The Highbank Power Station was constructed between 1939 and 1945, as part of a combined project to enhance farm production and generate electricity.
Water for the station is collected from the Rangitata River by means of a 66 km long irrigation race, which provides water for use by farms in summer, when demand for electricity is lower. In winter, when electricity demand increases, and the demand for irrigation water reduces, the surplus water is used for power generation purposes. Surplus water is used for generation during irrigation season and outside of this all water is available for generation.
The Montalto Scheme had its beginnings in 1958, when design work started on a project to generate electricity utilising the stepped flow of the Rangitata Diversion Race – an irrigation project completed in the early 1940s. Commissioning of the Montalto Power Station, which produces 1.1 MW during the irrigation season and 1.8 MW at other times, was completed in 1982.
In 2002 the Highbank plant, with an installed capacity of 28 MW, underwent a substantial electrical and ancillary equipment upgrade including the total rebuild of the 11/66kV switchyard along with installation of a hybrid excitation system, 400v local service, 110vDC systems, a standby generator, a machine circuit breaker, machine protection and generator cooling improvements.
The average annual output of the combined Highbank and Montalto Schemes is approximately 98GWh.
Generation from the Highbank Scheme is dependent upon irrigation requirements which take priority in the irrigation season. The scheme is guaranteed water for four months of the year, but typically generates for six to eight months, increasing to eleven to twelve months in particularly wet years.
Salmon migrating up the Rakaia River have previously become stranded in Highbank’s tailrace in late summer. This is an historical problem, however; TrustPower in conjunction with Fish and Game North Canterbury for the most part, resolved the entrainment issue. Key to solving this long standing problem was the design and installation of a Salmon Barrier at the end of the formed section of the tailrace, and a fish access channel to enable diverted Salmon to access a main braid of the Rakaia River.
The Hearings for the Rangitata Water Conversation Order concluded during November 2001 and ultimately resulted in the Minister confirming the Order for the river. Significantly the diversion volumes supplying the power schemes were found to have no significant effect and hence the historical take was in effect enshrined in the Order.
Resource Consents governing the operation of the Highbank and Montalto Power Schemes expired on 31 October 2001. These applications were not heard until a decision on the Rangitata Water Conservation Order was confirmed.
Ultimately the re-consenting process also confirmed the traditional patterns of use had no significant effects and the full suite of consents were confirmed by the Environment Court during April 2008 for a term of 35 years.