Under this doomsday scenario – which government research has modelled – suburbs like Blacksmiths, Pelican, Marks Point and Swansea would cease to exist. 

The Lake Macquarie Coastal Residents group is calling for action plans to be locked in to defend against this dire forecast.

Scientific models predict the Swansea-Belmont South peninsula could be inundated beyond the year 2100 – a risk the residents’ group says cannot be ignored. They want  triggers  stipulating when action will be taken to protect properties.

The call follows Lake Macquarie City Council releasing a final draft of a plan to manage its coast.

Coastal residents group vice-president Frank Mieszala said the community can’t wait ‘‘100 years until it becomes a problem’’ and called for the ‘‘protection of the two to three kilometres at Blacksmiths beach’’.

‘‘If Blacksmiths beach and Pelican get washed out, the lake is in big trouble,’’ he said.

Mr Mieszala said his group was opposed to defeatist attitudes of ‘‘planned retreat’’ and letting nature take its course.

Lake Macquarie independent councillor Barry Johnston said the council had shifted its position more towards defence over retreat. 

He warned the issue was not isolated to Lake Macquarie alone.

‘‘It’s not just a local issue, it cuts across the country,’’ Cr Johnston said, adding that most Australians live on the coast.

Mr Mieszala said defending against inundation would ‘‘be top’’ of the residents’ group’s agenda.

He said if water was allowed to penetrate Blacksmiths beach dunes in future during storms, Blacksmiths, Pelican and Marks Point could be engulfed.

‘‘You’ll have an opening to the lake that will become Lake Macquarie bay, rather than Swansea Channel,’’ Mr Mieszala said.

Cr Johnston said the problem of “storm surge” could heighten the risk of erosion and inundation.

The residents’ group had worked on an adaptation plan for Marks Point that involved raising land over time, as properties were redeveloped, to overcome the risk of permanent inundation.

The city council will be urged to approve the plan this year.

Additionally, the group planned to work with the council this year on an adaptation plan for Blacksmiths.

This would involve pushing the concept of a rockwall or breakwall at the beach to prevent inundation.

‘‘If we raise the land on the lakeside and put a rockwall on the beachside, the two will go hand in hand to protect property,’’ Mr Mieszala said.

Lake Macquarie council was ‘‘ahead of other councils on this’’, he said, but his group would continue to urge the council to support defence of property rather than retreat.

The final draft of the council’s Coastal Zone Management Plan proposes that the council ‘‘investigate and implement strategic planning to allow for the future planned retreat of low-lying private lands [beyond 50 years]’’.

This was the plan ‘‘if other measures such as foreshore protection and development controls prove insufficient to manage the increased risk’’.

The council engaged a consultant to prepare options to deal with risks from erosion, recession and inundation.

Options include: seawalls; beach nourishment; dune protection; an artificial reef or breakwater in the surf-zone; asset relocation; rebuilding structures with  designs to withstand hazards; and acquiring private properties at market rates, demolishing them and converting the sites to public land.

Under one contentious option, low-lying residential land at Catherine Hill Bay would be investigated for acquisition in future.

Mr Mieszala said his group would seek a second opinion on these options.

The  group supported monitoring at Blacksmiths beach, so when beach recession reached a certain level, or ‘‘trigger point’’, measures would be introduced to protect property.

He said this should be done ‘‘when it’s easy and when recession is 100 metres away from property, rather than late when it’ll be expensive and you’re controlled by whatever storm comes next’’.

Cr Johnston said the council had shifted its position towards defence, following consultation.

‘‘The first priority at this stage is for protection of properties,’’  he  said.

‘‘[Mr Mieszala] believes it should be the only option, but all options do have to be considered.’’

Cr Johnston said protection of properties, in some circumstances, ‘‘may not be feasible’’.

He said state and federal governments would have to provide money for costly solutions, but the community may have to contribute.

Lake Macquarie Greens convener Phillipa Parsons said it was “good that this conversation is happening and we’re accepting that sea level rise is happening”.

“We know humans are causing climate change, which is warming the seas, and that sea level rise will occur everywhere,’’ Ms Parsons, a former Lake Macquarie councillor, said.

She said the problem should not be ‘‘left in the lap of overburdened councils’’.

‘‘All three tiers of government need to work together to mitigate the effects on humans and human property, as well as biodiversity and ecosystems.’’ 

She said some political leaders had politicised the issue and shirked their responsibility.