Wyndham flood protection upgrade
Environment Southland is upgrading existing stop banks in Wyndham township (population 550 +). The aim in the near term is to provide a more robust and continuous flood defence scheme by focusing on areas that present the most risk to the community in the event of flooding in the short term. Once completed, the re-grassed stop banks will appear similar to the existing structures.
Wyndham 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.
Extensive flooding in Murihiku Southland in February 2020 saw stop banks in Wyndham tested by floodwaters to near capacity. Emergency management and council staff, alongside Southland emergency services, evacuated 4500+ people throughout the Mataura catchment, including residents in Wyndham.
The Wyndham stop banks were built in the early 1970s following widespread flooding in 1968. They were raised again after severe flooding hit the region again in 1978. The stop banks guard the town against the Mataura River to the north, west and south and its tributary, the Mimihau Stream, to the north.
The work
- Widening the stop bank east of Wyndham Road and extending it 100 m east. This section of stop bank has low points, ponding, and areas of cattle pugging.
- East of Wyndham Racecourse, three sections of stop bank are being widened, with buttresses constructed at the riverward toe. The work will address seepage at a section of stop bank east of the racecourse and an area with potential stability issues close to Mimihau Stream.
- North and west of Wyndham Racecourse the stop bank has low points, cattle pugging and instability. Several stands of trees have grown close to the base of the stop bank, some of which have been felled. The stumps and roots have the potential to affect stability and increase seepage. Works involve removing trees, tree stumps and roots close to the stop bank and reconstructing the stop bank throughout this entire section.
- At Ferry Street, an approx. 90 m new section of stop bank is being constructed to fill a gap in the existing network. The drain which runs west of the new section of stop bank will remain in place. However, recently planted vegetation near the new stop bank requires uplifting and replanting nearby.
Inspection, repair and extension of the existing culverts, headwalls and flapgates and associated flood protection infrastructure are being undertaken along with the remedial works.
Benefits
These upgrades will:
- Provide greater protection for properties, homes, and businesses in Wyndham by increasing the resilience of the current flood protection scheme.
- Provide flood protection where there is none by filling in gaps in the existing stop bank network.
- Enhance our ability to adapt to a changing climate and plan future asset upgrades.
Funding from central government has enabled this work to be brought forward in the Long Term Plan and delivered at a much lower cost to ratepayers.
Physical works completed 30 May 2023
During the 2022-23 construction season, we have:
- Sourced and stockpiled sufficient stop bank materials for the project.
- Contracted Linton Contracting.
- Commenced bulk earthworks: widened the stop bank east of Wyndham Road and extended it 100 m to the east (section 1) to fix low points, ponding and areas of cattle pugging.
- Inspected existing culverts that pass underneath stop banks using a camera to identify potential issues.
- Begun extending current drains at the Wyndham Road and Golf Course sections to accommodate the extra stop bank width, which will be added next season. Existing drains are being fitted with new wingwalls and flapgates.
- Started an extension to the existing stormwater drain running from Ferry Street into the vacant section adjacent to the planned stop bank extension (section 4). The work incorporates the installation of a manhole, extension of the pipes underneath the planned stop bank extension and fitting a flapgate and wingwall to the riverward side.
Next steps
- Re-grassing and re-fencing the completed section and ongoing drainage work across the scheme through the winter months as weather and ground conditions permit.
- Recommencement of bulk earthworks (stages 2,3,4) in November 2023.
- Completion of 2D hydraulic modelling for the Mataura, including Wyndham.
- 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.
