The Monowai Power Station, fed by the Monowai River from Lake Monowai in Southland, New Zealand, was one of the earliest hydroelectric power stations in the country. Originally commissioned in 1925, it was refurbished between 2005 and 2007 and now contains modern turbines and plant, though the original buildings are still in use.
Before its refurbishment, the station produced and of electricity per year.Southland Regional Energy Assessment Accessed 2008-09-29.) Generating capacity has now increased to 7.6 MW.
Location
The power station is located approximately 50 kilometres from the town of Tuatapere in Southland. The power station is accessed from Turbine Drive, which can be reached from Blackmount-Redcliff Road via Lake Monowai Road.
History
Development
The first considerations for a Monowai hydropower plant were raised as early as 1910, when the Invercargill Borough Council aware of the success of Dunedin's Waipori hydro-electric scheme had employed consulting engineer G. Symington to investigate the best means of providing more power to the borough. In his report submitted in March 1910 he had identified that while Monowai would provide the cheapest power its distance from Invercargill (which would require the building of lengthy transmission lines) coupled with the demand meant it would be more feasible for the borough to continue using its existing coal powered power station.Buckingham, page 24.
In 1914 a group of leading Southland businessmen and politicians established the Southland Progress League to promote and encourage growth in the region. One of the ten committees formed, focused on the potential and development of the region's natural resources. The League was granted access in 1916 to Symington's report, and other than requesting the government in July 1916 to investigate electricity generation options in Southland little was achieved and by March 1917 the league was in debt and consideration was being given to it being disbanded.Buckingham, page 25. In 1916, Frederick Kissel, an engineer in the Public Works Department reported to his manager in the department that Monowai was still an unrealistic option unless there was increased demand in the form of metallurgical or chemical manufacturing was developed in the Southland. The election of Alexander Rodger (1872 – ?) as the league president re-galvanized the league and saw it clear its debt. In 1917 the government in response to the league's request dispatched engineer Lawrence Birk (1874–1924) from the Public Work Department on the first of two visits (20 to 28 September and 1 to 8 December) to investigate the demand for electricity and potential for hydro-electric generation in Southland.Buckingham, page 274.
There was enthusiastic response in Southland to Birk's report, which resulted in the League receiving additional financial support. This allowed them to directly engage Gisborne consulting engineer F. C. Hay to investigate in more detail the best source of generation, the expected cost and how to reticulate the resulting electricity throughout Southland. Hay's identification of Monowai with its sizable fall from Lake Monowai into the Waiau River as the best source of hydro-electric generation and his estimation of costs was endorsed by the Public Works Department.Buckingham, page 36. Hay estimated that it would take three years to complete the power station as well as the transmission system, once authority was given to proceed.Buckingham, page 47.
At the same time the League believing that for Southland to progress, electricity needed to be made available throughout the province and not just to the major population centres. The League, taking the initiative, wrote the legislation for the Electric Power Boards Act of 1918. This legislation gave the Power Boards the right to produce, reticulate and sell power to areas that the Government did not supply. As a result of the legislation the Southland Electric Power Board (SEPB) was established and in December 1919 elected its first board members.Buckingham, page 39.
On 5 February 1920 the newly established SEPB formally adopted Hay's proposed Monowai design and it was agreed that the board request ratepayer permission to raise a loan of £1,500,000 to cover both the building of the power scheme and the distribution of electricity throughout the power boards district.
A poll of ratepayers in the board's district on 27 March 1920 approved obtaining the loan. Until the loan was obtained SEPB would temporarily fund its activities using a bank overdraft with the collateral being the ability to rate people in the district. Sir Joseph Ward who was soon to be visiting Britain on other business was asked to broker the loan.Buckingham, page 49. The New Zealand government subsequently agreed to guarantee SEPB's existing loan and to finance its activities until it could secure an overseas loan.Buckingham, page 57.
After unsuccessfully trying to employ either Lawrence Birk or Evan Parry as their engineer SEPB engaged the newly established Wellington firm of Hay and Vickerman (which consisted of F.C. Hay and Hugh Vickerman (1880–1960) and John Gill Lancaster (1983 - 1950) in partnership to undertake all engineering surveys, undertake all civil engineering design and construction, with Hay and Vickerman subcontracting the electrical design to Brown and Forsdick of Auckland. All of the designs were to be approved by the Public Works Department. Hay and Vickerman's fee was 2% to undertake the design with an additional 1% to be paid for supervising the construction.
The approved design called for building an earth dam with control gates to raise the lake level. The outflow would follow the river bed until at a weir it would be diverted into wooden pipelines to convey it to an 8,000 hp capacity powerhouse located by the confluence of the Monowai and Waiau Rivers.Buckingham, pages 44 to 45.
