Mighty Clutha

Cromwell Gorge ~ Pre-Dam

2009-04-16T12:57:00.000+12:00

Clyde Dam ~ The Human Cost

2009-04-15T16:25:00.016+12:00

'In all the history of Otago and of New Zealand, in peace and in war, the Clutha proposals must rank as the cruellist and most premeditated. Conceived in departmental ambition, nourished in secrecy and permitted by political indifference for people, the Clutha proposals hardened into unpalatable fact.' ~ Paul Powell, 'Who Killed the Clutha?'

Lowburn's Welcome Home Hotel, built in 1869 and the social focus of the community, was demolished and the area was flooded, '60ft under.'

Harry Perriam, orchardist, Lowburn. His apricot and apple trees were uprooted before his land was flooded.

Shorty Sutherland, and Pythagoras the cat, Lowburn. 'Someone should have shot him (Muldoon) years ago. Me, I wouldn't waste my ammunition. You can tell him that from me.'

Isie Scott, Cromwell. 'I feel our heritage, the land, is being wasted.' She was forced to leave her home on the banks of the Clutha.

Gary Forster, Station Master, and Carl the dog, Cromwell. The Cromwell station was demolished and the line through the gorge to Clyde was pulled up by the end of 1978. (Carl sitting on engine)

Rachael and Fanny Short, Bannockburn. 'I wish they wouldn't change it.'

Harry Gair, Cromwell. 'I've told my nephew (George Gair, Minister of Energy), but he won't take any notice of me.'

Jane and Ted Lawrence, and June the cat, Bannockburn. 'They (the Ministry of Works) say they'll make this place beautiful.'

Charlie Perriam, Lowburn. 'One hundred years of family lost.' The most fertile areas of his land were flooded.

Keith Lake, Northburn. His winter feed land, near the Clutha, was drowned.

Doug Stout, Presbyterian Minister, Cromwell and Lowburn. The Lowburn Valley was flooded. The church was moved to higher ground.

Rabbiters, Pest Destruction Board, Cromwell. The valley behind them was re-shaped and flooded.

These profound, haunting photos recording the human cost of the Clyde dam were taken in May 1978 by highly acclaimed New Zealand photographer Robin Morrison (1944-1993). They are displayed here with the kind permission of Dinah Keir and Jake Morrison, who note that 'The plight of the Clutha was very close to Robin's heart, as were the lives and histories of the inhabitants.'

The Cromwell Gap ~ Pre-Dam

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Clyde Dam ~ Building on an Active Fault

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1980, May

1980s, early

1980s

1984, 11 September, by David Wethey

1985

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

2009-03-29T17:43:00.021+13:00

- 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

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- 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

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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?

2009-03-21T22:43:00.005+13:00

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 …

Cromwell Junction ~ Views

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1856, by John Buchanan

1863, by John Buchanan

circa 1866, New 'Lattice Bridge'

1873-80, by Herbert Deveril

1926, by Albert Percy Godber

circa 1940s' Postcard

circa 1940s' Postcard

1948 Centennial Stamp

circa 1970s

circa mid-1980s

circa mid-1980s, by R.W. Kilgour

circa mid-1980s, Aerial View

Destruction of the Cromwell Junction

2009-03-19T11:53:00.001+13:00

Cromwell Junction before the Clyde dam

Cromwell Junction 1989

Cromwell Junction 1993

Cromwell Junction after the Clyde dam

The confluence of the Clutha and Kawarau Rivers at the entrance of the Cromwell Gorge has always been at the heart of Cromwell's identity. In fact, the settlement was originally called 'The Junction.' Even when the name 'Cromwell' was adopted in 1866, the town was often referred to as the 'Cromwell Junction' or sometimes 'the meeting of the waters.' Here, the clear turquoise waters of the Upper Clutha, mixed reluctantly with the silt-laden waters of the Kawarau.

This remarkable sight, viewed from high above, was often painted and photographed, and appeared on a New Zealand stamp. The once famous Cromwell Junction was perhaps the most spectacular river confluence in the world.

Perched high above the ‘Junction’ on a rock promontory, the historic gold-rush town of Cromwell boasted one of the most picturesques locations imaginable. Cromwell's historic main street was mostly intact with numerous gold-rush era buildings, and at the end of the street, the massive 1866 bridge crossed high above the famous Cromwell 'Gap' Rapid. A Chinese gold-mining settlement was virtually untouched on the encarpement of the Kawarau 'arm,' and further up the Kawarau was the most highly rated whitewater rapid in the world - Sargood's. Cromwell was poised to become a tourism icon, a historic town unlike any other, and a watersports Mecca.

However, 'think big' obliterated the 'Junction.' The dam builders were ruthless, not only flooding, but systematically destroying the 'Junction' as if to physically remove it from the hearts of those who loved it. When the Clyde dam is eventually decommissioned (it has a design life of about 80 years), the waters will gradually be lowered in stages and the 'Junction' will be revealed, but it will never be quite the same after restoration, which will be a long and difficult process. Large dam decommissioning and river restoration projects take about 10-15 years to complete. Worldwide, although only a few large dams have been decommissioned to date, such projects will become more common as an increasing number of ageing dams face removal. Typically, no provision is made for the cost of 'undoing the damage.' Decommissioning costs for large dams range from 35-150% in proportion to the cost of a new dam. The obvious question is, who will pay?

Landslides ~ Gravity Always Wins

2009-03-15T21:41:00.021+13:00

In 1973, a Clutha Valley Development Commission was set up to evaluate potential hydro-electric dam sites along the Clutha River. Test drilling in the Cromwell Gorge confirmed what local people already knew, that the gorge was highly unstable. A few years later in 1976, the National Government convened a Clutha Valley Advisory Committee to assess all the available information and to make a decision regarding proposals for high and low dams.

The Advisory Committee acknowledged that there was a serious instability issue, and finally voted to recommend the low dam option (Scheme H), however three members of the Committee who knew the gorge well, voted against any dam at all, referring to the prospect of inevitable landslide issues.

