Ōtaki Gorge Road slips

Another slip on the Ōtaki Gorge Rd at Blue Bluff (12km inland from SH1) means plans to open a cycle and walkway along the stretch of closed road have had to be cancelled. The road remains closed to vehicles and pedestrians for safety reasons.

Vehicle access to Ōtaki Forks remains closed.
Walkers are not to cross at Blue Bluff, for their own safety.
The Department of Conservation has established an alternative public walking access to the Tararua Forest Park.

There are now two slip areas in the Blue Bluff area:

The slow slip detected in September 2020 which has seen the road to slump towards the river and caused the original closure.
A second significant slip 100m further towards Ōtaki Forks which has completely covered the road. This occurred during the heavy rain event of 6-8 December 2021.

Next steps

The latest slip has significantly increased the scale of the challenge we face to reopen the road.

In light of this Council has engaged engineering consultants WSP to review the situation and support the development of options.

We aim to provide an update to Council in the first quarter of 2022, and will keep the community informed as this develops.

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Ongoing closure

We know it is frustrating to have had access to Ōtaki Forks closed for such a long time.

As the organisation responsible for the road Kāpiti Coast District Council understands the desire to see it reopen.

When there are significant safety issues, like the slip that has caused a section of the road to slump and risk of dropping out into the river, we have to put the safety of people first. While the road remained unstable closure was our only option.

Rushing into reopening a road that is showing this kind of movement is not wise. Fixing any road requires solid information about the ground underneath, a suitable design, funding and a process to select contractors to do the work.

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Work to date

Research work on the earlier slow slip was ongoing throughout 2021. Starting in April 2021 we began looking at how we might be able to open road access to Ōtaki Forks, moving from monitoring the slip to active investigation on the site. This involved specialised geotechnical work including test pits, core holes, and installing equipment to monitor groundwater levels.

Geotechnical investigation showed the slip zone runs deep into two types of material and that wet periods and heavy rain are key factors that accelerate movement. By the end of May, our investigation had found several metres of river gravels deposited when the river was much higher many thousands of years ago, with fractured greywacke bedrock underneath that.

This information would inform the development of options and a design for how the road could be reopened.

The wet period in June 2021 reactivated the slow slip and we observed significant deformation of the road and the slip face slump into the river.

In the latter part of 2021 the road had stabilised enough to reopen part of it for a walking and cycling track along the wall side of the road. Site works had progressed prior to the recent major slip.

This would provide much better access for those wishing to make the 4km journey to the Forks by foot or bike. Re-opening the road to vehicles was still not an option.

The slip triggered by rain event of 6 to 8 December 2021 has forced us to cancel that plan. This is incredibly disappointing as while cars would not have been able to make the journey, it would have been a one hour walk or 20 minute cycle down to Ōtaki Forks – manageable for anyone with moderate fitness levels.

Fortunately no one was underneath the slip at the time it happened, but as a result the road remains closed for the foreseeable future.

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About Blue Bluff

The Blue Bluff section of the Ōtaki Gorge Road is an a area that becomes active during wet weather.

The road is on a steep embankment above the Ōtaki River, which is naturally degrading the river bed and embankments. The Ōtaki Forks area receives intensive rainfall further adding to the challenges of this road.

The road has been closed to walkers and vehicles since September 2020, when heavy rain caused new damage to the bank. The road had been closed for seven months in 2016 due to slip activity at the same location.

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