[Speaker:Andrew Pomeroy]
My name is Andrew Pomeroy and I'm working with the Department of Energy, Environment and Climate Action here in the State of Victoria on the Silverleaves Coastal Process Assessment and this video is going to summarise some of the key work that's been undertaken and some of the results that have been determined from this piece of work.
The video is broken into five key parts.
The first part talks about what this study is about, so it's scope, the area considered, and some background information.
The second part of the video is a bit about the site and its history.
Things like geomorphology and site evolution over much longer time frames because ultimately context is important.
The third part of the video, where most of the content is actually located, is about some of the key changes that have been observed more recently, so over the last few decades, as well as the processes, both coastal processes and human processes that affect the shoreline.
So things like waves, currents, sand transport, various interventions, as well as the natural shoreline evolution. The 4th part of the video talks about coastal hazards, things like erosion and inundation.
And finally, the 5th part talks about where to from here, and it's really a preview about some of the adaptation planning work that's currently underway to draw upon what's been learned in this study so far and how that will shape the response of this area.
The aim of this project was to assess coastal processes at Silverleaves and how that impacts the coastline. And while Silverleaves itself was the key study area, it was obvious that you needed to consider much broader perspective than Silverleaves itself, because of course, there's lots of other interventions and factors at play on a coastline like this.
So it did extend much wider than that in order to capture the overall dynamics.There were several components to the project.
There was a community consultation component where we spoke with local community members and residents nearby to understand and to gain information from them about their lived experience in this area.
And that produced a lot of very valuable information that would contribute to this study. Over the duration of the project.We've also reviewed several previous studies.
There's been a few studies done now in this area. We didn't want to redo the work. We wanted to build upon the work. And to that extent, we've used that as a starting point and then filled in gaps where those existed.
We've used some numerical modelling to fill those gaps as well as reanalyzed a whole bunch of survey data that's being collected over the last few years in in very high resolution, and that was a key part of this project.
Finally, we undertook some erosion and hazard assessments to quantify the type of impacts that we're likely to expect to this area both now and in the future.
Let's start with a little bit about the broader context. So where does sand come from for this particular location?
Well, in essence sand is transported from offshore from Bass Strait into Western Point and around Phillip Island and you can see that here in the where we have this large arrow.
Sand is brought in from Bass Strait and it can be deposited and transported around the coastline of Phillip Island, but also around the adjacent coastline.
We see that in place like Balnarring and the like. We can also see some of these tails of sand in the environment and some of that sand also moves east and west with the different tidal currents that exist within Western Port.
That sand can be supplied either continually in relatively small volumes. So there's constant, if you want to call it a dribble of sand that enters into Western Port or as bursts of large volume sand, sometimes referred, sometimes referred to as lobes of sand where for whatever reason more sand comes through than than at other times.
It would be fair to say that we don't really know the sand transport mechanism or rates of transport particularly well in this area and that offshore to onshore transport process is relatively difficult to predict and to quantify.
But nonetheless we do know that that process exists and we can see it in the data, we can see it in the aerial imagery and we know from lived experience that that is what occurs.
It's worth recognising that Silverleaves has evolved quite substantially over geological timeframes. And so that context is important because unlike other areas of Victoria, silver leaves itself, but W import more generally, is a relatively dynamic area.
This figure here is produced by water technology several years ago now, and it describes a whole range of important geological and geomorphological factors and features in the landscape.
We see in this particular figure a few different things. We see the historic shoreline shown through here that existed, you know, thousands of years ago.
We see beach ridges that were built up over time in the past. We see submerged what were submerged bed forms that were transporting sand across to the shoreline.
Perhaps most importantly for Silverleaves itself are these three spits that are clearly distinguishable in the in the landscape. And what these show is that sand was originally transported from West to east.
And as it would do that, it would reach discontinuity in the landscape and would slowly prograde out to form a, a, what we call a spit, a long, a longshore accumulation of sand.
And you can see the modern one down here in the bottom right hand corner. But over time, we've seen three different spits form and the current shoreline really is the most recent in this series of Spit developments.
So Spit 3 and it has been extending now eastward for quite some time and it's continued to expand in the eastward direction. We also observed that whilst we've seen, you know, these obviously these features develop, there's been quite some substantial amount of infilling in this area here.
So the shoreline itself has, this whole area has infilled with sand over thousands of years. And we can even see in most recent or in recent aerial imagery, you know, how the shoreline has evolved and some infilling that's occurred, for example, around here, which now no longer exists, as well as the extension of the Spit further to the east.
