at Point Lonsdale Front Beach is an important recreational asset with the beach and nearshore areas also being part the Port Phillip Heads Marine National Park. As outlined above, the beaches are subject to fluctuations in level as a result of variations in the supply of sediment around Point Lonsdale and the local sediment transport processes. There is also uncertainty and natural variability in those processes. During periods of low sediment supply, the beach levels in front of the seawalls are typically low with associated issues except for the zones of influence of the three existing groynes.

The crest of the masonry seawall is relatively low and it is evident that it is already prone to overtopping along the majority of its length during storm conditions particularly with elevated water levels. Such overtopping events are likely to become more regular and severe with sea level rise as projected with future climate change. This will exacerbate the risk to the structural stability of the aging seawall and the threat of erosion and damage to the land and facilities behind.

The main issues therefore centre around or are exacerbated by periods of low beach level and with future sea level rise. Understanding and dealing with natural variability in regard to such processes is therefore important in considering the need for and extent of short and long term management options to address the issues.

Key issues requiring consideration as part of future coastal management planning at Point Lonsdale Front Beach are as follows:

 Fluctuating sand volumes and uncertainty surrounding the extent and duration of periods with low beach levels;

 Limited usable beach for recreational purposes, particularly at high tide during periods with low beach levels;

 The importance of the Marine National Park values and ensuring these are not compromised;

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 Direct wave attack on the aging seawall when and where sand levels are low with associated enhanced weathering and increased maintenance costs;

 Potential instability and damage of exposed sections of the seawall and the groynes during severe storms with high waves and elevated water levels;

 Public safety associated with wave overtopping of the seawall and potential damage during severe storms as well as high drops from the walls when and where beach levels are low;

 Exacerbation of all of the above issues and additional threats to the land behind the seawall with climate change influences of rising sea level and more wave energy reaching the shoreline.

Little or no usable upper beach also fronts the rock revetment seawall in the central section of the embayment. While fluctuations in the level of sand do occur, there are no groynes in this section to retain sand and hence low beach levels persist for extended periods along the majority of the foreshore. There are no specific condition reports relating to the rock revetment wall. However, its design and height are such that it is less prone to wave overtopping. Nevertheless, the wall will still be potentially subject to damage and require maintenance following major storm events. Key issues are therefore similar to Point Lonsdale Front Beach.

Further around the embayment to the north-east, a sandy beach extends from the end of the rock revetment seawall to Shortland Bluff. This beach, known as ‘Dog Beach’, is backed by a high dune and essentially remains as a natural beach with associated social and environmental values.

Terminal scour is evident in the shoreline alignment immediately at the end of the seawall and while fluctuations in the beach occur in response to the prevailing processes, the shoreline is generally regarded as being relatively stable at present. The beach further to the east towards Shortland Bluff has also experienced accretion in recent years.

While a reasonable undeveloped buffer remains seaward of existing development and infrastructure along this shoreline, the beach has also been considered very high risk to exacerbated erosion associated with sea level rise and accompanying wave climate changes.

The key issues requiring consideration as part of future coastal management planning for this section of the foreshore therefore relate to:

 Ongoing stability and management of the high dune scarp in the terminal scour area;

 Potential erosion and short term threats during storm events;

 Threats of long term recession particularly related to climate change effects of sea level rise and associated increased wave energy;

 The potential impacts of works carried out at Point Lonsdale Front Beach.

The identification of strategies and options to manage the above issues will need to take into consideration the gradual nature of long term changes and the uncertainty around the need and timing for implementation.

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Key Information and Knowledge Gaps

Substantial information is contained within the existing reports. However, there are certain gaps in knowledge which if filled, would help inform ongoing management decisions in terms of understanding the risk profile associated with the hazards as well as assessing options to manage identified risks.

There is a general understanding that the beaches are subject to fluctuations and similarly a broad understanding that those fluctuations are related to variations in the supply of sediment and the transport of that sediment along the shoreline under the prevailing coastal processes. The critical knowledge gaps of importance to inform ongoing management decisions relate to quantification of those factors and understanding how often, for how long and to what extent periods of reduced sediment supply might persist and the associated consequences.

The first important knowledge gap in this regard is quantitative information on beach fluctuations. Knowledge of such fluctuations, ideally linked to variations in the prevailing processes, will provide information on the extent and likely durations over which those fluctuations may occur. This will help to inform and consider the hazards associated with fluctuations and whether they are tolerable or not in the short or long term. It will also help inform the understanding of the driving processes as well as the conditions that may be experienced during extended periods of little or no sediment supply as well as periods when the beaches are built up.

Should it be decided that the existing hazards are not tolerable based on an analysis of the fluctuations as outlined above, further quantification of the processes driving those fluctuations would help inform consideration of options to manage and mitigate those hazards. Key factors in this regard are as follows:

 The sediment supply rate around Point Lonsdale and associated variations. This is one of the key drivers for fluctuations in sand volumes and beach levels and is difficult to quantify. It could be inferred from monitoring changes in sand volume linked to the prevailing wave climate and sediment transport potential to understand historical fluctuations and what might be expected into the future. However, it remains a stochastic process and coastal management decisions should take into consideration that there may be extended periods with little or no supply.

 Longshore sand transport potential along Front Beach and associated variations throughout the year and over longer time frames. Linked to the supply rate as discussed above, this will help inform how quickly sand may be transported away or build up and better understand beach fluctuations and how they could be managed.

 Potential long term recession and/or lowering of the beaches under climate change influences including sea level increases and higher wave energy impacting on the shoreline. While the processes will be gradual, adaptation strategies need to be based on knowledge of the potential changes, monitoring, and trigger points for implementation of further investigations or works. Coastal Management Considerations

A risk assessment framework for coastal management is a robust methodology for dealing with outcomes that are uncertain or have limited data, or for impacts with uncertain timeframes. Given

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the uncertainties and natural variability of contemporary processes as well as the need for adaptation associated with potential future climate change influences, it is considered a relevant approach for Lonsdale Bight. A risk based approach to coastal management is a multi-faceted task centred around:

 Hazard and risk identification based on the understanding of the processes in the local context and the specific hazards and risks related to those processes. These can include threats to the natural and built environment as well as social and economic values related to beach erosion and recession, coastal inundation and wave overtopping.

 An analysis of the risks including the likelihood and consequences to determine the overall level of risk (extreme, high, medium or low). The likelihood considers the possibility of the risks occurring now or in the medium term as well as over longer time frames including climate change influences. The consequences relate to the implications for existing or future development as well as the values (e.g. aesthetic, recreational, ecological, etc.) of the foreshore, beach and nearshore areas. It is both the likelihood and consequence of coastal risks combined that determines the level of risk.

 Evaluation of the risks in terms of the level of risk that is deemed acceptable, tolerable and intolerable. Coastal risks are prioritised and management effort shall be aimed towards the higher levels of risk (e.g. extreme and high) that are deemed intolerable.

 Following the identification and evaluation of the risks, coastal management options and strategies directly related to reducing or eliminating intolerable risks can be developed. Tolerable (low) risks can be flagged for monitoring with no further actions necessary. Management options can be designed to reduce the likelihood of the risks or the consequence of the risk or both.

 Further cost benefit analysis is then used to determine which of the risk treatments will provide the greatest benefit (relative to cost) in treating the highest priority risks. Advantages and disadvantages are ranked to determine the preferred strategy. Further, the cost benefit analysis ensures that other coastal management objectives are not compromised by the option. For coastal management, innovative strategies may be required to provide benefits across the community (social and aesthetic) and coastal ecosystems without adverse impacts, within the existing legislative framework and available funding.

 For strategies that involve monitoring to determine if/when future risk treatment works are needed, appropriate trigger levels are established for implementation. General Approach to Consideration of Options

Defining and assessing the risks based on an understanding the coastal processes including natural variability is a necessary first step in determining the need for and nature of coastal management options. While there is a broad understanding of the issues facing future coastal management of the Lonsdale Bight foreshore, a detailed assessment of the hazards and associated risks is yet to be undertaken. This would typically include identification of the risks, analysis of the associated likelihood and consequences, and evaluation of what might be tolerable in prioritising issues towards which management efforts should be aimed. Different stakeholders

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including community groups will have varying interests and requirements and it is important that these are taken into consideration as part of the assessment process. A clear understanding of the level of risk and priorities in terms of timing and location are important for consideration and implementation of options to manage the coastline.

Determination of specific options is therefore dependent on the outcomes of the risk assessment process. To aid this process, an overview is provided below of the types of options that may be considered to manage the broad issues as identified. For each of the three main foreshore compartments, broad considerations of the issues are presented and possible options identified. These include short term (temporary) options as well as potential longer term options to address the issues. A broad analysis of those options is also presented giving an overview and summary of the main advantages and disadvantages. Further investigations considered important to inform assessment of the options and future management decisions are also identified. This information can then be used as part of future consideration of if, where and how those options may be assessed in more detail and potentially used dependent on the outcome of the risk assessment and further investigations. Point Lonsdale Front Beach Options Overview

The main issues at Point Lonsdale Front Beach are associated with periods of low sand level in front of the masonry seawall along parts of the foreshore as well as wave overtopping of the seawall during storm conditions which may become more frequent and severe with any future rise in sea level. Decisions surrounding future coastal management options need to consider the risks and consequences of both as well as the potential implications for the Marine National Park in prioritising future strategies.

Broad considerations surrounding fluctuating sand levels and associated management options are outlined below. However, they are in the context of maintaining the existing masonry seawall. It should be recognised that the existing seawall is already prone to overtopping by waves and that consideration will also need to be given to options for managing this, particularly with the potential for future sea level rise. Such options are not presented in detail but could include major modifications to the wall in terms of its height, type and alignment to protect land and facilities behind. This could be with or without options to maintain sand in front of the wall which is likely to become more difficult as sea level rises.

Consideration will need to be given to what needs to be protected and whether retreat in some areas can be accepted including relocating the pedestrian pathway behind the existing seawall. Such works will involve major community, design and economic considerations and while the time frame surrounding the need for implementation is uncertain, the low crest and age of the existing seawall are such that the potential need in the not too distant future should be factored into planning decisions.

With respect to fluctuating sand levels, the extent and time frame that the beaches are low and the level of tolerance to associated risks are key considerations as well as priority areas for management of those risks. The periods of low beach level are generally related to sand being transported away faster than it is supplied around Point Lonsdale. Options to retain a sandy beach in the longer term therefore require either:

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 The sand supply to be artificially supplemented so that it arrives at least at the same rate and quantity that it is being transported away; or

 The sand to be artificially retained with the rate of transport along the foreshore and away being modified to match the rate of supply.

The uncertainty with respect to the timing and magnitude of future sand supply needs to be recognised and consideration given to the risk that low supply conditions could in the future continue for extended periods. Unless this uncertainty is able to be removed, it is considered that management options should be based on little or no sand supply for an extended period. Under this situation, the priority areas for retention of sand will need to be defined.

Different stakeholder groups will have varying priorities associated with specific values and constraints. As such, it is considered that no one single option will completely satisfy all stakeholders. Therefore the strategy to manage the issues will need a level of balance and potential compromise with respect expectations centred on minimising impacts and achieving an outcome that is acceptable to all.

A range of options have been identified with different levels of compliance in terms of short and long term benefits to aid consideration of the preferred approach. Variations and combinations of options within the broad categories are also discussed again to provide information for consideration in relation to the level of risk and consequences to be accepted. Different options can also be considered for different sections of the foreshore.

The five broad options identified are categorised as follows:

 Option 1: Do nothing and accept natural variability (short and/or long term)

 Option 2: Local redistribution of sand (short term)

 Option 3: Targeted beach nourishment (short term)

 Option 4: Groyne field modification - without and with beach nourishment (long term)

 Option 5: Offshore breakwaters (long term)

Option 1 - The “Do Nothing” option may be considered in areas where the level of risk is low or tolerable over a period of time given the natural variability of the processes. As such it may be viewed as a short term and/or long term option depending on that risk assessment.

It has no immediate direct costs for works but has potential increased consequential costs associated with ongoing seawall inspections and maintenance. It does not address the issue of existing wave overtopping of the seawall and the likelihood and consequences are also potentially enhanced with future sea level rise. By allowing the processes to continue naturally, albeit with the influences of the existing structures, the Marine Park values will not be adversely affected. Considerations for the “Do Nothing” option therefore centre on whether risks and the potential consequences of the issues surrounding low beach levels can be accepted in some or all areas given the uncertainty of future trends.

Option 2 - Consideration could be given to a local redistribution of sand as an adjunct to the “Do Nothing” option depending on stakeholder priorities. This could involve transfer of sand from the

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accreted area adjacent to the groyne and spreading it back along the beach further to the south or placing it on the downdrift (northern) side of the groyne in the low areas of concern. Such works do not introduce any new sand into the system and may in fact reduce the area of usable beach if it is placed below high tide level. While it may provide some temporary benefits to amenity, it will be potentially very short lived as the waves quickly redistribute the sand.

While the costs of such works are relatively modest, it may be perceived as being a waste of time and money in the event of rapid redistribution. The limited and temporary nature of redistribution works are such that they do not address the issues surrounding long term stability of the seawall or the influences of future sea level rise including wave overtopping of the seawall.

Such works will be a modification of the natural processes. However, as they will be limited and have temporary effects in zones subject to natural fluctuations, they are unlikely to have any long term adverse impacts on the values of the Marine National Park.

Considerations for the “Local Redistribution” option therefore centre on whether the minor temporary benefits in specific areas and associated expenditure can be justified in terms of the risk that they will be very short lived.

Option 3 – Minor targeted beach nourishment may be considered in conjunction with the existing groynes or additional groynes to address areas of concern prior to the high usage season subject to identification of a viable source of sand and associated social, environmental and economic considerations. This would have the advantage of adding sand to the active beach system and providing a net overall gain. However, it is still only a short term option and would be subject to potential rapid redistribution of the sand.

The cost would be somewhat greater than local redistribution of sand and the risk of only short term benefits remains unless larger scale regular nourishment is carried out. The limited and temporary nature of minor nourishment works is such that they do not address the issues surrounding long term stability of the seawall or the influences of future sea level rise including wave overtopping. Again this could be improved with larger scale more regular nourishment on an as required basis. However, the scale of nourishment required to meet objectives may not be practical or economically viable.

Such works will involve additional sand being placed typically in the upper tidal zone where sand fluctuations are regular. The implications of this for the Marine National Park values will need to be assessed but are likely to be consistent and within the range of natural variations.

Considerations for the “Targeted Beach Nourishment” option therefore centre on whether a suitable source of sand can be located and if the additional expenditure can be justified for what will still be temporary works but with potentially longer benefits depending on the volume and regularity of the nourishment.

Option 4 – Modifications to the groyne field is seen as being a viable long term option to retain sand along the foreshore as evidenced by the existing structures. While the amenity will be improved with a sandy beach, the groynes will generate greater visual intrusion to the vista along the beach. This can be reduced with low crested shorter groynes although such a design would require more groynes. Consideration can be given to the number and locations of groynes to target priority areas subject to detailed design.

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Lonsdale Bight Investigations Review and Options Overview xii Summary Report

Any impact to the beaches to the north including Dog Beach is likely to be negligible. Furthermore, the use of beach nourishment to artificially fill any new groynes when constructed would minimise any such small impact.

With future climate change including sea level rise, the groynes and retained sand will limit the threat to the seawall behind. However, future consideration would still need to be given to adaptation strategies which could include raising the level of the groynes and the crest of the seawall behind. Ultimately, the pedestrian path behind the seawall would also need to be raised or relocated.

Groyne construction works and associated sand transport modifications will be in a narrow zone along the foreshore where the processes are naturally dynamic and subject to fluctuations. Implications for the Marine National Park values will need to be assessed. There will be a relatively small footprint where the groynes themselves and the trapped upstream sand permanently cover the seafloor that was previously subject to intermittent cover with sand. Conversely the groynes and sandy beach will have other values of their own which need to be taken into consideration.

While groynes, with or without nourishment will be relatively costly, they do provide the benefit of a longer term solution to the existing issues. Consideration remains as to whether there are priority areas for such works and whether short term or do nothing options can be accepted in some areas if a complete groyne field cannot be constructed.

Option 5 – Offshore breakwaters could be considered as an alternative means of altering the wave climate and longshore transport rates along the shoreline to match the supply rate and retain a sandy beach. Configurations could include a number of detached breakwaters along the section of coast and/or a single larger breakwater off Point Lonsdale or connected essentially as headland extension. Such structures would need to be substantial and able to withstand and modify storm wave conditions and therefore come at a high cost.

