Moving Franz Josef township from fault line would cost $300m
Thursday, 26 October 2017
Moving the township of Franz Josef away from a major fault line and a rising river would cost around $300 million, a report has found.
It would be a significant capital cost for a community with fewer than 300 ratepayers.
Natural hazards threaten the town's ongoing existence, but there was no clear winner among the options to manage them, the report concluded.
The tiny West Coast community has a permanent population of 510, but hosts more than half a million visitors each year. They come to see Franz Josef glacier, which is one of the country's most visited attractions - about 700,000 visitors went there last year, one in every five that entered the country.
The township lies directly on the Alpine Fault, which on average produces a large earthquake every 300 years. The last such earthquake was in 1717.
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It is also adjacent to the Waiho River, which is increasingly prone to flooding as the riverbed aggrades. Much of the town is below the river level.
A report commissioned from Tonkin & Taylor and EY by the West Coast Regional Council analysed three options for the town's future.
One included moving the township to Lake Mapourika, abandoning the current location.
A compromise option would relocate some key assets away from the fault and the river's flood plain, but leave the town largely where it is.
Another possibility would leave the town in place and defend against the river by building stopbanks and digging gravel from the riverbed, reducing the risk of flooding.
A cost benefit analysis determined moving the township would cost around $300m. The benefits of doing so would amount to around $120m.
It would entirely reduce the risk of natural hazards, however, unlike the other options, and would create new opportunities for businesses and tourism.
The other two options would require acceptance of ongoing risks from both earthquakes and flooding, even with management. Both would also affect the area's visual amenity, through construction of large stopbanks and gravel pits, and have ongoing costs in perpetuity.
A major risk to the town was damage from a landslide prompted by an earthquake. The probability of such an event happening was unknown.
'In the event of a large rock landslide, loss of life and loss of capital is likely to be very high and could result in Franz Josef township being abandoned,' the report said.
Based on current patterns, the flooding risk from the river would increase, leaving the town uninhabitable if nothing was done.
'If left unmanaged, it is likely to be less than 30 years before the Waiho River is above the level of the township,' the report said.
'This places a level of urgency on a decision to manage the risk from this hazard.'
The community would be consulted on the various options in the coming months, before a business case was prepared.
While no option was overwhelmingly favoured above the others, there was a clear argument for something to be done, the report said.
Owing to the community's small size and its value to New Zealand, it would have to be a national discussion.
'The case for change has demonstrated that doing nothing in Franz Josef is not a viable option if the value that is present within the community is to be retained,' the report said.
'The scale of the value at stake in Franz Josef demonstrates that this is a local, regional and national conversation.'
The Westland District Council removed a fault avoidance zone from a district plan last year, despite being urged not to by four University of Otago scientists. They warned of the catastrophic danger posed by an earthquake.
It prevented businesses from developing on the faultl ine. The zone had been appealed to the Environment Court by a group of local business owners.