Tropical Cyclone Alfred in its meanderings through the Coral Sea and eventual coastal crossing last weekend as an ex-TC generated the most severe erosive wave event since at least 2001.

That statement is limited to South-east QLD and northern NSW of course, but the view is confirmed by Tweed Sand Bypass (TSB) engineers who have monitored wave heights, sand transport, and erosion since the bypass project began 25 yeasr ago.

For two weeks, the swell was from the eastern quadrant. Small to moderate at first, the waves became large and powerful as the cyclone approached the sub-tropics, and the size stayed there for at least a week.

After that extended barrage of large cyclonic surf, how have the beaches held up?

There are regional and intra-regional differences but to sum it up: Pretty good.

Let's take a quick look around the grounds...

Shot from Burleigh Heads looking north where the erosion pattern repeats (Hussain Photography)

Starting from the southern end of the effected area, which is the Mid North Coast, erosion has been on the mild side as observed by Swellnet forecaster Craig Brokensha.

Beach erosion usually leaves a steep cliff on foredunes known as a storm scarp and, while these scarps were present, they were small in size and limited to the northern ends of beaches with southern ends showing limited to no erosion.

Similar effects from Coffs to Yamba with the added cushioning effect that most of that coastline is part of Yuraygir National Park and thus has very little coastal development and fully intact dunal systems which can absorb storm swells moreso than shorelines featuring artificial rockwalls. Apart from some minor scarping on northern ends of the beaches the coastline has fared well.

Once we get to Ballina-Byron the coastline becomes more modified with higher densities of coastal development and beaches more susceptible to storm surf erosion due to coastal rockwalls. This is particularly the case at Lennox Head and Byron Bay, both of which have suffered extreme coastal erosion in past storm events, most recently a winter storm in 2009. Rockwalls protect structures behind them, but prevent the natural functioning of sand dunes in accreting during mild weather and eroding in response to storm surf.

Here again, the effect of TC Alfred has been surprisingly benign. Small storm scarps across Ballina's exposed south-east facing beaches and still generous beach widths from Ballina to Byron.

Some of the outcomes are truly surprising. On Wednesday last week I visited Broken Head, where large storm scarps are a feature during storm swells. During my visit, the waves were massive, breaking at least 500m seaward of the outer edge of the Cocked Hat Rocks. Gales from the south-east were whipping across the coast and wave run-up was into the edge of the dunes. It seemed a recipe for severe erosion as Alfred moved in closer.

Photos from Broken Head looking north, at left, and south, show a remarkable volume of sand and no change to the beach profile (Steve Shearer)

Revisiting the site a week later was astounding. No storm scarps at all and the beach was hundreds of metres wide at low tide. There was zero erosion, in fact sand had accreted, if anything. Moderate storm scarps were visible up the Tallows end of the beach.

In Byron Bay itself, despite massive storm surf which saw the entire bay breaking at times, including waves right over Julian Rocks, the embayment is largely unscathed.

In 2019 and 2020, erosion threatened buildings and a caravan park at Clarkes Beach. Trees and structures fell into the ocean and the entire corner of the bay was reduced to rock. Since then beach widths have rebuilt wide, stable structures, with the corner of Clarkes becoming so stable it has become a vegetated salt marsh. Following Alfred the salt marsh has been nibbled away at but beach widths remain very generous, all the way down to the Byron Bay Surf Club. Even on the Belongil side of the Wreck, erosion has been only moderate.

The sand budget for Byron Bay is highly variable as a result of headland bypassing which lies outside the scope of this article, but for now sand in the bay has held up well.

The Pass at Byron Bay also managed to escape erosion (Steve Shearer)

Storm bars have been incredibly effective at protecting the coastline in this region, reflecting widespread sand accretion on beaches and nearshore zones. As a case study of coastal processes being able to absorb storm events this one has beenstraight from the textbook.

From Brunswick Heads to Tweed Heads we start to see increased damage. Larger storm scarps across these beaches, although limited destruction into mid and hind dunes, suggesting a rapid rebuild. Sand movement in some areas of the Tweed has created new structures, including a sand Island in Cudgera Creek adjacent to Hastings Point. Dunes to the north of this have been cut back significantly, as have areas from Fingal up to Letitia Spit, where the sand bypass jetty is located.

Signifcant scarping at South Kingscliff on the Tweed coast with (Jono Kingston)

At the southern end of the Gold Coast, D-Bah has taken a hair cut, as it often does after serious storm events, while the Superbank is largely intact but severly misaligned - offshore from Rainbow Bay is a shallow section way out near the shark nets.

