Waitaki Dam
The Waitaki Dam is one of eight hydroelectric power stations which form the Waitaki hydroelectric scheme on the Waitaki River in the Canterbury Region of New Zealand. The dam was the first of three to be built on the Waitaki River and was constructed without earthmoving machinery; over half a million cubic metres of material was excavated, almost entirely by pick-and-shovel. The Waitaki Dam's construction was followed by the development of Aviemore Dam and Benmore Dam, and importantly, every dam built in New Zealand since the Waitaki has benefited from lessons learned during its construction.
The Waitaki Dam is unique; its construction lead to the germination of one of the world's first social welfare systems. Built during the Great Depression, the Waitaki Dam attempted to soak up unemployment as part of the Government's make work scheme and saw the trial of medical welfare where an individual could build a satisfactory life without fear of the inability to cope with age or poverty.
Initial construction of the dam began in 1928 and was completed in 1934 with full power being delivered from two 15 MW generators on 1 January 1935. Three additional generators were added between 1940 and 1949 and a further two generators were added between 1952 and 1954. With seven generators each delivering 15 MW, the total generative output of the Waitaki Dam is 105 MW.
Background
The first State-built power station in New Zealand was constructed at Lake Coleridge in 1915 designed to supply Christchurch and any additional consumer demand within reach of the transmission system. Consumers quickly tapped into this low-cost energy and the year-on-year load increase for Coleridge was 15%; by the 1920s a new power source was needed.The Waitaki River was selected as the most promising source of hydro-electric power, particularly for long-term needs the New Zealand government having recognised the electricity generation potential of the Waitaki Valley as early as 1904. With Lakes Ōhau, Pukaki and Tekapo controlling 80% of the flow into the Waitaki River's headwaters, flooding was not expected to exceed 5380 cumecs, a low threat to the safety of any proposed dam. In its middle reaches, the Waitaki River flows through bedrock gorges of low-grade schists, meta-greywackes and greywackes of the Rakaia Terrane. These gorges offered good dam sites with relatively stable rock upon which to build. The Waitaki River was also sparsely populated in the early 1920s meaning that resettlement would be a very minor issue following inundation by the dam's reservoir.
Site selection
Initial site investigations began in 1925 and would take over two and a half years before a final site was selected. The focus by 1927 was in the vicinity of Wharekuri/Roseneath which appeared to be most favourable. However, the presence of coal on the Otago side of the Waitaki River was of concern to engineers who felt it may act as a leak point beneath any proposed dam. Subsequently, a site further downstream, near the confluence with the Awakino River, was investigated and found to be suitable. The Awakino site, above Kurow, had only of shingle to remove before solid basement was reached, reducing the overall volume of material to be excavated. The final site having been selected for the Waitaki Dam was announced by the Government in April 1928, with an overly ambitious target for completion by 1931. The investigations of the Roseneath site were not in vain either Roseneath would later be adopted as the site of the Aviemore Dam.Engineers calculated that the Awakino site, backed-up by several years of Waitaki River flow records, would support a station generative capacity of 75 MW, although initially only two 15 MW generators and turbines were ordered.
Dam design
Early designs of the dam, in large part due to the infancy of hydroelectric engineering in New Zealand, had potentially serious flaws. In particular, there was no consideration of the pressure exerted by the hydrostatic head and impact of water entering cracks or joints in either the basement or the dam itself. The downstream slope of the dam was also considered too steep compared to European dams at a ratio of 3:2. Seepage troubles at the North Island's Arapuni Power Station in 1929 caused additional concerns and resulted in a Swedish hydroelectric engineer, Professor, being brought to New Zealand in 1930. While Professor Hörnell was specifically brought in to consult on remediation measures to be made at Arapuni, he also visited several other hydroelectric sites, including Waitaki. Despite most column inches at the time focussing on the exorbitant £4000 consultant's fee charged by Professor Hörnell, his comments on the Waitaki were that its cross section was too narrow and that measures should be incorporated to ensure adequate foundation drainage. Notwithstanding the Government's decision not to invest in a specific Waitaki Dam report from Professor Hörnell, several design modifications were made on the basis of his comments:- The base of dam was widened and the slope of the dam reduced
- A new gallery was added on the upstream face at the dam's base, forcing drainage from the lower levels of the dam and the foundations into it and then pumped to the downstream face of the dam
- Concrete cut-offs on both the downstream toe of the dam and upstream base around the new gallery were also implemented to further inhibit water penetration into the dam's foundations
Concern over the possibility of uplift forces on the base of the dam has persisted: further measures to alleviate this issue were introduced in the early 1960s when anchoring cables were drilled from the dam crest into the foundation rock, and again in 2016 when drainage holes were drilled in the foundation of the dam.
