BREAKING APART: Cracking sounds are coming from the storm-damaged houses on Collaroy Beach

Photo: UNSW Water Research Lab/ supplied.

Houses teetering on the edge of Collaroy Beach, north of Sydney, may crumble into the sea after “bangs and cracking” noises were heard following king tides last night.

The waterfront properties became threatened over the weekend after a massive storm eroded the beach front and sea wall. One house lost its pool to the ocean.

Business Insider spoke to professor Ian Turner, director of the UNSW Water Research Laboratory, who was at the scene last night.

“There were a number of structural engineers inspecting the homes along Collaroy beachfront around high tide last night and I was lucky enough to observe that,” he said.

“The beach has been completely removed around those properties. There were bangs and cracks coming out of those building as we were moving around them.”

Photo: UNSW Water Research Lab/ supplied.

The UNSW Water Research Laboratory has been recording data from the Narrabeen-Collaroy Beach for 40 years.

Over weekend, Turner estimates that 450,000 cubic metres of sand was stripped from the beach — that’s 150 cubic metres of sand for every one metre across the beach, gone, and the equivalent of 180 Olympic swimming pools, or roughly two shiploads from the world’s largest LNG carriers.

While dangerous conditions prevented researchers getting detailed data, they have been able to get an idea of the extent of the damage.

Here’s a look at the data recorded in recent days.

A. is a reading from June 3, which shows the beach width at 160 metres.

B. is a reading from June 6, which shows the beach width at 90 metres.

“We managed to get a crew down onto the beach for the first time yesterday after the storm,” Prof. Turner said, adding that the reading is probably more like a 50 metre difference, rather than 70 metres.

“We have seen the beach narrow by 50 metres over the weekend, and after last night’s king tide there would be a bit more damage than that now.

“We have been monitoring the Collaroy-Narrabeen Beach for 40 years, and during that time the width of the beach has varied by up to 80 metres — the beach widens and narrows.

“Through April and May the beach in front of those house was the best it has been ever. With the two high tides over the weekend, very large amounts of sand has been stripped from the beach, but it hasn’t been lost.”

Photo: UNSW Water Research Lab/ supplied.

While this has a devastating short-term impact for the nearby houses with an uncertain fate, Turner said the sand will come back.

“In the next week to a few months, most of the sand will be back on beach, while the dunes take a bit longer to recover… after a few years you won’t even notice any change,” he said.

“As soon as the conditions abate we will have more information.

“From a coastal engineering perspective, we have seen the worst of the storm. We do have a couple of large tides to go — one being at 10pm tonight — and I would anticipate there would be minor adjust of sand again, but I think we’ve seen worst of damage now.”

Turner said the engineers and council will be assessing the extent of the damage and “having a look at individual houses” at low tide today (3:43pm AEST).

Photo: UNSW Water Research Lab/ supplied.

Last night on Network Ten’s “The Project”, the owner of the property whose swimming pool was destroyed by the sea spoke about how the council had failed the community by not building an adequate sea wall.

“The council have known about this for a long time, and they should have put a wall up before then,” Zaza Silk said.

“They’ve known that the land there is unstable. They’ve had this incident happen before… the sea washed away a large part of the beach not too long ago, and they have done nothing about it.

“This could have been avoided.”

While Turner agrees the sea wall along the beachfront in that area was “rather ad hoc”, he said council had tried to establish better infrastructure.

“Where the houses are currently threatened is a gap in the existing sea wall,” he said.

“Warringah council (now the Northern Beaches council) is one of the most proactive councils in Australia when it comes to protecting private and public infrastructure (from erosion).

“My understanding is that a large majority of council ratepayers didn’t want a rock wall to be built.

“The council also had an active policy of purchasing beachfront property that was at risk, and turning them into parkland and public amenities.”

Photo: UNSW Water Research Lab/ supplied.

He says the best way to fix the beach now would be a sand nourishment program, similar to the Gold Coast’s approach.

“(The process involves) extensive sand being placed on the beach and during the next big storm that new sand will erode, not the existing sand.

“In my view this storm has highlighted it’s an option we need to think about adopting very seriously.”

Turner likens the recent storm to those experienced across the Australian east coast in the 1970s.

“The initial indications shows it’s comparable to the damage we seen in 1974, equivalent damage,” he said. “In the mid 1970s there was a series of storms that resulted in more widespread damage.

“We actually had an east coast low of similar magnitude in terms of wave height just last April.”

But he said this one was catastrophe for two reasons.

“First is that it coincided with the king tide, which are among the larges tides of the years, and the second, and most unusual, factor was that this storm hit Sydney from the east-north- east… most storms come from the south-east.”

This morning SES crews were reinforcing the area with 3000 sandbags to prevent any further destabilisation of the land.

“A major sandbagging operation is about to begin at Collaroy in the attempt to save more properties under threat of coastal erosion,” a spokesperson said.

“We urge people to keep well clear of the area to allow the emergency services access to the area and to keep you safe. There will be lots of trucks and vehicular movements on Pittwater Rd with lane closures in effect.”

Photo: UNSW Water Research Lab/ supplied.

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