Canterbury agriculture now contributes over $1.7 billion a year to the New Zealand economy. To integrate water use in the region, we are working with Environment Canterbury, and with the Barrhill Chertsey Irrigation (BCI) and Central Plains Water (CPW) schemes. Our Highbank Pumping Station has been supplying irrigation water to BCI via the Rangitata Diversion Race since 2010.
Utilising Lake Coleridge for irrigation
Lake Coleridge is a natural lake, west of Christchurch, managed by Trustpower and feeding Coleridge Power Station. It is near to and capable of supplying some of mid-Canterbury’s largest developing and established irrigation schemes.
In 2012, Trustpower secured a variation to the existing Water Conservation Order on the Rakaia River. With the change, water can be stored in Lake Coleridge for irrigation supply as well as for generation (there was no change to water allocation criteria protecting environmental aspects of the river system). Lake Coleridge storage, together with river take, can potentially provide high levels of reliability for up to 100,000 hectares (ha) of irrigation.
Barrhill Chertsey Irrigation and Central Plains Water
We have contracted stored irrigation water from Lake Coleridge, to both Barrhill Chertsey Irrigation (BCI) and Central Plains Water (CPW). In 2013, BCI supplied approximately 10,000ha of the ultimate potential 40,000ha supply area south of the Rakaia River. Our Highbank Pumping Station is a vital supply source to BCI.
CPW intends to develop a new irrigation scheme on the north bank of the Rakaia River, with a potential 60,000ha supply area. This scheme accesses river flow with low reliability, so storage from Lake Coleridge will be key.
Highbank Pumping Station stands alongside our existing Highbank Power Station and supplies irrigation water to BCI via the Rangitata Diversion Race. The pumping station was especially built to supply BCI with irrigation water.
Water is extracted from the Rakaia River, into a short canal alongside the existing Highbank Power Station tailrace and into the new pumping station. It’s then piped up the existing penstock and into the Rangitata Diversion Race for delivery to farmers. We envisage the pumping station will eventually be capable of supplying the Rangitata Diversion Race with 8 cubic metres per second of irrigation water.
Towards integrated irrigation in Canterbury
There is potential for Lake Coleridge to be integrated into the wider Canterbury irrigation water infrastructure. This could encompass both existing and future infrastructure, such as additional storage facilities and supply systems.
Trustpower is working with Environment Canterbury and irrigation users to develop infrastructure plans that would allow water to be conveyed and supplied over a much greater area of Mid and South Canterbury. A key focus is progressive sustainable development, over a number of years.
Once coupled with integrated infrastructure, Lake Coleridge would be fundamental to opening new irrigation areas, allowing water to be assigned to new users without negative impact on existing users. Integration means water could be traded amongst users, ensuring the highest value use.