Otago and Canterbury are the two driest regions in New Zealand, so the management of water has always been important there. They were the first places to begin irrigation.
In the 1880s, during the gold rush in Central Otago, water rights for sluicing were issued by the warden’s courts as property rights. Later, under the Mining Act 1898, the rights to take water from small burns, creeks and water races diverted from larger streams were classified as mining rights. When land use changed from mining to pastoral agriculture, these rights were used to irrigate grasslands by flooding them (wild-flood irrigation), and became a fiercely protected property right.
Irrigation trials started in mid-Canterbury as early as 1880, but large-scale irrigation did not start until well into the 1930s. The Public Works Act 1910 gave the government the power to construct irrigation systems.
Up until the end of the 1920s, the government assisted Central Otago farmers to use their water resources better by constructing storage dams and distribution channels. The facilities were owned and operated by the government, with minimal finance from water users for operation and maintenance.
The Rangitātā diversion race
In 1935 work began on constructing a large channel to take water from the Rangitātā River in Canterbury 67 kilometres north to the Rakaia River, near Methven. It was used for power generation at the Highbank power station, and for irrigation. It was opened in 1945. Irrigation water from this race was responsible for transforming a large part of mid-Canterbury into highly productive farmland.
Otago and Canterbury schemes in the 1930s
By about 1933, most irrigation came from government schemes in Central Otago. About 45,000 hectares was irrigated. From the early 1930s through to the post-war period, developing irrigation was seen as something government should fund because it made farmland more productive, and it also provided work for unemployed people through works programmes. Several small schemes in Canterbury – Redcliffs (1936), Levels (1937) and the Rangitātā diversion race (begun in 1935) – were primarily driven by this policy.
Over time, the Crown purchased many of the original mining rights and developed large irrigation schemes, often involving storage dams. The current mining rights based on these entitlements do not expire until 2021, and in parts of Central Otago, when put together, they actually exceed available river flow.