Roxburgh Dam
The Roxburgh Dam is the earliest of the large hydroelectric projects in the lower half of the South Island of New Zealand. It lies across the Clutha River / Mata-Au, some from Dunedin, some to the north of the town of Roxburgh. The settlement of Lake Roxburgh Village is close to the western edge of the dam.
History
Development
In 1944 the State Hydro Department estimated that even with the power stations currently under construction they would only be able to meet projected South Island load up until 1950 or 1951 and that a new large power station was required. Detailed investigations by the Public Works Department identified two alternatives, Black Jack's Point on the Waitaki River and Roxburgh Gorge on the Clutha River. A power station at Lake Roxburgh had the advantage of being less remote, requiring less geological investigation, half the materials for the same power output and a better climate in which to undertake construction work, which were important considerations at a time of serious shortages of labour and cement.Historical records showed that the long term flow of the river was and that a controlled flow of would be possible through the power station. The designers estimated that with an overall efficiency of 85% the mean output would be 160 MW and assuming an annual power factor of 50% the station could deliver a maximum output of 320 MW.
The Clutha River is fed from Lake Hāwea, Lake Wakatipu, and Lake Wānaka. There were already existing control gates on the Kawarau River at the outlet of Lake Wakatipu and it was decided to control the flows from the remaining lakes. After investigation found that the soil conditions were unsuitable at Lake Wanaka and only Lake Hāwea received new control structure. This was commissioned in 1958 and consists of four radial gates housed in an earth dam. The dam raised the existing lake level and currently provides approximately 290 GWh of storage.
In December 1947, the Labour Government approved plans to build a hydro power station on the Clutha River. Initially only three 40 MW generating units were to be installed with the station having an ultimate planned capacity of 320 MW. The Clutha River between Alexandra and Roxburgh runs through a deep gorge which offered a number of locations for a power station. Investigations identified five alternative schemes at the Pleasant Valley site, and one scheme at the Tamblyn's Orchard site. Initially Site No. 4 at Pleasant Valley, about upstream from Tamblyn's Orchard was favoured. Subsequent detailed design studies however found that Tamblyn's Orchard at Coal Creek where the river exited the Roxburgh Gorge near the town of Roxburgh offered the fullest possible head and thus the most power output, better tailwater conditions, the best access and would be closest to suitable locations for both construction and permanent villages.
In March 1949 the government committed to building at Tamblyn's Orchard and plans were prepared to enable work on the diversion channel to start in June 1949. In October 1949 at the request of the Ministry of Works and Development, John L. Savage visited the site and provided advice on the proposed design options. While an earth dam was more suitable at the wider Pleasant Valley location after considering various options it was decided in October 1950 that due to the geology at Tamblyn's Orchard a solid-concrete gravity dam would be more appropriate. Another consideration was that the MOW had limited experience with the construction of earthen dams and its only engineers with the necessary experience were engaged on the Cobb Power Station.
Many of the design decisions were based upon results from studies undertaken from 1949 to 1954 on a 1:80 scale model of the dam at the Department of Scientific and Industrial Research's Hydraulics Laboratory at Gracefield, Lower Hutt.
Initially the project was known as the Coal Creek scheme but after the Geographical Board had been consulted the name Roxburgh was chosen as name of the power station in 1947.
Construction
Work commences on site
The MOW was the government department responsible for designing and constructing the government power station in New Zealand. Though it was still unresolved who would be designing and building the dam and power station Fritz Langbein the engineer in chief of the MOW assumed that his organisation would be undertaking the design and would at the least build the diversion channel. Therefore, he put in place plans to build a construction village and in July 1949 had the MOW commence work on the excavation of the diversion channel. This channel would eventually be long, wide and deep which required the removal of of material.By the end of 1950, 720 workers were being employed on site.
Construction village
In 1947, to house the workforce, the Ministry of Works first built a single men's camp and cookhouse on the west bank of the river. In 1950, work began on erecting 100 workers' cottages. The following year began on building a YMCA hall, shops, a hospital and nurses accommodation and a further 225 cottages. Eventually the village grew to 724 houses complete with a 90-bed hostel, a 600-child primary school, a cinema, a social hall, 17 shops, three churches, a fire brigade and ambulance building, four tennis courts, a swimming pool and a piped sewage scheme. In addition there were four single men's camps containing a total of 1000 huts. These facilities cost a total of NZ£2,241,925.As the Otago Central Electric Power Board's network could not provide sufficient power to the village and the project, the government built a temporary power station containing two 1 MW and one 0.4 MW diesel generators, to supplement the supply.
