Start on keeping flood-prone section of SH1 near Oamaru high and dry


Work near Oamaru to reduce flood-related closures on a section of SH1 near the Kakanui River is about to begin.

A low-lying, 350 metre section of SH1 near the river, around 12km south of Oamaru, is about to be raised to a higher level.

Work is starting mid to late November and will take around eight to ten months to complete. Oamaru’s Whitestone Contracting Ltd won the $3 million contract to do the work, funded through the NZ Upgrade Transport Infrastructure Programme and Transport Resilience Fund.

Good traffic management is paramount to this project being carried out safely and efficiently, says Waka Kotahi NZ Transport Agency Senior Project Manager Jason Forbes.

“Prior to Christmas, temporary speed limits will be in place but the two-way flow will be maintained. Over the holiday period all traffic controls will be removed, and the highway will be back to normal traffic conditions.

“On establishing back to site in the New Year, traffic controls will be reinstated as temporary traffic signals. You can then expect the site to operate under traffic signals with single lane movements until the work is complete. People will need to build in a little extra time getting through the site.”

There is a rail crossing at the southern end of the site which remains operational, so Waka Kotahi asks all road users to ensure they follow the instructions of both the temporary highway lights and the rail signals.

“This stretch of highway experiences periodic closures of the highway due to flooding from the Kakanui River covering the road surface every three to five years. These closures can result in disruptions to traffic flow for up to two  days,” says Mr Forbes.

With no straightforward detour available, these closures cause serious disruption for freight and commuters on this key highway linking Canterbury and Otago, he says.

“Closures affect the lives of communities and businesses who depend on the goods and services that are moved on this key highway connection. Detour routes add several extra hours of travel, hundreds of additional kilometres, and add more cost to people’s journeys.”

Several options were investigated to reduce the flood risk on this vulnerable section of highway. Of those tested, the best involved retaining the current highway layout and raising the road height by a metre.

Waka Kotahi modelling shows a one metre increase in highway height significantly reduces the amount of floodwater covering the highway.

This work will mean SH1 should avoid flooding in a one in 50-year flood and  no closures for the more regular three to five-year floods.

Planned improvements

  • Raising a 350-metre section of SH1 by up to 1.25 metres through the Kakanui River floodplain.
  • New road surfacing and markings.
  • Better access to historic Clarks Mill and construction of a new bridge structure over the existing, historic Mill Stream Culvert.
  • Greater safety from a wider raised road featuring 300 metres of safety barrier on its western side. 

The benefits

  • Fewer flood related disruptions with the highway passable during one in 50-year floods.
  • Reduced number of flood-related delays on the main road freight route between Canterbury and Otago.
  • Improved road access to keep communities connected during major flooding.
  • Greater resilience on a flood-prone section of SH1 between Oamaru and Dunedin.

SH1 Kakanui flood protection improvements