Clyde Dam ~ Building on an Active Fault

1980, May


1980s, early


1980s


1984, 11 September, by David Wethey

1985

1985circa

1985circa

1986circa

1986circa


1986, 2nd December

1987

1987


1988, 14th December


1988


1988, Aerial View


1989


1993, 13th February, by Phil Reid


1993, 19th April, by Phil Reid

1996

Clyde Dam ~ The Shocking Facts

- 1973. The Clutha Valley Development Commission was set up to evaluate potential sites, and after drilling test tunnels in the Cromwell Gorge, advised against interfering with known landslide areas which were pronounced highly unstable.

- 1976. The Clutha Valley Advisory Committee, set up by the National Government, advised against the high dam (Scheme F), preferring the low dam option (Scheme H) which would not flood Cromwell, Lowburn, the Cromwell Gorge Highway, and cause landslide issues.

- 1976. The site for the high dam was chosen by politicians, not geologists.

- 1977 April. Ministry of Works' bulldozers moved onto the site and began work, before a Water Right had been obtained and before an environmental impact report.

- 1977 late. The Government applied for a Water Right, and was granted one for the low dam (Scheme H), because the low dam would be less affected by known landslide issues. However, work continued on the high dam (Scheme F).

- 1979 November. Construction work began on the right abutment above the level of the low dam, without a legal Water Right for a high dam.

- 1980. National Government M.P.,Warren Cooper, a strong Clyde high dam and ‘think big’ proponent, announced that NZ would need six or seven dams the size of the Clyde dam by 1995, contrary to evidence of a looming over supply.

- 1981 July. The Government approved the construction of the high dam despite still not having a legal Water Right, and previous warnings regarding gorge instability.

- 1981. It was realized that there was an over production of electricity and that the dam, especially Scheme F, was not required. Construction continued mainly to keep the work force employed.

- 1981 December. The Government put the Clyde dam project out to tender. Seven tenders were received. The Ministry of Works originally tendered at $156.4 million, later revising this to $117.3 million.

- 1982, April. The Clyde Dam construction contract was awarded to a joint venture of W Williamson & Co of Christchurch and Ed Zublin AG of Stuttgart, West Germany. The winning bid was $102.6 million. Zublins were partnered with Williams Construction of Christchurch as ‘window dressing’ (2.5% of the partnership). The so-called joint venture was plagued with industrial disputes throughout the contract. Their workers also suffered more accidents than workers employed by other contractors on the project.

- 1982. Workers discovered a faultline directly under the dam and spillways. (The River Channel Fault branching from the main Cairnmuir-Dunstan Fault crossing the gorge 3kms above the dam.) Vast amounts of slurry concrete were pumped into tunnels across the fault called “shear pins” to supposedly lock the fault, even though the fault was 12-15kms deep and such “dental concrete” would be instantly broken in a large earthquake.

- 1982. The dam was re-designed with a controversial “slip-joint,” supposedly allowing 2 metres of lateral movement, and 1 metre of vertical movement. Geological evidence showed much greater movements had occured and are possible, up to 9 metres laterally! Even more alarming, one of New Zealand's leading geotechnical scientists, Gerald Lensen, warned that the River Channel Fault was a secondary "tensional fault" (expanding), and therefore the "slip-joint" was NOT designed correctly. Despite compelling evidence supporting Lensen, he was ignored. He resigned in protest and the issue was covered up.

- 1982. The Government obtained a Water Right through the National Water and Soil Conservation Authority, whose chairman, Bill Young, was also a member of the Government and minister in charge of the project.

- 1982. Landowners appealled to the High Court, citing bias and that the Government did not have a legal Water Right for the Clyde dam, and they won their case.

- 1982. The National Government, under Prime Minister Robert Muldoon, enacted the Clutha Development (Clyde Dam) Empowering Act 1982, controversially over-throwing the High Court decision and a subsequent Planning Tribunal decision against the Government (Annan v National Water and Soil Conservation Authority and Minister of Energy, Gilmore v National Water and Soil Conservation Authority and Minister of Energy), suspending the legal/lawful rights of the individual enshrined in Westminster law, and shocking New Zealanders.

- 1986. Artesian water was discovered in what was previously considered to be dry landslides in the Cromwell Gorge, signalling serious issues with reservoir safety.

- 1986-7. Construction peaked with around 1000 workers on site.

- 1987. New Zealand Electricity Department (NZED) becomes Electricity Corporation of New Zealand (ECNZ / ElectroCorp) - a state-owned enterprise.

- 1987. WorksCorp sold the ‘dam’ to ElectroCorp (ECNZ).

- 1989. April. An intense investigation began into landslide issues, involving up to 40 geologists, revealing large numbers of highly permeable loess underlying large areas of broken rock slides, throughout the gorge.

- 1989. It was realized that the 1982 re-design had omitted one of the two sluice gates. A work-around was designed costing $2 million, reducing the dams generating capacity by nearly a third from 612 MW to 432 MW.

- 1989. ElectroCorp (ECNZ) admitted that they might have to ‘mothball’ the dam because it was fast becoming cost ineffective.

- 1990 March. Serious gorge stabilisation issues were admitted, and it was announced that the project could not be commissioned without another $337 million being spent on landslide mitigation to reduce, but not remove the risks.

- 1990 May. Warren Cooper M.P. denounced recommendations from an international review team of geologists, claiming they were creating “the biggest man-made work scheme on record.” Critics noted that he had been one of the project's leading proponents.

- 1992. Commissioned 1992 (began producing some power).

- 1993. Completed.

- 1994, 23 April. Officially opened.

