More than 200km of water races in one of Canterbury's oldest irrigation schemes are to be replaced with pipes.
The Ashburton Lyndhurst Irrigation scheme, established 70 years ago, supplies water to 234 farms and small holdings totalling more than 25,000ha, with water taken from the Rangitata diversion race.
About a third of the users are dairy farms; the rest are cropping, sheep, dairy support and horticulture.
Chairman John van Polanen says the savings mean a further 3000 - 4000ha will be irrigated and filling-in the water races will free about 100ha for production.
The upgrade is expected to cost about $90 million.
Mr van Polanen says other irrigation schemes are making similar moves to pipe their water, including the Valetta scheme, which also takes water from the Rangitata diversion race.