Department of Environment, Land, Water, and Planning (DELWP)€¦ · Drone air photos and...

Department of Environment, Land, Water, and Planning (DELWP)

Apollo Bay – Coastal Protection Study

30 November 2018

GHD | Report for DELWP ‐ Apollo Bay Coastal Protection, 3136559 | i

Table of contents 1. Introduction ................................................................................................................................... 1

1.1 Scope and purpose of this report ........................................................................................ 1

1.2 Limitations ........................................................................................................................... 1

2. Background .................................................................................................................................... 2

2.1 Description of the study area .............................................................................................. 2

2.2 Stakeholders ........................................................................................................................ 3

2.3 Previous relevant reports .................................................................................................... 3

2.4 Available surveys and air photos ......................................................................................... 3

2.5 History of shoreline change from air photo analysis ........................................................... 4

3. Coastal Processes ........................................................................................................................... 7

3.1 Water levels ......................................................................................................................... 7

3.2 Wave climate ....................................................................................................................... 8

3.3 Sediment transport ............................................................................................................ 12

3.4 Climate change impacts ..................................................................................................... 13

3.5 Recent storms (June ‐ July 2018) ....................................................................................... 14

4. Updated Hazard Mapping ............................................................................................................ 20

4.1 Methodology ..................................................................................................................... 20

4.2 Limitations ......................................................................................................................... 20

4.3 Coastal inundation hazard ................................................................................................. 20

4.4 Coastal erosion hazard ...................................................................................................... 21

4.5 Reduced foundation capacity ............................................................................................ 23

4.6 Hazard maps ...................................................................................................................... 24

5. Coastal Erosion Management Options ........................................................................................ 26

5.1 Comparison analysis criteria .............................................................................................. 26

5.2 Non‐protective actions ...................................................................................................... 27

5.3 Non‐structural protection options .................................................................................... 29

5.4 Structural protection options ............................................................................................ 33

5.6 Comparison of options ...................................................................................................... 47

5.7 Regulatory requirements ................................................................................................... 48

6. Immediate Remedial Works ........................................................................................................ 49

6.1 Need for remedial works ................................................................................................... 49

6.2 Proposed remedial works .................................................................................................. 50

6.3 Design approach ................................................................................................................ 50

GHD | Report for DELWP ‐ Apollo Bay Coastal Protection, 3136559 | ii

6.4 Extent of works .................................................................................................................. 51

6.5 Design conditions .............................................................................................................. 52

6.6 Detailed design .................................................................................................................. 54

6.7 Coastal impact assessment ................................................................................................ 57

7. Community Open House Sessions ............................................................................................... 61

8. Next Steps .................................................................................................................................... 62

Table index Table 1 Apollo Bay tidal planes ................................................................................................................ 8

Table 2 Storm tide height return levels for Apollo Bay ............................................................................ 8

Table 3 35 years of significant wave height vs peak wave direction offshore of Apollo Bay .................. 9

Table 4 35 years of significant wave height vs peak wave period offshore of Apollo Bay .................... 10

Table 5 Offshore wave height vs annual return period ......................................................................... 11

Table 6 Time and location of available data on Propeller website ........................................................ 15

Table 7 2018 Storm cut at Apollo Bay and Mounts Bay ......................................................................... 18

Table 8 Maximum 2018 storm cut at Apollo Bay and Mounts Bay ........................................................ 18

Table 9 AEP storm tide levels incorporating mean sea level scenarios (CSIRO 2009) ........................... 20

Table 10 Peak coastal inundation elevation scenarios for the study area (WT, 2012) .......................... 21

Table 11 Estimated shoreline recession over 10 years, incorporating long term recession

trend and sea level rise (m) ............................................................................................... 22

Table 12 Storm Cut width (m) ................................................................................................................ 23

Table 13 Zone of wave impact width (m) ............................................................................................... 23

Table 14 WT 2012 adopted widths of zone of reduced bearing capacity .............................................. 24

Table 15 Adopted widths of zone of reduced foundation capacity for this study ................................. 24

Table 16 Management options .............................................................................................................. 26

Table 17 Analysis against criteria for “Do nothing” option .................................................................... 27

Table 18 Analysis against criteria for “Planned retreat” option ............................................................ 28

Table 19 Analysis against criteria for “Beach nourishment” option ...................................................... 30

Table 20 Analysis against criteria for “Dune management” option ....................................................... 32

Table 21 Analysis against criteria for “GSC” option ............................................................................... 34

Table 22 Analysis against criteria for “Informal rock protection” option .............................................. 35

Table 23 Analysis against criteria for “Rock revetment” option ............................................................ 37

Table 24 Analysis against criteria for “Groynes or artificial headlands” option .................................... 39

Table 25 Analysis against criteria for “Offshore breakwaters, submerged artificial reefs and

beach sills” option ............................................................................................................. 42

GHD | Report for DELWP ‐ Apollo Bay Coastal Protection, 3136559 | iii

Table 26 Analysis against criteria for “Vertical seawall” option ............................................................ 45

Table 27 Comparison of long‐term performance of options ................................................................. 47

Table 28 Design wave parameters ................................................................................................... 53

Table 29 Estimated overtopping volumes.............................................................................................. 58

Figure index

Figure 1 Location plan and coastal sectors .............................................................................................. 2

Figure 2 Mounts Bay shoreline analysis (CES, 2005) ................................................................................ 4

Figure 3 Apollo Bay shoreline analysis (CES, 2005) .................................................................................. 6

Figure 4 Storm tide components (after fig 2.3 in Harper (2001)) ............................................................ 7

Figure 5 CAWCR wave model output point in vicinity of study area ....................................................... 9

Figure 6 Offshore storm peak wave conditions ..................................................................................... 10

Figure 7 Offshore wave height probability from all directions (data point: ‐38.79 ̊° N, 143.73°

E) ........................................................................................................................................ 11

Figure 8 Offshore wave height probability from SE (data point: ‐38.79 ̊° N, 143.73° E) ......................... 11

Figure 9 Simulated global average sea surface temperature change and mean sea level rise

(IPCC, 2014)) ...................................................................................................................... 14

Figure 10 Cross section comparison ‐ Marengo Beach ‐ South (Image source: Propeller

website, Accessed 13/09/18) ............................................................................................ 16

Figure 11 Cross section comparison ‐ Apollo Bay (Milford St ‐ Joyce St) (Image source:

Propeller website, Accessed 13/09/18) ............................................................................. 16

Figure 12 Sample cut/fill volume map (Image source: Propeller website, Accessed

14/09/18) ........................................................................................................................... 17

Figure 13 Apollo Bay areas for storm cut estimation (Image source: Google Earth, Accessed

13/09/18) ........................................................................................................................... 17

Figure 14 Offshore wave height, Apollo Bay, June and July 2018.......................................................... 19

Figure 15 Schematic illustrations of the Bruun (1962) model of beach profile response to

rising sea level (Image source: Davidson‐Arnott, 2005) .................................................... 22

Figure 16 – Definition of hazard zones due to storm erosion, dune slumping and instability

after Nielsen et al. (1992) .................................................................................................. 24

Figure 17 Locations in study area where retreat could be investigated if required .............................. 29

Figure 18 Mounts Bay Beach during nourishment in May 2017 ............................................................ 31

Figure 19 Nourishment underway at Apollo Bay opposite Cawood Street on 1 August 2018 .............. 31

Figure 20 Completed dune management at Mounts Bay in June 2017 ................................................. 33

Figure 21 GSC revetments at Portsea and Aspendale in Port Phillip Bay .............................................. 34

Figure 22 Informal rock protection between Joyce and Cawood streets. ............................................. 36

Figure 23 Rock Revetment recently constructed near Skenes Creek .................................................... 38

GHD | Report for DELWP ‐ Apollo Bay Coastal Protection, 3136559 | iv

Figure 24 Buried revetment concept sketch .......................................................................................... 38

Figure 25 Rock groynes forming artificial headlands at Hampton in Port Phillip Bay ............................ 40

Figure 26 Geotextile groyne at Busselton, WA at completion and 2 months following

completion ......................................................................................................................... 40

Figure 27 Concept of possible groynes in Apollo Bay ............................................................................ 41

Figure 28 Offshore Breakwaters in Norfolk, UK ..................................................................................... 43

Figure 29 Narrowneck artificial reef, Queensland, which was built to help protect coast from

erosion ............................................................................................................................... 43

Figure 30 Concept of possible offshore breakwaters in Apollo Bay ...................................................... 44

Figure 31 Bluestone seawall at Brighton in Port Phillip Bay .................................................................. 46

Figure 32 Walking path impacted by erosion in Apollo Bay (August 2018) ........................................... 49

Figure 33 Cypress trees which may be at risk (August 2018)................................................................. 49

Figure 34 Coastal erosion risk profile at Apollo Bay............................................................................... 52

Figure 35 DCP locations and estimated depth of refusal in m AHD ....................................................... 54

Figure 36 Detailed cross section of the remedial works around Milford St. ......................................... 55

Figure 37 Eroded walking path in Apollo Bay......................................................................................... 55

Figure 38 Typical cross section for the proposed crushed rock path .................................................... 56

Figure 39 Typical beach boardwalk ........................................................................................................ 56

Figure 40 Existing access stairs at Apollo Bay, south of Cawood St. ...................................................... 57

Appendices Appendix A – Coastal Erosion Hazard Maps

Appendix B – Short‐Term Remediation Works Revetment Design Drawings

Appendix C – Community Open House Summary

GHD | Report for DELWP ‐ Apollo Bay Coastal Protection, 3136559| 1

1. Introduction The foreshore at Apollo Bay has experienced significant erosion in a series of storms during

June and July 2018. The area of most concern is from approximately Cawood Street to

Marriners Lookout Road, where erosion of up to 5m has occurred, removing sections of the

coastal walking path and putting other assets such as sewer pipes, stormwater outlets, Cyprus

trees and the Great Ocean Road at risk.

GHD has been engaged by the Department of Environment, Land, Water, and Planning

(DELWP) to update coastal hazards risk maps, design short term remedial works and review

options for the long‐term management of coastal erosion.

1.1 Scope and purpose of this report

The purpose of this report is to document investigations, options assessment and design works

carried out by GHD for coastal protection at Apollo Bay. The scope of work includes:

Update of coastal hazard risk maps (Marengo to Skenes Creek), refer to Section 4.

Review of long‐term treatment options for asset protection, access and amenity (Marengo

to Skenes Creek), refer to Section 5.

Design of short‐term remedial works for the Apollo Bay foreshore (Cawood Street to

Marriners Lookout Road), refer to Section 6.

1.2 Limitations

This report has been prepared by GHD for DELWP and may only be used and relied on by

DELWP for the purpose agreed between GHD and DELWP as set out in section 1.1 of this

report.

GHD otherwise disclaims responsibility to any person other than DELWP arising in connection

with this report. GHD also excludes implied warranties and conditions, to the extent legally

permissible.

The services undertaken by GHD in connection with preparing this report were limited to those

specifically detailed in the report and are subject to the scope limitations set out in the report.

The opinions, conclusions and any recommendations in this report are based on conditions

encountered and information reviewed at the date of preparation of the report. GHD has no

responsibility or obligation to update this report to account for events or changes occurring

subsequent to the date that the report was prepared.

The opinions, conclusions and any recommendations in this report are based on assumptions

made by GHD described in this report. GHD disclaims liability arising from any of the

assumptions being incorrect.

GHD has prepared this report on the basis of information provided by DELWP and others who

provided information to GHD (including Government authorities), which GHD has not

independently verified or checked beyond the agreed scope of work. GHD does not accept

liability in connection with such unverified information, including errors and omissions in the

report which were caused by errors or omissions in that information.


2. Background 2.1 Description of the study area

The study area covers a total distance of approximately 10 km along the coastline from

Marengo to Skenes Creek. For the purpose of mapping erosion hazards the study area has

been divided into the following six sectors, as shown in Figure 1:

Skenes Creek

Wild Dog Creek

Apollo Bay North (Cawood St to Marriners Lookout Rd)

Apollo Bay South

Mounts Bay North

Mounts Bay South

Figure 1 Location plan and coastal sectors


2.2 Stakeholders

This following stakeholders are involved in this project, or will be involved as it progresses:

DELWP

Otway Coast Committee of Management

VicRoads

Colac Otway Shire

Barwon Water

Eastern Marr

Great Ocean Road Task Force

Community (local and visiting)

Political

Utility providers

2.3 Previous relevant reports

The following relevant reports were taken into consideration when completing this report:

Environmental Geosurveys P/L and AS Minor Geotechnical, September 2018, V1 – Under

Draft, Mounts Bay, Marengo – Is backshore sand renourishment a viable option for

managing coastal hazard risk?;

Treewatch Arborist, August 2018. Arboricultural Assessment and Report. Tree Evaluation

for Health and Safety. Location: Coastal land between Marriners Lookout Road and

Cawood Street Apollo Bay, Victoria. (Report to Otway Coast Committee)

Deakin University Marine Mapping Group, August 2018, Apollo Bay Comparison UAV

Flights. June 1st, June 21st, July 26th 2018.

DELWP, June 2018, Storm Damage Audit

GHD, May 2018, Great Ocean Road Coastal Protection Works Final Design Report and

Coastal Impact Assessment

Water Technology, February 2017, Marengo to Wild Dog Creek Sand Management Plan

AW Maritime, September 2015, Coastal Management Assessment, Cawood Street beach

recession.

