The story of a wave: from wind-blown ripples to breaking on the beach



By the time a wave reaches shore, it may have travelled tens of thousands of kilometres.
Ian Mitchinson / Shutterstock

Shane Keating, UNSW

It’s a cliché, but Aussies love the beach. And little wonder: with 36,000 kilometres of coastline, Australia is blessed with some of the best beaches in the world.

Around 20 million Australians live within 50 kilometres of the coast. As summer temperatures soar, we flock to the ocean to splash, swim, surf, paddle, and plunge in the waves.

But where do those waves come from? How do they form, and why do they break? As it turns out, what we see at the shore is just the last few moments of an epic journey.




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Great waves from tiny ripples grow

The waves we see crashing on the beach can begin their lives tens of thousands of kilometres away. Surface waves, as they are known, are born when the wind blows over the ocean, amplifying small ripples and transferring momentum from the atmosphere to the water.

The height of the wave depends on how long the wind is blowing and the distance – or fetch – over which it blows. The largest waves are created by distant storms, which churn up the surface of the ocean and radiate waves outwards like ripples in a pond.

Surface waves don’t move the water itself very far – each water molecule travels forward and back in a circle a few meters across and ends up back at its starting point.

As the wave crest rises, water molecules gather gravitational potential energy that is released as kinetic energy when the water descends into the trough of the wave. This energy is then passed onto the next crest in a see-saw of kinetic and potential energy that can propagate across an entire ocean basin.

The mounting wave

Once a wave leaves the open ocean and approaches land, the sea floor begins to exert its influence. Surface waves transmit their energy more slowly in shallow water than in deep water. This causes energy to pile up near the shore. Waves start to shoal, becoming taller, steeper, and more closely spaced.

Once a wave grows too steep to hold together, it breaks. Breaking waves come in different varieties.

Spilling breakers, which crumble gently into white water, occur when the sea floor rises relatively slowly.

By contrast, plunging breakers – the classic rolling waves favoured by surfers – form when the sea floor rises sharply, particularly near reefs and rocky headlands.

Finally, surging waves occur when the shore is almost vertical. These waves don’t produce breakers but rather a rhythmic rise and fall of the sea surface.

Bend it like bathymetry

The shape or topography of the sea floor – called bathymetry – can have remarkable effects on breaking waves. If the depth of the sea floor changes parallel to the coast, incoming waves will refract or bend so their crests line up with the shoreline.

The effect can be clearly seen near headlands: waves close to the headland move slowly because the water is shallow, while waves further out move more quickly. This causes waves to curl around the headland like a marching band rounding a corner.

Bathymetry is also responsible for some of the biggest waves on Earth. Famous big wave surf spots like Mavericks in Northern California and Nazaré in Portugal benefit from undersea canyons that refract incoming waves and focus them into monsters. The Nazaré wave originates from an undersea canyon almost 5 kilometres deep to produce waves as tall as an eight-storey building.




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Don’t risk the rip

The story of a wave doesn’t end when it breaks, however. Breaking waves push water towards the shore, raising the water level. This water will try to flow back offshore via the lowest point along the beach. The result is a rip current: a swift, narrow current that flows out to sea.

Rip currents are Australia’s number one coastal hazard, responsible for more fatalities per year than shark attacks, bush fires, floods, and cyclones combined. Inexperienced swimmers caught in a rip can panic and try to swim against the current, which is a dangerous recipe for exhaustion. Yet most Australians are unable to identify a rip current, and two-thirds of those who think they can get it wrong.

Purple dye traces the path of a rip current.
Rob Brander

To spot a rip, look for a gap in the waves, a dark channel, or ripples surrounded by smoother water. The safest thing to do is to stick to patrolled beaches and swim between the flags. If you do find yourself caught in a rip, Surf Lifesaving Australia advises you to stay calm and conserve your energy.

Rip currents are usually quite narrow, so swim at right angles to the current until you are outside the rip. If you are too tired to swim, tread water and let yourself go with the flow until the rip weakens and you can signal for help.

Above all, if you are unsure, don’t risk the rip. Sit back and enjoy the waves from a safe distance instead.The Conversation

Shane Keating, Senior Lecturer in Mathematics and Oceanography, UNSW

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Australia can expect far more fire catastrophes. A proper disaster plan is worth paying for


Dale Dominey-Howes, University of Sydney

Australia is in the midst of inconceivably bad bushfires. The death toll is rising, thousands of buildings have been destroyed and whole communities displaced. This scale is like nothing before, and our national response must be like nothing that has come before.

