Spillway work is done and dusted

Regional councillor Colin Kitchen checking progress on the 400-metre stretch of new spillway behind Juken New Zealand's triboard mill earlier this month. Photos / Northland Regional Council

The Northland Regional Council has completed hundreds of thousands of dollars' worth of what it says were critical improvements to the Awanui flood scheme, after several weeks of unscheduled delays caused by the Covid-19 lockdown.

An estimated 90,000 tonnes of soil was removed to transform a Kaitaia paddock into a new 400-metre spillway behind Juken New Zealand's triboard mill, part of the second stage of the council's ongoing multimillion-dollar upgrade of the flood scheme.

Te Hiku councillor Colin Kitchen says it had been hoped to finish the work by May, but the pandemic lockdown had thrown a spanner in the works, forcing a halt to construction for several weeks.

Ironically, when work resumed, a drier than normal start to winter it to continue beyond the usual end of the construction season, and effectively claw back much of the lost time.

Juken NZ had allowed its land to be used for the upgrade, which would provide better flood protection or the surrounding area, including the mill, one of the area's largest employers.

"An adjoining private land owner was also a great assistance, allowing their property to be used during the earthworks, and local tangata whenua provided valuable input into the programme," Kitchen said.

He says the existing (and aging) spillway, which would be retired within the next 12 months or so for a new life as a wetland, was literally just a stone's throw from the mill, he added. The new roughly 20-metre-wide, which had been built approximately 100m to the south-east, would be given a few months to stabilise and for grass cover to establish before it would be commissioned in autumn next year, with water from the river diverted into it.

While the new works were about two kilometres downstream from Kaitaia itself, they were an integral part of the upgraded scheme, helping to carry potentially damaging floodwaters away from the town more efficiently and quickly.

The flood scheme upgrade had begun in earnest last year, but because of its scale and cost, work would continue in stages over several construction seasons through to 2027.

The new spillway had accounted for most of the approximately $1 million spent this year, Kitchen saying much of the scheme had been built about a century ago, and until fairly recently the NRC's attention had of necessity been on much-needed maintenance and more immediate repairs.

"The upgrade programme will help future-proof the scheme for a number of years, including predicted effects from climate change, as well as deliver a considerably higher level of protection for Kaitaia and surrounding areas," he said.

Scheme-wide future flood risks would be mitigated largely via extensive modifications and improvements to stabilise existing stopbanks, which would allow the Awanui River, including critical sections upstream of the triboard mill, to carry up to 15 per cent more water, protecting urban Kaitaia in a 'once in a century' flood and a 1 in 20-year event in surrounding rural areas. The council had said previously that without the added protection the upgrade would offer, a large flood in urban Kaitaia could cause tens of millions of dollars in damage and potentially put lives at risk.

Seventy per cent of the cost was being paid by ratepayers Northland-wide via a regional flood infrastructure rate, with the balance coming from a targeted Awanui River management rate.