Ōtaki Gorge Road slips

Slips at Blue Bluff

Following slips on Ōtaki Gorge Road in 2020 and 2021 at the area known as Blue Bluff, it's been closed to vehicles and pedestrians for safety reasons. 

The road access to Ōtaki Forks remains CLOSED at this time. There are two slips in the Blue Bluff area:

• The September 2020 'slow slip', which continued to shift for many months and saw the road slump towards the river.
• The December 2021 'over slip' across the road, approximately 3000 cubic metres in volume and 100 metres in length, and which has continued to show signs of movement since.

Reopening access to Blue Bluff on track for early 2025

After a series of detailed geotechnical, environmental and engineering investigations, we’ve finalised the plan to reopen Blue Bluff on Ōtaki Gorge Road.

There are two slips that need to be fixed:

• the overslip where material has fallen onto the road from the hill above
• the underslip where the road is undermined by a collapse beneath it. 

To fix the overslip, we’ll clear the debris and rebuild the road along its original alignment. At the site of the underslip, we’ll cut back into the bank and realign the road further from the river.

Waka Kotahi NZTA funding has been approved and we’ve lodged resource consent applications with Council and Greater Wellington (the regional council). We plan to begin earthworks early next year. All going well the road will reopen around May 2025, restoring our community’s much-valued access to Ōtaki Forks and the Tararua Forest Park.  

Restoring access

After a significant period of monitoring and investigation Council has opted to proceed with reopening the road.

A range of options were explored and presented for consideration. These included:

• closing the road completely
• building swing bridges across the river
• building long-term walking access over the existing slips.

Staff recommended reinstating the road access and this option was adopted by Council.

Reinstating the road will be co-funded by Council and NZTA Waka Kotahi. 

This is likely the quickest solution and will provide the most accessible route into the Ōtaki Forks and Tararua Forest Park.

More information on all the options and the proposed construction methodology for rebuilding the road is available in the Agenda for the Council meeting on Thursday 9 May 2024.

Council aims to complete detailed design of the repairs and apply for resource consents by the end of 2024, with work on the repairs to follow.

Timeline

• September 2020 – Slow slip detected at Blue Bluff, Ōtaki Gorge Road closed for safety reasons.
• Early 2021 – Geotechnical monitoring and investigation into restoring access to Ōtaki Forks commences.
• June 2021 – Heavy rain reactivates slow slip, causing significant deformation of the road and the slip face to slump into the river.
• October 2021 – The road stabilised enough to reopen part of it for a walking and cycling track along the wall side of the road. Site works had progressed to allow this to happen.
• December 2021 – Heavy rain on 6–8 December triggers over slip across the road. Cycling track destroyed.
• June 2022 – Walking track built to allow for monitoring and geotechnical work. Plans to open it to the public put on hold due to continuing instability on the over slip.
• 2023–May 2024 – Ongoing investigations into options for restoring access.
• May 2024 – Council decides to restore road access. Detailed design work scheduled to be complete by October 2024.
• Early 2025 – Subject to funding, construction begins.
• May 2025 – Road due to re-open.

About Blue Bluff

The Blue Bluff section of the Ōtaki Gorge Road, 12 kilometres inland from the Peka Peka to Ōtaki Expressway, is an area that becomes active during wet weather.

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