Aniwhenua Power Station

In the late 19th century and early 20th century, numerous small local power generation stations were built by both private and local authorities. From the 1920s onward as the state electricity system expanded and the national grid was developed, development of small local power stations declined as the centralisation of electricity supply under state control increased.

The 1973–74 oil shock, nation-wide electricity shortages during the winters of 1973 and 1974, a renewed policy emphasis on regional development by central government, and increased uncertainty as to future wholesale electricity price trends lead to the New Zealand government to re-evaluate its policy regarding local hydro development. As a result, in 1977 the government announced that they would subsidize local power station schemes of less than 50 MW by providing grants to cover the investigation and design work, cheap loans to finance construction as well as loans from the NZED to cover operating losses in the early years of approved schemes. The government established the Committee on Local Authority Hydro Development (CLAHD) to evaluate applications for grants or loans from supply authorities.[1]

Taking up this opportunity the Bay of Plenty Electric Power Board which had begun operations in 1928 and engaged consultants to investigate a local hydro scheme in mid-1973. Preparation of a feasibility report was authorised in December 1973, with the report being completed in September 1974. The study determined that a power station on the Rangitaiki River at its confluence with the Pokairoa Stream, midway between Murupara and Whakatane. The scheme was technically feasible and financially viable. The main identified environmental impacts were significantly reduced flows over the Aniwhenua Falls, inundation of productive farm land and the displacement of one family, as well as the long term accumulation of sediment in the lake that the project would create. The issue of the reduced flow was managed by the imposing of a minimum residual flow over the falls.[2]

The estimated cost was NZ$12.5 million.[1]

Following the obtaining of water rights, government consent and other necessary approval, construction and equipment supply contracts were let in the second half of 1977.

The civil works which commenced by the end of 1977 constructed by Downer and Company which involved the excavation of one million tons of material and the placing of 270,000 cubic metres of fill, 20,000 cubic metres of concrete and 884 tonnes of reinforcing steel.[3]

Aniwhenua began generating on 3 October 1980.[1] The 1982 annual report for the board showed that the total cost of the station to 31 March 1982 was $27,767,203 of which $24,628,809 was financed by government loan.[1] The book value of the scheme as at 31 March 1992 was $21,109,000. By the 1985/86 financial year, the scheme was breaking even financially and was able to trade its way into long-run profit without any write-offs of debt. Over the period from 1989 to 1992 as its trading activities were making a loss the profits from Aniwhenua kept the power board in the black.[1]

The Energy Companies Act was enacted in 1992, and amended later that year. This act required the corporatisation of the electricity and gas undertakings of electric power boards and municipalities with the aim of ensuring a commercial and efficient approach to electricity distribution and supply.[4][1]

As a result, the power board was forced in August 1994 to vest all of its assets including Aniwhenua and associated water rights to the Bay of Plenty Electricity Limited.[5] Bay of Plenty Electricity subsequently became the first electricity company to be listed on the New Zealand stock exchange.

In July 1998 the New Zealand Government passed the Electricity Industry Reform Act which was intended to change the structure of the electricity industry to encourage competition. This Act required the operational separation of distribution and generation business activities by 1 July 1999 and separation of the ownership by 1 January 2004.[4]

As a result, in 1998 Bay of Plenty Electricity sold its retail and generation business, together with its name to Nova Energy, which was owned by the Todd Corporation.[6] On 1 April 1999, the remaining distribution assets were transferred to a new company, Horizon Energy Distribution Limited (which operates these assets under the name of Horizon Networks).

After a serious leak developed in the dam during Nova's ownership. Following investigations and development of a solution by consultants Tonkin + Taylor, the contracting firm of Waiotahi Contractors commenced in February 2006 the 58 day repair of the leak which took 58 day at a cost NZ$2.78 million.[7][8]

Looking to raise capital to invest in other energy projects in the North Island Nova agreed to sell Aniwhenua in November 2015 to Southern Generation Partnership (a partnership between Pioneer Generation Investments and Roaring Forties) for approximately NZ$100 million with ownership transferring in April 2016.[9][10] The Roaring Forties is a partnership between The Power Company and Electricity Invercargill.

At the beginning of December 2018 Pioneer Energy took over the services agreement with the Southern Generation Partnership to operate and maintain the power station.[6]

The headwaters of the Rangitaki River collect lightweight pumice sands and partly greywacke gravels which are deposited in the lake. During its first 15 years of operation the lake accumulated approximately 1.5 million m3 of sediment.[16] Loss of storage has been managed by constructing training banks to encourage the sediment to settle in the deeper areas of the lake as well as lowering of the lake and flushing during floods.[2]

In addition, it has been necessary to undertake limited dredging operations to remove sedimentation with 30,000 m3 removed in 2002.