Water Technology, October 2012, Coastal Hazards Management Plan Marengo to Skenes

Creek.

DELWP, May 2011, Fact Sheet – Where has my beach gone.

Coastal Engineering Solutions, August 2005, Apollo Bay Sand Study.

2.4 Available surveys and air photos

Drone air photos and photogrametry pre storm June 1st 2018.

Drone air photos and photogrametry post storm 21st June 2018.

Drone air photos and photogrametry post storm 26th July 2018.

Colac Otway Shire are in the process of commissioning drone footage for the Port (August

2018).


2.5 History of shoreline change from air photo analysis

A historical analysis of the coastline from Marengo to Wild Dog Creek was completed by

Coastal Engineering Solutions (CES, 2005), by comparing available aerial photographs from

1942 to 2004. A summary of these results are discussed below in the following subsections.

This analysis does not include the period 2004 – present, and should be updated.

2.5.1 Mounts Bay

The change in the vegetation line from 1942 to 2004 is shown below in Figure 2. The net

sediment transport to the north appears to cause erosion from Section ‘A‐A’ to ‘F‐F’ on Figure

2, primarily because there is insufficient inshore sediment to the south of Marengo to

replenish the coastline.

Figure 2 Mounts Bay shoreline analysis (CES, 2005)

Accretion begins just south of the Barham River mouth (Sections ‘G‐G’ and ‘H‐H’ on Figure 2),

which is caused by the river mouth and Point Bunbury Groyne impeding sand movement

towards the north. As the shoreline has accreted past Point Bunbury Groyne, sand is free of

obstruction until the Harbour where sand is funnelled into the Entrance with the tide and

waves.


Occasionally, the longshore sediment transport is to the south and Mounts Bay Beach is

replenished from the sand accumulated at the Barham River Mouth and south of Point

Bunbury Groyne. However, this does not occur often enough to prevent erosion of this section

of the coastline in the long‐term.

2.5.2 Apollo Bay

Following construction of the Harbour in the early 1950’s, the beach just south of Cawood

Street from Section ‘L‐L’ to ‘O‐O’ on Figure 3 accreted until approximately 1986, when the

beach appears to have become stable. The sediment dredged from the Harbour and

discharged off the north side of the Lee Breakwater would have contributed to this accretion.

While sediment is still discharged off the north side of the Lee Breakwater, from 1986 until

2004 this section of the beach then eroded slightly.

North of Cawood Street from section ‘P‐P’ to ‘R‐R’ on Figure 3, the coastline experienced both

accretion and erosion from 1952 to 2004.

North of Marriners Road to the groyne at Wild Dog Creek, the beach accreted from 1952 until

at least 1986, with only minor accretion following this just south of Wild Dog Creek groyne.

This assessment indicates that Apollo Bay Harbour provides a certain level of shelter from the

dominant southerly waves to Apollo Bay Beach which is proportional to the shoreline accretion

with a maximum at Apollo Bay Harbour and a minimum at Cawood Street. North of Cawood

Street, Apollo Bay beach is fully exposed to the dominant southerly wave energy.

The groyne at Wild Dog Creek has caused accretion to the south to about Marriners Road,

however is not long enough to cause further accretion to the south.

The shoreline north of Marriners Road is not expected to accrete further as the groyne at Wild

Dog Creek has reached its capacity. As this section of the coastline appears to have reached

equilibrium, any excess sand will bypass this groyne and continue northward.


Figure 3 Apollo Bay shoreline analysis (CES, 2005)

Shoreline Movements in Metres

Cawood Street


3. Coastal Processes The coastal processes in the study area have been summarised through a review of previous

studies available, photographs and survey information. It should be noted that GHD’s scope of

work excluded detailed analysis and modelling of coastal processes.

New coastal process analyses that has been undertaken for this study include:

Offshore wave climate (refer to Section 3.2.1)

Description of recent storm erosion (refer to Section 3.2.1)

Review of probability of recent storms (refer to Section 3.5)

Calculation of storm cut for recent storms (refer to Section 3.5.2)

3.1 Water levels

The total water level experienced at a coastal, ocean or estuarine site during the passage of a

storm event will be made up of contributions from a number of different influences, with the

predominant components being the astronomical tide, surge, and wave setup, as shown in

Figure 4. The combined or total water level, including the storm surge component is the storm

tide. In Australia this is referenced to mean sea level in metres Australian Height Datum (m

AHD). The following sections describe the contributors to a ‘storm tide’, which is one of the

key components in the design of any coastal shore protection structure. A storm tide level is

often known interchangeably as an extreme water level.

Figure 4 Storm tide components (after fig 2.3 in Harper (2001)1)

3.1.1 Astronomical tides

Astronomical tides are the daily rise and fall of sea levels caused by the combined effects of

the rotation of the earth and the gravitational attraction between the earth, moon and the

sun. Water levels which are frequently of interest are known as tidal planes.

1 Harper B.A. (Ed.), 2001. “Queensland Climate Change and Community Vulnerability to Tropical Cyclones Ocean Hazards Assessment Stage

1”.


The tidal planes for Apollo Bay have been extracted from Vic Tides (VRCA, 2018, Edition 2) and

Australian Hydrographic Service, 2010, and are summarised below.

Table 1 Apollo Bay tidal planes

Tidal Plane Australian Height Datum (AHD)

Chart datum (CD)

Highest Astronomical Tide (HAT) 1.1 m 2.3 m

Mean High Water Springs (MHWS) 0.8 m 2.0 m

Mean High Water Neaps (MHWN) 0.1 m 1.3 m

Mean Sea Level (MSL) 0 m 1.2 m

Mean Low Water Neaps (MLWN) - 0.1 m 1.1 m

Mean Low Water Springs (MLWS) - 0.8 m 0.4 m

Lowest Astronomical Tide (LAT) - 1.2 m 0.0 m

3.1.2 Storm tide (extreme water) levels

As shown in Figure 4, the storm tide is an extreme water level which incorporates tide, surge

and wave setup, and is used in the design of coastal structures. The 2009 CSIRO study “The

Effect of Climate Change on Extreme Sea Levels along Victoria’s Coast” reported model results

for Apollo Bay for storm tide levels, which are shown in Table 2 for various return periods.

Table 2 Storm tide height return levels for Apollo Bay

Return period (yrs) 2009 levels in m AHD

10 1.10

20 1.23

50 1.34

100 1.42

For this assessment, we have considered the CSIRO storm tide level of 1.42 m AHD for a 100

year return period for 2009 to be representative of current conditions, and have added 0.4 m

to account for approximately 50 years of sea level rise, as the design life of the coastal

structures for this study has been taken as 50 years. Wave setup was not included in the CSIRO

results and has therefore been added to estimate the design storm tide level. For further

information on sea level rise, refer to Section 3.4.1.

3.2 Wave climate

The main purpose of studying the wave climate is to estimate the possibility of occurrence of

storms with similar magnitude and duration to the recent storms. In order to achieve this

purpose three steps were taken which are summarized in this section:

Studying the long term wave data

Studying the recent storms

Estimating return period of recent storms


3.2.1 Offshore wave climate

3.2.1.1 Long term wave data

In order to understand the general wave climate of the area the output of a WaveWatch III

model was studied. This hindcasted dataset provides hourly wave data for the period of 1979

to 2014 and covers the Australian coastline with a spatial resolution of 0.4°. The model is

developed by CAWCR2 and is available on the CSIRO website. The output point which was

selected to represent the area is shown on Figure 5. This point is located 5.5 km offshore and

at a water depth of approximately ‐45.5 m AHD. The coordinates of the output point are ‐

39.79° N, 143.73° E.

Figure 5 CAWCR wave model output point in vicinity of study area

Table 3 below shows 35 years of significant wave height vs peak wave direction, and Table 4

shows 35 years of significant wave height vs peak wave period. The offshore storm peak wave

conditions are shown in Figure 6. The key outcomes from these tables and figure are also

discussed below.

Table 3 35 years of significant wave height vs peak wave direction offshore of Apollo Bay

Hs (m)

N NE E SE S SW W NW Total

0-1 0% 0% 0% 0.02% 0.07% 3.56% 0% 0% 3.64%

1-2 0% 0% 0.01% 0.99% 1.20% 54.81% 0% 0% 57.00%

2-3 0% 0% 0.04% 0.98% 1.36% 29.15% 0% 0% 31.52%

3-4 0% 0% 0.01% 0.19% 0.52% 5.90% 0% 0% 6.62%

4-5 0% 0% 0% 0.03% 0.13% 0.92% 0% 0% 1.08%

5-6 0% 0% 0% 0.01% 0.02% 0.10% 0% 0% 0.12%

>6 0% 0% 0% 0% 0% 0.01% 0% 0% 0.01%

Total 0% 0% 0.06% 2.21% 3.29% 94.44% 0% 0% 100%

2 Collaboration for Australian Weather and Climate Research

Apollo Bay

Marengo

Skenes Creek

Wild Dog Creek

Wave model output point

in vicinity of study area


Table 4 35 years of significant wave height vs peak wave period offshore of Apollo Bay

Hs (m) 0-4 s 4-8 s 8-12 s 12-16 s 16-20 s >20 s Total

0-1 0.003% 0.03% 1.13% 2.22% 0.25% 0.01% 3.64% 1-2 0% 1.09% 10.59% 39.97% 5.06% 0.30% 57.00%

2-3 0% 0.76% 3.63% 23.27% 3.75% 0.10% 31.52%

3-4 0% 0.02% 0.71% 4.46% 1.42% 0.02% 6.62%

4-5 0% 0% 0% 1% 0.32% 0% 1.08%

5-6 0% 0% 0% 0% 0.04% 0% 0.12%

6< 0% 0% 0% 0.006% 0.01% 0% 0.01%

Total 0.003% 1.89% 16.16% 70.67% 10.85% 0.43% 100%

Figure 6 Offshore storm peak wave conditions

3.2.1.2 Extreme value analysis

In order to achieve a better understanding of wave climate of the study area and to evaluate

wave heights for extreme storm events, an extreme value analysis (EVA) was performed. In

this analysis an extreme value model is formulated based on fitting a theoretical probability

distribution (Weibull in this case) to observe the occurrence probability of extreme values.

Results of the EVA and probability distribution of wave heights are displayed in Figure 7 and

significant wave height for various return periods are presented in Table 5.


Figure 7 Offshore wave height probability from all directions (data point: -38.79̊° N, 143.73° E)

Figure 8 Offshore wave height probability from SE (data point: -38.79̊° N, 143.73° E)

Based on Figure 7 and Figure 8, expected significant wave heights for larger return periods are

presented in Table 5.

Table 5 Offshore wave height vs annual return period

Return period (yr)

Hs from all directions (m) Hs from SE (m) Hs from SW (m)

1 5.3 3.8 5.3 10 6.3 4.9 6.3 50 7.0 6 6.9 100 7.2 6.5 7.2

The main outcomes of the wave analysis are as follows:

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

9.0

10.0

1 10 100 1000

Sig

nif

ican

t W

ave

Hei

gh

t, H

s (m

)

Return Period (Year)

Weibull Fit, k (Shape Factor) = 1.1

Hindcasted wave height

99% Confidence Interval

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

1 10 100 1000

Sig

nif

ican

t W

ave

Hei

gh

t, H

s (m

)

Return Period (Year)

Weibull Fit, k (Shape Factor) = 1

hindcasted wave height

99% Confidence Interval


South westerly is the dominant wave direction at Apollo Bay with waves propagating from

this direction 94% of the time;

South easterly and easterly waves occur approximately 5% of the time;

More than 70% of the waves are long period swell waves with a period of 16‐20 seconds;

Storm events from E and SE directions have a typical wave period of 8.5‐11.5 sec and wave

height up to 4.6 m;

Storm events from SW have a typical wave period of 10 ‐20 sec and average offshore wave

height of up to 7 m;

Offshore wave heights of approximately 5 m are estimated to occur with return period of

one year.

3.2.2 Nearshore wave climate

As waves move from offshore to inshore, wave heights and direction are modified by shoaling

and refraction. To determine the wave height and direction near the Apollo Bay shoreline,

numerical modelling is required to transform the offshore waves to locations of interest. As

numerical modelling is not included in GHD’s scope of works, nearshore wave climate has not

been estimated.

3.3 Sediment transport

Sand movements along the Apollo Bay coastline are generally driven by wave breaking and

wave‐induced currents. As waves impact shorelines, sediments are mobilised in suspension by

the moving water and transported along the beach.

The rate of sediments transport alongshore is dependent on factors such as on the size of the

waves, water levels and the type of sediment and grain size. Sediments can move in both

directions along the shore depending on the direction of the waves relative to the shore.

It is important to recognise that the volume of sand transported is dependent on the

frequency, strength and direction of storm events, and the sediment properties. There can

therefore be a significant variation in sediment transport rates from year to year, which is

often reflected as localised shoreline changes, particularly on sandy coastlines.

It is also important to acknowledge that man‐made structures such as the harbour and

groynes, as well as sand management practices have a significant impact on sediment

movements.

During storm events, significant volumes of sediment can be transported cross‐shore

(perpendicular) from the upper beach to the lower beach, and into the nearshore zone.