Construction commences
It was estimated that 5,000 tons of material would need to be transported to Monowai. from the nearest railhead which was at Tuatapere on the Tuatapere branch railway. Investigations were undertaken into how best to do this, with consideration given to trucks, horse-pulled carts, traction engine as well as transporting it up the Waiau River which would require some blasting to remove hazards. The decision was made to employ a traction engine and two trucks which required SEPB to upgrade the existing roads and also extend them to the construction site.Buckingham, page 50. Until the road was completed material was brought in by horses pulling wagons. In 1920 Alfred Pryde Walker (1891–1953) was appointed the resident engineer in charge of construction. Walker had experience as an engineer in Canada, South Africa, Ceylon, Fiji and Australia (where he had worked with Hay).Buckingham, pages 52 to 53. By the end of 1920 a total of 80 men and 40 horses were working in the project, building the road and preparing the sites for the construction camp and powerhouse.Buckingham, page 58. A Boving water wheel was established on site to provide power to the construction camp, but it was switched off at 10:00 pm. A timber mill was established on Diggers Hill on the Western side of the Waiau River to provided timber for the project. By early 1921 not only was the access road to Lake Monowai completed but also the construction camp as well as a new suspension bridge across the Waiau River at Sunnyside. Up until the completion of the bridge material and men had been conveyed across the river by a ferry.
After the Wallace Country complained about the impact of the increased vehicle traffic on its roads over the winter SEPB began using teams of horses pulling wagons instead of the traction engine and trucks over the winter months.
Recession
In 1921 there was a world-wide economic slump made worse by the termination of the commandeer system (which resulted in a dramatic fall in the export prices of meat, wool and dairy products), caused the New Zealand government to look at means of reducing public and private expenditure. As a result, they were no longer prepared to guarantee to fund SEPB.Buckingham, page 61 to 65. In compliance with the government directives to reduce expenditure Lawrence Birks who was by now Chief Engineer of the Hydro-Electric Branch of the Public Works Department wrote to SEPB on 19 April 1921 that with expenditure of £100,000 to date and contracts in place for another £100,000 they had to reduce capital expenditure in order to ensure that the supply and reticulation become profitable as easily as possible. Therefore, while he wanted Monowai to be completed it was necessary to reducing the area that was to be supplied and to change the system of charging consumers in order to reduce the total cost to £600,000. In response, Hay and Vickerman were requested by SEPB to provide a detailed estimate for a modified scheme costing £600,000. In June 1921 they replied with an estimate of £700,000 which lead the board to instruct Sir Joseph Ward who was then in London to arrange a load for £750,000.
With no money or credit or government approval the board of SEPB decided to cancel the contracts for the purchase of poles and insulators. As they had not been satisfied with the performance of Hay and Vickerman, they also decided to dispense with their services. Among the reasons were the absence of both Hay and Vickerman during the early stage of the work, their estimates were proving to be too low, progress was slow on upgrading the roads to allow their use in winter, materials were being purchased before they were required and at high prices. The cancellation of the contract would eventually lead to arbitration, which resulted in SEPB having to pay the firm 2% of the capital costs. While five staff members of Hay and Vickerman's staff were employed by SEPD, 112 men working at Monowai were let go. Ward meanwhile in July 1921 managed to obtain a loan for £750,000 at an interest rate of 6%, which would be guaranteed by the New Zealand Government.
With no engineer, SEPB approached Evan Parry who had left the Public Works Department in 1919. Despite a lucrative salary offer he turned it down.Buckingham, page 70. SEPB was eventually able to obtain the services of Herbert P. Thomas, who in January 1922 took up the position, which was now as an employee of SEPB.Buckingham, page 71. In the interim G.F. Ferguson who had been taken on from Hay and Vickerman was acting engineer.Buckingham, page 68.
Work restarts
Once he had taken up his duties Thomas reviewed the scheme and identified that the average flows from Lake Monowai would be less than had been originally been estimated. Taking into accounts what had been built to date he adopted the ideas of Alfred Walker and proposed that to construct a short dam to divert to the Monowai River through control gates, then a second longer earth dam would be built to raise the lake level by an additional 8 ft compared with the previous scheme. The water would flow through the control gates to a headpond where a weir would divert it into a canal to carry the water to a shortened steel pipeline. He also proposed to install only one 4 MW generator and later a 2 MW unit. He also proposed modifying the transmission system.Buckingham, pages 73 to 74. His design was adopted by the SEPB board. With the change to a steel pipeline, the one million of heart totara that had been cut and milled in preparation for making the previous pipeline design was used for lining houses at Monowai and the rest sold.
Work recommenced at Monowai in early 1922 with Thomas estimating that the station would be generating power by September 1923. Soon the workforce on site had risen to 800, working three shifts a day.Buckingham, page 80.