Gore flood protection upgrade
Environment Southland is upgrading the existing stop banks in the town of Gore (population 7300 +). The aim is to provide a more robust and continuous flood defence scheme for Gore by focusing on areas that present the most risk to the community in the event of flooding in the near term.
The Gore flood protection upgrade is a Resilient River Communities project. Resilient River Communities is a joint initiative between Kānoa - the Regional Economic Development & Investment Unit, regional councils, and local authorities focused on developing and upgrading vital river management and flood protection schemes in Aotearoa New Zealand.
By having resilient river communities, we hope to minimise environmental, economic, and social damage caused by flooding – making New Zealand safer for everyone.
The stop banks in Gore protect the main road and rail bridges that provide vital links between Murihiku Southland and the rest of the country.
Very high flows in the Mataura River in February 2020 saw Gore's stop banks tested 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 more than 2500 residents close to the river for a minimum period of 24 hours. Fortunately, the stop banks did a good job protecting those adjoining communities from river flooding, but damage to them was costly and time-consuming to repair.
The priority areas of work to late Spring 2023 are:
- Construction of new stop bank along Ontario and Toronto Streets to replace the existing concrete flood protection wall
- Alterations, replacement and installation of existing and new storm water culverts
- Removal of high-risk trees and tree stumps on the true right stop bank in Gore township along River and Richmond Streets
The planned tree removal, completed in April-May 2023, was part of our wider maintenance programme, which involves assessing trees on stop banks throughout the region. Work to remove the remaining tree stumps and re-grass these areas is expected to be completed by November 2023.
Trees and shrubs on and close to stop banks can interfere with the integrity of the stop bank and potentially lead to the banks failing. The roots of trees and vegetation can weaken stop banks; during a flooding event, water can begin flowing through this weak patch, often leading to a rapid failure. Trees can also be toppled in heavy winds, creating holes for water to flow through. Tree debris becomes a hazard during a flood, which can cause damage to infrastructure.
There will be some disruptions to the movement of traffic, cyclists and pedestrians while the work is underway. We will implement temporary traffic management plans to mitigate the increase in heavy transport vehicles and construction machinery, resulting in increased travel times. Temporary road, footpath and cycle track closures and detours will also be necessary.
- The upgraded flood protection network will provide adequate near-term protection for Gore's community, infrastructure and property against floods up to the current design level
- The design of the proposed works is 'future proofed', meaning that the height of the upgraded stop banks could be more easily raised in the future if appropriate
- Work completed with central government funding assistance
- Alignment with Gore District Council's flood-proofing work
Project status (15 September 2023)
- Establishment of a collaborative working group with Gore District Council
- Survey, geotechnical and engineering design work completed
- Engagement with landowners ongoing
- Community engagement ongoing
- Construction contract awarded to Linton Contracting Ltd. December 2022
- Public drop-in sessions to inform the community about associated stop bank maintenance, including removal of high-risk trees, in late February 2023
- Tree work completed April-May 2023
- Alterations, replacement and installation of existing and new storm water culverts completed
- Construction of a new stop bank along Toronto and Ontario Streets underway (May 2023), including the transfer of gravel from the gravel island downstream of Mataura Bridge
- Completion of earthworks for new stop bank along Toronto and Ontario Streets expected by mid-October, and re-grassing and re-fencing as weather and ground conditions permit
- Removal of tree stumps and associated earthworks on River and Richmond Street stop banks to be completed by November 2023
- Completion of 2D hydraulic modelling for the Mataura, including Gore
- Further community engagement
- Use 2D hydraulic modelling to better understand the capacity and integrity of existing flood protection infrastructure and determine the best design solutions for the next phase of climate resilience work