Flooding on Kimberley Road in the Auckland suburb of Epsom on 1 February 2023. Photo: RNZ / Rayssa Almeida
Planners are working on a national approach for improving how cities and towns manage stormwater runoff to minimise flood damage.
Stormwater was incredibly damaging in the Auckland anniversary day floods and Cyclone Gabrielle in February.
Water experts say how stormwater is managed will be pivotal to how Aotearoa copes with climate change.
But flood hazard modelling is not consistent across the country, and stormwater is called the "poor cousin" by the water industry, because far less is spent on it than on drinking water or sewage systems - more than $1.2 billion for the latter two, compared to just $385 million on stormwater nationally in 2020-21.
"It is also the network that we know least about," said Water New Zealand president Lorraine Kendrick in the agency's recent newsletter.
"Perhaps 2023 will be to stormwater what Havelock North in 2016 was to drinking water," Kendrick said. The Havelock North poisonings sparked the reform moves that led to Three Waters.
Most stormwater systems were overwhelmed by the storms this year.
"There is a need for new spatial planning" laws and better plans," Kendrick said. "It is vital that flood hazard information is freely available, nationally consistent and transparent."
However, "there is currently no national-scale standardised flood mapping methodology or database" according to 2021 research that compared the local approach with the United Kingdom's.
"Stormwater models are built to comply with regional guidelines."
The new $200,000 government-funded project aims to join that up into a nationally consistent process.
"The guide will give greater certainty for councils of how to apply flood-risk data to ensure urban stormwater networks are designed, developed, and operated to manage current and future risks (like climate change)," the Department of Internal Affairs said.
Auckland only last year adopted a new regional set of minimum standards for the design and construction of new public stormwater. Whether it will have to revisit this when national model guidelines come in, remains to be seen.
The stormwater project began in February and is currently looking at where the gaps are. It aims to be finished by November.