Queensland tsunami modelling shows how coastal communities will be impacted

Josh Bavas
Swellnet Dispatch

Three hours — that's the minimum amount of time Queenslanders would have to prepare in the event a destructive tsunami was headed towards Australia's east coast.

Millions of people would need to be warned and evacuations along the coast completed before low lying communities were swamped.

By the time the first wave hit Sandy Cape on the northern tip of Fraser Island, it would only take another hour to reach the mainland, but the first wave might not be the biggest.

It's one of the worst-case scenarios that has been modelled by Queensland's Environment Department to make sure emergency services, local councils and other state agencies are equipped to respond.

Communities most at risk

Modelling of Moreton Bay for one-in-750 year (left), one-in-3,000 year (centre) and one-in-10,000 year (right) tsunami, showing maximum wave amplitude. Orange zones are 5 to 6 metres waves, red zones are 8 metre waves.

Scientists have been working for seven years assessing what would happen in a one-in-750 year, 3,000-year or 10,000-year event — including the potential speed, height and inundation levels at various tides.

The modelling was based on tsunamis generated at three likely locations — the New Hebrides (Vanuatu region), South America and the Kermadec-Tonga region.

Computer-generated tests found tsunamis generated in the New Hebrides region would reach Queensland's coast in the shortest amount of time but waves generated in the Kermadec-Tonga zone would likely be the most extreme.

The arrival time of these waves could be anywhere between three to 17 hours.

In the event of a tsunami, ocean buoys off the coast managed by the Bureau of Meteorology and Geoscience Australia would send instant alerts to authorities.

Researchers found the Great Barrier Reef would provide some protection to the north coast by dissipating a tsunami as it travels through shallow shoals and that large islands would protect some areas.

But more exposed regions like the Gold Coast and the stretch of coast from Agnes Water to Bundaberg could see greater wave heights and inundation.

Department of Environment hydraulic engineer, Paul Boswood, said researches surprisingly found the most populated communities in and around Brisbane would largely be protected by Moreton and Stradbroke islands.

"We knew that swell waves don't really come into the bay because of the shallow shoals at the entrances," he said.

"We didn't know whether or not tsunamis would behave in a similar way but what we found was tsunamis lose a lot of energy as they come over those entrances ... they are about one fifth the size as they are on the ocean side."

"The lesson learned is that the impact within Moreton Bay is much less than might have been expected than not having done the study."

The long-running project was funded by the Commonwealth's Natural Disaster Mitigation Program initiated in the wake of the 2004 Indian Ocean tsunami and 2011 Japan disasters.

Mr Boswood said researchers conducted tests across 23 different scenarios.

"We picked scenarios that are very rare and unlikely to occur but would expect to produce a result that we could get some conclusions out of," he said.

"And we looked at different stages of tide because of course the tide plays a part as well. When you're looking at tsunamis of only 1 metre high and you've got tides of 2 metres, it has an impact.

"We used a static tide level at Mean Sea Level, Highest Astronomical Tide and we also introduced Sea Level Rise into it as well — so when you do all the permutations of those, we did about 23 runs."

Researchers found there was an amplified impact on coastal communities if sea levels were to rise with climate change.

The first four reports focussed on the Sunshine Coast, Hervey Bay and Brisbane regions, but researches hope to conduct further assessments into the Gold Coast region.

Spiro Spiliopoulos from Geoscience Australia said the three subduction zones used in the study were classified as the most likely to produce tsunamis that could threaten the Queensland coast.

"A subduction zone is where the plates on the surface of the Earth collide and one of the plates will then be thrust down into the mantle," he said.

"It's along these boundaries where you get the largest earthquakes and it's because of the friction.

"The New Hebrides zone and the Kermadec-Tonga zone are the two closest subduction zones to Queensland — they're very active zones.

"They produce large earthquakes but we don't have historical evidence of earthquakes above say 8.5 (magnitude) there so we then chose the South American subduction zone because even though it's quite some distance away ... we do have evidence of very, very large earthquakes there."

He said a one-in-10,000-year tsunami event could only be generated by an extremely large and rare earthquake.

"The largest earthquakes would have the longest return periods — so a one-in-10,000-year earthquake might be a magnitude 9," he said.

