The flooded Scenic Circle Mueller Wing on 23 March, 2016, after the nearby Waiho River broke through a stop bank and flooded the hotel complex. Photo: Greymouth Star/Brendon McMahon
A hearing opened on Friday in Greymouth to try and advance the stalled river protection project which would protect Franz Josef township for another 20 years.
The West Coast Regional Council project to improve and extend the Waiho River northern stop banks is to give the township more security ahead of a bigger decision about the viability of remaining where it is as the river bed continues to steadily aggrade.
The project has been on the books for three years since it successfully bid for $24 million of government money as part of a wider Waiho River protection scheme.
Council awarded a contract in May 2022 for the northern bank work start but it has partly stalled due to affected landowner Scenic Hotel Group declining late in the year to give affected party approval for the necessary resource consents.
At the time, in November last year, the insurers for Scenic Circle and the West Coast Regional Council second respondent the Westland District Council were in dispute over an unsettled $30million claim in damages.
This was a result of the March 2016 flood which ruined Scenic's Mueller Wing when the Waiho swung through the current stop bank by State Highway 6 and flooded the hotel.
However a confidential settlement of the $30m claim against both councils was reached earlier this year.
Under the northern bank Waiho scheme the regional council proposes to raise the height by 2m the existing stop banks, plus an extension from the SH6 Waiho River bridge to below the Westland District-owned Franz Josef wastewater treatment plant.
The Scenic Group hotel's Mueller Wing during flooding at Franz Josef in March 2016. Photo: Supplied/ Local Democracy Reporting/ West Coast Regional Council
The existing stop banks are collectively the Anglican Church, Franz Josef Helipad and Havill walls.
In a brief of evidence being presented for the regional council at the hearing today, senior hydraulic engineer and geomorphologist Dr Dai Thomas has outlined the proposal.
It includes erecting a new section of wall and raising the height of the existing walls by 2m to an average height of 6m.
It would mean the existing walls with the extension downstream increasing the length of stop bank protection skirting the township to about 2.3km.
The existing stopbanks will have rock protection placed on the river side, extending from the top of the existing rock to the top of the raised stopbank.
However the toe down depth of the rock along the existing stopbanks is unknown, Thomas said in his evidence.
"The council indicated that it is thought to be between 4 and 6 m."
The existing NZ Transport Agency stop bank which runs parallel with SH6 will not be altered.
According to other evidence the hydraulic conditions used as the basis for the design of the stopbanks is based on hydraulic modelling of the output of the Waiho River, for the regional council.
It was based on the river's geometry in 2021 and based on predicted sediment aggradation trends over a 20-year period.
"Due to ongoing aggradation of the Waiho River - and future aggradation which cannot be accurately predicted - the existing and new stopbanks have a finite lifespan," Thomas said in his evidence.
The proposed design for the northern stop banks improvement and extension was "a short-term measure" of 20 years, while longer term options are considered.
"The average raise of 2m for the existing stopbanks was selected to optimise the quantity of available rock, minimise impact on private property, and because it will provide sufficient protection at the design discharge including with the predicted 20-year aggradation," Thomas said.
Local Democracy Reporting is Public Interest Journalism funded through NZ On Air.