Gorge hillside still falling as region waits on remedy
Slips continue to fall in the Manawatu¯ Gorge, nine months after the road through it closed.
The main link between Manawatu¯ and Hawke’s Bay was shut in April 2017, when rocks covered the two-lane road. Three months later, the gorge was closed indefinitely because of the risks posed by the unstable hillside.
Several slips discovered this month show the rock face is still moving at a rate too unsafe for motorists to re-enter the highway, roading officials say.
New Zealand Transport Agency regional transport systems manager Ross I’anson said material had slipped from both sides of Kerry’s Wall – the site of a potential mass landslide, near the Ashhurst end of the gorge.
Previous predictions estimate as much as 630,000 cubic metres could fall, but it hasn’t dropped so far. That slip would be 170 times larger than the original two slips that caused the gorge to close in April.
I’anson estimates about 1000cum of new material has fallen around Kerry’s Wall this year. There was also a 40cum slip a few kilometres down.
These slips were minor, but Kerry’s Wall was still moving rapidly, I’anson said.
‘‘The slip is modelled to come down in four stages still, but its very nature is unpredictable.’’
Calculations show it moved 80 millimetres in August, compared with previous movements of about 60mm over 18 months.
‘‘Monitoring prior to Christmas showed continuing rapid movement of Kerry’s Wall and the rock face above the wall.’’
I’anson said the transport agency was expecting a monitoring report in the next couple of weeks for updated information.
The agency does not expect a slip as large as 630,000cum to reach the popular gorge walking tracks, above the unstable Tararua Range hillside. They remain open, but fences are in place to stop road access.
A replacement highway should be complete within five to seven years. The four options are an upgrade to the Saddle Rd, a new road north of the Saddle Rd road, a new road south of it, and a new road south of the Gorge.
The announcement on a preferred route is expected in the first quarter of this year.