Beaches In Retreat
“There’s not much sand left; all the beaches are in a very denuded state.”
I’m talking to Dr Mitchell Harley, who’s professional resume lists him as a Senior Lecturer at the University of NSW, but among those of us with a surf/science bent Dr Harley is the sand guy. Through his work at the Water Research Laboratory and CoastSnap he closely monitors beaches here in Australia, and also around the world, though right now he’s talking specifically about Australia’s East Coast.
“They’re not the worst I’ve seen them,” continues Dr Harley, “but in terms of erosion, certainly they’re in the lowest 10%.”
It’s a startling observation from someone who takes a broad view of all beaches, not just those within range of his daily surfs. And the reason isn’t to do with sand volume being in the lowest decile, but rather the timing. You see, our conversation was in March. Early autumn. When the beaches are traditionally at their very widest.
Viewed over years, the sand level on East Coast beaches will ebb and flow with the seasons. The pattern goes like this: During winter they erode under the barrage of southerly swells, often at their leanest during spring when a switch to smaller swell and northeast winds through summer will see the sand return, both broadening the width and raising the profile, providing a buffer for when the autumn and winter swells return.
When Dr Harley and I spoke, the beaches should theoretically have been at their widest - topped up in readiness for the winter onslaught - yet they were in a state more similar to what we’d see in September...a bad September. In other words, the coastal defences were down.
The reason it’s taken so long for this article to appear is because from the first week of April to early June, the East Coast went into an improbable and unseasonal slumber. Here at Swellnet the collective thought was that, though it’s come down to the wire, the beaches may be spared. Bit by the bit sand was accreting, slowly building up the beach widths, bringing them back from the precipice.
Yet with la Niña sustaining throughout the western Pacific the quiet times couldn’t last, and they didn’t. June saw a series of long range south swells, and the month ended with a more damaging East Coast Low unleashing chaotic short-range swell from the east, plus days of tropical rain - which presents its own problems, as we’ll soon see.
To get a grasp of what’s happening we need to zoom out, to look both beyond our local beach to the region in general, and also to assess what’s happening across time; to understand the changes over years not seasons. September 2020 is the obvious starting point, as that’s when the current la Niña kicked off.
The first year of COVID was above-average for swell, as the hordes of enforced WFHers could attest - it was pumping and crowded - which meant the beaches were slim come spring 2020. However, as mentioned, that’s to be expected after each winter. It was summer 2020/21 when the slide began, as a summer rife with east swell - not to mention a distinct lack of nor-easterly seabreezes - halted the seasonal sand build up. As la Niña celebrated her first birthday the beaches were in a terrible state.
Not only were the usual erosion zones, such as Old Bar, Wamberal, and Norah Head, suffering but in October 2021 the chronic erosion at Collaroy on Sydney’s Northern Beaches was ‘solved’ with the construction of a 13 metre high vertical concrete revetment wall stretching along 100m of the beach. Short of a tsunami, the private property was saved by this hard solution, but the beach in front of it was destined to part-time status.
Around the first anniversary of la Niña another peculiarity began to arise. All of the aforementioned erosion zones are in places largely protected from south swells, which is the predominant direction on the lower East Coast. Here, the coastline is geared for south swells, it has the capacity to mitigate and respond to them, so severe erosion usually only occurs when we get extended or oversized swells from the east that breach our quieter corners. Yet that was no longer the case.
Cronulla and North Entrance are two stretches of coastline aligned towards the south, and in mid-to-late 2021 both started to erode badly. Though it started in 2020, by the following year the erosion at North Entrance had exposed rocks and threatened property, requiring emergency works such as rock dumping and a sand nourishment program that was costly and short lived - as all sand nourishment programs are. Further north, a scarp up to five metres high made beach access difficult, as much for surfers as lifeguards at North Entrance SLSC trying to wheel rescue equipment onto the sand.
Meanwhile at Cronulla - for which Swellnet has another article coming shortly - 2021 ended with deep scarps marking the beach north of Elouera, however the very worst erosion was happening at the southern end, at North Cronulla Beach, which through the summer of 2021/22 marched slowly but inexorably backwards, towards the dunes and the clubhouse. Nippers could only be run at low tides and even then space needed to be found elsewhere, usually north of The Wall.
By my reckoning there was just one unsurfable day during summer 2021/22, making it the most consistent summer of waves in my forty years of surfing. Each day of swell took a little more of North Cronulla’s beach width, till by the time Dr Harley and I spoke in March the beach disappeared altogether at high tide meaning there was effectively no beach between South Cronulla and Elouera. Nor were there any banks: “The worst it’s been in years,” reported longtime Cronulla surfer Ben Horvath.
