Phillip Island Nature Parks Coastal Process Study 8 October 2014

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Jared Manning
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1 Phillip Island Nature Parks Coastal Process Study 8 October 2014

2 Project Overview

(>10m thick) covered in mix of sand and silt Limited

3 Coastal Geology Basaltic and fragmented lavas, granite at Pyramid Rock and Cape Woolamai Weathered basalt (>10m thick) covered in mix of sand and silt Limited accumulations of sand back from the shoreline Pyramid Rock

4 Coastal Geomorphology Continuously steep southern shoreline Broad & detailed character determined largely by physical character & structural variation in underlying basalt outcrops. No sand input from river. Coastal processes dominated by high wave energy. Aspect & exposure to wave action account for local variations in morphology.

5 Coastal Geomorphology Six major landform classes identified: Steep Coasts Shore Platforms Beaches, Dunes, Stream mouths, and Coastal Lagoons

6 Coastal Geomorphology

7 Coastal Geomorphology Landform classes: Steep coastline, with five major classes: Active Cliffs Active Mass Movement Slopes Bluffs Amphitheatres Plunging Cliffs

8 Coastal Geomorphology

9 Coastal Geomorphology

10 Coastal Geomorphology

11 Coastal Geomorphology Landform classes: Shore Platforms Beaches: Boulder/cobble Cobble/gravel Sand Dunes Stream Mouths and Coastal Lagoons

12 Coastal Geomorphology

13 Coastal Geomorphology

14 Coastal Vegetation Determined by wind exposure, salt spray, soil composition, geology, presence of sea bird colonies and past land management practices. Dune vegetation affects dune development and morphology Introduced species more effective in binding sand. Important function when considering storm impacts on beaches and dunes

15 Oceangraphic Setting Winds & Waves Dune build-up: trapping by vegetation Local wind waves i.e. storm waves, typically erosive Swell waves Longer period, typically beach building Coastal Water Levels Storm surge Sea Level Rise

16 Coastal Processes susceptibility to erosion Landform Class Steep Coasts Active Cliffs Active mass movement slopes Current Susceptibility to Erosion Active Cliffs, particularly those in sands or weathered volcanics Only where marine processes interact with slope toe Potential Changes to Coastal & Terrestrial Processes with Sea Level Rise Increased frequency of wave impact at cliff base resulting in increased hydraulic action, abrasion, and mass movement. Increased wave impact through hydraulic action, abrasion, and mass movement. Likely Landform Response There will be selective change due to varied rock resistance of the different cliff materials. An increase in cliff slope is likely due to toe removal and increased slope failure. There is likely to be a loss of sandy beach and increase in gravel/boulder beach volume. There is likely to be a depletion of sandy beach areas, an increase in gravel/boulder beaches, a loss of vegetation on lower slopes, increased rate of slope failure and increased delivery of slope debris to the base of the slopes. Bluffs Amphithea tres Not currently active Not currently active Potential reactivation of base of inactive cliffs by wave impact. This is dependent on the width and volume of beach & dune areas fronting the bluffs. Potential reactivation of base of inactive cliffs by wave impact. Responses include the reactivation of currently stable slopes through the depletion of the beach and dune areas in front. This would likely result in mass movement of slopes occurring. Reactivation of currently stable slopes.

17 Coastal Processes susceptibility to erosion Beaches & Dunes Boulder, Erosion in cobble, response to storm gravel events beaches Sand beaches Dunes Erosion in response to storm events Erosion in response to storm events Increased inundation with higher wave energy. Increased abrasive action on platforms and cliffs. Increase in high energy events resulting in more dynamic beach environment. Increased inundation with higher wave energy. Those closest to the shoreline likely to experience: An increase in high energy events. Increased inundation with higher wave energy. Increased potential for weeds. Introduction of larger material sizes, but reduction of size of gravels, An increased width and steepness of gravel beaches. Recession of the shoreline, with migration landward of beach crest and berms. Increased rate of shoreline retreat. This occurs inversely proportional to beach slope, with gently sloping profiles retreating at a faster rate. There will likely be a decrease in the steepness of the beach and a narrowing of beach above the high tide mark. Increased overwash and scarping of berms. Erosion/retreat of foredunes, and loss of foredune vegetation. Initiation of blowouts.

18 Coastal Processes Summerland Beach Coastal Processes Summerland Beach Sandy beach, formed in an embayment between 2 headlands. Cobble/gravel beaches at base of headlands. Beach profile varies, with narrow reflective high tide beach, Backshore comprises range of dune morpholigies.

19 Coastal Processes Summerland Beach Aerial imagery comparison ( ) & data analysis shows: Limited change in shoreline location Distinct landform changes due to increased vegetation cover. Short-term responses to storms (cliffing)

20 Coastal Processes Summerland Beach

21 Coastal Processes Summerland Beach Stand structures currently forward of shoreline Enhanced erosion due to stands

22 Coastal Processes Summerland Beach Trends: Recession of dune-beach profile with SLR On-going changes to dune morphology with vegetation, Short term responses to storm events will continue. May be enhanced under on-going SLR conditions, Coastal structures impacting erosion of beach-dune profile. Likely to increase with on-going SLR

23 Coastal Processes Smiths Beach Fine sand beach, with headlands to west and east and very wide complex shore platform Backed by mass movement slope, minimal/no dunes present Limited sand supply

24 Coastal Processes Smiths Beach Aerial imagery comparison ( ) & data analysis shows: Increased exposure of the underlying cobble/gravel beaches, Increased exposure of an underlying thin cemented layer overlying weathered volcanic material (such as at the foot of the current access ramp), and Exposure and erosion at the foot of the backslope.

25 Coastal Processes Smiths Beach Mass movement slope

26 Coastal Processes Smiths Beach Mass movement slope

27 Coastal Processes Smiths Beach Trends: Backshore slope constrains landward movement, enhances sand loss from the beach Continued loss of sand, increasing exposure of toe of slope (may enhance sand movement) Reactivation of mass movement slope

28 Coastal Processes Woolamai Beach A long sandy beach backed by steeply rising slope Slope comprises active sand cliff as well as sections of mass movement slope Limited sources of sand inputs

29 Coastal Processes Woolamai Beach Localised change over the last 75 years Density of vegetation most marked change

30 Coastal Processes Woolamai Beach

31 Coastal Processes Woolamai Beach Dune heights have increased Reduced sand transport to Cleeland Bight Vegetation removal will reinitiate windblown sand transport Will not provide additional sand supply to Woolamai Beach

32 Coastal Processes Woolamai Beach Trends: Likely to be a net loss of sandy material from the beach with on-going sea level rise Potential reduction in sand fans in front of active sand cliffs Marine influences increasingly interact with toe of slope/cliff. Reactivation of failure surfaces and recessions initiated

Coastal Processes Management Strategies In line with the VCHS: Risk Avoidance Precautionary approach to new development, infrastructure or

33 Coastal Processes Management Strategies In line with the VCHS: Risk Avoidance Precautionary approach to new development, infrastructure or services, relocation of existing assets Risk Reduction Engineering works, planning and controls Risk Sharing Information and education of stakeholders

34 Coastal Processes Recommendations To build upon this work and inform future decision making: Long term monitoring program (could integrate with existing Surf Cam) Identify and quantify short and longer term changes to beaches, shorelines, surf Adaptive management approach in response to the on-going monitoring

Australian Coastal Councils Conference

Australian Coastal Councils Conference 11 March 2015 Estimating Future Coastal Inundation and Erosion Hazards Dr Andrew McCowan Dr Christine Lauchlan-Arrowsmith Warwick Bishop Background Victorian Future