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Aparima flood infrastructure project

Ōtautau township sits on the floodplain formed by the Aparima River and Ōtautau Stream and is an important service centre for the wider rural area, including critical emergency services. The town and surrounding farmland have a long history of flooding, which is expected 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 affecting Ōtautau. The 1984 flood—the worst on record—occurred when floodwaters broke into the Ōtautau Stream. In response, the Aparima flood infrastructure scheme was developed to reduce future flood risk. While the flood banks have generally remained in good condition, recent floods in September 2023 and October 2024 led to the precautionary closure of the Main Street bridge in Ōtautau, highlighting the continuing flood risk for the community. These flood banks are a vital part of the region’s flood infrastructure network, helping reduce the impacts of flooding on people, property and critical services.

Strengthening works on the Ōtautau flood banks began in October 2024 and were completed in late November the same year. The second stage was finished in under three weeks by early February 2025, and the third stage was completed in May 2025.

New rock armouring along the Ōtautau Stream, parallel to Slaughterhouse Road and about 300 m upstream of the Ōtautau footbridge, strengthens the stream berm and stabilises the toe of the flood bank, helping to maintain the integrity and performance of the flood infrastructure network.

The work

Stage One (Ōtautau township)

  • Placed 3,600 tonnes of rock to protect the flood bank toe.
  • Removed ~2 hectares of crack willow to improve stream capacity.

Stages Two and Three (upstream of the Aparima River Bridge, northeast of Ōtautau; ~3 km of flood bank)

  • Stage Two (completed): repaired and strengthened five access ramps with ~250 tonnes of rock fill, and removed crack willow at three priority sites to restore channel capacity.
  • Stage Three (Mar–May 2025, completed): continued erosion protection along the same reach, with further crack willow removal and additional rockwork.

Why this work matters

These works restore sections of the Aparima flood infrastructure network to their intended levels of service by strengthening Ōtautau’s flood banks and improving channel capacity. Removing pest trees from flood banks and adjacent channels reduces root damage and debris blockages, lowering the risk of erosion and bank failure during high flows. Erosion-control planting stabilises river margins and supports long-term performance.

Together, these actions reduce the direct impacts of flooding, help sustain service levels as rainfall and flow patterns change, and shorten the duration of disruptions after events.

Benefits

  • Risk reduction and asset performance: preserves flood banks and channels, reducing future repair costs and improving performance during peak flows.
  • Adaptation support: maintains flow and sediment conveyance and improves capacity as extreme rainfall becomes more frequent.
  • Waterway co-benefits: stabilises margins, reduces sediment and contaminants, and supports aquatic habitats.
  • Local capability: builds practical expertise in river engineering and operations to support future flood-risk-reduction work.

Funding and collaboration

The project was delivered with experienced local contractors and partners on an accelerated timeline, reducing transport needs, lowering costs and emissions, and improving delivery efficiency.

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

These investments aim to reduce flood impacts, sustain agreed service levels and shorten disruption after events, delivering environmental, economic and social benefits for communities across Murihiku Southland.

Access ramps over the flood bank have been repaired and strengthened to protect the crest. This helps ensure that, if water overtops during a major flood, it spreads evenly along the bank, reducing erosion and the risk of breaches at weaker points such as ramps.

See how local contractors contribute to on-the-ground flood infrastructure works across Murihiku Southland in this recent Envirosouth feature:
Holding the Line – Envirosouth, Spring 2025

Local delivery: Stirling Contracting — Shane Dickson (centre) with Raymond Stirling (right) and Nathan Clarke (left) — delivering targeted upgrades on the Aparima and Ōreti flood banks.

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