Surprisingly, gorge instability was given little consideration when the high dam option (Scheme F) was chosen. But in 1982 dam workers discovered a faultline directly under the dam and spillways. Investigations revealed that this was a River Channel Fault branching from the main Cairnmuir-Dunstan Fault crossing the gorge some 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.

It was acknowledged that a fault directly through the dam and spillways warranted some attention. The dam was redesigned around the fault and the "slip-joint" was invented to sit over the fault. The dam was literally built in two "halves."

As time passed, more problems came to light. In April 1989, an intense investigation began into landslide issues, involving an international team of up to 40 geologists. This investigation revealed large numbers of highly permeable loess underlying large areas of broken rock slides, throughout the gorge. It was feared that when the reservoir was raised, the water would permeate through the toes of the slides, triggering landslides into the reservoir, creating waves that could overtop the dam.

Fourteen major slide zones were identified in the Cromwell Gorge, including one beside the dam itself - the Clyde landslide. Another three major slide zones were discovered in the affected part of the Kawarau Gorge, including the Ripponvale landslide. Water was the primary issue, since water entering the permeable loess (fine layers beneath the slides) from above or below, would literally lubricate them, resulting in accelerated movement or a sudden failure.

Cromwell Gorge Landslide Areas

The rate of landslide "creep" was difficult to measure since there was insufficient data available upon which to accurately assess the amount of movement in each slide. The new road cutting above the old road had actually increased the rate of movement in many slides by removing material from the toes of the slides. Geologists soon installed instruments and estimated movements ranging from millimetres to centimetres per week or per year, subject to rain/water and earthquake induced movement. The massive Nile Mile slide, seven kilometres long and 200 metres high, was moving several centimetres per week. The extent of the problem was vast. The international team of geologists described many of the slides as "potentially catastrophic" and "very dangerous." The cost of the proposed stabilisation measures kept going up, but the work began.

Major remedial work was undertaken at nine of the seventeen landslide zones, involving toe buttressing, pumped drainage, gravity drainage, capping to reduce infiltration from above, and the drilling of "grout curtains" to reduce leakage from the reservoir into the toe area of slides.

Cromwell Gorge Landslide Stabilisation Measures

Eighteen drainage tunnels were drilled into the sides of the gorge. From these "drilling stubs" drainage holes were drilled further into the slides. A total of 140kms of drilling was undertaken for drainage, and 6,500 measuring and monitoring instruments were installed.

To install "grout curtains," holes were drilled at regular intervals to varying depths into which concrete and water was pumped under pressure. Many of these holes collapsed during drilling because of the loose nature of the material, and each time this happened, the drillers pumped in concrete and water, and later re-drilled it. This was an extraordinarily time-consuming and expensive exercise.

Buttressing rock was also placed across the base of some slides to provide some frictional resistance. A total of 5 million cubic metres of rock was used in buttressing work.

The Cairnmuir landslide posed a significant challenge, since the upper material was particularly loose and permeable, and riddled with rabbit holes. A network of drainage tunnels combined with buttressing at the toe of the slide failed to stop it moving, so it was eventually decided to pave and terrace the top of the slide to seal out water, creating a bizarre amphitheatre. The rate of movement slowed, but the additional weight means that any increased infiltration could result in an even greater failure.

Cairnmuir Landslide during stabilisation work

Cairnmuir Landslide ~ Aerial View

In the end, the investigation and stabilisation work cost a staggering $936 million. Work on the Nine-Mile landslide alone, reportedly cost $60 million.

Landslide "creep" has been reduced, but monitoring indicates the continuing potential for slide zone failure. Monitoring has shown that movement of a known "active" part of the Brewery Creek landslide is triggered when the water level exceeds a critical threshold in a key piezometer (instrument for measuring hydraulic pressure). Records also show that movement of part of the Ripponvale landslide increases following prolonged rainfall, and that it is highly sensitive. Data indicates that the rate of movement of the Ripponvale landslide increases when the cumulative rainfall during a period of 3 to 4 months exceeds a total of about 300 mm. It has been suggested, alarmingly, that a failure of the seven kilometre long Nile Mile landslide could form a debris dam causing a catastrophic wave event, followed by widespread inundation in the Cromwell area.

Despite all that has been done, and the mind-boggling cost, major landslide zones in the Cromwell Gorge are still prone to failure under the impetus of heavy rain events, and of course earthquakes. The landslide risk has not been removed, and no one knows when the next major landslide will occur.

Lowburn ~ Sold Down The Reservoir

2009-03-15T17:18:00.019+13:00

Lowburn residents outside the Welcome Home Hotel, 1978

The Lowburn community began as a prominent ferry landing during the early years of Central Otago's settlement, when travellers moved between the goldmining reefs of Bendigo and the township of Cromwell. A ferry or punt began operating on the Clutha River at Lowburn from about 1873, and the crossing, with its tree-lined approaches and picturesque setting became not only an important link between Cromwell and the lakes at Wanaka and Queenstown, but also a popular tourist excursion. A bridge was built in 1938 replacing the punt, and the occasion was celebrated by a banquet at the Lowburn Ferry Hotel followed by a dance at the Lowburn Hall.

So important was the ferry, that even after the bridge was built, the community was still referred to as Lowburn Ferry. Beyond the settlement at the crossing, the valley extending up the river contained some of the most productive farmland in Central Otago, and some of the most scenic. Orchards also filled the smaller valley behind the hotel, where an ideal micro-climate suited the stonefruit grown there.

Clutha River, Lowburn, before the Clyde dam

The inner floodplain of the Clutha River, naturally braided as it approached Deadman's Point, had been extensively dredged above and below the crossing, and this unique section of the river had become a maze of river channels and swimming-holes, lined with mature willows, sometimes called the 'Hundred Islands'. Not surprisingly, the area had become popular with campers during high summer. Small tracks weaved among the old tailings, arriving at campsites and swimming-holes.

