Investigations Long term options to maintain a sandy

Point Lonsdale Groyne Investigations

Long term options to maintain a sandy beach

59918185

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

22 August 2018

22 August 2018 Cardno i Point Lonsdale Groyne Investigations Long term options to maintain a sandy beach

Contact Information Document Information

Cardno Pty Ltd Prepared for The Department of ABN 47 106 610 913 Environment, Land, Water and Planning Level 4 Project Name Long term options to 501 Swanston Street maintain a sandy beach 3000 File Reference 59918185_PtLonsdale_Groy

neIvestigation_Rev0.docx www.cardno.com Phone +61 3 8415 7777 Job Reference 59918185 Fax +61 3 8415 7788 Date 22 August 2018

Version Number Rev 0

Author(s):

Phebe Bicknell Effective Date 20/08/2018 Senior Engineer

Approved By:

Chris Scraggs Date Approved 20/08/2018 Principal Coastal Engineer

Document History

Version Effective Date Description of Revision Prepared by Reviewed by

V1 Internal Draft Phebe Bicknell David Provis Rev A Draft for Client Review Phebe Bicknell Chris Scraggs Rev B Draft for Client Review Phebe Bicknell Chris Scraggs Rev 0 Final Phebe Bicknell Chris Scraggs

© Cardno. Copyright in the whole and every part of this document belongs to Cardno and may not be used, sold, transferred, copied or reproduced in whole or in part in any manner or form or in or on any media to any person other than by agreement with Cardno.

This document is produced by Cardno solely for the benefit and use by the client in accordance with the terms of the engagement. Cardno does not and shall not assume any responsibility or liability whatsoever to any third party arising out of any use or reliance by any third party on the content of this document.

59918185 | 22 August 2018 ii Point Lonsdale Groyne Investigations Long term options to maintain a sandy beach

Table of Contents

1 Introduction 6 1.1 Overview 6 1.2 Scope of Work 7 1.3 Methodology 8 2 Study Area 9 2.1 Background 9 2.2 Site Inspection 12 2.3 How work 14 3 Existing Conditions 15 3.1 Currents 15 3.2 Waves 15 3.3 Sediment Transport 17 4 Concept Option Development 20 4.1 Preliminary Options 20 4.2 Concept Options 22 4.3 Options Summary – Layout, Efficacy & Considerations 23 5 Option Evaluation 30 5.1 Evaluation Criteria 30 5.2 Evaluation of options 31 6 Conclusions & Recommendations 38 7 References 39 Tables

Table 3-1 Mean wave conditions 16 Table 3-2 Summary of wave model cases 16 Table 4-1 Summary of Groyne Variables 20 Table 4-2 Groyne material options for Point Lonsdale 21 Table 4-3 Option: Maintain existing rock groynes 24 Table 4-4 Option: Extend existing groynes - Rock 25 Table 4-5 Option: Add additional groynes – Rock 26 Table 4-6 Option: Add additional groynes – Timber/Polymer 27 Table 4-7 Option: Combination – Rock & Timber Groynes 28 Table 4-8 Option: Combination – Rock & Timber Groynes with Small Breakwater 29 Table 5-1 Criteria Definitions 30 Table 5-2 Evaluation of Options – Summary 31 Table 5-3 Evaluation of Options – Detailed analysis 32

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Figures

Figure 1-1 Study Area (Nov 2017, Nearmap image) 6 Figure 1-2 Methodology Flow Chart 8 Figure 2-1 Annotated site map (Nearmap Image, Nov 2017) 13 Figure 2-2 Diagram of sediment movement along a beach and trapping by a barrier such as a groyne. 14 Figure 3-1 Distribution of wave direction and significant wave height (Hs) for waves approaching the Entrance from (data from PoMC buoys south east of Pt. Nepean) 16 Figure 3-2 Average wave energy vectors, with arrow length representing energy level; and direction of the arrow the direction of the wave energy at the origin of each arrow. (Nearmap Nov 2017) 17 Figure 3-3 Modelled shoreline at site of interest with existing groyne structures from an average 1-year wave time series. (Nearmap Nov 2017) 19

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Glossary

Symbol Name Definition AHD Australian Height The Australian Height Datum is a geodetic datum for altitude measurement Datum in Australia, "In 1971 the mean level for 1966-1968 was assigned the value of zero on the Australian Height Datum at thirty tide gauges around the of the Australian continent” BoM Bureau of Meteorology CD Chart Datum The datum to which soundings on a chart are referenced. It is usually taken to correspond to a low-water elevation, typically the lowest astronomical tide. Crest Height The height of the crest of the structure Ebb tide Outgoing or receding tidal , (that is, when water is flowing away from the line) leading to low tide. Fetch The maximum distance over water that winds of a given direction can generate waves. Areas such as Western Port are defined as fetch- limited meaning that wave heights will always be restricted by the area over which wind can blow. Groyne A rigid structure on a shoreline that interrupts water flow and limits the movement of sediment. These structures are effective at trapping material as it is moved along the coast by , creating or preventing them being washed away. Hs Significant wave height The significant wave height is originally defined as the average height of the largest one third of the waves in a given record. With the advent of digital processing techniques and spectral analysis of wave records, the significant wave height is now commonly defined as Hs=4 √m0, where m0 is the variance of the wave spectrum or the “zero order moment”. For the purposes of this study the definition based on variance is used. Wave heights referred to in this report are the significant wave height. For practical purposes, the significant wave height is close to the value reported by an experienced observer making visual observations of the wave height. Tp Spectral peak wave The period associated with the peak of the wave energy spectrum period Pdir Peak wave direction The wave direction associated with the peak of the wave energy spectrum. Directions are given as the direction the waves are coming from. SLR Sea-level rise

Swell Waves which have travelled away from the area where they were generated such as a remote storm system. Often appearing as a series of regular spaced waves of unbroken appearance. The waves may have travelled many 100’s of kilometres from their point of origin. Tidal current Movement of water associated with the rise and fall of the tides Wave Direction from which the waves are coming from and are given as the direction bearing, in degrees, clockwise from true north.

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1 Introduction

1.1 Overview The Department of Environment, Land, Water and Planning (DELWP) has commissioned Cardno to investigate long-term beach management options in the form of groynes to maintain at the Point Lonsdale Front Beach, starting from in front of the shops, up to the commencement of the rock revetment. This investigation looks to build on the existing efforts towards maintaining a long-term sandy beach.

Figure 1-1 Study Area (Nov 2017, Nearmap image)

The natural processes for this dynamic section of coast at Point Lonsdale have been significantly changed through intervention from manmade infrastructure including masonry seawalls, rock revetments and timber and rock groynes. The state of the beach fluctuates following exposure to certain storm events and at various times of the year.

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Modelling and analyses are required to understand the effectiveness the existing and alternate configuration opportunities for using groynes to capture and hold a beach at this location. This project aims to undertake a technical investigation to explore and present possible options, providing a scientifically informed analysis. The potential solutions from this assessment are to be presented in an Open House Community session to inform an outcome that reflects the feedback and opinions of this community.

1.2 Scope of Work DELWP’s key objectives as part of this project are to: > Understand the coastal processes at Point Lonsdale Front Beach and existing groyne configurations actions in influencing sand supply; > Identify and model options with the objective of maintaining a sandy beach > Compare options > Present technical report to major stakeholders

Deliverables:  Report – Presenting long-term options to maintain a sandy beach  Posters – “butcher paper” style poster for each option conveying both the technical aspects and development criteria of each option. Intended to promote discussion and feedback from the community.