Regions across the state with a higher tsunami hazard risk in descending order:

  • Gold Coast
  • Ocean side of Bribie, Moreton and Stradbroke islands
  • Sunshine Coast
  • Fraser Island
  • Bundaberg
  • Flying Fish Point
  • Capricorn coast
  • Agnes Water
  • Hervey Bay

Good and bad news for Brisbane and Moreton Bay

The hazard is significantly greater on the ocean side of the islands that protect Moreton Bay, producing a significant marine and land hazard with maximum currents up to 8 metres per second and waves of up to 10 metres.

Tsunamis generated from the New Hebrides have the shortest arrival time of just over four hours while waves from South America would arrive much later at more than 18 hours.

Once the leading wave reaches Cape Moreton, the additional time it takes to reach locations within the bay range between one and one-and-a-half hours and two-and-a-half hours to reach Indooroopilly within the Brisbane River.

Maximum water levels within the Brisbane River ranged between 0.4m and 0.6m with the waves slowing at about St Lucia.

There is a potential for shorter steep waves to travel on top of the underlying tsunami in areas where the tsunami wave steepened significantly (particularly close to the coast at Redcliffe and over the entrance sandbanks).

Sea level rise associated with climate change could exacerbate inundation in and around the bay in the event of a tsunami.

The good news is that infrastructure at the Port of Brisbane is situated at elevations that did not pose an inundation risk, according to the modelling.

The results showed there was also no significant risk to infrastructure at Brisbane Airport although there was potential for inundation of the north-eastern runway.

The modelling showed that ocean currents would also pose a marine hazard.

© Australian Broadcasting Corporation. All rights reserved.


dawnperiscope's picture
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dawnperiscope Sunday, 28 Jul 2019 at 10:26am

mmmm.. not sure that was money well spent

Laurie McGinness's picture
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Laurie McGinness Sunday, 28 Jul 2019 at 11:08am

It would be nice to think that the information will never be needed, but the tectonic histories of the locations mentioned and the evidence of previous large tsunamis striking the east coast suggest that it might be.

dawnperiscope's picture
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dawnperiscope Sunday, 28 Jul 2019 at 8:49pm

Fair enough. I'm all for advancing knowledge.
If the article provided some kind of an action plan after 7 years of computer modelling, I wouldn't have commented. Must have been a crazy amount of $ spent, just questioning the priorities.

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lisa.van-der-velde Sunday, 28 Jul 2019 at 11:29am

In my opinion, based on observations of the Japan Tsunami's impacts on the East Coast 2011, The model assumptions are incorrect. I believe that the tsunami would attenuate its effects though the coastal entrances into Moreton Bay, not along the barrier dunes. The tidal data in 2011 (tsunami) Moreton Bay, supports this opinion. I hope the modellers have referred to this data from realtimes events.

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mowgli Sunday, 28 Jul 2019 at 7:34pm

That is what the report says. That is, the bathymetry at the entrances to Moreton Bay takes a lot of the energy out. So not sure of your point?

Same goes for factoring in SLR. If all other things remain equal (not an insignificant 'if' by the way), then the bathymetry in nearshore zones should lift linearly with mean sea levels. But there's a few other factors that if they change as well...well, who knows.

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Tim Bonython Sunday, 28 Jul 2019 at 12:18pm

Any potential for some new slab options to be documented? Maybe Mark Visser & i we can set up a shoot but 750 years might be a long time to wait.

mowgli's picture
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mowgli Sunday, 28 Jul 2019 at 8:00pm

Maybe you'll only need to wait a year.

1-in-750 years means approximately a 0.13% (so a tenth of 1%) of occurring in a given year.

Say you've got another 20 yrs of film making left in ya (no idea how old you actually are....timeless?), there's only a 2.6% probability of seeing such an event in the next 20 years. If a person in the locations mentioned above lives for 80 years, there's a 10.1% probability they'll experience that tsunami in that location.

Over 80 years you've got a 0.8% chance of experiencing a 1-in-10,000 year scale tsunami event.

As slim as those odds seem, the risk is still probably rated a moderate given the sheer impact such an event would have. After watching footage of the Japan tsunami and what it did to multi-storey buildings....no thanks.

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wax-on-danielson Monday, 29 Jul 2019 at 8:20am

Do you love playing Texas hold ‘em poker?

Laurie McGinness's picture
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Laurie McGinness Sunday, 28 Jul 2019 at 2:32pm

Yeh Felipe Pomar will probably be the only one to actually ride a tsunami for the foreseeable future.

truebluebasher's picture
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truebluebasher Sunday, 28 Jul 2019 at 9:54pm

tbb wants to alert crew to near impossible Tsunamis triggered by our own coastline.