Careful design of any such structures would be needed to ensure the desired result is achieved and there would be risks around the uncertainty of achieving this, particularly given the complex processes and the influence of tidal currents. Furthermore, potential significant implications for the Marine National Park, surfing values and visual intrusion would need to be assessed. Central Section Options Overview

Broad considerations and options for the central section with the rock revetment seawall are similar to Point Lonsdale Front Beach with the notable exception being that this section does not contain any existing groynes to retain sand. Hence, under a Do Nothing option, it can be expected that there will be limited beach in front of the seawall for considerable periods of time. Similarly, local redistribution of sand and targeted beach nourishment are not considered viable without any retaining structures.

Much longer term planning could consider an option of removing one or two sections of the wall east of Golightly Park while retaining or reinforcing the wall at the eastern ends as artificial headlands. The foreshore to the west could then recede naturally and be retained as sandy pocket beaches. Detailed assessment would be needed to confirm the likely extent of recession to ensure

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Lonsdale Bight Investigations Review and Options Overview xiii Summary Report

the road behind is not threatened. However, with control structures at either end, it is considered that a stable beach may be formed.

Such an option would need acceptance of the loss of the reserve land and would come at considerable initial cost. However, it would most likely provide a long term sandy beach in the area and reduce the cost of adapting and maintaining the seawall with climate change. This is unlikely to exacerbate erosion further to the east as the beach to the west would be allowed to erode naturally and supply sand. Dog Beach Section Options Overview

This section of the foreshore to the east of the rock revetment seawall is characterised by high dunes with a substantial buffer to accommodate erosion. It is conceivable that erosion may threaten existing development landward of the terminal scour erosion scarp at Dog Beach. However, this extends only a short distance beyond the end of the existing seawall and a much larger buffer of over 100m exists immediately to the east. It is considered unlikely that this buffer will be breached or the road behind threatened by future erosion. Further investigation would be required to confirm this.

Given the substantial buffer at present, it is considered that an appropriate strategy would be:

 Let natural processes of erosion and accretion continue to occur.

 Continue with dune management of the high erosion scarp to minimise slumping and control pedestrian access at the top and bottom.

 Continue to monitor shoreline fluctuations and particularly recession of the top of the erosion scarp and assess rates of recession.

 Establish a trigger point for consideration of specific actions related to future erosion threatening the development behind. This would generally be when the remaining buffer behind the top of the scarp approaches the likely storm erosion distance including an allowance for slumping of the dune.

 Consider options for dealing with the threat of erosion to the property when the trigger point is reached. These would typically include:

○ Relocation of the limited development and let erosion continue naturally.

○ Protect the development with the most likely option being a limited extension of the seawall back and in front of the development.

 Allow erosion to continue naturally further to the east of the development.

The above strategy would involve least cost and mostly allow natural processes to continue with the retention of a usable beach. However, it is inherent that there will be some losses within the Queenscliff Natural Features Reserve. Further protection of that Reserve would come at a cost and may result in further loss of the beach or the transfer and exacerbation of the erosion further to the east unless costly beach nourishment is implemented.

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Lonsdale Bight Investigations Review and Options Overview xiv Summary Report

Further Investigations and Assessments

It is considered that the following investigations and assessments are important to address critical knowledge gaps and further inform coastal management decisions for Lonsdale Bight:

 An analysis of available data on historical fluctuations and variations in beach levels linked where possible to available information on prevailing coastal processes to help inform the understanding of the processes and associated hazards.

 A detailed risk assessment involving all stakeholders and the community to identify and analyse the issues, particularly at Front Beach, including consideration of the likelihood and consequences of specific risks as well as the level of tolerance and priority areas for further action.

 Depending on the outcome of the above risk assessment, an analysis of potential mitigation options as needed assessed against specified criteria and determination of a preferred strategy.

 Further analysis and detailed design and approval as needed of specific options identified in the preferred strategies. Depending on the options, this may involve more quantitative assessment of the processes and associated variations as an extension of the fluctuations analysis to inform consideration and design of sand retention options.

 Design and implementation of an ongoing monitoring program with establishment of appropriate trigger points as may be needed for specific strategies to inform future coastal management decisions and aid detailed assessments.

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Lonsdale Bight Investigations Review and Options Overview xv Contents

Contents

Summary Report i 1 Introduction 1 1.1 Background 1 1.2 Study Area 1 1.3 Objectives and Scope of the Project 3 1.4 Methodology 3 2 Review of Information 4 2.1 Reports Reviewed 4 2.2 Overview and Linkages of Reports 5 2.3 Other Information 6 3 Overview of Processes, Values and Hazards 7 3.1 Coastal Processes in General 7 3.2 Lonsdale Bight Coastal Processes 7 3.3 Summary of Historical Changes and Works 11 3.4 Port Phillip Heads Marine National Park Values 19 3.5 Interpretation of Issues 22 3.5.1 Overview 22 3.5.2 Point Lonsdale Front Beach (Area A) 24 3.5.3 Central Section (Area B) 26 3.5.4 Dog Beach (Area C) 27 4 Key Information and Knowledge Gaps 29 4.1 Overview 29 4.2 Tides and Currents 29 4.3 Waves 29 4.4 Sediment Supply to Lonsdale Bight 30 4.5 Sediment Transport along the Coast 32 4.6 Sediment Transport across Lonsdale Bight 33 4.7 Cross-shore Sediment Transport 34 4.8 Shoreline and Beach Fluctuations 34 4.9 Climate Change Influences 35 4.10 Summary of Knowledge and Information Gaps 35 5 Coastal Management Considerations 37 5.1 Risk Management Approach 37

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Lonsdale Bight Investigations Review and Options Overview xvi Contents

5.2 Key Issues and Objectives 40 5.3 Generic Options for Responding to Coastal Erosion 41 5.3.1 Beach Nourishment 42 5.3.2 Structural Protection Options 43 5.4 Review of Previous Works 45 5.4.1 Historical Seawalls and Groynes 45 5.4.2 Existing Groynes 46 6 Options Overview 49 6.1 General Approach 49 6.2 Options for Point Lonsdale Front Beach (Area A) 49 6.2.1 Broad Considerations 49 6.2.2 Identification of Options 51 6.2.3 Analysis of Options 52 6.2.3.1 Do Nothing (Short and/or Long Term Option) 52 6.2.3.2 Localised Redistribution of Sand (Short Term Option) 54 6.2.3.3 Targeted Beach Nourishment (Short Term Option) 55 6.2.3.4 Groyne Field Modification (Long Term Option) 57 6.2.3.5 Offshore Breakwaters (Long Term Option) 62 6.2.4 Material Sources and Costing Considerations 63 6.2.4.1 Local Redistribution of Material 63 6.2.4.2 Beach Nourishment 63 6.2.4.3 Groyne Structures 64 6.3 Options for the Central Section (Area B) 64 6.3.1 Broad Considerations 64 6.3.2 Identification of Options 65 6.3.3 Analysis of Options 65 6.3.3.1 Do Nothing (Short and/or Long Term Option) 65 6.3.3.2 Groyne Field or Offshore Breakwaters 65 6.3.3.3 Artificial Headland with Pocket Beach (Long Term) 66 6.4 Options for Dog Beach (Area C) 67 6.4.1 Broad Considerations 67 6.4.2 Identification of Options 67 6.4.3 Potential Strategy 68 6.5 Further Investigations and Assessments 69 6.5.1 Analysis of Historical Changes and Linkage to Coastal Processes 69 6.5.2 Detailed Risk Assessment 70 6.5.3 Establish a Monitoring Program 70

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Lonsdale Bight Investigations Review and Options Overview xvii Contents

6.5.4 Detailed Investigations for Specific Options 71 6.5.4.1 Point Lonsdale Front Beach 71 6.5.4.2 Central Section 71 6.5.4.3 Dog Beach 71 6.5.5 Summary of Key Further Investigations and Assessments 72 7 Conclusions and Recommendations 73 7.1 Summary of Main Findings 73 7.2 Recommendations 74 8 References 76 Appendix A Summary of Reports Reviewed A-1

List of Figures

Figure 1-1 Study Area 2 Figure 3-1 Wave propagation into Lonsdale Bight (Cardno 2007) 10 Figure 3-2 History of Seawall Construction (Vantree 1998) 12 Figure 3-3 Point Lonsdale Front Beach circa 1936 (Bird 2011) 12 Figure 3-4 Point Lonsdale Front Beach circa 1982 (Bird 2011) 13 Figure 3-5 Existing Southern Groyne (November 2016) 14 Figure 3-6 Existing Northern Groyne (Sep 2016 top, Nov 2016 bottom) 15 Figure 3-7 Existing Central Groyne (November 2016) 16 Figure 3-8 Point Lonsdale Front Beach Fluctuations 17 Figure 3-9 Central Section Rock Revetment Wall (September 2016) 18 Figure 3-10 Dog Beach Terminal Scour (September 2016) 18 Figure 3-11 Sandy Beach East to Shortland Bluff (September 2016) 19 Figure 3-12 Port Phillip Heads Marine National Park, Point Lonsdale Section 21 Figure 3-13 Lonsdale Bight beach sections 23 Figure 3-14 Low Beach in Front of Southern Wall (November 2016) 24 Figure 3-15 Low Beach North of Southern Groyne (November 2016) 25 Figure 3-16 Southern Wall Wave Exposure (mid-tide September 2016) 25 Figure 4-1 Estimated net sand transport (Vantree 1998) 31 Figure 4-2 Estimated net sand transport (Cardno 2007) 32 Figure 5-1 Risk Management Framework (ISO 31000:2009) adapted to Coastal Zone Management 38 Figure 5-2 Southern Groyne Sand Bypassing (September 2016) 47 Figure 6-1 Indicative Groyne Field Modification 61

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Lonsdale Bight Investigations Review and Options Overview 1 Introduction

1 Introduction

1.1 Background The Department of Environment, Land, Water and Planning (DELWP) has commissioned this independent review of investigations and reports relating to coastal processes and management of the Lonsdale Bight coastline. This stretch of foreshore at the entrance to Port Phillip Bay is exposed to complex and dynamic coastal processes and has a history of seawall and groyne construction in response to shoreline erosion and fluctuating beach levels. There have been numerous investigations and reports in relation to those processes and works over many years.

DELWP, the Borough of Queenscliffe (BoQ) and Parks Victoria (PV), all of whom have responsibilities in management of the area, recognise the importance of understanding the coastal hazards and associated risks as well as the consideration of future strategies and actions to manage and mitigate those risks where needed. Given the considerable body of knowledge already gained through the previous investigations and reports, DELWP has commissioned this independent review of those reports since 1997 as the next step in moving forward.

1.2 Study Area Lonsdale Bight is a five and a half kilometre stretch of coastline extending from Point Lonsdale at the south-west end to Queenscliff in the east (see Figure 1-1). This embayment is the first section of coastline that is considered part of Port Phillip Bay and forms the west/north boarder of the Bay’s entrance. As such, the foreshore is exposed to complex and varying coastal processes including strong tidal currents through the entrance to Port Phillip Bay (The Rip), as well as ocean swells penetrating through that entrance and waves generated across the bay. Natural headlands and rocky reefs and shelfs also influence sediment transport processes in the area.

The foreshore is an important recreational asset which has experienced fluctuations in sand volumes and alignment in response to the complex and varying coastal processes. This in turn has impacted on the amenity and resulted in a direct erosion threat at times to infrastructure and other assets in close proximity. As a consequence, numerous works have been undertaken over many decades including the construction of seawalls and groynes of different types and characteristics aimed at managing the threats. These works have been subject to damage and modified and have had varying degrees of success. They in turn have also influenced the prevailing sediment transport processes with associated implications for shoreline alignments and sand levels/volumes.

The study area foreshore is also partly within the Port Phillip Heads Marine National Park which extends to High Water Mark and is recognised for its state-wide environmental, cultural and recreational values as expanded further in Section 3.4. Ongoing management of risks associated with coastal hazards therefore needs to encompass the broad range of environmental, social, economic and technical considerations.

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Lonsdale Bight Investigations Review and Options Overview 2 Introduction

Figure 1-1 Study Area

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Lonsdale Bight Investigations Review and Options Overview 3 Introduction

1.3 Objectives and Scope of the Project The objectives of the project are to provide an independent review of all reports and investigations conducted since 1997 within the Lonsdale Bight coastline (from Pt Lonsdale to Shortland Bluff, in Victoria) and to draw linkages between issues these reports raise as well as to highlight gaps in knowledge of importance to coastal management. Based on this review, recommendations are to be made for further investigations/studies required to inform future coastline management decisions. This includes consideration of the information necessary to identify and assess the risks, as well as strategies to manage those risks as required. Potential suitable options for short and long term sand management are also to be identified where possible based on available information.

The scope has included a review of available reports and information, a site inspection and stakeholder liaison. An interpretation of the processes, issues and options for management of those issues has been made based on the above. Gaps in knowledge and further investigations required to aid the understanding of the processes and risks as well as inform future management strategies have been identified. An overall approach to coastal zone management based on a risk management framework is also presented for consideration.

The review of reports considered the content provided in the documents but did not extend to detailed review of the validity of the information unless clearly obvious. It should be noted that not all details were readily available in this regard. No further detailed assessments have been made and conclusions are based on interpretation of the available information. Further investigations may be required to confirm or provide additional information as noted.

1.4 Methodology The broad methodology adopted involved:

 Stakeholder liaison to provide an overview of the requirements, specific areas of concern and a history of shoreline fluctuations and associated works;

 Site inspection to gain an overview and understanding of the processes, works and issues;

 Review of available reports and information on processes, values, works and historical changes with consideration of linkages and gaps in knowledge;

 Interpretation of the processes and key issues based on all of the above and identification of further investigations needed to fill the knowledge gaps required for future management decisions;

 Identification of broad options and strategies to deal with key issues together with their advantages and disadvantages as based on available information and the interpretation of processes;

 Identification of an overall approach to future coastal management and further investigations required to inform consideration of strategies and the assessment of specific options.

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Lonsdale Bight Investigations Review and Options Overview 4 Review of Information

2 Review of Information

2.1 Reports Reviewed The reports provided and reviewed for this project are listed below with a summary of relevant information and the linkages between the reports provided in Appendix A. A discussion of knowledge gaps is provided in Section 4 following interpretation of key processes, values and issues as outlined in Section 3.

(1) Marine Science & Ecology Pty Ltd (1997) Report on Seabed Survey of the Lonsdale Bight

(2) Environmental Geosurveys Pty Ltd (1997) Lonsdale Bay Analysis of Beach, Dune and Offshore Sand

(3) Lawson and Treloar Pty Ltd (1998) Lonsdale Bight Coastal Processes Investigation – Wave and Current Measurements

(4) Lawson and Treloar Pty Ltd (1998) Lonsdale Bight Coastal Processes Investigation – Numerical Modelling

(5) Vantree Pty Ltd (1998) Lonsdale Bight Coastal Process Investigation Summary Report

(6) GHD (2001) Lonsdale Groyne Assessment

(7) SKM (2006) Point Lonsdale Seawall Terminal Scour. Coastal Study and Recommendations

(8) Parks Victoria (2006) Port Phillip Heads Marine National Park Management Plan

(9) Cardno Lawson Treloar (2007) Hydrodynamics and Coastal Processes Head Technical Report

(10) P.J.Yttrup & Associates Pty Ltd. Consulting Engineers (2010) Cliff Stability Investigation Report

(11) Oldfield Consulting Australasia (2010) Point Lonsdale Seawall Condition Assessment

(12) Bird (2011) Changes on the Coastline of Port Phillip Bay

(13) Cardno (2011a) Sediment Transport Modelling Great Sands, Port Phillip

(14) Cardno (2011b) The Great Sands and Adjacent Coast and Beaches

(15) Worley Parsons (2012) Port Phillip Beach Nourishment Update of Priorities

(16) Department of Environment and Primary Industries (2013a) Report on Coastal Adaptation Options for Point Lonsdale Cliffs

(17) Department of Environment and Primary Industries (2013b) Report on Coastal Processes and Adaptation Options at Point Lonsdale Dog Beach

(18) Atkins Maritime Engineering Pty Ltd (2013a) Point Lonsdale Sand Management

(19) Atkins Maritime Engineering Pty Ltd (2013b) Dog Beach Adaption Concepts

(20) Victorian Coastal Council (2014) Victorian Coastal Strategy

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Lonsdale Bight Investigations Review and Options Overview 5 Review of Information

(21) A.S. Miner Geotechnical (2014) Review of Cliff Stability Investigation Report at Point Lonsdale

(22) Oldfield Consulting Australasia (2015) Point Lonsdale Seawall 2015 – Condition Assessment

(23) Cardno (2015) Inundation Report Bellarine Peninsula – Corio Bay Local Coastal Hazard Assessment

(24) N J Rosengren (2016) Queenscliff to Point Impossible Geomorphology and Coastal Processes

2.2 Overview and Linkages of Reports A detailed summary of the reports reviewed is provided in Appendix A. These reports date back to 1997 and generally cover one or more of the following broad topics:

 Geomorphology and historical changes

 Coastal processes and related hazards

 Environmental values

 Cliff stability and management

 Coastal management options and works

 Seawall and groyne condition and structural stability.

