page_title: Rangitata Diversion Race
section_title: Barrhill-Chertsey irrigation scheme
hierarchical_section_title: Rangitata Diversion Race / Associated irrigation schemes / Barrhill-Chertsey irrigation scheme
caption_attribution_description: English: This image forms part of a series showing aspects of the canal and associated structures that were constructed to divert water from the Rangitata river for irrigation and power generation purposes. The canal terminates at the Highbank power station which releases the water into the Rakaia river.
context_page_description: The Rangitata Diversion Race or RDR is a combined irrigation and power generation scheme that diverts water from the Rangitata River to irrigate over 100,000 hectares of farmland in Mid-Canterbury, New Zealand.The RDR project was the first major river diversion in New Zealand, and the largest irrigation scheme in the country. It was originally constructed by the Public Works Department between 1937 and 1944. The main canal is 67 km long, 10 m wide and 3 m deep.
  The RDR supplies three community irrigation schemes, two hydroelectric power stations, the Ashburton District Council stockwater race system and various private stockwater and irrigation schemes.
context_section_description: In 2010, a pumping station was commissioned adjacent to Highbank Power Station.  The pumps lift water from the Rakaia River into the Rangitata Diversion Race, to provide additional water for the Barrhill-Chertsey irrigation scheme that supplies about 17,600 hectares of farmland. The pumping station is used when the Highbank power station is not generating.   RDRML supplies up to 8 cumecs to the Barrhill-Chertsey irrigation scheme via a water swap arrangement with the consents held by Barrhill-Chertsey Irrigation for water diversion from the Rakaia River.
  A short canal alongside the existing tailrace from Highbank Power Station is used to divert water from the Rakaia River into the intake of the pumping station.  Pumps then pass the water via a pipeline into the existing power station penstock, so that it flows up and into the Rangitata Diversion Race.   
  There are six pumps, each capable of delivering one m³ per second. Each pump is driven by a 1.55 MW electric motor.
  Technical features of this development include the large bifurcation or ‘tee’ that was required to connect the new pump station pipeline to the original power station penstock.  Another feature is a large 40 m³ air chamber that is used to manage pressure variations during pump station operations.
  The pumping station was originally developed as a joint venture between Barrhill-Chertsey Irrigation and Electricity Ashburton, but the irrigation company took full ownership in 2017.
caption: Air chamber at Highbank pump station
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