A significant highway has been closed indefinitely by the threat of massive rock slips.

The NZ Transport Agency said this morning new geotechnical information has highlighted major safety risks in the Manawatu Gorge which are likely to keep the road closed for some time.

The State Highway 3 link from Hawke's Bay-Wairarapa to Manawatu and State Highway 1 on the southern side of the gorge, which separates the Tararua and Ruahine ranges, closed on April 24 because of a slip.

A release from NZTA said an urgent programme of additional work will get underway immediately to significantly improve the alternative Saddle Road route.

Advertisement

Regional transport system manager Ross I'Anson said a significant amount of work has been undertaken in the gorge to clear the slips which have come down since April, but geotechnical engineers have now confirmed that a large area above the Kerry's Wall rock face is highly unstable, with an imminent risk of further significant slips or rockfalls.

Netting was installed on part of the new slip through the Manawatu Gorge.
Netting was installed on part of the new slip through the Manawatu Gorge.

"Geotechnical assessments have confirmed that the entire hillside is moving, and the rate of that movement is accelerating. That's an indication that a slip as large or larger than the 2011 slip which closed the road for 14 months could come down at any time."

Mr I'Anson said the immediate risk of another large slip coming down in the gorge has required the Transport Agency to remove all contractors from the current work sites for safety reasons, and those same risks mean the road cannot be safely re-opened for motorists.

"We know that this news will add to the considerable frustration and stress which local businesses and residents are already dealing with. We understand the impact that this ongoing closure has on people's lives, but the safety of road users is paramount and the current unstable conditions in the gorge mean it simply cannot be opened to traffic until more work is done to fully understand the risks and how they might be mitigated.

"We're committed to keeping people informed as the situation develops, and we'll continue to work closely with the Tararua District Council to do everything possible to help people and businesses in the region for as long as the Gorge remains closed."

Mr I'Anson said it was not possible to carry out further work at the site or predict when the road might re-open until the movement of the hillside at Kerry's wall slows or stops.

The Transport Agency is already investing $8.5 million in an upgrade to improve the safety and resilience of the Saddle Road, allowing it to better cope with increased traffic volumes at times like this when the Manawatu Gorge is closed, Mr I'Anson said.

He said more work is planned.

"The significant length of the current closure has put the Saddle Road under added pressure, and the Transport Agency will be working to upgrade the road and keep it safe. The reality is that the Saddle Road will effectively be functioning as the state highway connection for this part of the country for some time."

The Transport Agency has agreed to take over full responsibility for the maintenance and management of the Saddle Road from the Tararua District Council for as long as the gorge remains closed, so that any repairs and remedial work are managed and funded by the Transport Agency.

While wet weather has delayed work which was planned for earlier this week, Mr I'Anson said pavement upgrades and repair work are beginning today (7 July) on sections of the Saddle Road which haven't yet been upgraded.

Mr I'Anson says in parallel to the work to address the issues in the Gorge and support the current detour routes, the Transport Agency will also be looking at a range of long term options to bypass or replace the current Manawatū Gorge route.