The scope did not extend to a full literature review and hence there may be other reports, documents and data, particularly prior to 1997, related to the study area that have not been sighted. Nevertheless, the extensive document list does provide a good overview of the processes, values and issues at hand with respect to management of the Lonsdale Bight foreshore.

In terms of linkages, there is general agreement throughout the reports with respect to the broad coastal processes. The 1998 reports of Vantree and Lawson and Treloar provide a detailed assessment of those processes although there are some limitations and gaps in knowledge (refer Section 4). Further detailed and updated data collection and modelling of hydrodynamics, waves and sediment transport has been undertaken as part of more recent studies for the Channel Duplication Project by Cardno Lawson and Treloar (2007) and subsequently Cardno (20011a and b). However, the same broad description and split in sediment transport across the Bay and along the foreshore as described in the earlier reports is repeated in these and other reports.

The description of the geomorphology of the region and historical changes including seawall and groyne construction is also generally consistent and repeated in the relevant reports. The seawall condition reports (Oldfield Consulting 2010 and 2015) indicate general stability of the masonry seawall at present with ongoing maintenance requirements. Deterioration and the need for increased maintenance and potential failure from increased wave exposure and overtopping with future sea level rise is highlighted by others (Cardno 2015), particularly in areas with low sand levels in front.

Options for coastal management are discussed in a number of the reports and again the context is generally consistent with the benefits of an adaptive risk management approach also discussed in

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Lonsdale Bight Investigations Review and Options Overview 6 Review of Information

some (DEPI 2013a and b and Cardno 2015). This is particularly with respect to managing cliff stability and the terminal scour area at Dog Beach. However, there has been no clear assessment of the hazards and issues apart from seawall overtopping along the remainder of the foreshore. Similarly the basis and assessment of options that are presented are not detailed.

2.3 Other Information In addition to the above reports, historical photographs and references as presented on the following Facebook pages were reviewed and provided useful information:

 Save Pt Lonsdale Front Beach - https://www.facebook.com/SavePtLonsdaleFrontBeach/

 Friends of the Point Lonsdale Lighthouse Reserve - https://www.facebook.com/Friends-of-the- Point-Lonsdale-Lighthouse-Reserve-272196809616831/

Recent aerial photography available through Google Earth and Nearmap has also been reviewed.

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Lonsdale Bight Investigations Review and Options Overview 7 Overview of Processes, Values and Hazards

3 Overview of Processes, Values and Hazards

3.1 Coastal Processes in General Beach and shoreline fluctuations occur in response to the prevailing coastal processes and the influences of controlling features. These fluctuations can sometimes be accompanied by associated hazards and risks to the natural and built environment. Consideration of strategies to manage such hazards needs to be based on an understanding of the prevailing processes.

Sand movements include complex interactions of longshore, cross-shore and nearshore processes under the driving forces of waves and currents over the range of water levels experienced in the immediate area. These are in turn influenced by the nearshore bathymetry and the presence of natural hard material as well as man-made structures. Also of importance are the characteristics of the sand, the supply of that sand to the local system and the amount available in the nearshore region.

Sand is typically moving along and across the beach and variations in the rate of that movement results in beach and shoreline fluctuations. In broad terms, beaches will build up and accrete under appropriate wave conditions and when sand is supplied to an area at a greater rate than it is transported away. Conversely, beach lowering and erosion will occur under severe wave conditions particularly with elevated water levels and when sand is transported out of an area at a greater rate than it is supplied. The reduction or interruption of sediment supply to an area is a common cause of beach erosion.

The driving forces and shoreline response are subject to variability seasonally throughout the year and over longer annual and decadal cycles associated with meteorological phases as well as over geological time scales and with future climate change. Knowledge and understanding of contemporary and longer term processes are essential in developing appropriate coastal management strategies. Dealing with natural variability and uncertainty with respect to the nature, timing and extent of future changes are key considerations.

3.2 Lonsdale Bight Coastal Processes The following overview of the coastal processes influencing Lonsdale Bight has been based on the review of available reports and information as well as site inspections and liaison with key stakeholders. No detailed assessments have been undertaken as part of this review and it is not intended to be a detailed quantitative description of the coastal processes and hazards.

The foreshore of Lonsdale Bight is exposed to a complex and dynamic range of coastal processes. The dominant high energy ocean waves approach the open coast to the west of Point Lonsdale and enter the Bay from a narrow offshore direction (SSW-SW). These waves transport sand along the Bass Straight coast from west to east to Point Lonsdale and the entrance to Port Phillip Bay.

The sand that reaches Point Lonsdale and the entrance is then moved under the combined and complex action of the waves and strong tidal currents and as influenced by the complex bathymetry of the area. It is estimated (Cardno 2007) that about half is carried offshore by the ebb tide or directly into the deep areas of the entrance. The remainder moves into the Bay under predominantly flood tide conditions with a narrow band along the base of the cliffs and the

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Lonsdale Bight Investigations Review and Options Overview 8 Overview of Processes, Values and Hazards

remainder across the nearshore platform. It is further observed that there is considerable variability in the transport of sand depending on weather conditions. Sediment moves in pulses in response to the occurrence of storms and the rate will vary within and between years (Cardno 2011a). Sand within the Bay has been identified as having the same characteristics as and therefore originating from the open ocean beaches.

There is also discussion (Bird 2011 and Rosengren 2016) about sediment supply in geological time scales with an onshore supply of sand to the coast as sea level has risen. With sea level being at its present level for about the last 6,000 years, the possible decline of this supply has been noted which will then ultimately affect the supply to Lonsdale Bight with gradual shoreline evolution in response. In a similar fashion, any future sea level rise has the potential to affect the supply of sand to the coast as well as transport along the coast and past Point Lonsdale. Such potential affects have not been quantified.

It is therefore evident that the supply of sand to Lonsdale Bight is intermittent and variable depending on the prevailing conditions. It may also be subject to long term decline associated with shoreline evolution at geological time scales.

Within the Bay, varying current, wave and water level conditions drive sediment transport processes. These processes are also influenced by natural headlands and nearshore rocky reefs as well as man-made structures such as seawalls and groynes. The shoreline has evolved and beach levels respond to these local processes in combination with the broader influence of sediment supply to the Bay.

Strong tidal currents occur particularly through the main entrance to Port Phillip Bay. On the flood tide, momentum drives the flow towards the northern shore of the embayment and strong currents to the east develop along the coast and past Shortland Bluff. In the western embayment, flood tide currents close to the coast to the north are smaller. On the ebb tide, an eddy with reduced and reverse currents forms off the shoreline to the west of Shortland Bluff. The ebb tide currents off Point Lonsdale Front Beach are to the south and stronger than the flood tide.

The offshore waves which arrive at the entrance are modified through diffraction, refraction and shoaling by the seabed and strong tidal currents as they enter the Bay. Modelling (Cardno 2007) indicates a zone of focused wave energy off Point Lonsdale (see Figure 3-1). The waves approach Front Beach at a steep angle which generates strong longshore wave-induced currents and longshore sand transport potential. Due to the relatively shallow rocky nearshore profile, the larger waves are typically limited in height by the depth, particularly at low tide. At high tide and under storm surge conditions, the wave energy reaches the upper beach and waves impinge directly on the seawalls where/when the beach is low. Wave reflections off the seawall further exacerbate the turbulence and mobilisation of sediment in front of the wall for transport by the prevailing currents.

As the waves propagate further into the Bay, they progressively lose height and approach the shoreline at a more shore-normal angle due to refraction and the changing alignment of the coastline which curves around to the east. The waves are also modified by the strong tidal currents and typically exhibit increased wave length and reduced height during the flood tide while they are shorter and steeper with opposing currents during the ebb tide. Locally generated wind

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Lonsdale Bight Investigations Review and Options Overview 9 Overview of Processes, Values and Hazards

waves which approach from the east across the Bay are typically small and infrequent and do not have a significant influence on coastal processes.

The sand that enters the Bay at Point Lonsdale is transported partly along the coastline close to the beach and partly across the seabed of the embayment towards Shortland Bluff under the influences of the waves and tidal currents. The longshore sand transport potential near the beach is dominated by wave induced longshore currents at Point Lonsdale Front Beach where the waves approach the shoreline at a steep angle. Further north as the shoreline curves around to the east, the waves reduce in height and approach the beach at a smaller angle. Accordingly wave induced longshore currents and transport potential would be expected to reduce further to the north and east towards Shortland Bluff. However, measurements and modelling of tidal currents indicate their increasing importance, particularly on the flood tide enhancing nearshore transport to the east in this area.

The transport of sand across the seabed of the embayment is driven by the complex interaction of the waves and the strong tidal currents. The presence of exposed rock across much of the seafloor indicates that sand is transported across the seabed in a thin veneer and that the transport capacity most likely exceeds the supply (Vantree 1998). The sand transported across the seabed most likely re-joins and enhances the littoral transport along Dog Beach and east towards Shortland Bluff.

The coastal processes within Lonsdale Bight are subject to natural variability throughout the year. Inter-annual and decadal climate variability also affects sea level and the prevailing wave climate (Cardno 2011b) and therefore sediment transport processes. Storms with elevated water levels and higher waves typically occur during winter months and can result in overtopping of the seawalls. Enhanced sediment transport and erosion potential occurs during such times including the potential lowering of beaches in front of the seawalls and erosion of upper beach and dune areas.

The storms are also important for the potential intermittent transport of sand around Point Lonsdale and subsequent supply of sand and a build-up of the beaches on a more gradual basis over summer months. The variability in the supply of sand and the ongoing transport potential through the local driving forces means it is likely that there are periods when the potential sand transport is greater than the supply leading to erosion and lowering of the beaches and vice versa.

The key coastal processes of relevance to ongoing management of the Lonsdale Bight foreshore are therefore the dominant wave induced longshore transport of sand along the coast coupled with offshore transport during storm events, both of which are subject to seasonal, inter-annual and decadal variations. These variations lead to fluctuations in the volumes of sand, levels of the beaches and alignment of the foreshore. In addition to this, the intermittent and potentially reducing supply of sand around Point Lonsdale and into the compartment adds further variability and uncertainty with respect to fluctuations in the volumes of sand along the foreshore.

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damage to structures. Such processes will be gradual and necessitate ongoing and potentially increased maintenance of structures and associated adaptation strategies.

Figure 3-1 Wave propagation into Lonsdale Bight (Cardno 2007)

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3.3 Summary of Historical Changes and Works Fluctuations in the shoreline and levels of the beaches of Lonsdale Bight have been reported and observed over many years with various works carried out in response (refer Vantree 1998 and Bird 2011). Construction of a masonry seawall first commenced at Point Lonsdale Front Beach in 1900. Severe erosion occurred in 1934 and timber groynes were initially constructed in 1935 in an attempt to retain sand and halt the erosion. The masonry wall was extended between 1939 and 1947 to address ongoing back shore erosion. Recession of the shoreline continued to the north of the masonry wall and following the failure of a small timber section, the seawall was progressively extended as a rock revetment structure. This was also constructed in sections following the erosion as it continued around the embayment. The final section to Dog Beach was completed in 1977 with refurbishment works completed in 1996. (See Figure 3-2 for summary).

The original timber groynes at Front Beach became dilapidated and were replaced with further timber groynes of a different design. The early groynes reportedly had varying levels of success in retaining a usable sandy beach and fluctuations in beach level over time are evident (refer Vantree 1998 and Bird 2011 and Figure 3-3 and Figure 3-4). With sand levels low and the timber groynes again deteriorating, the decision was made to remove them and construct two hybrid rock/timber groynes in 1999-2000 (see Figure 3-5 and Figure 3-6). A third rubble mound (rock) seawall was constructed between these two groynes in 2005 where sand levels remained low (see Figure 3-7).

Further discussion surrounding the history and performance of the groynes is provided in section 5.4. These three groynes remain in place (2016) and have been effective in retaining some sand in the local vicinity although beach levels and extent continue to fluctuate (refer Figure 3-8). While past periods of substantial sand build up are evident, the areas of usable upper beach are presently limited to near the groynes with sand levels elsewhere in front of the masonry seawall being low and variable.

Sand levels in front of the rock seawall further to the north have fluctuated but have been typically low as at present with limited or no upper beach for most of its length (see Figure 3-9). The groynes and exposed sections of all seawalls require regular maintenance to repair damage caused by waves during storm events, particularly with elevated water levels.

Further around the embayment to the north-east, terminal scour with a significant erosion scarp in the high dune is evident in the shoreline alignment at the end of the seawall at beach known as ‘Dog Beach’ (See Figure 3-10). A stable sandy beach subject to natural variations extends eastwards to Shortland Bluff at Queenscliff.

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Figure 3-2 History of Seawall Construction (Vantree 1998)

Figure 3-3 Point Lonsdale Front Beach circa 1936 (Bird 2011)

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Figure 3-4 Point Lonsdale Front Beach circa 1982 (Bird 2011)

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Figure 3-5 Existing Southern Groyne (November 2016)

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Figure 3-6 Existing Northern Groyne (Sep 2016 top, Nov 2016 bottom)

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Figure 3-7 Existing Central Groyne (November 2016)

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Figure 3-8 Point Lonsdale Front Beach Fluctuations

"I:\B22316_I_GML_Queenscliff\JPG\161124\Figure 3-8.jpg"

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Figure 3-9 Central Section Rock Revetment Wall (September 2016)

Figure 3-10 Dog Beach Terminal Scour (September 2016)

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Figure 3-11 Sandy Beach East to Shortland Bluff (September 2016) 3.4 Port Phillip Heads Marine National Park Values Victoria’s Marine National Parks (MNP) and Marine Sanctuaries aim to protect natural marine ecosystems from the effects of inappropriate activities. The system targets state-wide representative examples of undisturbed natural marine habitat for biodiversity, cultural heritage and aesthetic values and for recreational purposes.

The Port Phillip Heads MNP, managed under Victoria’s National Parks Act 1975, lies within Port Phillip Bay between the Bellarine and Mornington Peninsulas. The Point Lonsdale section of this MNP comprises approximately 415 ha of marine ecosystem and includes 3 km of coastline extending along, and offshore, from Clarkes Beacon to west of Point Lonsdale, excluding an area 50 m on each side of the pier (see Figure 3-12). The Marine National Park extends to High Water Mark and therefore the beach and nearshore areas of this section of foreshore are part of the Park.

Plummer et al. (2003) and Barton et.al. (2012) provide comprehensive overviews of the important natural values within the MNP, including details on the Point Lonsdale section which is recognised for its state-wide environmental, cultural and recreational values, including (after Parks Victoria, 2006):

 Natural Values:

○ intertidal reef platforms that support the highest invertebrate diversity of any calcarenite reef in the State;

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○ diverse and abundant algal assemblages on Lighthouse Reef;

○ deep undercuts in the Lonsdale Reef which are uncommon along Victoria’s open coast and which support algae communities more typical of deeper waters;

○ diverse fish and invertebrate assemblages on the Lonsdale Wall, including extensive encrusting communities such as ascidians, bryozoans and sponges;

○ calcarenite shore and reef platforms that are of regional and state significance for shorebird feeding; and

○ threatened marine mammals such as Australian Fur Seal (Arctocephalus pusillus), Southern Right Whale (Eubalaena australis) and Humpback Whale (Megaptera novaeangliae).

 Cultural Values:

○ heritage-listed shipwrecks and shipping history;

○ botanical and scientific survey sites of research and historical significance;

○ historical significance as one of the first marine reserves protected in Victoria.

 Tourism and Recreation Values:

○ swimming, surfing, walking, birdwatching, nature observation and passive recreation leisure activities

○ Internationally recognised subtidal reef dive sites

○ snorkelling sites between Lightning Reef and the Point Lonsdale Pier

○ recreational boating and sailing

○ opportunities for guided marine education and nature-based tourism

○ scenic landscapes.

The Point Lonsdale coastline consists of highly dynamic natural coastal processes involving natural accretion and attrition of beaches, causing sand to cover and uncover the reefs and other nearshore habitats (Parks Victoria, 2006). These natural processes have contributed to the values of the Marine National Park and have been influenced by the construction of groynes and a seawall in Lonsdale Bay. Any modifications to these structures or other works to influence coastal processes will need to consider potential impacts on the environmental, cultural and recreational values recognised within the Marine National Park. Furthermore, any such works will also need authorisation in writing from the relevant Minister as well as Coastal Management Act Consent.

