Last week work started on a $600,000 project to install a piped extension to the scheme, which irrigates land around Duntroon.
Irrigation company chairman Kelvin Weir said the project would increase the area of irrigated land on the scheme from 800ha to more than 2000ha. It would also result in improved flows in the Maerewhenua River.
Some of the farms that would receive water from the extension had previously taken water from the Maerewhenua River for irrigation purposes, but these water permits would now be surrendered, he said.
''The company has invested significantly in this project, and also in replacing our intake and head-race structure last year.
'' Not only are we increasing the area under irrigation, but by working alongside Environment Canterbury and the farmers on the Maerewhenua River, we have been able to increase flows in the Maerewhenua, which is great for the river's health, as well as recreational river users.''
He said construction work would finish next month, and the expansion would begin during the next irrigation season, beginning in September.
The success of the project was down to the willingness of farmers to invest in a process that would benefit the environment and meet the requirements of the Canterbury Water Management Strategy Lower Waitaki-South Coastal Zone Committee, he said.
''We now need to ensure the water that's going back into the Maerewhenua River can stay there and won't be able to be abstracted in the future.''
Zone committee chairman Robin Murphy said the area's farmers had shown ''terrific'' initiative in producing a project that aligned with the Canterbury Water Management Strategy. Farmers involved with the expansion had invested ''at considerable cost to themselves''.
The sorting out of the water takes from the river and returning farmers' water allocation back to the river was ''a major achievement by all involved'', he said.
''This shows how local solutions fix local issues.''