Assuming adequate sediment supply to the area, this sediment is then stored in nearshore

bars until calmer weather conditions gradually return the sediment to the upper beach. The

extent of erosion or beach recession is dependent upon the characteristics of the storm event,

and the water levels and wave heights present during the storm. Estimation of the expected

beach erosion during a specified storm event can be determined through numerical modelling

or detailed beach monitoring information.

GHD’s scope of work did not include a detailed analysis of sediment transport, however

observations about sediment transport from previous relevant reports are as follows:

The estimated net sediment transport is 80,000 m3/year towards the north. This was

estimated by PMC in 1989 primarily based on dredging records and has been adopted by

all studies since.


The direction of the net longshore sediment transport is from south to north, however as

noted in CES, 2005 “Whilst there is a net northerly sediment transport for most months,

there were 9 months over the 6‐7 year period modelled where the net sediment transport

was to the south”.

The shoreline analysis included in CES, 2005 indicates that construction of the Apollo Bay

harbour in the 1950s impacted the longshore sediment transport along the Apollo Bay

shoreline (Figure 3). The shoreline accreted rapidly in the lee of the new harbour, from the

Harbour north to Cawood street, and eroded slightly from Cawood Street to Mariners

Road. Shoreline change due to the harbour stabilised around 1990, noting that sand

bypassing is ongoing.

The groyne at Wild Dog Creek has trapped sediment on the southern side causing

accretion of the beach, but has now reached its capacity. As this section of the coastline

appears to have reached equilibrium, any excess sand will bypass the groyne and continue

northward.

Further studies, surveys and numerical modelling are recommended in order to determine the

sediment transport regime at Apollo Bay.

3.4 Climate change impacts

The response of coastlines to the various processes detailed previously is further complicated

due to the impacts of climate change, particularly sea level rise.

Climate change induced sea level rise may influence existing coastal processes in more ways

than simply raising water levels. It is also forecast by climate change scientists that the

intensity and frequency of storms will increase. Ultimately, climate change will potentially

result in more severe coastal erosion and inundation (in terms of extents of impacts and

frequency).

3.4.1 Sea level rise

The sea level rise planning policy for decision making is the Victorian Coastal Strategy 2014

which states:

“Plan for possible sea level rise of not less than 0.8 metres by 2100, and allow for the

combined effects of tides, storm surges, coastal processes and local conditions such

as topography and geology, when assessing risks and coastal impacts associated with

climate change”

This policy position is based on the 2014 Intergovernmental Panel on Climate Change (IPCC)

assessment of predicted rises in sea level to the end of the 21st Century. Figure 9 provides an

indication of the rate and uncertainties associated with the projected sea level rise.

Accordingly, this assessment has adopted a rise in sea level of 0.4 m, as the design life for the

coastal structures in this study has been taken as 50 years.


Figure 9 Simulated global average sea surface temperature change and mean sea level rise (IPCC, 2014))

3.4.2 Changes to the wave climate and sediment transport

There may be changes to the wave climate affecting the coastline as a result of increased sea

levels and increased wind speeds. CSIRO (2011) suggested that winds may become stronger

and there may be an anti‐clockwise shift in the dominant wind direction.

Given the projected increases in water levels, wind speeds, potentially ocean wave heights,

and storm frequency, it is anticipated that changes to existing sediment transport processes

will occur. It is expected that there will be an increase in the gross sediment transport, which

will result in increased seasonal variability of beach steepness, and progressive shoreline

retreat as sea levels rise. Given the direction of net sediment transport along the coast from

the south‐west to the north‐east, this may result in a reduction of the net transport rate.

The projected sea level rise due to climate change is expected to result in accelerated

recession of erodible shorelines.

3.5 Recent storms (June - July 2018)

3.5.1 Description of erosion

The foreshore at Apollo Bay has experienced significant erosion in a series of storms during

June and July 2018. VicRoads are concerned that ongoing erosion could threaten the Great


Ocean Road. The area of most concern is from approximately Cawood St to Marriners Lookout

Rd, where the dune area that acts as buffer between the road and the beach is relatively

narrow, typically 10 to 25 m before the recent storms.

The recent storms have formed an erosion escarpment that has advanced towards the road up

to 5 m between 1/6/2018 and 26/7/2018. The walking path and dune vegetation has been lost

in a number of locations and several large cypress trees may be at risk.

In the worst affected area, a stretch of approximately about 250 m, centred on Milford St, the

distance from the erosion escarpment to the edge of the traffic lane on the Great Ocean Road

is now 6 to 8.5 m. Another series of storms similar to those recently experienced could put the

road at risk, noting that a zone of instability extends landward of the erosion escarpment.

The erosion escarpment is typically 1 to 2 m high. The material exposed in the erosion

escarpment is principally sand. In some places fill consisting of silty sand and clay is present. A

large number of sandstone boulders are also exposed in the escarpment and on the beach,

which are likely informal rock protection placed in response to previous erosion events. The

effectiveness of this protection varies.

3.5.2 Storm cut

In order to estimate the storm cut value along Apollo bay beach, high resolution aerial images

from the Propeller website were compared. The Propeller website is a visual and easy‐to‐use

drone data analytics platform. Aerial photos from three dates were available on the website

(Table 6). The aerial photos were taken shorty after severe storms in winter 2018, and

provided a valuable resource for calculating storm cut and erosion volume.

Table 6 Time and location of available data on Propeller website

Beach Compartment First survey Second survey Third survey

Apollo Bay June 1st 2018 June 21st 2018 July 26th 2018

Marengo June 1st 2018 June 21st 2018 July 27th 2018

The beach profiles after these three storms in June and July 2018 are compared in Figure 10

and Figure 11. It can be seen that after the first storm (14th/15th June 2018) the dune profile

retreated approximately 3 m between Milford St and Joyce St. The impact of the second storm

(5th July) was less significant, which is consistent with this storm’s wave height being less (as

shown in Figure 14.


Figure 10 Cross section comparison - Marengo Beach - South (Image source: Propeller website, Accessed 13/09/18)

As can be seen in Figure 10, in Marengo despite the high storm cut volume, severe dune

erosion was not captured by this survey between the two first storms, although erosion

probably occurred. The reason that erosion was not captured is due to the beach nourishment

operation which took place between the first and second surveys in “Marengo south”. Further

erosion occurred between 21st June and 27th July 2018.

The storm cut for the worst affected area in Apollo Bay (centred around Milford St) is shown in

Figure 11 and Figure 12, where most of the erosion occurred between the first two storms.

Figure 11 Cross section comparison - Apollo Bay (Milford St - Joyce St) (Image source: Propeller website, Accessed 13/09/18)


Figure 12 Sample cut/fill volume map (Image source: Propeller website, Accessed 14/09/18)

For calculation of storm cut, the main study areas (Figure 1) were divided into multiple sub‐

sectors as shown in Figure 13. The escarpment/vegetation line from each photo was digitized

and the erosion widths (change between photos) was measured.

Figure 13 Apollo Bay areas for storm cut estimation (Image source: Google Earth, Accessed 13/09/18)

Marriners to Milford St.

Milford St. to Joyce St.

Joyce St. to Cawood St.

Cawood St. to Thomson St.

Thomson St. to surf club

Surf club to skate park

Skate park to harbour


Storm cut volume and length during winter 2018 for different sectors of the shoreline is

calculated and presented in Table 7.

Table 7 2018 Storm cut at Apollo Bay and Mounts Bay

Sub sector Length (m)

Storm cut volume over sub sector

(m3)

Cut volume per metre (m3/m)

Retreat length* (m)

1st - 2nd survey

2nd – 3rd survey

1st - 2nd survey

2nd – 3rd survey

1st - 2nd survey

2nd – 3rd survey

To Marriners Lookout Rd

75 163 50 2.2 0.6 0.5 0.5

Marriners - Milford St

236 2901 246 12.3 1.04 1.2 1.0

Milford St – Joyce St

279 3035 454 10.87 1.6 0.5-5 1.3

Joyce St- Cawood St

382 5679 374 14.86 0.98 0.7-4.9 1.5

Cawood St- Thomson St

248 3256 124 13.13 0.5 0-3.7 0.5

Thomson St- Surf club

323 2161 315 6.7 0.97 ~1 ~ 0

Surf club - skate park

212 3841 839 18.12 3.96 ~1 ~ 0

Skate park – harbour

250 2367 1026 9.47 4.1 ~ 0 ~ 0

Marengo North

580 3385 1508 5.8 2.6 ~ 0 ~ 0

Marengo South

490 - 2970 - 6.1 - 1.5

* Retreat length refers to dune erosion or where the scarp line had moved landward. High

storm cut value does not necessary correlate with higher retreat length, since cut volume is

based on the entire beach and not just at the foot of the scarp.

Table 8 shows the maximum retreat length for each sector after two consecutive storms.

Results of this table in addition to risk maps are reliable tools to identify the priority of beach

protection programs.

Table 8 Maximum 2018 storm cut at Apollo Bay and Mounts Bay

Sub sector Length (m)

Cut volume (m3) Storm cut (m3/m) Retreat length (m)

Jun 1st - 21st

Jul 21st -26th

Jun 1st - 21st

Jul 21st - 26th

Jun 1st - 21st

Jul 21st - 26th

Marriners - Milford St

7 - 2.4 - 0.34 - ~ 2

Milford St – Joyce St

10 242 - 24.2 - ~ 5 -

7.5 - 23 - 3.06 - ~ 2.5

10 198 - 19.8 - ~ 5 -


Joyce St - Cawood St

7 - 4.2 0.6 - ~ 2

Cawood St- Thomson St

11.5 296 - 25.7 - ~ 3.7 -

Marengo North

21 200 90 9.5 4.3 ~ 1 ~ 0.5

Marengo South

15 - - - 2.7

3.5.3 Wave climate of recent storms

During the 2018 winter a number of consecutive storms caused severe erosion along the

shoreline of Apollo Bay and Marengo. As mentioned previously, it is of high importance to

estimate the probability of recurrence of the wave climate during June and July 2018. Figure

14 represents offshore wave height fluctuations in Apollo Bay during this period.

Figure 14 Offshore wave height, Apollo Bay, June and July 2018

Figure 14 shows that the offshore wave height of the recent storms was approximately 5 m.

The impact of each of the individual storms on the shore is briefly discussed in Section 3.5.

Figure 7 shows that the return period of an offshore wave of 5 m in Apollo Bay is only one

year. This does not mean that a 1‐year storm will happen regularly every year, or only once in

a year. In fact, in any given year, a 1‐year event may occur once, twice, more, or not at all, and

each outcome has a probability that can be computed.

0

1

2

3

4

5

6

20/05/2018 30/05/2018 9/06/2018 19/06/2018 29/06/2018 9/07/2018 19/07/2018 29/07/2018 8/08/2018

hs (m

)

date

Second stormThird storm

First storm


4. Updated Hazard Mapping 4.1 Methodology

The coastal hazard mapping undertaken by Water Technology (WT) in 2012 (Coastal Hazards

Management Plan Marengo to Skenes Creek, WT, 2012) has been reviewed and updated in

light of the recent storm erosion. Our analysis follows WT’s 2012 methodology and hazard

tables, which have been updated to show both the WT 2012 estimates (in black), and the

revised estimates by GHD (in red). Our assumptions and adopted allowances are described in

this section of the report.

The coastal hazards included in this analysis are inundation, coastal erosion and reduced

foundation capacity. Hazard zones are defined as distances landward of the current erosion

escarpment (or vegetation line) that could experience a hazard in the next 10 years.

Following WT’s methodology, hazards are estimated for three different levels of probability:

Almost certain to occur in a 10 year time frame (10% AEP storm);

Unlikely to occur in a 10 year time frame (1% AEP event); and

Rare ‐ worst case scenario for a combination of factors (<1% AEP)

It should be emphasised that this is a high level assessment based on previous studies and

available data, and not on a rigorous study of coastal processes. It is however suitable for

assessing the relative level of risk to different parts of the coastline and prioritising short term

remedial works.

As the wave exposure and shoreline orientation vary throughout the study area, it has been

divided up into six sectors for the purpose of hazard mapping, as shown in Figure 1.

4.2 Limitations

‐ No updated data was available along Wild Dog Creek and Skenes Creek;

‐ No nearshore wave data was available (eg. refraction coefficient); and

‐ The 2005 air photo analysis has not been updated to include more recent aerial photos

and surveys.

4.3 Coastal inundation hazard

The WT report (WT, 2012) calculated coastal inundation extents in the study area by adding

wave run‐up and wave set‐up values to extreme storm tide levels (10% and 1% AEP) in Apollo

Bay. Three probability scenarios were defined based on different exceedance probabilities of

storm tides and different design wave heights. The same methodology has been used in this

study.

4.3.1 Storm tide

Storm tides with an AEP of 1% and 10% at Apollo Bay have been estimated by the CSIRO

(CSIRO, 2009) as discussed in Section 4.3.1. These are also displayed in Table 9.

Table 9 AEP storm tide levels incorporating mean sea level scenarios (CSIRO 2009)

Storm Tide Scenario Storm Tide Level (m AHD)

Apollo Bay (10% AEP) 1.10


Apollo Bay (1% AEP) 1.42

4.3.2 Wave setup and wave run-up

GHD has analysed the offshore wave climate at the study area (Section 3) but further analysis

on wave transformation is required to identify the nearshore wave heights and therefore the

wave run‐up. Since the refraction coefficient was not provided in available reports and

numerical modelling is not included in the scope of this study, the results from WT 2012 were

used to prepare the coastal inundation hazard maps. Estimated values for coastal inundation

levels by WT are presented in Table 10 and have been adopted for this study.

