A comparison of NSW government seabed survey data has found that between 2000 and 2018 on average 85,300 cubic metres of sand, or 136,500 tonnes, was lost from the beach every year, which is more than double previous predictions.

According to the analysis, conducted as part of joint research project between the University of Newcastle and Newcastle-based data specialist company Anditi, erosion saw 1.54 million cubic metres of sand stripped from a 3.84-square-kilometre section of the beach, resulting in an average seabed drop of 0.4 metres, from 2000 to 2018.

Mapping of the laser survey data shows some of the hardest hit sections, including areas closest to the shore, have dropped by two metres and sand loss is occurring in water depths from 12 metres, all the way to the Newcastle harbour channel depths of 18 metres to 20 metres.

City of Newcastle told the Newcastle Herald this week that 500,000 cubic metres of sand was needed to renourish the beach and 40,000 cubic metres would maintain it each year.

But the University of Newcastle's Dr Ian Taggart and Anditi managing director Peter Jamieson said the beach could "easily take 2 million cubic metres of sand", or four times what was earlier predicted.

The pair said previous estimates of sand loss did not reveal anywhere near the true extent of the environmental crisis and without a re-evaluation of what was causing the sand loss and "serious" replenishment the erosion would get worse.

They warned that as the seabed continues to drop, larger waves will reach the shore wreacking havoc on Stockton's already crippled coastline and smaller storms will do much greater damage than previously.

Dr Taggart, of the university's school of engineering, said the problem had been neglected for too long and 500,000 cubic metres of sand was now "small change" and sadly insufficient.

"The sand loss number is awfully big and it's awfully accurate," Dr Taggart, a Stockton resident, said.

"The beach is now in a state it's never been in before, this is not cyclic. This sand loss is going one way and I would use the word vulnerable to describe the beach now.

"You can argue that the shoreline has been eroded this far before, but the level of sand is now much lower and what was a modest storm before that would do no damage, well today it does lots of damage. This is real, the data is very clear."

It would take 24 semi-trailer loads of sand every weekday for a year, costing more than $4 million, just to replace what is being lost.

Mr Jamieson, a former environmental consultant who authored the 2002 Shifting Sands at Stockton Beach report commissioned by Newcastle council, said authorities had "stuck their heads in the sand for too long".

"We knew there was significant erosion up until 2000 and there was argument about the volume and magnitude," he said.

"What we didn't know then is how fast it is occurring over such a large area. The sand losses are bigger than thought and it's happening in much deeper water, the trends are clear and it's much worse than what people believe."

The pair warned that without sand to protect the beach, storms would continue to batter the shoreline undermining the Mitchell St seawall that has already dropped significantly in recent years.

As the seabed continues to lower, higher energy waves will pound the coast doing much more damage. But Mr Jamieson warned that a seawall was not the solution, because without sand all beach amenity would be lost.

"It would look just like Queens Wharf, except it would have bigger waves crashing over the top of the rockwall," he said.

"Six metre waves will become eight metre waves, the more the sand erodes off the beach the higher those waves will be impacting on the shore and therefore the higher the rockwall will need to be to fix the problem. It would be a hell of a shame for Stockton, it would be the next industrial port."

Fifth-generation Stockton resident and surfer Lucas Gresham said he watched in disbelief in last month's storm, that almost washed three holiday cabins into the sea, as "four-to-six foot swell, that didn't break until it hit the rocks" pounded the Mitchell St seawall.

With no sand, the wall- that is dropping and moving - is the only thing that stands between the ocean and a row of beachfront homes. The swell is now so powerful that residents feel their homes increasingly "shudder and shake" and waves regularly crash halfway across Mitchell St, that has a gas main running along it.

As part of formulating its Coastal Management Plan that will identify a long-term solution for the crisis, City of Newcastle has commissioned sediment-transport studies for Stockton Bight to track the movement of sand and a spokesman said a review of the state government seabed survey data, that has been analysed by Dr Taggart and Mr Jamieson, was underway. The Newcastle Herald understands it is due to be completed by May.

University of NSW's beach profile database shows north of the Stockton Centre the beach is growing, but at the southern end it is fast disappearing.

Dr Taggart, who said he offered to share the latest analysis with City of Newcastle but received no reply, said he was surprised the data hadn't already been evaluated.

3D mapping of the findings by Anditi staff reveal dramatic changes at the southern end of the beach, including "drainage channels" running along the northern side of the Stockton breakwater leading to what the men believe is causing most of the sand loss, a "large scour" hole at the tip of the wall.

Dr Taggart and Mr Jamieson said more work needed to be done to determine where the sand was going, but they believe the large hole, or scour depression, off the tip of the breakwater - at the harbour entrance - was acting like a "plughole", ripping sand off Stockton beach.

