Storm ready: (left to right) Christopher Drummond, Kristen Splinter, Mitchell Harley and Ian Turner. Credit: Grant Turner
At least 600 times over the four years he was earning the ‘Dr’ before his name, Mitchell Harley methodically combed northern Sydney’s Narrabeen-Collaroy beach on Australia’s east coast. Back and forth, like a kid mowing a vast sandy lawn, Harley rode a tech-packed quadbike, collecting data, logging his position on the beach – on the planet – to within 15 millimetres.
“I knew every grain of sand,” he jokes. The 3.6 km arc of sand, stretching and shrinking with the seasons and the storms, is etched in his memory.
In 2010, when Harley moved to Ferrara, Italy, for coastal engineering work, he could still picture Narrabeen Head rising in the north; the rocky cliffs to the south; seas reaching out to the eastern horizon; and westward, the line of beachfront homes facing the waves and surfing the ever-rising tide of coastal property values.
Narrabeen-Collaroy is Australia’s longest-running coastal monitoring program and one of few sites worldwide to have been measured over 40 years, starting with a handful of scientists in the 1970s with nothing but graduated poles and measuring tape.
“If you continue for long enough, you see all sorts of patterns that have never been seen before.”
Their work has grown into a rich archive for UNSW’s Water Research Laboratory. The program won global renown in April 2016 when the data was published in the Nature journal Scientific Data.
Unusually, the lab made the data freely available for anyone seeking to understand beach erosion and the impact of climate change on our coasts.
“Many coastal-monitoring measurements start and happen for a year or two, or at most five years,” says the lab’s director, Ian Turner, who oversees both its academic research team and high-end applied-research consulting group.
“But if you continue for long enough,” says Harley, one of Turner’s senior research associates at the lab, “you see all sorts of patterns that have never been seen before.”
Patterns in the Narrabeen-Collaroy data show that El Niño and La Niña cycles can intensify coastal hazards. Across the Pacific, we now expect changing storm patterns associated with extreme coastal flooding and erosion.
This rich data set emphasises that sea-level rise is not the only factor in coastal vulnerability – the patterns of storm erosion, and their increasing impact at the coast, are becoming more apparent, too.
Not your big-picture climate change
Patterns are an engineer’s bread and butter. And they are what led UNSW engineers Ashish Sharma and Conrad Wasko to look for changes in the way that rain falls, in an article published in Nature Geoscience (June 2015) and in Geophysical Research Letters (April 2016) with colleague Seth Westra from the University of Adelaide.
Any third-year engineering student learns to study rainfall’s temporal patterns – because the ‘when and where’ of downpours is crucial to design structures able to withstand flooding when it occurs.
“This is something nobody in the climate community knows about; it’s a very engineering-specific thing,” Sharma says.
“The climate guys think about big-picture stuff – things that happen over continents, over years.
“We are talking about a storm that might last 15 or 20 minutes, and it can create a flood. That is what we need to consider to design a little spillway, a little culvert, the foundations, or the plinth level of a house.”
The ways in which rain falls in a warming climate’s increasingly intense storms seemed to Sharma an obvious area to investigate. So he and his team systematically gathered all the independent data meticulously collected at schools and post offices across the nation, some of it for 200 years. Because Australia is so vast, the data covers all of the world climate zones, save for polar ones.
Among the insights drawn from the data, Sharma explains, is that as the atmosphere warms, not only do storms become more intense, they get ‘peakier’. At its peak, rain falls faster and over smaller areas. You get intense downpours, in smaller windows of time and space.
“It was a very clear result; it wasn’t one of those wobbly messages that often comes with research papers,” Sharma says. “It was black and white. Rising temperatures exacerbate damaging flooding.”
Sharma presented his results across North America and Europe throughout 2016. The research has implications not just for developed nations (Australia has already partly adjusted its national flood-planning guidelines as a result of the research), but also for cities like Jakarta, Mumbai and Karachi, places which will have more and more instances of floods, according to climate models. And they will likely be lethal.
Harley was back on the Narrabeen-Collaroy beach. The air was still; his nerves were alert: something extraordinary was going on. He readied the technology at the lab’s disposal: drones, jet skis and a twin-engine airplane loaded with the laser sensing technology LiDAR, plus the building-mounted cameras and lasers that were always taking thousands of photos every hour and scanning the beach four times a second, day and night.
In five decades of close observation, Narrabeen-Collaroy had not seen a storm like this.
“It showed six-and-half metre waves to hit on Sunday – that’s reasonably big for our coast, but not massive. The really concerning thing was the direction they were coming from.”
Like all coastal engineers, those at UNSW’s Water Research Laboratory (WRL) work at the dynamic nexus of sand and sea. At Narrabeen-Collaroy, it’s also the location of some very expensive residential property.
On Monday, 30 May 2016, as happens every day, Harley collected the forecast from Australia’s national weather agency, the Bureau of Meteorology. Routine work; run it through the algorithms the lab had developed to predict storm impacts on the beach.
Then the data for the coming Sunday – 5 June 2016 – came back. And it went off the charts. Harley ran it again. Off the charts again. It wasn’t just that the waves would be big.
“It showed six-and-half metre waves to hit on Sunday – that’s reasonably big for our coast, but not massive,” Harley says.
“The really concerning thing was the direction they were coming from.”
Generally, the March-August storms that hit this part of the Southern Hemisphere come from the south. Australians call them East Coast lows (akin to American Nor’easters). But this one looked to be hitting from east-northeast.