Table 10 Peak coastal inundation elevation scenarios for the study area (WT, 2012)

Probability Coastal

Inundation Scenario

Mounts Bay (m AHD)

Apollo Bay (m AHD)

Wild Dog Creek

(m AHD)

Skenes Creek (m

AHD)

Almost certain

10% AEP storm tide + 5m Hs0, 14s

Tp

3.61 2.11 - 3.44 3.61 3.61

Unlikely


Tp

3.91 2.41 - 3.74 3.91 3.91

Rare


Tp

4.59 2.64 - 4.36 4.59 4.59

4.4 Coastal erosion hazard

The coastal erosion hazard relates to the formation and movement of an erosion escarpment

at the back of the beach as storm waves erode sand from the dune and move it to offshore

sand bars. This is also called the ‘zone of wave attack’ following the method of Nielsen (1992)

(refer Figure 16).

In this section, coastal erosion hazard extents previously estimated by Water Technology (WT,

2012) are reviewed and updated. The coastal erosion hazard zone is the distance behind the

current escarpment that may suffer erosion during the planning timeframe (10 yrs), and it has

been calculated by combining estimates of long term shoreline recession and storm cut

widths.

The results of this current study are included in Table 11, Table 12, and Table 13 in bold, red,

italics text, together with the results from WT (2012), which are shown in black for comparison

purposes.

4.4.1 Medium-term shoreline recession width

Shoreline recession was calculated under three probability scenarios by WT (2012):

Almost certain: considering shoreline recession from 1942‐2004 from (CES, 2005)

Unlikely: considering effect of sea level rise with a low depth of closure and occurrence of

significant wave height of 5 m, plus shoreline recession as above


Rare: considering effect of sea level rise with a high depth of closure and occurrence of

significant wave height of 7 m, plus shoreline recession as above

Following our review of the CES air photo analysis, GHD has adopted a higher and more

conservative recession rate for the “almost certain” scenario.

The “unlikely” and “rare” scenarios were developed by considering the Equilibrium Profile

Theory (Bruun theory, 1962). According to this theory, as relative water level increases, the

shoreline will retreat landward in order to achieve the equilibrium profile (Figure 15).

Figure 15 Schematic illustrations of the Bruun (1962) model of beach profile response to rising sea level (Image source: Davidson-Arnott, 2005)

Since results from bathymetric survey comparisons or numerical wave modelling are not

available, and the WT (2012) calculations were based on equations which are broadly used in

coastal engineering literature, GHD adopted the WT (2012) results in our calculations of the

unlikely and rare shoreline recession widths. The results for estimated shoreline recession over

10 years are shown in Table 11.

Table 11 Estimated shoreline recession over 10 years, incorporating long term recession trend and sea level rise (m)

Probability

Mounts

Bay

south

Mounts

Bay

north

Apollo

Bay

south

Apollo

Bay

north

Wild Dog Creek

Skenes Creek

Almost certain

2 0 0.8 2 2 2

0.9 0-0.2 0-0.2 0-0.2

Unlikely 4 2 2.8 4 4 4

2.2 2.2 2.2 2.2

Rare 5.2 3.2 4 5.2 5.2 5.2

3.25 3.25 3.25 3.25

* WT (2012) values in black, GHD values in red

4.4.2 Storm cut width

‘Storm cut width’ refers to the maximum retreat of the erosion escarpment in a single storm.

Much of the storm cut is expected to recover with onshore movement of sand after the storm.


The storm cut values for the Apollo Bay and Mounts Bay shoreline were updated by analysing

recent aerial photos taken before and after the June and July 2018 storms. Storm cut values

under the three probability scenarios are displayed in Table 12.

Table 12 Storm Cut width (m)

Probability

Mounts

Bay

south

Mounts

Bay

north

Apollo

Bay

south

Apollo

Bay

north

Wild Dog Creek

Skenes Creek

Almost certain

2 0.5 1 3 3 3

3 1-3 3 3

Unlikely 4 2.5 2 5 5 5

5 2-5 5 5

Rare 7 5.5 3 8 8 8

8 3-8 8 8


The combined coastal erosion width for the study (shoreline recession + storm cut) under the

three probability scenarios are presented in Table 13.

Table 13 Zone of wave impact width (m)

Probability

Mounts

Bay

south

Mounts

Bay

north

Apollo

Bay

south

Apollo

Bay

north

Wild Dog Creek

Skenes Creek

Almost certain

4 0.5 1.8 5 5 5

3.9 3 3 3

Unlikely 8 4 9.0 9.0 9.0 9.0

7.2 7.2 7.2 7.2

Rare 12.2 8.7 13.2 13.2 13.2 13.2

11.25 11.25 11.25 11.25


4.5 Reduced foundation capacity

The zone of reduced foundation capacity (zrfc) refers to the extents of structural

incompetence of unconsolidated sand which extends landwards of an erosion escarpment.

Within the zrfc the bearing capacity of the sand under the foundations is reduced. High

loadings in this area could lead to slip failures through the erosion escarpment.

It is not clear how WT (2012) calculated the zrfc, and it has therefore been recalculated from

first principles for this study.

The principal asset of concern for this study is the Great Ocean Road (GOR). The method of

Nielsen (1992) has been used to calculate the width of the zrfc for the GOR (Figure 16). Note

that this is a very conservative method which assumes that all material in the profile is sand

with the depth of scour being deep. This is however not likely to be the case in Apollo Bay,

where there are clay layers outcropping on the beach. Since these have not been mapped, it is


therefore appropriate to use Nielsen (1992) for an initial risk screening and assessment of

relative risk levels. To quantify the actual risk levels a geotechnical investigation would be

required.

Figure 16 – Definition of hazard zones due to storm erosion, dune slumping and instability after Nielsen et al. (1992)

Table 14 shows widths of the reduced bearing capacity zones for each erosion scarp height as it has been calculated by WT, 2012.

Table 15 shows widths of zone of reduced foundation capacity which GHD have adopted for

this study.

Table 14 WT 2012 adopted widths of zone of reduced bearing capacity

Erosion Scarp Height (m) Zone of Reduced Bearing Capacity Width (m)

3 4

5 7

Table 15 Adopted widths of zone of reduced foundation capacity for this study

Mounts

Bay

south

Mounts

Bay

north

Apollo

Bay

south

Apollo

Bay

north

Wild Dog

Creek

Skenes Creek

Road elevation typical (m AHD) 6 7 5 4 4 4

Zone of reduced foundation capacity width (m) 11 15.4 11 8.8 8.8 8.8

4.6 Hazard maps

Maps of predicted hazard zones for coastal erosion and reduced foundation capacity over the

next 10 years are provided in Appendix C. These maps show:

The July 2017 erosion escarpment (magenta line)


Zone of wave impact (three dashed grey lines) – this is the maximum predicted landward

movement of the erosion escarpment over the next 10 years under ‘almost certain’,

‘unlikely’ and ‘rare’ scenarios. Note that it is not expected that the whole shoreline will

move this far, but this is the possible extent of movement at the worst locations.

Zone of reduced foundation capacity (zrfc) (three solid grey lines) – this is the area where

the foundation capacity could be compromised by proximity to the erosion escarpment.

i.e. a geotechnical hazard for the Great Ocean Rd and any buildings. The zrfc is measured

from the future erosion escarpment, so even though there is one width for the zrfc, there

are three lines relating to the three zones of wave impact lines described above. Note that

this analysis is a first‐pass risk screening only. Geotechnical analysis would be required to

properly quantify the risk.

Asset data provided by DELWP ‐ sewer, water, walking path, Cypress trees, beach access

points and existing rock structures.

Coastal Inundation Maps – this map shows the areas which are likely to be inundated

under the three probability scenarios.


5. Coastal Erosion Management Options A wide variety of options exist for the long‐term response to coastal erosion, as shown in Table

16. These are described briefly in this section with comments on their suitability for the study

area, and an evaluation against the criteria in Section 5.1. A comparison table for all long‐term

options is included in Section 5.5.

Table 16 Management options

Non-protective options Non-structural protection options

Structural protection options

Do nothing Beach nourishment Geotextile sand container revetment

Planned retreat Dune management Informal rock protection Rock revetment Groynes and artificial

headlands Offshore breakwaters,

submerged artificial reefs and beach sills

Vertical seawalls

It is likely that a combination of some of the above options may be necessary to assist in the

management of the study area coastline.

5.1 Comparison analysis criteria

The criteria used to compare long‐term management options is below, together with

questions considered when rating each option.

5.1.1 Effectiveness as a long-term coastal defence solution

How effective is it as a long‐term coastal defence solution to protect assets, including making

an allowance for future climate uncertainty?

Are there any key risks of the option such as structural failure, increased erosion at the end of

the treatment (end scour), or erosion further along the coast?

5.1.2 Impacts to beach use, access, amenity

How will the option impact on the beach area available for recreational use? Will it tend to

increase or decrease the area of beach available for use through processes such as toe scour?

Is the beach likely to experience erosion at different times of the year, or as a permanent/ long

term loss? Are the materials friendly to public recreation?

Does it affect access to the shore? Does it preserve the along‐shore walking track?

Does the solution have a positive or negative impact on coastal landscape values? Will the

structure have a higher crest than the existing dune height, thereby potentially reducing sea

views? Will it maintain or enhance vegetation e.g. cypress trees?

5.1.3 Public safety

Are there any risks to the public resulting from the solution?

5.1.4 Capital cost and constructability

Capital cost ‐ Is the initial cost high?


How difficult is it to construct? Will local contractors be able to construct it? Is construction

risky due to the exposure to waves?

5.1.5 Ongoing maintenance cost

Does it need expensive maintenance?

5.2 Non-protective actions

5.2.1 Do nothing

If no action is taken, then further storms could put assets including the Great Ocean Road at

risk. This option allows nature to take its course and involves accepting the resulting losses.

A decision to take no action and allow erosion to continue is the best course of action when

the threatened land has little value. Such a course of action requires no expenditure on

protective measures and involves minimal interference with existing beach behaviour.

However, residents will often take action to protect their homes and Government agencies will

also wish to protect their assets and amenities, making this approach impractical in developed

areas.

5.2.1.1 Suitability for study area:

The Great Ocean Road is Australian National Heritage listed and is an important tourist

attraction in the region, including in the study area. Doing nothing in the study area where the

Great Ocean Road is at risk is not considered a feasible option. The foreshore path is also an

important tourist attraction.

For locations where the Great Ocean Road and the foreshore path are not currently at risk, and

the value of any other assets that may be at risk have been taken into consideration, the do

nothing option may be feasible. However, it is very important that monitoring of the shoreline

alignment is carried out on a regular basis, and trigger values are established to identify when

future erosion may pose a risk to the foreshore path or road.

Table 17 Analysis against criteria for “Do nothing” option

Criteria Comments

Coastal defence effectiveness

Beach continues to behave naturally. Erosion will most likely continue and land and critical assets including roads may be lost. Therefore, this is not an effective tool to protect assets from erosion.

Impacts to beach use, access, amenity

This option will preserve the beach area for a time at the expense of the dune. Formal beach access points, trees, the along-shore walking track will be lost. Eventually road will be damaged and a seawall built which will damage beach amenity.

Public safety Assets such as walking tracks, carparks and roads can initially become damaged, unstable and unpredictable before being lost. The Barwon Water assets in the study area are of high importance to the public and potential damage to these assets is also a public safety concern.

Capital Cost and constructability

Initially no direct expenditure required on protective measures.

Ongoing maintenance

In time expenditure will be required to repair and protect or relocate the road. It is very important that appropriate monitoring of the shoreline alignment is carried out on a regular basis, to provide an improved understanding of the long term behaviour of the coastline and allow decisions about future coastal protection to be made within suitable timeframes.


5.2.2 Planned retreat

Retreat as a response to coastal recession involves allowing the erosion to continue while

relocating assets further inland. This option involves a decision to no longer use an area at risk

of coastal erosion for built infrastructure.

An advantage of retreat is that it can preserve a natural coastline and range of coastal habitats

by allowing them to move inland. A planned retreat will result in the natural coastline being

able to adjust to different conditions, giving it a higher degree of resilience to coastal change,

provided land‐use planning allows sufficient scope for coastal movement. A resilient shore is

one that has the capacity to fluctuate, and a planned retreat would allow for fluctuations using

sediment eroded from coastal dunes as an important source of material for the coast,

enhancing the capacity for recovery of the adjacent coast. The natural coastline also has a high

amenity.

However, a planned retreat is rarely implemented in developed and populated areas due the

cost and disruption associated with relocation of assets such as roads and houses.

In cases where the development can be re‐established elsewhere at reasonable cost, buffer

zones can be provided where they previously did not exist. Such provision may necessitate

moving amenities, roads and even houses with payment of compensation to the owners

involved. The financial and social costs involved in relocation and compensation payments are

usually very high especially in densely populated areas.

In spite of its apparent drawbacks, in some areas a planned retreat may well be a better

solution in the long run than alternative protection works.


In Apollo Bay, the land directly inland from the Great Ocean Road is privately owned and

developed, and therefore retreat is unlikely to be feasible.

