A tidal breakthrough at Bribie Island in 2022 has accelerated water level increases in the Pumicestone Passage by more than 20 years.
Sunshine Coast Council has revealed that the remarkable event has essentially led to higher-than-expected tides, intensified by big swells.
The Caloundra, Golden Beach and Pelican Waters coastal fringes were swamped earlier this week, when a 2.1m high tide combined with large and powerful swells.
Locals captured photos and footage of inundated parks and streets and battered beaches and rock walls.
Council has started a huge clean-up.
Related story: See how area has changed after tidal breakthrough
“High tides, coinciding with offshore wave heights of up to 7m, have increased water levels in all our creeks and river systems …. general erosion can be seen along the entire coastline,” a spokesperson said.
“Council is waiting for the swell and erosion to subside before repair works can take place.
“Based on an early assessment, work will likely focus on repairing any impacted beach accesses.”
Trees from Bribie Island and from the mainland have been scattered through the passage and along the foreshore.
“The recent high tides and weather conditions have left debris and caused some damage to the pathway and foreshore park area at Golden Beach,” a spokesperson said.
“This has also delayed some of our maintenance services.
“Council officers will assess and undertake the necessary clean-up and maintenance work.
“We thank our community and visitors for their patience during this time.”
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Council has previously said that the breakthrough had forced changes to tide heights, but now they have detailed how extreme the situation is – and that the region is more vulnerable during high tides and storm surges.
“As a result of the breakthrough, at Golden Beach monitoring in Pumicestone Passage has shown water level increases equivalent to predicted 2041 conditions,” the spokesperson said.
“The increase in water levels associated with the breakthrough exacerbates these types of events where a large swell and high tide takes place at the same time.”
The spokesperson said tidal monitoring in the passage showed a reduction in the tidal attenuation in the passage (a reduction in tidal profile between two locations).
That can lead to an increase in the water level in narrower and shallower areas, due to the concentration of tidal energy and water volume.
The spokesperson said Marine Safety Queensland had updated the level of the highest astronomical tide, which has increased by 310mm.
“Conditions within the Pumicestone Passage are continuing to change.”
“Tides are dependent on many factors such as the width of the entrances, the sand bars in the delta, storm/wave surges and barometric pressure.”
Council is implementing initiatives to counter coastal impacts including erosion.
A Bribie Island breakthrough action plan has been in place since 2014, listing threats to the Golden Beach foreshore in the event of a breakthrough, including actions to reduce the effects.
The Sunshine Coast Coastal Hazard Adaptation Strategy outlines council’s response.
It includes: focusing on maintenance and upgrade of groynes and seawall infrastructure; reviewing planning controls; encouraging resilient homes; drainage investigations; beach nourishment and coordination of risk mitigation at Fraser Park; and longer-term adaptation planning.
Majola Avenue, the Caloundra Power Boat Club, Currimundi Lake and foreshore parks were among the areas swamped by the wild conditions earlier this week.
Caloundra Coast Guard’s waverider buoy, 2.5km east of the breakthrough, recorded wave heights of six metres last weekend.
The group’s commander Roger Pearce said they would assess the breakthrough (also known as the Bribie Bar) in coming days.
“We don’t know what the constant pounding of this big surf has done to the bar,” he said.
“It was relentless for about five days.”
He said no one had attempted to cross the bar in recent days, due to the conditions.
“But the swell is dropping, and we’ll put some boats over the bar this weekend to see what depth it’s at now. We’ll soon be able to se what changes have developed.”
Mr Pearce urged boaties to be careful of debris in the passage.
“We’re concerned,” he said.
“There have been people ringing us, telling us about kids on inflatables being towed by jet-skis and dinghies.
“They’re going to hit one of these (trees) and it won’t be pretty.”
His comments came as a boy was seriously injured by a stick in the surf off North Stradbroke Island on Thursday.
“There’s a lot of debris: the council have a massive clean-up,” Mr Pearce said.
“The south-easterly wind has blown everything on to Golden Beach, Diamond Head and Caloundra.”
The wild conditions even caused one of the passage markers to wash up on the beach.
Meanwhile, the ocean has again rolled over another section of Bribie Island on high tide.
The area, south of the Bribie Bar near Lions Park, has been a subject of discussion since photos a month ago showed the high tide had flowed over it, leading to some suggestions there could be another breakthrough, although a leading academic suggested that was unlikely to occur.
Still, Coastguard will assess the area this weekend.
“There’s not much water going out (of the passage) at low tide, but water is still coming in at high tide,” Mr Pearce said.
“So, a lot more water is coming over there (that section of island) now and a lot of timber has been removed from there.
“We’ll have a look around to see how bad it is.”
He didn’t expect it to open up like the Bribie Bar, which is hundreds of metres wide.
“There’s a lot of mud on the eastern side of it, so it won’t be quite as bad,” he said.
“It (overflow) only happens at high tide.
“When Cyclone Seth came in 2022, as soon as the water flowed out at low tide the island opened up (to create the Bribie Bar), but there is no major water flow at this newer one.”
Mr Pearce said Seth essentially turned a then-2.1m high tide into a 2.6m high tide.
He believed the surge earlier this week essentially turned a 2.1m high tide into a possible 2.3m or 2.4m high tide.\
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