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We’ve finished laying the first seal on a newly built road retreat just north of Kukuta Road. The 'retreat' has moved the road alignment away from the river., and returned this section to two lane traffic We’ll continue to maintain and monitor the road through winter. We’ll then complete work on this section by laying the final seal towards the end of summer, to ensure the road’s finished to the highest possible standard.
Over several years we’ve progressively repaired several sites along State Highway 4. Each site has brought its own challenges in areas of design, engineering, property, and consenting. These sites have included the Otoko Pā slip, the South Raupiu retreat, Whiskey Corner, and Hapokopoko Curve Rock, and this one – near Upokongaro.
The need for this road retreat stems from a period of extreme weather that hit New Zealand in late June 2015. The South Island suffered heavy snow – closing airports, schools, and roads. And the central North Island was hit with major rainfall and flooding. Civil Defence declared a state of emergency in the Rangitikei, South Taranaki, and Whanganui districts. In Whanganui alone, 400 residents were evacuated due to the largest ever recorded flooding in the area. At one point, Whanganui River reached a level of 9.1 metres at Town Bridge.
The storm led to major infrastructure damage throughout the region including to sections of State Highway 4 with flooding contributed to dozens of slips. One of those sections was the area around 11km north of Whanganui which runs alongside Whanganui River.
The slip, which eventually came down in September that year, affected around 100 metres of riverbank, with the road subsiding all the way to the centreline. Initial remedial work was completed on the site, but this work failed.
“The initial fix was to do a retaining wall,” says Gareth Howie, Waka Kotahi Project Manager.
“But we couldn’t get a deep enough grounding, so the build rotated on itself and slipped back into the Whanganui River.
“Then we started thinking that we needed to go deeper, but the deeper you go the more engineering you need. And there was the issue around how to fill back behind a retaining wall if you don’t have a strong foundation underneath the wall. So that wasn’t a viable option. This meant the best option was to build a road retreat."
While we’ve been progressively completing repair work on sites along State Highway 4 – physical work on this section of road began in March 2021.
“There’ve been a few challenges to get it to this point," adds Gareth. "There’s the design side of things as well as working through property and consenting.
“But it’s good to know we’re almost there and the project’s now in a good place."
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