Heavy seas and high winds mid-November exposed a large section of the old Cobden rubbish dump along the foreshore.
A staff report to the Grey District Council this week noted "a significant amount" of coastal erosion currently.
"Staff are having the area surveyed to determine the full extent of the erosion. The West Coast Regional Council was immediately notified," the report said.
Cobden resident Marie Tern said the area had been steadily eroding for quite a while and was somewhat surprised council seemed unaware of it when she contacted them about it last week.
"I was sort of gobsmacked that the council didn't know anything about it," she said.
"It's been going on for the last few months. Every big tide or high sea takes away another metre or so."
Ms Tern said what particularly grabbed her attention last week was large pieces of plastic protruding from the eroded face of the mound of the old dump.
The erosion is most evident along the beachfront, south of the rock work fronting the Jellyman Park car park and past the old dump mound towards the tiphead.
"Apparently this is partly due to the fact that there hasn't been a recent, notable river flood to create offshore gravel banks, which in turn mitigate the effect of big tides on the beach."
While work was apparently in the wings to extend the rock wall, it needed addressing now or it could turn into a disaster with debris carried up the spectacular Punakaiki coast on the northward drift.
"They can't just leave it."
The area was used from the 1970s until the 1990s as a rubbish dump.
Ms Tern pointed out that quite toxic materials were routinely dumped in landfills during that period.
The report to council this week said "corrective actions" cleaned up and removed loose waste material and "the remaining exposed material was covered over". A "way forward" was now being assessed.
"If a seawall is to be constructed to protect the old waste mass the cost will be in the hundreds of thousands of dollars," the report said.
West Coast Regional Council consents and compliance manager Heather McKay, said they would be keeping an eye on the area.
"Grey District Council advised that they were cleaning up the site and would be considering what needed to be done long term. We will follow up as needed," Mrs McKay said.
Last June, the Grey council decided to apply to for funding to study erosion of the foreshore from Jellyman Park towards the Cobden tiphead after it notified the regional council of its concerns.
A month later severe erosion of the frontage for Jellyman Park, immediately north of the old dump, saw council do some rock wall work.
A Niwa report for the regional council tabled in June this year noted Cobden Beach as "relatively healthy" and not experiencing widespread erosion.
However, it noted the defences around the recently improved car park at Jellyman Park continued "to interfere" with natural beach processes.
- Brendon McMahon
