Some riverbeds could be widened as part of an overhaul of flood protection management should the country’s regional councils secure a co-funding arrangement with the government.
The councils are seeking $150 million a year of co-investment to assist with the maintenance and construction of flood schemes and to address what they calculate needs to be spent on protection works.
Councils are spending about $200m a year on maintaining and building new flood defences, but with peri-urban expansion and aging infrastructure, more investment is needed.
Graeme Campbell, the convener of the NZ River Managers Special Interest Group for Local Government NZ said that, if successful, the money will not just be spent on new or upgraded stock banks but in some cases on widening riverbeds, land use change and spatial planning.
Some rivers have been strangled by flood protection works and will not deal with the more frequent heavy rain events expected in the future.
Schemes designed to protect farmland are now required to provide protection for peri-urban development, such as those adjacent to the Ashley, Waimakariri and Selwyn rivers in Canterbury.
“If we are to deal with flooding challenges in the future, our rivers are going to need more room and that is part of what we have got to address,” Campbell said.
Meeting higher water quality standards also requires a new approach to flood protection works.
ECan councillor Ian Mackenzie said council engineers are considering the merits of widening the north branch of the Ashburton River, which 20 years ago was narrowed so the force of water would wash gravel deposits downstream.
Options being considered include using 60ha of leased land and acquiring 40ha of private farmland to redevelop the stop bank further back from the river, widening the bed to slow the speed of the water and allow gravel to be dispersed over a wider but more accessible area.
Mackenzie said flood schemes have been piecemeal and not kept pace with peri-urban developments, so need extension or strengthening to provide protection.
“The level of protection is not sufficient to protect urban expansion, there is a different level of expectation,” Mackenzie said.
Campbell said the government stopped funding flood protection work in the 1980s, even though schemes protect government assets and infrastructure.
A report on the proposal by regional councils for the government estimates an extra $10m-$20m of flood protection would have saved $100m in damage in and around Westport from recent flooding.
“The 2021 Canterbury, Westport and Marlborough floods are all examples of an increasing series of recent major flood events experienced throughout New Zealand,” the report states.
The councils propose a cost-share formula of 75% towards the cost of whole-catchment climate change adaption work, 50% for upgrading capital works for existing river management and flood protection schemes, 33% towards maintenance of existing schemes and 75% for emergency repairs.
It estimates that NZ averages one major flooding event every eight months, with existing flood protection schemes providing an annual benefit of more than $11 billion each year, five times the capital cost of replacement.
“They provide protection to around 1.5 million hectares of our most intensely populated and used land,” the report says.
In 2020 councils received a one-off $215m grant for 55 shovel-ready climate resilient flood protection schemes.
Mackenzie said ECan collects about $15m from river rates and is in discussion with the Selwyn District Council about a new funding model.
It would be a district-wide targeted rate with all the money raised invested back in the catchment and related water systems.
“This is a more comprehensive approach to managing the system.”
If accepted, ECan could take the model to other district councils.
Regional councils are hoping to get government support for the co-funding model in time for consideration for the 2023 budget round.
Associate Minister for local Government Kieran McAnulty said the government is considering what support for flood protection could be available to councils through its Climate Emergency Response Fund.
This covers existing natural flood risks, the increasing number and value of assets that are vulnerable to flooding, climate change resilience and adaptation and how flood protection will be covered by work such as the Future of Local Government review.