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Getting the Caversham Tunnel reopened for the public to use was, until now, to be the first stage of a multistaged trail development being led by the Dunedin Tunnels Trail Trust.
However, initial investigations showed considerable work was needed to make the tunnel, through which old pipelines and utility services run, safe.
Trust member Gerard Hyland said a geotechnical inspection of the Chain Hills Tunnel showed the smaller number of modern pipelines running through it provided fewer obstacles to getting it open to the public, although a structural assessment was still required.
The cost of getting the Caversham Tunnel opened was known to be around $1.6 million, while that for getting the Chain Hills Tunnel open had not yet been ascertained.
However, for the $100,000 the council had set aside in 2012-13 for the project, the trust could achieve more at the Mosgiel end, including further investigations in the Chain Hills Tunnel, help with the cost of securing access rights (easements) across private land to the tunnel and/or initial track construction costs.
''If the Chain Hills end can be done sooner for a lot less dollars, we would do it. We need to get something on the ground that people could be using."
A report to yesterday's full Dunedin City Council meeting said this approach would allow the trust to build some momentum and achieve results more quickly than a continued focus on Caversham Tunnel.
The next step would be getting the structural report on the Chain Hills Tunnel done.
Once that was received, a decision would be made on which tunnel to focus on first, Mr Hyland said.
• An important hurdle was passed yesterday, as the council agreed to a memorandum of understanding with the trust which outlined both parties' roles in the project, and which allowed the trust to start raising funds.
The council will take over maintenance of the trail once it is built.
The trust will raise the money for the project and build the trail.