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Port Phillip Heads Marine National Park Management Plan, Parks Victoria, July 2006

Figure 3-12 Port Phillip Heads Marine National Park, Point Lonsdale Section

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3.5 Interpretation of Issues

3.5.1 Overview As outlined above, the shoreline of Lonsdale Bight is exposed to a range of complex and dynamic coastal processes. Management of the coastline firstly requires an understanding of the risks those processes pose to the environmental, social and economic values of the region. Strategies and options to manage those risks can then be considered again in the context of the environmental, social and economic values as well as the technical viability and likelihood of success.

A complete identification of hazards and analysis of the risks has not been undertaken. However, it is evident that there are issues surrounding ongoing fluctuations in the level of sand along parts of the foreshore and the potential for longer term erosion and damage, particularly with climate change influences related to sea level rise and higher wave energy reaching the upper beach.

The main coastal process related issues identified as part of this project are outlined below. The embayment has been divided into 3 main areas for reference purposes as follows:

A. Point Lonsdale Front Beach – this covers the area of foreshore backed by the masonry seawall.

B. Central Section – this covers the area of foreshore backed by the rock revetment seawall.

C. Dog Beach – this covers the sandy beach area from the end of the rock revetment up to Shortland Bluff.

These three areas are illustrated in Figure 3-13 and have been further subdivided for reference purpose as shown.

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Figure 3-13 Lonsdale Bight beach sections "I:\B22316_I_GML_Queenscliff\JPG\161124\Figure 3-13.jpg"

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3.5.2 Point Lonsdale Front Beach (Area A) The foreshore at Point Lonsdale Front Beach is an important recreational asset. The beach and nearshore areas are also part the Port Phillip Heads Marine National Park which is recognised for its state-wide environmental, cultural and recreational values. A popular promenade extends along the whole length of the foreshore behind the masonry wall. The southern section (Area A(i)) fronts the main shopping precinct with extensive playground and recreational facilities behind the seawall. A recreational reserve containing various park facilities backs the remainder of foreshore.

The masonry seawall was constructed progressively in response to erosion with the majority of it now being in place for more than 70 years and the initial southern section more the 100 years. Beach levels in front of the seawall have fluctuated over the years and groynes of different design have been constructed. The history and performance of these groynes and the seawall are discussed further in Section 5.4.

There are presently three groynes extending out from the masonry seawall. The amount of sand these groynes holds has varied and while they are effective in providing upper usable beach areas, the extent of these areas is often limited. With ongoing fluctuations in sand volumes, there are sometimes periods such as after winter storms when the beach level is low along substantial lengths of foreshore beyond the influence of the groynes. At such times, little or no usable beach remains in front of the wall in these areas (see Figure 3-14.and Figure 3-15). As a consequence, the wall in these areas is subject to direct wave attack and potential wave overtopping at high tide and during storms with elevated water levels. The southern section of the wall in Area A(i) (refer Figure 3-10) is most vulnerable in this regard due to its exposure and alignment (see Figure 3-16).

Figure 3-14 Low Beach in Front of Southern Wall (November 2016)

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Figure 3-15 Low Beach North of Southern Groyne (November 2016)

Figure 3-16 Southern Wall Wave Exposure (mid-tide September 2016)

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The wall and groynes have been subject to damage and require regular monitoring and maintenance works. While recent condition reports of the seawall indicate general stability (Oldfield 2015), there are also reports identifying the risks of instability and failure when the sand level in front of the wall is low and particularly with future sea level rise (Cardno 2016).

It is noted that the crest of the masonry seawall is relatively low with the capping block being at a level of 2.7m CD which is only about 0.9m above HAT. Under normal day to day wave and tide conditions, wave run-up pushes sand trapped by the groynes up the beach towards the top and sometimes over the seawall onto the path behind. It is also evident that the seawall is already prone to overtopping along the majority of its length during storm conditions particularly with elevated water levels as experienced in May 2016. Such overtopping events are likely to become more regular and severe with sea level rise as projected with future climate change. This will exacerbate the risk to the structural stability of the seawall and the threat of erosion and damage to the land and facilities behind.

Key issues requiring consideration as part of future coastal management planning at Point Lonsdale Front Beach are as follows:

 Fluctuating sand volumes and uncertainty surrounding the extent and duration of periods with low beach levels;

 Limited usable beach for recreational purposes, particularly at high tide during periods with low beach levels;

 The importance of the Marine National Park values and ensuring these are not compromised;

 Direct wave attack on the aging masonry seawall when and where sand levels are low with associated enhanced weathering and increased maintenance costs;

 Potential instability and damage of exposed sections of the seawall and the groynes during severe storms with high waves and elevated water levels;

 Public safety associated with wave overtopping of the seawall and potential damage during severe storms as well as high drops from the walls when and where beach levels are low;

 Exacerbation of all of the above issues and additional threats to the land behind the seawall with climate change influences of rising sea level and more wave energy reaching the shoreline.

The main issues centre around or are exacerbated by periods of low beach level and with future sea level rise. Understanding and dealing with natural variability in regard to such processes is therefore important in considering the need for and extent of short and long term management options to address the issues.

3.5.3 Central Section (Area B) In this section the seawall continues along the foreshore as a rock revetment with the promenade behind. The Royal Park and GoLightly Park Caravan Parks are located landward of the southern section of the seawall while a broad undeveloped reserve backs the northern section.

Little or no usable upper beach fronts the seawall in this section for extended periods which constrains the recreational amenity. While fluctuations in the level of sand do occur, there are no

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groynes in this section to retain sand. There are no specific condition reports relating to the rock revetment wall. However, it will potentially be subject to damage and require maintenance following major storm events. The crest elevation of the rock revetment seawall is higher than the masonry seawall and its design is such that it will also absorb some of the impinging wave energy. As such, it is less prone to issues associated with wave overtopping.

The key issues requiring consideration as part of future coastal management planning for this section of the foreshore therefore relate to:

 Fluctuating sand volumes and uncertainty surrounding the extent and duration of periods with low beach levels;

 The lack of a usable beach for recreational purposes, particularly at high tide during periods with low beach levels;

 The importance of the Marine National Park values and ensuring these are not compromised;

 Direct wave attack on the rock revetment seawall and potential damage during severe storms with high waves and elevated water levels;

 Exacerbation of all of the above issues with climate change influences of rising sea level and more wave energy reaching the shoreline.

While the above issues are influenced and exacerbated by fluctuations in sand level, without any controlling structures like in Area A, the issues persist along the full section for the majority of time.

3.5.4 Dog Beach (Area C) Further around the embayment to the north-east, a sandy beach extends from the end of the rock revetment seawall to Shortland Bluff. This beach, known as ‘Dog Beach’, is backed by a high dune and essentially remains as a natural beach with associated social and environmental values.

Terminal scour is evident in the shoreline alignment immediately at the end of the seawall (Area C(i)). Various stabilisation and protection works have been carried out in the terminal scour area where a high dune scarp remains. Fluctuations in the beach occur in response to the prevailing processes and the shoreline is generally regarded as being relatively stable at present. The beach further to the east towards Shortland Bluff has also experienced accretion in recent years.

As the supply of sand to Dog Beach includes longshore transport around the coast from Point Lonsdale, consideration needs to be given to the potential for any works at Front Beach to alter this supply and exacerbate the erosion threat. While a reasonable undeveloped buffer remains seaward of existing development and infrastructure along this shoreline, the beach has also been considered very high risk to exacerbated erosion associated with sea level rise and accompanying wave climate changes (DEPI 2013b and Rosengren 2016).

The key issues requiring consideration as part of future coastal management planning for this section of the foreshore therefore relate to:

 Ongoing stability and management of the high dune scarp in the terminal scour area;

 Potential erosion and short term threats during storm events;

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 Threats of long term recession particularly related to climate change effects of sea level rise and associated increased wave energy;

 The potential impacts of works carried out at Point Lonsdale Front Beach.

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4 Key Information and Knowledge Gaps

4.1 Overview Substantial information exists in the large body of reports and investigations already undertaken. However, based on the review of those reports and interpretations of the coastal processes as described above, there are key knowledge and information gaps of relevance to consideration of coastal management strategies for Lonsdale Bight. Where possible, these gaps should be filled to provide a more detailed understanding of the processes and an assessment of the risks associated with those processes as well as to allow detailed assessment of options to manage those risks.

Outlined below are the main gaps noted through the review process. Some of these are related to quantification of the complex processes and difficulties remain with such quantification. Understanding these and dealing with the uncertainty will be important for consideration of coastal management strategies. Alternative means of gaining the necessary information are also discussed.

The gaps are discussed below in terms of the primary coastal process components. It should be noted that identified gaps are based on the reports made available and reviewed for this study. There may be other sources of information not sighted which contain relevant information in this regard. A full literature review was beyond the scope of this commission.

4.2 Tides and Currents Substantial data collection and numerical modelling of tidal hydraulic processes have been undertaken in southern Port Phillip Bay. Accordingly a good broad understanding exists of the complex processes through the entrance and Lonsdale Bight.

Data was collected to calibrate early modelling for the Vantree (1998) investigation. However, current data in the Lonsdale Bight embayment was limited to 2 locations over a 2 month period in the northern part of the embayment as well as some ADCP transects which were noted as being during a period of strong winds and high waves which limited the quality and coverage of data available (Lawson and Treloar 1997).

Detailed and updated modelling of the tidal hydrodynamics has been undertaken as part of the Channel Deepening Project and other recent studies. Specific data collection to validate the model in the nearshore region of Lonsdale Bight as part of this or other studies is not evident. The hydrodynamic models provide useful tools to simulate and describe the current patterns in Lonsdale Bight. However, there is no evidence of detailed measurements of current patterns in the nearshore region of the Bight apart from ADCP transects undertaken in 1997 under less than ideal conditions (Lawson and Treloar 1997). While not critical, such current measurements would be beneficial to confirm current patterns if management options which could influence or be influenced by tidal currents are considered.

4.3 Waves Similar to tidal currents, substantial information is available on wave propagation in Lonsdale Bight through data collection and numerical modelling. Again data collection within the Lonsdale Bight

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embayment was limited to 2 locations for the early Vantree (1998) investigation (Lawson and Treloar 1997). Indicative nearshore wave modelling was undertaken in the Front Beach area for 2 specific groyne scenarios.

More detailed bathymetry is now available and updated wave propagation modelling has been undertaken as part of the Channel Deepening Project and other studies. These models again provide useful tools for assessing and describing the waves approaching the Lonsdale Bight shoreline in general. However, in the area immediately north of the Point Lonsdale headland the waves are subject to rapid changes through refraction, diffraction and shoaling processes and approach the shoreline at steep angle. They also reflect off the rocky headland and seawall structures. Detailed nearshore wave modelling using up to date bathymetry will be necessary to assess the wave patterns and their influence on sediment transport processes as part of consideration and design of any works in this area.

4.4 Sediment Supply to Lonsdale Bight A critical factor for consideration of coastal management strategies within Lonsdale Bight is the ongoing supply of sand to the compartment. It is evident from the reports reviewed (Vantree 1998, Cardno 2007, Bird 2011 and Cardno 2015) that the primary supply is from the beaches to the south of Point Lonsdale. Detailed quantification of the rate and variability of transport has not been sighted in any of the reports reviewed. However, it has been estimated (Lawson & Treloar 1998) to be 400,000 m3/yr with variations from year to year depending on the number and severity of storm events. It should also be noted that Rosengren 2016 identifies that there is some evidence to indicate that the volumes of transport along the open coast may be smaller and the opposite direction in places with examples given of areas further to the west.

Of the sand that reaches Point Lonsdale and the entrance, it has again been estimated (Lawson & Treloar 1998 and Cardno 2007) that about half enters the Bay under the influences of waves and predominantly flood tide conditions (see Figure 4-1 and Figure 4-2). As discussed in Section 3.2 above, it is evident that the supply of sand to Lonsdale Bight is intermittent and variable depending on the prevailing conditions. Sediment moves in pulses predominantly in response to the occurrence of storms and the rate will vary within and between years.

Only broad estimates have been made on the long term average supply of sand along the coast to Point Lonsdale and the amount that is then transported into Lonsdale Bight. While the intermittent and variable nature of the supply is noted, no details are evident of these variations or time scales throughout the year or from year to year related to the incident conditions including storm events. It may also be subject to long term decline associated with shoreline evolution at geological time scales (Bird 2011 and Rosengren 2016). Such potential affects also have not been quantified.

The supply of sand has an important bearing on the fluctuations in beach levels along the shoreline of Lonsdale Bight. Therefore knowledge of the rates and variations, particularly the frequency and length of periods with reduced or no supply is a key factor in considering coastline management strategies. It is important for understanding and considering the risks associated with how often and how long the beach levels may be low as well as for consideration of options to manage those risks.

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This is a critical gap in knowledge which is not only difficult to quantify historically, but also predict into the future with natural variations on different time scales. While further knowledge will help inform coastal management decisions, they will still need to take uncertainty into consideration.

Figure 4-1 Estimated net sand transport (Vantree 1998)

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Figure 4-2 Estimated net sand transport (Cardno 2007)

4.5 Sediment Transport along the Coast The sand that enters the Bay at Point Lonsdale is transported along the coastline close to the beach and across the nearshore zone to Shortland Bluff under the influences of waves and tidal currents. The littoral transport along the coast at Point Lonsdale Front Beach is dominated by the waves which approach at a steep angle generating strong longshore wave-induced currents and longshore sand transport. Wave reflections off the seawall further exacerbate the turbulence and mobilisation of sediment in front of the wall for transport by the prevailing currents.

The wave induced longshore currents and transport reduce further to the north and east towards Shortland Bluff with reducing wave heights and angles. However, as discussed in Section 3.2 tidal currents have an increasing importance in the northern section, particularly on the flood tide enhancing transport to the east.

While some calculations of the littoral transport capacity along the shoreline have been carried out as discussed below, these are limited to the section from the beginning of the rubble seawall near Jordan Street around to Shortland Bluff (areas B and C in Figure 3-13). There is discussion in a number of the reports about the high potential for longshore transport, particularly immediately north of the Point Lonsdale headland (area A (i)) where the waves approach the shoreline at a steep angle. However, no specific calculations appear to have been made for any of the Front Beach section in front of the masonry seawall (Area A).

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The history of sand trapped by the three groynes in this section does provide an indication of the longshore transport processes which is of value for coastline management considerations. However, again no detailed analysis of this has been carried out. Such analysis and ongoing monitoring would add value to the understanding of the processes, particularly with respect to variability for consideration of the risks and the design of any such similar structures north of the southern groyne (in areas A (ii) to (iv)). The complex wave and sediment transport processes immediately north of the headland in Area A (i) would require further investigation for design of any specific works.

Littoral transport rates have been calculated (Lawson and Treloar 1998 and CLT 2007) at five representative sections along the shoreline from around Jordan Street to Shortland Bluff (area B and C in Figure 3-13). The calculations utilise a representative cross-shore profile and sediment characteristics for each section with offshore wave and current conditions as determined from the wave and tide models. The estimated rates from the 1998 study were approximately 50,000 – 80,000 m3/yr. With updated models of wave and currents, the 2007 estimates varied along the beach from 50,000 – 200,000 m3/yr. The large uncertainty and sensitivity of the calculations to input parameters, particularly wave direction, are noted. Nevertheless, they provide an indication of the longshore sand transport rates along the coast.

4.6 Sediment Transport across Lonsdale Bight A similar volume of about 100,000 m3/yr is also estimated to be transported across the seabed of the Bight towards Shortland Bluff in water depths less than 15m under the influences of tidal currents and waves. The reports note that these are only estimates. The presence of exposed rock across much of the seafloor indicates that sand is transported across the seabed in a thin veneer and that the transport capacity most likely exceeds the supply. The sand transported across the seabed most likely re-joins and enhances the littoral transport along Dog Beach and east towards Shortland Bluff.

The complexities of modelling and quantification of the sediment transport processes across Lonsdale Bight are noted in the reports along with limitations related to the lack of data and difficulties with model calibration. The models developed in previous studies have been used to provide a basis for understanding the processes and assess relative impacts of projects such as the Channel Deepening. Early modelling (Lawson & Treloar 1998) provides an indication of net sediment transport rates under the influences of currents and waves over a tidal cycle. While net transport to the east past Shortland Bluff is indicated, the net transport off Point Lonsdale Front Beach is to the south back out the entrance. The basis of the net 100,000 m3/yr across the seabed is therefore unclear.

