Benmore Irrigation Scheme

Location: Mackenzie Basin, South Canterbury
Duration: 12 Months, 2005
Client: Benmore Irrigation Ltd
Value: $4.0 million
Delivered on Time and Budget?:  Yes

This scheme utilises 4.0cumecs of water from the Ohau River to irrigate 8,000ha via pipework and 22km of open race down the side of Lake Ruataniwha, and then south/west towards Omarama.

There were significant earthworks quantities with this project including 800,000 m3 of cut and 25,000m3 of liner borrowed and placed. Due to the variable nature of the ground approximately 6km of the Benmore race had to be lined. This was completed by laying the material in the race invert, the material was then cut up, mixed and recompacted with the in-situ gravels to provide a 350 to 450mm deep liner, which has worked exceptionally well.
The intake is automated and comprises concrete structure, hydraulic gates and four gallery fishscreens to prevent fish ingress. Further down the system there are two automated water turnout points to deliver water to the shareholders.

Winter conditions were extremely difficult with ice, snow and temperatures to 13deg C. This affected liner placement but good management meant that the project continued on schedule.


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