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The warning came from University of Otago coastal processes specialist Dr Mike Hilton yesterday, as the council's Ocean Beach hearings committee backed plans for a holding pattern in the area for the next decade.

The holding pattern would include beach monitoring and replenishment work as required, and could cost up to $8 million over the decade.

It was to be followed by even more expensive work to protect the area, including a buried backstop wall, managed retreat and clean-up of an old landfill under Kettle Park.

The options - covering the area from St Clair to Lawyers Head - were detailed in a report by Tonkin and Taylor, which led to public consultation and yesterday's deliberations.

However, Dr Hilton told the meeting yesterday the timeframes for when the work would be required remained uncertain, and could be "quite wrong" if more severe weather struck.

The margin of error east of the St Clair sea wall was "quite small", with protective sand sausages already exposed by the elements, he said.

The council had been "quite lucky" since severe storms in 2007 led to emergency repairs and prompted the start of the planning process for the future management of Ocean Beach.

However, another severe weather event could force the council's hand at any time.

"We could be very unlucky at any time," Dr Hilton said.

Richard Reinen-Hamill, the author of the Tonlin and Taylor report, agreed, saying the work timeframes in his report were "just predictions".

"We are dealing with uncertainty and trying to manage uncertainty." However, the prospect of a sudden bill for major work would also be "problematic" for the council, given present financial constraints, council community and recreation services manager Mick Reece told the meeting.

"Paying for it in the next financial year has never been an option," he said.

The discussion came as councillors endorsed recommendations contained in the report, beginning with the holding pattern over the next decade costing up to $8 million.

That was to be followed by construction of an expensive buried backstop wall, costing up to $3 million, inland from the sand dunes, stretching 300m east from the end of the existing St Clair sea wall. Elsewhere, the report recommended a managed retreat along a 1km front at Middle Beach, allowing the sea to reclaim parts of Kettle Park, or a second buried backstop wall to protect the playing fields.

A managed retreat would cost up to $16 million, as a historic landfill under the playing fields would need to be cleaned up, while a second buried backstop wall could cost $10 million.

The committee yesterday endorsed plans for the managed retreat at Middle Beach, but chairman Cr Colin Weatherall stressed that did not mean the area was being abandoned, although some Kettle Park playing fields would be lost.

Council parks manager Lisa Wheeler said the council would work with the Dunedin Rugby Football Club - which used the park - to accommodate its needs as part of a wider review of sportsfield capacity.

Also yesterday, committee member Cr Bill Acklin questioned whether it would be better to bring forward work on the buried backstop wall and managed retreat.

That would allow funding of $250,000 a year - included in the council's draft long-term plan for the next decade - to be used to offset loan servicing costs to pay for the major work, he suggested.

However, Mr Reece said the annual sum in the draft budget was a contingency fund, and might not need to be spent from year to year.

Delaying the work by up to a decade would also allow more data to be collected, helping shape the best options to protect the coastline.

It was possible work could be brought forward when the council's financial position was "more favourable", and work on consents and designs could begin in the meantime, he said.

Following the deliberations, committee chairman Cr Colin Weatherall asked staff to report back in June with recommendations.

chris.morris@odt.co.nz