Waihōpai Invercargill stop bank upgrade
Environment Southland is upgrading the Waihōpai River (true left) stop bank to meet the increase in extreme sea levels in the Kōreti New River Estuary resulting from climate change. The work is part of a broader vision to enhance the city's flood defences, including developing solutions for Otepuni and Kingswell streams and opportunities to enhance and protect the lower reaches of the Waihōpai River.
The Waihōpai River stop bank 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.
Waihōpai Invercargill is at risk from flooding from the three waterways surrounding the city and from high sea level/storm surge events in the estuary. As a result, the flood protection for the city has evolved and developed over time. The last significant improvement to these protection measures followed the devastating January 1984 floods, when floodwaters forced more than 5000 people from their homes. Substantial investment in flood protection infrastructure followed, including construction of the Waihōpai River flood detention dam (large enough to hold a volume of water equivalent to 800 Olympic-sized swimming pools).
There have been no significant upgrades to this infrastructure since this time (essentially over the last 30 years).
The latest climate resilience initiatives for the city include widening and raising the eastern side stop bank on the Waihōpai River between the Ohai Rail Line Crossing and Stead Street and the installation of rip rap rock. The existing stop bank is approximately 3.2 km long and is a combination of reclaimed land and constructed stop bank. Work is being undertaken in four sections, beginning with Beatrice Street north to the railway line crossing.
This project will create a more robust flood defence for Waihōpai Invercargill City and is the first phase of work to future-proof the Waihōpai River stop banks. An upgrade to the western side stop bank will happen in the next phase of climate resilience projects.
To complement this work, Invercargill City Council has replaced the Stead Street stop bank with a sheet pile wall and widened and raised the height of the adjoining Cobbe Road stop bank.
Together the projects will systematically begin to address the vulnerabilities Waihōpai Invercargill has to climate change and provide much more resilient flood defences for our community and Invercargill's critical infrastructure.
Multi-purpose pathways that have been developed along the stop banks will be reinstated. These pathways will be wider and consistent with other shared pathways in the region.
Each section of stop bank will have diversions in place for cyclists and pedestrians while the work is underway. Traffic management will be in place to ensure the safety of track users while heavy transport vehicles and construction machinery are on the track.
The stop bank has several areas of trees and shrubs, which unfortunately need to be removed, but the team will be looking at alternative areas for planting and salvaging plants from these areas where possible.
- Widening the Waihōpai stop bank makes it more robust and provides an opportunity for us to increase the height in future, as our understanding of the impacts of climate change and climate models change over time
- Increased protection for people, homes, communities, and critical infrastructure
- Work completed with central government funding assistance
Project update (10 November 2023)
- Site investigations and detailed design associated with the Waihōpai stop bank modifications completed
- Engagement with affected landowners and key interest groups is ongoing
- Consents and approvals finalised for the eastern stop bank upgrade
- Construction contract awarded to Ryal Bush Transport Ltd. December 2022
- Contractors on site from late January 2023
- Work on the section between Beatrice Street and the railway line commenced in early February 2023, and bulk earthworks are complete
- Bulk earthworks on the section from Victoria Street to Beatrice Street are fifty per cent complete, with work suspended over the winter months while the ground conditions are too wet
- Shared pathway north from Victoria Street reopened
- Work recommenced from Fox Street south to Stead Street, November 2023
- Removal of high-risk trees near the Waihōpai River and Otepuni Stream
- Complete bulk earthworks on the section from Fox Street to Stead Street, re-grass and reinstate shared pathway
- Expected completion of the eastern Waihōpai River stop bank upgrade in the 2023-24 construction season
- Progressing plans to upgrade the stop bank on the western side of the Waihōpai River