$380m flood defences along Avon River to protect 2200 properties against rising risk

Wednesday, 17 June 2026

Flood protection work along the Ōtakaro Avon River Corridor is expected to protect 2200 homes and buildings during a one-in-200-year storm, but will cost ratepayers $380 million.

However, Christchurch City Council says the cost of not doing the work will be $630m.

The information has come from a study, which began in 2017, into how a range of hazards will affect planned flood defences along the lower reaches of the Avon River from near Barbadoes St to the Ihutai Avon-Heathcote Estuary.

The study, released by the council on Tuesday, shows that without additional flood defences along the Avon River, the risk of above-floor flooding in an extreme event will be two-and-a-half times greater by 2100 as it is today.

This will mainly be driven by sea-level rise, more rainfall, and ongoing land settlement, council three waters head Gavin Hutchison said.

The study took a broad approach and did not look at the risks to individual properties, he said.

The overall flood protection plan is already set out in the river red zone regeneration plan and includes building about 22km of stopbanks further away from the river and 18 pumping stations.

This work, expected to cost $380m (plus or minus 50%) and be completed over the next 10 years, was designed to meet the area’s needs for 30 years.

The scheme would see 2200 fewer flooded buildings by 2060, based on a one-in-200-year flood event and a sea level rise of 45cm.

The work would need to be extended after 2060 to prevent more buildings from being flooded. If that new work were to happen, there would be 3700 fewer buildings flooded and the damage avoided would total about $2.2 billion by 2100, the study said.

The planned defences would be designed in a way that they could be adapted in the future.

“This study shows that significant flood risk will remain, even when these defences are in place, and we will need to do more to manage these risks beyond the next 30 years,” Hutchison said.

The costs of the 30-year scheme were not fully budgeted for due to the timeframe, so regular approvals would need to be made by the council and the Ōtakaro Avon River Corridor (ŌARC) committee, Hutchison said.

The plan to regenerate the 602-hectare ŌARC is on the Government’s fast-track project list, which is designed to accelerate resource consents and get big projects built quicker.

Council surface water engineer Tom Parsons told a council briefing on Tuesday there was an incentive for the council to act because the stopbank repair work done following the earthquakes was built to last 25 years, so they only had another eight to 13 years of life left in them.

The council has already built a number of new flood defences, including new stopbanks in the Waitaki St area and Avon Park and a new flood wall next to Anzac Dr in Bexley.

Other planned work includes stopbanks and flood walls upstream of the Bridge St bridge. Stormwater pumping stations will also be needed to manage stormwater that arrives on the dry side of flood defences.

Councillor Aaron Keown asked at the briefing if staff had looked into building tidal gates in the estuary.

The idea to build a barrier from the Southshore Spit to near Shag Rock was mooted by mayor Phil Mauger last year.

He believed it could be built to hold back the advancing tide, allowing the rivers to drain more freely into the estuary, preventing flooding in the river catchments.

Parsons said that option had been looked at previously, but the planned flood defence scheme along the river was deemed to be better and cheaper.