If there is no action soon, a breach of the ponds could effectively close down the tourism industry and ruin its reputation, West Coast Regional Council representatives have been warned.
The warning came after the regional council wrote to the Westland District Council last August about the worsening situation as the river’s channel changed course to flow into the neighbouring Tatare River.
The combined flow is now steadily advancing towards the Franz Josef wastewater treatment plant, built by the district council right on the edge of the Waiho River.
The Waiho began flowing into the Tatare about two years ago and since then 95% of the main river, which flows directly from the Franz Josef Glacier, has continued in that direction while also cutting upstream to run hard up against the Havill Wall, built to protect the wastewater plant and sewage ponds.
West Coast Regional Council chief executive Darryl Lew told the Greymouth Star prior to the council’s operations committee meeting this week that the formal advice was the threat to the ponds was now "very urgent".
"I really want to stress that’s advice from technical experts," Mr Lew said.
Capital programme manager Tom Hopkins told councillors the latest satellite-based modelling showed the Waiho’s changed course had advanced eastwards by up to 65m along the true right (north) bank since October.
This placed the advancing river right into the path of the sewage ponds.
"We expect that lateral erosion to continue to the east towards Havill Wall and the wastewater treatment plant," Mr Hopkins said.
The riverbed had also deepened as it continued its eastward pattern into the Havill Wall.
Mr Lew told councillors the resulting risk to the ponds was now immense.
"I’ve got to express significant concern about the progression of the avulsion, and 65m of further lateral erosion in three months is very significant and probably exceeding what we were predicting," he said.
"It’s got to be recognised ... there is significant risk."
The lateral erosion risk meant Franz Josef as a tourism service centre "is compromised", Mr Lew said.
"We have a real risk now with the rate of this back-cutting erosion, in very, very moderate rainfall times."
A single significant flood soon could have a dire effect.
"I want to state for the record real concern about the risk to the oxidation ponds now.
"I think it’s a risk to the town, to the tourism of the West Coast and the economy of the West Coast."
Cr Allan Birchfield questioned the advice and said he thought the risk was being exaggerated.
However, Mr Lew reinforced the expert basis.
Council chairman Colin Smith said the more he learned, "the more concerned I become for the Franz Josef community and the industry that relies on it".
The present situation had "serious implications" for the viability of Franz Josef tourism plus the wider Hokitika tourist service economy and the entire West Coast sector.
"Because if there is a breach of the sewerage ponds then that will effectively close down tourism in Franz Josef.
"And not only that, a significant effect on brand West Coast in terms of tourism going forward."
Cr Chris Coll, a surveyor, said he wanted to see ground monitoring as relying on weather-dependent satellite data alone was "risky".
"Is it accelerating, is it steady or is it slowing down?"
Cr Andy Campbell said local opinion, including sentiment on the risk to the ponds, was that it was "a joke".
"Who do you believe?"
Cr Ewen said he agreed with Cr Coll.
But given 95% of the main river had now moved north, a big event now could mean the oxidation ponds problem could now "creep up very quickly".
He noted the April 2016 breach, where the Waiho had ruined the oxidation ponds.
Mr Lew said he was relying on the consulting engineer and the Waiho Technical Advisory Group that the avulsion would continue to develop and would intercept and undermine the Havill Wall.
"All I can do is tell you what very, very experienced engineers are telling me."
Cr Smith said the council was now working "very actively" with the Westland District Council on a plan to re-site the ponds.
"But that’s not an overnight outcome, so in the interim we need to ensure via the most appropriate means to continue to keep those ponds while that planning is undertaken."
Westland District Mayor Helen Lash said both councils had been communicating informally on the matter, including meeting Mr Lew and Cr Smith last week. — Greymouth Star
