Residents of Gore, Mataura and Wyndham may need to be evacuated from their towns at a lower flood river level than they have previously, after Environment Southland found issues with the capacity and integrity of stop banks on the Mataura River. (File photo)
Issues with the integrity of stop banks mean residents in three eastern Southland townships may need to be evacuated at a lower flood river level than before.
Environment Southland as part of climate resilience works had flood protection experts investigate, and it was found further work including detailed geotechnical investigations and 2D hydraulic modeling, needs to be undertaken urgently to better understand the capacity and integrity of the stop banks.
This means that urban communities in Gore, Wyndham and Mataura may need to be evacuated at a lower river level than they have previously, but that new level has yet to be specified.
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ES integrated catchment management general manager Paul Hulse said: “We know that most of our stop banks are at least 30 years old, and they have some design limitations that may reduce their ability to hold large volumes of water or sustained volumes of water, putting the community at increased risk of flooding.
The stop banks at Gore, Mataura and Wyndham on the Mataura River, were designed to address flooding issues at the time, and increased, and more extreme weather events as a result of climate change have put them under pressure, he said.
The February 2020 floods on the Mataura River have contributed to the stop bank situation and, while some remedial work was carried out soon after this, more work would need to be done, he said.
Any evacuations would be handled by Emergency Management Southland and each event would be handled on a case-by-case basis.
The council is however, saying residents in these areas should be prepared for evacuations in the future. Drop-in information sessions will also be held in the towns in the future to discuss the stopbanks and how to be prepared.
Mataura resident Laurel Turnbull, who was evacuated in the 2020 floods, the council needed to dredge the river to get rid of gravel in it, and that would alleviate flooding concerns and pressure on the stop banks.
The gravel was now one meter deeper at the town’s bridge than it was after the 1978 floods.
“Everyone is complaining about how Environment Southland’s councilors are doing nothing about it, from right up to the top of the river down to here. There’s a gravel bank growing into a gravel mountain here at Mataura after the 2020 floods and they have done nothing about it.”
ES catchment operations manager Randall Beal said he was aware of the gravel build up south of the township that Turnbull referred to, and while it was causing some riverbank erosion, it was not threatening any stop banks.
The council had engaged a contractor and consultant to prepare for global consent to take gravel from rivers after the February 2020 floods and that work was still underway.