Other locations within the study area are less developed, and a planned retreat, i.e. moving

the Great Ocean road further inland, may be a feasible option if required, as shown in Figure

17. The financial and social costs involved would need to be evaluated, together with an

evaluation of long term processes such as shoreline recession due to sea level rise, which may

increase the level of risk of assets remaining in their current location over time.

Table 18 Analysis against criteria for “Planned retreat” option

Criteria Comments


Planned retreat effectively solves the beach erosion problem for any infrastructure that is moved away from the risk. This option allows for future climate uncertainty by increasing the buffer zone to infrastructure.


Public reaction against relocation is usually strong, however a planned retreat would actually retain the high amenity of the natural coastline. The impact on coastal landscape values would be positive in the long term. Beach access points and alongshore paths could be improved and designed to accommodate ongoing retreat.

Public safety As this would result in the natural coastline being retained, there would be no elevated risks other than during the relocation of infrastructure.


Planned retreat is generally expensive, and compensation payments may be prohibitive. In spite of its apparent drawbacks it may be cheaper in the long run in some areas. Road construction would generally be straightforward and be able to be undertaken by local contractors. Low risk construction.

Ongoing maintenance

Ongoing maintenance costs would only be associated with maintaining the beach access points and foreshore path where these were still at risk.


Figure 17 Locations in study area where retreat could be investigated if required

5.3 Non-structural protection options

5.3.1 Beach nourishment

Beach nourishment involves the placement of additional sand on the beach to rebuild the

profile after storms and provide a buffer against further storm erosion. This can be effective if

suitable sources of sand are available. The disadvantage is that used in isolation nourishment

does nothing to address the underlying causes of erosion and the placed sand is often lost very

quickly. Even in the best case scenario nourishment is only a temporary solution and typically

needs to be repeated within 1 to 10 years.

Beach nourishment is commonly used in Australia and internationally, often in combination

with structural options to help retain the nourishment sand on the beach. In general,

nourishment improves the aesthetics of a hardened shoreline and provides improved

recreational amenity. Structural measures such as groynes or offshore breakwaters can

increase the longevity of the nourishment by trapping sand on the beach or sheltering the

beach from severe wave action.



Beach nourishment has been undertaken for many years at various locations within the study

area, including targeting higher risk areas in recent years, as shown in Figure 18. This

nourishment has involved taking sand from the Point Bunbury groyne and using it to repair

erosion hot spots at Marengo, Apollo Bay, Wild Dog Beach and Skenes Creek.

Although nourishment by itself has been an effective short term option in reducing risk to key

assets and maintaining beach amenity, it has limitations in the study area including the volume

of sand available for nourishment and the cost to shift it.

As stated above, the disadvantage is that used in isolation, nourishment does nothing to

address the underlying causes of erosion and the placed sand is often lost very quickly. This

has been the case within the study area. It is likely that beach nourishment will continue to be

a feasible option for the study area, and an important element of any long term solution,

however nourishment used in isolation is unlikely to be a suitable long‐term solution.

Table 19 Analysis against criteria for “Beach nourishment” option

Criteria Comments


Nourishment as a stand-alone option is not an effective long-term solution as the placed sand is often lost very quickly. However, it can be effective as a short term measure to repair erosion and increase the buffer in critical areas by providing a continued supply of sand to the local dune system and increasing the buffer to coastal structures.


Nourishment increases the buffer zone width and enhances the natural beach. Recreational conditions and opportunities are generally improved. Landscape values are not affected if the beach size or nourishment material colour don’t change the beach substantially or it is restored to historical extents. The beach is still likely to experience erosion as the underlying causes of erosion have not been addressed.

Public safety As this would result in the natural coastline being retained, there would be no elevated risks other than during the construction works.


Nourishment is generally not as expensive as the construction of “hard” engineering options such as seawalls and groynes. Nourishment is heavily dependent on sand sources which are not always available and/or close by. Construction would generally be straightforward and be able to be undertaken by local contractors. Low risk construction.

Ongoing maintenance

Maintenance activities can be expensive, particularly to replace eroded sand if large quantities of sediment are required over time. Maintenance frequency is dependent on the frequency and severity of storm events, and is best supported by the establishment and funding of a maintenance plan.


Figure 18 Mounts Bay Beach during nourishment in May 20173

Figure 19 Nourishment underway at Apollo Bay opposite Cawood Street on 1 August 2018

5.3.2 Dune management

Imported sand or sand scraped from elsewhere on the beach can be used to rebuild the dune

profile. The rebuilt dune can then be vegetated and further stabilised by the vegetation. This

approach can assist in the establishment of a ‘natural’ foreshore dune, however it is a

temporary solution and will not protect assets from a series of severe storms in quick

succession.

Non‐vegetative methods of encouraging dune growth include the use of matting (such as

brush or seaweed), and dune fencing, with the latter also controlling access and capturing

3 Image source: https://www.otwaycoast.org.au/index.php/occ‐news/193‐occ‐news‐20170505


wind‐blown sand. Fencing can be temporary and consist of biodegradable materials (such as

branches), or permanent structures (e.g. post and wire with or without shadecloth mesh) in

areas of high pedestrian usage. The design of any fencing also needs to consider usage of and

access to the dune by local fauna. Sediments accumulated by these methods need to be

stabilised by vegetation.


Dune management was undertaken at Mounts Bay in May 2017 as shown in Figure 20. This

consisted of around 16,000m3 of sand being carted from nearby harvest areas and used to

create a new dune. The new dune incorporated a number of additional trials into the design,

including incorporating Spinifex with the sand, placing coconut husk ‘coir’ logs and jute

matting on the dune, planting local coastal dune species, and scattering sterile Rye Corn seed

on the top of the dune4.

It is likely that dune management will continue to be a feasible option for the study area,

however for this to be a long‐term solution it may need to be combined with another long‐

term option as described in the following sections.

Table 20 Analysis against criteria for “Dune management” option

Criteria Comments


Fully developed dunes can potentially cope with a higher erosion risk from sea level rise if monitoring and maintenance programs are established. However for this to be a long-term solution it may need to be combined with another long-term option.


Coastal dunes provide natural habitat for flora and fauna, and are a natural formation on sandy coastlines. The impact on landscape is positive although dune height increases and/or vegetation growth may reduce sea views, which can cause social conflicts between the community and affected property owners. Dunes can reduce unofficial access to the shore, but offer the benefit of controlled access, therefore it is considered that accessibility is improved. The beach is still likely to experience erosion as the underlying causes of erosion have not been addressed.

Public safety As this would result in the natural coastline being retained, there would be no elevated risks other than during the construction works.


Dune management and restoration is generally not as expensive as the construction of “hard” engineering options. Dune restoration is heavily dependent on sand sources. Community involvement can reduce costs - for example assistance with planned planting and maintaining vegetation. Construction would generally be straightforward and be able to be undertaken by local contractors. Low risk construction.

Ongoing maintenance

Maintenance costs are low if storms do not erode the dune quickly. However, this is unlikely to be the case and if constant maintenance is required costs will be high and alternative options, or dune management combined with another long-term option may be more appropriate. Maintenance frequency is dependent on the frequency and severity of storm events, and is best supported by the establishment and funding of a maintenance plan.

4 https://www.otwaycoast.org.au/images/occ/projects/erosion‐management/2017_Marengo_Sand_Nourishment_Fact_sheet_2.pdf


Figure 20 Completed dune management at Mounts Bay in June 20175

5.4 Structural protection options

Intervention using structural protection may have wider consequences than intended or may

even exacerbate problems. They therefore require careful planning and application.

5.4.1 Geotextile sand container (GSC) revetment

A revetment constructed from sand‐filled geotextile containers (bags) along the alignment of

the existing erosion escarpment could be an effective means of preventing further erosion in

the short to medium term. GSCs have been successfully used in applications around the world

and in Australia. This is a measure that is often used as a temporary response to beach erosion,

however can also be used as a longer term solution.

There are a few available formats including geotextile tubes and sand containers (bags). The

tubes are generally used for larger applications such as offshore reefs or as foundations for

breakwaters. Groynes and revetments are generally constructed from containers/bags which

are stacked together to form the structure.

Advantages are:

Low visual impact as they tend to blend in with the natural surrounds.

Can be implemented reasonably quickly.

Suitable for temporary protection – can be easily removed or relocated.

May be perceived as a more user‐friendly solution than rock for beach users, as the end

result is softer and there is less risk of rock spill onto beach.

There are also a number of disadvantages to the use of geotextile bags:

They are vulnerable to mechanical damage and vandalism. Effective life is typically 5 to 10

years; however, this could be greater for composite ‘vandal deterrent’ geotextiles.

Geotextile container/bag revetments are relatively impervious to waves, leading to

increased wave reflection and scour in front of the wall. This process can slow or reduce

the seasonal recovery of the beach, when sand tends to build up during calmer summer

months. There is also a risk of end scour when using GSCs.

5 Image Source: Mounts Bay, Marengo: Is backshore sand renourishment a viable option for managing coastal hazard risk? Environmental

Geosurveys P/L (Neville Rosengren) and Asminer Geotechnical (Tony Miner), V1 September 2018


Sand for the fill may be difficult to source locally in the quantities required.


A GSC revetment positioned along the current erosion escarpment at the back of the beach

would be effective at protecting coastal assets from costal erosion in the short to medium

term (5‐10 years), however the beach in front of the revetment would be at risk from

increased erosion from reflected waves.

A GSC revetment is a feasible option to provide a “last line of defence” protection to the road,

services and the foreshore walking path, however to minimise the impact on beach area for

recreational use, this solution should be combined with beach nourishment.

Table 21 Analysis against criteria for “GSC” option

Criteria Comments


Properly designed and constructed GSC revetments can be effective measures to protect coastal assets from storm tide and projected sea level rise in the short to medium term (5-10 years). GSC revetments can potentially have a longer effective life if composite ‘vandal deterrent’ geotextiles are used. There is a risk of end scour and erosion further along the coast when using GSCs, as well as increased wave reflection and scour in front of the wall.


Low visual impact as they tend to blend in with the natural surrounds, therefore may be perceived as a more user-friendly solution than rock. If beach accretes, the GSCs would be left in place as a buried revetment. It is more likely that the beach will experience erosion in front of the revetment leading to the loss of available recreational beach, unless this option is combined with nourishment.

Public safety “Soft” construction that is readily traversed by beach users and can be stepped to provide access to the beach. GSCs do get some growth on them in the intertidal zone which can be slippery, so care needs to be taken.


Moderately expensive compared to other options. Can be constructed by local contractors however relies on the availability of the Geofabrics filling frame (for 2.5m3 bags) as they are hydraulically filled in “J-bins”.

Ongoing maintenance

GSCs are vulnerable to UV damage and vandalism. If a bag becomes dislodged from wave action, replacing the bag can be expensive. There may be ongoing costs associated with monitoring and management of end scour, as well as renourishing the beach after storms if this option is combined with nourishment. Given the short to medium term life of the structure, GSC revetment may require expensive upgrades in the future.

Figure 21 GSC revetments at Portsea and Aspendale in Port Phillip Bay


5.4.2 Informal rock protection

Rock can be placed on the beach during or immediately after a storm to slow the rate of

erosion and protect assets. The rock can be tipped from the top of the escarpment and no

attempt is made to construct a toe or graded layers.

This approach can be effective in the short term, but in the medium term the rock berm

collapses due to toe sour, overtopping or wash‐out of material behind the wall. The long term

result is scattered rock buried in the beach providing little or no erosion protection.


There is evidence that informal rock protection has been used extensively along the Apollo Bay

coast in the past as it is exposed in the erosion escarpment on the beach, mainly toward

Cawood St. As shown in Figure 22 the rocks are scattered across the beach and erosion is

occurring landward of the rocks. Informal rock protection is a suitable option when access is

particularly difficult or when a short term solution is required reasonably quickly. As this is not

considered to be the case in the study area, informal rock protection is not considered to be

suitable.

Table 22 Analysis against criteria for “Informal rock protection” option

Criteria Comments


This may protect assets in the short term, however is not an effective tool to protect assets from long term erosion. The rock berm tends to collapse due to toe sour, overtopping or wash-out of material behind the wall leaving scattered rock buried in the beach.


Adversely affects the beach as long term rock is left scattered on the beach not providing sufficient protection from erosion. The beach is still likely to experience erosion as the underlying causes of erosion have not been addressed, and this erosion might progress landward of the informal rock protection.

Public safety “Hard” construction which can have sharp edges or be unstable underfoot, particularly if wet, and cause injury if care is not taken. Over time the rocks tend to disperse over the beach where they can be partially buried where they present a tripping hazard to beach users.


Familiar construction technique for local contractors, only requires excavator/grab bucket. Generally not as expensive as the construction of long term “hard” engineering options.

Ongoing maintenance

If a formal rock revetment is required as the final solution, the existing rock placed during this stage can be kept and reinforced. This would likely have an increased crest height and possible larger armour rock or a secondary layer. The costs to construct the formal rock revetment would be moderately expensive.


Figure 22 Informal rock protection between Joyce and Cawood streets.

5.4.3 Rock revetment

A formal rock revetment consisting of several layers of armour rock and geotextile, designed

for the site conditions, can provide reliable long term protection.

One disadvantage of a rock revetment is that it can reflect waves and increase scour of the

beach as described for the geotextile sand container (GSC) revetment above, however as a

rock revetment has a higher porosity it tends to absorb more wave energy and thus causes less

scour than a GSC revetment or vertical wall.

Another disadvantage of a rock revetment is the width of the footprint and consequent loss of

beach area. The rock may also be perceived as visually poor and unfriendly to beach users.

These issues could be mitigated by burying the revetment within a constructed and vegetated

dune incorporating foreshore access paths. The foreshore path could be reconstructed on top

of the revetment as shown in Figure 24.

The revetment solution could have a number of impacts on coastal processes:

Reflected wave energy from the revetment can increase scour on the beach, slowing the

natural recovery after storms. The design of the revetment can mitigate this effect by

positioning the revetment as far landward as possible. This impact can also be avoided by

burying the revetment in a constructed dune profile after storms, as already occurs at

Apollo Bay.

Increased erosion or ‘end scour’ is expected to occur in the dune at either end of the

revetment. This effect can be seen in the post storm survey of Apollo Bay where the

erosion adjacent to the armoured stormwater outlets is approximately 1 to 2 m deeper

than surrounding areas. This impact can be mitigated in the design by positioning the ends

of the revetment against an existing hard structure (e.g. armoured stormwater outlet) or

in an area with sufficient dune buffer to accommodate the end scour. Rebuilding the dune

profile after storms would also be an effective way of managing this impact.


A rock revetment with a defined design life could be constructed quickly in the study area,

noting that VicRoads already have rock sources and plant mobilised for similar works close by


on the Great Ocean Road, such as for the recently constructed rock revetment at Skenes Creek

as shown in Figure 23.

A rock revetment at the existing erosion scarp would be effective in protecting coastal assets,

including the road, from erosion in the short to medium term. To preserve the landscape

character and view from the road the rock revetment would be designed with a low crest. This

would result in overtopping, even with the current sea level. To reduce the impact on the

recreational beach, the footprint (width) of the rock revetment would be minimised. The rock

revetment may also be vulnerable to toe scour. The rock revetment would need to be

monitored, maintained and probably upgraded (crest raised) in the future.

A rock revetment is a feasible option to provide a “last line of defence” protection to the road,

services and the foreshore walking path. The beach in front of the rock revetment would still

be likely to experience erosion, however to minimise the impact on beach area for recreational

use, this solution should be combined with beach nourishment. Burying the revetment in the

dune would reduce the visual impact, however this would also require maintenance,

particularly following storms.

Rock revetments in the study area are discussed further in the following section on short term

remedial work.

Table 23 Analysis against criteria for “Rock revetment” option

Criteria Comments


A properly designed and constructed rock revetment would be an effective measure to protect the road, foreshore path and services from storm tide and projected sea level rise for 50+ years.


Adversely affects the beach. Reflected wave energy from the revetment can increase scour on the beach and there can also be end scour. The beach is therefore still likely to experience erosion in front of the revetment, leading to the loss of available recreational beach, unless this option is combined with nourishment.

Public safety “Hard” construction which can have sharp edges or be unstable underfoot, particularly if wet, and cause injury if care is not taken. However, this is a familiar type of structure, so majority of beach users will be familiar with risks associated with climbing on rock if they choose to do this. Formal beach access points would be constructed to discourage climbing on rock.


Moderately expensive compared to other options. Can be constructed by local contractors.

Ongoing maintenance

Monitoring and maintenance costs are low. Infrequent high cost maintenance may be required after severe storm events or near the end of the design life of the structure. If long term sea level rise is not allowed for initially, the revetment may require expensive upgrades in the future.


Figure 23 Rock Revetment recently constructed near Skenes Creek

Figure 24 Buried revetment concept sketch

5.4.4 Construction of groynes or artificial headlands

Groynes are shore‐normal rock or GSC walls which can be an effective way of stabilising the

foreshore in areas with significant along‐shore sediment movement. The amount of sand that

is trapped is governed by the local sediment transport rates, and the length and height of the

groynes. If there is an insufficient supply of sand to a beach area, a groyne will be ineffectual.

Erosion of the beach immediately down‐drift of the groyne can be offset by “filling” the groyne

at the time of construction, so that natural bypassing can occur immediately. Groynes have the

disadvantages of significant alteration to the beach alignment and character, and increased

risk of erosion down drift.

An ‘’artificial headland’’ works in a similar manner to a groyne. It alters the shoreline alignment

and can separate the beach into discreet compartments. Careful study is required to design

the groynes/headlands and new coast alignment to ensure they achieve the coastal protection

objectives without causing unintended consequences such as erosion further down the beach.

Groynes do not prevent coastal erosion during storms, but by trapping sediment they can

create and maintain a buffer between assets and the storm erosion.



Apollo Bay does experience longshore sediment movement, however the current erosion is

caused by cross‐shore sediment movement during storms where large waves erode sand from

the back of the beach and deposit it in offshore sand bars. For groynes or artificial headlands

to be effective at Apollo Bay they would need to be combined with significant beach

nourishment to provide a buffer against storm erosion. In the study area groynes could help to

maintain a beach that may otherwise be lost in front of a revetment.

Due to the high‐energy nature of the beach at Apollo Bay and the wide surf zone the groynes

may need to be very large, possibly one hundred meters long. A relevant example of a groyne

in the study area is at Wild Dog Creek, which has been effective at trapping sediment from

longshore transport, and has “widened the beach by about 45 metres”6. Additional groynes

are also likely to be effective, however maintenance after major storm events is likely to be

required, with ongoing sand nourishment maintenance costs.

Other disadvantages of groynes in the study area would be a change in the beach character,

and the risk of down drift erosion. To minimise the risk of down drift erosion, a staged

construction could be undertaken with one groyne being constructed at a time, starting with

the northern end of the beach closest to Wild Dog Creek. The effectiveness and any

unintended consequences could be monitored, and if the groyne was considered to be a

success, once it was filled a second groyne further south could be constructed and monitored.

Further groynes could be constructed like this as required, with nourishment of the beaches as

necessary. This process could potentially take 10 years to fully establish all groynes, with

example locations shown in Figure 27.

Table 24 Analysis against criteria for “Groynes or artificial headlands” option

Criteria Comments


Used in combination with nourishment groynes would be effective in maintaining a wider beach and dune system providing a buffer against erosion. Groynes used in isolation are unlikely to be effective in the study area since the current erosion is caused by cross-shore sediment movement during storms rather than longshore transport.


Groynes can have a negative impact on coastal landscapes. Well-designed artificial headlands can have a positive impact on coastal landscapes. If found to be suitable for the study area then overall there would be positive benefits to general beach availability.

Public safety Increased caution may be required around navigation and water based activities around submerged groyne extents. If the groynes were constructed from geotextile sand containers, climbing over the landward ends of the groynes should be safe and possible.


Construction can be expensive, and is heavily dependent on form of structure, physical extent and materials used. Construction is likely to be more difficult than structures positioned at the back of the beach.

Ongoing maintenance

Maintenance after major storm events may be required. Groynes and artificial headlands are likely to come with ongoing sand nourishment maintenance costs.

6 Apollo Bay Sand Study, Coastal Engineering Solutions, 2005


Figure 25 Rock groynes forming artificial headlands at Hampton in Port Phillip Bay

Figure 26 Geotextile groyne at Busselton, WA at completion and 2 months following completion


Figure 27 Concept of possible groynes in Apollo Bay

5.4.5 Offshore breakwaters, submerged artificial reefs and beach sills

An offshore breakwater is a man‐made structure located close to the shoreline, with its

primary purpose being to trigger wave breaking. This reduces wave energy reaching the shore

and allows sediment to accumulate in the calmer wave climate in the lee of the structure. This


approach, in combination with beach nourishment can be effective at preventing erosion due

to long‐shore and cross‐shore sediment movement.

An artificial reef for coastal protection purposes is similar to an offshore breakwater. It also

comprises a man‐made structure placed on the sea bed, with its primary purpose being to

trigger wave breaking. A variety of materials are used for artificial reefs, from sunken vessels,

engineered concrete blocks, to geotextile bags. Materials are chosen based on the intended

function(s) of the reef, availability of materials and funding, and to encourage colonisation by

marine organisms.

Very shallow detached breakwaters are also known as beach sills. These low profile structures

are usually located very close to the shoreline and are often exposed at low tide. They only

affect wave breaking during higher tides or elevated water levels. Beach sills have a greater

focus on wave breaking rather than salient formation.


In the study area offshore breakwaters, submerged artificial reefs or beach sills are likely to be

effective in building up beach to some extent, depending on the type and extents of the

structure. Example locations of offshore breakwaters are shown in Figure 30. The

environmental, financial and social costs of these structures should be taken into

consideration. There are several major disadvantages to these structures in the study area:

Very large structures would be required in the study area, which would be very expensive

to construct in the near‐shore zone.

Major alteration of alignment and character of the beach and surf zone.

Increased risk of erosion down drift (to the north east). Because of the sediment trapping

capability of breakwaters and artificial reefs, it can potentially deprive down drift beaches

of sediments, resulting in erosion of those beaches. Recovery of down‐drift beaches will

only occur once the structure no longer traps sediment and natural bypassing can resume,

which, depending on the site, may be many decades.

Design, approval and construction are complex and risky. These structures have a higher

risk of not working exactly as intended, and of having unintended consequences. They are

also difficult to implement quickly.

Considerable improvements are still needed in the design and construction of offshore

structures, in particular artificial reefs.

Offshore structures may pose a significant threat to beach users in the study area (surfers,

vessels, swimmers). Safety concerns may be prohibitive.

Table 25 Analysis against criteria for “Offshore breakwaters, submerged artificial reefs and beach sills” option

Criteria Comments


Used in combination with large scale nourishment may to be effective in building and maintaining a beach, however successful design is difficult. Structures can settle and/or suffer from localised scour which can result in actual crest level being lower than designed crest level, and beaches do not always respond in manner expected.


Even if submerged these structures have a significant impact on the shape and character of the beach. However, if successful could create a much larger area of beach. Can also provide reef habitat to support diving and fishing activities. Offshore structures will impact on surfing breaks.


Public safety Submerged structures may pose a significant threat to beach users (surfers, vessels, swimmers) if not designed and constructed appropriately. Larger emergent structures however can create sheltered pocket which allow for safer bathing


Cost is usually prohibitive, as too expensive, but will depend on size and materials used. Installation of an offshore structure is considered as a major decision, and specialist contractors may be required depending on the location and materials used. Construction is likely to be the most difficult compared to other options.

Ongoing maintenance

Monitoring is required to maintain functionality although maintenance is infrequent if appropriately designed. Maintenance and sand nourishment after major storm events may be required. If structure settles more than anticipated maintenance may be required to increase crest level.

Figure 28 Offshore Breakwaters in Norfolk, UK

Figure 29 Narrowneck artificial reef, Queensland, which was built to help protect coast from erosion7

7 Image source: https://boatgoldcoast.com.au/how‐narrowneck‐copied‐nature/


Figure 30 Concept of possible offshore breakwaters in Apollo Bay

5.4.6 Vertical seawalls

Effective erosion protection can be provided by vertical structures such as sheet piles, masonry

or concrete seawalls. Seawalls provide a last line of defence along a coastline but tend to

exacerbate the erosion of the beach in front, leading to loss of beach amenity. Since these

structures have the highest wave reflection of all the options considered, they may have the

worst impact on the beach of all options discussed.


The seawall form is dictated by the usage of the seaward and landward areas, and by the

economical availability of suitable materials. Access to the beach can be provided as part of

the seawall design. Vertical walls are common where there is limited space landward of the

shoreline to accommodate a wall. In general, the smoother and more vertical the seawall, the

more wave energy is reflected, and the greater the potential for scour at the seaward base of

the structure, which can ultimately lead to undermining.

Whilst seawalls are useful for preventing further erosion of protected land, they can

exacerbate the impacts of an existing deficit in sediment supply, and lock up sand sources used

to supply adjacent beaches. The impact of seawalls on erosion is therefore complex and

significant erosion impacts on adjoining unprotected shorelines can be generated by them.


A vertical seawall would be effective in protecting coastal assets including the road, foreshore

walking track and services from coastal erosion, storm tide and projected sea level rise.

However, the beach would still be likely to experience erosion as the underlying causes of

erosion have not been addressed.

The intent would be to align the seawall as close as possible to the natural bay shape of the

coast, which will assist in the coast reaching and maintaining an equilibrium state. The seawall

could provide “last line of defence” protection to important infrastructure, however to ensure

that there is still beach area available for recreational use, this solution should be combined

with beach nourishment seaward of the wall.

Table 26 Analysis against criteria for “Vertical seawall” option

Criteria Comments


Properly designed and constructed vertical seawalls are effective measures to protect coastal assets from coastal erosion. Seawalls may affect property values (positive and negative). Protection of assets from damage/loss due to erosion is the primary positive benefit. There can be scour at the seaward base of seawalls and they can exacerbate erosion at adjacent beaches.


Exposed seawalls may have a negative impact on coastal landscape values. Seawalls can be designed with an along-shore walking track landward of the seawall and can have formal access points built into them to access the beach. Exposed seawalls can reduce recreation opportunities on the beach as the beach is likely to experience more frequent and severe erosion in front of the wall, unless this option is combined with ongoing sand nourishment. Vertical seawalls should be designed to preserve landward recreation opportunities.

Public safety Seawalls tend to reflect waves and cause erosion and deeper water close to shore which increases danger to swimmers. When exposed to direct wave attack they may have significant overtopping which poses a hazard to pedestrians behind the wall.


Construction is generally expensive, and is heavily dependent on sources of materials. Construction is more difficult than other options, however local contractors may still be able to complete construction.

Ongoing maintenance

Monitoring and maintenance costs are low. Infrequent high cost maintenance may be required after severe storm events or near the end of the design life of the structure. If long term sea level rise is not allowed for initially, seawall may require expensive upgrades in the future.


Figure 31 Bluestone seawall at Brighton in Port Phillip Bay


5.6 Comparison of options

The various options considered have been rated on their suitability as long‐term (10 years or

more) costal protection options at Apollo bay, based on the comments against criteria in the

above sections.

Rating

Very negative ×× Negative × Neutral - Positive Very positive

Table 27 Comparison of long-term performance of options



Public safety


Ongoing maintenance

Do nothing ×× × × - ××

Planned retreat ××

Beach nourishment

× ×

Dune management

× ×

Geotextile bag (GSC) revetment

- - - -

Informal rock protection

× ×× × ××

Rock revetment × - -

Groynes and artificial headlands (with nourishment)

- - × ×

Offshore breakwaters, submerged artificial reefs and beach sills (with nourishment)

× ××

Vertical seawalls ×× × ×


5.7 Regulatory requirements

The selection of the most appropriate coastal management at any particular location must

include consideration of any relevant legislation and planning requirements.

The Marine and Coastal Act 2018 has established objectives and guiding principles for the

planning and management of the marine and coastal environment for Victoria. This includes

describing requirements for coastal and marine management plans which would contain

specific requirements for particular types of development in selected locations which need to

be addressed.

This study does not include an analysis of regulatory requirements or the selection or

recommendation of long‐term treatment options. These requirements will need to be

addressed as part of the long term strategy, prior to the selection of suitable long‐term

treatment options.


6. Immediate Remedial Works GHD were commissioned by VicRoads and DELWP to design a coastal protection structure to

protect the Great Ocean Road in the highest risk area, a stretch of approximately about 250m,

centred on Milford St. This section describes the design process and outcome.

6.1 Need for remedial works

The foreshore at Apollo Bay has experienced significant erosion in a series of storms during

June and July 2018. The area of most concern extends from Cawood Street to Marriners

Lookout Road, where the dune area that acts as a buffer between the road and the beach is

relatively narrow, typically 10 to 25 m prior to the recent storms.

During the storms of June and July 2018 the dune has retreated up to 5 m landward. The

walking path (Figure 32) and dune vegetation has been lost in a number of locations and

several large cypress trees may be at risk (Figure 33).

Figure 32 Walking path impacted by erosion in Apollo Bay (August 2018)

Figure 33 Cypress trees which may be at risk (August 2018)

In the worst affected area, a stretch of approximately about 250 m, centred on Milford St, the

distance from the erosion escarpment to the edge of the traffic lane on the Great Ocean Road

is now 6 to 8.5 m. Another series of storms similar to those recently experienced could put the


road at risk, noting that a zone of instability extends further landward of the erosion

escarpment.

The erosion escarpment is typically 1 to 2 m high. The material exposed in the erosion

escarpment is principally sand, and in some places silty sand, clay or sandstone boulders are

present.

6.2 Proposed remedial works

In order to address this problem GHD were commissioned by VicRoads in August 2018 to

prepare an options analysis for protection of the Great Ocean Road from coastal erosion at

Apollo Bay. Objectives were to identify high risk areas and protection solutions that can be

implemented quickly to protect the Great Ocean Road in the short term, and can form part of

a long term solution, or can be removed or remodelled to be incorporated into a long term

solution.

The recommendation of this study was construction of a rock revetment over 240 m of the

foreshore around Milford St. The coastal hazard mapping, risk assessment and options

assessment in this study have confirmed this is an appropriate treatment.

6.3 Design approach

The primary design objective of the revetment as agreed with DELWP and VicRoads is to

protect the Great Ocean Road from coastal erosion. Other objectives and requirements were

taken into consideration:

The works needs to be implemented quickly to reduce risk to the GOR. It is noted that

VicRoads already have suitable rock available and contractors mobilised for revetment

construction at nearby sites on the GOR.

Protect the walking path and vegetation including cypress trees that line the foreshore.

Preserve sea views and landscape character – The height of the structure should be

consistent with current dune.

Provide path and beach access – The structure should be designed to allow for a walking

path and beach access which should be consistent with, or improved from current

conditions;

Minimise impact on beach – The structure should be designed to minimise the impact on

the beach area available for recreational use.

Structure can be modified or incorporated into long term erosion strategy for Apollo Bay

To meet these design objectives, the revetment has been positioned as far landward as

possible (at the location of the existing erosion escarpment), the toe is buried and the crest

matches the existing dune level. In addition, it is recommended that the revetment is buried

in a constructed dune and vegetation established on the top and seaward face.

Armour stone in the revetment has been sized for a 100yr ARI storm occurring any time in the

next 50 years, allowing for an increase in water depth and wave heights due to climate change.

With the above design approach, particularly taking into consideration the preference to

preserve views and minimise the impact on the beach, some maintenance is likely to be

required within 50 years. High overtopping will be experienced similar to the existing situation

and minor damage to the crest or areas landward could occur during severe storms. Upgrades

could include works to raise the crest to reduce overtopping, which would in turn negatively

affect views, or works to strengthening the toe if major ongoing loss of sediment from the

beach occurs.


6.4 Extent of works

In order to determine the extent of the remedial works required, a risk profile has been

prepared for assets at Apollo Bay beach over the next 10 years (Figure 34) based on the coastal

hazard mapping (section 4.6). On the risk profile colours represent different levels of risk to

assets:

Red – Extreme risk to road: The Great Ocean Road lies within the ‘unlikely’ zone of wave

impact and the ‘almost certain’ zone of reduced foundation capacity.

Purple ‐ High risk to road: The Great Ocean Road lies within the ‘almost certain’ zone of

reduced foundation capacity.

Pink – High risk to other assets: the sewer, water supply, significant trees or path lie within

the ‘almost certain’ zone of wave impact.

Yellow – Medium risk: assets (sewer, water supply, significant trees or path) lie within the

‘unlikely’ zone of wave impact or the GOR lies within the ‘unlikely’ zone of reduced

foundation capacity.

Based on this risk profile the revetment has been designed to protect the 250 m long area of

‘extreme risk’ around Milford Street. The full extent of the revetment is shown on the

drawings in Appendix B.


Figure 34 Coastal erosion risk profile at Apollo Bay

6.5 Design conditions

6.5.1 Water levels

The design water level is a combination of the 100yr ARI storm tide level (1.42m AHD, refer

section 3.1.2), an allowance for wave setup (1m) and allowance for sea level rise over the next

50 years (0.4m).

6.5.2 Design waves

Offshore wave climate is discussed in Section 3.2. At the revetment site dominant offshore

waves propagate from the SW (Figure 6), then refract and change their direction (to easterly)

as they approach the shoreline.


The worst case for the stability of rubble mound structures is waves breaking directly on the

structure. The depth‐limited breaking wave height (Hb), which is the largest wave that can

break and plunge directly onto the structure, has therefore been used to calculate rock armour

sizes. These have been calculated using empirical methods given in the Shore Protection

Manual (USACE, 1984) and Revetment systems against wave attack: A design manual (HR

Wallingford, 1998) that take into account water depth, nearshore seabed slope, and wave

period. Waves larger than Hb will break further offshore and lose energy through friction

before they impact the structure as a smaller broken wave.

An allowance for beach scour of 0.5m below the July 2018 profile has also been included in the

calculation of the depth‐limited breaking wave height. It is noted that the July 2018 profile is a

heavily eroded profile surveyed after a series of three major storms.

The design wave parameters are presented in Table 28.

Table 28 Design wave parameters

Level of toe (m AHD)

Allowance for scour

(m)

Design water level (m AHD)

Water depth at toe (m)

Depth limited breaking

wave, Hb (m)

Peak wave period, Tp

(s)

1.6 0.5 1.82 0.22 2.2 14

6.5.3 Geotechnical Conditions

No formal geotechnical investigations have been conducted for the site. From observations on

site the beach material and material exposed in the erosion escarpment is principally sand, and

in some places silty sand and clay layers are present. Sandstone boulders are exposed in the

erosion escarpment in some places, these are likely the remains of informal rock revetment

works (refer Figure 32 and Figure 33).

6.5.3.1 Dynamic Cone Penetrometer (DCP) tests

Although formal geotechnical studies have not been undertaken for this site, GHD performed

five informal DCP tests on site on 1st August 2018 to determine the beach material’s in‐situ

resistance to penetration. Our main objective was to establish approximate levels of refusal, to

determine if any less erosive material was present under the sand, and an approximate level

for that material. In four of the five test locations refusal was met with an estimated depth

between approximately 0.15 m AHD and ‐0.74 m AHD. This indicates that a harder material is

present in these locations at approximately these levels. No refusal was met at the fifth test

location, which means that if a harder layer is present, it would be below the level tested

(approximately ‐0.4 m AHD in this instance).

The approximate DCP test locations, and their estimated depth of refusal in m AHD are shown

in Figure 35.


Figure 35 DCP locations and estimated depth of refusal in m AHD

6.6 Detailed design

6.6.1 Cross section design

The structure primary and secondary armour layers are double layers to provide additional

resilience to storm damage. Armour is sized using Hudson’s equation with minor (5 to 10%)

damage in a 100yr ARI storm occurring any time in the next 50 years, giving a primary armour

mean mass of 2.5t. Geotextile is specified to reduce the loss of fine material from behind the

structure, reducing the risk of outflanking, over‐steepening and subsidence.

Crest width was determined to be three armour units wide, which is an approximate width of 3

m, representing a balance between reducing the risk of overtopping and limiting the structure

footprint. The crest level is a minimum of 3.5m AHD, and may be higher to match the dune

surface in some areas.

The toe of the revetment is buried at a level of 0m AHD, approximately 2m below the eroded

profile surveyed in July 2018. A toe berm of primary armour rock is not specified as it is

considered unlikely that significant scour below this level will occur, noting that DCP tests hit

refusal between 0.15 and ‐0.7m AHD. If a toe berm were included it would significantly

increase the width of the structure protruding through the sand on the beach and potentially

impact on beach amenity.

The final design cross‐sections are presented in Figure 36 and Appendix B.


Figure 36 Detailed cross section of the remedial works around Milford St.

6.6.2 Walkways (walking path)

The existing walking path in Apollo Bay is mainly eroded between Marriners Lookout Rd and

Cawood St. An extreme case of erosion of the walking path is shown in Figure 37.

For the area behind the proposed revetment at Milford street, a new path is proposed to be

built landward of the revetment. The top layer of the walking path is recommended to consist

of crushed rock. Path materials shall be compacted to the relevant minimum characteristic

DDR8 of 90%. It is recommended to achieve the thickness of 175 mm (maximum) after

compacting the top layer material. A typical cross section for the path is shown in Figure 38.

Figure 37 Eroded walking path in Apollo Bay

8 Dry Density Ratio

Recessed walking path, Apollo Bay


Figure 38 Typical cross section for the proposed crushed rock path

For the remaining areas not protected by the proposed revetment a new realigned gravel path

or a boardwalk could be used. This section of the path is not included in the immediate

remedial works. A typical beach boardwalk is shown in Figure 39.

Figure 39 Typical beach boardwalk

6.6.3 Beach access stairs

In order to protect the existing vegetation on the dunes, it is proposed to create formal access

stairs between the foreshore path and the beach, and reduce the number of informal access

points. Over the rock revetment, DELWP has suggested the access point to be located at

Milford Street, similar to the existing wooden stairs south of Cawood Street (Figure 40). Since

this structure has withstood the recent storms, GHD consider this as a suitable form of

structure for the site. Design specifications for this are to be in compliance with AS1657 and

AS1720.


Figure 40 Existing access stairs at Apollo Bay, south of Cawood St.

6.6.4 Dune Management

It is recommended to bury the rock revetment under a constructed dune profile using sand

sourced from the Harbour or Point Bunbury Groyne as part of the ongoing sand management

at the Harbour. Sand burial and dune management have various benefits:

‐ Maintaining aesthetic values of the beach;

‐ Reducing the impacts of wave reflection at the toe of the structure; and

‐ Reducing the footprint of rock exposed on the beach and therefore reducing impact on

beach amenity.

It is proposed that sand be carted by truck from the main harvest area at Apollo Bay Harbour

and be bulldozed over the revetment, as per the current practice of beach nourishment. This

dune management operation should be planned considering public safety and tide levels.

Dune re‐vegetation, protective mats and sand fencing should be used to stabilise placed sand

and reduce the wind transport of sand onto the road and adjacent properties.

6.7 Coastal impact assessment

This section discusses the proposed revetments impact on coastal processes and public safety

and amenity. The major safety issue is overtopping by storm waves and this is discussed

separately.

6.7.1 Overtopping

This section discusses the overtopping performance for the designed rock revetment at Apollo

Bay. ‘Overtopping’ is the process of storm waves running up the face and over the crest of the

structure .In other words wave Overtopping occurs when height of the incident wave (after

effects of shoaling, breaking and run‐up) exceeds the crest height of the structure.