What's important to recognise here is that there's been over long periods of time, there's been large amounts of sand that have moved from from West to east and that really has evolved the landscape over time.
It also means that our this this area has been dynamic for quite some periods of time and that the shoreline itself has been moving over, you know, hundreds of thousands of years.
And this is important when we consider the overall dynamics of this site. We also know that this shoreline has had a lot of changes over the last 100 years.
So more contemporary changes. Now these things have included, you know, groyne fields that have been constructed. So these timber structures that extend from the shoreline further to out to the sea. Most of you may be familiar with those.
Those have existed all along East Cowes Beach for many, many decades as well as across Silverleaves, which you can see here. We know that the back of the beach, particularly at Cowes East all around through here has rock revetment.
We know that in the past there's been timber revetments, so timber seawalls that have been, it's now been changed to a rock revetment relatively recently.
We also know that the land use has all changed through these areas. But one thing that we can say despite all these changes is what these all lean towards telling us is that retention of sand at the shoreline, if you want to call it a beach, has been a persistent issue for decades.
What we can see though is if we look at this shoreline here, this was the historical shoreline and how much it has changed. The lighter colour is the current shoreline. So it has evolved quite dramatically over the last, particularly maybe the last 40 to 40 plus years.
So some of the key takeaways, the shoreline is dynamic over geological time. The sand that comes to the shoreline is supplied from Bass Strait and we'll come back to that in a few minutes.
The area has formed as a consequence of sand transport from West to east and as large sandy spits. And the shoreline here throughout this region has been modified for for decades. Now, let's talk a little bit about Silverleaves itself.
So the shoreline here has also been evolving since at least the 1950's. The earliest recording that we have that's quantitative, that's useful for analysis is from the 1940s.But the 1950s is a good benchmark.
And what we've seen here is we've plotted the shoreline position over since 1967 here and we see a few things in the shoreline. What we see is just as a bit of a kind of a side point,
This is a vegetation line and the reason we choose the vegetation line as the reference point is as relatively stable relative to the sand water interface. So it's, it's a, it requires a lot of stability for vegetation to establish, but also a lot of energy for the vegetation to be removed.
So we've assumed that the shoreline is going to fall back, but of course it's probably, you know, reasonable to appreciate and most people probably understand this is that it, it wouldn't be as simple as that.
There's a lot of other things that that may prevent the shoreline from moving back in a consistent manner like that, but it provides a typical extent that could be expected up to 2100.
And as we can see from this is that, you know, there's already hazards in this particular area. A substantial portion of civil leaves is also at risk of inundation.
And So what that means is there's two forms of inundation. There's permanent inundation. So that's really the, if you want to call it the drowning of land by sea level rise. And then there's temporary inundation, which is caused by storm events essentially or extreme weather events.
What what the data shows, and this is where it's been done previously and is already available to the public, but it shows that permanent inundation will affect large areas around this area over the next 50 to 100 years.
So mean sea level today plus 80 centimeters, which is roughly 2100 will extend quite substantially over over these areas.
But don't forget that we've talked about mean sea level here. There's also things like, you know, the tidal variability, so high tide versus low tide. So there is a little bit of variability around these these maps, but perhaps more importantly during storms we see substantial implications across this whole area.
And in essence the take home message really is that whilst there's a coastal erosion problem and some storm related implications, this area is also subject to hazards from behind. So water coming in from Rhyll Inlet which could also affect this area.
And so it'd be fair to say that a comprehensive management plan is probably going to be needed for the entire area because it's not going to be solved by simply dealing with the coastal protection structures themselves.
So what are some of the key takeaways from the coastal hazards assessment?
Well, we can say that erosion can be expected to continue to occur along much of this shoreline. There's most certainly some uncertainty in the erosion extent with time. And really the assessment assumes a couple of things. It firstly assumes that there's going to be no intervention. It also assumes that the shoreline is fully mobile, which of course it is not because there's vegetation, houses and other infrastructure and all those will change the rate of shoreline change.
Finally, there's also some important assumptions in the analysis that make this assumption, this assessment, somewhat conservative, as in the worst case scenario, and they're detailed a little bit more in the report.
The assessment also shows that inundation is going to be a substantial hazard and is going to have large impacts in this area, both in spatially. That piece of work is currently being refined by others. So I'm sure there'll be some more information that'll come out about that as that project proceeds.
But nonetheless, we can see that there's going to be some substantial implications for this area both in terms of permanent and temporary inundation. Those that inundation is likely to be predominantly caused from behind, so through real inlet and into silver leaves.
But some seaside breaches may also occur. You know, breaches through the landscape during particularly large events.