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1.3 Methodology Cardno’s methodology was designed to align with DELWP’s scope of works (Figure 1-2). This method was informed by our experience and knowledge of the Heads (PPH) and Point Lonsdale foreshore and similar groyne investigations within Port Phillip Bay. Each of the components to be undertaken as part of the Project is presented in more detail the sections below.

Figure 1-2 Methodology Flow Chart

> Data Inputs – Site data (survey, wave measurements, available site literature) was combined with experience and knowledge from Cardno’s previous work was used as the basis of the project’s analytical approach. > Analysis & Design – Existing wave models will be used to establish wave climate to informed the development of groyne concepts. The most suitable groyne options were selected for detailed analysis through sediment transport modelling. Modelling results were used to update and refine options. > Outputs – - Technical Report – This document presents the results of the investigation and includes sections on site context, coastal processes overview, options development, modelling and analysis details, evaluation of options and recommended solution. - Community Materials Posters – While conducting modelling, analysis and design, focus on was also placed on generating deliverables that will be used to convey this information to the wider community. through was mapping, figures and tailored content.

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2 Study Area

2.1 Background

2.1.1 Overview Point Lonsdale foreshore is a highly modified section of coast with a combination of seawall, revetments and groynes. The seawall acts to increase wave reflection which scours the beach in front. High volumes of sediment transport through the system in a north eastwards direction which lends itself to the possibility of sand capture through the use of groynes. The beach is underlain by a rock platform, which is intermittently exposed and buried by sand. Seasonal conditions see the beach fluctuate at different times of the year. As sand movement is most dynamic during storm events with increased waves and water levels, the beach can become eroded during these periods (typically during winter), with the beach rebuilding again over the calmer periods. As a result, the beach is often still in a state of rebuilding during high foreshore usage periods, December and January. Various groynes have been present at Point Lonsdale, and over the years, there have been changes to the number, location, lengths and material of these structures. Currently three groynes, a combination of rock and timber, are in place and appear to be effectively holding sand on the beach, although the spacing of these structures means the beach is not always continuous. However, the functionality of these structures may change in the future. Various options have been identified in previous studies that may be effective in keeping a beach at Point Lonsdale. These options are to be considered in further detail, to determine the feasibility and likely success of such a solution. The recent BMT WBM investigation (BMT WBM, 2017), states that the existing groynes provide some sand retention during low sand supply and that continued maintenance and ‘do nothing’/status quo is a valid short and long-term option. While it may not provide a continuous beach for the entire foreshore, it does act hold enough sand such that there is some beach present at all times of the year.

2.1.2 Foreshore management The management of the Point Lonsdale foreshore and its assets is primarily the responsibility of the . However, it is noted that DELWP also play an important role in coastal protection assets, here and throughout the state. Currently the foreshore assets, including groynes, seawalls and revetments undergo minor maintenance on an “as needs” basis. In recent years’, significant maintenance undertaken to the groynes has included rock armouring of the timber groynes and removal of relic/remnant groynes. There is no manual redistribution of sand undertaken on the beach, meaning all sand placement is driven by the natural processes and their interaction with the existing groyne structures. The MNP jurisdiction for the area means that any major works are done in close consultation with Parks Victoria

2.1.3 Site significance Highly renown for the environmental, recreational, cultural heritage and economic values that it provides for the community and its visitors, Point Lonsdale is recognised as a site of significance. Part of the beach is protected, with portions of the Point Lonsdale foreshore and nearshore areas of Lonsdale located within the Port Phillip Heads Marine National Park (PPHMNP), as park boundaries extend to High Water Mark, the Point Lonsdale foreshore and its surrounds are highly protected. An overview of the Marine Park values is shown here, as outlined in the BMT WBM review (BMT WBM, 2017).

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NATURAL VALUES CULTURAL VALUES RECREATIONAL VALUES

> Intertidal platforms, supporting > Heritage-listed shipwrecks and > Swimming, surfing, walking, diverse invertebrate shipping history; birdwatching, nature observation and passive recreation leisure > Diverse and abundant algal > Botanical and scientific survey sites activities assemblages on Lighthouse Reef; of research and historical significance; > Internationally recognised subtidal > Deep undercuts in the Lonsdale Reef, reef dive sites supporting algae communities more > Historical significance - One of the typical of deeper waters; first marine reserves protected in > Snorkelling sites between Lightning Victoria; Reef and the Point Lonsdale Pier > Diverse fish and invertebrate assemblages on the Lonsdale Wall, > Recreational boating and sailing including extensive encrusting communities such as ascidians, > Opportunities for guided marine bryozoans and sponges; education and nature-based tourism > Calcarenite shore and reef platforms- > Scenic landscapes. significant for shorebird feeding; and

> Threatened marine mammals such as Australian Fur Seal, Southern Right Humpback Whales

The dynamic nature of the sediment transport processes means that nearshore habitats and reefs are intermittently exposed because of changing transport and sand coverage. Human intervention, such as seawalls and groynes, has already significantly impacted the natural processes. The potential environmental, cultural and recreational impacts of making additional changes to the foreshore and its structures will be an important consideration in determining the feasibility of options. A critical aspect in evaluating the potential options is ensuring that these values are not compromised. The approvals process associated with constructing or modifying groynes at this site will also require consideration.

2.1.4 Approval Requirements Point Lonsdale is one of six marine areas or sections that make up the Port Phillip Heads Marine National Park (PPHMNP). As such, the area is protected under the National Parks Act 1975, National Parks Regulations 2013. The management objectives for marine national parks and sanctuaries are set out in Section 17D National Parks Act 1975. Which states: (3)(a) The Secretary (DELWP), subject to this Act will ensure that each marine national park and marine sanctuary is controlled and managed in accordance with the objects of this Act in a manner that will – (i) preserve and protect the natural environment and indigenous flora and fauna of the park and any features of the park which are of geological, geomorphological, ecological, scenic, archaeological, historic or other scientific interest; and (ii) promote the prevention of the introduction of exotic flora and fauna into the park; and (iii) provide for the eradication or control of exotic flora and fauna found in the park; and

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(b) subject to paragraph (a) – (i) provide for the use, enjoyment and understanding of Marine National Parks and Marine Sanctuaries by the public; and (ii) promote and understanding of the purpose and significance of Marine National Parks and Marine Sanctuaries; and (c) prepare a plan of management in respect of each marine national park and each marine sanctuary.

The Point Lonsdale Section of the section of the PPHMNP is recognised for its ecological values and protected as one of the first marine reserves in Victoria since 1979. In summary, this section includes:  Intertidal reef platforms that contain the highest invertebrate diversity of any calcarenite reef in Victoria  Diverse and abundant algal assemblages on Lighthouse Reef  Deep undercuts in the Lonsdale Reef with algae communities more typical of deeper waters — a geological feature that is seldom found along Victoria’s open coast  Part of the area occupied by the Port Phillip Bay entrance deep canyon marine community falls within the boundary of the Point Lonsdale section of the Port Phillip Heads Marine National Park. The community is dominated by sessile invertebrates, predominantly sponges, with ascidians, bryozoans, hydroids and corals. The biota is diverse in terms of the variety of sponges and other invertebrate forms present (including species listed as protected under the Victorian Fisheries Act 1995, and the EPBC Act 1999 - weedy seadragon Phyllopteryx taeniolatus. And is one of two marine communities in Victoria listed under the FFG Act 1988.  Calcarenite shore and reef platforms that are of regional significance and state significance for shorebird feeding habitat (including species listed under the FFG Act 1988 or the Victorian Rare or Threatened Species (VROTS) list.