“I’d seen storms from that direction during my PhD that were a lot less intense, but I had been surprised how much damage even small storms did,” Harley says. “So imagine, twice as big, from that direction. I almost literally spat out my coffee.”
To make it a triple-threat, the storm would coincide with king tides.
“Biggest of the year,” Harley says. “Water levels then are several tens of centimetres higher than usual, so the waves are already going to attack higher up the beach than they normally would.”
“In future decades, what’s now a king tide will be an average high tide. And we’ll still have king tides.”
This potentially epic event was still days away. And the forecast would ebb and flow over the next 48 hours, along with Harley’s adrenaline.
The WRL team was aiming for something rare and precious in coastal-monitoring: accurate pre-storm data. All around the world, researchers collect copious data after a storm. But they rarely see storms coming in time to mobilise detailed recording immediately beforehand. The comparison, however, is what is most telling.
With careful measurements before and after a big storm, the team could accurately analyse the impact of storms and the resulting erosion and damage. They would be able to understand much more about how sand moves, and then accurately model and predict the impact of future storms, Turner says.
He tells the story of Albert Einstein warning his son off studying sedimentary transport because it was too complicated. Climate change, Turner laughs, only adds to the complexity.
“Sea levels are rising, and we should anticipate a shift in wave patterns,” Turner says. “Not necessarily bigger storms, not necessarily more storms, but storms from different directions.”
The team had been preparing for this one. Over recent years, they’d come up with the algorithms that triggered Harley’s initial alert. They had also put together detailed mobilisation procedures jointly with the state’s Office of Environment & Heritage, which suppled staff, jet skis and boats. These were about to be thoroughly tested.
“We had to develop our own internal storm-warning system,” Turner says, brandishing the laminated plan-on-a-page he carries everywhere, “because we had to get out onto the beach in the 48 hours before the storm to measure the data we really wanted.
“It wasn’t by chance that we were there.”
Calm before the storm
On Wednesday prior to the storm, the Pacific seas were, in Harley’s words, “like a mill pond”. The dead-calm conditions ensured the jet skis could go out to survey the sand to a depth of 20m, and Water Research Laboratory pilots could fly the lab’s drones overhead.
The quadbikes, now in touch with 15 to 20 geostationary satellites, GPS-checked every aspect of the beach. A UNSW Aviation plane flew above with its mounted LiDAR, making three-dimensional scans of the whole area.
A disappointed local surfer asked Harley what all the activity was about.
“I said, ‘Looks like there’s going to be a massive storm on Sunday, so we’re doing measurements ahead of it.’ And he’s like, ‘Nah, mate, you’re wrong. You guys have got to ask the surfers. They know best.’”
As the weekend neared, the lab forecast increasingly showed a major storm event. The last tool Turner decided to deploy was a sophisticated – and expensive – wave buoy.
There was a good chance the storm would claim it. The buoy is capable of measuring every wave as it is about to hit the beach. They had to risk it, Turner decided. On Friday, a boat anchored the buoy 300m out to sea. They waited.
$56 million damage to property
When the storm hit on Sunday, the impact was dramatic, and the engineers captured it all – the science and the sensation. Global media relayed Harley’s social media posts – such as “About six houses cracking up right now at #Collaroy with #kingtide. Grave conditions #SydneyStorm” – almost in real-time.
Residents were evacuated, roads closed. A swimming pool slipped into the sea, building foundations fell, emergency services struggled with more than 10,000 requests for help.
At Collaroy, more than half a dozen houses were severely damaged by the storm that left an estimated $56 million worth of damage in its wake. Worse, across Australia, at least five lives were lost to floods and wild surf.
The beach itself lost 50m in width. It was the largest erosion event recorded during Narrabeen-Collaroy’s 40-year monitoring program. Harley marvels that 12 million cubic metres of sand – “enough to fill the international Melbourne Cricket Ground stadium seven times, to the brim” – shifted during the storm.
The expensive buoy survived, and like the rest of the WRL tools, delivered much valuable information.
“In future decades, what’s now a king tide will be an average high tide. And we’ll still have king tides,” Turner says. The storm came from an unusual direction, as did the waves, accounting for the severity of the overall damage.
Relatively subtle changes. Huge impact.
“We are heavily focused now on being able to model and predict and indeed to forecast that type of event,” Turner says. Now they have the very precise data they need on which to base that kind of analysis.
And with it, researchers around the world can begin to build vastly more accurate coastal erosion models, to predict damage days before a storm hits.
The WRL team wants to build a national network of monitoring sites, to add to the insights from Narrabeen-Collaroy and other places. The lab has plans to develop and test a national coastal hazard and coastal erosion early-warning system, similar to those currently being developed in the USA and Europe, to identify and predict likely storm-affected areas down to a few metropolitan blocks, or whether the northern, middle or southern end of a beach will be hit the hardest.
There are still many questions.
“Where do we need to focus our resources? Where do we need to evacuate people? Where do we need to sand-bag?” says Turner.
WRL engineers are also in long-term planning discussions about the value of seawalls, sand nourishment and other buffer zones, or of beachfront-property acquisition and restoration. They’re helping raise and answer critical questions about how we protect infrastructure like arterial roads, ports, harbours and oil refineries.
“Now climate change is an important part of the picture, how do we adapt and modify as the opportunities arise?” Turner says. “Populations are increasing, and our infrastructure is increasing – we have to come up with solutions.”
– Lauren Martin
To read more stories from the frontline of engineering research, check out Ingenuity magazine.