Coastal Erosion

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GUEST OBSERVER
Australia is a huge continent, but a coastal nation.
About 80 percent of Australians live within 50km of the coast, and a sea-level rise of 1.1 metres (a high-end scenario for 2100) would put about A$63 billion (in 2008 dollars) worth of residential buildings at risk. 
Anyone who lives along Sydney’s northern beaches, especially in Collaroy, saw at first hand the damage the ocean can wreak on coastal properties when the coastline was hit by a severe east coast low during a king tide in June.
There are many different factors that determine which coastal homes or suburbs are most at risk of inundation or erosion, either now or in the future. In a review published as part of a series produced by the Australian Energy and Water Exchange initiative, we investigated the causes of extreme sea levels and coastal impacts in Australia, how they have changed, and how they might change even more. While significant progress has been made over recent decades, many questions remain.
The first factor to consider is the average sea level, relative to the land elevation. This “background” sea level varies, both from year to year and season to season. Depending on where you live and what the climate is doing, background sea level can fluctuate by up to about 1m. Around Australia’s northern coastline, for example, El Niño and La Niña can cause large variations in year-to-year sea levels. 
On top of this are the tides, which rise and fall predictably, and whose range varies by location and phase of the moon. Most places have two tides a day, but curiously some only have one - including Perth. 
<a href="/images/2016/11/28/image-20161114-9065-mho9m6.png" target="_blank">Click to enlarge</a>
<img src="/images/2016/11/28/image-20161114-9065-mho9m6.png" alt="">
Map of tide pattern variations. Red: one high and low tide daily (diurnal); blue: two high and low tides per day (semi-diurnal) with a mixed tidal regime between. OZEWEX, Author provided
On top of that again is the effect of the weather, the most notable short-term effects being storm surges and storm waves. During a surge, the storm pushes extra water onto the coast through a combination of wind pressure, wave buildup, and atmospheric pressure changes. Obviously these factors are much more localised than tides.
Extreme sea-level events, such as the one that hit Sydney in June, can arise from isolated events such as a storm surge. But more often they are due to a combination of natural phenomena that on their own may not be considered extreme. In Sydney, several factors aligned: a storm surge driven by an east coast low, an uncommon wave direction, a king tide, and a higher-than-average background sea level.
These processes already have the capacity to destroy coastal homes and infrastructure. But for the future, we also need to factor in climate change, which will raise the background sea level and may also change the frequency and intensity of storms.
<h2>Long-term trends</h2>
Average sea levels in Australian waters have been rising at rates similar to (but just below) the global average. Since 1993, Australian tide gauges show an average rise of 2.1mm per year, whereas satellite observationsreveal a global average rise of 3.4mm per year. 
What really counts is extreme sea levels, and these have been rising at roughly the same rate, meaning that the rising background sea level is a fairly good guide to how extremes are increasing. 
This trend will continue in the future, although more energetic storm systems may also cause larger storm surges and hence higher rates of extreme sea levels in some places. More frequent storms are also set to make extreme sea-level events more common.
By 2100, global average sea level is projected to rise by 0.28-0.61m, relative to the period 1986-2005, if this century’s global warming can be held to about 1℃. But if greenhouse emissions continue to increase at their current rate, the world is in line for sea-level rises of 0.52-0.98m. 
This rise will not be uniform around Australia’s coastline. The east coast is likely to experience up to 6cm more sea-level rise than the global average by 2100, because of the expected warming and strengthening of the East Australian Current.
Trends in Australia’s weather and waves are harder to predict. Satellite measurements over the past 30 years suggest that waves are getting slightly higher in the Southern Ocean, and climate models suggest that this may continue. As the tropics continue to expand with climate change, the band of westerly winds over the Southern Ocean will retreat further south and strengthen, whipping up higher waves that will travel to Australia’s southern coast as swell. On the other hand, weakening winds nearer to Australia may help to dampen down wave heights. On Australia’s eastern coast, climate models suggest fewer large wave events due to decreasing storminess in the Tasman Sea in the future. 
A significant challenge we face is not having the data available to monitor the changes along our southern coastline. Australia has the longest east-west continental shelf in the world, but we have only a handful of wave buoys to measure these processes; much of the coastline is not monitored despite widespread coastal management concerns.
Our understanding of extreme sea-level change in Australia is also limited by available tide gauge coverage. Only two digital tide gauge records (in Fremantle and Fort Denison) extend back to at least the early 20th century, and records elsewhere around the coast typically span less than 50 years. 
However, our investigation discovered that there is an opportunity to increase the length of available records by digitising old paper tide gauge charts. This could extend several records along our southern and tropical coastlines.
We also have major gaps in our knowledge about how our coastlines will be changed by flooding and erosion. The simple methods used to predict coastal erosion may underestimate erosion significantly, particularly in estuaries. 
Given the considerable urban infrastructure located within estuaries, and the fact that they are vulnerable both to coastal storms and river floods, this is one of the many crucial questions about life on the coast that we still need to answer.
Kathleen McInnes is senior research scientist, CSIRO and can be contacted <a href="https://theconversation.com/profiles/kathleen-mcinnes-303453" target="_blank">here</a>.
Mark Hemer is senior research scientist, Oceans and Atmosphere, CSIRO and can be contacted <a href="https://theconversation.com/profiles/mark-hemer-302723" target="_blank">here</a>.
Ron Hoeke is littoral oceanographer, CSIRO and can be contacted <a href="https://theconversation.com/profiles/ron-hoeke-315391" target="_blank">here</a>.
All are authors for The Conversation.
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jchancellor-FAypfDUnLy

