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A lot of volunteer help has been given to farmers and landowners with flood damage, but there is still much to be done, Environment Canterbury councillor Ian Mackenzie says.
Many who had land inundated with shingle from redirected waters were in need of diggers and dozers to remove it and some of the damage in the hill country could take years to fix or heal.
Although rivers had been made safe for now, it was a temporary measure and a plan was being developed “with some urgency” to improve the resilience of the damaged flood protection infrastructure, he said.
“Landowners have been encouraged to report any concerns about weaknesses in the river banks to the [ECan] engineering team,” he said.
An initial review of the performance of the flood protections infrastructure suggested it did what it was designed to do, Mr Mackenzie said.
“Though this may be cold comfort to those immediately below a breach.”
The stopbanks protecting Ashburton and Tinwald were designed for a 1-in-200-year flood, which it was, and they held, he said.
“The floodbanks protecting the rural areas are designed for a 1-in-50-year event. Clearly a 1-in-200-year event is going to get out and that’s what this flood did.”
Most of the river flooding followed existing flood channels but, in a couple of places, the river breached stopbanks in unpredictable ways.
The breach north of the Ashburton River north bank, towards the Methven highway, was an example of that, he said.
ECan has come under increasing criticism over river management but Mr Mackenzie said this needed to be tempered with an understanding of the funding position.
Shingle buildup in the north branch had been ongoing for more than 100 years. But for many years commercial interests removed shingle from the river to maintain flood protection capacity.
In the past 10-15 years alternative sources for shingle, and easier to access, had been found, and there was less commercial interest to remove sufficient shingle to keep the river in a preferred state.
The river rating district would need to fund another $1million per year, double the existing budget, to provide sufficient funds to remove shingle buildup.
“The river rating district, with some justification, argued they couldn’t afford that,” he said.
A workshop, timed for June, was set to review funding options for the Ashburton River to find solutions, but “the floods have intervened”.
Historically, the Ministry of Works funded a significant amount of flood protection infrastructure but this stopped in 1989. Since then the value of assets protected by floodbanks had increased exponentially, Mr Mackenzie said.
“As has the public’s intolerance of getting wet.”
“[ECan], alongside Local Government New Zealand [which represented 78 local, regional and unitary authorities] are developing a case to propose to central government that there is a case for them to assist with this increase flood protection as a tangible and proactive way of addressing some of the challenges of climate change,” he said.