A report obtained by the Nelson Weekly shows that the slip that closed the historic Dun Mountain Walkway earlier this year was caused by construction of a track for the Brook Waimarama Sanctuary’s predator fence and that options for repairing the damage could cost more than $110,000.
The report by Nelson Consulting Engineers also shows that the Sanctuary Trust, Nelson City Council and contractors, ignored geotechnical advice by cutting the track too close to the Dun Mountain Walkway, increasing the risk of a slip.
They may also have breached the conditions of the resource consent by changing the alignment of the track specified in plans to “inside the preferred 50m minimum separation to the walkway”.
However, the Brook Waimarama Sanctuary Trust and Nelson City Council would not comment on the report which was sent to them on April 28.
The trust’s general manager Hudson Dodd says he can’t comment on the report until they have completed the insurance process for the damage to the track and walkway.
The council’s only response was “we are still working through the issues with the Brook Waimarama Sanctuary Trust, to effect a permanent fix”.
The report also provides six options for repairing the damage caused by the 35m long slip, that wiped out a 20m section of the historic, 150-year-old Dun Mountain Walkway and carried debris downhill onto the fence track. The walkway was closed following the slip and was only reopened after a temporary repair was completed on April 24.
The options include stabilising the walkway and slip using retaining walls and posts, and replanting the slip, with the most expensive option costing “$110,000 or more”. Another option, to develop an alternative alignment for the fence track and fill in the slipped section of the walkway, would be “very expensive”, while a simple clean-up of the debris and replacing limited fill on the walkway would only be a high-risk temporary solution.
Well-known mountain biking advocate, Bryce Buckland, and Nelson Residents Association president, Mike Rodwell, say the report has confirmed their fears about the alignment of the fence track. Mike says the risks associated with the fence “were obvious to any practical person” and it’s disappointing the geotechnical advice was ignored.
Bryce says he is also concerned that the fence track will cause slips on other parts of the Dun Mountain Walkway and asks “who is going to pay for that?” Although the report identified the 70mm of rain that fell on March 6 as a contributing factor, Bryce says that wasn’t the main reason for the slip.
“The track’s been there for 150 years and all of a sudden it becomes unhinged? What does that show?”
Bryce also says the report shows that a daily rainfall of 70mm or more was recorded five times in the last year, with 105mm falling on April 15, 2014.
Mike, who is a former trustee of the Dun Mountain Trail, says both he and Bryce warned the council about the potential risks of conducting significant earthworks near the walkway. Bryce says the terrain near the slip is so steep “the probability of slope failure was obvious and the fence should not have been allowed near it”.