The relevant plan for the Point Lonsdale section is the Port Phillip Heads Marine National Park Management Plan (2006) (the Management Plan). The Management Plan provides a strategic guide for the management of the park. The Management Plan states that a number of uses and activities may be permitted in the park, subject to specified conditions to minimise impacts. Section 7 of the Management Plan (Strategies for Authorised and Adjacent Uses) includes the following strategies:  Review all uses of the park that do not conform with the objectives of the National Parks Act.  Allow uses to continue only in accordance with authorisations that are consistent with legislation and include conditions that effectively minimise the impacts of uses on the park.  Permit authorised uses with appropriate conditions, and monitor authorised activities to ensure conditions are met. Assess the effectiveness of conditions of authorisations in protecting the park and seek review of authorisations if necessary to mitigate impacts.

In summary, it would appear possible for a consent under the Marine and Coastal Act 2018 to be issued by the Secretary or their delegate. However, the development of the groynes would need to be considered against the objectives of the National Parks Act 1975. Any impacts on the recognised ecological values would need to be minimised so as not to affect the natural environment. A review of the project against these objectives should be completed as part of the next phase of the study.

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2.2 Site Inspection A site visit of the study area was undertaken by Cardno on June 1, 2018. Arriving on site at 9:30 am, the tide was in flood phase with low tide occurring at 7:19 am and high tide at 2:23 pm. The study area comprises of three groynes delineating four beach compartments, starting from the end of the seawall in the south to the start of the rock revetment to the north. Inspection of the Point Lonsdale front beach delivered the following key observations:  Compartment 1 – 120 m in length from southern seawall to southern groyne (Groyne 1). The compartment was full to groyne height in the northwest corner, at least 1 to 1.5 m higher than in the southwest corner due to angle of the incoming waves. The beach slope is relatively steep in this corner.  Groyne 1 – Southernmost, 70 m in length. The original timber structure has been armoured with rock material. Some of this rock material had been displaced on the south side toward the landward end. The north side of the timber had solid rock interlocking which maintained structure integrity.  Compartment 2 –140 m in length. Much higher sand build-up in the north west corner than the south west corner, with a mound approximately 10-15 m south of Groyne 2, reaching almost to the top of the seawall.  Groyne 2 – Middle groyne, 55 m in length. Approximately 1 m diameter rock armour, with no timber in this structure. Some rock movement had occurred, not all being interlocked, exposing the geotextile layer.  Compartment 3 – 230 m in length. The beach was scoured around the outlet of a storm water drain outflowing from the seawall. Half way along, around the bend of the cliffs, the exposed seawall was 2 m in height, showing a low beach level. Water level was at the toe of the seawall, with the base exposed. Beach builds back up from the access point to Groyne 3 at the northern end of the compartment and reaches the top of the sea wall.  Groyne 3 – Northern groyne 50 m in length. Similar structure to Groyne 1 with timber running through the middle of rock armour, though armour is a little less organised and interlocked, and shorter in length.  Compartment 4 – Running from Groyne 3 to the start of the rock revetment at 270 m. Very big compartment with similar scour/exposed seawall footing halfway along.  The breaking waves were visually turbid, having high amount of sand (brown/discolour) in the water.  Given the highly modified nature of this coastline, complex interactions between the waves, the and the masonry seawall, particularly toward the southern end, scouring sand away for this section of beach in front of the shops.  Winds was light, meaning waves on the day were mostly swell incoming at an angle 45 degrees to the general beach alignment, going toward the north west. This wave direction may explain the battered condition of the groynes on the south sides, with the angled waves impacting on the groynes which run approximately east west). Angled groynes better aligned with the dominant wave direction may be a design option.  Three sediment samples were taken along the beach and particle size distribution (PSD) was carried out for sediment sizes for use in modelling.

Sample Location D50 (mm) D90 (mm)

SAMPLE 1: 10 m south of Groyne 1 and 35 m seaward of seawall 0.25 0.47

SAMPLE 2: Within Compartment 3, Beach Access Point toward 0.27 0.57 north of compartment, near seawall

SAMPLE 3: Within Compartment 2, 10-15 m south of Groyne 2 0.30 0.59 and 20 m seaward of seawall

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Sand build up in North West corner to height of seawall Locations known to have sand over seawall

Exposed footing of seawall where beach had eroded

COMPARTMENT 1 COMPARTMENT 2

COMPARTMENT 3

Groyne 1 Beach is regularly cut Groyne 2 COMPARTMENT 4 back, exposing rock Groyne 3

Southern edge of Short interlocked rock armour Groyne 1 is damaged groynes allowing sand to build up beyond length and transport Long Compartments to next compartment Cut back in southern end of each compartment N Sediment Sample

Figure 2-1 Annotated site map (Nearmap Image, Nov 2017)

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2.3 How groynes work In order to demonstrate possible groyne solutions for the Point Lonsdale Foreshore, it is important to understand how groynes work in shaping and holding the beach. When waves approach a beach at an angle, they tend to move sediment along the beach. When there is a barrier in the beach, such as a groyne, this captures sand which is moving along a coast and thus builds up a beach. This is represented diagrammatically in Figure 2-2.

Barrier or groyne

Figure 2-2 Diagram of sediment movement along a beach and trapping by a barrier such as a groyne. When sediment builds up sufficiently, it will be moved around the end of the barrier or groyne into the next beach compartment or cell. The sediment on a beach will move until the beach is aligned at right angles to the direction of the incoming wave energy. Thus in a situation such as Point Lonsdale, where the wave direction is relatively constant (or at least predominantly from one direction) (see Section 3.2), groynes are often used to maintain a beach, or series of beaches, along a general alignment which would otherwise not allow the formation of a beach other than a narrow strip of sand.

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3 Existing Conditions

Cardno have undertaken various projects at this site, initially as part of the Vantree (1998) investigation when initial modelling of waves and potential groyne configurations was included and estimates of the longshore transport undertaken. Subsequent investigations are included in the studies as part of the Deepening Project (Cardno Lawson Treloar, 2007 and Cardno, 2011) and include modelling of waves, currents, water levels and sediment transport.

Existing hydrodynamic models (DELFT3D) and wave models (SWAN) have been tailored for this analysis, to determine the nearshore metocean conditions at Point Lonsdale. Previously calibrated models were updated using the bathymetric data available from LADS surveys undertaken as part of the Future Project by in 2007 and 2008/9. Offshore areas, not covered by LADS and Lidar surveys, using bathymetry derived from the Australian Bathymetry and Topography Grid, Geoscience Australia (2009) which has a resolution of 9 arc seconds. (~ 250 m at the equator).

3.1 Currents

3.1.1 Model The hydrodynamic model (Delft3D) was used to define the astronomical tidal-currents at the site. Currents and water levels at Point Lonsdale were extracted from a validated hydrodynamic model for Port Phillip, including Port Phillip Heads, the entrance and adjacent waters of Bass Strait. This numerical model was developed through the FLOW module of the Delft3D modelling system developed by Deltares. For swell penetration, swell in Bass Strait imposed at the relevant boundary of a SWAN wave model (Ris et al. 1999) based on the results of analysis of waves from the Port of Melbourne wave data at Port Phillip Heads. The current fields from this modelling (ebb, flood and slack scenarios) were used in the swell-wave modelling below.