'Hundred Islands' above the Lowburn crossing

Rumours of further hydro-electric development that might inundate more gorges and valleys had circulated since the completion of the Roxburgh dam in 1956, and these rumours surfaced with a vengeance in the 1970's. Uncertainty over the future of the Lowburn area became a topical subject in the Lowburn pub as locals contemplated the possible demise of their community.

In the lead up to the New Zealand elections in 1975, one aspiring candidate was Warren Cooper. When questioned at the Lowburn pub by Shorty Sutherland, a retired gold-miner who lived across the road, Mr Cooper promised not to flood Lowburn and the pub. Mr Cooper said: "If you want water in your whiskey, vote Labour."

Shorty Sutherland, and Pythagoras the cat, Lowburn. 'Someone should have shot him (Muldoon) years ago. Me, I wouldn't waste my ammunition. You can tell him that from me.' He was assured by MP Warren Cooper that Lowburn would not be flooded.

In 1977, Warren Cooper MP, strode onto the recently constructed Clyde dam lookout, beyond which work had begun on the dam that would eventually flood the Cromwell Gorge, part of Cromwell and much of the Lowburn area including five orchards and the Lowburn pub - where he had made his earlier promise not to flood the hotel and the surrounding area. He had come to address a protest group called "Clutha Rescue," who had set up camp at the lookout. Mr Cooper asked: "Why can't you support me over the construction of this dam?"

The building of the dam was opposed by five landowners at Lowburn and two in the Cromwell Gorge. They took their case against the Government to the High Court in Wellington, who ruled in their favour, determining that there was no end user for the power at Clyde and that the applicant had no water right.

But Prime Minister Robert Muldoon rallied his supporters. In the end, legislation was passed with the help of the two Social Credit MP's. The Clutha Development (Clyde Dam) Empowering Act was enacted on the 30th of September 1982. All legal avenues for legitimate objection had been removed.

Lowburn pub sign in the 1980's ~ 'In 198? this hospitable place could be 20 metres beneath the new Lake Dunstan.' This sign of a man having a beer through a snorkel was placed on Lowburn's Welcome Home Hotel in the 1980's. It voiced the stoic despair of a community facing inundation if, and when, the Clyde dam reservoir would be pronounced safe enough to fill.

The Lowburn community had been cast aside, sold down the reservoir, lock stock and beer barrel. Outside the pub, a sign appeared showing a man drinking a beer through a snorkel. In 1988, the bulldozers arrived to demolish the hotel and 'reshape' the valley. The Welcome Home Hotel, the Motor Camp, the houses along the main street, five orchards, the concrete arch bridge across the Clutha, the "hundred islands" with numerous popular campsites and swimming-holes, and some of the best farmland in the region, all disappeared into the pages of a bitter history.

Lowburn area after the Clyde dam

Clyde Dam ~ The Slip-Joint Problem

2009-03-15T09:49:00.007+13:00

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?

2009-03-10T11:00:00.029+13:00

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

2009-03-07T11:29:00.025+13:00

'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.

Roxburgh Dam ~ Building

2009-03-06T18:33:00.014+13:00

Diversion channel, 16 October 1950, by Jack Debnam Stewart

Coffer dam to divert river, circa 1950

Diversion channel, true right, circa 1951

Dam site and workers' accommodation aerial, 1955

Construction site aerial, 1955

Concrete delivery cranes, east side, circa 1952-55

Construction aerial, 1955

Construction view from east, 1955

Nearing completion aerial, circa 1956

Roxburgh Dam, 1968

Roxburgh Dam, circa 2005

Roxburgh Dam

2009-03-06T17:38:00.032+13:00

In the post WW2 era of New Zealand, one of the marvels of the age was electricity for the masses. It was gradually reaching into the lives of ordinary people, providing convenience in a fledgling consumer society where household appliances were making life easier. The Roxburgh dam was New Zealand's first large dam.

The site on the Clutha River at Coal Creek was chosen in 1947. Few people lived in the area, and it would be fair to say that New Zealanders at the time had little in the way of an environmental conscience. Besides, the Clutha River was regarded as a southern resource that belonged to the people of New Zealand, a mind-set that has lingered into the 21st century.

Electricity was a passport to prosperity, and the wonders of the Roxburgh Gorge were expendable. In hindsight we can understand why it was built, but we can also lament the loss of 'New Zealand's Grand Canyon' and this country's largest rapids, notably the Golden Falls at Island Basin, and the Molynuex Falls.

To Māori the Roxburgh Gorge was known as Kā Moana Haehae (the division of the waters). After the 1998 Ngāi Tahu settlement this name was applied to the bed of the Roxburgh reservoir.

Unlike the Cromwell Gorge, no one fought for the Roxburgh Gorge, so we cannot say that it was stolen. The Roxburgh dam, from the outset, provided the region with benefits that improved the lives of the population, and it has continued to contribute well into old age.

When the Roxburgh dam was built, technology was beyond question, and there was a belief that nature could be tamed by engineers. The lordly State Hydro-Electric Department (SHD), later renamed in 1958 as the New Zealand Electricity Department (NZED), ruled in all matters relating to power supply, and appeared to operate with impunity. Planning knowledge was accorded only to the privileged few, and any consultative process was undertaken with an air of disdain and irritation.

Cost overruns drew public criticism, but the cause of the mounting costs - inadequate investigation work and a ‘design as you go’ mentality, escaped public scrutiny. The final cost of the project was put at NZ£17,000,000, but it was probably much higher.

Commissioned in 1956, the Roxburgh dam, reportedly, had a design life of 50 years. That time has elapsed, so the obvious question is "What now?" This is not a popular question, but it cannot be ignored forever. Decommissioning is inevitable.