Hurt by sea: how storm surges and sea-level rise make coastal life risky

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GUEST OBSERVER
The wild storms that lashed eastern Australia earlier this year damaged property and eroded beaches, causing millions of dollars' worth of damage.
As sea levels rise, the impact of storms will threaten more and more homes, businesses and services along the coastline.
CSIRO projections suggest that seas may rise by as much 82cm by the end of the century. When added to high tides, and with the influence of winds and associated storms, this can mean inundation by waters as high as a couple of metres.
As a community, we have to start deciding what must be protected, and how and when; where we will let nature take its course; how and if we need to modify the way we live and work near the coast; and so on. Many of these decisions fall largely to local governments.
We have launched a website to help local councils and Australians prepare for a climate change future. CoastAdapt lets you find maps of your local area under future sea-level scenarios, read case studies, and make adaptation plans.
<h2>How will sea-level rise affect you?</h2>
Using sea-level rise modelling from John Church and his team at CSIRO, CoastAdapt provides sea-level projections for four greenhouse gas scenarios, for individual local government areas. This also provides a set of inundation maps for the selected local government area.
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<img src="/images/2016/08/30/image-20160826-11176-120dovl.png" alt="">
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Sydney’s possible sea level in 2100 under a worst-case scenario. Inundated areas shown in pale blue. NCCARF
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The inundation maps (developed by the Cooperative Research Centre for Spatial Information) show the average projected sea-level rise for a particular climate change scenario, combined with the highest tide. The method provides an approximation of where flooding may occur.
Because water is simply filled onto the map according to elevation, it doesn’t account for things like estuary shapes and water movement, the behaviour of waves and so on.
<a href="/images/2016/08/30/image-20160826-11170-15t7h38.jpg" target="_blank">Click to enlarge</a>
<img src="/images/2016/08/30/image-20160826-11170-15t7h38.jpg" alt="">
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Brisbane’s possible sea level in 2100 under a worst-case scenario. Inundated areas shown in pale blue. NCCARF
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But both the maps and the sea-level projections are a useful way to start thinking about where risks may lie in any given local government area.
CoastAdapt also looks at what we know about coastal processes in the present day. Understanding these characteristics helps us understand where and why the coast is vulnerable to inundation and erosion.
For instance, sandy coasts are much more vulnerable to erosion than rocky coasts. The information will help decision-makers understand the behaviour of their coasts and their susceptibility to erosion under sea-level rise.
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<img src="/images/2016/08/30/image-20160826-11160-1wt2v2r.png" alt="">
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Darwin’s possible sea level in 2100 under a worst-case scenario. Inundated areas shown in pale blue. NCCARF
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<h2>Local councils already adapting</h2>
Adaptation is already happening on the ground around Australian local councils. We have highlighted several of these on CoastAdapt.
In the small seaside town of Port Fairy in southeast Victoria, for example, an active community group is monitoring the accelerated erosion of dunes on one of their beaches. The council and community have worked together to prioritise protecting dune areas with decommissioned landfill to prevent this rubbish tip being exposed to the beach.
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Other councils have already undertaken the process of assessing their risks and drafting adaptation plans.
Low-lying areas in the City of Lake Macquarie already experience occasional flooding from high seas. This is expected to become more common and more severe.
Lake Macquarie Council has successfully worked with the local community to come up with 39 possible management actions, which the community then assessed against social, economic and environmental criteria. The area now has a strategy for dealing with current flooding and for gradually building protection for future sea-level rise.
This approach has engaged community members and given them the opportunity to help decide the future of their community.
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<img src="/images/2016/08/30/image-20160826-11170-tz5wgk.png" alt="">
<h4>
Melbourne’s possible sea level in 2100 under a worst-case scenario. Inundated areas shown in pale blue. NCCARF
</h4>
<h2>Getting prepared</h2>
What stumps councils and other coastal decision-makers is the scale and complexity of the problem. Each decision-maker needs to have some sense of the risk of future climate change to their interests, then develop plans that will help them to cope or adapt to these risks. Planners and adaptors must navigate uncertainty in where, when and how much change they must consider, and how these changes interact with other issues that must be managed.
To better understand the risk, decision-makers need access to timely, authoritative advice presented in ways and levels that are useful for their needs. This is particularly true for an issue such as climate science, which is technically complex.
Climate projections, particularly at the local level, come with a level of certainty and probability. The further we look into the future, the more extraneous factors are unknown – for example, will global policy succeed in bringing down greenhouse emissions? Or will these keep increasing, which will necessitate planning for worst-case scenarios?
Add to this the questions around legal risk, financing adaptation measures, accommodating community views and so on, and the task is daunting.
That’s the thinking behind CoastAdapt – the first national attempt to create a platform that brings together a range of data, tools and research that have been developing and growing over the last decade. As well as maps and case studies, we’ve also built an adaptation planning framework (Coastal Climate Adaptation Decision Support) and set up an online forum for people to ask questions, exchange ideas and even pose questions to our panel of experts.
Sarah Boulter is research fellow, National Climate Change Adaptation Research Facility, Griffith University and author for The Conversation. She can be contacted <a href="https://theconversation.com/profiles/sarah-boulter-16628" target="_blank">here</a>.
The author would like to acknowledge the work of staff of the National Climate Change Adaptation Research Facility. CoastAdapt is in beta version and is <a href="https://www.nccarf.edu.au/CoastAdapt-beta-release" target="_blank">seeking feedback</a>. The final version will be released in early 2017.
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Coastal councils are already adapting to rising seas 