Prime Minister Robert Muldoon and 'Rob's Mob'

(Muldoon 2nd from left, Warren Cooper 2nd from right)

- 1996. ElectroCorp (ECNZ) was split into two state-owned enterprises - ECNZ and Contact Energy, the latter controlling the Clyde and Roxburgh dams.

- 1999. Contact Energy was privatized, with 40% purchased by Edison Mission Energy (EME) which subsequently increased its shareholding to 51%.

- 2004. EME onsold its majority shareholding to Origin Energy of Australia, which thereby obtained a controlling interest in one of NZ's largest and most expensive infrastructure assets, originally paid for by NZ taxpayers.

- 2009, May 2. Clyde high dam: “The single most monstrous environmental sin over the last 30 years.” - Michael Cullen, Radio NZ, speaking of his biggest regrets after retiring from the Labour Party. Labour inherited the dam fiasco from the Muldoon government in a snap election in July 1984, called by Muldoon after he had lost the confidence of parliament and New Zealanders. Unfortunately, Labour persevered with the ever-more problematic Clyde dam, and after National became the government in 1990, the 'monstrous environmental sin' was completed.

Clyde Dam Statistics

- Site chosen: 1976
- Construction: 1977-1993
- Commissioned: 1992-1993
- Type of Dam: Concrete gravity dam (largest in NZ)
- Dam Height: 102 metres
- Net Head of Water: 60 metres
- Width at Base: 70 metres
- Width at Top: 10 metres
- Length at Top: 490 metres
- Penstocks: 4 (plus 2 encased in concrete)
- Spillways: 4 with radial arm gates
- Sluices: 1 low level with radial arm gate
- Planned Capacity: 612MW
- Installed Capacity: 432MW
- Lost Capacity: 180MW (due to re-design error in 1982)
- Turbines: 4x Francis fixed-blade turbines connected to 108MW salient pole generators
- Total Concrete Poured: Approx. one million cubic metres
- Steel used in Penstocks: Approx. 1,350 tonnes
- Total Steel used: Unknown
- Weight of Dam: Approx. 3 million tonnes
- Annual Energy Generated: Averages 2,100GWh
- Reservoir Size: 26.4 square kilometres
- Reservoir Fill Time: 18 months (reached full operating level September 1993)
- Major Landslide Zones: 14 extending along the gorge from Cromwell to the dam
- Stabilisation Tunnels: 18kms of tunnels dug during gorge stabilization work
- Measuring and Monitoring Instruments: 6,500 originally installed
- Drainage Mitigation: 140 kilometres of drilling for drainage
- Landslide Buttressing: 5 million cubic metres of rock used in buttressing work
- Land Flooded: 2,300 hectares
- Operational Range of Reservoir: Between 193.5 to 194.5 metres above sea level
- Reservoir Storage Capacity: Described as "Not much"


Stabilisation Cost: $936 million (2005 value)

TOTAL Project Cost: $1.4 to 2 Billion (exact cost is unavailable or unknown)


Operation: The reservoir does not have much storage capacity, so the Clyde dam operates mainly on a ‘run of the river’ basis, with the average flow past the dam reflecting the natural flow of the Clutha and Kawarau Rivers. The expected variation of the reservoir is about 50cms. When inflows are low, storage at Lake Hawea is drawn down to compensate. The high dam option (Scheme F) was built supposedly to maximise generation and cost-efficiency. But the low dam option (Scheme H) could also have operated on a ‘run of the river’ basis with only 2% less output, avoiding the loss of old Cromwell, Lowburn, and a massive cost overrun. The low dam (Scheme H) would also have incurred fewer landslide issues, retaining 16kms of the original 21 km highway through the Cromwell Gorge. However, both options were inherently flawed, and were not defensible when measured against the geo-technical risks, landslide mitigation costs, long-term reservoir sedimentation issues and costs - including eventual decommissioning, loss of ecosystem integrity, and heritage and human costs.

A Brief History

Long before the Clutha Mata-Au had a name, before the Moa-hunters, and before the gold-rush, a mighty earthquake ripped through the Cromwell and Kawarau Gorges, providing new outfalls for Lakes Wanaka and Wakatipu. The Upper Clutha Mata-Au and the Kawarau Rivers were born, and the confluence of these powerful rivers cut the famous 'Cromwell Junction.'

Maori explorers, Ngai Tahu and Kai Tahu ki Otago, followed the Mata-Au inland, through a wild and untouched land, hundreds of years before Abel Tasman sighted New Zealand. Their seasonal explorations yielded prized argillite stone, fibres from flax, from the fronds of the cabbage tree and from the leaves of the Celmisia mountain daisy. They also came for foods such as Moa, eel, duck and pigeon. In time, they established campsites and seasonal inland settlements.

Nathaniel Chalmers, a young twenty-three old in search of good sheep country, was the first European to ascend the river in 1853. He was guided by two old Maoris, Chief Reko and Kaikoura, paying them in advance with a three-legged iron pot. The old Maoris were veterans of the river route, such that when Nathaniel Chalmers fell ill, they simply constructed a mokihi, or koradi (flax flower-stalk) raft, and guided him down the river, fearlessly running major rapids in the Cromwell and Roxburgh Gorges.

Perched above 'the meeting of the waters' grew the 1860's gold-rush town of Cromwell, overlooking the spectacular Cromwell Gap Rapid. When the gold workings declined, farming and fruit-growing became the town's mainstay. Little changed until the 1980's, when the then National government's 'Think Big' agenda brought massive upheaval as plans for New Zealand's largest concrete gravity dam moved ahead, despite widespread protest.

The exploitation of the Clutha for maximum power at any cost, was driven by departmental and political ambitions that would prove too insidious to be checked, even by the courts. The inexorable weight of the NZED (New Zealand Electricity Department) and the MOW (Ministry of Works), coupled with a secret deal made by naive government ministers providing COMALCO (Rio Tinto) with cheap electricity, set the agenda and fuelled the official lust for power.