That issue aside, old dams and old reservoirs become increasingly problematic with age. The reservoir's sedimentation issue is well-known, but what is not widely known is that, geo-technically, the Roxburgh Gorge is similar to the Cromwell Gorge, with its own faultline and landslide areas. However, when the dam was built, these issues were not properly investigated, and little if any mitigation was carried out. The adage 'ignorance is bliss' comes to mind.

Also not well-known is the leak that occurred in 1963, the seismic cracking, and the vibration problem during high spillage. Given that the Roxburgh dam is close to a faultline at Coal Creek, and that a major quake along the Great Alpine Fault is expected in the next 1-20 years, this aging dam might be described as a ticking time-bomb. Most people believe that it is less able to withstand a major earthquake than the Clyde dam.

But it is the sediment build-up or aggradation issue that is the immediate problem. Proponents say that since the sediment has not yet filled the last section of the reservoir near the dam, that there is more life in the dam. However, this is because the movement of sediment is being restricted by the 'Gates of the Gorge' just below Alexandra, where the gorge is reduced to 39 metres in width. This is followed by a long section known as the 'Narrows' above Island Basin. As a result, much of the sediment burden is building up around Alexandra and in the Manuherikia confluence instead of escaping down the gorge. This, of course, raises the level of the river bed, and has already caused serious flooding at Alexandra, in 1994, 1995 and 1999. The obvious problem, therefore, is at the head of the reservoir.

In their Annual Environmental Report (February 2002) Contact Energy stated: 'The most significant environmental effect associated with the company's hydro operations on the Clutha River/Mata-au is considered to be the exacerbation of flooding at Alexandra caused by sediment build-up in Lake Roxburgh.'

Repeated attempts have been made to 'flush' the gorge by drawing down the reservoir ahead of high flows, to get the sediment moving through the bottleneck at the 'Gates.' Although this has achieved some movement of sediment down the reservoir, it is a temporary mitigation measure that is likely to become less and less effective. Some work has also been done to physically remove sediment that has accumulated at the Manuherikia confluence adjacent Alexandra, but again this is a short-term measure.

Physically removing the sediment from the constricted area of the gorge would be extremely costly, and is therefore not an option. The only long-term solution is to remove the dam. Decommissioning the Roxburgh dam will not come onto the agenda, however, until this issue worsens. Few people will take notice until there is another flood, perhaps higher than the Alexandra flood wall.

In 2007, Contact Energy was granted renewed consents to operate its Clutha hydroelectric dams for an additional term of 35 years. It is likely that further sedimentation and flooding issues with arise before this term expires.

The decommissioning of the Roxburgh dam, whenever it occurs, will take some years to complete. Perhaps, one day in the distant future, Alexandra will become the whitewater capital of New Zealand. Those magnificent rapids were not physically destroyed. They were simply flooded and gradually mothballed in silt. Another treasure of the Clutha, waiting to be re-discovered.

Wonders of the Roxburgh Gorge

2009-03-04T22:29:00.017+13:00

Before the Roxburgh dam was commissioned in 1956, the 30 km Roxburgh Gorge was up to 400 metres deep, and so narrow that in places its towering walls rose vertically above the boiling waters of the Clutha Mata-Au. The river was so constricted that it flowed as swiftly as 40 kilometres an hour through narrow chutes hundreds of metres long. In other sections the current slowed - but not much, flowing over landslide obstructions that had at one time dammed the gorge, before being overtopped by massive rapids. Today's sedate current bears no resemblance to the powerful torrent that once echoed through the gorge, drowning out the voices of men.

The first feature of the gorge, 675 metres below the Manuherikia confluence, was a constriction formed by schist bluffs on both sides that reduced the width to just 39 metres. This is now known as the "Italian Bend," but the early gold-miners called this the "Gates of the Gorge." Foot-tracks were etched precariously along the steep and boulder-tumbled walls of the gorge on both sides, as the miners hunted up gold and dug cave-like shelters under large slabs of fallen schist.

"Gates of the Gorge" below Manuherikia Confluence

Just over five kilometres down the gorge from the "Gates," and nearly two kilometres beyond Butcher's Point, the true left wall of the gorge had long ago collapsed, blocking the river. The resulting over-topping waters had cut through the obstruction with unimaginable force, forming a torrential rapid that had over time, at its foot, scoured out a large, amphitheatre-like basin within high walls of unstable rock. This rapid, descending through a narrow chasm, was known as the "Golden Falls." It filled the "Narrows" with a crashing din so loud that shouting men could not hear each other. In the centre of this basin below the rapid, the deeply driving waters had pushed up a shingle island. Hence, the name "Island Basin." The Golden Falls and Island Basin were astonishing features in a remarkably dramatic location.

The Golden Falls entering Island Basin

View of Island Basin and Landslide Face

Beyond Island Basin at Doctor’s Point, two powerful rapids known as Doctor’s Falls No 1 & 2 dropped through a boulder strewn constriction below a maze of gold workings, stone cottages and cave shelters etched into the true-left side of the gorge.

Nearly two kilometres below Doctor's Point, the river again met a sudden obstruction. A huge schist slab had slid down from the true left into the river, against which river-borne shingle and boulders had jammed up, creating a rapid so tumultuous that the gold-miners called it the Molyneux Falls. Here was a ferocious whitewater descent, tumbling violently some four-metres down a twenty-metre section of boulders, at breathtaking speed. At normal or low flow, these falls were deadly. In high flow they were somewhat washed out, but still incredibly swift.

Molyneux Falls

The gold-miners, dreaming of lowering the river above the falls to expose gold, tried several times to blast the huge thirty by twelve metre schist slab that lay at the head of the Molyneux Falls. But time and again the slab didn't move. Drilling and blasting merely succeeded in cracking the slab, so that it settled into place even more.

Further down the gorge, other rapids also raced through narrow chutes, until finally, at the southern end of the gorge, after boiling through massive eddies near McKenzie's Beach, the current eased slightly as it passed another bluff at Coal Creek - a site selected for the construction of the Roxburgh dam in 1947.