More alarming than the lack of banks was the local council’s release of the Bate Bay Coastal Management Program that included provision for a breakwall at North Cronulla. “Given the risk to Dunningham Park and the North Cronulla Surf Life Saving Club building, a seawall is proposed for North Cronulla beach. This involves replacing the existing informal rock wall with an engineered structure that could comprise some combination of rock revetment, vertical wall or concrete bleachers.” The Program was published around the same time the Collaroy wall was being constructed so Cronulla surfers needn’t exercise their imagination to foresee what could happen to the beachfront - it was all across the news.
Cronulla is a unique case as it’s not only an embayment with a largely trapped sand system, it’s also had many millions of cubic metres of that sand removed via sand mining. Sand that otherwise would have fed through the closed system - from the dunes to the near shore zone and beyond during storms, then back onto the dunes at quiet times - has been taken away leaving the beaches with a weakened defence mechanism - and surfers with deeper banks.
That said, Cronulla has been here before; the erosion was perhaps not as chronic but arguably as acute. In May 1974, a series of storms smashed the North Cronulla beachfront leaving it in a similar state to what we see today. The difference now is the aforementioned lack of sand in the system to naturally repair storm damage, which leaves Cronulla surfers and policy makers with some difficult decisions to make. This week, the council stepped in and, without community consultation, began dropping boulders onto the beachfront at North Cronulla in readiness for another onslaught as la Niña persists throughout the western Pacific.
It’s la Niña that links these erosion events, and that’s why it helps to zoom out and view the time scale. 1973-1976 were la Niña years - a triple dip la Niña in fact - so was 1983, 1989, 1998, and 2007, all of them la Niña and all of them years the East Coast had great runs of swell, with the fall out being severe erosion. The phenomenon only hit the mainstream in the early-90s, and even then only one side of it - el Niño. Surfers tried to find a correlation between this new broadscale weather pattern and good waves, but it wasn’t till la Niña was introduced and hindcasting became available that the pieces fell into place for East Coast surfers.
A feature of la Niña, of course, is increased rain along the Eastern Seaboard. The warmer water in the western Pacific increases evaporation which creates clouds that drop their load on the coast. In March, we saw the extreme end of that when flooding overran north coast towns, most dramatically at Lismore. Further south, away from the great northern rivers and their catchment systems, the rain fell into creeks, rivulets, and stormwater drains that attacked the beaches from behind, and at times it was just as devastating as the waves.
On the 7th March, Manly Dam overflowed sending a torrent of water downstream, flooding houses, but also blowing out the lagoon entrance at Queenscliff. Such actions happened all along the lower East Coast, where excess rain - Sydney received its annual rainfall in just three months - blew open lagoons leaving them vulnerable to wave action. This is what happened, again at Manly, when a wave breached the defenceless lagoon and travelled 500m upstream again flooding backyards and houses.
Other examples of compound hazards - rain erosion enabling wave erosion - were reported at Avoca Lagoon, the Shoalhaven, and multiple places on the far South Coast where the mountains abut the coast so floodwaters have little time to slow before they reach the ocean, often through lagoons and natural entrances.
A similar mix of rain and wave damage is occuring where I live in Wollongong's northern suburbs. Since 2020, I've taken weekly photos of the local headland where houses are perched high on a clay-based bluff. Viewed in their entirety, those photos show the upper land slumping as sodden clay deforms and slips, while during storms waves attack the base. Here, the coast is being reshaped by both rain and waves - and each is happening due to la Niña.
Along with his work at the Water Research Laboratory, Dr Harley has also set up a citizen science project called CoastSnap. The purpose is to create a wide network of eyewitnesses providing visual evidence of the ever-changing coastline. Again there's that will to zoom out, to take in a wide region and view it over a wide timeframe.
"After an event," says Dr Harley, "humans tend to go back to their original ways, so we kind of forget, or block out, the changes that are happening." So CoastSnap is a means of logging those changes and getting a better understanding of them, which is especially necessarily if, as many scientists predict, we're on the cusp of human-induced climate change.
As Dr Harley says, CoastSnap, and indeed the imagery from this current la Niña event, "gives an insight into what we can anticipate with, say, twenty to thirty centimetres of sea level rise." Even with what we currently know and see, coastal planning is still being decided that doesn't take into account long term trends, such as climate change, or even the next la Niña. "Anything that's built too close to the coast and is inside the zone where the beach naturally likes to fluctuate is a concern," Dr Harley dryly explains.
Yet this story is starting to get ahead of itself. As I write this, yet another la Niña-fuelled weather event is bearing down on the East Coast. This time it's a low pressure system set to deepen off the Queensland coast - the weather map is more akin to January than July - spraying the whole East Coast with 8-10 feet of east swell. La Niña is again loading the artillery, and meanwhile the beaches are denuded and defenceless.
If Dr Harley had some lingering optimism when we spoke in March, it's now fast disappearing, going the way of the sand.
"The beaches are sitting ducks if we see further erosion."
// STU NETTLE