Threatened landowners went to the High Court, winning their case against the Government. But the democratic provisions of the New Zealand legal system were over-ruled by the Government, lead by Prime Minister Robert Muldoon, and the dam went ahead, in what can only be described as one of the most shameful chapters in the history of New Zealand.

During construction of the dam, the bed-rock was found to be microfractured because of a major earthquake faultline. Vast amounts of slurry concrete were pumped into the rock to stop water leaks. Subsequent landslide stabilization problems halted the project while experts debated safety issues. Eventually, the Government decided to proceed, and 18kms of drainage tunnels, with 24-hour pumping and monitoring stations, were embedded in the 'slide zones' of the gorge. A massive cost blow-out brought the total cost to nearly $2 billion, amidst continuing controversy over the dam's safety, viability and necessity.

In 1992, the rushing waters of the Cromwell Gorge were silenced as the reservoir behind the Clyde Dam began rising. Filled in three stages between 1992-93, the reservoir gradually flooded the spectacular Cromwell Gorge, the historic heart of Cromwell, many orchards and homes, the settlement of Lowburn and the surrounding fertile farmland - a total of 2300 hectares of the best orchard and farmland in Central Otago.

The lifespan of the dam is estimated to be 80 years, but opponents doubt that it will survive that long, given the ongoing instability of the Cromwell Gorge, the risks posed by earthquakes and landslides, and the speed of reservoir sedimentation.

Clyde Dam Burst ~ What Would Really Happen?

It is often said that if the Clyde dam ruptured, the resulting torrent would bypass the town of Clyde allowing sufficient time for the residents to leave before the waters arrived. This is an official myth.

What would cause a dam burst?

Earthquake:
Obviously, a large quake along the Alpine Fault could wrench the Cairnmuir-Dunstan faultline laterally a few metres or even several metres. This fault is some 3 kilometres above the dam. Gerald Lensen, one of New Zealand's leading geotechnical scientists when the dam was being built, maintained that this fault movement would tend to open up the secondary River Channel Fault which branches off the main fault and runs directly under the dam. This opening movement is described as “tensional," and alarmingly the “slip-joint” is designed for lateral movement, not tensional. Regardless of this argument, a large earthquake has the potential to rupture the dam. Earthquakes are the main cause of concrete dam failures.

Earthquake Generated Wave:
Just as earthquakes cause ocean tsunamis, they can also cause wave events on inland waters. The Alpine Fault is moving laterally while one side tilts upward and the other side is subducted. The Clyde “slip-joint” is designed to cope with a maximum of 1 metre of vertical movement, and two metres of lateral movement. If such a 1 metre vertical movement occurred in a strong earthquake event, the bed of the reservoir on the upward side of the fault would be abruptly lifted. It has been calculated that a 1 metre lift would move 23 million cubic metres of water, generating a swift and destructive wave. It would carry debris from the sides of the gorge that when combined with the force of the wave, could do catastrophic damage to the dam. Such an earthquake-induced wave would at least overtop the dam with devastating consequences.

Landslide Generated Wave:
Any large landslide in the Cromwell Gorge could cause a wave capable of overtopping the dam. The likely cause of such a landslide is heavy rain or an earthquake. The wave would travel in both directions, towards the dam, and towards Cromwell, and could be powerful enough to do considerable damage. For example, if the massive Nine Mile slide collapsed into the reservoir it could easily block the gorge creating a fast-moving and devastating wave. It is possible that the dam could survive a wave strike reasonably intact, though the Clyde dam is not the stronger arch design. Even if the dam wasn't breached, the overtopping wave could still cause a major disaster. The wave could be 100 metres high and such a wave would travel at around 160-240 kilometres per hour, devastating a large area below the dam.

Earthquake, Landslide, Wave:
In the event of a large earthquake, any one or all three of the above scenarios could occur. For example, an earthquake could rupture the dam without causing a significant wave, or both a rupture and a wave could occur. Also, an earthquake might do minimal damage to the dam, but cause a large landslide generating a powerful overtopping wave, which might rupture the dam or flow over it, causing a disaster either way. Worst of all, is the combination of an earthquake rupturing the dam, followed by a wave induced by the same earthquake, and also landslides caused by that earthquake, in turn causing more waves.

So what would really happen in an overtopping or dam burst event?

It is ironic that the “slip-joint,” hailed as an innovation to mitigate earthquake damage, could itself become a weakness if it failed to work as designed. If the wedge pulled apart during an earthquake or was damaged sufficiently to cause a breach, the resulting leak would be under immense pressure, and what would happen then is open to speculation. If the flow increased, how that could be stopped from rapidly deteriorating into a catastrophic dam burst is unknown.

The dam was built in two “halves” either side of the 2 metre wide join. The left side (facing), furthest from Clyde, was built by the Ministry of Works, while the right side (facing), closest to Clyde, was built by Zublin-Williamson. During construction the German contractors (98% of the so-called Zublin-Williamson “joint venture”) were found to be rushing the preparation of the concrete batches, pouring them so fast that “honeycombing” was occurring. The supervising contractor, the Ministry of Works, repeatedly asked for sub-standard poured blocks to be drilled out and re-poured. This has led to a widely held view that the right side of the dam has weaker block work than the left side.

In January of 1990, Electrocorp released a report of their findings following a computer modelling exercise using a US software programme called ‘Dambrk.’ The software was developed to determine the extent of damage in the event of a dam being overtopped or breached. The results depended entirely on the data input, and in this case Electrocorp entered the scenario of a 20% outflow of the reservoir, said to be the equivalent of a maximum flood. They expected this water to be released through the three “blocks” nearest the right side abutment, presumably the weakest part of the dam.

Whether a rupture occurred through the “slip-joint” or on the right side, in both parts or elsewhere, the sudden release of water would be phenomenal. The water would blast through the dam at 160-240 km per hour, scouring everything as it went, carrying ever more debris as it pulverised everything in its path. Rocks and boulders, trees and buildings, cars and people, would all be swept away in the disaster.

Impression using Photoshop of a failure in the Clyde dam "slip-joint" caused by an earthquake

An overtopping landslide wave would have less pressure but would still travel almost as fast as water rupturing through the dam. If the dam survived the wave strike, the wave pouring over the dam could still scour down the block work or scour into an abutment. The water would blast through any weakness. Such a wave would not necessarily travel directly down the gorge, but could wash from side to side, and therefore could strike the dam initially on either side.

Impression using Photoshop of a breach in the right facing blocks of the Clyde dam caused by a landslide wave

According to Electrocorp, however, the waters issuing from an overtopping or dam burst event would take a full 6 minutes to reach Clyde, even though this is longer than it takes for the river to cover the same distance in normal flow. They said that the Clyde Bridge would be washed away, and that a “gentle swell” would go down the river and reach Alexandra in 1.5 hours, where the river would be some 12.5 metres above normal at the Alexandra Bridge, supposedly equivalent to a 1000 year flood. The report said that there would be some flooding in Alexandra, and more serious flooding in the Manuherikia area, before the water would flow down the Roxburgh Gorge.

Electrocorp’s version of events was unbelievably benign. Strangely, they considered their ‘Dambrk’ report to be insufficient for the purpose of Civil Defence planning. This alone, suggests that the report was too unreliable, too deficient in realistic input data, too fictional, to be taken seriously. In short, they belittled what is a gravely serious issue, trying to make it palatable to the public.

What would happen to the Roxburgh Dam?

Remember, all that water has to go somewhere, and a wall of water and debris travelling at 160-240 kms per hour doesn’t give much warning, or allow much preparation for the coming disaster. The main form of mitigation at the Roxburgh dam, Electrocorp said, would be lowering the level of the reservoir. The Roxburgh dam, they said, if it was discharging and generating to capacity, could lower the Roxburgh reservoir 45cms in 6 hours.

It is difficult to imagine that this would be enough to contain the water surging down the gorge. The narrowness of the upper gorge would certainly restrict but also speed up the flow, and at the lower end of the gorge where it turns in an ‘S’ shape and opens out around McKenzie’s Beach, the wave would diminish, but the dam would still be faced with more water than it could safely spill. If the initial surge left the dam intact, the rising reservoir would soon overtop the dam and there would be no way to prevent widespread, catastrophic flooding, and probably a major dam failure.

We are supposing, of course, that if the cause of the devastation at the Clyde dam was an earthquake, that the Roxburgh dam was spared, and did not also breach or receive an overtopping wave at the same time. But either way, the Roxburgh dam is unlikely to survive.

Millions of tonnes of silt would be drawn down and spread out over the Teviot Valley. The surge of water, silt and debris would be partially restricted at Dumbarton Rock, but would nevertheless continue towards the sea, destroying and burying everything in its path. At Balclutha, the speed of the flood would be slowing and the level of silt and debris would be reduced to perhaps a few metres, and yet the waters would still inundate the town within minutes, flowing out across Inch Clutha into the Pacific.

Is there a dam disaster like this on record?

The Cromwell Gorge has been compared to a valley in northern Italy, where a dam was completed on a tributary of the Piave River in 1961. The 262 metre high Vajont arch dam was regarded as an engineering triumph. The people living below the dam were assured that the dam was safe. The sides of the gorge above the dam became unstable when the reservoir was partly filled. The reservoir was repeatedly raised and lowered as the landslide areas were monitored. Engineers and officials were reluctant to admit there was a serious threat to the dam.

On October 9, 1963, at approximately 10.35pm, heavy rain caused a 260 million cubic metre landslide into the reservoir, moving at up to 110 kms per hour. The wave that overtopped the dam was 100 metres high. It reportedly advanced down the valley with incredible speed, preceded by an atmospheric shock-wave. It soon engulfed the towns of Longarone, Pirago, Rivalta, Villanova and Faè, destroying everything in its path, killing 1,450 people. The torrent then swept into smaller villages in the territory of Ert e Casso and into the village of Codissago.

Almost 2,000 people (some sources report 1,909) perished in the Vajont dam disaster. The devastated region was described afterwards as a “mud-covered coffin.” Remarkably, only part of the dam, the top of the right side, was damaged, demonstrating that arch dams provide excellent resistance to wave events, albeit a disaster can still occur. It was later shown that geological investigations had been deficient.

Aftermath of the Vajont dam disaster

It is sobering to realise that such a deadly disaster could occur as the result of an overtopping event. Surely, a dam breach in a non-arch dam would prove even more devastating because a much greater volume of reservoir water would pass through such a ruined dam.

Money and pride first, safety last?

When it comes to admitting the possible extent of the devastation following a dam disaster at Clyde or Roxburgh, there is a noticeable paucity of official information. When the 1999 flood caused serious damage to Alexandra, because of the silted up river bed at the top end of the Roxburgh reservoir, a hue and cry went out to Contact Energy, the dam owners, to fix the problem. Reluctantly, they offered up limited compensation and some remedial flood protection work. They readily exploit the river, but when their activities cause damage, they are difficult to hold to account. This is indicative of a “head in the sand” approach to dam safety issues (perhaps that should be “head in the silt”). Profit drives any business, and dams are built and managed with a degree of conquering arrogance that never really understands that rivers, and tectonic plates, always have the last say.

The Clyde dam is a monument to engineers and politicians. Few among them would admit that they have built a potential disaster. That pill is too bitter to swallow. But the landslides in the Cromwell Gorge are still feeling the impetus of gravity. The rain still falls, sometimes in thunderstorms. Earthquakes still happen, and the “big one” along the Alpine Fault is overdue. When the Earth or the sky rumbles, let the dam builders explain how safe their dams are, and ask yourself ~ why should they be able to risk your town, or your life?

An independent review into the safety of the Clyde and Roxburgh dams is urgently needed. Grave mistakes have been made, and it’s time to face up to the potential consequences of dam failures on the Clutha. Of course, it usually takes a tragedy to kick start such a process.

If you are standing in the main street of Clyde when a wave overtops the dam, don’t wait 6 minutes for it to “gently” arrive. You will probably have a few seconds …

Clyde Dam ~ The Slip-Joint Problem

The Clyde dam "slip-joint" has been hailed as a design and engineering triumph. When dam workers discovered a faultline during foundation work in 1982, little was known about the geotechnical characteristics of the site, and although instability was a known issue in the Cromwell Gorge, the underlying reasons for this had not been investigated in any detail.

So what exactly did the dam workers discover?

In this case, the fault was essentially a band of pulverised schist rock, running along the bed of the gorge on the right side of the dam (facing). This fine material, between solid rock structures, indicated that substantial movement had occurred on either side.

Some remarkable decisions followed the discovery of the fault, before the full extent of the problem was known. Vast amounts of slurry concrete were pumped into "shear-pin" tunnels drilled across the fault. This grouting was intended to lock the fault blocks together under the dam foundations.

The River Channel Fault, however, is 12-15 kms deep, and critics maintained that the grouting would simply be torn apart, along with the surrounding rock, in a large earthquake. The grouting was described as "dental concrete."

The dam was rather hastily re-designed in 1982, so much so that a sluice channel was omitted from the plans, and the dam workers, of course, built the dam without the missing sluice gate. A later "work around" solution cost $2 million and reduced the dam's generating capacity from 612MW to 432MW.

The most important feature of the re-design was the "slip-joint." It was not based on a known and tested design. However, it was innovative and was regarded as "state-of-the-art" geotechnical engineering. As such, the designers won an award.

Location of the Clyde dam join and "slip-joint"

The design premise of the "slip-joint" is that the fault will "slip" sideways and perhaps uplift in a large earthquake. To mitigate such movement, the dam was built in two "halves" with a two metre gap between them, sealed on the reservoir side by a vertical concrete "wedge plug" that is held in place by water pressure. The theory is that this "wedge plug" will allow up to 2 metres of lateral and 1 metre of vertical movement, while the water pressure holds it in place against the dam.

Inside the Clyde dam join looking toward the "slip-joint" wedge


Looking up the wedge


Looking down the wedge

An obvious issue arises if the movement exceeds the design capability. Research has revealed that both small and large movements have occurred on the site, and have been as much as 9 metres laterally. The Alpine Fault has not had a major rupture since 1770, and one is expected within the next 1-20 years in the order of magnitude 8+. Such an event has the potential to result in more than 2 metres of lateral movement through the dam. This shearing action would render the "slip-joint" ineffective, and water under enormous pressure would be forced through the join, perhaps precipitating a catastrophic failure.

But there is another issue that raises a serious question, to say the least. Was the "slip-joint" design premise correct?

The River Channel Fault is described as a "Secondary Fault" because it branches from the main Dunstan-Cairnmuir Fault that dissects the gorge some 3 kms above the dam. Gerald Lensen, one of New Zealand's leading geotechnical scientists involved in active fault research and mitigation planning, maintained that the River Channel Fault was tensional (apart rather than lateral), and therefore the "slip-joint" was NOT designed correctly.

Lensen's analysis becomes clear when the geotechnical structure is examined. The "slip" movement will naturally occur in the main Dunstan-Cairnmuir Fault, and since the secondary River Channel Fault is at right angles to this, it will pull apart as the main fault moves laterally. This opening process had contributed to the formation of the Cromwell Gorge.

The extent of this tensional movement is difficult to estimate, but any such movement must be a serious issue for a "slip-joint" that was not designed to accommodate any significant tensional movement. In a major earthquake, it is possible that the two metre wide “slip-joint” would simply open up and a serious failure could occur as the two 102m high dam "halves" separate. Such an earthquake could also trigger one or more landslides in the gorge, compounding any dam rupture.

Can we have confidence in the "slip-joint?"

It is disturbing to think that the "slip-joint," accordingly, should have been a "tension-joint," or in other words an expansion joint. The folly of building a large concrete dam on an active fault, with an ineffective engineering solution, is both alarming and potentially tragic. Presumably, the dam builders, and the "slip-joint" designers, have faith in their solution. But it is difficult to understand how experts could disagree on such an important issue.

Given the penalty for failure, and the high degree of uncertainty, there was only one safe and rational solution - not to proceed with the dam. But the "think big" politicians and the dam builders were not prepared to swallow such a bitter pill. They decided to accept the risks, on our behalf.

It is precisely because of the complex nature of geotechnical issues that the International Commission on Large Dams (ICOLD) advises against building concrete dams on active faults.

The fact that the Clyde dam was completed in the face of such risks is an indictment against all those responsible. The fate of the dam is, chillingly, in the lap of the Gods. For safety reasons, there is a compelling case for early decommissioning, but the same attitudes that built the dam would certainly dismiss such a call.

Sadly, it will probably take a major rupture of the Alpine Fault, and a failure of the "slip-joint," to draw attention to this potentially deadly issue.

Is the Clyde Dam Safe?

This question has been vigorously debated since the discovery of the ‘River Channel Fault’ beneath the dam, after which investigations revealed that major geo-technical hazards exist throughout the Cromwell Gorge.

The fault beneath the dam is 12-15kms deep and is connected to the larger Dunstan-Cairnmuir Fault a few kilometres above the dam. This system is part of the Great Alpine Fault. The pre-eminent New Zealand geologist of the 20th century, Harold W. Wellman (1909-1999), defined the Alpine Fault as one of the major transcurrent faults in the world, and one of the most regularly active.

An international review team of geologists was highly critical of the lack of proper pre-dam construction investigation work. It was not at all clear if and when the dam could be made safe. Some experts were adamant that no amount of remedial work, on the dam design and to the landslide zones, could reduce the risks to an acceptable level.

Gerald Lensen (1921-2004), a colleague of Harold Wellman, and one of the leading scientists on active fault research in New Zealand, strongly opposed siting the dam above the fault. Lensen, despite being well-known and highly respected internationally, was regarded by the Government as a nuisance. His brilliant contribution to the New Zealand Geographical Survey, Department of Scientific and Industrial Research (DSIR), ended in 1981, when he resigned in protest (the official line is that he ‘retired’).

Lensen’s view, that concrete dams should not be built on active faults, is now the accepted international norm, espoused by the International Commission on Large Dams (ICOLD).

Controversially, the dam was re-designed in 1982 to incorporate a “slip-joint” intended to accommodate up to 2 metres of lateral movement and 1 metre of vertical movement, in the event of a major earthquake. However, research has revealed that as much as 8-9 metres of lateral movement has occurred on the site in the past and is possible again. Other research points to an imminent "great earthquake."

Associate Professor Jim Davies, Canterbury University, in a talk given at Cromwell, Wanaka and Queenstown, 8-10 October 2007, stated that:

‘The historical patterns of earthquakes and current research on the Alpine Fault indicate that it is likely to rupture very soon. It is 280 years since the last earthquake. The current pressures in the tectonic plates make it probable that the next earthquake will occur in the next 1-20 years.

With an expected magnitude of 8+ this will be considered a "great earthquake" not simply a strong one. The force will result in a horizontal earth shift of up to 8 metres, and a vertical displacement of 4 metres. The effects will be worst in West Otago, diminishing eastward.

The effects will be amplified in South Island mountainous regions and high country where enormous damage can occur to peaks and ridges. Countless landslides can be expected of all sizes. In areas where the magnitude is plus or minus 9, many tens of millions of cubic metres of rock and scree may collapse from slopes.

Damaging aftershocks are likely to continue for several weeks afterwards and the event will have disastrous consequences across many regions. Less intense shaking will continue for months. Liquefaction and widespread ground damage will occur.’

So what would happen to the Clyde dam in such an earthquake?

A report prepared for the ECNZ in 1995, included a seismic analysis of the Clyde dam, stating:

‘The Clyde dam block stresses and accelerations were estimated using linear elastic finite element methods taking account of reservoir and foundation interaction for both the Operating Base Earthquake (OBE) and Maximum Design Earthquake (MDE) loading cases. Concrete stresses were generally less than 1.5MPa for the OBE and showed that cracking was possible in the MDE. These higher MDE stresses were judged acceptable.’

Given that the MDE (Maximum Design Earthquake) is one that would result in no more than 2 metres of lateral movement, and that the expected earthquake could result in 2 to 4 times this amount of lateral movement, it would appear that the “slip-joint” is poor mitigation, at best. Gerald Lensen also insisted that the fault movement would be tensional (would pull apart), and as such the “slip-joint,” which is not designed for tensional movement, would not work effectively.

If the dam survives the next "great earthquake," liquefaction of the loess within the Cromwell Gorge landslide zones could still cause massive deformation, resulting in waves overtopping the dam and reaching areas up the reservoir around Cromwell.

A staggering $936 million was spent stabilising fourteen major landslide zones in the gorge, to hopefully prevent this scenario. Yet most of the gorge is potentially unstable on both sides and in a regional magnitude 8+ earthquake movement must be considered likely in some areas, including some of the known landslide zones.

So what are the likely scenarios for the Clyde dam?

It is expected that a MDE (Maximum Design Earthquake) resulting in no more than 2 metres of lateral and 1 metre of vertical shift, would cause cracking. The “slip-joint” would be ‘spent’ and possibly leaking. The vertical concrete "wedge" on the reservoir side of the "slip-joint," held in place by water pressure, would be pushed against the two deformed sides of the joint, and intense pressure loading could cause further rupturing. If the fault movement is tensional (apart), the two metre wide “slip-joint” would simply open up and a major failure could occur as the two 102m high dam "halves" separate. An MDE could also trigger one or more landslides in the gorge, compounding any dam rupture.

If the next earthquake exceeds the MDE, it is likely there would be multiple failures in the dam and within the landslide zones in the gorge. The Clyde landslide zone directly above the west side of the dam is a particular concern. The consequences of such failures would be catastrophic and many lives could be lost.

But even if the dam performs to its design specification, and a disaster is averted, what happens to a dam that has used up its design capability to withstand an earthquake?

The Clyde dam was built to last 80 years. Regardless of how long it survives, decommissioning will be an expensive exercise involving the removal of the dam, and the restoration of the Cromwell Gorge. Decommissioning and river restoration costs for a large dam are calculated as a proportion of construction costs, and are between 35% and 150%. De-silting the reservoir will be a major cost component, requiring a staged restoration plan, taking years to complete.

What is often overlooked, is that in any large earthquake, the Roxburgh dam would be at greater risk. There was no specific earthquake mitigation incorporated into the dam design, and there was no landslide stabilisation work undertaken in the Roxburgh Gorge, where large landslide zones are also known to exist. The Roxburgh dam had a leakage problem as early as 1963, and it has already sustained a number of seismic cracks. An active fault runs close to the dam at Coal Creek.

