South Canterbury river works strengthen community resilience
In December 2019, significant rain fell across South Canterbury, causing widespread flooding and damaging flood protection infrastructure in the Rangitata and Waitaki Rivers. Since then, we've spent $8.5 million on repair and rebuilding.
The 2019 flood was one for the history books. The Rangitata River broke out of the main channel in five different locations, causing significant damage to flood protection, roading, rail, electricity supply, farms, and other assets.
Some 130 kilometres to the south, the lower Waitaki River had its own challenges, including the looming threat of erosion.
After almost $8.5 million of funding, including central government’s one-off climate resilience funding and local investment, resilience has been improved across both rivers.
Mighty flood pushes flood protection limits
In December 2019, river flows in the Rangitata peaked at a massive 2307 cumecs, significantly more than the 1500 cumecs the flood protection scheme is designed to withstand.
"The flood event was 35 times the usual flow in the Rangitata, so the main branch of the river broke through five different sites between Arundel and the State Highway 1 bridge, including the usually dry south branch," Catchment Committee Chair, Councillor Ian Mackenzie said.
"While the south branch is a known and mapped floodway, the sheer scale and speed of this event caught many off guard – there hadn’t been a significant flow down this channel for 24 years."
In December 2019, the Rangitata River broke out of the main channel, causing widespread damage.
Further south, the Waitaki River experienced erosion at 12 sites between Kurow and the coast. With erosion threatening the public water supply, urgent works were carried out.
"Another three significant rain events hit the Waitaki catchment across the following three years, which meant the 2019 flood recovery works were continually tested, often coming out second best," Cr Mackenzie said.
"While we were able to improve the resiliency of the Waitaki River across most sites, ongoing rain events meant we were unable to complete the works to the level initially scoped."
Enhanced flood protection in South Canterbury
After the flood, repair work on the Rangitata River flood protection assets was done to keep the community safe. Further works totalling $8.5 million across both Rangitata and Waitaki rivers enabled us to enhance the flood protection on these rivers.
Additional work over the following three years included stopbank reinforcement and stabilisation, native planting, large-scale pole planting, protection of the Peel Forest landfill, debris clearance at the Rangitata Huts and aerial weed control across more than 260 hectares of the Rangitata.
More than 60 per cent of the cost of works were covered by one-off central government funding and the rest from local rates, contributions from infrastructure owners (NZ Transport Agency Waka Kotahi, KiwiRail, Transpower, Rangitata South Irrigation Ltd) and local government (regional and district councils).
We are continuing to advocate for central government funding to support ongoing flood protection to keep communities safe against the growing threat of climate change.
Before: The south branch of the Rangitata was a former channel that hadn't seen a significant flow for 24 years.
After: The breakout point at south branch after significant flood protection works had been completed.
Multiple benefits for rivers and communities
Not only did this one-off co-investment enable the recovery work to be delivered much faster than with rates alone, but most of the contracts were also awarded to local businesses strongly impacted by COVID-19, providing a much-needed economic boost.
"It’s been three years of hard work but being able to look back and say we’ve provided employment or contracts to over 24 local businesses, reduced flood risk to around 10,000 hectares of land, and placed nearly 20,000 tonne of rock, it’s pretty incredible," Cr Mackenzie said.
Other benefits from the Rangitata and Waitaki works include:
Pockets of native plants help support flood protection on the Rangitata.
- 20 kilometres of flood protection enhanced
- 17,400 plants installed
- 1.74 hectares of native vegetation enhanced
- 1.14 hectares of wetlands enhanced
- More than 400 hectares of weed control carried out.