Clyde Dam ~ The Slip-Joint Problem

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

So what exactly did the dam workers discover?

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

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

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

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

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

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

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

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


Looking up the wedge


Looking down the wedge

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

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

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

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

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

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

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

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

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

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

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

Is the Clyde Dam Safe?

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

So what are the likely scenarios for the Clyde dam?

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

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

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

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

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

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

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

References:
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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.

Decommissioning the Roxburgh Dam

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.

Deadman's Point Bridge

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.