Unbelievably, the politicians responsible for the Clyde dam believed that the potentially catastrophic risks were ‘acceptable.’ Officially, there appears to be a ‘head in the sand’ approach to this risk. There has been, and still us, an astonishing and reckless disregard for public safety. Tragically, the most expensive concrete structure in New Zealand is also, considering the evidence, our largest single man-made hazard.

The grim reality is that no one really knows what will happen in the next major earthquake. This fact alone, is an indictment against the dam builders. Meantime, tension continues to increase in the Alpine Fault, and those who would suffer the most – the people of the Clutha River communities, wait …

References:
More...
Martin Wieland, Chairman, ICOLD Committee on Seismic Aspects of Dam Design, Poyry Energy Ltd., Zurich, Switzerland.
A. Bozovic, Former Chairman, ICOLD Committee on Seismic Aspects of Dam Design, Consultant, Belgrade, Serbia.
R.P. Brenner, Past Chairman, ICOLD Committee on Dam Foundations, Consultant, Weinfelden, Switzerland.
‘Natural event and human consequences in Queenstown Lakes and Central Otago’ Tim Davies, Associate Professor, Canterbury University, Mauri McSaveney, GSN Science, 2007.
‘Risk assessment earthquakes, volcanoes, floods and dams in New Zealand’
M.D. Gillon, Electricity Corporation of New Zealand.
‘Seismic Considerations for the Design of the Clyde Dam Transactions’
IPENZ Vol. 14 3/CE, November 1987. Hatton J.W. and Foster P.F.
‘Dams and Earthquakes in New Zealand’
Bulletin of the NZ National Society for Earthquake Engineering, Vol.1, No.2, June 1978. Hatrick A.V.
Chapter 7, Fault Provisioned Design Examples, 7.1 Mitigation Measures, after Bray, 2001, Hamada, 2003.
Hatton, J. W., Black, J. C. and Foster, P. F. (1987). “New Zealand’s Clyde power station,” Water power & Dam Construction, 15–20.
Hatton, J. W., Foster, P. F. and Thomson, R. (1991). “The influence of foundation conditions on the design of Clyde dam, “ 16th Conference on large dams, 157–177.

Large Dams on Active Faults ~ Expert Opinion

'As a general guideline, if significant movement along a fault crossing the dam site is accepted as a reasonable possibility during the lifetime of the dam, the best advice is to select an alternative site, less exposed to geodynamic hazard. Such a standpoint is supported by the fact that no dam, foreseen to successfully survive the shearing action of a fault slip in its foundation, has ever been exposed to actual test under such event.

In general, concrete dams should not be accepted for sites affected by active tectonic features.'

Quote from:
'Dam design - the effects of active faults,' by -
Martin Wieland, Chairman, ICOLD Committee on Seismic Aspects of Dam Design, Poyry Energy Ltd., Zurich, Switzerland.
A. Bozovic, Former Chairman, ICOLD Committee on Seismic Aspects of Dam Design, Consultant, Belgrade, Serbia.
R.P. Brenner, Past Chairman, ICOLD Committee on Dam Foundations, Consultant, Weinfelden, Switzerland.
Dated Tuesday, August 19, 2008.
International Commission on Large Dams (ICOLD).

References:
More...
Allen, C.R. & Cluff, L.S., 2000. Active faults in dam foundations: an update. Proc. 12th World Conf. on Earthquake Engineering, Auckland, New Zealand, Paper 2490, 8p.
Amberg W. & Lombardi G., 1982. Abnormal behaviour of Zeuzier arch dam in Switzerland, Static analysis, Wasser Energie Luft, Special Issue to ICOLD, 74(3):102-109.
Bray, J.D., Seed, R.B., Cluff, L.S. & Seed, H.B., 1994. Earthquake fault rupture propagation through soils. J. Geotechnical Engineering, ASCE, 120(3):543-561.
Gillon M.D., Meija L.H., Freeman S.T. & Berryman K.R., 1997. Design criteria for fault rupture at the Matahina dam, New Zealand, Int. J. on Hydropower and Dams, 4(2):120-123.
Hatton J.W., 1991. Clyde Dam slip joint, Trans. 17th Congress on Large Dams, Discussion Q.66-7, 5:365-367.
Gilg, B., Indermaur W., Matthey F. Pedro, O., Azevedo, M. & Ferreira, F., 1987. Special design of Steno arch dam in Greece in relation with possible fault movements. Proc. Int. Symposium on Earthquakes and Dams, Beijing, Chinese National Committee on Large Dams, 1:202-218.
ICOLD, 1989. Selecting Seismic Parameters for Large Dams, Guidelines, Bulletin 72, Committee on Seismic Aspects of Dam Design, ICOLD, Paris.
ICOLD, 1998. Neotectonics and Dams, Bulletin 112, Committee on Seismic Aspects of Dam Design, ICOLD, Paris.
McMorran, T. & Berryman, K., 2001. Late Quaternary faulting beneath Matahina dam. Proc. Symp. on Engineering and Development in Hazardous Terrain, Christchurch, New Zealand Geotechnical Society, pp. 185-193.
Mejia, L., Walker, J. & Gillon, M., 2005. Seismic evaluation of dam on active surface fault, Proc. Conf. Waterpower XIV, Austin, Texas, USA, Paper 066, HCI Publications Inc., July, 2005.
Sherard J.L., 1967. Earthquake considerations in earth dam design, J. Soil Mechanics and Foundations Division, ASCE, 83(SM-4):377-401.
Sherard J.L., Cluff L.S. & Allen C.R., 1974. Potentially active faults in dam foundations, Géotechnique, 24(3):367-428.
Wells D.L. & Coppersmith K.J., 1994. New empirical relationships among magnitude, rupture length, rupture width, rupture area and surface displacement, Bulletin Seismological Society of America, 84(4):974 -1002.
Wieland M.; Brenner R.P.; Sommer P. 2003. Earthquake resilience of large concrete dams: Damage, repair, and strengthening concepts. Trans. 21st Int. Congress on Large Dams, Montreal, Q83-R10, 3:131-150.

The Cromwell Gorge Railway

'The Dunstan (Cromwell) Gorge is a scene such as Salvator Rosa would have loved to paint; and if it were brought within the reach of cheap steamboats or Parlimentary trains, it would be thronged with artistic visitors, and vulgarised by gaping tourists.' ~ Vincent Pyke, Chapter 3, 'The Story of Wild Will Enderby', 1873.

As early as 1873 it was apparent to Vincent Pyke and the residents of Central Otago that a railway might one day reach inland as far as Cromwell, providing not only a freight and passenger service, but also bringing tourists to admire the dramatic landscapes of the region.

Construction of the Otago Central Railway began on June 7, 1879, when Vincent Pyke turned the first sod at Wingatui, 12kms south of Dunedin. Progress was slow, however, and within a year the line had become a victim of the economic depression of the1880s. A decade passed before the first section to Hindon (27kms) was opened in 1889. Over the years, scores of labourers, stonemasons, blacksmiths and engineers worked through frozen winters and scorching summers to push the line further inland, reaching Middlemarch (64kms) in 1891, Ranfurly (123.5kms) in 1898, Omakau (178.5kms) in 1904, Alexandra (207kms) in 1906, and Clyde (216kms) in 1907. Here work stopped until 1914 after which the last 20km section of line through the Cromwell Gorge to Cromwell (236kms) was finally completed in 1921.

Cromwell Station, by Albert Percy Godber, 1930.

The Cromwell Station was opened in July 1921. It consisted of a station building, a 60ft x 30ft goods-shed, a loading bank, and cattle / sheep loading yards. Since it was a terminal station it also had an engine-shed, turntable and coal and watering facilities. The station sidings could accommodate nearly 100 wagons.

Wool bales from the Criffel run arriving at the Cromwell Station, circa mid-1920's.

In 1942 the station burnt down and a new station was built. The fire was later attributed to leaking and self combusting science chemicals awaiting delivery to the local school. The station was closed in 1976, the same year that the site for the Clyde dam was chosen. The 20km section of line, through the gorge from Clyde to Cromwell, was closed in 1980. Officially, the closures were blamed on declining activity, but it's clear that the government did not want the line to remain open because of the dam project, and that this hastened its demise.

Various steam locomotives serviced the Cromwell Station, including a 37 ton E class, a 30 ton R class, the 57 ton UB class in the 1920s and 1930s, the 78 ton A class, the 72 ton Q class in the 1940s, and the 87 ton Ab class which was used on the line from 1936. The last regular steam-hauled train left Cromwell on 23 February, 1968.

Cromwell Station with Ab663, by Stephen Buck, 1958.

Diesel-electric locomotives were introduced on the Otago Central Railway in February 1957 with the Dh class running as far as Clyde. They were re-classed as Dg in 1968 and withdrawn by 1983. These Dh/Dg class engines were too heavy to run on the lighter rails of the Cromwell Gorge. However, when the much lighter Dj class diesel locomotives (with 10.3 tonne axle loading) were introduced on 26 February, 1968, they were allowed to run through to Cromwell, replacing the remaining Ab class steam engines which were withdrawn. Di class diesels also worked on the Otago Central Railway from 1978 to 1984 but being fewer in number were seen less often than the Dj class engines, which were the mainstay of the line until its closure in 1990.

Passenger services began on the Otago Central Railway in 1900 and were replaced with mixed trains in 1917, with passenger trains only running during the busier holiday periods. The passenger trains were reinstated in 1936. One of these trains was involved in the Hyde rail tragedy in 1943. Passenger trains were again replaced with mixed trains in 1951, and in turn replaced with Vulcan Railcars in 1956. The railcar initially ran to Cromwell, but was cut back to Alexandra in May of 1958. Railcars ceased running on 25 April 1976.

Cromwell Gorge Railway in winter, by Robin Morrison, 1979.

The Otago Central Railway played a major role in the development of the region transporting thousands of tons of livestock, wool bales and fruit to market. One of the line’s busiest years was 1960 when almost 500,000 sheep left Central Otago in double-decker sheep wagons heading to sale yards and freezing works. In a good year up to 4,000 tons of fruit would leave Central Otago orchards by rail for destinations as far as Auckland. The railway also served as a supply line for equipment, food and merchandise, mail and newspapers, and excursion trains ran for the Blossom Festival and at Easter.

Ab663 in the Cromwell Gorge, 1962.

Although other branch lines in the South Island declined in the 1980s, the line to Clyde was kept open to transport construction materials such as cement and steel to the Clyde dam project. When the dam was completed, the line had little other traffic and the section from Middlemarch to Clyde was closed by the New Zealand Railways Corporation on 30 April, 1990.

The line beyond Middlemarch was lifted during 1991, and the track-bed as far as Clyde was handed over to the Department of Conservation in 1993, becoming the Otago Central Rail Trail, now a major tourist attraction.

In 1995, the Otago Excursion Train Trust, in partnership with the Dunedin City Council, formed Taieri Gorge Railway Limited, purchasing the line to Middlemarch along with some locomotives. The 60km Taieri Gorge Railway has become one of Otago’s premier tourist attractions, operated with the assistance of the Trust’s volunteer members.

Sadly, the tourism potential of the Cromwell Gorge railway was never realized.