3.2 Waves Offshore wave measurements are available from Triaxys wave buoys located approximately 6 km south east of . These measurements are available from 2003 and a five-year period 2011-2015 inclusive has been selected for use in this study (Cardno, 2016).

The analysis of the wave climate shows the dominance of swell waves from the south west with some contribution from locally-generated wind waves. Figure 3-1 shows the distribution of significant wave height against incoming wave direction and demonstrates the very narrow range of directions, especially for larger wave heights.

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Figure 3-1 Distribution of wave direction and significant wave height (Hs) for waves approaching the Entrance from Bass Strait (data from PoMC buoys south east of Pt. Nepean)

An analysis of five years of wave measurements within Port Phillip Heads, from 2011 to 2015 established a mean wave climate.

Table 3-1 Mean wave conditions Hs (m) 1.52 Tp (s) 11.5 Dir (from) 207°T

Frequency of occurrence tables were used to determine suitable scenarios for modelling in order to reproduce a representative wave climate at Point Lonsdale. The cases selected for the major variables are shown in Table 3-2. Combining each of these gives a total of 54 scenarios. This combination of scenarios covers the majority of the actual wave conditions for the 5-year measurement period.

Table 3-2 Summary of wave model cases Variable Cases for each variable Currents (3 cases) Ebb Flood Slack Hs (m) (3 cases) 0.5 1.5 2.5 Tp (s) (3 cases) 11 13 15 Directions (2 cases) SSW (202.5°T) S (180°T)

Using a year of measured wave data (2014) combined with all the model runs, wave time-series were synthesised at various nearshore locations along the Point Lonsdale foreshore. For each measured condition, the relevant model run was selected and the model results for that case selected for each of the output locations selected in the study area. The resulting time series were used to calculate an annual average wave-energy for each location.

In order to determine suitable groyne options, the likely stable shoreline alignment must be determined. The direction at which the average wave-energy approaches the shoreline provides a robust measure of the potential coastline alignment. The coastline is generally stable at an alignment approximately perpendicular to this wave-energy direction. Note that this direction is an average and in reality will vary at different times of the year with the seasonality of the local wind climate, however the offshore wave directions at this location do not vary markedly with the seasons.

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Figure 3-2 Average wave energy vectors, with arrow length representing energy level; and direction of the arrow the direction of the wave energy at the origin of each arrow. (Nearmap Nov 2017)

The average wave energy direction seen here shows excellent alignment with the shoreline and breaking waves in the Nearmap image from November 2017. This was consistent with the wave direction noted during the site inspection. It clearly demonstrates the shoreline equilibrating approximately perpendicular to the wave energy. Several observations can be made from these results. The average wave direction was reasonably consistent, while the wave energy is reducing to the north along this coastline. The directionality confirms that, for the existing groyne configuration, the spacing between the groynes is too long for groynes of this length, or conversely, groynes are too short for compartments of this distance. Therefore, a sandy beach cannot be held within the entire length of the compartment. It is understood that there is some variability around the average alignment of the shoreline. This can lead to more or less beach width in each compartment. There was no clear seasonality in the average wave energies. However, the measured waves from offshore (Figure 3-1) show that waves from the easterly quadrant do occur and these may be more significant at Point Lonsdale, which is more exposed to this direction than the offshore wave buoy location. Waves from the east would cause a temporary realignment of the shoreline. Similarly, large waves occurring with a high sea-level, such as during a storm, are likely to result in sand movement seawards off the beach and into the general longshore currents experienced during such events. This can result in a significant loss of sand and require some time for the beach to rebuild during less severe weather conditions.

3.3 Sediment Transport There is a significant amount of longshore sediment transport occurring along this section of coast, coming from the open coast to the west, moving and in a northerly direction around the headland at Point Lonsdale, up towards Dog Beach and eventually around to Queenscliff. Volumes transported are estimated to be 80 to 100,000 m3/year (e.g. Vantree, 1998). The amount of sediment movement is such that you can regularly see suspended sediment in the nearshore zone when looking down on the water from cliffs and pathways above. Using the wave time-series synthesised at various nearshore locations along the Point Lonsdale foreshore, a one-line coastal processes model has been developed using the LITLINE module of the LITPACK coastal processes modelling system.

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This modelling system has been developed by the Danish Hydraulics Institute. It is used internationally for the assessment of coastal processes. LITPACK includes a number of modules. One of these, LITDRIFT, computes longshore sediment transport from a time-series of wave parameters. Natural beach profiles, graded sediments, currents, wind and local roughness are included. Generally, the highest transport rate occurs in the zone. LITLINE is a module of LITPACK and is used to determine changes to a shoreline over time using spatially and temporally varying longshore transport. It includes coastal structures such as groynes and revetments (seawalls). In this case, the existing groynes were included in a model of the Point Lonsdale shoreline. Further structures, such as groynes and offshore breakwaters, were later added, with the difference being offshore breakwaters are not modelled to trap sand where groynes are, though both still allow for wave diffraction effects. Note that groynes in LITLINE can be specified to have an apparent length; that is, sand bypassing can commence before sand builds-up fully on the updrift side to the full length of a groyne. This process is important because it more closely describes what happens naturally than the alternative of delayed bypassing. The extent of bypassing depends on this apparent length and the shore normal profile of longshore sediment transport in different wave and water level conditions. The operating length of a groyne is also dynamic in terms of the shore normal profile and reduces as a beach builds-out against the updrift side of a groyne. LITLINE includes realistic shore normal beach profiles, the active depth limitation and height in computation of shoreline changes. LITDRIFT and LITLINE use the basic Engelund and Fredsoe (1976) transport formulation which includes combined wave and current motion as well as bed and suspended sediment loads. It takes account of the threshold shear stress for initiation of sediment transport through the Shields Parameter and includes graded sediments. For this study, basic beach profile survey data has been used to develop existing shoreline profiles using a simplified straight coastline. The coastline is defined as the 0 m AHD contour line and alongshore grid points were set at 10m intervals. In the shore normal direction, the resolution was 2.5 m so that a good description of nearshore wave breaking could be achieved. A median sediment particle size (D50) of 0.27mm was adopted, based on sediment sizing. Using the data described in Section 3.2, a wave parameter time series spanning 1-year was used to assess the longshore transport. Shown in Figure 3-3, the shoreline has been modelled using this wave parameter time series along with the existing shoreline groyne structures placed into the model. While the aerial image represents a snapshot in time, the modelled shoreline with the inclusion existing groyne structures closely relates to the actual shoreline. These results give context to the dynamic coastline and validate the model.

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Figure 3-3 Modelled shoreline at site of interest with existing groyne structures from an average 1-year wave time series. (Nearmap Nov 2017)

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4 Concept Option Development

4.1 Preliminary Options Based on the existing conditions at Point Lonsdale, three options have been identified as feasible ways to hold the beach at the Point Lonsdale Foreshore. Three preliminary options have been considered: - Do nothing - Construct new groynes - Modify existing groynes Within these options there are various configurations and design variables that will influence the feasibility of the options. Some of these influence the functionality and effectiveness of the structure in retaining a long term beach. Some also have secondary effects, such as safety, maintenance requirements, costs, environmental effects. Key variables include alignment, crest height, material and aesthetics (Table 4-1).