Prime Minister Scott Morrison on Sunday somewhat acknowledged the need for unprecedented action. He took the extraordinary step of calling up 3,000 Australian Defence Force reservists and mobilising navy ships and military bases to aid the emergency response. This has never before happened in Australia at this scale.




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But it’s not enough. As this horrific summer of disaster continues to unfold in coming weeks, we clearly need to overhaul our emergency management plan with a workforce that’s large, nationally mobile, fully funded, and paid – rather than using under-resourced volunteers.

The United Nations Office for Disaster Risk Reduction says weather and climate related disasters have more than doubled over the last 40 years.

Although expensive, the cost of not acting on disaster risk, planning and preparation will be greatly outstripped by the cost of future climate and weather catastrophes.

Our disaster management system needs upgrading

The states and territories are primarily responsible for disaster preparedness and response. Typically, the federal government has no direct responsibility, but lends a hand when asked through a variety of programs, policies and initiatives.

This may have worked in the past. But with ever larger and more complex disasters, these arrangements are no longer fit for purpose.

Our national emergency management workforce is largely made up of volunteers, who are stretched to the bone, exhausted and some say, under-resourced.

What’s more, experts led by former Fire and Rescue NSW commissioner Greg Mullins have called for significant changes in Australia’s disaster management preparedness and response. They’ve signalled the need for new resources, policies and processes to tackle more frequent and complex disasters.




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We’ve also seen how consultation and collaboration between the Commonwealth and states are not working smoothly.

NSW Rural Fire Service Commissioner Shane Fitzsimmons only learned that Defence reservists would be deployed when it was reported in the media. And it wasn’t immediately clear how new reservists would be integrated into existing response activities.

Finding a bipartisan way forward

The decade-long ideological battle between the left and right of Australian politics has paralysed climate policy development. This cannot continue.

Well-funded disaster preparedness and response inevitably builds resilience to climate change and extreme weather events like bushfires. This is something both sides of politics agree on – in fact, it was noted in the federal government’s own recent report profiling our vulnerability to disasters and climate change.

Aside from needing bipartisanship, an overhaul of Australia’s disaster management will require money. While we’re lucky to have a dedicated, paid and exceptional set of state and territory disaster and emergency management agencies such as the NSW Rural Fire Service, most heavy lifting is done by agency volunteers.

But with fire seasons starting earlier and lasting longer, we can no longer rely for months at a time on volunteers who must also work, pay their bills and feed their families.

We need a larger, paid, trained, professional emergency management workforce. I reject claims that such a workforce would stand idle most of the year. Severe weather seasons are starting earlier and lasting longer, so these professionals will be busy.

The workforce could be divided in to areas of expertise to tackle specific disaster types, and focus on different aspects of the disaster cycle such as prevention and preparation. These continue year-round.

Alternatively, volunteers could be compensated through direct payments for lost income, tax offsets for volunteers and their employers, or rent or mortgage assistance.




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What’s more, a new national disaster management approach must intersect with state and local governments to help reduce disaster risk.

These might include contributing to land-use zoning plans, building design and standards for construction in at-risk areas, or building partnerships with the private sector.

Funding disaster preparedness

All this will cost money. Australia must accept that taxpayers will pay for future disaster preparedness, response and recovery. We need a bucket of cash for when disasters strike. Scott Morrison yesterday announced A$2 billion for recovery, but disaster funds should be ongoing.

This would be no different to the national Medical Future Research Fund – a A$20 billion fund to focus on solving nationally important medical issues funded through savings from the health budget.

There are several ways the money could be gathered. Commonwealth, state and territory governments could rethink their insistence on achieving budget surpluses, and instead spend money on a disaster fund. A “disaster levy” could be applied to household rates bills, a tax on carbon introduced, or planned tax cuts for middle and high income earners abandoned.

The public could also contribute to the fund directly. The ABC’s recent Australia Talks survey found on average, Australians would be willing to chip in A$200 each per year to pay for adaptation to climate change. If every Australian contributed, there’s another A$5 billion per year for the fund.




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Future disaster management will require Australia to step up. It means making hard choices about what we want the future to be like, how we’ll pay for that, and what level of risk we are prepared to tolerate. It also means demanding that our leaders deliver meaningful climate change adaptation, including disaster planning.The Conversation

Dale Dominey-Howes, Professor of Hazards and Disaster Risk Sciences, University of Sydney

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Koalas are the face of Australian tourism. What now after the fires?



