A Partnership for Good
As a result of collaboration between Trustpower and Central Plains Water, in 2015 reliable water supply will start flowing to 20,000ha of Canterbury land.
Reliability of water supply is the cornerstone of any irrigation scheme. But without storage, Central Plains Water (CPW) scheme in Canterbury could only provide shareholders with 70% reliability of water supply. Under its consents, CPW abstracts water for irrigation from the Rakaia River, but the river must be at a minimum level before abstraction is allowed.
In 2013, CPW signed an agreement with Trustpower to have water stored in Lake Coleridge, and have it released for shareholders’ use when the Rakaia River is below the minimum. Under the historic agreement, CPW can take up to 50 million cubic metres of stored water per year, for Stage One of its scheme.
CPW’s Chief Executive Derek Crombie said the agreement is critical for the scheme’s viability, increasing reliability of supply to 95%. Without the agreement, CPW would have had to consider building large water storage facilities throughout the project area, which would have been uneconomic for many users.
The $375 million CPW scheme will be built in three stages over a total of 60,000ha, between the Rakaia and Waimakariri Rivers. The $140 million Stage One, spanning 20,000ha, is targeted to start delivering water in September 2015. Future stages are under design, with construction to match uptake and future storage capacity over the next five years.
Work on Stage One has started. Stage One will include a 17km headrace canal, with 13 bridges that each span approximately 25m (10 farm bridges, three public road bridges) plus a 130km pipeline network. When complete, the network will have a number of pump stations and four main pipelines, extending from the headrace canal down the Canterbury Plains.
CPW plans to have the headrace canal and bridges substantially complete by mid-2015, including lining the canal. This means it should be able to fill the canal in July, giving nearly two months of testing and commissioning before water officially flows in September 2015.
Mr Crombie said that the CPW scheme will provide wide-reaching environmental benefits. “In Stage One we will be replacing 100 million cubic metres of water that is normally extracted from the groundwater aquifers, with river water. In addition, the scheme has capacity to release targeted flows of water into the lowland aquifers to augment the natural flows during summer. Over time this will help replenish the aquifers and improve water quality in lowland areas, especially around Lake Te Waihora. Irrigation also means that farmers can better control and monitor the amount of nitrates they use, thereby cutting down on the amounts leached into the groundwater system.”
While Trustpower’s agreement with CPW at this stage provides stored water only for Stage One, there is scope to more than double the quantity supplied as CPW grows.
"We see this as only the start of our relationship with Trustpower. As we move into Stage Two and Three of the scheme, we will continue to look at various options in relation to water storage, water use enhancement and reliability. This will ensure wide-reaching envinronmental benefits for the Canterbury Plains."
Derek Crombie, Chief Executive CPW