Table 4-1 Summary of Groyne Variables

Variable Description

Alignment This refers to the angle of the structure. Groynes function most effectively at retaining a beach when they are aligned with the mean wave direction. The existing groynes at Point Lonsdale are at an angle approximately perpendicular to the seawall, which is different to the average wave direction (by ~30° to 40°). This alignment exposes the groynes to larger wave forces. In this situation, the structures act more like a breakwater, dissipating wave energy rather than just holding sand. The damage evident on the most southern groyne is evidence of this exposure. . Maintain existing alignment . Adjust the alignment to mean wave direction

Crest This refers to the height of the structure. The existing height is effective in capturing sand, raising Height the height could capture more sand. With the existing configuration and alignment, increasing the height will not change the shoreline orientation, but it may raise the height and extent of the beach. Given the existing compartments are quite full at the northern end of each compartment, it is likely to result in overtopping of the groyne and the seawall, with sand encroaching on the footpath as the compartment becomes “overfull”. This is already occurring intermittently under existing conditions, and clear sand build up was noted during the site inspection. An increased crest height can also result in safety risk as a result of drop off between the compartments. . Maintain existing crest heights . Increase crest height

Material This refers to the material used to build the structure. Materials have varying lifespans, design constraints, costs, maintenance requirements and constructability implications. Further considerations regarding the material options are presented in Table 4-2 . Rock . Timber . Polymer . Concrete . Geotextile

Aesthetics This refers to the appearance of the structure conserving how it looks and fits in with its surrounds. Factors that can influence the look and feel of the design include the size and crest height, alignment and material selection

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Table 4-2 Groyne material options for Point Lonsdale

Material Approximate Advantages Disadvantages Cost $5000/m Low Maintenance Large footprint (20 times wider than a vertical structure) Resilient during a storm Most expensive

Sustainable material Relatively high demolition cost

ROCK In keeping with surrounds

$3500/m Small footprint Relatively high maintenance – Timber planks are vulnerable to rot and marine borer Relatively cheap and easy to build High reflection from vertical wall can lead to

greater scour during storm events Timber piles are durable

TIMBER Protruding elements can be a safety hazard if not maintained. Sustainable material (if exotic timbers are avoided) Vertical drop on the downdrift side may be a safety hazard. $4000/m Small footprint UV degradation can cause colour to fade

Very low maintenance Subject to vandalism

Can be made to look like Relatively high upfront cost for a vertical structure timber or sand colour Longer ‘lead times’ for material generally Can be used in combination with durable timber piles

POLYMER COMPOSITE Vertical drop on the downdrift side may be a safety hazard.

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Considering each of these variables in conjunction with various combinations available for the preliminary options, the list of feasible options can be reduced. Key exclusions for the more detailed analysis are: > Usage of timber and polymer for extended/longer groynes - larger wave energies further offshore, not able to withstand these loads. A timber structure of this length would also create a significant drop-off hazard on the northern side of the groyne. > Usage of timber and polymer on the existing alignment – history has shown that timber groynes are not durable enough to withstand wave energy on the existing alignment. Increased wave loads experienced in this scenario > Raising of groyne heights is likely to result in increased sand accumulation in against the seawall. Levels are likely to overtop and encroach of the footpath, limiting access and creating hazards on the pathways. Maintenance required to manage this. Additionally, increased levels on the southern side will increase the drop-off hazard on the northern side of the groyne. > Geotextile and concrete were excluded as material options, predominately due to the associate costs. Geotextile bags would end up being a similar price to rock but are unlikely to offer the same durability, likely needing more regular maintenance and repair. The preferred structure orientation should be similar alignment to the mean wave direction. In determining modelled shoreline resulting from different groyne configurations, LITLINE modelling assumes the groyne is positioned perpendicular to the coast. Therefore, as part detailed design, consideration should be given to aligning the structures closer to the wave direction, as it will likely result in an improved shoreline response and lessen the structure exposure (and hence structure longevity). It has not been considered further as part of modelling or options analysis.

4.2 Concept Options Six concept options have been developed, based existing configuration, metocean conditions and the likely coastline alignment as per the calculated average weighted wave direction.  Option – Maintain existing rock groynes  Option – Extend groynes – Rock  Option – Add additional groynes – Rock  Option – Add additional groynes – Timber/Polymer  Option – Combination: Rock & Timber Groynes  Option – Combination: Rock & Timber Groynes with Small Breakwater The layout of each option are presented (Table 4-3 to Table 4-8). For the purposes of comparison, each option has been applied to the entire study area extent, compartments 1 to 4. However, given the sediment transport mechanism and beach response is compartmentalised, there is the opportunity to construct the groynes in a staged manner, likely prioritising the southern and middle compartments (Compartment 1 and 2 as per Figure 2-1). The numbers, positions, alignment and lengths of the structures are indicative of what is required to maintain a beach at this location and have sufficient level of specification detail for option evaluation. Precise dimensions, would need to be confirmed at detailed design. The nominated locations of new structures have been selected based on the distance between compartment and the shoreline alignment response due to the wave angle. The existing beach access points have also been considered. An additional feature that can be incorporated into any new rock structures is to have a lowered crest height, (potentially buried) at the shoreward end, to improve the connectivity and beach access and enable a clearer passage for beach users along the beach between compartments. This will reduce the likelihood of overtopping, allowing some bypassing of sand over into the next compartment, as well as adding additional material to the, at times, sand depleted south west corners of the groyne compartments. This approach is consistent with response of the existing structures, having been later lowered at the shoreward end, and recommendations in the BMT WBM report, (BMT WBM 2017).

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4.3 Options Summary – Layout, Efficacy & Considerations The concept options have been modelled though LITPACK to give a conceptual understanding of the resultant shoreline and efficacy of the option. A 1-year wave time series was applied to the region, generating a resultant shoreline. Note that the altering alignment of groyne structures is a more complex exercise, not something that can be easily applied within this simplified model. Given the time and scope of this project, groynes on wave directional alignment were not simulated. All options involving the addition of groynes have simulated the structure running perpendicular to the coastline. The modelled shoreline response under average yearly wave climate has been presented for each option in the following tables (Table 4-3 to Table 4-8). The initial existing coastline has also been shown to demonstrate the possible change that can be made that option. Note that simulations have been undertaken using an average wave climate, and the shoreline position will still fluctuate at different times of year. However, this modelling does provide a reasonable indication of likely capture of sand and possibility for widening and lengthening of the beach through groynes. Considerations, impacts and secondary effects have been highlighted for each option and have been incorporated in the option evaluation in Section 5.

