Rangitata Diversion Race Reliability Modeling – MSCI Hons 2010

Trustpower logo.JPG



Data Analysis




About the Authors


The following is adapted from TrustPower’s online website.


In New Zealand, TrustPower owns 36 small to medium size Hydro Generating Stations and a large Wind Farm. They produce electricity exclusively from renewable sources and their power stations produce enough electricity for around 220,000 households. As an electricity generator, TrustPower operates a business that is reliant on natural and physical resources to provide the energy needs of communities and businesses throughout New Zealand.


As a business, TrustPower must perform to a level that can attract and retain investment. At the same time, it must be equally aware of society’s environmental performance expectations, and the need to deliver energy at a reasonable cost to consumers and minimal cost to the environment.


TrustPower is very conscious of the environmental expectations of its stakeholders, including communities that live in that environment, and investors. It is also well aware of the bigger picture, and the need to operate in a sustainable manner.

Rangitata Diversion Race

The following is adapted from RDRML’s online website.


The Rangitata Diversion Race was a dream in the minds of the pioneering farmers in Mid Canterbury when the 750,000 acre plain was first farmed in the mid-19th Century. Regarded as the largest area of nearly flat land in New Zealand, all development was closely linked to water problems – water races to supply stock on light soils and water courses to drain heavy swamp lands.


Despite high expectations of development, it took the massive unemployment of the 1930s depression to provide the catalyst for the work to start in what would become the RDR. Work began on the scheme on April 2nd 1937 and was completed in November 1944. Race water first generated electric power at Highbank power station on June 8th 1945. Expected to cost £1.5 million pounds, the scheme costs grew to £2 million pounds.


The RDR takes water from the Rangitata River, restricted by resource consents. This water is then directed across the Canterbury plains by the RDR canals and a series of syphons. On the way, draw offs are made by three major irrigation schemes, Mayfield-Hinds (MHIS), Valetta (VALIS), and Ashburton-Lyndhurst (ALIS). As the RDR passes by the South Ashburton River more water is taken, again limited by resource consent. Figure 2-1 shows the key features of the RDR scheme as it currently stands.


Figure 21: Schematic of key features in the RDR scheme

Since 1945 there have been a number of amendments to refine the efficiency of the RDR. Montalto, the second hydroelectric power station was built in 1981 and started producing electricity a year later. The Sandtrap was designed and built at a similar time to remove much of the suspended sediment from the water by reducing the velocity of the flow. The sediment causes wear and tear on the hydro electric turbines and can cause gastric problems for sheep and lambs when washed out onto paddocks. Conversely the sediment is a good bonding agent that can help to plug microscopic holes in the race lining.


One of TrustPowers many assets is the Highbank power scheme, comprised of the Montalto and Highbank Hydro generation power stations. In winter, when electricity demand increases, and the demand for irrigation water reduces, most of the available 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.

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.



Owen Warburton and Chris Blackmore, University of Canterbury Management Department 2010