The ugly reality facing Franz Josef


Franz Josef is a picturesque town in Westland District. It is nestled against the lower flank of the Southern Alps, with the Waiho River immediately to the south of the township. The town and the nearby Franz Josef Glacier are named after the Austrian Emperor Franz Joseph, by explorer and geologist Julius von Haast.

But for all of its mighty charm nestled in temperate rainforest, Franz Josef is caught between a rock and a hard place. In terms of geological and geomorphological hazards it is in a location that in the long term, and increasingly likely in the short term, untenable. This article takes a look at the danger facing Franz Josef.

Why?

New Zealand straddles the boundary of two tectonic plates. To the west is the Indo-Australian Plate and to the east is the Pacific Plate. The onshore boundary is denoted by the Alpine Fault, a large fault line with a repose period of 300-350 years and a tendency to only move in magnitude 8.0+ earthquakes. The last one was about 1717AD.This onshore boundary is where about 25-30mm of tectonic uplift occur per annum as well as a similar amount of erosion, which means there is a continuous supply of sediment waiting to enter the catchments of the West Coast and east coast rivers.

This relentless uplift creates a lovely mountain range with steep hydrology – from the summit of Mt Cook to the Tasman Sea is about 45 kilometres. Being in the prevailing westerly belt of winds that sailors call the “Roaring Forties” because of the latitude, moist westerly air comes off the Tasman Sea and empties its moisture content – often over 200 millimetres and up to 500 millimetres in a day – on the West Coast side. Unsurprisingly flooding becomes a major problem.

How does this affect Franz Josef?

Immediately after one crosses the Waiho River heading south, the road takes a hard right turn. In the corner is a hotel that sits behind a substantial stop bank. On the other side of that stop bank is a riverbed that is rising at a rate of about 300mm each year. The rise is because a large volume of sediment is continually entering the Waiho catchment. This poses an increasing flood risk on a river where water levels start responding to heavy rain in less than an hour.

Franz Josef straddles the Alpine Fault, which runs right through the middle of the township. It crosses the Waiho River in the immediate vicinity of the Milton Hotel, which was flooded and suffered severe damage in a 2016 outbreak. Westland District Council published Plan Change 7 (P.C.7), which was meant to identify a zone through central Franz Josef, where there is high confidence of the Alpine Fault’s exact location, with a view to moving essential services and businesses out of the zone. However after considerable public opposition, P.C.7 was scrapped.

When?

Time is running out. The stop bank is about as tall as it can realistically get without massive supporting earth works. When the river tops it, it will start eroding away the stop bank and try to reclaim the riverbed that the stop bank was originally built over. This may claim several farms when it happens.

But there is a bigger problem. The Alpine Fault is now due for another earthquake. Should it rupture whilst Franz Josef is in its current location, the town will be subject to immediate and unmistakably violent shaking lasting up to 3 minutes. There will be between 8-10 metres lateral displacement to the right and up to 3 metres vertical displacement. Only the newest structures would probably be still standing.

Before then though, there may be another rain storm of similar magnitude to the one that occurred between 25-27 March. Should that happen, similar damage to what happened as a result of that storm should be expected. This has a high probability of including the bridge over the Waiho River, which was destroyed on Tuesday 26 March. The next rain fall event might not even need to be that big.

What is the solution?

In the absence of P.C. 7 existing, one option is to give up on the stop bank and let the Waiho River reclaim the riverbed. The problem here is that several farms and the air field would have to move. It also does not address the long term problem of the Alpine Fault. Perhaps the most feasible option is progressively relocate Franz Josef township’s population and amenities to neighbouring towns. Westland District Council and West Coast Regional Council have a duty of care to the residents and the tourists and other visitors to their District/Region to make sure that they are in no undue danger.

Where could the people go?

There are several nearby townships where the people of Franz Josef could be moved to. Ross and Whataroa are two, though these are quite near the Alpine Fault. Harihari is a third. All are on the same road, State Highway 6, as Franz Josef. It would be likely that West Coast Regional Council and Westland District Council would need to prepare a joint request for Government assistance purchasing land and working out appropriate resource management issues.

For their part the Government would most likely need to provide assistance. The West Coast is economically one of the poorer parts of New Zealand. It has a small rate payer base and this has a good chance, even if well planned and executed, of blowing whatever budget is set. And if the plan went ahead, it might have to be applied to Fox Glacier as well, as it too is very near the Alpine Fault.

 

 

2 thoughts on “The ugly reality facing Franz Josef

  1. IN THE EARLY 1980’s the stop bank on the south side of the Waiho was constructed, at that time it was a considerable distance from the bottom of the bridge to the river bed. However the resulting confinement between the two stop banks, natural aggradation quickly raised the bed of the river . The south bank was built up to protect a small group of motel units. which were later removed due to flood risk. Later a few farms were developed on the south side. The decision to build the south bank and restrict the river from releasing aggregate as to date has since resulted in a cost I believe to be close to $100mil . The bridge has been washed out twice resulting in months of road closures with loss of business income throughout Westland. The Southern Circle Hotel Complex was destroyed, which is resulting in a $60mill claim against Westland District Council. The Old rubbish dump was eroded with costs incurred over many months to clean up the beaches and river, with ongoing costs to dig out the remaining site and transfer to Hokitika , nearly a two hour drive away. Also the Sewerage ponds had to be relocated. Millions were spent rebuilding both the Nth and Sth stop banks after the farms were flooded. To date the river bed is continually aggradating One cannot argue the $ return to the tax payer from the protected 2 or 3 farms on the south side of the Waiho would even come remotely close to the money spent in protecting them. A question that must be asked in these times of increasing natural hazards is, should the Tax payer be responsible for the personal financial decisions made by others? The elephant in the room is the initial decision to construct the south stop bank. There is now a suggestion to spend $20million to raise the banks further. Now is the time to remove the south bank and let the river make its own way. Of course the fault line is a major threat that is still to be addressed which makes the decision to spend even more money on the stop bank untenable.

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    • Welcome to Will New Zealand Be Right, Greg. Useful comment and I agree about the elephant in the room.

      Do you live around there or have an interest – I did a Postgrad Diploma in Hazard Management in 2005-06 and my supervisor led a field trip to examine the combination of hazards posed.

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