Overtopping of the dune and inundation of the GOR already occur at the site under current

conditions, and as the new revetment will match existing dune levels the overtopping

performance is expected to be similar.


Implications of overtopping and thresholds for overtopping hazard are given in Coastal

Engineering Manual, 2006 and Eurotop9, 2007.

Approximate mean wave overtopping discharge for the designed revetment with a crest level

of 3.5 m AHD has been calculated by the formula below (Wave Overtopping of Sea Defences

and Related Structures: Assessment Manual, 2007):

.0.2. exp 2.3

.

With

Hm0: wave height at the toe of the structure (m) γβ: influence factor for oblique wave attack (‐) γf: influence factor for roughness elements on a slope (‐) Rc: freeboard of the structure (m) q: average wave overtopping discharge (m3/s/m)

Mean overtopping discharges for various return periods and water levels are shown in Table

29.

Table 29 Estimated overtopping volumes

Time Storm ARI

(years)

Estimated overtopping rate (L/s/m)

Implications for safety

Implication for structure

2018

(Present)

1 2 Safe for aware pedestrians.

Safe for driving at

low and moderate

speed

No damage to the

revetment

Start of damage to

vegetated area between

revetment and the GOR

2018

(Present)

10 3 Safe for aware pedestrians.

Safe for driving at

low and moderate

speed

No damage to the

revetment

Start of damage to



2018

(Present)

50

5 Safe for aware pedestrians.

Safe for driving at

low and moderate

speed

No damage to the revetment

Start of damage to



2018

(Present)

100 6 Dangerous for pedestrians.

Safe for driving at low and moderate

speed


Start of damage to



9 EurOtop: Wave Overtopping of Sea Defences and Related Structures: Assessment Manual


2068

(50 years

time)



speed


Start of damage to vegetated area between revetment and the GOR

2068

(50 years

time)



speed



2068

(50 years

time)


Unsafe for vehicles at any speed.



According to Table 29 the present situation is currently dangerous for both pedestrians and

the cars. The level of danger is expected to increase in future due to sea level rise and

occurrence of bigger wave heights.

Crest height, batter slope and slope material significantly influence wave overtopping volumes.

Sea view is one of the limiting criteria in design of the coastal protection in Apollo Bay. The

structure is designed at a height to minimize sea view blockage. Raising the crest can

significantly reduce overtopping discharge. By increasing the height of the revetment 0.5

metre, the estimated overtopping for year 2068 with 1% AEP will decrease to 5 L/s/m.

6.7.2 Impact on Coastal Processes

6.7.2.1 Longshore sediment transport

The structure is located at the landward side of the beach against the existing erosion

escarpment. The northern end is tied into an existing storm water outlet and the southern end

into a slightly wider section of dune.

Overall the structure is expected to have no significant impact on the longshore transport of

sediment because it does not protrude into the active zone for longshore sediment transport.

6.7.2.2 Cross shore sediment transport

By protection the remaining dune area from erosion the structure will prevent further storm

cut delivering sediment to the beach system. The impact is expected to be small because

longshore sediment supply (~80,000 m3/yr) is much greater than the volume generated by

storm cut (in the recent June/July storms approximately 3,000 m3 of sediment was eroded

from the area of the proposed revetment).

While the impact of the current proposed structure is minor, if it is extended in the future (as

is likely – see below) the cumulative effect could become significant, reducing sediment supply

to down‐drift areas (beach to the north).

6.7.2.3 Beach and toe scour

Reflected waves off the revetment can cause additional local bed scour in front of the

revetment, lowering the beach level during storms and slowing the recovery of the beach after

storms. These impacts can be mitigated by placing sand in front of the structure as necessary

to build the beach up and reduce reflection.


6.7.2.4 End scour

End scour is the additional erosion that typically occurs at the transition from a hard (rock

revetment) to soft (dune sand) material on the coastline. Examples of end scour can be seen

either side of the rock armoured stormwater outlets on Apollo Bay beach where the erosion

has progressed typically 1 to 2 m further than surrounding areas.

The northern end of the proposed revetment is tied into an existing rock armoured

stormwater outlet so it will not cause any additional end scour beyond that already occurring

at this location due to the outlet.

The southern end of the proposed revetment in not tied into any hard point and a new end

scour point is expected to develop here. This will need to be monitored and managed by

periodically filling with sand or extension of the revetment to prevent undermining of the

walking path and GOR.

6.7.3 Impact on safety and amenity

The revetment has been designed for minimum impact on beach amenity, safety, landscape

character and views by keeping the footprint as small as possible and the crest height similar

to the existing dune. Nonetheless, there could be impacts on amenity due to reduced beach

width and a hard rock structure forming a barrier between the beach and the foreshore. These

impacts can be mitigated by burying the structure in a constructed dune, ongoing sand

management as required and provision of formal access points across the revetment.

Safety risks for beach users due to the presence of the structure include wave overtopping,

tripping on buried rocks and entrapment in large voids between the armour rocks.

Overtopping during storms can present a risk to pedestrians and vehicles, as discussed in the

section above. The level of risk will be similar to the existing conditions and is best addressed

through awareness and signage.

The toe has been designed to be buried well below the beach level so large partially buried

rocks are not expected to present a hazard to beach users.

Voids between armour rocks on the sloping face of the revetment are necessary for the

structure to absorb wave energy, thereby reducing wave reflection and overtopping. Such

voids can however pose a risk of tripping or entrapment of limbs. This hazard has been

mitigated by filling the voids on the crest with smaller rock so it is safe for able‐bodied

pedestrians.

GHD | Report for DELWP ‐ Apollo Bay Coastal Protection, 3136559

7. Community Open House Sessions On 5th and 6th October 2018 two open house sessions were held in Apollo Bay for the

community, and a comments page was opened on the Engage Victoria website. The aim of

these sessions was to present to the community both the immediate remedial works and the

possible long‐term treatment options for the study area, and to gain the community’s

feedback on these options.

In general, there was support for the rock revetment to be constructed for the immediate

remedial works, with suggestions that the work be continued further along the beach.

The ten long‐term options which are included in this report were presented to the community,

with the following general feedback:

1. Do Nothing: There was no support for this approach;

2. Planned Retreat: This approach generated some ambivalence. This included costs, and

whether the Government would make appropriate compensation/arrangements for

alternative access;

3. Beach nourishment: This should be continuous and ongoing, potentially taking sand from

the spit, allowing the sea to again flood the river;

4. Dune Management: Not seen as a long term solution, but an expectation that such work

will be carried out in the short‐term;

5. Geotextile sand container revetment (sand bags): Generally seen as a temporary solution;

6. Informal Rock Protection: Most comments were that it would be a waste of time;

7. Rock revetments: General support for the technique in conjunction with other techniques;

8. Groynes: There was a lot of support for constructing groynes;

9. Breakwaters, artificial reefs: Strong support for the concept, but concern about how they

will work and how they will affect the natural coastline; and

10. Vertical Sea Walls: Views on this approach were quite polarised. Some were that the

approach was inappropriate and visually unaesthetic, others were that it is an effective

approach to erosion and successfully used in many other places in the world.

DELWP’s summary of comments, issues and ideas received from the community is included as

Appendix C.


8. Next Steps Taking into consideration the information presented in this report, together with feedback

from the community open house sessions, the following next steps are recommended:

Undertake a comprehensive coastal process study, including:

o Update the CES 2005 air photo analysis of the shoreline position, incorporating

photos from 2004 to the present;

o Reassessment of the longshore sediment transport. All previous studies have

adopted the figure of 80,000 m3/yr estimated by PMC in 1989 which should be

reviewed in light of recent information.

Investigate the feasibility of the viable long term options favoured by the community

feedback, recognising that different options, or combinations or options, will be

appropriate in different parts of the study area. Options should include:

o Progressive construction of groynes to increase the width and amenity of the main

beach at Apollo Bay Township.

o Realignment of the Great Ocean Road in areas outside the township areas.

Although there was little support for ‘planned retreat’ in community session, there

was a preference for focusing the beach management effort on the townships, and

realignment of the road in other areas would allow this to happen.

Review of sand management and bypassing at the harbour to ensure sand is being used for

maximum benefit in light of updated coastal process understanding and long term erosion

control options.


Appendix A – Coastal Erosion Hazard Maps


Appendix B – Short-Term Remediation Works Revetment Design Drawings


Appendix C – Community Open House Summary

delwp.vic.gov.au delwp.vic.gov.au

These sessions were designed to allow the community to have their say about short and long-term treatment options for coastal erosion in the area, and for community members to contribute ideas for coastal protection considerations.

93 people attended the sessions, with the majority of people from the 3233 post code. 27 contributed to the online page.

The Event

This interagency event was organised into three areas:

• What is being planned in the short-term for storm damage remediation

• Possible long-term coastal protection measures

• Other capital works projects being planned in the community

Participants were invited to comment in a variety of ways on these pieces of work, the following being a summary of the comments received.

Storm remedial work

There was general support for the rock revetment as a technique, with suggestions that the work be continued further along the beach.

There was also wide support expressed for keeping the cypress trees that line the foreshore. It was mentioned that they are a memorial. A general view is that if/when they are removed other types of trees should be considered as replacements. The replacement suggestions include: Auraceae family, Banksias and Norfolk Pines.

The boardwalk suggestion was received positively, with various suggestions around the type of construction.

Concern was expressed about the general condition of the carparks on the foreshore, the potential of losing spaces and the need for sealing and linking with beach access.

Revegetation was seen to be an important element of remedial work, with concern expressed on the need to ‘get it right’.

Fencing: There was no support for wire mesh, and a strong preference for robust, multi-wire ‘climb proof’ fencing and/or post and rail.

Long-term Coastal Protection Work

Clarification was sought on what ‘long-term’means.

Ten different approaches were presented for participants to consider.

1) Do nothing: there was no support for this approach

2) Planned retreat: this approach generated some ambivalence. This included costs, and whether the Government would make appropriate compensation/arrangements for alternative access.

Apollo Bay and Marengo Foreshore Open House Summary of comments, issues and ideas received

Two community Open House sessions were held on the 5th and 6th of October for the Apollo Bay and Marengo communities, and a comments page was open on the Engage Victoria website.

“Boardwalks – use the Canadian example, they are fantastic”

“Happy to have some input.”

ERROR! UNKNOWN DOCUMENT

PROPERTY NAME.

Apollo Bay and Marengo Foreshore Open House

delwp.vic.gov.au

3) Informal rock protection: Most comments were that it would be a waste of time.

4) Dune management: Not seen as a long-term solution, but an expectation that such work will be carried out in the short-term.

5) Beach renourishment: This should be continuous and ongoing, though some see it as being only a short-term solution – potentially taking sand from the spit — allowing the sea to again flood the river.

6) Sand bags: Generally seen as a temporary solution

7) Rock revetments: General support for the technique in conjunction with other techniques.

8) Groynes: There was a lot of support for constructing groynes

9) Vertical seawalls: Views on this approach were quite polarised. Some were that the approach was inappropriate and visually unaesthetic, others were that it is an effective approach to erosion and successfully used in many other places in the world.

10) Breakwaters, artificial reefs: Strong support for the concept, but concern about how they will work and how they will affect the natural coastline.

Coastal protection investment priorities

Participants were asked where they felt future coastal protection investment should be prioritised. The order of priority was: 1) The town foreshore area 2) Mounts Bay 3) The Point 4) Between the Coastal Reserve and the Point 5) Skenes Creek end of the Bay.

General comments about coastal protection

• Both timing and adequate funding are critical elements to a good solution

• There needs to be more studies on the area

• It’s a complex problem requiring a mix of solutions to achieve a functional and aesthetically pleasing result

Other Items

We also heard comments and suggestions on matters other than coastal protection. These included:

• Construct a new by-pass road on the land side of the town

• Maintain the village atmosphere

• Traffic concerns in Apollo Bay

• The need for work on the harbour

• The need to maintain and expand tourist attractions

• The issue of levies for tour buses and access to toilets

• Bike path between caravan park and town

Interest in Future Engagement

In terms of future engagement processes, there were a few people happy with surveys, strong support for similar type events as this one, and a few interested in being part of small group discussions. There is a need for agencies to consult directly with the business community.

Feedback on the event

There was an appreciative response to the event, especially the mix of information and being able to contribute early into the decision-making process.

“The problem requires a mix of solutions.”

“We need action now for the long-term.”

“A second road in and out of Apollo Bay back to town is vital.”

“Keep doing the engagement.”

© GHD 2018

This document is and shall remain the property of GHD. The document may only be used for the purpose for which it was commissioned and in accordance with the Terms of Engagement for the commission. Unauthorised use of this document in any form whatsoever is prohibited.

G:\31\36559\Report\REV 0 ‐ FINAL\Apollo Bay – Coastal Protection Study ‐ Rev0‐20181130.docx

Document Status

Revision Author Reviewer Approved for Issue

Name Signature Name Signature Date

A –

Preliminary

Draft

J. Munro

M. Moalemi

C. Taylor *C. Taylor 21/9/18

B ‐ Draft J. Munro

M. Moalemi

C. Taylor *C. Taylor 17/10/18

0 ‐ Final J. Munro

M. Moalemi

C. Taylor *C. Taylor R. Hill *R. Hill 30/11/18

www.ghd.com

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