Koalas have long featured in tourism ads, including this new one from Tourism Australia. Amid our bushfire crisis, this digital ad has been ‘paused’.
Tourism Australia

Kevin Markwell, Southern Cross University

In 1936, The Evening News in Rockhampton wrote:

The time has arrived when Australians must decide whether or not they will accept responsibility for the perpetuation of the koala […]

It seems extraordinary that this animal which is so greatly admired, not only by overseas visitors, but by Australians, is being allowed to suffer extinction.

The preservation of the koala was not talked about so much in environmentalist terms: instead, the koala was seen as a crucial icon of Australian identity and tourism.

The earliest picture postcard featuring a koala I have found was postmarked 1903, and it has been a mainstay of tourism advertising ever since.

A 1903 postcard featuring a ‘native bear’.
Author provided, Author provided

In the latest ad from Tourism Australia, the koala has been recruited, once again, to market Australia, starring alongside Kylie Minogue, chilling in a graceful eucalyptus on Sydney Harbour.

But amid Australia’s ongoing bush fire crisis, airing of the digital ad has been “paused”.

Up to 30% of the koala population from the NSW mid-north coast is expected to be lost in the fires, alongside 50% of the koalas on Kangaroo Island – the last remaining wild population not infected by deadly chlamydia.

Eighty four years on from the Evening News’ story, we are still talking about the possible extinction of koalas, our national tourism icon.

The creation of an icon

Koalas were exhibited at Melbourne Zoo from 1861 and at Taronga Zoo from 1914. But at the same time, koalas were hunted ruthlessly for fur throughout much of the 19th century. This practice only came to a halt at the end of the 1920s.

The original 1933 publication of Blinky Bill.
Trove

By the 1930s, three koala-themed wildlife parks – the Koala Park in Pennant Hills, Sydney, Lone Pine Koala Park on the Brisbane River and the Adelaide Snake Park and Koala Farm – had opened for business.

1933 saw the publication of Dorothy Wall’s Blinky Bill. Zoologist Ellis Troughton’s book Furred Animals of Australia (1931) and natural historian Charles Barrett, with Koala: The Story of the Native Bear (1937), also influenced public attitudes towards the native animal.

In 1934, the Sydney Morning Herald called the koala “Australia’s national pet”.

Perhaps most famously, it was the star of a Qantas advertising campaign from 1967 to 1992.

A 1981 Qantas advertisement, published in American magazines.
Qantas

The loss of a tourism icon

A 2014 study suggests koala tourism could now be worth as much as A$3.2 billion to the Australian economy and account for up to 30,000 jobs.

In 2020, Australia has 68 zoos and wildlife parks exhibiting just under 900 koalas. A photograph with a koala is a must-have souvenir for many international tourists.

But it is impossible to look at Kylie hanging out with her koala mates without bringing to mind the shocking images of badly burned koalas and other wildlife as the devastating wild fires destroy millions of hectares of bushland habitat.

The plump, relaxed, pampered koalas in the Tourism Australia ad are far removed from the horrific realities of fire. These catastrophic fires have compounded the threatening processes that already affect koala populations: habitat destruction and fragmentation, disease, car accidents and dog attack.

Recent research has shown koalas are also vulnerable to climate change through changes in the nutritional status of eucalyptus leaves, excessively hot temperatures and these canopy-destroying wildfires.




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A life beyond extinction?

Australians have clearly shown they are willing to take action to protect the animal, with the GoFundMe campaign to raise funds for the Port Macquarie Koala Hospital raising almost A$2 million.

The outpouring of emotion and financial support reflects the strong connection that Australians feel for the koala, formed out of the interplay of the animal’s baby-like features and its multitude of representations in popular culture, including, of course, tourism marketing.

Sadly, it is more than likely the koala will go on serving the national interest through its role in tourism even if it was to tragically go extinct in the wild.

The Tourism Tasmania logo features the extinct thylacine.

Most koala tourism is based on experiences with captive koalas. And extinction hasn’t been a problem elsewhere: Tasmanian Tourism uses a stylised image of the thylacine in its logo.

The long term survival of the koala ultimately rests with governments and their policies on forest clearing, fire management and climate change.

If future tourists to Australia are to experience the koala in the wild, it is imperative that governments act now to strengthen the protection of the species and most crucially, its habitat.The Conversation

Kevin Markwell, Professor in Tourism, Southern Cross University

This article is republished from The Conversation under a Creative Commons license. Read the original article.