Transportation of materials and equipment
In May 1946 the PWD and the New Zealand Railways Department held a meeting to determine what would be needed to transport materials to the proposed site of the power station. The main loads associated with the first four generating units were as follows: thirteen generator transformers, each 39.5 tons, 15 ft 6 in long, 10 ft 4 in high, 8 ft 2 in wide; twenty-four stator sections; each about 19 tons gross, 14 ft 9 in by 9 ft 1 in by 6 ft ; four shafts and thrust plates, each 33½ tons gross, 20 ft long by 6 ft 6in by 7 ft 10 in ; four turbine runners, each 25 tons, 12 ft 10 in diameter, 6 ft 7 in high; four generator bottom bearing brackets, each 20 tons gross, 12 ft by 12 ft by 6 ft 1 in.The most direct rail route was via the Roxburgh Branch line to its terminus at Roxburgh. However this line had an uncompensated 1 in 41 grades and five chain curves that would limit the loads to 180 tons per engine. As well, four tunnels including those at Manuka and Round Hill on the line restricted the physical size of what could be transported, leading to consideration being given to enlarging them. This would have been expensive and restricted use of the line while it was being undertaken. As an alternative, an investigation was undertaken into lengthening the Tapanui Branch line from its terminus at Edievale though a tunnel and some clay cuttings in the Dunrobin Hills to the Clutha River where it could connect with the Roxburgh branch line. Eventually, it was decided to use the Roxburgh branch line for all construction materials and smaller items of equipment wherever possible. These were transported on the Main South Line to Milton where they transferred to the Roxburgh branch which conveyed them to Roxburgh, and from there transported by road to the power station. Consideration was given to extending the line to the construction site but this wasn't proceeded with due to the difficulty of getting past the east end of the existing Roxburgh suspension bridge. To improve the line's carrying capacity, some curve easements were undertaken near Round Hill.
As the load carrying capacity of the existing roads was constrained by bridges at Henley it was decided that due to the fact that the Waikaka Branch railway line had no constricting tunnels, it would be used to transport out of gauge heavy items such as the turbine runners and bottom bearing brackets. These items were transported on the Main South Line from the port at Bluff to the junction at McNab and then via the Waikaka branch line to its terminus at Waikaka. From there, they were transported by road to the power station using a specialised transporter. This assisted in the transfer from rail to road transport, and a 4-pole 30 ton gantry was erected at the Waikaka railway station to aid with the transport. The road between Roxburgh and the construction site was upgraded, and a second bridge was built on the over the Teviot River on the eastern side of the Clutha River to supplement the existing bridge. At the construction site, a long single-lane Bailey bridge with a carrying capacity of 24 tons was installed in 1949 to provide access across the river.
Timber used in the construction of the power station and the village was sourced from the Conical Hills Mill at Tapauni and taken via the Tapanui Branch to the Main South Line which provided a connection via the Roxburgh branch line to Roxburgh. At its peak up to 15,000 to 20,000 ft of timber was being transported by rail on a daily basis.
At the Roxburgh railway station the PWD erected silos to store the expected 50,000 tons of cement a year that would be consumed at the project's peak as well as a six-pole 60 ton lifting gantry It was expected that Shipments of bulk cement began in mid 1953 and by July of that year 600 to 1,100 tons were being shipped per week. By July 1955 demand had dropped to 800 tons per week with shipping of cement finishing in November 1956. By April 1956 Milburn had supplied 105,000 tons of cement with another 10,000 tons still to be delivered to complete the project.
NZR operated occasional sightseeing trains from Dunedin and Christchurch. The cost of a combined return rail and transfer bus ticket from Dunedin to the site of the power station was 16 shillings.
Wherever possible, equipment was shipped on the Dunedin-Roxburgh Railway Line to Roxburgh and from there transported by road to the power station. For instance, the transformers were railed from Port Chalmers to Roxburgh on the 40-ton well-wagons and then taken to the power station site on a Rogers 40-ton tank transporter. The stator sections and shafts followed a similar route.
Because of the line, larger tunnels on the Waikaka Branch railway line the turbine runners and generator bottom bearing brackets were transported on this line. From the line's terminus at Waikaka, they were transported by road to the power station using a specialised transporter.