Cars can be seen crossing the Wairau River Bridge on SH1 between Blenheim and Picton on 20 August, 2022. Photo: RNZ / Angus Dreaver
Scientists say flood protection works are absolutely needed in the short term, but the government needs to consider funding a more modern, holistic approach to river management into the future.
Documents - since redacted - show the local government minister expected to take a multimillion-dollar Budget proposal to Cabinet to speed up flood protection works on rivers around the country.
It would see the government spend $257 million to help regional councils speed up 92 river projects.
The councils also suggested further ongoing funding, rising to $250m a year from 2027/28, to help protect against the kinds of devastation seen in the wake of Cyclone Gabrielle.
Massey University professor in physical geography Ian Fuller told RNZ river flood management would be essential.
"We do need to take rivers very, very seriously moving forward. If we don't, very regrettably, more people will lose their lives and that's just unacceptable, surely," he said.
Massey University Professor in Physical Geography Ian Fuller. Photo: Ian Fuller / Supplied
"We can expect more of this, more floods and bigger floods as we move move through this century. And I think we have to be ahead of ahead of the game, we have to be prepared."
He said from his conversations with regional councils, he believed the central goverment should be contributing funding to flood protections.
"The bill cannot simply be laid upon the Regional Councils and Unitary Authorities, it needs to be accommodated by society as a whole because it's a societal issue."
He said in the short term, traditional approaches to river management were the only option - but in the long term, a different approach was needed - and it would likely require central government involvement.
"We have to move away, I think, from kind of putting the bandage- putting the plaster on the broken artery," he said.
"It can't be [only] short term. As I say, this is a multi-generational thing, this is something which is going to be with us for not just the next couple of years ... if it's done properly it's going to take decades to resolve.
"It is not just about 'on the banks of the river', it's about catchment, it's about strategic, holistic, catchment thinking that we need at this time, it's got to be a long-term investment. I tend to think that central government should be stepping up."
University of Auckland geomorphology senior lecturer Jon Tunnicliffe agreed a more holistic approach to river management was needed.
"I think we've had a habit of going straight to hardening banks and reinforcing river positions but I think a more holistic process is required in order to make these decisions and think about the longer term trajectory that the river is on before imposing some sort of regime that nails the river in place."
He said this could be achieved with the use of Light Detection and Ranging (LIDAR) technology - which offers high-resolution imagery of floodplains over time - combined with long-term analysis of sediment movements in rivers.
River scientist Jon Tunnicliffe Photo: Supplied
"Rivers are always in a constant state of adjustment so we've in the past we've had a habit or arresting the river in place but if we know the river is eroding along a certain trajectory - if we know there's a meander band that's in the process of adjusting or we know there's a historic place where the river used to switch between courses, we can take those longer-term considerations.
"If we can pre-emptively give the river some space to erode as it would naturally - many countries use this concept of an erodable corridor where the river has a place to erode as it would."
Fuller agreed with that.
"We need to ... live with our rivers as dynamic entities in our landscape. They cannot be fixed, they cannot be controlled, and we need to recognise their dynamism."
Local Government Minister Kieran McAnulty confirmed the government was considering the proposals to set up a co-investment fund, but said any decisions would be communicated as part of the Budget in May.
Regional councils and unitary authorities, who banded together under the banner of Te Uru Kahika, said the 92 projects in their proposal would go ahead with or without the funding - it's just a matter of speeding them up.
They said it would be "touch and go" for some regions, with climate change bringing more frequent, damaging floods - and every dollar spent will be worth at least five if it protects communities.