A warning sign for people to stay away from the bed of the dangerous Waiho River, just west of the State Highway 6 bridge at Franz Josef. Photo / Brendon McMahon
A warning sign for people to stay away from the bed of the dangerous Waiho River, just west of the State Highway 6 bridge at Franz Josef. Photo / Brendon McMahon
West Coast Regional Council chairman Peter Haddock said about 50 per cent of the main channel had returned to the Waiho Flat side.
He said a new survey had also just revealed more than 1 million cubic metres of sediment had built up upstream of the State Highway 6 bridge and needed to go somewhere.
Yesterday, Haddock said he was due to be briefed on that, including how far upstream it was of the bridge.
Waiho Flat resident Richard Molloy said a large portion of the river’s main channel suddenly switched back to the south side late last week.
The braided river bed is known for sudden shifts and raised alarm for the Westland District Council after most of the river swung north close to the Franz Josef sewerage ponds in late January.
Molloy said the latest shift happened overnight Thursday, with the channel splitting about 1km below the State Highway 6 bridge.
Molloy said the river had largely moved away from the Westland District Council Franz Josef sewerage ponds area on the north side as of yesterday.
Council chief executive Darryl Lew could not be reached for comment yesterday, but Haddock said the sudden shift was no surprise.
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“It’s a dynamic braided river,” Haddock said.
He had enlisted a local helicopter operator at the weekend to confirm to him the river’s main channel had split just below Franz Josef township.
About 50 per cent of the flow was south past the Waiho Flat, Milton and Others stopbank, with the rest of the main flow still going north via the Tatare Stream, Haddock said.
Waiho River sediment build-up
The gorge of the Tatare Stream augmented by 95 per cent of the Waiho River flow after the river shifted north in late January. In the distance is the Waiho Flat farming area. Photo / West Coast Regional Council
Meanwhile, the new Lidar imaging of the river in the gorge upstream of the bridge revealed 1.05 million cubic metres of sediment built up in the past six months, he said.
Haddock said he had an urgent meeting on Friday with Regional Development Minister Shane Jones.
This was also to brief the pending formal approach to Government about plans to abandon Waiho Flat in about 10 years by pulling down the existing stopbanks to let the river flow south.
“It’s a dynamic braided river that is carrying a lot of sediment,” he said.
“We stressed that to the minister: it’s a one-off type of river. Long term you can’t continue with that river carrying that much - it will continue to build up.”
Haddock said the huge buildup of sediment needs to go somewhere, but a lack of natural flushing and the barrier of the Waiho Loop glacial moraine were inhibitors.
An aerial view of the Franz Josef sewerage ponds, right, with the Waiho River running along the north bank, 10 days ago. Photo / West Coast Regional Council
“The minister did ask if it was an opportunity to dredge the river out.”
Haddock said the many thousands of truck movements needed for such an operation made it impossible to contemplate.
Meanwhile, Molloy criticised the council for being too slow to do urgent maintenance on the Waiho Flat stopbanks while the riverbed had been dry.
Molloy said this slow approach caused “the biggest frustration” and he accused council of not knowing “a bloody thing about this river”.
However, Haddock said its engineering team had urgently assessed the south bank stopbanks and they were moving as quickly as possible - including pushing for the release of $8.77 million Kanoa funding set aside for the area.
“I know people are criticising, but they’ve got to do a proper evaluation and for a costing on that work.”
He said he expected the council may see a proposal at a committee meeting today.
- LDR is local body journalism co-funded by RNZ and NZ On Air.