More recent and comprehensive sediment transport modelling for the Channel Deepening Project (CLT 2007, Cardno 2011a&b), provides limited detail for Lonsdale Bight although sediment fluxes of about 100,000 m3/yr into the Bay past Point Lonsdale and about 50,000 m3/yr across the western embayment are indicated. Ongoing accretion at Queenscliff indicates a net transport to the east out of the Lonsdale Bight compartment.

While limited detailed information is available on the rate of sand transport across Lonsdale Bight, this is not seen as critical gap for understanding and dealing with issues at Point Lonsdale Front

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Beach. It is however, important for considering longer term processes and shoreline evolution along Dog Beach.

4.7 Cross-shore Sediment Transport Onshore – offshore transport of sand is an important consideration in terms of understanding and dealing with coastal management risks. Erosion of the upper beach through offshore transport of sand can occur rapidly during storms with high waves and elevated water levels. Subsequent return of that sand under mild wave conditions is typically gradual and occurs over extended periods. It is dependent on sand being available and can be constrained if the sand transported offshore is carried away by strong longshore currents including tidal currents.

The potential extent of storm erosion has been calculated for the sandy foreshore at Dog Beach. While the remainder of the foreshore has a seawall to protect against recession, offshore transport has the potential to lower the level of sand in front of the wall and also remove sand retained by the groynes. This potential is noted (Bird 2011) but has not been quantified. Consideration needs to be given to cross-shore sediment transport processes in terms of the risks it generates as well as the likely performance of any works aimed at retaining a sandy beach.

4.8 Shoreline and Beach Fluctuations Photogrammetric analyses of the shoreline has been undertaken in some studies (Vantree 1998, SKM 2006, DEPI 2013b) with 2012 being the latest photography date analysed. These analyses have focussed primarily on fluctuations of the sandy shoreline along Dog Beach although the early study (Vantree 1998) makes reference to a small fillet of sand that comes and goes in front of the seawall. Limited survey profile data exists for the analysis of beach fluctuations and broad scale analyses have been made of recent changes as determined from Laser Airborne Depth Sounder (LADS) data (Cardno 2011a).

While the coastal alignment is essentially fixed by the seawalls along much of the embayment, fluctuations occur to the level of the beach in front of walls and around the groynes. Analysis of these fluctuations does not appear to have been assessed in any detail. Such information and ongoing monitoring would aid the understanding of natural variability in the processes and the influences of the structures. The lack of data and benefits of ongoing monitoring are discussed in a number of the reports (DEPI 2013b, Cardno 2015, Rosengren 2016). While historical information is limited, even qualitative analysis of available photography would be of value.

Over recent years, particularly since construction of the three existing groynes, much more information including aerial photography from a number of sources would be available for analysis. Again qualitative and where possible, quantitative analysis of changes that have occurred would provide information on the influence and effectiveness of structures such as the groynes as well as the extent and time frame of changes associated with seasonal variations, storm events and subsequent recovery. Furthermore, a continuous record of wave and water level data for the region is available to link observed changes to the processes.

While not a present day gap, ongoing monitoring of fluctuations along the shoreline through a properly designed and implemented monitoring program is an integral part of coastline management.

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4.9 Climate Change Influences The potential implications of climate change are discussed in a number of the reports including sea level rise with associated increased wave energy impinging on the shoreline at a higher level. For the sections of the coast backed by a seawall, the implications of overtopping and direct wave attack are raised in terms of the stability of the seawall and public safety (Cardno 2015). However the potential implications for the land behind are not discussed in detail. The potential for long term recession of the sandy beach areas is also raised as a risk (Rosengren 2016). However, the potential extent of such recession and /or lowering of the beaches has not been quantified. Implications include changes to sediment supply as well as direct impact on the local driving processes of waves, currents and sediment transport.

4.10 Summary of Knowledge and Information Gaps Based on the review of available reports and interpretations of the coastal processes as described above, the key knowledge and information gaps of relevance to consideration of coastal management strategies for Lonsdale Bight are as follows:

 While all data may not have been sighted, there is no direct reference to data collection on nearshore currents off Point Lonsdale Front Beach apart from limited ADCP transects under less than ideal conditions and references are made to the use of estimates. Limitations and difficulties with model calibration refer to limited data.

 Detailed modelling of nearshore wave conditions at Front Beach is limited to indicative modelling in 1998. More up to date modelling under a range of conditions using presently available detailed bathymetry and representations of existing structures would help inform decisions.

 Limited quantitative details are available on the supply of sand around Point Lonsdale with only estimates provided. While it is evident that sand is transported around intermittently in pulses driven by waves and currents particularly during storm events, no detailed analyses or even estimates of the variability are provided in the reports. This is a key consideration for coastal management strategies.

 Following on from the above, the proportional split of sediment transport along the coast and across the seabed of the Bight is not definitive. Rates provided are noted as being estimates.

 No calculations of littoral sediment transport capacity appear to have been carried out along Front Beach. While rates have been calculated across sections initially for the 1998 report and then again as part of the channel deepening project, these are only for the section of coastline from the beginning of the rock seawall around to Shortland Bluff.

 There is no reporting on detailed modelling of wave and sediment transport processes across Lonsdale Bight. Early modelling (1998) was only indicative and trends unclear. More recent and detailed modelling appears to have been undertaken associated with the Channel Deepening Project. However, sediment transport results are only presented east of Queenscliff.

 There is a lack quantified analysis of long term and recent historical changes to the shoreline in the vicinity of the existing groynes that may be related to seasonal or longer term variations in

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sediment supply and transport as well as the subsequent influence those structures have had on local coastal processes in light of those variations. Historical changes are evident in photographs but this does not appear to have been linked to driving forces or particular events.

 There has been no detailed assessment of potential wave climate variations and shoreline evolution under climate change scenarios. Potential long term recession and associated risks with or without climate change have not been quantified.

There is a general understanding that the beaches are subject to fluctuations and similarly a broad understanding that those fluctuations are related to variations in the supply of sediment and the transport of that sediment along the shoreline under the prevailing coastal processes. The critical knowledge gaps of importance to inform ongoing management of the Lonsdale Bight foreshore relate to quantification of those factors.

The first important knowledge gap in this regard is quantitative information on beach fluctuations. Analysis of such fluctuations, ideally linked to variations in the prevailing processes, will provide information on the extent and likely durations over which those fluctuations may occur. This will help to inform and consider the hazards associated with fluctuations and whether they are tolerable or not in the short or long term. It will also help inform the understanding of the driving processes as well as the conditions that may be experienced during extended periods of little or no sediment supply as well as periods when the beaches are built up.

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5 Coastal Management Considerations

5.1 Risk Management Approach A risk assessment framework for coastal management is a robust methodology for dealing with outcomes that are uncertain or have limited data, or for impacts with uncertain timeframes. Uncertainties associated with natural variability of processes including future climate change presents huge challenges to government agencies and the wider community, who need to consider and manage future risks. Decisions made today are likely to have ramifications for up to 100 years (depending on the development), so consideration of an extended timeframe is essential, even though risks may not manifest for several decades. A full risk assessment study is beyond the scope of this project. However, an overview of the approach is presented below for consideration as part of future coastal management planning.

The approach enables agencies to prepare for impacts that are greater than expected, or manifest earlier than expected, by monitoring for trigger levels to implement strategies, developing short, medium and long term strategies, and using a suite of strategies to reduce likelihood and consequence from coastal risks. The use of a risk-based approach to managing coastal hazards is a requirement of most state guidelines in Australia, and accords with current international best practice for natural resource management.

Described below, and presented schematically in Figure 5-1, are the steps involved in a risk assessment (adapted from the Australian Standard for Risk Management ISO 31000:2009), adjusted to suit the coastal zone management process. It is considered a relevant approach for Lonsdale Bight given the uncertainties and natural variability of contemporary processes as well as the need for adaptation associated with potential future climate change influences.

 Establish the Context – the requirements of a coastal zone management plan typically as set by state guideline documents provides the context of the risk assessment and intended outcomes. The context, objectives and performance indicators / targets shall be tailored to the scenario in consultation with government agencies and other key stakeholders and community.

 Identify the Risks – namely, beach erosion and recession, coastal inundation and wave overtopping, and to a lesser degree sand drift and erosion at stormwater outlets. The risks have and will impact upon coastal values, which include cultural, recreational, economic and ecological values, typically identified during the literature review and consultation with stakeholders and community.

 Analyse the Risks – this involves considering the likelihood and consequence of the identified risks, to determine the overall level of risk (extreme, high, medium or low).

The likelihood of risks largely relates to the extent of coastal hazards, now and in the future. The likelihood of erosion and recession (incorporating existing processes and future changes in hazard extents due to sea level rise) and coastal inundation (including wave overtopping, and changes with future sea level rise) at the immediate, 2050, 2100 timeframes is typically determined based upon historical data, reports and numerical modelling capabilities.

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Lonsdale Bight Investigations Review and Options Overview 38 Coastal Management Considerations

Establishing the context

What are our objectives for Coastal Zone Management?

Risk Assessment Risk Identification

What are the built, natural and community assets at risk from coastal hazards?

Risk Analysis

What are the likelihood and the

consequence of each coastal risk? What is the level of risk (high, medium low)?

Risk Evaluation

What is a tolerable level of risk? Are there controls / mitigating ing Performance our Indicators? actions already in place?

andReview Monitoring Stakeholderand Community Liaison

rewe meet

Communication and Consultation Communicationand A Risk Management Options

What management strategies can we use to reduce the level of risk to a tolerable level? What are the costs and benefits of the strategies? At what trigger level do we implement the strategies?

Implement Management Strategies

Figure 5-1 Risk Management Framework (ISO 31000:2009) adapted to Coastal Zone Management

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The consequence of the risks will largely relate to the extent of existing or future development and the values (e.g. aesthetic, recreational, ecological, etc.) associated with land and assets along the shoreline, including the beach itself.

The type of impact (e.g. short term inundation compared with long term recession of land) is also considered when assessing the consequence of the different coastal risks. It is both the likelihood and consequence of coastal risks combined that determines the level of risk.

The consequence and likelihood are combined using GIS processing to determine and map the level of risk for assets and land in the coastal zone. Existing controls (e.g. by Council or other state agencies) that may reduce the level of risk are then considered and included as required. A register of the level of risk to various assets forms an output of the risk mapping process.

 Evaluate the Risks – in consultation with government agencies and other stakeholders, the level of risk that is deemed acceptable, tolerable and intolerable is determined. Coastal risks are prioritised and management effort shall be aimed towards the higher levels of risk (e.g. extreme and high) that are deemed intolerable.

 Manage the Risks – the process of developing coastal management options is directly related to reducing or eliminating intolerable risks. Tolerable (low) risks can be flagged for monitoring, with no further actions necessary. Management options can be designed to reduce the likelihood of the risks (e.g. planning setbacks to reduce the likelihood of shoreline recession impacts) or the consequence of the risk (e.g. emergency management to reduce the consequence of shoreline recession) or both.

Further cost benefit analysis is then used to determine which of the risk treatments will provide the greatest benefit (relative to cost) in treating the highest priority risks. Further, the cost benefit analysis ensures that other coastal management objectives are not compromised by the option. For coastal management, innovative strategies may be required to provide benefits across the community (social and aesthetic) and coastal ecosystems, within the existing legislative framework.

For strategies that involve monitoring to determine if/when future risk treatment works are needed, appropriate trigger levels are established for implementation.

 Implement Management Strategies (Risk Treatments) – A coastal zone management plan provides the forum to detail how the recommended management options (risk treatments) shall be implemented (costs, timeframes, etc.) and funded. Preferred strategies and options are then determined and implemented with monitoring to confirm their effectiveness and need for adaptation or response to triggers being reached.

All coastal management options have advantages and disadvantages and need to be assessed against a range of criteria such as:

 Environmental Impact, to identify where the option may compromise or enhance environmental values or have trade-offs with the surrounding environment;

 Social Impact and Community Acceptability, which is based upon assessment and general feedback from the local community on matters including beach amenity, access and public

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safety (it is recommended that specific community consultation be undertaken before proceeding with any major option);

 the ability for the option to be Reversible / Adaptable in the Future, which is particularly relevant where there is considerable uncertainty and/or long time frames for a future impact;

 Effectiveness Over time, to consider where an option presents a long term solution or a short term solution that would require additional management action or upgrades in the future;

 Legal / Approval Risk, to highlight the legislative and approval requirements (or impediments) to implementing an option within the current legal framework;

 The Technical Viability, to highlight where certain options may or may not be technically feasible or would require significant engineering (or other) investigations and construction / implementation capabilities; and

 Capital Cost and Recurrent Cost, with values based upon best estimates that would require confirmation based on detailed investigation and design before proceeding.

The approach adopted here is to identify and interpret information of relevance to the key issues and based on that understanding, identify potential options. Information is presented on generic and specific options with associated advantages and disadvantages as well as limitations for consideration as part of a future detailed risk assessment.

5.2 Key Issues and Objectives The key coastal management issues for Lonsdale Bight have been outlined in Section 3.5. They relate primarily to:

 The importance of the Marine National Park values and ensuring these are not compromised.

The processes are subject to uncertainty and natural variability into the future and therefore a risk based approach to coastal management as outlined above is considered to be warranted. Consideration has been given primarily to possible options for short and long term sand management (retention) to address the above issues. In the context of a risk management approach, consideration also needs to be given firstly to the risks and associated levels of tolerance to those risks as well as the importance of the MNP values in considering the need to implement specific works as part of future coastal management strategies.

Longer term strategies for adapting to climate change may need to consider the coastline in a somewhat different form. While uncertainties in the time frames and extent of such changes create challenges, they should be included where possible in future coastal management planning.

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5.3 Generic Options for Responding to Coastal Erosion There are two basic strategic approaches for dealing with the joint problems of erosion threat to development and loss of beach, namely:

 Allow natural erosion processes to occur and remove assets from areas prone to erosion; or

 Hold or improve the present coastal alignment by implementation of coastal protection in one of many ways.

Retreat or Do Nothing options

Often the best course of action is to do nothing and let coastal processes occur naturally. This is particularly the case where risks are low and a natural undeveloped buffer exists to accommodate erosion. Beach fluctuations can continue to occur and mostly a natural sandy beach will remain unless otherwise constrained. In this case the costs of expensive works which may have other adverse impacts are avoided.

Where development or assets are threatened, the option again exists to retreat by removing or relocating those assets and again allowing a natural sandy beach to evolve. If structures have been previously constructed to protect assets, these would need to be removed as well. While such retreat options can be effective in providing a natural sandy beach, they often come with substantial social and economic and sometimes environmental costs that need to be factored into a cost / benefit analysis.

Protection options

A range of generic erosion management options are available for consideration, which may be classified in terms of their consistency with natural coastal and environmental processes and the natural character and values of the coastline as follows:

“Soft” Options: Options which restore and/or preserve the natural character, behaviour and values of the coastal system. These will ensure the sustainable existence and natural character of the sandy beaches and dunes such that future erosion, both during short term storms and over the longer term, can be accommodated in a coastal buffer zone without threat to development requiring engineering works.

Soft options may include works aimed at restoration of the beach/dune system such as beach nourishment with sand or planning solutions that require development to be outside the zone of potential erosion.

“Hard” Options: Options that involve construction of works either to form a barrier to natural coastal erosion to protect development (seawalls) or to alter the natural processes to change the way in which the beach behaves (groynes and breakwaters).

Combinations of options or “hybrid” management approaches are also possible.

The most common feasible works options for overcoming shoreline problems include the following and are discussed in more detail below:

 beach nourishment with sand to restore the beach and dune system;

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 seawalls to protect coastal infrastructure;

 groynes to control the longshore movements of sand; and

 offshore breakwaters or submerged reefs to modify wave processes which erode the beach.

Such works options are generally costly, and the ‘hard’ structural options typically may have adverse side effects on the beach system. Ongoing maintenance requirements must be considered in both the design and financing. Experience indicates that careful design in full cognisance of the prevailing coastal and ocean processes and the short and longer term effects is essential for success and cost-effectiveness of such works.

An overview of the characteristics and general considerations associated with these protection options is provided below.

5.3.1 Beach Nourishment Beach nourishment refers to the direct placement of additional sand onto the beach by pumping or by conventional earthmoving techniques, with the primary intent to offset sand volumes that have been lost from the beach unit. The main driver for beach nourishment can be to preserve the existence of a recreational beach or restore an adequate buffer zone width to accommodate natural beach fluctuations.

Beach nourishment is in particular an effective measure to control erosion at shorelines that suffer from a progressive loss of beach material. In these situations, the nourished sand effectively replaces the deficit of sand that is causing the erosion.

