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Aparima flood protection upgrade

Ōtautau township sits on the floodplain of the Aparima River and Ōtautau Stream and is an important service centre for the wider rural area, including providing critical emergency services. The town and surrounding farmland have a long history of flooding, which is predicted to worsen as climate change brings more frequent and intense storms.

Historically, the Aparima catchment has experienced frequent and damaging floods, with major events in 1984 and 1987 severely impacting Otautau. The 1984 flood, the worst on record, inundated the town when floodwaters broke into the Otautau Stream. In response, the Aparima Flood Protection Scheme was developed to reduce future flood risk. While the stop banks, part of the scheme, have generally remained in good condition, recent floods in September 2023 and October 2024 forced the precautionary closure of the Main Street bridge in Otautau, highlighting the ongoing flood risks to the community. These protections remain vital for safeguarding people, property, and infrastructure in the face of extreme weather events.

Strengthening flood protection for the Ōtautau community began in October 2024 and was completed in late November. The project’s second stage was completed in under three weeks by early February 2025, and the third stage is anticipated to reach completion in April 2025.

New rock armouring has been installed along the Ōtautau Stream, parallel to Slaughterhouse Road and 300 metres upstream of the Ōtautau footbridge. This protects the stream berm and the toe of the stop bank from erosion, helping to maintain the integrity and stability of the flood protection system.

Key upgrades

This project has strengthened critical sections of the Aparima Flood Protection Scheme to reduce erosion, improve river stability, and increase the capacity of the river channels to handle higher flows.

  • Stage One involved placing 3,600 tonnes of rock to protect the stop bank toe and removing 2 hectares of crack willow to improve stream capacity within Ōtautau township.
  • Stages Two and Three focus on a 3-kilometre section of stop bank upstream of the Aparima River Bridge, northeast of Ōtautau.
  • Stage Two has been completed and included repairing and strengthening five access ramps with 250 tonnes of rock fill, as well as removing crack willow at three key sites to restore channel capacity.
  • Stage Three, planned for March–April 2025, will continue this work along the same stretch of stop bank. It will include further crack willow removal and additional erosion protection measures to enhance resilience.

Why these upgrades matter

These improvements restore sections of the Aparima Flood Protection Scheme to their intended level of service, strengthening Ōtautau’s stop banks and improving resilience to more frequent and intense rainfall and flow events projected due to climate change.

The work also prepares the flood protection scheme for future upgrades by improving floodplain capacity through pest tree removal and erosion control planting. Removing trees and shrubs from stop banks prevents root systems from weakening these vital structures, which could lead to breaches during high flows.

Additionally, these upgrades support climate adaptation by improving river flow and sediment transfer, reducing erosion risk, and maintaining channel capacity as extreme weather events increase.

Benefits

  • Protects local infrastructure, reducing future repair costs and safeguarding homes, businesses, and productive farmland.
  • Enhances the health of waterways by stabilising river margins, reducing sediment and contaminants, and improving habitats for aquatic species.
  • Builds local capacity and expertise in river engineering, supporting future resilience efforts.

Funding and collaboration

The project involved experienced local contractors and partners in delivering the work efficiently, with an accelerated timeline providing cost savings, reduced transport costs, and a lower carbon footprint for greater sustainability.

It is a national Resilient River Communities initiative and is part of Environment Southland’s $3.6 million Before the Deluge 2.0 programme announced in 2024, co-funded by central government and Environment Southland through Kānoa – the Regional Economic Development & Investment Unit.

By having resilient river communities, we hope to minimise environmental, economic, and social damage caused by flooding – making Aotearoa New Zealand safer for everyone.

Access ramps crossing the stop bank have been repaired and strengthened to prevent damage to the crest. This work ensures that, in the event of a flood greater than the design capacity, water overtops the stop bank evenly along its length, reducing the risk of erosion, breaches, or failure at weak points such as ramps.

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