Work to strengthen, raise and reshape the stop bank at Boundary Creek, north of Mataura, is expected to be complete by the end of February.
Improvements to the Boundary Creek stop bank are among several works Environment Southland are undertaking to upgrade the stop banks protecting the town of Mataura (population 1500+). The stop bank has also been extended to the west by 380 metres.
Extensive flooding in Southland in February 2020 saw stop banks in Mataura tested by floodwaters to near capacity, with the largest volume of water to pass under the Gore and Mataura bridges in recorded history. Emergency management and council staff, alongside Southland emergency services, evacuated 1500 residents in Mataura alone and 4500+ throughout the Mataura catchment.
Environment Southland catchment operations manager Ramon Strong said, “Stop banks throughout the Mataura catchment performed well during the 2020 floods. They did for the most part what they were supposed to do, which is to provide protection against flooding up to a specified level. However, the Boundary Creek stop bank was breached by water coming over the top and around the western end. Boundary Creek was a logical place to prioritise planned upgrades and the most straightforward in terms of scale, design and approvals.”
“We know that climate change will bring more intense flooding for longer periods to Southland. These upgrades will increase the protection standard for the town to align with climate change projections,” Mr Strong says.
Additional works to protect the town will include 800+ metres of engineered rock edge protection to stabilise both banks and upgrading the Mataura Terrace and Selbourne Street stop banks.
The work will also involve strengthening and reshaping the Waimumu stop banks. Survey work of the Gore and Wyndham stop banks begins this week, prior to planned upgrades by Environment Southland.
The Mataura Flood Protection Upgrade is a Resilient River Communities project, one of six Climate Resilience projects being delivered by Environment Southland.
Other upgrades and repairs include flood protection infrastructure in the Mataura, Waiau and Waihopai catchments and construction of a pump station near Invercargill airport.
These projects are co-funded by Environment Southland and central Government, through Kānoa (the Regional Economic Development & Investment Unit within the Ministry of Business, Innovation and Employment).
Beginning this week, Cook Costello will begin a geophysical survey of the Gore and Wyndham stop banks using several high-tech methods to capture soil profile images of the stop bank and foundations, removing the need to drill or excavate.
Through these techniques potential weaknesses in a stop bank’s structure can be more thoroughly assessed, with the work needed to address any issues incorporated into the final designs for the upgrades.
Stop banks are a critical part of Southland’s flood defences, providing a level of security in the face of potentially devastating flooding effects. In urban areas they protect homes, businesses and infrastructure, while the rural schemes protect the land and property outside the stop banks.
The survey work in Gore and Wyndham is expected to take up to three weeks, and the Wyndham stop bank upgrades will be underway this year.