Kaitāia on Friday, a day after the town flooded, triggering evacuations. Photo / Jason Dorday
Major upgrades to Kaitāia’s flood-control scheme prevented loss of life in the town this week, Northland Civil Defence chair Colin “Toss” Kitchen says.
His comments come after 400 people were evacuated in the dark from their homes in north Kaitāia at 9.30pm on Thursday, as “unprecedented” amounts of water poured through the Awanui River catchment. Water levels rose rapidly and began spilling over stopbanks.
Kitchen, Northland’s top Civil Defence leader, said it was not an exaggeration to say the upgrades had potentially saved lives and millions of dollars in damage in the town of 6000.
MetService figures show Kaitāia received 210mm of rain in 10 hours from 10pm Wednesday to 8pm Thursday as a major tropical depression hit.
“This was an extraordinary event with very intense hourly rainfall which tested the [flood protection] scheme to its limits,” Kitchen, who is also a councillor on Northland Regional Council (NRC), said.
Far North District Council Civil Defence declared a state of emergency on Thursday.
Four hundred people were evacuated from 118 homes in the north of Kaitāia after a joint decision by Civil Defence, New Zealand Police and Fire and Emergency New Zealand.
Most stayed with family and friends but 44 spent the night at an emergency evacuation centre set up at Kaitāia College.
Provisional NRC figures show this week’s deluge pushed almost twice the volume of water through the Awanui River compared with the 1958 flood that inundated the town.
About 410cu m of floodwater flowed down the river every second.
This compares with 220cu m a second down the river during the town’s catastrophic 1958 flood when central streets were inundated and 1m-deep standing waves formed.
The flood became a defining event in Kaitāia’s history. This week’s Awanui River volumes also compared with 258cu m a second in July 2007, when Kaitāia flooded and people were evacuated.
NRC infrastructure committee deputy chair Joe Carr said much of Kaitāia escaped serious damage, despite this week’s vast and unprecedented flows.
Carr acknowledged some stopbank overtopping this week but said it was mainly in part of the scheme yet to be or being upgraded.
“There was some costly flooding and associated evacuations as stopbanks did overtop both upstream and downstream of SH1 Bridge Waikuruki and in the lower Whangatāne spillway, all of which are works in progress, but overall the $15 million-plus, multi-year scheme upgrade performed very well,” Carr, the chair of the Awanui River Working Group, said.
While some had overtopped, the stopbanks remained intact. The scheme also protected the Claud Switzer Residential Care home, a major concern in previous floods, given the complex nature any evacuation there required.
Carr said NRC had assumed responsibility for the scheme 20 years ago.
Much of the upgrade work begun in 2018 was designed to protect the Kaitāia township and $2.5m of work was underway or planned over the next two years to remove weak points.
Work to date included 6km of stopbanks, 5km of benching, 2.2km of spillways, 1.2km of scour protection, 200m of timber floodwalls, 750,000cu mof earthworks, 15,000cu m of rock stabilisation, the replacement or upgrading of 24 floodgates and the installation of an extra span at the Quarry Rd bridge.
The scheme is predominantly ratepayer-funded. The Government recently contributed $11.1m to the project.
The Awanui River flood management scheme manages flood risk from rainfall and runoff, including major tributaries such as the Takahue River, the Victoria River, the Karemuhako Stream and the Tarawhataroa (Whangatāne) Stream, as well as urban waterways like the Kaitāia Stream, which runs through the town.
Kaitāia lies in the lower Awanui River catchment, covering about 45,500ha of hill country, rural land and tributary streams upstream of the town.
Its flood risk is driven by catchment-wide rainfall draining towards the lower river beside Kaitāia, even when there is little or no rainfall in the town.
■ LDR is local body journalism co-funded by RNZ and NZ On Air.