Summary of Scheme Details - Central Plains Water Irrigation Scheme

The CPW proposal is to build a massive earth dam, 55m high and 2 kilometres long, across the mouth of the Waianiwaniwa Valley in the Malvern Hills. ( The village of Coalgate would sit in the shadow of the dam).

The basal footprint width of the dam will be ~300m wide. 280 million cubic metres of water will be stored in the reservoir behind the dam. The reservoir will cover 1200 hectares of the Waianiwaniwa Valley and will be filled by water conveyed through a 10km long tunnel from the upper intake site, above the Kowai confluence, on the Waimakariri River. The tunnel will transport water through the Malvern Hills at Sheffield to the reservoir. The CPW scheme is a run-of-river scheme with water to be taken from the Waimakariri when available, to fill the reservoir.

CPW have applied to take up to 40 cubic metres per second (cumecs) of water from both the Rakaia and Waimakariri Rivers. Water from the Rakaia will be shared equally with Joint Applicants, the Ashburton Community Water Trust, who plan a hydro power/irrigation scheme on the south side of the Rakaia River at Barrhill. When river flows allow, run-of-river water will be conveyed approx. 60km across the plains between the Waimakariri River and the Rakaia River via a 50m wide level headrace canal on the 235 contour line. It is proposed to take water from two intake sites on the Waimakariri River and two on the Rakaia river. Water from the headrace canal will be distributed across the Central Plains area via a network canal system. THE MHPS estimates 450km of network canals. Water will be taken from the reservoir at times of low flows in the rivers.

The CPW proposal will irrigate 60,000 hectares of the Upper Central Canterbury Plains. CPW assumes the irrigation scheme will double the area in dairying, from 22,000 hectares to 46,000 hectares.