The quantity of sand required will be dependent on the design philosophy with respect to the level of initial and ongoing protection and the use of structures to enhance the longevity of the works. Sufficient sand should ideally be provided to be able to accommodate short term (storm) erosion and a period of long term recession associated with longshore sediment transport differentials and sea level rise.

The design of any nourishment program must be undertaken carefully, recognising that renourishment may be required from time to time to provide ongoing protection. Provision should be made for the placed sand to extend across the full beach profile to nourish depleted nearshore areas as well as the upper beach, the total quantity of sand being determined accordingly. If the sand is placed only on the upper visible portion of the beach, redistribution will quickly occur to establish an equilibrium beach profile giving the impression that the sand is ‘lost’ and the project is a failure. In such a case, the sand is, in fact, not ‘lost’ but remains in the active system providing an overall net gain commensurate with the quantity placed after cross-shore distribution.

Dune construction and stabilisation works to prevent sand loss due to wind erosion usually needs to form part of any substantial beach nourishment scheme aimed at restoring the beach and dune system. In that case, it would incorporate design provisions to prevent dune overtopping and oceanic inundation as well as to accommodate the effects of climate change including sea level rise. Where the aim of the nourishment is to re-establish a beach in front of an existing seawall without provision of a dune, the need for stabilisation works such as establishment of native dune vegetation would depend on the potential for wind erosion resulting from the works.

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While beach nourishment may affect the ecological values of the beach and nearshore areas, it needs to be recognised that the nourishment sand would be placed in the active zone where the natural environment is one of substantial fluctuations and disturbances to which the ecological communities adapt naturally. The nourishment would effectively rebuild the beach. As such, while there may be some short term ecological impacts, in the longer term the environment will generally adapt and recolonise to behave as a natural beach system.

One of the inherent advantages of beach nourishment is that it maintains the natural character and recreational amenity of a beach while also providing protection to coastal assets. As such, where the beach is severely depleted, it provides many intangible benefits to the general community, as well as a direct economic benefit to those businesses that rely on tourism and the presence of a usable beach.

A disadvantage of beach nourishment is that sand will continue to be eroded if the shoreline recession is progressive and ongoing maintenance nourishment may be required to maintain the beach. This may be seen by some as a temporary solution and a waste of resources.

Furthermore, identification and access to sources of suitable nourishment sand is often a key issue, as is cost (dependent on the applied volume, the sand source and method of placement). Transport of sand to the beach is generally most cost-effectively achieved by dredging procedures. The use of trucks to import large volumes of sand is usually slow and costly, with adverse impacts on the local community and road infrastructure.

5.3.2 Structural Protection Options Structural options provide protection of property against ongoing erosion either directly through the construction of a seawall or by rebuilding of the beach through the construction of groynes. They are options that could be considered in the event that sufficient beach nourishment sand is not available and/or retreat options are not viable. However, there are always some adverse impacts of such an approach where no additional sand is provided, as outlined below.

Such structures would typically be of flexible rubble mound design with rock being sourced and trucked to the site from quarries in the region. While they may be effective in protecting property or providing a localized wider beach, they are generally accompanied by associated costs related to adverse impacts on the adjacent beaches. This cost is typically made up of direct costs associated with lost income from the tourist industry and other intangible costs associated with the natural coastal amenity, beach access, loss of recreational beach area and degradation of ecological values.

Revetments

Revetments are a common feature around Port Phillip Bay and are built with the intent of providing terminal protection against shoreline erosion. Revetments are robust structures constructed along the shoreline which provide a physical barrier separating the erodible material immediately behind the structure from wave and current forces acting on the beach itself. They are typically constructed of loosely placed rock or as a masonry/concrete (vertical) wall.

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Revetment walls are generally successful at controlling shoreline recession. However, revetments can transfer erosion of the adjoining beach by locking up sand reserves in the dunes, and prevent a new beach from building up.

By constructing a revetment wall along the existing erosion escarpment, sand landward of the wall is isolated from the active beach system and the volume of sand available for normal beach movements is limited to that seaward of the wall. During storm events, when sand is transported offshore, limited sand volume stored in the upper beach can be quickly eroded, resulting in the reduction of beach levels. When waves break against the wall, the loss of sand is further hastened due to increased turbulence at the toe of the seawall, leading to further lowering of beach. Scour and lowering of the beach in front of the wall ultimately exposes it to higher wave attack. This may compromise the accumulation of sand during periods of accretion and prevent the re-establishment of a beach in front of the seawall all together.

Furthermore, on a receding shoreline, a seawall becomes progressively further seaward on the beach profile over time. This leads to a gradual increase in the quantity of sand effectively lost from the beach system, with:

 lowering and eventual loss of the beach in front of the wall; and

 exacerbation of the erosion on the downdrift end of the wall where the losses are transferred and concentrated.

Groynes and Artificial Headlands

Groynes and artificial headlands are impermeable structures constructed at right angles to the shoreline and extend across the beach and the nearshore surf zone. Their function is to trap sand moving along the shoreline under longshore transport processes to build up and stabilise the alignment of the beach on the updrift side. By necessity they starve the beach of sand supply on the downdrift side causing erosion.

The sand trapped on the updrift side provides a buffer of sand to accommodate short term storm erosion and a recreational beach. The shoreline alignment will also change providing greater stability and reduced long term erosion immediately updrift of the structure. The extent of accretion and length of shoreline affected is dependent on the length of the structure as well as the characteristics of the longshore transport processes. Generally, the longer the groyne, the more sand it will trap over a longer distance with decreasing influence away from the structure.

However, there is a physical limit to the length of shoreline affected and therefore a number of structures may be needed if substantial benefit or protection is required over a long stretch of shoreline. In such a case, there is a balance between the length and spacing of groynes that needs to be optimised as part of a detailed design process.

An artificial headland is a substantial groyne type structure that has a physical width at its head in comparison to a conventional narrow groyne. It is believed that this width alters the mechanisms of sand transport past the end of the structure and may allow a wider/longer beach to be retained on the updrift side for the same protrusion offshore. This could have the benefit of minimising the need for, or maximising the spacing of, additional structures to provide protection for a long stretch

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of coastline. However, such headland type structures would be larger and more expensive to construct and conflict with the values of the Marine National Park.

Groynes or artificial headlands can thus be used to rebuild a beach and stabilise the shoreline against ongoing recession on the updrift side. However, in the absence of other works such as beach nourishment, this comes at the cost of exacerbated erosion on the downdrift side to where the erosion trend is transferred.

Another consideration associated with groynes is their potential visual intrusion to the vista of a long sweeping beach and interruption to direct access along the beach. There are various design options with respect to the style and crest height of the structures that could be considered to minimise such adverse effects.

5.4 Review of Previous Works

5.4.1 Historical Seawalls and Groynes As discussed in Section 3.3, extensive structural works have been carried out in the Lonsdale Bight compartment in response to erosion threats and in an effort to retain a usable sandy beach. Seawalls have been constructed which commenced with a masonry wall at Point Lonsdale Front Beach and have progressively been extended to the north as erosion continued. Near the Royal Park Caravan Park, the wall continues as a rubble mound seawall which was again gradually extended up to its present end at Dog Beach near Murray Road.

The seawalls have been effective in preventing further recession of the shoreline and protecting the land and assets behind. However, retention of a usable sandy beach in front of the walls has been an ongoing issue. Groynes of various forms have been built over many years in attempts to retain a beach. As reported by Bird 2011, storms in 1934 stripped Front Beach at Point Lonsdale and exposed underlying outcrops of dune calcarenite rock, as well as cutting back the cliff of dune sand and calcarenite. A number of short, low level timber groynes were constructed at Front Beach in 1935 prior to the commencement of the masonry seawall in an attempt to retain a sandy beach. Historical photographs do not show any significant updrift build-up of sand against one side of the groynes although the horizontal planks appear to be buried in the upper part of the beach. The width of the upper beach appears narrow and the Foreshore Erosion Board (1936) found that these groynes failed to retain a wide beach (Bird 2011).

The masonry seawall was extended behind these groynes between 1939 and 1947 and a 1950 postcard shows a lowered beach between derelict groynes (Bird 2011). Other historical photos uploaded on the Friends of Point Lonsdale Lighthouse Reserve Facebook page also show the beach at a very low level in front of the wall and some of the groynes in disrepair. Conversely there are also photographs at times, possibly somewhat earlier, with substantial sand on the beach and essentially all of the horizontal planks of the original groynes buried.

Numerous short timber groynes of another design were subsequently built in front of the seawall with 8 being evident in a 1982 photograph. These were relatively closely spaced and photos show the central groynes as having vertical planks with gaps between to allow sand to pass through. Again there is no evidence of significant updrift accretion against one side of these groynes. The

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upper sand levels appear to be low with very little beach in front of the masonry wall at high tide (Bird 2011).

It is evident from the reports reviewed that the timber groynes were subject to deterioration and considered ineffective at retaining sufficient beach volume. Historical photographs indicate that the low level permeable nature of the early groynes did not result in substantial updrift trapping of sand and there were times with essentially no beach. The historical photos also show periods, particularly in early years before the initial masonry wall was extended, where there is a substantial beach in front of the initial wall and all of the horizontal planks on the groynes are buried.

It is therefore considered that during the period with the initial timber groynes, the beach was subject to fluctuations in sand supply and erosion associated with storm events. In periods of presumably high sand supply, the beach was in good condition with sand essentially ‘swamping’ the groynes. However, during storms or when supply was limited, the beach was significantly lowered and the short permeable groynes were ineffective in retaining a beach in front of the wall. The timber groynes also deteriorated and suffered damage over time.

5.4.2 Existing Groynes With beach levels low, the Vantree 1998 Coastal Process Investigation was undertaken to provide a technical basis for the development of better strategies for coastal and foreshore protection of the area. In particular, short and long term management strategies were required to address the shortage of sand at Point Lonsdale Front Beach. Following a detailed investigation, wave modelling of two options was presented:

 A single long (200-300m) groyne extending out from the northern end of the Point Lonsdale headland.

 A series of four shorter (100m) groynes spaced along the foreshore. The southernmost groyne is shown extending out from the Point Lonsdale Headland with the other three spaced along the Front Beach area.

The report states that shorter groynes would be ineffectual. The detailed report (Lawson and Treloar 1998) that supports the Vantree summary report, indicates that wave modelling of the above options was undertaken to demonstrate that a suitable groyne option could be developed. It also states that the investigations were not intended to present a definitive design for the groynes and that other factors need to be considered before construction of groynes could be recommended. These included whether there is sufficient supply of sand moving past to maintain the beaches.

It is understood that following on from this, the old timber groynes were removed and the decision was made to initially construct two hybrid rock/timber impermeable groynes and monitor to determine whether any additional foreshore protection works were necessary. The northern (50m) and southern (70m) groynes were constructed in 1999-2000. No information has been sighted on the design and consideration of the location of these two groynes and they appear to be close to 2nd and 4th groynes (south to north) in the abovementioned wave modelling examples.

The southern groyne was damaged in a storm soon after construction and there were subsequent investigations and reports surrounding the concept design, design criteria and the validity of the

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design methodology used. The two groynes were reportedly successful in trapping and increasing sand levels. However, a small section of shoreline in between the two groynes did not accrete and at this location there was still insufficient sand in front of the wall for recreational amenity and to assist protection of the wall.

A 3rd groyne was subsequently constructed in 2005 between the two original groynes but closer to the southern one. It was designed and built as a low crested rock groyne 52 m long with the previous hybrid rock/timber design being abandoned following observed issues. The above three groynes remain today (2016).

While a detailed investigation of the performance of these groynes has not been undertaken, a qualitative review of Nearmap aerial photography since 2009 indicates fluctuations in beach level, width and extent along the shoreline in the vicinity of the groynes (see Figure 3-8). Similar to the discussion above relating to the original timber groynes, there are periods of apparent high beach levels presumably during periods of high sand supply and conversely periods where the beach levels are low when supply is limited. However unlike the permeable timber groynes, the present day impermeable groynes retain a wedge of sand on the updrift (southern) side when sand levels are low elsewhere (as at present). These wedges of sand provide a usable recreational beach, albeit small at times, and afford protection to the seawall behind. However, there remain sections of the shoreline where there is essentially no usable recreational beach and the wall is exposed to direct wave attack at high tide.

While the groynes are impermeable to sand passing through, they are low crested and allow waves and sand to spill over particularly at high tide and during storm events with elevated water levels. This has the advantage of allowing some sand to bypass through to the next compartment (see Figure 5-2). However, it also limits the amount of sand that is able to be retained on the updrift side of the groyne.

Figure 5-2 Southern Groyne Sand Bypassing (September 2016)

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It is understood that for the groynes as originally designed and constructed, wave runup under prevailing conditions pushed and built up the sand adjacent to the groyne to the extent that it was spilling over the top of the seawall behind. This added to maintenance issues for the path behind. It should be noted that the crest of the seawall is RL 2.7m CD which is only about 0.9m above HAT.

It is also understood that the original 2 groynes were constructed to RL 2.15m CD at the upper inshore end and these have since been cut down to about RL 1.5m CD to reduce the sand build up and ingress over the seawall behind. This new groyne crest level is around MHHW tide level and about 0.3m below HAT. Accordingly wave action at high tide will regularly bypass sand over the groyne and limit the build-up on the southern side. As well as limiting the height the sand will build up to, it will limit the width of beach at the groyne and the distance the wedge extends along the shoreline.

The acute angle of wave attack, particularly just north of the Point Lonsdale headland and when sand supply and associated sand levels are low, results in a relatively acute angle for the updrift sand wedge which will typically evolve to the dominant wave angle. While conceptually a longer groyne will trap more sand and retain a wider/longer updrift beach, the low inshore crest elevation allowing bypassing at the upper beach end somewhat negates the effect of the length. The effect of the angle of wave approach and height of the groynes can also be seen with the shorter central and northern groynes appearing to hold sand for a longer distance along the shore and with a larger fillet of sand down drift than the longer southern groyne (see Figure 3-8). These two groynes are further around the curved shoreline where the angle of wave approach is less.

The beach at present (2016) appears to be at a relatively low level and while there are sections with essentially no usable beach in front of the seawalls, the groynes are being effective in retaining updrift wedges of sand along some parts of the foreshore. It is reasonable to conclude that under these low supply conditions, there would be very little usable beach in the absence of the existing groyne structures. This is also exemplified by the lack of beach in front of the remaining seawall extending around to Dog Beach.

Furthermore, while the existing groynes are being effective in retaining sand, it is evident that their spacing in relation to their length and height is not optimal under low supply conditions with sections of low sand in between.

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6 Options Overview

6.1 General Approach Defining and assessing the risks based on an understanding the coastal processes including natural variability is a necessary first step in determining the need for and nature of coastal management options. While there is a broad understanding of the issues facing future coastal management of the Lonsdale Bight foreshore, a detailed assessment of the hazards and associated risks is yet to be undertaken. This would typically include identification of the risks, analysis of the associated likelihood and consequences, and evaluation of what might be tolerable in prioritising issues towards which management efforts should be aimed. Different stakeholders including community groups will have varying interests and requirements and it is important that these are taken into consideration as part of the assessment process. A clear understanding of the level of risk and priorities in terms of timing and location are important for consideration and implementation of options to manage the coastline.

6.2 Options for Point Lonsdale Front Beach (Area A)

6.2.1 Broad Considerations Fluctuating sand levels and particularly issues surrounding periods when sand levels are low are of increasing community concern along Point Lonsdale Front Beach. However, a full assessment of those risks including areas of most importance has not been undertaken. It is also evident that the height of the old masonry seawall is such that it is presently subject to overtopping by waves particularly during storms with elevated water levels. Such occurrences will potentially increase in frequency and severity with any future sea level rise thereby exacerbating the threat of erosion and damage to land and facilities behind over time unless further protection works are carried out. Decisions surrounding future coastal management options need to consider the risks and consequences of this as well as low beach levels and the potential implications for the Marine National Park in prioritising future strategies.

Broad considerations surrounding fluctuating sand levels and associated management options are outlined below. The implications of these with respect to climate change influences including sea

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level rise are also discussed. However, they are all in the context of maintaining the existing masonry seawall.

It should be recognised that the existing seawall is already prone to overtopping by waves as outlined above and that consideration will also need to be given to options for managing this, particularly with the potential for future sea level rise. Such options are not presented in detail here but could include major modifications to the wall in terms of its height, type and alignment to protect land and facilities behind. This could be with or without options to maintain sand in front of the wall which is likely to become more difficult as sea level rises. Consideration will need to be given to what needs to be protected and whether retreat in some areas can be accepted including relocating the pedestrian pathway behind the existing seawall. It should be recognised that the design requirements will be greater and the potential to maintain sand in front of the wall will be harder the further seaward it is constructed. Such works will involve major community, design and economic considerations and while the time frame surrounding the need for implementation is uncertain, the low crest and age of the existing seawall are such that the potential need in the not too distant future should be factored into planning decisions.