A similar scour depression caused the collapse of Pelican Marina into Lake Macquarie in 2016.

Anditi's seabed contour mapping shows a "steep", "unstable sand face" at the tip of the Stockton breakwater where the scour depression dips to the level of the harbour channel at the port entrance.

"Any current washing over that is going to take sand away, that's far too steep...," Dr Taggart said.

"Now we can identify a sand loss mechanism and it's the plughole.

"The issue is we need to fix the plughole. I don't think authorities want to publicly state how much impact it is having, or they don't know."

Stockton Surf Life Saving Club veteran and former ironman John Anderson said he had never seen the southern end of the beach worse.

Mr Anderson, who has spent 50 years training at Stockton, confirmed a noticeable change in the way the beach is working.

"There are definitely more rip currents running along the breakwater," he said.

"There used to be a lot of sand there but now there is none, it's appears to be running out there."

In 2016, Newcastle lifeguards Paul Bernard and Scott Hammerton were given bravery awards for rescuing three young surfers sucked out to sea along Stockton breakwater in mountainous swell in the middle of an east coast low.

The scour depression, first identified in Mr Jamieson's 2002 report, has increased in size and dropped two metres in depth from 2000 to 2018.

"You will continue to loose sand off the system until something is done about the loss of sand at the end of the breakwall and the channel area immediately adjacent to it," Mr Jamieson said.

"This is a harbour management issue. The sand loss is from an unnatural cause, something is making it happen and someone is responsible for it."

The Port of Newcastle is licensed by the federal government to remove 650,000 cubic metres of silt and sand from Newcastle harbour a year.

On average, about 500,000 cubic metres are removed annually by dredger the David Allen, including 25,000 cubic metres of sand from the harbour entrance that is dumped off Stockton.

Dr Taggart said it appeared the sand being dumped off Stockton by the David Allen was most likely sand being stripped off the beach.

He described a difference map produced by Anditi showing changes in landforms from 2000 to 2018 as "striking" because it was like "a tracer experiment for the sand the David Allen has dropped".

"You can see the rip current take the David Allen spoils south along the beach and you can see it turn the corner and run along the breakwall," he said.

The research shows sand from Stockton beach is gently falling to channel depths, technically known as beach drawdown, with no evidence of sand being carried to Stockton from the south due to Newcastle breakwater and the depth of the shipping channel.

Both men warned any deepening of the harbour would severely compound the erosion issue at Stockton.

University of Newcastle's Conjoint Associate Professor in Earth Sciences Ron Boyd has raised concerns with Port of Newcastle that sand from the David Allen was being dumped in too deep water off Stockton for it to make its way onto the beach. He has been lobbying the port to find a way to place the sand directly onto the beach.

A spokesman for the Port of Newcastle said where the David Allen dumps sand is determined by its operating licence and and the port had no discretion to change it.

According to the Shifting Sands at Stockton Beach report, between 1812 and 1900 about 4.5 million cubic metres of sand was lost off Stockton beach.

For the next 80 years the beach was relatively "stable", losing about 1 million cubic metres of sand. After the harbour was deepened, from 1977 to 1983, the rate of sand loss increased dramatically, with 1.9 million cubic metres stripped from the beach in the 20 years to 2000.

Mr Jamieson said any further deepening of the harbour would likely trigger another "significant increase" in the rate of sand loss.

The official depth of the harbour is 15.2 metres in the main channel, with the deepest level about 20 metres and a Port of Newcastle spokesman said there was "no" long-term plan to deepen it.

Residents are campaigning for the Port of Newcastle to help fund a long-term solution to the erosion problem but the spokesman said the breakwaters and Macquarie Pier, that connects Nobbys to the mainland, are NSW government assets and their length had not changed in more than 100 years.

The Port of Newcastle was privatised in 2014 for $1.75 billion to a 50/50 joint venture between Chinese and Australian interests. Soon afterwards, the new owners revalued the business to be worth $2.4 billion.

Asked if the port was aware of a scour hole off the end of the Stockton breakwater, the spokesman said hyrdographic surveys were conducted of the channel entrance and approach for navigational safety.

"We do not survey outside of the areas required for safe navigation," he said.

The spokesman said the port was assisting City of Newcastle and the Department of Planning, Industry and Environment in their investigations into the erosion problem by sharing technical data and providing sand from the dredge.

Residents also argue that the NSW government, that receives millions each year in coal royalties from the port, should foot the bill for a long-term solution.

Last year Stockton residents engaged the NSW Environmental Defenders Office to investigate if the state government has a duty of care to repair the beach due to the devastating erosion caused by the breakwaters.

Mr Gresham said the community felt "let down" by authorities that had failed to properly act on the problem for decades leading to a crisis.

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