Mataura River stop banks

In August 2022, an evaluation of the Mataura River stop banks by a specialist engineer was received that identified concerns about their capacity.

The evaluation was part of the climate resilience works undertaken, which included investigations by flood protection experts. The investigations highlighted that further work was required urgently to better understand the capacity and integrity of the stop banks.

Most of our stop banks are at least 30 years old and were designed to address flooding issues at the time. Challenges such as increased and more extreme weather events as a result of climate change have put them under pressure.

There is now good information on the likely impacts of climate change. We also know that we are in a cycle of increased flood events and high river flows due to the Interdecadal Pacific Oscillation, an oceanographic/meteorological phenomenon.

The stop banks held up well during the February 2020 floods on the Mataura River, but some remedial work was carried out in some areas.

Our catchment team is gathering the necessary information, including geotechnical data and hydraulic modelling, to help us establish the best options to protect Gore, Mataura and Wyndham. We are already working to a plan for the Gore stop banks, but the Mataura situation is a bit more complicated for a number of reasons, including the proximity of the stop bank to the road. Following the evaluation, we sought more data so that we could be clear about the appropriate remediation options.

We received the preliminary geophysical report in November 2022 and, on that basis, confirmed that there is no apparent structural damage to the stop banks on the Mataura River as a result of the 2020 flood event. However, river engineers did raise concerns about a 600 m of river bank upstream of Te Au-Nui-Pihapiha-Kanakana / Mataura Falls. High river flows could create erosion, leading to the stop bank's failure and the township's flooding on the true left bank– upstream of the old Mataura paper mill.

In mid-January 2023, councillors and staff from Environment Southland and the Gore District Council, as well as members of the Mataura Community Board and Hokonui Rūnanga, all visited the site and were updated about the strengthening work being undertaken.

The rock strengthening work was completed in October 2023.

Read the complete Mataura flood protection flyer here.

Community safety – evacuation

Because the frequency of flooding events is likely to increase, we are working closely with Emergency Management Southland to take a precautionary approach to keeping the communities of Gore, Mataura and Wyndham safe.

This means that people living in these communities may need to be evacuated sooner and at a lower river level/flow than they have previously, while we work to better understand the current capacity of the stop banks.

Residents across all communities, as part of being prepared for emergencies, are encouraged to prepare for evacuation. Have a plan, gather supplies and get connected – go to the Emergency Management Southland website for more information. If any evacuation does need to happen, being prepared will help to make it easier and less stressful.

In the event of a flood event, Emergency Management Southland (EMS) will make the decisions about when and if to evacuate and will lead any evacuation. EMS can provide advice to people to evacuate and once a state of emergency is declared by the mayor, EMS can make evacuation mandatory. Each event will be assessed on a case by case basis, as it is not possible to predict conditions for every situation.

We do have some factors working in our favour, including being able to predict how quickly flood waters travel. Our hydrological team will know up to 12 hours ahead of time, what the situation is likely to be around the catchment. We also know from experience during the 2020 floods that we can quickly and effectively evacuate these communities within a couple of hours.

Read the Gore District Prepare to Evacuate flyer here.