It is worth remembering that the wonderful features of the old Roxburgh Gorge were never physically destroyed prior to the filling of the Roxburgh reservoir. They were flooded, and now lie mothballed in silt. Given the limited lifespan of the ageing Roxburgh dam, and the silting, flooding and instability issues of the gorge, there is an ever-growing case for dam decommissioning and gorge restoration.

Inevitably, some time in the future, the largest high volume rapids in New Zealand - the once thunderous Golden and Molyneux Falls, will be re-born. Gradually, decades of trapped sediment will be stripped away, and the long-hidden wonders of the Roxburgh Gorge will be revealed.

McKenzie's Beach left foreground, Coal Creek bluff dam site distant right

Roxburgh Dam Statistics

2009-03-03T12:50:00.013+13:00

- Site chosen: 1947
- Construction: 1948-1962
- Commissioned: 1956-1962
- Type of Dam: Concrete gravity dam (largest in NZ)
- Dam Height: 76 metres
- Net Head of Water: 46 metres
- Width at Base: 61 metres
- Width at Top: 10.7 metres
- Length at Top: 358 metres
- Penstocks: 8
- Spillways: 3 with upgraded gates
- Sluices: 2 low level gates (non-functional?)
- Planned Capacity: 320MW
- Installed Capacity: 320MW
- Current Capacity: 320MW
- Turbines: 8x Francis fixed-blade turbines connected to 40MW salient pole generators
- Total Concrete Poured: Approx. half million cubic metres (over 1,422,466 tonnes)
- Total Steel used: Unknown
- Weight of Dam: 1.5 million tonnes
- Annual Energy Generated: Averages 1,650GWh
- Reservoir Size: 6 square kilometres (one estimate 4.5 square kilometres)
- Reservoir Fill Time: reportedly filled over several days
- Major Landslide Zones: reportedly 2 known large landslide areas
- Stabilisation Tunnels: Nil
- Measuring and Monitoring Instruments: Nil originally, now?
- Drainage Mitigation: Nil
- Landslide Buttressing: Nil
- Land Flooded: Unknown, but minimal.
- Operational Range of Reservoir: 1.85 metres
- Reservoir Storage Capacity: Described as "Not much"

TOTAL Project Cost: Reportedly NZ£17,000,000 (exact cost is unavailable or unknown)

Operation: The reservoir does not have much storage capacity, so the Roxburgh dam, like 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, and the Clyde dam. The expected variation of the reservoir is about 1.8 metres, compared to the Clyde dam’s range of about 50cms. When inflows are low, storage at Lake Hawea is drawn down to compensate.

Decommissioning the Roxburgh Dam

2009-02-06T17:52:00.031+13:00

New Zealand’s first concrete gravity dam was commissioned in 1956 on the Clutha River near Roxburgh. It represented the progress and hope of a new era, bringing electricity to the masses. At the time, large dams were designed in relative isolation to their environments, with little regard given to future impacts, and none whatsoever given to the ultimate challenge of decommissioning. Today, thousands of ageing dams around the world are nearing the end of their economic life cycle, and dam removal and river restoration is becoming an accepted reality.

Although large concrete gravity dams have a theoretical design life of 80-100 years, the actual lifespan of a dam is determined by the rate at which its reservoir fills with sediment. In severely eroding catchments, millions of cubic metres of sediment can be transported annually. The average lifespan of a large dam in China is 45 years.

Roxburgh Dam - lifespan limited by sedimentation.

Roxburgh Reservoir Sedimentation
The Clutha River is New Zealand’s most volatile in terms of volume and flow variation. Historically, it has transported large volumes of sediment, especially from the Shotover catchment. Flooding events can also transport significant sediment loads from numerous tributaries, including the Manuherikia and the Cardrona Rivers. Despite this, the engineers who designed the Roxburgh dam never expected its reservoir to “silt up” so quickly. There have been unconfirmed reports that the dam’s two low level sluice gates were jammed and rendered inoperable within the first 15 years, indicating reservoir-wide sediment transport to the dam wall.

In 1995, ECNZ estimated that 1.5 million cubic metres of sediment annually had been deposited in the reservoir between 1956 and 1992 (when the Clyde dam was commissioned upriver) totalling some 54 million cubic metres. Reports as to the percentage of sediment in the reservoir vary from 40-80%. The area of the reservoir appears to be shrinking accordingly, from 6 square kilometres to 4.5 square kilometres in a recent study.

The first obvious signs of silting up (aggradation) were visible beds of sediment at the Manuherikia confluence and an ever-expanding shingle-bed on the inside of the adjacent bend. Subsequent sediment beds developed along the sides of the reservoir in the Gorge Creek and Shingle Creek areas of the gorge. The reservoir has highly unfavourable impoundment geomorphology, having both a river confluence and a severe natural constriction at its head. Gold-miners knew this narrow section, some 675 metres below Alexandra, as the “Gates of the Gorge.”

Flooding is the expected consequence of reservoir aggradation. Subsequent flooding events inevitably increase in severity, despite remedial works such as “flushing,” sediment removal or the construction of flood defences.

Alexandra is no stranger to floods. Major pre-dam floods occurred in 1863, 1878 (4,650 cumecs) and 1948, while major post-dam floods have occurred in 1987 (2,088 cumecs), 1994 (2,343 cumecs), 1995 (3,212 cumecs) and 1999 (3,760 cumecs). But before the Roxburgh dam the river level was much lower and the threat to the town more remote. The highest volume flood on record in 1878, measuring 4,650 cumecs, did not climb as far into Alexandra as the highest post-dam flood in 1999, measuring 3,760 cumecs. The 1999 flood was the most devastating, despite peaking at only about 80% of the volume of the 1878 flood.

Alexandra Bridge on the evening of 17 November, 1999.

Records clearly indicate that the profile of the riverbed at Alexandra has risen considerably since 1956 when the Roxburgh dam was built. The historic bridge piers, in normal flow, bear mute testimony to the raised river level, now over halfway up the formally exposed lower arches.