Alert (1)
Consider Qld Coast as a dormant ring of fire with 100's of (5+) Earthquakes..
2004- 2015 (100) Earthquakes rattled from Bundaberg towards Harvey Bay.
2015-2018 (20) Earthquakes travelled south to offshore Fraser Island
2018-2019 (5) Earthquakes skip north to Bowen

Alert (2)
Now factor in a mega unstable Coastal Shelf ready to collapse just 50kms offshore.
Qld doesn't have massive volcanoes or ice shelves but we got massive sand dunes.
So massive that a mega spilling dune slide could raise continuous tsunamis on tap.

Alert (3)
This has happened right here on colossal scale 12,000 years ago.
A massive sand Island lies collapsed between Moreton & Fraser Islands!

Alert (4)
(1976) Point Lookout Wave Buoy sits 10kms off shore in 76m of ocean
(2006) Buoy recorded 2nd highest East Coast Waves @ 16.75m
Any major land slip here would trigger massive 20m high waves as a starting range.

Alert (5) tbb has unearthed a local news article revealing worst case scenario is real!
Not only real, this bizarre wave event happened as recently as 100 years ago.
Skipper Les Thompson of Southport sailed since age 7...considered the finest.
Knew Moreton Bay better than any & sailed from the Reef to Sydney.
Specialises in fishing grounds from Tweed to Maryborough.
1914: On board the "Liberty" Fishing off Flat Rock.
"A tidal wave occurred on a calm moonlit night!"
"Without warning a tremendous sea broke in ,40 ft of water followed by other seas 100 yards apart and about 30ft in height!" The disturbance kept up for 4 hours!"
"During which time 2 other fishing boats were smashed on Cape Moreton!"

It was probably one of the biggest disturbances of it's kind ever experienced on the southern portion of the Qld coast.

Truth is stranger than fiction!
"Undersea Sand Dune Tsunamis" = (4 hr sessions ripe for the pickin')
Moreton Marine Park Rangers mega sand dune avalanche control during off season.
[Surfing Moreton Marine Park tsunamis is kinda dangerous] Experienced surfers only!

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truebluebasher Monday, 29 Jul 2019 at 1:06am

So what would happen in an actual Tsunami...well we do know that answer! Kinda!
Rounding up the last 3 Queensland Tsunami warnings paints a broader picture.


Just as Qld coastal folk crowd the State border snowfields during the coldest snap.
The country folk want a selfie with Ma' in front of the Big GC Tidal Wave.

Emergency crews & CWA get trucked in from the back of the Great Dividing Range

Every square cm of beach is lined with spectators & patrolled by the Civil Guard.
CWA towel flick the Bikini Babes off beaches & Scouts bash bodybasherz
Chopper cowboys rustle up Fishermen from beach & rocks.

Pro Surfers are/were banned from surfing the Quicky Tsunami.

Every OZ Boardrider & Hand planer is conscripted to cut Tsunami down to size.
Ice cream lid or Maccas Tray & you too can save the day.
Record numbers of boardriders that day...Tsunami had no chance of getting thru!

Without floaties you were told to fuck off the beach by nuns & tuck shop ladies.
tbb visited many beaches that day, each time told don't even think about it punk!

Airports were next to cancel flights.
Fuel Station queues block the main roads outta town.
Local tip: GC Hwy + [M1] > Route (90) > /15\ Warwick < (Supply Route) > Ipswich

Parents collect kids from Day Care clinging tight to their last ray of hope.

Are there Gold Coast Tsunami Shelters? [yes] ...But only for the chosen few.
Reedy Creek 7th day Adventists community Tsunami Bunker is 20m above sea level.
Y2K saw a flurry of Govt funded Doomsday Shelters but strictly kept private.

Year 2000 (20m Tsunami Level) is revised down with Climate Change..(Now 10m).

Last resort is to head up high to town's Dams as they need to stay accessible
Tip! Only scale high ground if it has a supply route beyond otherwise you'll starve!

These events reflect recent Qld Tsunamis.
In the wash-up, more came to surf Gold Coast than escape...That will never change!

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GuySmiley Monday, 29 Jul 2019 at 12:24pm

I find this stuff really interesting.

A few disjointed comments.

I watched a science program years (15+ years ?) ago about geographical evidence of tsunamis hitting the east coast of Australia. From what I remember there is evidence of such events in the Sydney area, more precisely really massive boulders being spun around by a tsunami but wait for it, these boulders are inland from massive coastal cliff tops. It was suggested this tsunami was caused by a volcanic event in New Zealand.

New Zealand takes tsunamis seriously. Everywhere you drive along the coast on the North Island there are advisory signs. When daylight saving time starts and ends they test their tsunami warning sirens and procedures.

I’m not sure whether they do the same on the South Island as I haven’t been there for a few years now but I remember reading the modelling they have done includes a massive earth quake destroying much of the west coast which in turn could generate a tsunami that would hit Australia’s east coast.

The only place I have seen such warning signs in Australia was at Adventure Bay on Bruny Island Tasmania. Adventure Bay has a wave or two and a fresh water creek that Cook took water from on his voyage. It also saw many whaling stations. Many of Hobart’s grand stone buildings were built off the whales killed there.

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northeasterly Monday, 29 Jul 2019 at 2:19pm

Years before the 2004 tsunami there was a tsunami alert for the east coast of Australia after a large quake in Chile. I was freaking out as I'm a 'worst case scenario' type of guy and remember hearing about people taking their kids, many in prams, down to Manly to watch the tsunami break. A mate who lives in Byron Bay took his young family to the beach at the Pass to watch the tsunami come in. When I mentioned that he and his family could have been killed he laughed it off and said that would never happen. Luckily for them and everyone else it was only a very small sea level rise. It's crazy to think what could have happened. At least this study is preparing for how to respond.

I read somewhere a while back that 60,000 years ago Sydney was stripped back to sand stone by a large tsunami. Maybe there were aboriginals here to see it. Incredible to think what something like this must look like.

thermalben's picture
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thermalben Monday, 29 Jul 2019 at 2:57pm

The SES has a paper on NSW tsunamis. Here's the historical info from it (link below):

"The NSW coast has experienced some 44 tsunami since European settlement, many which have been too small to produce noticeable effects. Since 2007 four tsunami events have been observed to impact NSW including tsunamis originating from earthquakes off the Solomon Islands, New Zealand, Chile and Japan (7)."

"The maximum run-up for a historical tsunami was 1.71m at Eden which was generated from the Chilean earthquake in 1960 (8). Damage was limited primarily to vessel moorings, although the oyster industry did suffer some losses. There were two unconfirmed reports of minor injury and some reports of people having to flee beaches and tidal rock shelves, indicating that the tsunami did create a risk to life along the coast of NSW (8)."

"Historic records indicate that the Black Sunday event of February 1938 at Bondi produced a number of large waves in quick succession. Reports at the time showed around 250 people required assistance with 35 near drownings and 5 fatalities (9). Waves were also reported on adjacent beaches and as far north as Newcastle. There is a suggestion that this event may have been a tsunami generated by a localised submarine landslide, however this has not been verified. (2)"

"Geological studies (5) also suggest tsunami impact along the NSW coast with seven events documented with the oldest event dated at 105,000 years ago and reported to have been generated by submarine sediment slides off Lanai, Hawaii. The six youngest paleo-tsunami events all occurred during the Holocene (10,000 years ago). The causes of these other six events are unknown. The maximum run-up for a paleo-tsunami is reported at possibly as much as 130 m above sea level at Steamers Beach, Jervis Bay, NSW, while another event is reported to have inundated the coast to distances of 10 km inland. Some scientists have begun to question the evidence reported for these events. Most recently, one of the key sites for a paleo-mega tsunami deposit has been re-examined (at Minnamurra Point, Kiama, NSW), finding that the proposed tsunami deposited sediments were an in-situ soil horizon. Further July 2018 Tsunami Hazard and Risk in NSW Page 9 work is required to examine the paleo-tsunami record in order to check the accuracy of the paleo-tsunami record (5)."


GuySmiley's picture
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GuySmiley Monday, 29 Jul 2019 at 9:57pm

Great stuff

savanova's picture
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savanova Monday, 29 Jul 2019 at 5:47pm

On a side note wondering what the GC doomsday prepers will be stocking their basements with? Silicon? Botox? Pingers? Stuffed koalas?

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Feralkook Tuesday, 30 Jul 2019 at 6:11pm

Evacuate millions in three to seventeen hours. On QLD roads ROFLMAO! Yea we will see how that works out. Imagine it, three am everyone in bed, get a txt, Tsunami, three hours to get to high ground, carnage.
Then again, if the majority go to the beach, natural selection will make the traffic a bit lighter.
Looking at the footage of the Japanese tsunami, I am just not seeing the outcome they propose, even recognising the context and events they are basing the research on is significantly different.