At times like this surfers look to the TSB to help remedy the situation, however it might be a while before sand can be pumped across the Tweed River due to diminished sand volumes at Letitia Spit - they can't pump what isn't there. This week, TSB begins a thorough post-Alfred survey to locate and measure sand volumes and determine the pumping regime - stay tuned to Swellnet for the results of that.

Over time the wide outlying bank will move shoreward, a process that will be accelerated by the normal seasonal longshore sand transport which reaches a peak through late autumn. Sand pumping, when or if it begins, will assist that natural process.

The sand sometimes moved in irregular ways. A classic example being the protuberance of sand offshore from Rainbow Bay, visible by satellite, at left, and by surf camera

The northern Gold Coast copped the most spectacular beach erosion from Alfred with moderate/severe impacts and large storm scarps several metres high. Though eye-catching, it's not unusual and as in other regions, sand build-up from a long accretive phase and dunal vegetation has been a good counterweight to the erosion. Along with natural processes, the Gold Coast avails itself of modern engineering. Mayor Tom Tate has already made use of dredging and subsequent bowcasting to replenish beaches. Absent a major follow up storm rapid repair would be expected.

It's worth considering what a 'follow up storm' might mean. In the lead up to Alfred, the year 1974 was often referred to as it was the last time a cyclone crossed the Queensland coast. What wasn't mentioned, however, was that just two months after TC Wanda crossed the coast near Noosa, Severe Tropical Cyclone Zoe ran parallel to the coast between Noosa and Byron wreaking havoc on the still-vulnerable beaches. Arguably it was the second cyclone, Zoe, that caused most of the damage, attacking the beaches while they were in a vulnerable state.

Before and after shots of Narrowneck at the northern end of the Gold Coast. Narrowneck is the Gold Coast's most vulnerable stretch, hence why an artificial reef was built there in 2003 (Hussain Photography)

The same patchy erosive effect from Alfred has been observed on the Sunshine Coast with geographer Dr Javier Leon admitting in an ABC article, "Even though I was expecting that, it's just amazing to see one beach being fully eroded and then the next one is just perfect."

Generally speaking through, apart from some moderate storm scarping at Peregian and other more northern beaches the Sunshine Coast has escaped major damage. As in some other areas, beachbreak banks have even been improved after a long period of below average banks.

Bribie Island has been the most severely impacted. Not all of this can be sheeted home to the effects of TC Alfred. In fact, for much of the event Bribie was in the swell shadow of Moreton Island, a fact island surfers are only too aware of. The very thin northern tip of the island was broken through by swells from TC Seth in January 2022, which led to the long term closure of the old Caloundra Bar and establishment of a permanent opening at the breakthrough site. Swells from TC Alfred further eroded the remaining tip of the island and produced another breakthrough point.

Bribie Island is in a long-term state of erosion, particularly at its northern end, but also at the populated southern end of the Island. A visit to Woorim in January showed very narrow beach widths along the southern end of the Island. Unlike other areas there was very little sand buffer there to withstand storm swells.

The Queensland sand islands are young and dynamic - subject to dynamic processes of longshore sand transport which are unique on a world scale. In the case of Bribie, sand travelling along Moreton Island, moves north-west into large sand deposits offshore from Northern Bribie causing the sand banks to grow and migrate slowly to the northwest over a decadal time period.

Satellite imagery shows north-flowing sand leaving Moreton Island yet largely bypassing Bribie Island on its way to Caloundra and the lower Sunshine Coast

Unfortunately, that sand is not available to Bribie and is becoming less so as it becomes concentrated into large sand banks which are increasing the ebb tide currents in the north-west channel off Caloundra and Bribie (the shipping channel). With Moreton blocking south and south-east swells Bribie also suffers from an attenuated littoral drift of sand from that direction, effectively creating a double whammy. It's cut-off from sand supply from the north-west via a deep channel (Pumicestone Channel) with increased tidal currents, and from the south-east by swell shadowing from Moreton Island. Any large swells from the north-east to east are simply going to exacerbate this long-term structural deficit in sand.

What to do is outside the scope of this article, although some means of mechanical shifting of sand from the Spitfire banks east of Bribie Island may need to be considered for the long term stability of the Island.

A SE QLD cyclone crossing has highlighted the dynamism of the coastal processes in the sub-tropical region, especially with its high concentrations of surf breaks and population centres. Those processes are only going to become more dynamic and acute as we grapple with a changing climate and oceanography, including a stronger East Australian Current which will increase the chances of water warm enough to sustain a full blooded tropical cyclone into the SEQLD/NENSW region.

In the immediate wake of Alfred, however, everything worked exactly as it should and the coastline has absorbed the impact of the cyclone with only superficial damage.

// STEVE SHEARER