A leading geoscientist has said two popular Cairns beaches will become mudflats over the next few decades in a revelation that could shock shoreline property owners.
Cairns’ modern esplanade is famous for its man-made lagoon, rich wader fauna and long brown mudflats – but a century ago tourists encountered a markedly different scene.
Photos and historical accounts depict an esplanade lined with white sand as recently as the 1920s, with some contemporary reports speculating that decades of navigation channel dredging are to blame for the transformation.
Jonathan Knott, an adjunct professor at James Cook University, disagrees and says the shift from beach to mudflat was due to entirely natural causes.
“One of the most telling pieces of evidence is a map of Trinity Bay and Trinity Inlet from 1878,” he says.
“It shows a beach without mangroves.
“There were mangroves on the airport side of Trinity Bay – or at least what is now the airport side.
“But there was only a sandy beach along where the mudflats are now.”
Mother Nature’s Changing Moods
The map shows that the mouth of the River Barron was once further south than its present location – and the delivery of sand into Trinity Bay was its responsibility.
“We know that in the 1930s the Barron changed its mouth to where it now exits at Machans Beach. It moved north,” Dr Knott explained.
“It effectively cut off the supply of sand to Cairns Bay.
The sandy beach along the Cairns Esplanade has never been the deep and wide foreshore as tourists enjoy it along the Williams Esplanade in Palm Cove – at least not so much as the photography or the testimonials of holidaymakers Europeans were a factor.
Dr. Knott says it’s a fairly narrow strip of sand that separates the city from the ocean.
However, it was significant enough to elicit heavy verbosity from a visiting writer in 1922.
Historian Timothy Bottoms, writing in A History of Cairns: City of the South Pacific 1770–1995, described the beach as stretching “like a strip of pearls and saffron along the edge of the blue water, strewn of palms, giant, flamboyant fig trees just bursting into bloom”.
The following year, a correspondent for the Northern Herald newspaper had a very different assessment, noting that the popular strip of sand along the esplanade had become “anything but pleasant” because of the roughness.
“Previously they galloped on the soft sand by the side of the road, but now against the wall.”
Either way, Dr. Knott says the disappearing act of the beach is natural.
“There’s kind of a balance between the amount of sand delivered and the amount of mud delivered,” he said.
“That report has changed, there is now more mud and less sand.”
A story of coastal transformation
Ribs are a fluid thing, and history shows that what is now considered the norm is by no means static.
Sand deposits can still be found far from the Cairns Esplanade – although much of the natural topography has been obscured by development.
“The whole of the Cairns CBD area is built on sand deposits,” Dr Knott said.
The best place to see these natural beach ridges is at the Pioneer Cemetery on McLeod Street, a few blocks from the city’s public hospital.
“Because the cemetery is sacred ground, so to speak, it was not built,” Dr Knott explained.
“It’s made up of very coarse sand particles, and these sand ridges were actually put there by tropical cyclones.
“Thousands of years ago, this is where the beach was.”
The hospital had to be evacuated during Cyclone Yasi in 2011 due to its proximity to the ocean.
The coastal shape-shifting routine still happens today – and it could have significant implications for residents of two seaside suburbs in this lifetime.
Muddy prediction for two Cairns beaches
The mouth of the Barron River currently empties into the ocean just south of Machans Beach.
It also feeds Thomatis Creek, which in turn reaches the ocean about 5.5 kilometers further north along the coast between Yorkeys Knob and Holloways Beach.
Nature is a big fan of finding the path of least resistance – and Dr Knott expects the Barron River to make another significant change in the not-too-distant future.
“In future the Barron will change to exit at the north end of Holloways Beach from the south end of Yorkeys.
“It makes it a shorter route for the Barron to the ocean.
“I don’t know exactly what the period will be, but there is potential for it to happen in the next 50 to 100 years.”
Dr. Knott predicts that Thomatis Creek will eventually become the main channel of the Barron River and that its flow to Machans Beach will gradually decrease until it is completely exhausted.
This means less sand delivery to counteract the natural accumulation of sediment in this area.
And that means the emergence of mudflats where the sandy foreshores of Machans and Holloways beaches are now.
Ongoing battles against the march of the mudflats
There are ways to artificially counteract the natural reduction in sand input, but Dr. Knott believes they are useless in the long run.
“That’s what the [Cairns Regional] The Council tried to do, really,” he said.
“They hauled sand from Half Moon Bay, just north of Yorkeys Knob, and dumped it on the foreshore to make an artificial beach. [at the far northern end of the esplanade].
The council and local port authority, Ports North, are also battling nature to prevent the Cairns mudflats from becoming a mangrove forest.
Contractors are employed to dig out any saplings that have the nerve to stick out of the mud – otherwise the sweeping view of the Glitter Strip would soon be obscured by vegetation.
Bringing the beaches back to the esplanade
Dr Knott says the sandy beaches could theoretically be brought back to the esplanade, with major engineering work to redirect the Barron River back to its former course.
However, that would be about as popular as a snake in a sleeping bag.
“There’s a thing called the 4 o’clock club where everyone meets at the Esplanade every day to watch the waders in the mud,” Dr Knott said.
“I actually did some consultancy work with the council on this as the sand was starting to settle on the mudflats – and it was no longer encouraging waders to come out there.”
It turned out that the council’s own storm drain outlets were the culprit.
“When we get heavy rain, the water that comes out of the pipes pulls the sand into a sort of big delta and gets pushed over the mud flats,” Dr Knott said.
Either way, the veteran geoscientist doesn’t believe there’s any appetite to artificially re-contour a major river in an effort to make beach access easier.
Cairns Regional Council ruled out considering any realignment on the River Barron, but noted that it had recently adopted a Coastal Hazards Adaptation Strategy.
“The strategy assesses potential risks to council, community and private assets, and proposes a number of measures to mitigate those risks,” a council spokesperson said.
“Importantly, the strategy identifies which assets are most at risk, what the community in each locality values most, and which adaptations should be prioritized.”
Busting the Myths on the Mulgrave River
He’s already ruled out dredging as the cause of the Esplanade Beach’s disappearance, but Dr Knott also wanted to pour water on another oft-repeated claim.
“Many people in Cairns have made the argument that the Mulgrave River used to flow into Trinity Inlet, and has now changed and gone further south,” he says.
“It’s a myth. It never happened.”
Only time will tell if the predictions come true, and the beaches of Machans and Holloways are doomed to a sandless future as the mudflat walk continues its foray north.