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Table 4-3 Option: Maintain existing rock groynes

Option – Maintain existing rock groynes

CONSIDERATIONS > No capital costs on new structures > No further environmental impact > No guarantee of beach all year around, beach will fluctuate > The alignment of the existing groynes means they are exposed to higher wave loads, resulting in increased repair and maintenance requirements > There may be an opportunity to undertake some redistribution of sand. However, it must be carefully timed to limit the possibility of loss of sediment to storms (suggest during the calm near the beginning of summer). The beach will still realign and will not provide a constant beach

MODELLED OUTCOMES  Shoreline dynamics and alignment are expected to continue behaving in the same way  Shoreline will continue to intermittently accrete and erode with changing metocean conditions  Seawall of northern compartments (three and four) will continue being vulnerable to wave action  Does not create a beach in front of shops

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Table 4-4 Option: Extend existing groynes - Rock

Option – Extend existing groynes – Rock

CONSIDERATIONS > No increase of structure footprint on beach. > Increased structure footprint offshore, near to MNP > Increased beach width, but may not run full compartment length > Very little change on visual aesthetics > Asymmetric beach compartments, similar to existing alignment, with beach building out on the same angle, but positioned further offshore (wider beach) > Constructability, working in water increasing cost > Overtopping of sand at onshore end of structure likely to increase as more sand captured by longer groyne. Sand will accrete in north west corners, where sand may be blown onto pedestrian footpath backing seawall > Encroaching on , MNP boundaries > Safety concerns by having a structure extend further offshore, enabling people climbing on the structure to reach deeper water and bigger waves. > Proposed extension length (~25-30% longer) is unlikely to create a continuous beach for the entire compartment, given the spacing between the existing groynes, in particular compartment 3. > The alignment of the existing groynes means they are exposed to higher wave loads, resulting in increased repair and maintenance requirements

MODELLED OUTCOMES  Increased sediment trapping on the lee side of the extended Groyne 2  Little to no change to shoreline elsewhere

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Table 4-5 Option: Add additional groynes – Rock

Option – Add additional groynes – Rock

CONSIDERATIONS > Reduced compartment size yielding a more even spread of sandy beach > Increased control of beach erosion > Maintain current beach and groyne extents, limiting incursion on MNP > Increased structural footprint on beach > Increased safety concerns with more structures on the beach > Increased visual intrusion > Modified beach connectivity with increased number of structures. There is an opportunity to lower shoreward end of groyne. > Wave load on structures on this alignment > Constructability working predominantly on land > The alignment of the existing groynes means they are exposed to higher wave loads, resulting in increased repair and maintenance requirements, particularly the more southern groynes > As wave height and energy varies throughout site, rock sizing will need to consider wave climate relevant to each individual location

MODELLED OUTCOMES  Greater coverage and spread of sandy beach across entire Front Beach  Beach width does not extend as far offshore, due to altered compartment size and shape  Extended beach to the south of Compartment 1

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Table 4-6 Option: Add additional groynes – Timber/Polymer

Option – Add additional groynes – Timber/Polymer

CONSIDERATIONS > Easier constructability working, predominantly on land > Reduced compartment size yielding a more even spread of sandy beach > Likely to be shorter in length than existing groynes, as timber groyne can’t withstand wave loads in the deeper water. Requires more individual, smaller groynes > Safety concerns from shear drop-off created by a vertical structure on the down drift side of the groyne and also due to more with more structures on the beach > Maintains existing beach and groyne compartment extents, limiting incursion on MNP > Increased structural footprint on beach - much smaller than rock, but more individual structures > Modified beach connectivity > Increased visual intrusion with more structures – but smaller impact than rock > Could use polymer material instead of timber is a longer lasting option > The timber/polymer structure would be continuous. Permeable timber groynes are not suitable for this site

If structure orientation be adjusted to align with average wave direction it would mean: > Lower wave loads on structures on this alignment. Less maintenance required

MODELLED OUTCOMES  Greater coverage and spread of sandy beach across original Compartment 3.  Beach width is slightly narrower towards north of original Compartment 3  Little to no change to shoreline across original Compartments 1 and 2 (southern sections), suggesting less suitable option in compartments 1 & 2

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Table 4-7 Option: Combination – Rock & Timber Groynes

Option –Combination: Rock & Timber Groynes

CONSIDERATIONS > Reduced compartment size yielding a more even spread of sandy beach > Requires more individual, smaller groynes > Increased control of beach erosion > Safety concerns from shear drop-off created by a vertical structure on the down drift side of the groyne and also due to more with more structures on the beach > Maintains existing beach and groyne compartment extents, limiting incursion on MNP > Increased structural footprint on beach > Modified beach connectivity > Increased visual intrusion with more structures > Use of the polymer material instead of timber is a longer lasting option > The timber/polymer structure would be continuous. Permeable timber groynes are not suitable for this site

With alignment as > Lower wave loads on structures on this alignment. Less maintenance required > Inconsistency with existing structures, may be less visually appealing. However, this is less noticeable at beach level.

MODELLED OUTCOMES  Greater coverage and spread of sandy beach across entire Front Beach, particularly in original Compartments 1 and 2  Beach width is slightly narrower towards north of original Compartment 3  Extended beach to the south of Compartment 1

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Table 4-8 Option: Combination – Rock & Timber Groynes with Small Breakwater

Option – Combination: Rock & Timber Groynes with Small Breakwater

CONSIDERATIONS As above in ‘Combination: Rock & Timber Groynes’

Design Considerations with respect to the Small Offshore Breakwater: > Increased structural footprint on beach > Requires larger rock sizing, and structure dimensions to act as a breakwater > Increased visual intrusion > Increased safety concerns with more structures on the beach > Modified beach connectivity with increased number of structures.

MODELLED OUTCOMES As above in ‘Combination: Rock & Timber Groynes’ Modelled Outcomes with respect to the Small Offshore Breakwater:  Extended beach to the south of Compartment 1.  The breakwater at the southern end shelters this section of beach from the high wave energy and its scouring effects against the seawall, allowing the beach to build up.

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5 Option Evaluation

5.1 Evaluation Criteria Evaluation criteria were developed to compare and evaluate the six options against defined evaluation criteria, tailored for the needs of this site and project. The following list has been developed in conjunction with the Project Control Group (DELWP, Parks Victoria, Borough of Queenscliffe), (Table 5-1)

Table 5-1 Criteria Definitions

Criteria Definition Scale

Likelihood of achieving a sandy beach under existing VERY LOW (Poor Technical conditions. Considers how effective the structure at Performance) to VERY HIGH Effectiveness capturing and retaining sand. (Excellent Performance)

Technical VERY LOW (Poor Likelihood of achieving a sandy beach under climate Effectiveness Performance) to VERY HIGH change conditions. Considers how effective the structure in the longer (Excellent Performance) at capturing and retaining sand with increased waves term (changing heights and water levels. climate)

The upfront cost of building the structure - labour, VERY LOW (Low Cost) to materials, equipment. VERY HIGH (High Cost) Cost (Design, The amount of construction required to build the construct, structure. Considers complexities of on land/in water, maintain) material type, required equipment. The ongoing costs associated with maintaining the structure - labour, materials, equipment.

Longevity of the structure. Likelihood that the structure VERY LOW (Low will experience failure under existing and future Maintenance/Failure) to VERY Design Life conditions, based on the material lifespan the location HIGH (High and the structure alignment. Maintenance/Failure)

The space the structure will take up. Considers overall VERY LOW (Low Amenity footprint - length, width, height, and the how this may Impact) to VERY HIGH (High Amenity effect visual amenity. Amenity Impact) Impact on beach connectivity. Does it divide the beach into isolated sections?

