Central Plains Water Enhancement Scheme (CPWES)
The Central Plains Water Enhancement Scheme is an irrigation scheme in Selwyn District, Canterbury with the capacity to irrigate 63,000 hectares of farmland between the Rakaia and Waimakariri Rivers. The Scheme was constructed in three stages between 2014 and 2018. Operated by Central Plains Water Ltd (CPWL), it is the largest irrigation scheme in the South Island with an estimated value of $422M and is owned by a cooperative of 380 farmer shareholders. Shareholders include dairy, cropping and beef and sheep farmers. Every farmer maintains commitment to a farm environment plan regime.
As early as 1883 there was talk in Canterbury of establishing an irrigation scheme to service central plains farms. In 1936 the first approach was made to central government by the then Malvern County Council to use the Public Works Act to build a scheme for the central plains. After thirteen years deliberation, this was declined in 1949. It wasn’t until 51 years later that the idea gained ground.
In May 2000, the CPWES Steering Committee, a joint committee of the Christchurch City Council (CCC) and Selwyn District Council (SDC), was established and funded to assess the feasibility of water enhancement schemes for the Central Plains area. This feasibility study confirmed the validity of an affordable scheme.
In April 2003 the Central Plains Water Trust (CPWT) was established to replace the Steering Committee and progress the project.
The Trust is a public venture, with Trustees appointed by the CCC, SDC and Ngāi Tahu. The first role of the Trust, following establishment, was to raise sufficient share capital to fund the process to obtain the consents necessary to proceed with the project. The consents are owned and administered by the CPWT which licences the use of these consents to CPWL.
CPWL was established in September 2003 and is responsible for the implementation and operation of the Scheme.
Following granting of consents, in November 2004, CPWL issued a prospectus to raise funds. The prospectus was oversubscribed and successfully raised the required $4.7 million to start construction of the CPWL scheme. Shares were available to anyone, and once issued carried rights to water. Shares were fully subscribed by farmers within the Scheme area. There are 380 farmer shareholders.
In June 2005 CPWL lodged a “take” consent application for the upper Waimakariri intake site. This was followed in November of the same year by a “use” consent application.
The initial Central Plains Water scheme proposed a 280M m3 water storage reservoir. The reservoir was to be located west of Coalgate, where the Waianiwaniwa Valley opens out to the Canterbury Plains.
In April 2009, Environment Canterbury Commissioners advised this consent application was declined. However, they gave CPWL the opportunity to propose a revised run-of-river scheme which was subsequently consented in 2010.
In 2012 CPWL received a $5 million loan from the SDC to progress to detailed design work on Stage 1 of the Scheme. This was augmented in early 2013 by $5.7 million of funding from the Ministry for Primary Industries’ Irrigation Acceleration Fund (IAF).
In early 2013 the Government accepted Environment Canterbury’s recommendation to change the Water Conservation Order (WCO) covering the Rakaia River. The WCO allows Trustpower to release water from Lake Coleridge for irrigation when the river is low, increasing the reliability of the water supply. The Trustpower proposal included construction of a canal that runs along the north side of the Rakaia River linking Lake Coleridge with the CPWL Scheme.
Detailed design and the procurement of project finance and construction was completed by an inhouse team of 25 and contracts for initial Stage 1 construction were let in early 2014.
Contractors completed work on construction of Stage 1 in September 2015.
Stage 1 of the Central Plains Water Scheme included 23,000 hectares hectares of irrigable area and included construction of a 17-kilometre-long canal delivering water from the Rakaia River into a piped distribution network. The canal is 30 metres wide and five metres deep. It is lined with 50 hectares of plastic (HDPE) liner as well as 80 hectares of geotextile underlay. The 130-kilometre-long distribution network has four lateral pipes from the canal that provide pressurised irrigation water to each farm.
Stage 1 also involved the movement of 3.4 million cubic metres of earth and the construction of 13 bridges and 12 pump stations. This construction cost $157M and took approximately 18 months to complete.
Following the completion of Stage 1, work commenced on the Sheffield section of the Scheme, constructed between December 2016 and October 2017. This section of the Scheme comprises a 2.5MW pump station, a 2M cubic metre storage pond and 37 kms of pipeline. The Sheffield section supplies irrigation to 4,424 hectares hectares and cost $42M to complete.
Stage 2 of the scheme, covering an area of 20,000 hectares hectares between Stage 1 and Sheffield, was constructed between January 2017 and October 2018. 22.5kms of GRP pipeline was installed, feeding from the Head Race Canal and supplying 177kms of HDPE pipeline.
Stage 2 provides irrigation to 152 farms. The total cost of Stage 2 was $182M.
At this time not all shares are subscribed and an increase of approximately 10% of irrigated area is available, as shown in the Table below.
|Scheme Stage||Built Capacity||Currently Subscribed||Percentage Subscribed|
|Stage 1||25,000 hectares||23,000 hectares||92%|
|Stage 2||20,000 hectares||17,000 hectares||85%|
|Sheffield||4,424 hectares||4,100 hectares||93%|