Alexandra Bridge showing the Clutha in normal flow, 1903.

Since 1992, when it was commissioned, the Clyde dam has trapped the majority of the sediment load (97%) in the Kawarau Arm, providing a respite for the Roxburgh reservoir, but this did not stop serious floods occurring in Alexandra in the 1990’s, and will not prevent further floods. Briefly, sediment still reaches the reservoir, especially in high flows, and the sediment bottleneck at the “Gates of the Gorge” will inevitably cause further, and higher flooding.

Remedial Strategies to "Buy Time"
A sediment monitoring programme was developed after the acquisition of the dam by Contact Energy in 1996, and a formal programme was implemented between Contact Energy and the Crown in 2001. Monitoring has included cross-section surveys, suspended load sampling of inflows and outflows, and particle size analysis of suspended depositions. As a result, it is known that the reservoir traps all the bedload entering it and 80% of the suspended load.

“Flushing” is the first remedial strategy. Flushing involves lowering the reservoir ahead of higher flows in an attempt to move sediment beyond the constricted areas. It is claimed that this has reduced the flood level at Alexandra by 1.7 m compared to 1994 levels. However, bedload re-distribution tends to decrease with each subsequent flushing cycle, and although some sediment is moved into deeper parts of the reservoir nearer the dam, very little of this achieves sufficient suspension to be washed out into the lower river. Flushing is simply a way of “buying time.”

When flushing proves increasingly futile, the next strategy is the physical removal of sediment at pressure points. There are two critical areas near Alexandra: the junction of the Clutha and Manuherikia Rivers, and the constricted area at the “Gates of the Gorge.” Some sediment removal has been attempted at the junction, but it is hardly practicable to remove sediment from the “Gates” area. Large scale sediment removal from steep-sided reservoirs is cost prohibitive because of the need to transport millions of cubic metres of material to a suitable location.

Sediment can also be removed from the bed of the Manuherikia River, particularly in the Galloway area, to ease the flooding issue there and reduce sediment transport into the confluence, but again this is a temporary measure, and such work can be undone by a single flood.

In the face of the sediment threat, it is easy to understand why the Crown and Contact Energy reached an agreement in 2000 to co-fund the acquisition of flood affected properties or easements in the Alexandra area, and to construct flood protection walls to protect the town. The flood walls provide for flood events up to 143.6 metres above sea level. In many ways, flood protection is an admission of defeat, because clearly it is not feasible to keep building up the flood defences as the sediment accumulates.

But the most desperate measure is to raise the operating level of the reservoir (the current range is 1.85m). This would extend the dam’s viable operating years while increasing the risks associated with flooding events. Simply, while the water would move more freely, more sediment would be deposited at the upper end of the reservoir, and major floods could overtop Alexandra’s flood wall more quickly. Correspondingly, it would take less time for floodwaters to overtop the dam crest if the spillways were overwhelmed. The higher water level could also trigger reservoir-wide impacts, not the least of which could be the activation of known landslide areas. In the life cycle of the dam, raising the operating level could be called the “Russian roulette phase.” (Postscript: In November, 2009, Contact Energy was granted consent to raise the operating level .6m, raising the maximum operating level of the reservoir from 132m to 132.6m.)

Given that cost-effective remedial options are limited, the sediment problem seems set to evolve into an issue of legal liability, lost in a quandary of indecision over how long this situation can continue. Contact Energy will claim, naturally, that they are doing all they can to solve the problem. The Crown will also claim, naturally, that they are doing all they can to protect the public.

Truly, heads are buried in the sand (sediment) over this, because everyone knows that the problem has not been solved, that trouble is ahead, and that someone must pay.

Spillway Capacity and Safety
Moreover, the dam itself is now facing a critical safety issue. The Roxburgh dam was not built to accommodate the kind of extreme flooding events that are becoming more frequent and severe with climate change. Lack of spillway capacity is a leading cause of dam failure, and many older dams are now categorized as “high hazard” for this reason. Worldwide, an increasing number of large dams with inadequate spillways, deemed too expensive to upgrade, are being decommissioned.

“Most alarmingly, the world's more than 54,000 existing large dams have not been built to allow for the erratic hydrological patterns that climate change is bringing. In this sense, all dams should now be considered unsafe. More extreme storms and increasingly severe floods will have major implications for dam safety.” – International Rivers

The old spillways of the Roxburgh dam, according to first-hand accounts, barely coped with the 1999 flood. Can the dam and spillways cope with an even greater flood? Damage undoubtedly occurred during the spilling in 1999, but the extent of this remains a matter for speculation. Certainly, significant erosion occurred at the base of the spillways and remedial work was later undertaken.

Subsequently, it was established that the 3 spillway gates were highly susceptible to seismic failure, and so their counterweights were removed and replaced with more reliable hydraulic mechanisms. The 1999 flood may have alerted staff to the urgency of this issue. One rumour suggested that the dam shook so violently that dam workers were evacuated as a precaution. If this is true, one wonders why the communities below the dam were not warned.

Roxburgh Dam spilling floodwaters, 1999.

When a dam is overwhelmed by inflows, it suffers maximum stress loading above and beyond its design parameters as spillways strain to release an increasing volume of water. Vibration throughout the dam can cause structural failures in the dam crest, abutment interfaces, and the foundation before or during overtopping. Modelling has shown that the relatively thin dam crest is the weakest structural element and the most vulnerable to movement decay. Even more serious is the potential for foundation displacement, risking total failure.

Liability and Who Pays?
A deluge of issues now arise. If the Roxburgh dam experienced an overtopping event, would it survive? If the dam or an abutment breached, who would be liable? Would the dam owners claim that, since the Government built it, they (the taxpayer) should shoulder most of the burden or all of it? What damage would the torrent cause downriver? If the flooding event triggered landslides in the gorges, what further damage and loss of life could occur? What landslide issues exist in the Roxburgh Gorge given the strong history of instability akin to the Cromwell Gorge? Has the fault-line at Coal Creek weakened the dam? Has the historical leakage (1963-65) recurred in the right-facing abutment rock interface?