Geology
The Ahuriri, Ōhau, Pukaki and Tekapo rivers rise in glaciated catchments which feed the Waitaki River. These tributaries flow from the Mackenzie Basin into Lake Benmore before forming the Waitaki River. Several bedrock gorges, separated by small tectonic basins, lie beneath the string of artificial lakes occupying the middle reaches of the fault-controlled Waitaki Valley. Downstream of Kurow, the valley widens to a plain, with paired alluvial terraces on either side of a braided river channel. At the Waitaki Dam, the Waitaki River occupies a fault-angle depression between the greywacke of South Canterbury and the schist of North Otago. The valley fill comprises a sequence of Quaternary river and glacial outwash gravels that overlies Upper Tertiary sedimentary strata, which in turn overlies the Mesozoic basement.Both basement and covering sediments have been affected by late Quaternary faulting, including reactivation of earlier Cretaceous fault systems. Geodetic results indicate that strain rates in the lower Canterbury region are low to very low, though strain increases considerably toward the west and proximity with the Alpine Fault. The Waitaki region, along with the rest of the south-eastern South Island, has had a low level of large earthquake occurrences in historic times, with one of the largest recorded earthquakes in the vicinity of the Waitaki Dam occurring near Oamaru in 1876. Paleoseismic studies on individual faults in the Waitaki area suggest that the recurrence interval of large earthquakes is on the order of thousands or tens-of-thousands of years. The primary fault associated with the Waitaki Dam is the Dryburgh Fault; this fault has been noted as having a considerably long recurrence interval of >62 000 years. While the impacts of regional faulting at the time of the dam's construction were not well understood, the Dryburgh Fault was recognised as an issue, particularly when excavating the Hörnell Gallery. Basement rock had been reduced to gouge across the fault zone which was remediated by excavating and successfully cementing the gouge zone deeper than the competent rock either side of the fault.
Construction
When the final Awakino site was selected for the dam, the Public Works Department engaged Roland Packwood as the District Engineer in charge of the dam's construction. Packwood's task was to get the power station operational as quickly as possible and involved the completion of the dam across the Waitaki River followed by installation, testing and commissioning of the electrical and mechanical equipment. Given an overly ambitious goal of an operational power station by 1931, it soon became obvious that such a rapid completion was unrealistic.Packwood's first task was to extend a spur from the Kurow Branch railway line to the dam site a simple extension which was approved and surveyed in August 1928, with Public Works Department traffic operating on the line by December 1928. With the railway and the existing gravel road from Kurow providing equipment and material access, the project was able to start in earnest.
Lake Waitaki village
Before any major works at the Waitaki site were undertaken, a camp was required to accommodate up to 1000 workers in addition to their families. The harsh climate of the Waitaki Valley with its cold winters and strong winds, plus the long-term nature of the project, meant the Public Works Department opted for more permanent wooden accommodation in favour of their typical use of canvas tents. Senior staff were allocated houses built of concrete blocks which would become permanent staff quarters in the future, while junior staff and single men were accommodated in wooden houses and huts. In all, the Public Works Department were to construct approximately 350 houses and another 700 huts which were primarily located on two river terraces on the true right river bank immediately upstream of the dam. There were four separate living areas in the wider camp: the main camp occupied the upper terrace, 'Siberia' was located on the lower river terrace, 'Geddesville' was located downstream from the construction site, and 'Willows', located close to the Awakino bridge. In addition to accommodation, the camp included a YMCA hall, post office, small shops, tennis courts and a football ground.At the dam's completion, the camp was dismantled apart from the permanent structures of Lake Waitaki village which were occupied by the permanent dam staff. When the Electricity Corporation of NZ moved its staff out in the 1980s, the remaining concrete block houses, hostel and environs were threatened with demolition. However, pressure from the community resulted in a heritage covenant with Heritage New Zealand to protect the village as a historic area in 1995. After passing through several owners it went up for sale in 2015 but languished unsold for several years. Interest in purchasing Lake Waitaki village was rejuvenated in 2018, when global media outlets caught hold of the story that a village was up for sale.
Lake Waitaki village now serves as accommodation for vacation rentals.