Issues with stop banks another reason to be prepared for floods
Media release
11 August 2022
Issues with stop banks another reason to be prepared for floods
Southlanders in the Mataura catchment are being urged to prepare for flooding events. An evaluation of the stop banks by specialist engineers has identified concerns about their capacity.
Environment Southland general manager integrated catchment management, Paul Hulse, said as part of the climate resilience works being undertaken, investigations have been carried out including assessments by flood protection experts. These investigations have highlighted that further work, including detailed geotechnical investigations and 2D hydraulic modelling, 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, while we continue to better understand the current capacity of the stop banks.
“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 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. We now have good information on the likely impacts of climate change and we also know that we are in a cycle of increased flood events and high river flows as a result of the Interdecadal Pacific Oscillation, an oceanographic/meteorological phenomenon.
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 will need to be done.
“We now know that the frequency of flooding events is likely to increase and we will be working closely with Emergency Management Southland to take a precautionary approach to keeping our communities safe.”
Emergency Management Southland will make any decisions about when and if to evacuate and will lead any evacuation. Each situation will be assessed on a case by case basis, as it is not possible to predict conditions for every situation.
“Where we are fortunate, is in being able to predict how quickly flood waters travel and 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 that we can quickly and effectively evacuate these communities, having done it most recently in 2020 within a couple of hours.
“Our catchment team is gathering the necessary information, including geotechnical data and hydraulic modelling, to help us establish the best options to protect these areas in the future. We already have a work plan underway 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. We need more data before we can consider what the remediation options here might be,” Mr Hulse said.
As part of being prepared for emergencies, Emergency Management Southland encourage all of the region’s residents to have a plan, gather supplies and to get connected (go to cdsouthland.nz). Being prepared will help to make any evacuation easier and less stressful.
We will be holding a number of drop-in sessions for people to come along and ask questions to help them better understand the current situation. These will be held in Mataura, Gore and Wyndham and details will be advertised and available on our website as soon as possible.
