Calls for more flood protection along the Mataura River

By Monique Steele of RNZ

Officials are working to bolster flood resilience for communities living along Southland’s Mataura River, in light of some community pushback over worst-case scenario flood modelling.

Rural service township Gore, with a population of more than 8300, is bordered by the 240km river, considered a fisher’s paradise for brown trout.

But a history of significant flooding in nearby townships Gore, Mataura and Wyndham, dates back to 1957, 1978 and most recently in 2020.

A heavy rainfall event in September 2023 prompted evacuations, while floodwaters overwhelmed the area’s stormwater and wastewater systems.

Nationwide, councils were legally required to manage flood risks in planning decisions, especially with more frequent adverse weather expected because of climate change.

It was costly work and could impact people’s property values, especially in areas confirmed to have flood risk.

The Southland Regional Council recently completed work to widen a section of the river channel south of the main bridge entry into Gore, removing nearly 22,000cu m of sediment to increase flow capacity.

Meanwhile, the district council’s proposed plan required new builds in the Gore township to be constructed metres higher than what many were now, so they were prepared for a one-in-200-year flood.

The flood modelling scenario and subsequent construction requirements for those in the flood zone prompted some appeals against the plan.

Gore Mayor Ben Bell said regardless of the plan process outcome, flood risk management would need to be looked at.

“We will have to have a conversation as a community around whether Southland spends a lot of money on flood mitigation, which in my personal opinion I think is a good thing. I think that you can mitigate the Mataura River,” he said.

“Or whether it is that managed retreat.”

He said locals and riverside farmers would be impacted by future flood resilience decisions.

“We have a very large catchment, so there’s lots of opportunity to do river mitigation further up,” he said.

“But it’s really the responsibility of the regional council to get on with that and listen to the views of the community.”

Bell said other districts such as Buller on the West Coast lacked flood mitigation options, so were having more active conversations around managed retreat.

One district plan appellant, advocacy group Groundswell, awaited mediation proceedings with local government officials.

Last week, it took a petition against Gore’s flood modelling requirements with more than 3200 signatures to the district council chambers.

Co-founder Bryce McKenzie said the requirement to plan and build for a one-in-200 year flood was unworkable and put a “massive burden” on residents in the flood zone.

“There’s things that we think could be looked at rather than put all the cost and burden on to the residents that live in that zone,” McKenzie said.

He said more flood mitigation work had to be done in affected areas, like removing mud and gravel from the Gore bridge’s piers.

“[The regional council’s] just done some widening of the river at the bottom end of Gore, and they claim that’s going to increase the flow by 13%.

“Flood banks could actually be widened and even made a bit higher as well,” he said.

“There’s always been opposition to cleaning rivers out. But let’s face it, if we don’t start doing that, we’re going to be in major trouble.”

Further flood mitigation work underway

As part of the Mataura River Flood Resilience project, Environment Southland was now reviewing 14.5km of flood management assets including stopbanks, many of which were owned by the Gore District Council.

It would also assess existing mitigation infrastructure and identify improvements needed.

The project had about $10.8 million in Government co-funding, with $7.2m from Environment Southland.

Environment Southland said some flood assets were upgraded in Gore, Mataura and Wyndham between 2021 and 2024, also supported by Government co-funding.

General manager of integrated catchment management, Lucy Hicks, said climate change was expected to bring more intense rainfall, larger floods and more frequent severe weather events.

She said the Matarua River Flood Resilience Project would be delivered in stages to improve resilience.

“The river has a long history of overflowing onto its floodplain,” Hicks said.

“As communities, businesses, farmland and infrastructure have developed alongside the river, the consequences of flooding have become more significant.

“Ongoing investment in maintenance, upgrades and targeted adaptation is needed to sustain agreed service levels, recognising that flood defences reduce effects but cannot guarantee protection in all events.”

Hicks said it expected to complete a list of possible works by mid-next year.

“[The project] will help identify potential future work and may support subsequent business cases and applications for Government co-funding.

“Any future projects would remain subject to further investigation, funding decisions and necessary approvals. This process will be commencing in the next three months.”

She said the Mataura Blueprint will bring together technical information, community perspectives and other evidence to inform longer-term flood-risk decisions and investment, and was expected to be completed by mid-2028.

The regional council was also purchasing new river-level and rainfall monitoring sites and cameras, with funding from a separate co-funded $500,000 Mataura Flood Warning Network Resilience Project.

This story was first published on rnz.co.nz