In terms of managing present day fluctuations in sand levels, it has been identified that the sediment supply to the Front Beach foreshore is intermittent while the processes that transport sand along the beach and away are more consistent. It is evident that there have been periods when the supply of sand exceeds the transport capacity along the shoreline with associated build up and stability of the beaches being observed. During these periods, issues surrounding low beach level are minimal. Conversely, there have been periods where the supply has been low or negligible and the transport capacity along the foreshore has been greater resulting in lower beach levels and associated issues.

Furthermore, in times when the sand levels are generally low, the present groyne structures do retain a sandy upper beach, albeit sometimes small in area. Accordingly, issues associated with low sand levels do not apply along the full section of the shoreline. The extent and time frame of low beach levels and the level of tolerance to associated risks are therefore key considerations as well as priority areas for management of those risks. It also needs to be recognised that while maintaining a sandy beach through artificial works offers certain benefits, not adversely impacting the values of the Marine National Park within which the beach lies is also an important consideration.

The issues surrounding low beach levels relate primarily to limited areas of sand for recreational purposes, direct wave attack and potential damage to the old masonry seawall along the foreshore and associated economic and safety considerations. The periods of low beach level are generally related to sand being transported away faster than it is supplied around Point Lonsdale. Options to retain a sandy beach in the longer term therefore require either:

 The sand supply to be artificially supplemented so that it arrives at least at the same rate and quantity that it is being transported away; or

 The sand to be artificially retained with the rate of transport along the foreshore and away being modified to match the rate of supply.

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Furthermore, if detailed assessment of options indicates that long term retention of sand is difficult to achieve, consideration can be given to options which provide shorter term benefits. Again the level of tolerance and acceptability of an option which may provide only short term benefits needs to be weighed up against a longer term option that may have other constraints.

6.2.2 Identification of Options At present there are four main areas at Point Lonsdale Front Beach where sand levels are low in front of the masonry wall and consideration is required with respect to future management:

 North of the Point Lonsdale headland (within Area A(i)) – extending from the beginning of the seawall northwards to the sand retained updrift of the southern groyne. Sand levels in this section (~150m) are often very low with the seawall being directly exposed to high wave energy and wave overtopping during storms with high waves and elevated water levels.

 Immediately north of the southern groyne (within Area A(ii)) – this is only a small section (~50m) where the influence of the updrift accretion of the middle groyne often does not extend and the beach in front of the seawall is sometimes low.

 North of the central groyne (within Area A(iii)) – this section (~100m-150m) is dependent on the extent of updrift accretion retained by the northern groyne and is influenced by the relatively wide spacing between the central and northern groynes.

 North of the northern most groyne (within Area A(iv)) – there is a section (~200m) prior to the beginning of the rock seawall where there are no structures to retain sand and the presence of a beach in front of the masonry seawall is totally dependent on the supply of sand.

Maintaining a sandy beach along the full length of Point Lonsdale Front Beach is challenging as evident by various attempts over the last century. The processes are complex and variable with technical solutions not being simple and subject to varying degrees of cost and potential success. Furthermore, the social values of beach amenity and public usage together with public safety need to be managed in the context of the somewhat related environmental values of the area including those of the Port Phillip Heads Marine National Park which extends to High Water Mark on the beach.

Potential options will all have different levels of compliance and implications with respect to the above guiding considerations. In addition, different stakeholder groups will have varying priorities associated with specific values and constraints. As such, it is considered that no one single option will completely satisfy all stakeholders. Therefore the strategy to manage the issues will need a level of balance and potential compromise with respect expectations centred on minimising impacts and achieving an outcome that is acceptable to all.

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The five broad options identified are categorised as follows:

 Option 1: Do nothing and accept natural variability (short and/or long term)

 Option 2: Local redistribution of sand (short term)

 Option 3: Targeted beach nourishment (short term)

 Option 4: Groyne field modification - without and with beach nourishment (long term)

 Option 5: Offshore breakwaters (long term)

Detailed description of each broad option and variations within are provided in the following sections together with their advantages and disadvantages in the context of the four main assessment criteria:

 Social values and community expectations with respect to beach amenity, public use and public safety;

 Environmental values particularly with respect to the Port Phillip Heads MNP;

 The technical viability and likelihood of success in achieving desired outcomes; and

 The capital and ongoing costs to implement the strategy.

6.2.3 Analysis of Options

6.2.3.1 Do Nothing (Short and/or Long Term Option) Overview

The “Do Nothing” option has been included for consideration as part of a detailed risk assessment in which it may be determined that the level of risk is low or tolerable over a period of time for some or all of the foreshore given the natural variability of the processes. As such it may be viewed as a short term and/or long term option depending on that risk assessment.

The existing three groynes are retaining sand which provides a usable beach and a degree of protection to the masonry seawall behind for about 25% of its length. This will continue if the present groynes are maintained in terms of their effectiveness. It is also evident that beach levels along Front Beach fluctuate in response to variations in the supply of sand around Point Lonsdale and the prevailing local coastal processes. There have been periods with substantially more sand than at present and a usable beach extending along much of the foreshore. Accordingly, if no specific actions are taken, it is possible that at least parts of the presently low beach areas will build up again albeit on a temporary basis.

The beach is presently relatively low in areas in relation to natural variations (subject to further investigation). With the “Do Nothing” option, the issues associated with amenity, safety and

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seawall stability will remain in these low beach areas until such time as future build up occurs again. These issues will also return in future periods of beach lowering.

As such, there is uncertainty and risk associated with how long it may be before (or if) sand build up occurs again as well as when and for how long it may occur again in the future. It does not address the issue of existing wave overtopping of the seawall and the likelihood and consequences are also potentially enhanced with future sea level rise. The area of greatest exposure with respect to low levels of sand fronting the seawall is immediately north of the Point Lonsdale headland at the beginning of the seawall (Area A(i)). This area is exposed to high wave energy at a steep angle to the shoreline with reflections off the seawall. Accordingly, sediment transport potential is high with limited potential to retain a sandy beach.

The “Do Nothing” option has no immediate direct costs for works but has potential increased consequential costs associated with ongoing seawall inspections and maintenance. By allowing the processes to continue naturally, albeit with the influences of the existing structures, the Marine Park values will not be adversely affected.

Considerations for the “Do Nothing” option therefore centre on whether risks and the potential consequences of the issues can be accepted in some or all areas given the uncertainty of future trends.

The advantages and disadvantages are summarised below.

Advantages

 No direct impact on Marine National Park values

 No immediate direct expenditure

 Sand fluctuations allowed to occur naturally within constraints of existing structures

 Others as determined by stakeholders

Disadvantages

 Existing diminished amenity remains in low beach areas until sand build up occurs and will return in times of future depletion

 Existing safety concerns remain in low beach areas until sand build up occurs and will return in times of future depletion

 Potential increased seawall inspection and maintenance costs in low beach areas, particularly if it occurs for extended periods

 Uncertainty with respect to the timing and extent of future build up of sand in presently low beach areas

 Does not address existing seawall overtopping or the enhanced risk of seawall overtopping and instability with future sea level rise in areas prone to low levels of sand

 Others as determined by stakeholders

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6.2.3.2 Localised Redistribution of Sand (Short Term Option) Overview

The beach conditions vary along the shoreline and evolve under the prevailing coastal processes. The three present groynes retain sand on the updrift (southern) side and as discussed above, there are presently areas with a usable beach and other sections where the sand levels are low. Some of the identified issues relate to beach amenity and public safety. These are most prevalent during summer months when beach usage is high.

Sand movements are greatest during storm events with large waves and elevated water levels. This typically occurs during winter months and can leave the beaches in an eroded state. The build up of sand and recovery after storms is typically a gradual process which occurs under milder wave conditions.

If there are areas where sand is particularly low, consideration could be given to a local redistribution of the available sand as an adjunct to the “Do Nothing” option depending on stakeholder priorities. This could involve transfer of sand from the accreted area adjacent to the groyne and spreading it back along the beach further to the south or placing it on the downdrift (northern) side of the groyne in the low areas of concern.

While such works may appear to improve amenity and safety in local areas, there are certain limitations which need to be understood and considered. As no additional sand is added into the active system there will be no overall net gain in terms of supplementing the natural supply or adding available beach area. In fact the area of usable beach at high tide may reduce if the sand is spread into and remain in areas below high tide.

The modified beach will also be out of equilibrium with the prevailing conditions and the controlling influences of the groynes. Waves will continue to move the sand in the system and the beach configuration will evolve back to be in dynamic equilibrium with the incident conditions. This could happen rapidly in a matter of days or a single storm event depending on the conditions that occur and therefore any benefit will be temporary and potentially short lived. It is therefore considered as being only a short term option and may need to be continually repeated as and when needed if its temporary benefits are considered effective. While the costs of such works are relatively modest, it may be perceived as being a waste of time and money in the event of rapid redistribution.

The limited and temporary nature of redistribution works are such that they do not address the issues surrounding the overtopping and long term stability of the seawall or the influences of future sea level rise.

The advantages and disadvantages are summarised below.

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Advantages

 No long term impact on Marine National Park values

 May provide some localised temporary benefits in terms of amenity and safety

 Only small direct expenditure

 Others as determined by stakeholders

Disadvantages

 Does not provide any long term benefit or net gain

 May reduce the useable area of beach above high tide

 Likely to be short lived and may be quickly reversed rendering the expenditure ineffective

 Does not address issues surrounding overtopping and long term stability of the seawall or the influences of future sea level rise in low sand areas.

 Others as determined by stakeholders

6.2.3.3 Targeted Beach Nourishment (Short Term Option) Overview

Beach nourishment is the practice whereby external sand reserves are brought in to widen the beach/dune system, remediate storm erosion impacts and restore beach amenity. It is dependent on the availability and practicality of a suitable source of sand and is typically used to supplement sand supply when the erosion is related to gradual differentials in the rate of longshore transport along the coast.

While the erosion at Point Lonsdale Front Beach is related to variability in the supply of sand, a beach nourishment programme alone is not considered viable to supplement the intermittent supply of sand. It is evident that there are extended periods when the transport capacity along the shoreline exceeds the supply. Therefore to be effective in the long term, controlling structures to hold the nourishment sand and/or regular renourishment to continually top up the supply to match the transport rate would be required. To do this fully and rely solely on beach nourishment to retain a sandy beach in the long term is not considered to be practical or economically viable.

However, minor targeted beach nourishment may be considered in conjunction with the existing groynes or additional groynes as discussed below. In a similar fashion to the discussion above, instead of carrying out a local redistribution of sand to address areas of concern prior to the high usage season, consideration could be given to importing additional sand from an external source. This would have the advantage of adding sand to the active beach system and providing a net overall gain. Existing areas of sand build up would not need to be compromised and the quantity would not be constrained by that already available on the beach.

While adding sand provides benefits to the overall beach system, it will not be a long term solution and the beach will again evolve to a dynamic equilibrium with the prevailing conditions. Under normal conditions, the benefits would be expected to last longer than local redistribution and longer again if more sand is added. However, the risk remains that it may be quickly transported away

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from the placement location in the event of a major storm. As such it is still only regarded as a temporary short term solution but could be used to target key areas of concern on a regular as needed basis prior to the summer season.

The areas most likely to benefit the longest from such works are the low areas immediately to the north of the existing groynes. While sand could also be placed in the section just north of the headland (Area A(i)), this area is the zone of highest transport potential and therefore the risk of it being transported way quickly is the greatest.

The cost and viability is also dependent on a suitable source of sand which is subject to further investigation. Given the presence of the Marine National Park, it is considered likely that the sand would need to be trucked in. The sand would also need to match the existing beach sand and such potential sources could include land based sand pits with similar characteristics. It is understood that the sand in the accretion areas to the north of Queenscliff are likely to be too fine.

The cost would be somewhat greater than local redistribution of sand and the risk of only short term benefits remains unless larger scale regular nourishment is carried out. The limited and temporary nature of minor nourishment works is such that they do not address the issues surrounding the overtopping and long term stability of the seawall or the influences of future sea level rise. Again this could be improved with larger scale more regular nourishment on an as required basis. However, the scale of nourishment required to meet objectives may not be practical or economically viable.

The advantages and disadvantages are summarised below.

Advantages

 Implications for Marine National Park values likely to be in the range of natural variability

 Will provide some localised short term benefits in terms of amenity and safety

 Additional sand will benefit the overall beach system

 Larger and more regular nourishment will enhance the benefits

 Others as determined by stakeholders

Disadvantages

 Will not provide any long term benefits unless larger regular nourishment is carried out

 Cost and viability will be dependent on a suitable source of sand

 Sand will most likely need to be trucked in with associated social implications

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 The potential to be short lived and quickly reversed rendering the expenditure ineffective

 Does not address issues surrounding overtopping and long term stability of the seawall or the influences of future sea level rise in low sand level areas unless larger and more regular nourishment is carried out.

 Others as determined by stakeholders

6.2.3.4 Groyne Field Modification (Long Term Option) Overview

As discussed in Section 5.4.2, it is evident that the existing groyne structures have demonstrated to be an effective means of retaining sandy sections of beach under low supply conditions. Sand is trapped on the updrift side of the groynes and the beach realigns itself so that the transport of sand matches the lower supply rate. In times of low supply, the retained fillet beach alignment relative to the seawall alignment will be at a relatively large angle and the volume retained at its minimum. With increased supply of sand the beach will rotate around and out with more sand trapped along the shoreline.

In isolation, a single groyne will retain sand along a limited section of shoreline. A properly designed groyne field with multiple structures can act to retain sand in compartments along the shoreline and provide a sandy beach over the distance of the groyne field. In this regard it can be regarded as long term solution for the section of foreshore covered.

The success of a groyne field is dependent on a suitable supply of sand to fill the groynes. If the natural supply is limited, artificial beach nourishment could be considered to provide the sand with added benefits of minimising downdrift erosion as discussed below. There is also a risk of sand being transported offshore during storm events and the beach being depleted until it returns. While the erosion can occur quickly, the return of the sand will be gradual over a much longer time frame and can be constrained by supply rates. While the seawall behind will provide protection during such events, the implications for long term retention of a sandy beach should be investigated further.

It is considered that a properly designed and complete groyne field, potentially with some associated beach nourishment, is likely to meet the desired objective of retaining a sandy beach in the long term. While the amenity will be improved with a sandy beach, the groynes will generate greater visual intrusion to the vista along the beach. This can be reduced with low crested shorter groynes although such a design would require more groynes.

Groynes by their nature trap sand and transfer that loss of sand further drowndrift (north) along the shoreline. Such impacts have already been manifested from the existing groynes and the shoreline has responded accordingly. The shoreline to the north and east is protected by a rock seawall and been exposed to and adjusted to periods of low supply over many years. The volume of sand that would be trapped by additional groynes along Point Lonsdale Front Beach will be small in comparison to the volume in the system. Ultimately the sand transport through the system will adjust to the rate of supply around Point Lonsdale which will not be altered. Accordingly any impact to the beaches to the north including Dog Beach will be negligible. Furthermore, the use of

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beach nourishment to artificially fill any new groynes when constructed would minimise any such small impact.

The advantages and disadvantages are summarised below.

Advantages

 Will provide long term benefits in terms of added beach amenity, safety and protection for the seawall behind with reduced maintenance costs for the seawall if properly designed and constructed

 Use of beach nourishment in conjunction with groynes will enhance the benefits and minimise potential impacts

 Groynes and semi-permanent sand will add other environmental and social values

 Can be adapted to address the influences of future climate change including sea level rise although other adaptation strategies surrounding raising and/or relocating the seawall and pathway behind will also be required

 Others as determined by stakeholders

Disadvantages

 Implications for Marine National Park values will need to be assessed in terms of areas permanently covered

 Will add further visual intrusion into the vista along the shoreline

 Potential for downdrift erosion although this is likely to be negligible given the presence of seawalls and previous works and can be mitigated with beach nourishment but at an additional cost

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 High initial capital cost if the full length of Front Beach is to be addressed with a number of groynes and increased ongoing maintenance costs

 Others as determined by stakeholders

Design Considerations

Potential modifications to the existing groyne field to achieve the desired objectives are outlined below. While the reports reviewed provide limited information to inform the design of groynes, interpretation of the behaviour of the existing groynes does provide an insight into potential future works. Given the constraints and interpretation of historical performances outlined in Section 5.4.2 it is considered that the groynes should have the characteristics as outlined below. Further investigations and detailed design will be required to inform some of these.

 Be impermeable – this will allow the build-up and retention of sand on the updrift (southern) side.