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<img src="https://counter.theconversation.edu.au/content/57114/count.gif" alt="The Conversation" width="1" height="1">
GUEST OBSERVER
Eastern Australia’s wild weather has left coastal homes teetering on the brink of collapse, and has eroded beaches by up to 50m in parts of Sydney.
Now the attention turns to the clean-up. There are several legal issues for owners of damaged properties, particularly the question of if and how they can be compensated.
While the recent events cannot be attributed directly to climate change, they are certainly consistent with a warming world. Our institutions are ill-prepared for a potential increase in the frequency and severity of such events.
<h2>Insurance</h2>
Unfortunately, the success of insurance claims for damaged homes in Sydney will depend entirely on the terms of their policies. Some policies don’t cover erosion at all. Some policies only cover it if it occurs within a certain proximity of another insured event (for example, within 48 hours of a named storm event). Some policies also comprehensively exclude coverage for damage caused by actions of the sea.
What’s more, while insurance will cover damage to buildings, policies do not extend to cover damage to or loss of land. This is especially problematic in the case of damage caused by waves and storms, because erosion will often result in loss of land.
Under the traditional law doctrine, where land is lost to erosion, the Crown automatically gains title to the inundated land, without any obligation to pay compensation. So even if a home-owner is insured, they may find themselves with no land to rebuild on.
<h2>Legal proceedings</h2>
Another potential avenue for home-owners to pursue is proceedings against the relevant local government for negligent approval of development. The success of this type of proceeding is highly speculative – much will hinge upon when the development was approved and how much information on the coastal hazards was available at that time.
Where development was approved decades ago, it may be difficult to prove that a local government was negligent, because of the limited state of knowledge at the time. In the case of more recent development approvals, there may be an argument that a local government had a high level of knowledge of the risk and control of risk information. These are the type of factors a court will look at in assessing negligence.
On the flip side, a court may also find that a landholder knew of and accepted the risk. Negligence proceedings are by no means a guaranteed avenue for landholders to recoup their loss, but are an avenue that Collaroy landholders may be able to explore.
<h2>Disaster assistance</h2>
Where insurance is not available, and there are no strict legal rights against government, landholders may request disaster relief or assistance from government.
Despite the lack of any legal compulsion to do so, Australian governments have a long history of providing disaster relief to citizens when an extreme weather event causes property damage.
A recent Productivity Commission report estimated that, over the past decade, the federal government spent A$8 billion on post-disaster relief and recovery. State governments spent a further A$5.6 billion.
However, the availability and amount of a payment are not guaranteed. This may depend upon the number of other claims for assistance, and any other demands on government resources. A claim for disaster relief from government may be an option for Collaroy landholders, but many other home-owners are also affected by flooding due to the recent extreme weather – and so potentially there are many other requests for relief.
<h2>What should we learn from this event for the future?</h2>
While the pictures of houses being lost to the sea in Collaroy are confronting, these images may become more commonplace. The most recent scientific report from the Intergovernmental Panel on Climate Change suggests that, under a business-as-usual scenario, a global sea-level rise in the range of 0.53-0.97m by 2100 is likely.
Even if emissions are immediately reduced, a global sea-level rise of 0.28-0.60m by 2100 is still possible. This will be especially problematic in Australia, with an estimated 711,000 residential addresses located within 3km of the shore and less than 6m above sea level – not to mention the billions of dollars' worth of government infrastructure also located in these regions.
As sea levels rise, some properties may be permanently inundated. Others may be hit by storm surge impacts or erosion, which may be exacerbated by sea-level rise.
If these events continue to attract disaster relief, the financial burden will become too great for governments to bear. Furthermore, government disaster assistance does not solve the more intractable problem of land being lost to the sea.
The pictures from Collaroy should therefore prompt a discussion about how we, as a society, can deal with the potential impacts of coastal hazards on existing developments.
This is a challenging question to answer, but there is an opportunity to address it in a planned and co-ordinated fashion.
Justine Bell-James is lecturer in law, The University of Queensland and author for The Conversation. She can be contacted <a href="https://theconversation.com/profiles/justine-bell-james-39245" target="_blank">here</a>.
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Coastal Erosion

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