So from this work, what were some of the immediate recommendations?
Well, in the short term, one of the key recommendations was to undertake adaptation planning for Silver Leafs and to address to address the identified short term challenges.
There was also a recommendation to look at adaptation planning for the Silver Leafs Township to look at the short term inundation hazards.
And the third recommendation was to implement some ongoing maintenance and strategic nourishment of the groyne fields and perhaps some growing modifications in front of the new revetment to try to alleviate the loss of sand to Chaos Bank and try to re establish some of the flow, that of sand along the shoreline here.
There's more on these in the actual report.
So where to from here?
So a lot of people of course have obviously got some interest about where this, you know, what to do now.
And so the next step is to undertake a process of what's called an adaptation planning. And that's really a strategic approach to plan for the future. And so really a forward looking plan if you want to call it a North Star or a road map.
And you know, you might say to me, Andrew, why wouldn't you just go and solve this problem today?
Well, we use adaptation planning quite deliberately because it allows us to develop adaptation strategies that consider the values as well as the hazards. So, you know, there are things about silver leaves that people love and that they they love the feel of silver leaves and those those other values that are important to retain the character of the area. So they're part of the story.
We also need to identify the most appropriate response for a particular area and really the key because you know, every area is slightly different, but perhaps most importantly, what we want to avoid is the process of maladaption. So that's really the process where we do something in order to alleviate one problem without necessarily appreciating the extent to other areas, the extent that they may have on impacts that they may have on other areas.
And so this process is really going to go through now those three steps, identifying what's important, what options are on the table and how can we best execute those options to minimise impacts elsewhere.
And this process is, is governed by a framework. So there's several steps involved and I've kind of shown it pictorially here, but it's guided by what's called the Victoria's Resilient Coast. And that large framework. I've got the website on the on the slide here. I'd encourage you to go and have a look and have a bit of a read of, of that guideline of that framework. It provides a very clear and relatively easy to read description of the steps that go through in order to develop solutions to deal with these types of problems.
But where are we in this process?
So we've done some scoping and preparation and that piece of work has been done. We've done coastal hazard and vulnerability, which is what we've been talking about in this video. We're about to do some work on values, visions and objectives, as well as adaptation actions and pathways. And that's both those pieces of work have been started as part of the current project.
And what does this all look like in the end?
So if you say, Andrew, what am I expecting out of this process?
Well, what we produce at the end of this process is essentially this type of road map. And this is an example. It's a piece of work which shows what the current hazards are and how they're going to change over time, which we've already done. And then we look at all the different options to deal with these hazards over time. And they range from things like from doing nothing essentially to and avoiding the problem through to different types of nature based methods or accommodating or potentially retreating as well as, you know, protections of the more traditional approaches.
And these maps, how you read these maps are is that we look at, you know, what interventions may happen or in this case, no intervention may happen until some point and you reach what we call a trigger. And there'll be some event or some time where we'll change our approach and we'll move to a different option. So in this case, move from a non intervention to an avoid or a nature based method.
Of course, we could have also gone straight to an avoid situation and then trans to avoid the problem altogether. So these maps come out which will provide, you know, a pathway to addressing the hazards both now but over the longer time as well time frame as well.
And that longer term perspective is important. Some of the options that we'll be considered during this process are things like, and they range really into three categories. So things related to Land Management, planning and design. So things like how we use our land, the type of planning overlays that exist, things like setbacks and development requirements. We also consider things like nature based methods. So can we do things with vegetation? Can we do things with June restoration or on site works to help help nature help itself, so to speak? And of course there's the engineering options that are probably more familiar to a lot of people. Things like, you know, structures, sea walls, revetments, groynes, breakwaters, those types of things which each which may also play a role.
Of course, each of these different options that you've seen on this slide and on the previous may have a different role to play in this particular problem. And So what we're working through at the moment is looking at each of these options, seeing what may be appropriate, may not be appropriate to try to plot out some viable pathways to deal with existing problems, but also future problems.
So that's the current update of where the project is at.
I'd like to thank you for taking the time to watch this video and I hope you've been able to find some really useful information amongst this and get a bit of an overview of what's being done to date.
If you want to find out more about this project and where it's going and where we are in in the various stages of this project, you can find that out by going to the Marine and by going to the Marine and Coastal page and have a look at the Gibson projects that's listed on the screen there.
Or if you need to get in touch with the project team to provide some information or if you have questions or concerns, please do get in touch via the email address that's on the screen.
To the Gippsland Coastal Projects team.
Page last updated: 10/09/24