River engineers are concerned a 600-metre section along Mataura River could fail if high river flows cause erosion. (file picture) Photo: RNZ / Tess Brunton
A Southland community is being warned to be prepared to evacuate their homes at lower river flows than they might have in the past, and at short notice following erosion concerns for its stop bank.
A recent report found no obvious structural damage to the stop banks on the Mataura River following flooding in 2020.
But river engineers are concerned a 600-metre section along Mataura could fail if high river flows cause erosion, flooding upstream of the old paper mill on the true left bank.
Environment Southland commissioned the geophysical report in September.
Integrated catchment management general manager Paul Hulse said the council was immediately procuring 27,000 tonne of rock for a permanent solution for the Mataura township.
The work would begin as soon as possible in 2023, but an active monitoring programme was already in place.
"Engineers are monitoring the stop banks weekly, and will move to daily monitoring if river levels and weather forecasts change," Hulse said.
"It is reassuring to know that the stop banks are sound, but our immediate concern is the risk of erosion.
"Our message to the Mataura community is the same as it has been since we first identified a potential issue, earlier this year: 'Be prepared to evacuate your homes at lower river flows than you might have in the past, and at short notice'."
Emergency Management Southland makes the call about when and if to evacuate and will be informed of rising river levels and flows, which are monitored around the clock.
On Tuesday, Environment Southland delivered supporting information to letterboxes in the Mataura community on the left bank.
They will be hosting community drop-in sessions in February to discuss the issue and solutions.