 Be low crested – this will allow bypassing of sand over the top of the groyne at the inshore end and minimise the ingress of sand on to the path behind the due to the low crest level of the seawall. It will however, limit the area of usable beach at high tide. A higher crest elevation would allow the beach to build up higher, wider and further along the shoreline but with the need to manage the ingress of sand on to the path behind. A low crest also limits the visual intrusion of the vista along the shoreline.

 Be relatively short (~50m) – in accordance with and to match the low crest condition. A longer groyne will not necessarily hold more sand under low supply conditions if the crest elevation is low and allowing bypassing at the upper end. This will also limit the further visual intrusion of the vista along the shoreline as well as intrusion into the Marine National Park.

 Be of rubble mound (rock) construction with an impermeable core – which can be designed to withstand the prevailing conditions and minimise ongoing maintenance needs and costs. While alternative material types such as timber and geofabric bags could be considered, experience has shown that these are more prone to damage and have higher ongoing maintenance costs.

 Be optimally spaced – the spacing needs to be in accordance with the crest elevation and length design criteria to provide a usable beach along the foreshore during low supply conditions. A better understanding of the variability in the sediment supply will also aid consideration of the spacing.

It is evident that the spacing of the existing groynes in relation to their length and height is not optimal under low supply conditions with low sections of beach occurring between the groynes. If the design process was undertaken again with the present knowledge, a groyne spacing somewhat less than that between the existing southern and central groynes would be more likely to retain sand along the full section between.

An indicative groyne configuration is illustrated in

Figure 6-1 building on and utilising the existing groynes. Ideally some of the spacings would be less. However, this would necessitate the removal and relocation of one or more of the groynes and the inclusion of an additional groyne which becomes a cost consideration. With the spacing as

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shown, there may still be small sections (eg north of the existing southern groyne) where the beach remains low but this could be potentially managed with one of the shorter term options described above.

If a complete groyne field is not to be constructed, consideration will need to be given to the number and priority locations of new groynes based on need and value with input from all stakeholders. In Figure 6-1, five new groynes are illustrated with the numbering being for reference purposes and not a suggested priority.

Groynes 1 and 2 (Area A(i)) are in the embayment just north of the Point Lonsdale headland where wave exposure and reflections off the seawall and associated sediment transport potential is greatest. This area is somewhat different to the section of coastline further north where the existing groynes have been constructed. The higher wave energy and different alignment of the shoreline means the behaviour of newly constructed groynes in this area is likely to be different to the existing groynes. Design of any works in this area would therefore require further investigation to inform the concept and detailed design as discussed below.

Groynes at locations 3 (Area A(iii)), 4 and 5 (Area A(iv)) on the other hand could be expected to behave in a similar fashion to the existing structures and therefore information gleaned from their historical behaviour could be used to inform design. Such information may also help inform the possibility of reducing the length of the existing southern groyne for which the outer section appears to be redundant.

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Figure 6-1 Indicative Groyne Field Modification

"I:\B22316_I_GML_Queenscliff\JPG\161124\Figure 6-1.jpg"

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6.2.3.5 Offshore Breakwaters (Long Term Option) Overview

Offshore breakwaters could be considered as an alternative means of altering the wave climate and longshore transport rates along the shoreline to match the supply rate and retain a sandy beach. Configurations could include a number of detached breakwaters along the section of coast and/or a single larger breakwater off Point Lonsdale or connected essentially as headland extension. Such structures would need to be substantial and able to withstand and modify storm wave conditions and therefore come at a high cost.

The design intent would be to reduce wave energy and alter the angle of approach with associated modification of sediment transport processes leading to the build-up of sand as a tombolo behind. A single breakwater immediately to the north of the Point Lonsdale Headland (Area A(i)) could offer potential benefits to this area of high wave energy with a steep angle of wave approach to the shoreline. Careful design of any such structures would be needed to ensure the desired result is achieved and there would be risks around the uncertainty of achieving this, particularly given the complex processes and the influence of tidal currents. If properly designed, constructed and maintained, offshore breakwaters can provide long term benefits in terms of sand retention.

However, there are potential significant implications for the Marine National Park, surfing values and visual intrusion associated with offshore breakwaters that would need to be assessed.

The advantages and disadvantages are summarised below.

Advantages

 Could potentially provide long term benefits subject to detailed investigation and design

 Use of beach nourishment in conjunction will enhance the benefits and minimise potential impacts

 Structures and semi-permanent sand will add other environmental and social values

 Others as determined by stakeholders

Disadvantages

 Potential implications of works in the Marine National Park

 Visual intrusion into the vista along the shoreline and across the Bay

 Implications for surfing would need to be investigated

 Potential for downdrift erosion although this is likely to be negligible given the presence of seawalls and previous works and can be mitigated with beach nourishment but at an additional cost

 Detailed investigations would be required into the likely success given the importance of tidal currents

 Risk that offshore breakwaters would not successfully retain a stable beach

 Very high capital cost and potentially high maintenance cost

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 Difficult to adapt to address the influences of future climate change including sea level rise and does not fully address overtopping of the existing seawall

 Others as determined by stakeholders

6.2.4 Material Sources and Costing Considerations The implementation of coastal protection works is dependent on suitable material being able to be obtained and placed in a practical, economical and environmentally acceptable manner. General considerations associated with sourcing, cost and applicability of different material types are discussed below, including preliminary estimates in terms of unit costs for capital and ongoing maintenance works provided on the basis of available information.

Cost estimates for the various options can be developed based on these unit rates for comparison purposes. This will be dependent on the extent and combination of hybrid options. Specific recommended works would be subject to detailed design, impact assessment and tendering processes that may influence the final cost. There will also be on costs associated with the design, impact assessment and approval processes for the recommended options.

6.2.4.1 Local Redistribution of Material This will typically involve the use of earth moving equipment on a daily rate. Movement of small quantities could therefore be expected to cost of the order of $10,000.

6.2.4.2 Beach Nourishment The feasibility of beach nourishment is dependent on the practical and cost-effective availability of a suitable source of sand. Sand should be of suitable quality (grain size and colour) and would ideally match the existing beach sand. When nourishment sand is imported from outside the beach system, sufficient quantities of sand should be available for both initial and ongoing nourishment.

Sand for beach nourishments should be able to be obtained and placed without adverse environmental impacts. In environment sensitive areas, this may be challenging. Potential nourishment sand sources would need to investigated and could include accretion areas near Queenscliff or local land-based sand pits. The presence of the Marine National Park will limit the potential for use of offshore sand.

Therefore it is likely that small quantities of sand would most likely need to be trucked to the site from land-based sources. The cost to supply and deliver in place is likely to be in the range of $40- $50 per cubic metre with minor nourishment with say 1,000 cubic metres costing around $50,000 (plus ancillary costs). How much nourishment sand is required will be dependent on the present beach levels and slopes and the length / width of beach to be nourished. It should ideally be placed to mirror the existing beach slopes and alignments. As an example, 1,000m3 would provide an average 20m3/m over a length of 50m or 10 m3/m over a length of 100m which provide only a small benefit. Accordingly a greater benefit will come at a greater cost for more sand.

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6.2.4.3 Groyne Structures Coastal protection structures are typically of a flexible mound construction type to allow for some movement and to absorb some of the wave energy. Rock is the dominant material used in such structures and is dependent on suitable local sources being available. Alternative construction materials such as concrete armour units and sand filled geotextile bags could also be considered for such structures but have limitations such as high cost and poor visual amenity of concrete units and short practical life due to decay, failure and vandalism of geotextile units. Timber groynes are also subject to deterioration over time as exhibited by the historical structures.

Rock armour units would need to be obtained from local hard rock quarries. While the specific extent and limitations of the available resource is not known, it is evident that sufficient rock would be available but would need to be sourced by truck from quarries at substantial distance and cost. A significant constraint associated with rock armour is the need to truck the material to the site over local roads. For large projects, this can mean frequent truck movements over an extended time frame.

Indicative cost estimates for the supply and transport to site of rock based on typical experience are as follows:

 Armour rock supply to site: $30 - $40 / tonne

 Quarry run rock supply to site: $20 - $30 / tonne

On this basis, the cost for a typical rock groyne structure is estimated to be about $2,000 / metre. Therefore a 50m long groyne could be expected to cost approximately $100,000. Information from previous groyne constructions will allow confirmation of likely costs.

Rock structures by their nature are subject to movement and settlement over time. They are also subject to damage during storm events although they are designed to withstand major wave attack. A typical design criterion is for less than 5% damage during a 50 year storm. As such, ongoing maintenance will be required to ensure the structural stability is not compromised.

This will necessitate maintaining access to allow maintenance works to be carried out. Minor slumping of groyne structures after initial construction is generally not such an issue provided that the function and structural stability are retained. An ongoing maintenance cost of 1% per year is typically adopted for rock structures subject to storm wave attack.

6.3 Options for the Central Section (Area B)

6.3.1 Broad Considerations The central section of Lonsdale Bight is backed by a rock revetment seawall with little or no useable beach in front. Future coastal management considerations for this section of the foreshore centre on the desire or need for improved recreational beach amenity balanced against the potential environmental implications for the Marine National Park and the costs associated with achieving such outcomes. The implications of sea level rise and enhanced wave energy impacting on the wall with future climate change also need to be considered. This includes the need for adaptation and potential increased damage and maintenance costs. It is noted that the crest

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elevation of the rock revetment seawall is higher than the masonry seawall in Area A and is less prone to wave overtopping. Its rubble mound structure is also more readily adaptable to modifications to accommodate any future sea level rise.

Consideration of the need for specific works would be best achieved through a detailed risk assessment process as outlined above.

6.3.2 Identification of Options Broad considerations and options are similar to Area A with the notable exception being that this section does not contain any existing groynes to retain sand. Hence, under a Do Nothing option, it can be expected that there will be limited beach in front of the seawall for considerable periods of time. Similarly without any structures to retain sand, short term options of local redistribution of sand and minor targeted beach nourishment are not considered viable.

The seawall protects the caravan parks from shoreline recession at the southern end of this section and it is assumed that such ongoing protection will be required. However, the northern section of seawall is backed by a wide undeveloped reserve. Much longer term planning could consider an option of removing one or two sections of this wall while retaining or reinforcing the wall at the eastern ends as artificial headlands. Further details for consideration of this as a potential long term option are outlined below.

The broad options identified are therefore as follows:

 Option 1: Do nothing and accept natural variability (short and/or long term)

 Option 2: Groyne field - without and with beach nourishment (long term)

 Option 3: Offshore breakwaters (long term)

 Option 4: Artificial headland with pocket beach (long term)

6.3.3 Analysis of Options

6.3.3.1 Do Nothing (Short and/or Long Term Option) As outlined above, the Do Nothing option for this section of beach has similar considerations to Area A at Point Lonsdale Front Beach. The main differences relate to:

 The lack of any existing structures to retain sand indicates that it can be expected that there will be limited beach in front of the seawall for considerable periods of time.

 The rock revetment wall in this section has been identified as being less prone to wave overtopping and associated stability issues under present day and climate change scenarios (Cardno 2015). It would also be more readily adaptable to accommodate sea level rise influences.

6.3.3.2 Groyne Field or Offshore Breakwaters Construction of structures such as groynes or offshore breakwaters could be considered to retain a sandy beach in specific areas depending on stakeholder needs and requirements. Similar considerations as outlined for Area A at Point Lonsdale Front Beach would apply. A significant

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number of structures at a large cost would be involved if a sandy beach is required along an extensive length of foreshore.

If a large number of structures are built and sand allowed to build up naturally without artificial beach nourishment, there would be the potential for further erosion at Dog Beach which would need to be investigated.

6.3.3.3 Artificial Headland with Pocket Beach (Long Term) Overview

As outlined above, much longer term planning could consider an option of removing one or two sections of the seawall to the east of the GoLightly Park Caravan Park while retaining or reinforcing the wall at the eastern ends as artificial headlands. The foreshore to the west could then recede naturally and be retained as sandy pocket beaches. Detailed assessment would be needed to confirm the likely extent of recession to ensure the road behind is not threatened. However, with control structures at either end, it is considered that a stable beach may be formed providing long term benefits.

Such an option would need acceptance of the loss of the reserve land and would come at considerable initial cost. However, it would most likely provide a long term sandy beach in the area and reduced the cost of adapting and maintaining the seawall with climate change. This is unlikely to exacerbate erosion further to the east as the beach to the west would be allowed to erode naturally and supply sand.

A similar option without the removal of the seawall could be considered with the construction of an artificial headland at the end of the rock wall. This was suggested as a possibility by Vantree (1998) and would include a headland type structure extending (say) about 150m offshore. Sand would be trapped to the west like a groyne with a beach being retained in front of the seawall. However, downdrift erosion along Dog Beach would be a significant constraint without associated beach nourishment.

The advantages and disadvantages for an artificial headland option on the existing seawall alignment are summarised below.

Advantages

 Would allow foreshore to recede naturally without the need for maintaining protection if designed appropriately

 A natural sandy pocket beach would evolve with associated environmental and social values

 Unlikely to adversely affect Marine National Park and may introduce additional marine habitat areas

 Can readily adapt with climate change influences

 Others as determined by stakeholders

Disadvantages

 Will result in the loss of reserve land

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 Need for detailed design to ensure the road behind is not threatened and the caravan parks remain protected with associated risks if it doesn’t perform as expected

 High initial capital cost to remove existing seawall and promenade in sections and strengthen the wall at the eastern end as an artificial headland

 Need to relocate walking path and manage vegetation loss as the shoreline recedes

 Need for extensive community engagement and education

 Others as determined by stakeholders

6.4 Options for Dog Beach (Area C)

6.4.1 Broad Considerations At the end of the seawall at Dog Beach, substantial erosion has occurred in the form of terminal scour. The beach is backed by high a dune and while various stabilisation and protection works have been carried out, slips still occur in the high dune scarp that remains. Fluctuations in the beach also occur in response to the prevailing processes while the shoreline is generally regarded as being relatively stable at present. The beach further to the east towards Shortland Bluff has also experienced fluctuations with observed accretion in recent years.

A substantial buffer remains in front of development behind the present erosion scarp and this is even greater immediately to the east. While the potential extent of storm erosion has been assessed, there has been no detailed assessment of the potential for longer term recession particularly with respect to climate change effects including sea level rise and associated increased wave energy. The key objective for Dog Beach is to identify strategies and options to deal with such future erosion potential.

Storm erosion can happen rapidly and the potential extent of this has been previously assessed as about 10m. This is influenced by the large volume of sand available in the high dune. While further slumping of the dune may occur following such an event, a substantial buffer would still remain seaward of the development and infrastructure. Longer term recession associated with variations in sediment supply and longshore transport rates will typically occur more gradually. Changes in such processes with climate change and sea level rise will also occur gradually and so time will typically be available to respond to a longer term erosion threat. However, planning should occur so that those responses are known.

6.4.2 Identification of Options In areas where a substantial undeveloped buffer exists, the common coastal management approach is to let nature take its course and allow the erosion to continue naturally. This minimises the cost and generally results in the retention of a natural sandy beach as observed at Dog Beach. While a usable beach is retained, this approach is also dependent on acceptance of the loss of any values of the eroded area.

The alternative strategy is to protect the land behind from ongoing erosion which is likely to be costly and may result in the loss of the beach in front depending on the option adopted. This is exemplified along the section of coast to the west where a seawall has been constructed to halt the

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erosion and the beach in front has been lost. In this case while the land and associated values behind are protected, it has been at the expense of a usable beach in front.

It is generally not viable to alter broad scale processes that generate long term recession including those associated with climate change. Planning strategies for dealing with future erosion threat are usually based on knowledge of the potential extent and timing of such threat. While assessments of the potential short term storm erosion have been carried out, there has been no quantification of the potential for long term erosion. Assessments have indicated periods of minor fluctuations with general stability and recent accretion being observed. However, the risk of gradual recession with climate change including sea level rise and enhanced wave energy is recognised.

The area is characterised by high dunes with a substantial buffer to accommodate erosion. It is conceivable that erosion may threaten existing development landward of the terminal scour erosion scarp at Dog Beach. However, this extends only a short distance beyond the end of the existing seawall and a much larger buffer of over 100m exists immediately to the east. It is considered unlikely that this buffer will be breached or the road behind threatened by future erosion. Further investigation would be required to confirm this.

Given the substantial buffer and relative stability of the beach at present as well as the likely gradual and unknown timing and extent of potential future long term recession, it is considered that no specific works or actions to protect against shoreline recession are necessary at this time. Nevertheless, a strategy should be adopted for future management the area taking into consideration the potential for future recession, particularly with climate change influences.

6.4.3 Potential Strategy It is considered that an appropriate strategy for Dog Beach would be as follows: