Coastal Hazards Management Plan Marengo to Skenes Creek

Transcription

1 Coastal Hazards Management Plan Marengo to Skenes Creek October 2012 ISO 9001 QEC22878 SAI Global

2 DOCUMENT STATUS Version Doc type Reviewed by Approved by Date issued v04 Final Report GLR TJW 26/10/2012 v03 Final Report GLR TJW 28/08/2012 v02 Draft GLR TJW 19/07/2012 v01 Draft Report GLR TJW 12/07/2012 PROJECT DETAILS Project Name Coastal Hazards Management Plan Marengo to Skenes Creek Client Client Project Manager Tammy Smith Water Technology Project Manager Tim Womersley Report Authors TJW, EAL Job Number Report Number R01 Document Name _R01v04_ApolloBayCHP.docx Copyright Water Technology Pty Ltd has produced this document in accordance with instructions from Department of Sustainability and Environment for their use only. The concepts and information contained in this document are the copyright of Water Technology Pty Ltd. Use or copying of this document in whole or in part without written permission of Water Technology Pty Ltd constitutes an infringement of copyright. Water Technology Pty Ltd does not warrant this document is definitive nor free from error and does not accept liability for any loss caused, or arising from, reliance upon the information provided herein. 15 Business Park Drive Notting Hill VIC 3168 Telephone (03) Fax (03) ACN No ABN No / R01 v04-26/10/2012 ii

3 TABLE OF CONTENTS Glossary v 1. Introduction Study Area Study Context Coastal Management Policy Framework Stakeholders Coastal Processes Coastal Geomorphology & Processes Historical Shoreline Change Historical Coastal Hazard Impacts Risk Identification Asset Audit Great Ocean Road Barwon Water Assets OCC Assets Heritage Listed Trees Stormwater Drainage Network Apollo Bay Harbour Coastal Hazards Coastal Inundation Hazards Coastal Erosion Hazards Risk Analysis Risk Analysis Method Likelihood Definitions Consequence Definitions Risk Ranking Risk Analysis Results Mounts Bay Apollo Bay Wild Dog Creek Skenes Creek Risk Treatment Mounts Bay Apollo Bay Wild Dog Creek Skenes Creek Monitoring and Review Bibliography / R01 v04-26/10/2012 iii

4 LIST OF FIGURES Figure 1-1 CHP Methodology and Scope... 1 Figure 1-2 Study Area Extent and Coastal Compartments... 2 Figure 2-1 Overview of Coastal Processes and Geomorphology... 6 Figure 2-2 Shoreline Erosion Scarp Following Storm Event at Mounts Bay (T. Stuckey)... 8 Figure 2-3 Coastal Erosion Impinging on Car Park at Mounts Bay (T. Stuckey)... 9 Figure 2-4 Coastal Inundation Impacting the Great Ocean Road in Apollo Bay (G. Mc Pike 2005) Figure 2-5 Coastal Erosion Impacting Car Parks and Walking Paths in Apollo Bay () Figure 2-6 Elevated Coastal Water Levels Due to Storm Tide and Wave Setup at Wild Dog Creek (D. Webley, 2008) Figure 2-7 Erosion Associated with the Dynamic Interaction of Wild Dog Creek and the Coastal Figure 2-8 Processes (D. Webley, 2009) Coastal Erosion Impacts to Beach Access and Adjacent to Barwon Water Assets at Skenes Creek (G McPike, 2011) Figure 3-1 Overview of GIS Asset Database Figure 3-2 Coastal Inundation Hazard Extents Figure 3-3 Coastal Erosion Hazard Extents Figure 4-1 Mounts Bay Coastal Asset Risk Profiles Figure 4-2 Apollo Bay Coastal Asset Risk Profiles Figure 4-3 Wild Dog Creek Coastal Asset Risk Profiles Figure 4-4 Skenes Creek Coastal Asset Risk Profiles LIST OF TABLES Table 2-1 Overview of Agencies with Assets and or Management Responsibilities in the Coastal Zone... 3 Table 3-1 Adopted Widths of Reduced Bearing Capacity Table 3-2 AEP Storm Tide Levels Incorporating Mean Sea Level Scenarios (CSIRO 2009) Table 3-3 Peak Coastal Inundation Elevation Scenarios for the Study Area Table 3-5 Adopted Short-term Erosion Demand Extents for the Study Area Table 3-6 Coastal Erosion Scenarios for the Study Area Table 4-1 Risk Likelihood Definitions Table 4-2 Risk Consequence Definitions Table 4-3 Risk Assessment Matrix Table 4-4 Risk Profile Definition Table 4-5 Mounts Bay Coastal Asset Risk Profiles Table 4-6 Apollo Bay Coastal Asset Risk Profiles Table 5-1 Proposed Mitigation Strategies and Priorities for Mounts Bay Coastal Compartment Table 5-2 Sand Carting Cost Estimate from Bunbury Point Groyne to Mounts Bay Table 5-5 Offshore Sediment Bypassing Cost Estimate Table 5-6 Sand Carting Cost Estimates from Bunbury Point to Apollo Bay Table 5-5 Proposed Mitigation Strategies and Priorities for Apollo Bay Coastal Compartment / R01 v04-26/10/2012 iv

5 GLOSSARY Accretion Australian Height Datum (AHD) ARI AEP Astronomical tide Beach Berm Chart Datum Design Wave Diurnal Ebb Tide Exceedance Probability Flood Tide Foreshore Geomorphology Holocene HAT MHHW H s (Significant Wave Height) Intertidal Littoral Zone Littoral Drift Processes The accumulation of material which may eventually lead to the creation of new land mass A common national plane of level corresponding approximately to mean sea level Average Recurrence Interval Annual Exceedance Probability: The measure of the likelihood (expressed as a probability) of an event equalling or exceeding a given magnitude in any given year Water level variations due to the combined effects of the Earth s rotation, the Moon s orbit around the Earth and the Earth s orbit around the Sun A plateau often found at the back of the primary sand dune, separating the beach area from other geological features further inshore Common datum for navigation charts. Typically relative to Lowest Astronomical Tide The wave conditions for a design conditions, for example, the 100 year design wave is representative of a wave which could be expected to occur, on average once in a 100 year period A daily variation, as in day and night. The outgoing tidal movement of water resulting in a low tide. The probability of an extreme event occurring at least once during a prescribed period of assessment is given by the exceedance probability. The probability of a 1 in 100 year event (1% AEP) occurring during the first 25 years is 22%, during the first 50 years the probability is 39% and over a 100 year asset life the probability is 63% The incoming tidal movement of water resulting in a high tide The area of shore between low and high tide marks and land adjacent thereto The study of the origin, characteristics and development of land forms The period beginning approximately 12,000 years ago. It is characterised by warming of the climate following the last glacial period and rapid increase in global sea levels to approximately present day levels. Highest Astronomical Tide: the highest water level that can occur due to the effects of the astronomical tide in isolation from meteorological effects Mean Higher High Water: the mean of the higher of the two daily high waters over a long period of time. When only one high water occurs on a day this is taken as the higher high water Hs may be defined as the average of the highest 1/3 of wave heights in a wave record (H1/3), or from the zeroth spectral moment (H m0 ) Pertaining to those areas of land covered by water at high tide, but exposed at low tide, eg. intertidal habitat An area of the coastline in which sediment movement by wave, current and wind action is prevalent Wave, current and wind processes that facilitate the transport of water and sediments along a shoreline / R01 v04-26/10/2012 v

6 MSL Neap Tides Pleistocene Semi-diurnal Spring Tides Storm Surge Storm tide Tidal Planes Tidal Range Tides Velocity Shear Wave runup Wave setup Wind Shear Mean Sea Level Neap tides occur when the sun and moon lie at right angles relative to the earth (the gravitational effects of the moon and sun act in opposition on the ocean). The period from 2.5M to 12,000 years before present that spans the earth's recent period of repeated glaciations and large fluctuations in global sea levels A twice-daily variation, eg. two high waters per day Tides with the greatest range in a monthly cycle, which occur when the sun, moon and earth are in alignment (the gravitational effects of the moon and sun act in concert on the ocean) The increase in coastal water levels caused by the barometric and wind set-up effects of storms. Barometric set-up refers to the increase in coastal water levels associated with the lower atmospheric pressures characteristic of storms. Wind set-up refers to the increase in coastal water levels caused by an onshore wind driving water shorewards and piling it up against the coast Coastal water level produced by the combination of astronomical and meteorological (storm surge) ocean water level forcing A series of water levels that define standard tides, eg. 'Mean High Water Spring' (MHWS) refers to the average high water level of Spring Tides The difference between successive high water and low water levels. Tidal range is maximum during Spring Tides and minimum during Neap Tides The regular rise and fall in sea level in response to the gravitational attraction of the Sun, Moon and Earth The differential movement of neighbouring parcels of water brought about by frictional resistance within the flow, or at a boundary. Velocity shear causes dispersive mixing, the greater the shear (velocity gradient), the greater the mixing. The vertical height above the still water level a wave will run up over the face of a sloping wall or beach profile. Run up varies with structure or beach shape and roughness, the depth and slope of the bed next to the beach or structure and the actual wave conditions. The super elevation of nearshore water levels due to the transport of momentum associated with pressure and velocity fluctuations of breaking waves propagating in a shoreward direction The stress exerted on the water's surface by wind blowing over the water. Wind shear causes the water to pile up against downwind shores and generates secondary currents / R01 v04-26/10/2012 vi

7 1. INTRODUCTION Water Technology was engaged by the (DSE) to prepare a Coastal Hazards Management Plan (CHP) for the coastline between Skenes Creek and Marengo, including Apollo Bay, in south western Victoria. The CHP has employed a risk management methodology in accordance with the Victorian Coastal Hazard Guide (). The risk management methodology provides a strategic framework for identifying and responding to coastal hazard risks in the study area and to develop a plan for mitigating risks to key assets and infrastructure over a 10 year management time frame. The risk management methodology adopted comprises the following main components and tasks as displayed below: Establish Context Review of key strategic drivers, policies and stakeholder agencies relevant to the development of the CHP. Overview of existing coastal process and hazard risks within the study area Risk Identification Identification of the main sources of coastal hazard risk in the study area and determination of the extent and magnitude of the hazards considering a 10 year management timeframe Identification of the type, extent and value of assets (built, environmental, historic) potentially at risk from coastal hazards in the study area Risk Analysis Development of risk profiles for key assets in the study area based on the evaluation of the product of the likelihood and consequence of the potential coastal hazard impacts to these assets. Risk Treatment Evaluation and prioritisation of mitigation measures to treat unacceptable coastal hazard risks to assets Figure 1-1 CHP Methodology and Scope / R01 v04-26/10/2012 1

8 1.1 Study Area The CHP has been developed considering the following four coastal compartments within the study area: Mounts Bay (Marengo to the southern boundary of Apollo Bay Harbour (Point Bunbury)) Apollo Bay (Northern boundary of Apollo Bay Harbour to just beyond Marriners Lookout Road Wild Dog Creek (Just beyond Marriners Lookout Road to the end of the beach at the entrance of Wild Dog Creek. Skenes Creek (3 kilometre shoreline between Wild Dog Creek and Skenes Creek Caravan Park) Figure 1-2 displays the extent of the study area and four main coastal compartments. Figure 1-2 Study Area Extent and Coastal Compartments / R01 v04-26/10/2012 2

9 2. STUDY CONTEXT The context in which the CHP for the study area has been developed has been summarised in the following sections. 2.1 Coastal Management Policy Framework The Coastal Management Act 1995 is the key Act guiding use and development of the coast. The Act aims to provide for co-ordinated strategic planning and management for the coast. To achieve these objectives the Act directs the Victorian Coastal Strategy 2008 (VCS) to provide for long-term planning of the Victorian coast. The VCS provides a comprehensive integrated management framework for the coast of Victoria. The CHP developed in this study takes into consideration the hierarchy of principles approach and associated policy directions provided in the VCS. Coastal Action Plans (CAP) are regional to local scale plans that aim to further develop the broad principles and priorities of the VCS to provide long term strategic directions for particular locations and sets of issues on the Victorian coast. A CAP for the Skenes Creek to Marengo has been completed by the Colac Otway Shire under the guidance of the Western Coastal Board. The CAP addresses a number of pressures and issues affecting the coastline between Skenes Creek and Marengo and provides a series of prioritised recommendations for protecting and managing the coastline. The recommendations contained within the Skenes Creek to Marengo CAP have been incorporated into the development of the CHP for Apollo Bay. 2.2 Stakeholders A following range of agencies have assets in the study area and/or are involved in planning and management in the coastal zone. The relevant stakeholders/agencies and their roles and responsibilities within the study area are summarised in Table 2-1. Table 2-1 Agency Overview of Agencies with Assets and or Management Responsibilities in the Coastal Zone Role/Responsibility Western Coastal Board Strategic planning for the coastline under the Coastal Management Act 1995 Vic Roads Colac Otway Shire Council Department Sustainability Environment (DSE) of and Otway Foreshore Committee of Management Barwon Water Corangamite Catchment Management Authority Great Ocean Road planning and works Stormwater, land use planning, traffic, works on minor roads, managing Apollo Bay Harbour DSE has responsibilities under the Coastal Management Act 1995 as delegated by the Minister for Environment and Climate Change, and further responsibility on behalf of Government as the landowner of Crown land in Victoria. Under the Crown land (Reserves) Act 1978 (the Act) the Minister for Environment and Climate Change can delegate management responsibilities to committees of management. DSE provides advice and guidance to Committees and may make grant funding available. Operation and management of coastal crown land including recreational reserves and camping grounds Water supply and sewerage assets Catchment management, planning and waterway works / R01 v04-26/10/2012 3

10 2.3 Coastal Processes The study area has been subject to a number of previous coastal process studies to identify potential solutions to the sedimentation issues at the entrance to the Apollo Bay Harbour and to develop an improved understanding of existing coastal erosion and inundation hazards more generally within the study area. The following previous relevant coastal process investigations have been undertaken in the study area Vantree Pty Ltd (1996) Apollo Bay Coastal Processes Vantree Pty Ltd (1997) Mounts Bay Beach: Report on Coastal Erosion Coastal Engineering Solutions (2005) Apollo Bay Sand Study GHD (2009) Apollo Bay Sand and Dredging Options Study A considerable body of knowledge on the coastal processes in the study area therefore currently exists. The following provides an overview of the main findings of these previous studies in the context of understanding the causes and potential extent of the coastal hazard risks in the study area Coastal Geomorphology & Processes Apollo Bay is located at the foot of the Otway Ranges which consist of uplifted Cretaceous sedimentary formations reaching elevations of approximately 300m above sea level behind Apollo Bay. The Cretaceous sediments are however rich in feldspar rather than quartz and the erosion of these formations do not supply appreciable quantities of sand sized sediments to the coastline. The littoral sediments comprising the sand bars, beaches and dunes in the region are therefore derived from sediments drifted shoreward from the floor of Bass Strait following the end of the last glacial phase and subsequent marine transgression. The main features of the coastal geomorphology and processes of the study are displayed in Figure 2-1 and discussed below. Mounts Bay beach is a component of a Holocene barrier that has built out across the floodplain of the Barham River by longshore drifting of sediment. The Great Ocean Road extends along the crest of this Holocene barrier formation. Behind the present day barrier, a series of abandoned lagoons, tidal channels and early barrier formations indicate the present barrier most likely formed recently following relative sea level fall during the late Holocene (<5,000 years before present). Between Apollo Bay and Wild Dog Creek, a continuous, crenulate shaped bluff exists behind the present day shoreline, indicating the location of an earlier cliffed shoreline that most likely occurred along this coastline during relatively higher sea level conditions of the mid Holocene (6,000-7,000 years before present). The relative fall in mean sea levels since the mid Holocene has facilitated the development of the present day dune and beach system in front of this earlier cliffed coastline. The beach systems within the study area are composed of medium to fine grained, calcareous sand. Previous analysis undertaken by CES (2005) estimated that the net sediment transport potential is approximately 80,000m 3 /yr towards the north-east. Following construction of the Apollo Bay Harbour, the longshore transport around Point Bunbury was captured by the breakwater and Harbour. The construction of the harbour also created a wave shadow along the beach in its immediate lee to the north. The reduction in wave energy along the shoreline in the lee of the breakwater, as well as likely local changes to wave directions due to wave diffraction around the breakwaters, resulted in a reduction in the potential north-east longshore transport of sand. The reduction in the longshore sediment supply along the Apollo Bay shoreline has resulted in significant accretion of sand in the southern corner of the beach at Apollo Bay, / R01 v04-26/10/2012 4

11 extending north to approximately Cawood Street. This accretion has been further enhanced by regular sand bypassing of the Harbour entrance which has deposited sand within the wave shadow zone in the lee of the Harbour. The disruption of the longshore sand transport continuity along the beach at Apollo Bay caused by the construction of the Harbour has contributed to longterm shoreline recession observed along the beach at Apollo Bay beyond Cawood Street to the north of the Harbour / R01 v04-26/10/2012 5

12 Figure 2-1 Overview of Coastal Processes and Geomorphology / R01 v04-26/10/2012 6

13 2.3.2 Historical Shoreline Change Analysis of historical aerial photography of the study area has been undertaken previously CES (2005) and Vantree (1996). The analysis identified and mapped the extent of the historical shoreline changes in the study area. The following summarises the main conclusions drawn from the previous analysis: Mounts Bay Major changes in the position of the vegetated shoreline have not been observed in this shoreline compartment, except in the vicinity of the Barham River entrance The vegetated shoreline extent has however tended to retreat, particularly since the mid 1980 s. The average rate of recession of the vegetated shoreline extent was estimated at approximately 9cm/yr. Apollo Bay Significant accretion and subsequent advancement of the shoreline south of Cawood Street has occurred at an average of approximately 83cm/yr. However, since the mid 1980 s the shoreline has receded slightly, indicating the period of shoreline adjustment following the construction of the Harbour may now be largely complete North of Cawood Street, the vegetated shoreline extent has been receding by approximately 2cm/yr on average. More rapid recession has historically been observed at the location of the stormwater outfalls. Wild Dog Creek North of Mariners Road to the groyne at Wild Dog Creek, the vegetated shoreline extent has advanced at an average rate of approximately 49cm/yr. The groyne compartment at Wild Dog Creek is however now full and sand is likely to be bypassing around the groyne such that ongoing advancement of the shoreline is considered unlikely. Wild Dog Creek beach is very dynamic due to the interaction of the Wild Dog Creek streamflows and the coastal processes. This results in significant changes to the alignment and location of the creek entrance into Bass Strait along the beach from month to month. Skenes Creek Historical shoreline changes at Skenes Creek have not previously been mapped from historical aerial photography. It is however understood that fencing, formalisation of beach access and revegetation have resulted in a more resilient shoreline extent which has only experience relatively minor changes following large storm events Historical Coastal Hazard Impacts Sections of the study area and associated assets and infrastructure have historically been exposed to coastal hazard impacts. The coastal impacts have generally been associated with large storm tide events in combination with wave action that has resulted in significant shoreline erosion as well as inundation of low lying areas. The following main coastal impacts have been previously observed and documented at Apollo Bay: / R01 v04-26/10/2012 7

14 Mounts Bay Assets and infrastructure located close to the shoreline of Mounts Bay have historically experienced some moderate impacts associated with short term, storm related erosion. Some examples of the impact of historical storm related erosion at Mounts Bay are displayed in the photos provided by T. Stuckey below. Specific impacts to assets and infrastructure associated with these hazards have included the following at Mounts Bay: A toilet block located between the Great Ocean Road and the Mounts Bay shoreline was threatened by shoreline erosion. In an attempt to protect the toilet block, rock was dumped on the shoreline in front of the toilet block. A sewer rising main has historically been exposed in the dune scarp following large erosion events. It is understood that this sewer main has been decommissioned. A carpark and a number of beach access points have been impacted by erosion of the shoreline. A number of traffic signs associated with the Great Ocean Road have been impacted and/or lost due to erosion of their foundations Figure 2-2 Shoreline Erosion Scarp Following Storm Event at Mounts Bay (T. Stuckey) / R01 v04-26/10/2012 8

15 Figure 2-3 Coastal Erosion Impinging on Car Park at Mounts Bay (T. Stuckey) Apollo Bay Assets and infrastructure located close the shoreline of Apollo Bay have historically experience some relatively significant impacts associated with storm related erosion as well as inundation. Some examples of the impact of historical storm related erosion and inundation at Apollo Bay are displayed in the figures below. Historical impacts to assets and infrastructure associated with these hazards have included the following at Apollo Bay: The sewer rising main between Skenes Creek and Apollo Bay has been exposed historically near Marriners Lookout Road. Significant sections of the foreshore walking path have been repeatedly lost following major erosion events A number of long standing Monterey Cypress Trees (Cupresses macrocarpa) have had their roots undermined following major erosion events A carpark and a number of beach access points have been impacted by erosion. Significant inundation of the Great Ocean Road has occurred near Marriners Lookout Road due to wave runup and overtopping / R01 v04-26/10/2012 9

16 Figure 2-4 Coastal Inundation Impacting the Great Ocean Road in Apollo Bay (G. Mc Pike 2005) Figure 2-5 Coastal Erosion Impacting Car Parks and Walking Paths in Apollo Bay () Wild Dog Creek Observations on the potential extent of the coastal hazard at Wild Dog Creek have been drawn from photos and observations provided by David Webley, an estuary watch volunteer for the CCMA for the Wild Dog Creek Estuary. The morphology of the beach at Wild Dog Creek is highly variable due to the complex interaction of the Wild Dog Creek streamflows and the coastal processes. These interactions result in rapid / R01 v04-26/10/

17 changes to the creeks alignment along the beach in response to changing streamflow rates and prevailing wave and sediment transport directions. Changes to the creek alignment and the lowering of the beach berm can potentially result in erosion and inundation impinging close to the Great Ocean Road and/or its foundations as well as exposing the groyne to the eastern end of the Wild Dog Creek beach in this coastal compartment. Figure 2-6 Elevated Coastal Water Levels Due to Storm Tide and Wave Setup at Wild Dog Creek (D. Webley, 2008) Figure 2-7 Erosion Associated with the Dynamic Interaction of Wild Dog Creek and the Coastal Processes (D. Webley, 2009) / R01 v04-26/10/

18 Skenes Creek Limited information on the long term exposure of this coastal compartment to coastal hazards was identified during the course of the study. Some impacts to beach access ramps and fences have been observed near the caravan park historically as displayed in Figure 2-8. Figure 2-8 Coastal Erosion Impacts to Beach Access and Adjacent to Barwon Water Assets at Skenes Creek (G McPike, 2011) / R01 v04-26/10/

19 3. RISK IDENTIFICATION To facilitate the development of an informed and strategic plan for managing future coastal hazards in the study area, the following analysis has been undertaken: An audit of the type and extent of the assets and infrastructure potentially at risk in the study area has been undertaken and assets have been incorporated into a GIS asset database. The main sources of the coastal hazard risks in the study area have been identified and the potential extent and magnitude of the coastal hazards have been estimated for a range of probability scenarios considering a 10 year management timeframe 3.1 Asset Audit The following summarises the type of assets that have been identified as potentially at risk for the study area and the method for obtaining/assimilating these assets into the GIS asset database. An overview of the GIS database of all assets potentially at risk from coastal hazards is displayed in Figure Great Ocean Road The Great Ocean Road is one of Victoria s most popular tourist destinations and attracts visitors from around Australia and Internationally. The Great Ocean Road is the principle piece of transport infrastructure in the study area and is vital to supporting the tourism and economic activity in the study area. The Great Ocean Road also serves an important emergency management function. The Great Ocean Road is zoned Road Zone Category 1 and differs from other local roads in the study area in that planning and works associated with the Great Ocean Road are managed by VicRoads. The Great Ocean Road has been digitised as polygon feature from aerial imagery for this study. The spatial extent of the Great Ocean Road has been interpreted as covering a width of the tarmac plus one metre either side. In addition to the Great Ocean Road, an asset relating to the competence of the Great Ocean Road foundations has been delineated to assist in the risk analysis. The structural incompetence of unconsolidated sand is such that a zone of reduced bearing capacity extends landward of a shoreline erosion escarpment. The stability of the roads foundations located within a zone of reduce bearing capacity will be compromised unless appropriate measures have been considered in the design of the road foundations. The width of the zone of reduced bearing capacity is influenced by a number of factors including the angle of repose of the dune sand, the height of the erosion scarp and the presence of water table gradients. Stability factors relating to determination of these zones have been defined by studies undertaken by Nielsen et al (1992). For the purposes of the risk analysis of the study area, the widths of reduced bearing capacity seaward of the edge of the Great Ocean Road have been delineated for different dune scarp heights and varied based on the DTM of the study area. The widths of reduced bearing capacity adopted for the risk analysis are summarised in Table / R01 v04-26/10/

20 Table 3-1 Adopted Widths of Reduced Bearing Capacity Erosion Scarp Height (m) Indicative Zone of Reduced Bearing Capacity Width (m) Barwon Water Assets Barwon Water has a large number of assets in the study area associated with the provision and treatment of potable water and sewerage respectively. A number of these assets have historically been impacted by coastal hazards or are potentially at risk in the future. The potable water and sewerage network for the study area was provided by Barwon Water as linear features in a GIS format. The pump station at Skenes Creek was digitised from aerial imagery for the study OCC Assets The OCC is responsible for the management of a range of foreshore assets in the study area. Significant assets managed by the OCC and at risk of coastal hazard impacts include the following: Skenes Creek Camping Ground and associated toilet blocks, office, BBQ facilities etc Pedestrian pathways and fencing Foreshore parking areas Public toilets, barbecue facilities, picnic tables, signs and shelters These assets were identified from aerial imagery and digitised for inclusion into the GIS database Heritage Listed Trees An avenue of Monterey Cypress trees, planted in the 1890 s, provide a distinctive gateway to Apollo Bay and these trees are considered to have heritage value. These trees were identified from the aerial photography and incorporated into the GIS database Stormwater Drainage Network A total of 10 stormwater outfalls were identified in the study area. The majority of these are located along the Apollo Bay shoreline. The Colac Otway Shire Council provided the stormwater drainage network including pits, pipes and outfalls in a GIS format. Pipes and outfalls were delineated as linear features. Pits were delineated as point features Apollo Bay Harbour The Apollo Bay Harbour is the only working port and safe haven between Queenscliff and Warrnambool. The harbour services a small commercial fishing fleet, associated fisherman s cooperative and incorporates a boat ramp facility and moorings for recreational vessels. The harbour was created initially by the construction of a southern breakwater in the 1950 s with subsequent extensions and modifications to the harbour and breakwaters undertaken since in an attempt to limit siltation of the harbour and entrance and to improve protection to moored vessels. The Apollo Bay Harbour is zoned as Public Park and Recreation Zone. The Apollo Bay Harbour is operated by the Otway Colac Council which includes management of maintenance dredging activities / R01 v04-26/10/

21 Figure 3-1 Overview of GIS Asset Database / R01 v04-26/10/

22 3.2 Coastal Hazards An analysis of the potential extent of coastal hazards has been undertaken for the study area. The coastal hazard analysis provides the basis for informing the extent of the risk to assets and infrastructure in the study area and for prioritising and evaluating measures to treat or mitigate these risks. Estimation of the coastal hazard extents has been undertaken using conventional coastal engineering methods and techniques and existing coastal information and data for the study area. It should be recognised that the processes giving rise to coastal hazards are extremely complex and significant uncertainty exists in the estimation of their potential extents. The objective of the analysis of coastal hazard is therefore to provide a precautionary, risk based assessment of their potential extent, considering an approximate 10 year management timeframe. The following sections summarise the analysis undertaken to identify potential coastal hazard extents and their probabilities in the study area. The coastal hazard analysis includes consideration of both coastal erosion and inundation hazards Coastal Inundation Hazards The potential extent of the coastal inundation in the study area have been determined by adoption of available storm tide recurrence interval estimates for Apollo Bay and calculations of potential wave setup and run-up at and within the coastal compartments in the study area. The different coastal water level estimates and calculations have been combined to develop a series of peak coastal inundation elevations for the study area that are considered to have varying probabilities of occurrence over the 10 year management timeframe. Storm Tide Estimates of 10% and 1% Annual Exceedance Probability (AEP) extreme coastal water levels (storm tides) at Apollo Bay have been developed by the CSIRO (CSIRO, 2009) for different planning and sea level rise scenarios as part of the Department of Sustainability s Future Coasts Program. The estimated levels under existing sea level conditions for the 10% and 1% AEP storm tide are displayed in Table 3-2 for Apollo Bay. Table 3-2 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 Wave Setup & Run-up The study area coastline is exposed to the high swell wave energy from Bass Strait. The action of this wave energy can contribute significantly to water levels in the near shore zone along the study area. Wave setup is the super elevation of nearshore water levels due to the transport of momentum associated with pressure and velocity fluctuations of breaking waves propagating in a shoreward direction. Wave runup is the vertical height above the still water level a wave will run up the face of a sloping wall or beach profile. Run up varies with structure or beach shape and roughness, the depth and slope of the bed next to the beach or structure and the actual wave conditions / R01 v04-26/10/

23 To enable estimation of the contribution of wave action in the near shore zone to local coastal water levels, in terms of both wave setup and extent of wave run-up, estimates of design wave conditions offshore of the study area have been developed from the previous wave climate analysis undertaken by CES (CES, 2006). The amount of wave setup that could be expected under various design offshore wave conditions can be determined from the excess momentum flux due the presence of waves at the shoreline using linear wave theory. The theoretical solutions have been extensively validated to field measurements by Guza and Thornton (1981). In general, the wave setup can be estimated as approximately 20% of the design offshore significant wave height. The propagation of waves onto dry beach is referred to as wave run-up and is defined as the vertical displacement of the shoreline, measured relative to the still water level, due to the swash motions of waves. Comprehensive studies of run-up on natural beaches has been undertaken by Holman (1986) and Nielsen and Hanslow (1991). These studies defined the parameter R 2% which is the run-up height exceeded by 2% of the wave run-up events on the shoreline. The relationship between R 2% and the incident wave conditions and beach slope was determined as follows: R 2% = 0.366g 1/2 tanβh 0 1/2 T where: g = acceleration due to gravity tanβ= average shoreline gradient H 0 = deep water significant wave height T = spectral peak wave period The adopted storm tide and design wave conditions for three probability scenarios are summarised along with the resulting peak coastal inundation elevation for relevant sections of the study area in Table 3-3. The peak coastal water level estimates displayed in Table 3-3 have been mapped to the coastal DEM to provide an estimate of the potential extents of coastal inundation in the study area for each scenario and are displayed in Figure 3-2. Table 3-3 Probability Almost Certain Peak Coastal Inundation Elevation Scenarios for the Study Area Coastal Inundation Scenario 10% AEP storm tide + 5m Hso, 14s Tp Mounts Bay (m AHD) Apollo Bay (m AHD) Wild Dog Creek (m AHD) Skenes Creek (m AHD) Unlikely Rare 1% AEP storm tide + 5m Hso, 14s TP 1% AEP storm tide + 8m Hso, 14s TP The coastal inundation extents displayed in Figure 3-2 show that coastal inundation extents are largely confined to the coastal foreshore fringe. The analysis is however unable to account for the potential increase in inundation extents that could occur due to shoreline erosion. It is noted that the analysis displayed in Figure 3-2 indicates that minor inundation of the Great Ocean Road near / R01 v04-26/10/

24 the intersection of Marriners Lookout Road is predicted under the Almost Certain inundation scenario. This location has historically observed multiple, minor inundation events due to wave runup and overtopping onto the Great Ocean Road. This is considered to provide some degree of validation to the coastal inundation hazard levels and extents developed in this analysis / R01 v04-26/10/

25 Figure 3-2 Coastal Inundation Hazard Extents / R01 v04-26/10/

26 3.2.2 Coastal Erosion Hazards The potential extent of the coastal erosion in the study area have been determined by adoption of previously determined historical shoreline recession rates and additional calculations based on theoretical models of potential shoreline erosion for sandy shorelines in the study area. The different coastal erosion hazard estimates and calculations have been combined to develop a series of coastal erosion extents for the study area considered to have varying probabilities of occurrence over the 10 year management timeframe. Longterm Shoreline Recession Rates Estimates of longterm shoreline recession rates for the study area have been developed. The recession rates are considered to have a range of potential probabilities of occurring over a 10 year management timeframe. Long term shoreline recession with a high probability of occurring over a 10 year management timeframe have been adopted from the historical aerial photographic analysis undertaken by CES (2006). The extent of long term underlying recession of the shorelines for each coastal compartment in the study area has been inferred from the analysis undertaken by CES. Where the coastline has historically accreted (advanced) due to construction of coastal structures such as the Harbour and groyne at Wild Dog Creek, the future response of the shoreline has been assumed to be equivalent to the more recent trends in the shoreline position observed over the last decade. The average annual shoreline recession rates determined by the CES study have been factored over a 10 year management timeframe. Table 3-4 displays the estimated extent of the long term shoreline recession considered to have a high probability of occurring ( Almost Certain ) over a 10 year management timeframe. More conservative estimates of the potential rates of shoreline recession in the study area have been developed by consideration of equilibrium shoreline profile theory. Equilibrium profile theory assumes that where all else remains equal, such that the shoreline is neither gaining nor losing significant volumes of sediment, a rise in relative sea level will lead to erosion as wave action erodes the beach face and transports sediment offshore. Over time, this process translates the previous shoreline profile shoreward and upward in response to the relative higher sea levels. The process results in the redistribution of sediment across the profile but does not lead to net gain or loss of sediment. The equilibrium profile model was first suggested by Bruun (1962) and has been expanded and modified upon by others. A number of parameters are required to enable estimates of potential long term shoreline recession rates to be determined using equilibrium profile theory for the study area. These are discussed below: Sea Level Rise Global sea levels rose approximately 0.17m during the 20 th Century (Reference). The global rate of sea level rise between 1950 and 2000 was 1.8mm/yr based on tidal gauge data (Reference). Satellite altimeter data estimates the rate has exceeded 3mm/yr(Reference). The rate of sea level rise estimated from the Australian Baseline Sea Level Monitoring Project station at Lorne is approximately 2.8mm/yr. Eustatic sea level rise due to climate change and thermal expansion of the worlds oceans are projected to result in increases in mean sea level of between m by the end of this century, however, much of this increase is expected in the second half of this century. Over the next approximate 10 years, an increase in mean sea level of approximately 2.8cm could be therefore be expected by extrapolating the existing rate of sea level rise observed at Lorne / R01 v04-26/10/

27 Depth of Closure The depth of closure determines the offshore extent to which the shoreline profile adjustment due to sea level rise is considered to extend offshore. The estimates of shoreline recession using equilibrium theory are therefore quite sensitive to the assumed depth of closure of the shoreline profile. The depth of closure for the study area shorelines has been determined from an estimate of the significant wave height that could be exceeded for approximately 12 hours per year based on the previous wave climate analysis undertaken by CES (2006). This wave height has been estimated at approximately between 5 and 7m significant. The resulting depth of closure for the study area shoreline profiles has been estimated at between 10.7 and 16.5m based on this wave height and using the relationship developed by (Hallermeier, 1978). The two depth of closure estimates for the shoreline profiles in the study area have been used to develop two long term shoreline recession scenarios based on equilibrium shoreline theory that are considered to have low ( Unlikely ) and very low ( Rare ) probabilities of occurring over the 10 year management timeframe. Table 3-4 displays the estimated extent of the long term shoreline recession derived from the equilibrium profile for two probability scenarios. Table 3-4 Probability Estimated Longterm Shoreline Recession Extents and Probabilities for the Study Area Mounts Bay (m) Apollo Bay (m) Wild Dog Creek (m) Skenes Creek (m) Almost Certain 0.9m 0-0.2m 0-0.2m 0-0.2m Unlikely Rare Short-term Erosion Demand/Storm Bite The analysis of the historical aerial photography previously undertaken by CES (2006) has been reviewed to identify the magnitude of the short term, storm related erosion extents in the study area. The estimates derived from this analysis have been varied within each coastal compartment based on the observed extent of the short term dynamics in the vegetated dune extents identified by the CES (2006) study to provide a range of short term erosion extent probabilities displayed in Table / R01 v04-26/10/

28 Table 3-5 Probability Adopted Short-term Erosion Demand Extents for the Study Area Mounts Bay Apollo Bay Wild Dog Creek (m) (m) (m) Skenes Creek (m) Almost Certain Unlikely Rare The total coastal erosion extents (long term recession + short term erosion demand) for the three probability scenarios for the study area are summarised in Table 3-3. The coastal erosion extents displayed in Table 3-3 have been mapped to the coastal DEM to provide an estimate of the potential extents of coastal erosion within the study area for each probability scenario and are displayed in Figure 3-2. Table 3-6 Probability Coastal Erosion Scenarios for the Study Area Mounts Bay Apollo Bay Wild Dog Creek (m) (m) (m) Skenes Creek (m) Almost Certain Unlikely Rare / R01 v04-26/10/

29 Figure 3-3 Coastal Erosion Hazard Extents / R01 v04-26/10/

30 4. RISK ANALYSIS The coastal hazard risk analysis provides a method for understanding the following: The coastal hazard risk profile of assets in the study area How the asset risk profiles vary spatially within the study area Identifying priority risks to assets in the study area. The risk analysis methods and likelihood and consequence definitions adopted for the assessment are described in the following section. 4.1 Risk Analysis Method The coastal hazard risk analysis involves considering both the likelihood and consequence of the identified coastal hazard risks to assets in the study area. The definitions relating to the likelihood and consequence of coastal hazard risks to the study area assist in transparently conveying the uncertainty that exists in the analysis of the coastal hazard extents and in the relative consequences that have been attributed to the different assets and land uses impacted by coastal hazards in the study area. The likelihood and consequence definitions adopted for the risk assessment are discussed in the following sections Likelihood Definitions The likelihood or probability of coastal hazard impacts extending certain distances landward of the existing shoreline has been defined for the study area for a number of discrete probability definitions as described in Section 3.2. The likelihood definitions have been developed to provide a degree of transparency in relation to the level of uncertainty, limitations and assumptions that are considered to be contained within the analysis of the potential coastal hazard extents for the study area over the 10 year management timeframe. The discrete probability definitions that have been developed for the coastal hazard extents in the study area discussed below and summarised in Table 4-1. The Almost Certain probability definition represents a coastal hazard scenario and extent of impact that could be considered imminent and/or could be expected to occur over the 10 year management timeframe based on historical observations of shoreline recession rates and coastal inundation extents. The Unlikely probability definition represents a coastal hazard scenario and extent of impact that generally exceeds that which could be expected based on historical observations of the study area but which can be predicted from theoretical analysis such that infrequent or isolated occurrences of the hazard are possible. The Rare probability definition represents a coastal hazards scenario and resulting extent of impact that significantly exceeds that which could be expected based on historical observations of the study area but can be predicted from conservative theoretical analysis / R01 v04-26/10/

31 Table 4-1 Risk Likelihood Definitions Probability Definition Hazard Scenario Example Almost Certain Coastal hazard impacts would be expected Based on observed historical shoreline recession rates and storm erosion demand and storm tide and wave run-up levels Likely Possible Unlikely Rare Not Assessed Not Assessed There is a low probability of coastal hazard impact based on historical observations, however, infrequent and isolated occurrences of the hazard are possible There is a very low probability of coastal hazard impact, hazard would only occur in extreme circumstances High shoreline erosion rates and wave runup estimates based on theoretical analysis and assumptions. Extreme shoreline erosion rates and wave runup based on maximum theoretical values Consequence Definitions The relative consequence of coastal hazard impacts to assets in the study area is influenced to a significant degree by the value that a particular stakeholder attributes to those assets. The consequence definitions therefore include the following broad consequence values: Community Assets and Services Economic Environmental Public Safety Table 4-1 displays the different consequence values and discrete consequence definitions for the coastal hazard risk assessment / R01 v04-26/10/

32 Table 4-2 Consequence Catastrophic Major Moderate Minor Insignificant Risk Consequence Definitions Community Assets Infrastructure & Services Long term loss of community assets and regional infrastructure. Major asset damage, severe impact and disruption to community services and regional infrastructure and assets Considerable impact upon access to and function of community services and assets Minor short term impacts (mainly reversible) on low value community services and assets Little to no impact on communities and their access to services Economic Health & Safety Environment Severe, i.e. over $10 million or more than 50% of assets Major, i.e. between $100,000 and $1M or 10 to 50% of assets Moderate, i.e. between $10,000 and $100,000 or 10% of assets Minor, i.e. up to $10,000 or 1% of assets Impact below MHW mark Multiple fatalities and/or severe irreversible disability to multiple persons Single fatality and/or severe irreversible disability to one or two persons Serious Injury. Moderate irreversible disability or impairment to one or more persons Significant Injury. Reversible disability requiring hospitalisation Minor injury. No medical treatment required. Irreversible damage to ecosystem or landforms Alteration or loss of sustainability of one more ecosystems or several components of these systems Alteration or disturbances of a component of an ecosystem but sustainability unaffected Localised temporary effects on environment beyond natural variability Localised temporary effects on environment within natural variability / R01 v04-26/10/

33 4.1.3 Risk Ranking A risk matrix has been defined to describe the combination of likelihood and consequence that produces a given level of risk to assets in the study area. The risk matrix adopted for the study is displayed in Table 4-3. The level of tolerance to the risks to assets determined from the risk matrix can be interpreted from the risk profile definitions displayed in Table 4-4. Table 4-3 Likelihood Risk Assessment Matrix Consequence Insignificant Minor Moderate Major Catastrophic Almost Certain Low Medium High Extreme Extreme Likely Low Medium High High Extreme Possible Low Medium Medium High High Unlikely Low Low Medium Medium Medium Rare Low Low Low Low Medium Table 4-4 Risk Profile Low Medium High Extreme Risk Profile Definition Response Tolerable Risk. A level of risk that is manageable without active intervention Moderate Risk. A level of risk requiring modest, precautionary intervention/treatment to mitigate risks to acceptable levels Major Risk. A level of risk requiring significant, priority intervention/treatment to mitigate risks to acceptable levels Extreme Risk. A level of risk to assets that cannot be practically mitigated. 4.2 Risk Analysis Results The coastal hazard extent probability zones developed in Section 3.2 were intersected with the coastal asset database in a GIS to determine the risk profile for key assets in terms of the number, length and/or area of potential coastal hazard impacts. For each of the assets determined to be potentially impacted by coastal hazards, a consequence was assigned based on an evaluation of the different values that can be attributed to the asset and the level of impact that could be expected to the assets function or service in relation to these values due to its exposure to the coastal hazard. The results of this analysis are described for each coastal compartment in the following sections Mounts Bay The risk analysis has determined risk profiles for coastal assets in the Mount Bay coastal compartment. The asset risk profiles are displayed spatially in Figure 4-1 and summarised in Table 4-5. A number of assets have been determined as having risk profiles of medium or greater due to their potential exposure to coastal hazards and consequences to the impacted assets function or service. The following summarises the key risks to assets in Mounts Bay: / R01 v04-26/10/

34 Approximately 145m of Barwon Water Sewer, and a similar length of water main, that is located between the Great Ocean Road and the shoreline erosion scarp has been identified as having a high risk profile. The high risk profile is due to a combination of the proximity to the existing shoreline erosion scarp and the importance of the service this asset provides to the community. Approximately 531m of the adopted Great Ocean Road foundation buffer is considered to have a high risk profile. The high risk rank has been determined due to the potential for the bearing capacity of the Great Ocean Road dune foundation being compromised by coastal erosion and the subsequent consequence to the function of the Great Ocean Road. Additional medium risk ranks have also been identified for a toilet block, car park and a number of beach access paths. The medium risk rank for the beach access paths relates primarily to the potential public safety risks associated with the high erosion scarps developing at the base of these paths. Table 4-5 Mounts Bay Coastal Asset Risk Profiles Mounts Bay Asset Length (m) Area (m^2) Approx. Length (m) Count () Low Revetment 5 Sewer 190 Walking track 353 Water Supply 191 Car parks 7958 GOR Foundation Buffer Great Ocean Road Beach access 5 Medium Revetment 77 Sewer 62 Walking track 142 Water Supply 33 Car parks GOR Foundation Buffer Great Ocean Road 21 Beach access 9 Toilet blocks 1 High 419 Sewer 146 Water Supply 274 GOR Foundation Buffer / R01 v04-26/10/

35 Figure 4-1 Mounts Bay Coastal Asset Risk Profiles / R01 v04-26/10/

36 4.2.2 Apollo Bay The risk analysis has determined risk profiles for coastal assets in the Apollo Bay coastal compartment. The asset risk profiles are displayed spatially in Figure 4-2 and summarised in Table 4-6. A number of assets have been determined as having risk profiles of medium or greater due to their potential exposure to coastal hazards and consequences to the impacted assets function or service. The following summarises the key risks to assets in Apollo Bay: Approximately 100 metres of sewer rising main have been identified as having medium risk profiles due to the potential impact of coastal erosion. Two short sections of sewer were identified as having a high risk profile. These sections of sewer rising main have previously been exposed following are large erosion event in 2005 and remain vulnerable to further storm erosion events Some minor sections of the adopted Great Ocean Road foundation buffer have been identified as of at risk from coastal erosion between Joyce Street and Marriners Lookout Road. The probability of this buffer being impacted is however still considered to be Rare and the risks are considered to remain essentially Low. Approximately 11 beach access paths were identified as having a medium risk profile due to the public safety risks associated with erosion scarps developing at the base of the access points following large storm events / R01 v04-26/10/

37 Table 4-6 Apollo Bay Coastal Asset Risk Profiles Apollo Bay Asset Length (m) Area (m^2) Approx. Length (m) Count () Low Groyne 18 Seawall 20 Sewer 80 Walking track 795 Car parks 1592 Great Ocean Road 8 2 GOR Foundation Buffer Other roads 105 Private Dwelling 159 Beach access 5 Medium Groyne 35 Seawall 70 Sewer 80 Walking track 213 Car parks 14 GOR Foundation Buffer Other roads 188 Beach access 11 High 39 Sewer / R01 v04-26/10/

38 Figure 4-2 Apollo Bay Coastal Asset Risk Profiles / R01 v04-26/10/

39 4.2.3 Wild Dog Creek The risk analysis has determined risk profiles for coastal assets in the Wild Dog Creek coastal compartment. The asset risk profiles are displayed spatially in Figure 4-3 and summarised in Table 4-7. A number of assets have been determined as having risk profiles of medium or greater due to their potential exposure to coastal hazards and consequences to the impacted assets function or service. The following summarises the key risks to assets in the Wild Dog Creek coastal compartment: A number of short sections of sewer main were identified as having medium risk profiles. The risks profiles for these assets are increased around the stormwater outfalls where the shoreline has been eroded around these structures leaving relatively limited buffer distance between the sewer main and the existing shoreline. Significant lengths of the Great Ocean Road have been identified as having a Low risk profile due to the potential but rare likelihood of coastal inundation impacting the Great Ocean Road in this coastal compartment. Some smaller sections of the Great Ocean Road have also been identified as having a Medium risk profile due to the potential for more frequent coastal inundation to impact these sections of the Great Ocean Road. No historical observations of significant inundation of the Great Ocean Road within this coastal compartment are however understood to exist, suggesting the inundation analysis maybe somewhat conservative for this coastal compartment. Nevertheless, the elevation of the Great Ocean Road within this coastal compartment is low and inundation due to combinations of storm surge, wave setup and runup remain possible for this section of the Great Ocean Road. A significant length of the adopted Great Ocean Road foundation buffer has been identified as at low risk of erosion with a smaller section identified as at medium risk. These risks relate to the section of the Great Ocean Road that runs behind the beach at Wild Dog Creek. The morphology of the beach at Wild Dog Creek is highly variable due to the complex interaction of creek streamflows and the coastal processes. These interactions result in rapid changes to the creeks alignment along the beach in response to changing streamflow rates and prevailing wave and sediment transport directions. There is the potential for these changes in morphology to cause erosion of the foundations of the Great Ocean Road, compromising the bearing capacity of the road base. However, the bluff separating the Great Ocean Road from the beach is very well vegetated and the berm that is generated by wave action on the seaward face of the beach at Wild Dog Creek tends to limit the ability for large waves to directly impact this bluff such that the risks are considered to remain predominately Low / R01 v04-26/10/

40 Table 4-7 Wild Dog Creek Coastal Asset Risk Profiles Wild Dog Creek Asset Length (m) Area (m^2) Approx. Length (m) Count () Low Groyne 32 Sewer 482 Walking track 866 Water Supply 8 Car parks 1824 GOR Foundation Buffer Great Ocean Road Other roads 737 Beach access 4 Medium Groyne 15 Sewer 35 Walking track 22 Car parks 345 GOR Foundation Buffer Great Ocean Road Other roads Beach access 1 High 10 Sewer / R01 v04-26/10/

41 Figure 4-3 Wild Dog Creek Coastal Asset Risk Profiles / R01 v04-26/10/

42 4.2.4 Skenes Creek The risk analysis has determined risk profiles for coastal assets in the Skenes Creek coastal compartment. The asset risk profiles are displayed spatially in Figure 4-4 and summarised in Table 4-8. A number of assets have been determined as having risk profiles of medium or greater due to their potential exposure to coastal hazards and consequences to the impacted assets function or service. The following summarises the key risks to assets in the Skenes Creek coastal compartment: A small section of the Great Ocean Road located approximately mid way between Wild Dog Creek and Skenes Creek has been identified as having a High risk profile due to the potential for coastal erosion to compromise the bearing capacity of the road foundations as well as impact the road itself. The site inspection identified that rock armour has been placed between the road and the shoreline along a small section of the coastline at this location to mitigate the erosion risks to the road at this location. However, significant sections of the Great Ocean Road foundation are not protected from coastal erosion at this location and the risks are considered to remain significant that the roads function could be compromised due to an erosion event. The Barwon Water pump station and toilet block located on the crown land adjacent to the Caravan Park at Skenes Creek has been identified as having a medium risk profile due largely to the potential for coastal inundation to impact this assets function. The pump station is also located close to the mouth of Skenes Creek and some underlying risk of erosion impacting the hazard remain possible but are considered low. A stormwater outfall is located under the shore platform at the eastern end of Skenes Creek. Where the stormwater pipe crosses the shoreline the risk to this asset have been identified as high due to the likelihood of coastal erosion impacting this asset. However, the depth at which the pipe has been laid is not known and it is possible that the pipe would not be exposed and therefore impacted by coastal erosion. Under this scenario, the risk profile for this asset may in fact be Low. Risks to the Caravan Park associated with coastal inundation have been identified however the probability of impact is considered to remain rare and hence the risk profile is Low / R01 v04-26/10/

43 Table 4-8 Skenes Creek Coastal Asset Risk Profiles Skenes Creek Asset Length (m) Area (m^2) Approx. Length (m) Count () Sewer 129 Stormwater 209 Car parks 1090 Caravan Park 6572 GOR Foundation Buffer Great Ocean Road Other roads 307 Beach access 2 Toilet blocks 1 Medium Sewer 6 Stormwater 7 Caravan Park 0.5 GOR Foundation Buffer Great Ocean Road Beach access 7 Pump station 1 High Stormwater 6 GOR Foundation Buffer / R01 v04-26/10/

44 Figure 4-4 Skenes Creek Coastal Asset Risk Profiles / R01 v04-26/10/