Roxburgh Dam leakage incident, 1963-65.

Time is running out for the Roxburgh dam, and the burden of responsibility rests with the dam owners, Contact Energy, and the dam regulators, the Crown. Decommissioning a large dam is a complex and expensive process that can take decades to complete. The costs involved are significant, and have been estimated at 35-150% in proportion to the cost of dam construction at current values. Typically, there is no provision for these long-term costs when a dam is built. Such provisions would render most large dams uneconomic from the outset.

Forward planning is vital to clearly establish legal liability, dam removal methods, monitoring systems, and a staged timetable to control sediment loading downriver in order to minimise community and abstraction impacts.

River Restoration Opportunity
It has been said that dam decommissioning spells not only the end of a dam, but the renewal of a river. In this sense, dam decommissioning is a restorative and creative process bringing enormous opportunities to local communities. It will take a decade or more to remove most of the sediment from the Roxburgh Gorge using the natural flow of the river and weathering. The geomorphology of the river will change, immediately upriver, and throughout its downriver course which will no longer be starved of shingle and beach sand. The finer suspended sediment will also reach the coast and begin replenishing beaches as it is carried north by ocean currents. Historically, this contained white quartz particulate, which accounts for the loss of the former white sand beaches remembered by local people.

The rediscovery of the Roxburgh Gorge will make national and international news. Gold-mining relics, and the largest rapids in New Zealand, will gradually re-appear, including the Molyneux and Golden Falls, beckoning the white-water fraternity from around the world. Flooded trails along the gorge, cut by gold-miners, will become passable and will be further developed. Alexandra and Roxburgh will reap the benefits of new recreation and tourism opportunities.

A First For New Zealand?
In New Zealand, for consenting purposes, dams are regarded as buildings. As a first step toward decommissioning the Roxburgh dam, a feasibility study is needed to determine the methodologies of dam removal and de-sedimentation – the largest issue. When this is complete, an application will be required under the Resource Management Act to obtain consents to remove the dam and the impounded sediment.

The Roxburgh dam will probably be the first large concrete gravity dam to be decommissioned in New Zealand. The obvious question is, when? In 2007, Contact Energy was granted consents to continue operating its dams on the Clutha River for another 35 years. It seems highly unlikely that the reservoir will remain viable until 2042. The most likely scenario is that another major flood will prompt an investigation into the decommissioning issue, but probably only after further significant damage occurs. A major earthquake could also hasten this process.

Of course, it would be better to prevent the escalation of sedimentation and safety issues before another disastrous flood, or dam failure. Unfortunately, there is nothing forward-looking about the hydropower industry, and the consenting authorities in New Zealand have insufficient expertise and are disinclined to acquire it and act on it.

It’s time to face the fact that decommissioning the Roxburgh dam is inevitable. The costs and impacts will be substantial, so planning should begin sooner rather than later. To delay is to invite greater costs and risks.

Fruitgrower's Road ~ Pre-Dam

2009-01-18T13:12:00.005+13:00

Here's a view looking up the Cromwell Gorge from Clyde, along Fruitgrower's Road, before construction work on the Clyde dam carved up this landscape, eventually flooding both the roads visible in this scene.

Lost Orchards and Farmland

2009-01-18T12:52:00.021+13:00

Cromwell Gorge orchard, Fruitgrower's Road, before the Clyde dam

Before the Clyde dam, the Cromwell Gorge produced some of New Zealand's best fruit. The reservoir behind the Clyde dam flooded a total of 2,300 hectares of productive land, including 12 large orchards on the river terraces along both sides of the Cromwell Gorge, 5 orchards at Lowburn, and fertile farmlands on both sides of the Clutha River in the Lowburn area.

The orchards in the Cromwell Gorge and a few orchards at Lowburn had frost-free micro-climates producing fruit early, earning good prices over the Christmas and New Year period. The Government, however, maintained that profitable late maturing fruit could be grown in the Earnscleugh area with a new irrigation scheme from the Clyde dam. They claimed that late maturing nectarines and peaches could realise $50,000 to $60,000 per hectare per year. Growers were sceptical, and MAF (Ministry of Agriculture and Fisheries) publicly said that this was unlikely.

The Clyde dam proceeded in the face of numerous objections, and the much touted irrigation scheme eventually only delivered limited water from the top of the Clyde dam to Earnscleugh, to help maintain flows in the Fraser River. The late nectarines and peaches never realised the projected returns.

Meanwhile, some of the most fertile farmland in Central Otago, bordering the Clutha River at Lowburn, disappeared under the Dunstan reservoir.

Clutha River, Lowburn, before the Clyde dam

The Cromwell Gorge Railway

2009-01-17T21:06:00.016+13:00

'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.

The Cromwell Bridge

2009-01-16T16:17:00.015+13:00

Cromwell "Lattice" Bridge, circa 1866

The promontory overlooking the confluence of the Clutha and Kawarau Rivers was originally referred to as 'The Point' by the first runholders in the 1850s, but when a gold-rush town sprung up in the early 1860s it became known as 'The Junction.' On the 16th of October, 1866, the town officially became the borough of Cromwell, with Captain William Jackson Barry as the first Mayor.

Before the river was bridged, a boatman rowed travellers across the river charging 'half-a-crown per head.'

The first bridge across the Clutha River was erected at Deadman's Point, 4 kilometres upriver from the Cromwell Junction, by Henry Hill, and opened in May, 1863. It was a suspension footbridge suitable for packhorses.

"The connection between Cromwell and the country lower down the Clutha River, was a pack-bridge erected over that river by Mr. Henry Hill. Wagons with stores and goods had to unload, and everything was packed across on horses." - Past & Present, and Men of the Times, by Captain William Jackson Barry.