Public safety - Potential hazard the structure presents. VERY LOW (Low Impacts) to Considers drop-off in beach elevation between the two VERY HIGH (High Risk) Key Risks sides of the groyne (difference 1-2 m), beach users climbing on the structure, trip hazards, cuts/abrasions

Environment/ VERY LOW (Low Effects on the intertidal reef, rockpools, biodiversity Effects on Environmental Impacts) to Intertidal Reef Construction, footprint within the MNP VERY HIGH (High Communities Environmental Impacts) Modification to sediment transport in PPH MNP

Further work VERY LOW (Low Cost) to required VERY HIGH (High Cost) Amount of extra work required for detailed design phase (Design, Include analysis, further data collect (survey) analysis monitoring)

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5.2 Evaluation of options The evaluation criteria have been applied each option, where the comparison is in relation to the other groyne options. It does not consider other protection solutions / coastal structures or scenarios. Each criterion rated on a scale from Very Low to Very High. As each criterion had a varying scale, rating have been coloured coded to convey well performing options, where green shading is a good result and red shading is a poor result. Table 5-2 provides a summary of the evaluation while Table 5-3 presents further context around each of the ratings provided, consider for each individual option.

Table 5-2 Evaluation of Options – Summary

Criterion

-

(changing (changing

struct,

/work

climate)

Technical Technical

PPH MNP PPH

term

Amenity

Required

Key RisksKey

Technical

maintain)

con

Environment Environment

Design Life

Effectiveness Effectiveness

Cost (Design,

Effectiveness

design/analysis

long

/Effects on Intertidal on Intertidal /Effects

Reef Communities in in ReefCommunities

Option – LOW LOW LOW LOW LOW LOW N/A MODERATE Do Nothing

Option – Extend BELOW BELOW MODERATE HIGH LOW MODERATE HIGH MODERATE existing groynes AVERAGE AVERAGE

Option – VERY VERY VERY VERY ABOVE ABOVE HIGH HIGH Add additional HIGH HIGH HIGH HIGH AVERAGE AVERAGE groynes – Rock

Option – BELOW BELOW ABOVE Add additional MODERATE MODERATE MODERATE MODERATE MODERATE groynes – AVERAGE AVERAGE AVERAGE Timber/Polymer

Option – Combination: VERY ABOVE ABOVE Rock & Timber HIGH HIGH HIGH HIGH HIGH Groynes HIGH AVERAGE AVERAGE

Option – Combination: VERY VERY VERY ABOVE VERY VERY Rock & Timber HIGH HIGH HIGH HIGH HIGH AVERAGE HIGH HIGH Groynes with Small Breakwater

NB. The colour coding assigned to the rating changes due to varying rating scales for each criteria. In general, green is considered a GOOD rating, while red is considered a POOR rating.

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Table 5-3 Evaluation of Options – Detailed analysis

Criterion Technical Technical Cost Design Life Amenity Key Risks Environment Further work Effectiveness Effectiveness in /Effects on Required (Design, the longer term Intertidal Reef construct, (Design, analysis Communities in (changing maintain) monitoring) PPH MNP climate)

Some sand is Similar to Design & Existing Beach Public Safety - No further Run a controlled being held on existing, though Construction - structures connectivity influence. trial of the Large height beach, but not likely to erosion N/A currently same as existing. redistribution offset between continuous. effects. Likely to damaged. sand within the compartments be exacerbated Already failing. No change to compartment at from being too with SLR and Continual Footprint same current effects calmer times of full in corners. Strong increases in maintenance is as existing. experienced by year. Creates a drop dependence on strength and likely required to Alignment and Noting that the intertidal off between seasonal frequency of structures due to size appear to structures are reef compartments. influence. storm events existing design be ill-designed, undersized. communities (poor alignment, but are still

undersized, no functional. Likely Sand blown over

Do Nothing Conditions are core and filter to worsen with – footpath. likely to remain layers). time unless similar, if not Associated costs significant

Option worsen will be minor repairs are

overtime. ongoing repairs undertaken. to relay and

replace displace rocks

RANKING LOW LOW LOW LOW LOW LOW N/A MODERATE

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Technical Cost Environment/ Further work Effectiveness in (Design, Effects on Technical Required Criterion the longer term construct, Design Life Amenity Key Risks Intertidal Reef Effectiveness (Design, analysis (changing maintain) Communities in PPH MNP monitoring) climate)

Some minor Minor Will require Structure will be Connectivity Large height Extends into Detailed design improvement, improvement, some upgrade of exposed to same as existing. offset between of groyne More sensitive though not but not an existing bigger waves compartments extension zones of the across entire effective long structures to being deeper. from being too MNP, closer to Site Survey beachfront term solution improve Increased full in corners. Retaining reefs. structure offshore Sand blown over Small increases existing integrity. footprint. footpath. in beach width at orientation select spots Rock is more means structure Small change to along coastline. expensive is exposed to sediment Structure material. higher wave transport extends further Approximately energies on this through Marine offshore Average beach $5000/m of alignment National Park. exposing public width increase - structure. Less Design will need to larger waves new materials Compartment 1: to consider and deeper required only Construction 0 m conditions in water extending efforts entering

Extend existing groynes Compartment 2: sizing material

existing and Marine National

– Up to +15 m and structure upgrading Park. Compartment 3: design. structures. Up to +5 m Rock is long Construction lasting and

Option Option effort increased structure will working further last if suitably offshore designed (deeper, larger waves)

RANKING BELOW BELOW ABOVE MODERATE HIGH LOW MODERATE HIGH AVERAGE AVERAGE AVERAGE

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Technical Technical Cost Design Life Amenity Key Risks Environment/ Further work Effectiveness Effectiveness in Effects on Required (Design, the longer term Intertidal Reef construct, (Design, analysis Communities in (changing maintain) monitoring) PPH MNP climate)

Shortened Large Rock is Rock is long More groyne Increased Large rocks on Detailed design compartments Improvement expensive lasting and structures on number of beach rock flats. of timber improves beach across entire material. structure will the beach will structures. groynes

Moderate holding capacity beach front Approximately last with site alter change to region Site Survey $5000/m of specific design. connectivity. Improved width Large sediment

Rock structure across entire Improvement If kept on same transport. – study area. across entire Works will be alignment as More large Construction beach front with onshore and existing groynes, Average beach groyne efforts within more spread and offshore. experiencing width increase - structures Marine National symmetrical higher wave extending Park. Compartment 1: compartments loads. Advise offshore. Up to +25 m angling structure Works onshore Compartment 2: more in to and offshore Up to +30 m average wave Compartment 3: direction Up to +30 m

Advise that

Add additional groynes structure is

– designed on an orientation that aligns with average wave

Option Option direction.

RANKING ABOVE ABOVE VERY HIGH HIGH VERY HIGH VERY HIGH VERY HIGH HIGH AVERAGE AVERAGE

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Technical Technical Cost Design Life Amenity Key Risks Environment/ Further work Effectiveness Effectiveness in Effects on Required (Design, the longer term Intertidal Reef construct, (Design, analysis Communities in (changing maintain) monitoring) PPH MNP climate)

Shorter Large Timber is Timber is less Increased Increased Smaller Detailed design

compartments improvement cheaper than durable and not number of number of beach structure. Piling of timber improves beach through rock. a strong as rock. smaller groyne structures. into beach. Small groynes holding capacity, Compartment 3; Improved structures on to moderate Smaller Timber Site Survey though timer Little to no effect alignment will the beach will change to region structures. Less structures create structure unable in reduce repeat alter sediment material. vertical drop-off to extend as far Compartments 1 wave impact connectivity. transport. between offshore and 2 Works largely on structure. compartments shore. Notable increase Climbing, trip

Timber/Polymer

in Compartment Approximately hazards. – 3. Little change $3500/m of elsewhere. structure Average beach width increase - Compartment 1: 0 m Compartment 2: 0 m Compartment 3: Up to +10 m Timber structure should be

