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International trends


New Zealand irrigation project brings surface water to farmers


By Mark McKenzie


The Central Plains Water Enhancement Scheme is a farmer-owned irrigation scheme in New Zealand. It is located between the Rakaia River and the Waimakiriri River in the Canterbury region of the South Island. Central Plains Water Limited was established in mid-2003 and is responsible for the construction and operation of the scheme. CPWL farmers have provided the funding for the $450 million scheme. Funding includes $88 million of farmer equity with the balance funded by debt, which will be repaid over 40 years.


Providing reliable water supply to farmers for irrigation is the primary role of the scheme. However, it also provides considerable environmental, social and recreational opportunities to address issues such as groundwater recharge and


community prosperity. All stages will be completed by September 2018.


The scheme can irrigate up to 60,000 hectares within a region covering 100,000 hectares. The CPWES is made up of three separate components, each at different stages of development.


Stage 1 covers 23,000 hectares of irrigable area and consists of a 17-kilometer-long canal delivering water from the Rakaia River into a piped distribution network. The canal is 30 meters wide and 5 meters deep. It is lined with 50 hectares of plastic (HDPE) liner as well as 80 hectares of geotextile underlay. A 130-kilometer-long distribution network has four lateral pipes from the canal that provide pressurized irrigation water to each farm.


CPWL has just completed its second successful irrigation season operating stage 1. The scheme is successfully delivering reliable alpine-fed river water to its farmers. Stage 1 has enabled existing groundwater irrigators to switch off 75 percent of their groundwater abstraction volume during the 2015 through 2017 seasons. Environmentally, this has resulted in 60 million cubic meters of water remaining in the ground.


Stage 2 of the scheme is currently under construction and will service another 20,000 hectares.


A key difference between stages 1 and 2 is that stage 2 uses a 23-kilometer-long large diameter (2.5 meters) glass reinforced plastic [GRP] main trunk pipe. The GRP pipe


Stage 1 – headrace intake area


34 Irrigation TODAY | July 2017


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