The radical shift of the Waiho River at Franz Josef in the past 10 days and what can be done about it remains an open question for local authorities.
However, West Coast Regional Council officials are now commissioning new technical Lidar information on the trajectory of the riverbed — to be undertaken in the middle of next week.
A full assessment of the river’s shift into the Tatare by council engineering staff and members of the Waiho River Technical Advisory group will be done on February 8-9.
In the meantime council engineers will be assessing the existing Millton and Others stopbank on the south side to undertake maintenance.
That stopbank, which protects the Franz Josef aerodrome and Waiho Flat, has been left high and dry after 95% of the river’s main channel swung north.
The shift emerged by January 24 as the floodwaters receded from the January 19-20 ‘red alert’ weather event.
Council chief executive Darryl Lew said training the river back to its normal course is not yet on the radar but council is seeking further technical information.
Lew said any options to address the river’s change would have to be put to the Franz Josef Joint Committee, including Ngāi Tahu, Westland District, and the NZ Transport Agency, for its recommendation prior to coming to the council table for final approval.
“In terms of what to do with the avulsion, staff will not be making any decisions,” he told the January 29 council meetings.
“I understand there are people who say we should leave it alone, it’s doing what it is doing… staff have no ability to make any decisions on that.
“Whatever we do is a decision at a later date at this council table.”
Chairman Peter Haddock said it was difficult to say if the avulsion of the Waiho into the Tatare Stream was “a good thing or bad thing”.
“I really don’t know. The benefit, I suggest, with the river stretching over to the north bank, it allows evaluation of the south bank,” he said.
He noted the $8.77m previously allocated by Kanoa for a co-funded scheme “to buy time” for Waiho Flat on the south side of the river remained allocated for that area, under the 10-year Waiho River Management Strategy.
In the “worst case scenario” the main flow of the Waiho north into the Tatare could end up in Lake Mapourika or even Okarito. Meanwhile, Lake Pratt, next to the Tatare Stream was receiving sediment from the new Waiho River channel, Haddock said.
Lew said staff continued to monitor the situation, but commissioning fresh Lidar information once the river level dropped and undertaking “a good inspection” of the south banks was their first priority.
Haddock said he did not believe what had happened with the river’s radical shift north would require a response beyond a local one and “some informal discussions” with Government representatives had begun.
The adverse publicity about the area in the past fortnight, including weather forecasts, had turned visitors away.
However, Haddock said it had been “business as normal” at Franz Josef and there was currently no risk to the tourist hot spot.
Lew said the strategic plan is to eventually retreat from the south side starting in 10 years, and to pull down the stop banks to let the river run over Waiho Flat.
“It still remains the objective that we don’t continue with that plan to strengthen the south side banks.
“A flood tomorrow could see the water come back within the Waiho and back to it’s normal channel. The river will do what it will do.”
The council was working to get a meeting with the appropriate Government ministers to advance the 10-year strategy.
Lew said council was also looking to pencil in a fresh meeting of the Franz Josef Joint Committee in February.
By Brendon McMahon, Local Democracy Reporter
Local Democracy Reporting is local body journalism co-funded by NZ On Air and RNZ