Add additional groynes

designed on an – orientation that aligns with average wave direction

Option Option RANKING BELOW BELOW ABOVE MODERATE MODERATE MODERATE MODERATE MODERATE AVERAGE AVERAGE AVERAGE

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Criterion Technical Technical Cost Design Life Amenity Key Risks Environment / Required Effectiveness Effectiveness in design/analysis (Design, Effects on the longer term /work construct, Intertidal Reef (changing maintain) Communities in climate) PPH MNP

Improved width Improved width Combination of Timber is less Less impact on Increased Large rocks on Detailed design: across entire across entire timber and rock durable and not beach number of beach rock flats. - Rock groynes study area. Even study area. Even proves nearly as a strong as rock. connectivity structures. Moderate spread of sand spread of sand effective, but at Improved with less large - Timber Timber change to region across across cheaper cost alignment will rock structures groynes structures create sediment compartments compartments reduce repeat Timber vertical drop-off transport. wave impact Approximately between structure. But Construction Site Survey $3500/m of compartments Average beach shorter efforts within structure width increase - structures to Climbing, trip Marine National Rock limit exposure to hazards. Park. Compartment 1: Approximately wave energy Up to +25-30 m Works onshore $5000/m of Compartment 2: Rock is long and offshore structure Up to +10 m lasting and Works will be structure will Compartment 3: onshore and last with site Up to +10 m offshore. specific design.

Advise angling structure more in to average

Combination: Rock & Timber Groynes

wave direction –

Option Option

RANKING ABOVE ABOVE VERY HIGH HIGH HIGH HIGH HIGH HIGH AVERAGE AVERAGE

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Criterion Technical Technical Cost Design Life Amenity Key Risks Environment / Further work Effectiveness Effectiveness in Required (Design, Effects on the longer term construct, Intertidal Reef (Design, analysis (changing maintain) Communities in monitoring) climate) PPH MNP

Improved width Improved width Combination of Timber is less Less impact on Increased Large rocks on Detailed design: across entire across entire timber and rock durable and not beach number of beach rock flats. - Rock groynes study area. Even study area. Even proves nearly as a strong as rock. connectivity structures. Moderate spread of sand spread of sand effective, but at Improved with less large - Timber Timber change to region across across cheaper cost alignment will rock structures groynes structures create sediment compartments compartments reduce repeat but large rock Timber vertical drop-off transport. - Breakwater wave impact structure within Average beach As waves and Approximately between structure. But vicinity of key Construction width increase - storm get bigger $3500/m of compartments shorter location on the efforts within limits wave structure Site Survey Compartment 1: structures to site. Climbing, trip Marine National energy reaching Up to +25-30 m Rock limit exposure to hazards. Park. Requires further the location Compartment 2: Approximately wave energy environmental where beach Structure Works onshore Up to +10 m $5000/m of assessment and most desired, Rock is long extends further and offshore structure monitoring at Compartment 3: enabling sand lasting and offshore More and around Up to +10 m build up near Works will be structure will exposing public environmental headland shops. onshore and last with site to larger waves Limits wave impacts with offshore. specific design. and deeper

ith Small Breakwater energy reaching structure located water

w the location Advise angling nearer to where beach structure more headland – rock

Combination: Rock & Timber Groynes

most desired, in to average pools – enabling sand wave direction

build up near

shops.

Option Option

RANKING VERY HIGH HIGH VERY HIGH HIGH VERY HIGH ABOVE AVERAGE VERY HIGH VERY HIGH

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6 Conclusions & Recommendations

Cardno’s investigation looked at long-term beach management options in the form of groynes, to maintain sand at the Point Lonsdale Front Beach. The assessment determined the wave climate at the site to inform possible options to maintain a beach along the point Lonsdale foreshore. The average wave climate was found to be consistent in directionality along the coast, with higher wave energy in the south (1.91 kN/m2) than in the north (~0.55 kN/m2). The average wave direction was found to align well with the typical shoreline position. In contrast, the groynes have been constructed at right angles to the seawall. It is suggested as part detailed design, consideration should be given to aligning and new groyne structures closer to the wave direction, as it will likely result in an improved shoreline response and lessen the structures exposure (and hence structure longevity). Modelling results showed that various groyne types could help to create more beach along the point Lonsdale foreshore. A variety of combinations were considered, extending groynes, adding groynes and a groyne/breakwater structure. Various materials were also considered – rock, timber and polymer, which influenced structure specification such as the length, height and alignment. A sediment transport model, LITPACK, was used to assess the effectivity each option. The larger rock structures were shown to capture sand across the study area, while smaller timber structures were able to effectively hold sand further north, with a minimal structure footprint. A small breakwater, south of the shops, was shown to help limit bigger waves reaching the seawall and beach. This, along with wave diffraction effect, should reduce scour from wave reflection on the southern section of the seawall, and enable the beach to build up in this area. Options were assessed against evaluation criteria tailored for the needs of this site, and considered key aspirations of this project including desired targeted locations for beach improvement, costs and environmental sensitivities. To enable a robust and in-depth comparison between each of the options, a more detailed multi-criteria analysis is recommended. This analysis requires key stakeholders to determine clear objectives to be achieved by this project, highlighting the priorities. This will allow associated weightings to be incorporated into the analysis, aiding in the differentiation between options and the decision making. Cardno suggest that an option that uses a combination of the suggested structures could be effective in creating more beach at the Point Lonsdale foreshore, allowing for a balance between effectivity, cost, amenity and environmental considerations. In terms of functionality, the option Combination: Rock & Timber Groyne with a small breakwater has been nominated as a suitable option to maintain a beach along this foreshore, particularly at the beach in front of the shops. However, this option does have additional considerations that must be taken into account, particularly environmental concerns, potential impacts of wave interaction with the adjacent cliffs and possible bypassing effects of the southern-most groyne. Therefore, it will need to be investigated in further detail. Cardno also recommend that DELWP look to undertake works in a staged approach, working from south to north. This will manage funding and allowing the beach to respond and adjust as well as targeting priority areas, nearer to the shops. All options have been presented at a concept level and require detailed design to be undertaken to further validate and appropriately design the nominated option. It is noted due to the sensitivity of this site, any development/construction will present significant challenges in regards to approval processes.

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7 References

BMT WBM, 2017, Lonsdale Bight Investigations Review and Options Overview, prepared for Department of Environment, Land, Water and Planning Cardno ,2011. The Great and Adjacent Coast and Beaches. Report prepared for the Port of Melbourne Corporation by Cardno. Report No. RM2289_LJ5518, Ver 1.0 Cardno, 2016. Wave Data in the Entrance of Port Phillip. Unpublished report prepared for the Port of Melbourne Corporation by Cardno, report 59916509_R01. Cardno Lawson Treloar, 2007. Hydrodynamics and Coastal Processes. Prepared for the Port of Melbourne Corporaion, Head Technical Report, Channel Deepening Project RM2124_LJ5508 Geoscience Australia ,2009. Australian Bathymetry and Topography Grid, 2 DVD set Parks Victoria & DELWP, 2017, Lonsdale Bight:consultation, options and actions summary Ris, R.C., Booij, N. and Holthuijsen, L.H. 1999. A third-generation wave model for coastal regions, part II: Verification. J.Geophys. Res., 104, C4, 7649-7666. Vantree, 1998. Lonsdale Bight: Coastal Process Investigations, prepared for the Department of Natural Resources and Environment

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