Hill's bridge, however, was swept away that Spring by a devastating flood that ripped away riverbanks, mining-camps, and buildings along the length of the river, claiming over a hundred lives.

In 1864 the Government commenced the construction of a single-lane truss bridge close to the 'point', at a cost of £28,000. Completed in 1866, this massive bridge, supported by three stone piers, connected the main street of 'The Junction' with the route from Clyde on the east side of the Cromwell Gorge. "Superintendent Thomas Dick conducted the opening ceremony amidst great jubilation. A bullock was roasted whole, free beer was served out, and the township was for some days what a euphemistie writer might term a scene of jollity." - The Cyclopedia of New Zealand, 1904.

The original Cromwell Bridge was of a timber-truss design, and having a lattice-like appearance it was sometimes referred to as the "Lattice Bridge." When the timbers began to age, the bridge was rebuilt in 1891 as a steel-truss structure. The dramatic location of the bridge, spanning the roaring Cromwell Gap rapid and commanding the junction of two great rivers of different colours, meant that it featured on numerous calendars and postcards.

Cromwell Bridge, circa 1988

Remarkably, this bridge served for a hundred years, until traffic was re-routed over the new Deadman's Point Bridge in the early 1990s. The decking of the historic bridge was removed, its Cromwell-side approach was entirely dug away, and it was inundated by the rising waters behind the Clyde dam in 1993.

Deadman's Point Bridge

2009-01-15T11:42:00.001+13:00

Deadman's Point Footbridge (second), 1926, by Albert Percy Godber.

Deadman's Point holds a unique place in the history of the Clutha River, and of the Lowburn / Cromwell area. Here, the full force of the river suddenly converged into a narrow chasm at the beginning of the infamous Cromwell 'Gap'. Here, the first bridge spanned the river, and here countless gold-miners crossed and re-crossed en-route to their diggings, witnessing raging floods, and occasionally death in the vortexing waters of the 'Point'.

The first bridge across the Clutha River was erected at Deadman's Point by Henry Hill and opened in May, 1863. It was a footbridge suitable for packhorses, and it provided the shortest route for gold-miners heading to the strike on the Arrow River, which was then accessed via the Cardrona Valley. Prior to this bridge, gold-miners would continue upriver to Sandy Point, where they could cross on a ferry established by George Hassing and William Ellacott in March, 1863.

"The connection between Cromwell and the country lower down the Clutha River, was a pack-bridge erected over that river by Mr. Henry Hill. Wagons with stores and goods had to unload, and everything was packed across on horses." - Past & Present, and Men of the Times, by Captain William Jackson. Barry.

Hill's bridge, however, was swept away that Spring by a devastating flood that ripped away riverbanks, mining-camps, and buildings along the length of the river, claiming over a hundred lives.

The Second Deadman's Point Bridge In Flood.

The Deadman's Point footbridge was eventually replaced (date unknown) by a well-built structure that survived subsequent floods. Although the footbridge was sited at the narrowest part of the river between Lowburn and Cromwell, the massive new traffic bridge, opened in 1866, was located at the Cromwell Junction directly adjoining Cromwell's main street, in order to facilitate traffic through the town.

The footbridge at Deadman's Point provided convenient foot and horse access to the diggings at Quartz Reef Point and Bendigo well into the 20th century.

Just how Deadman's Point acquired its name is unknown, but as the river at this point converged into a narrow precipitous 'gap' and surged with immense speed down a series of rapids to the Junction at Cromwell, it is likely that it was considered a 'point of no return'.

The reputation of the river was formidable, due in no small part to the perilous experiences of the log-raftsmen on the Upper Clutha. The log-rafting enterprise was started in 1862 by George Hassing and Henry Hill to supply much-needed lumber from the western forests to the virtually treeless interior. The first log-raft to negotiate the river as far as Clyde (Dunstan) arrived on October 6th, 1862.

"It was decided not to try and negotiate the gorge with these craft. They were navigated to a landing-place between Lowburn and Cromwell, but it was frequently a most difficult procedure to catch the landing-place. Once past it, there was absolutely no choice but to allow the raft to shoot through the roaring, rocky gorge above Cromwell. The raftsman had the alternative of either abandoning ship or of taking his chance aboard his craft. One man known as the Boatswain, having been caught in this predicament, took the consequences of remaining at the tiller. His raft, after entering the gorge, turned a complete somersault. He managed to climb aboard again and bring it into an eddy near the Kawarau Junction, where he was secured by a shore man - very wet, but grateful that he had escaped unhurt." - The Wanaka Story, by Irvine Roxburgh.

The Cromwell Gap, 1977, by Robin Morrison.

The Deadman's Point footbridge had always provided the most direct access to Bendigo, but only for travellers on foot or horseback. Obviously, the new 1866 traffic bridge at Cromwell provided access for wagons and later motor vehicles, and in 1938 when the new concrete bridge was opened at Lowburn, the old footbridge at the 'Point' was used even less.

By the 1970s the footbridge was gone, and the Clutha River was the focus of evermore speculation over future dams. During the following decades, hydro plans came and went, but almost all of them doomed the productive river flats around Lowburn to inundation. The eventual plan included the destruction of old Cromwell and the construction of new roads, and a new bridge, at Deadman's Point. In a bitter twist of fate, the towering columns of the new bridge rose above the site of the original footbridge, connecting the new Cromwell centre with the east side of the gorge.

The 'New' Deadman's Point Bridge, before the 'Point' was flooded, circa 1990.

Remarkably, Deadman's Point was not physically destroyed during the construction of the bridge. In the future, when the reservoir is decommissioned (it was planned to last 80 years) the 'Point' should be easily revealed when de-silted. By comparison, the distinctive Cromwell Junction, which was almost obliterated by earth-moving machinery prior to the filling of the reservoir, will be difficult to restore.

The 'New' Deadman's Point Bridge, after reservoir filling.

Today, the 'new' Deadman's Point bridge stands high above the flooded 'Point', and few people who drive over it realize the significance of either the name, or the location.