Source: Northland Regional Council
The Far North’s upgraded Awanui flood scheme has successfully handled a record amount of floodwater – almost twice that of an infamous 1958 event that saw floodwaters more than a metre deep inundate Kaitaia township.
Northland Regional Councillor Joe Carr, who chairs the Awanui River Working Group and is deputy chair of the council’s Infrastructure Committee, says provisional hydrology figures from this week’s deluge showed a record up to 410 cubic metres of floodwaters were flowing down the Awanui River every second.
That compared to a figure of 220 cubic metres a second during the catastrophic 1958 flood and 258 cubic metres in a more recent, July 2007 event that had caused a lot of flooding and evacuations.
Councillor Carr says while there had been some overtopping of stopbanks this week – mainly in areas of the scheme that had yet-to-be, or were being upgraded – much of Kaitaia had escaped serious damage despite the vast and unprecedented flood flows.
“There was some costly flooding and associated evacuations as stopbanks did overtop both upstream and downstream of SH1 Bridge Waikuruki and in the lower Whangatane Spillway, all of which are works in progress, but overall the $15 million-plus, multi-year scheme upgrade performed very well.”
While some had overtopped, all of the stopbanks had remained intact and the scheme had also protected the Claud Switzer Residential Care home, a major concern in previous flooding events given the complex nature any evacuation there would require.
Councillor Carr says the NRC had assumed responsibility for the scheme 20 years ago and work on the upgrade had begun in earnest with the adoption of the council’s Long Term Plan in 2018.
Work that had been carried out to date included 6km of stopbanks, 5km of benching, 2.2km of spillways, 1.2km of scour protection, 200 metres of timber floodwalls, 750,000 cubic metres of earthworks, 15,000 cubic metres of rock stabilisation, the replacement or upgrading of 24 floodgates and the installation of an extra span at the Quarry Rd bridge.
Much of that work was specifically designed to protect Kaitaia township and another $2.5 million work is already underway or planned for the next two years to remove scheme weak points.
Fellow regional councillor Colin ‘Toss’ Kitchen, who chairs the Northland Civil Defence Emergency Management Committee (CDEM), says it is not an exaggeration to say the upgrade had potentially saved lives – and many millions in damages – during this week’s torrential rain.
“This was an extraordinary event with very intense hourly rainfall which tested the scheme to it limits.”
Both councillors say the scheme would not be the success it was without the work and support of many people.
They included landowners – some of whom had allowed the council to set back stopbanks on their land without compensation – previous and current councillors, the many members of the Awanui River Management Liaison Group (including tāngata whenua partners) and some dedicated council staff and contractors.
Councillor Carr says there had also been some very generous funding from Central Government in recent years.
“Late last year we (NRC) publicly thanked the Minister for Regional Development Shane Jones for his role in facilitating $11.1M of central government support for the project, which has significantly reduced the amount the local community has had to pay directly.”
The two councillors say the Awanui upgrade is an example of the benefits of central and regional government and communities working together for the greater good.
Councillor Carr says the council’s rivers staff would over the coming weeks analyse a mountain of data captured during this week’s rainfall.
This would be used to improve future scheme upgrade work and ensure any lessons learned were factored in to make the scheme the most resilient it could be. Lessons learned would also help Civil Defence in its work in future.
Meanwhile, Cr Kitchen also acknowledged the wider community, kaitiaki on the ground, local marae and emergency services for the “amazing work they have collectively been doing to keep themselves and others safe during the weather event”.
