Storage Dam for Pump Irrigation Water

New Zealand Journal of Agriculture, Volume 98, Issue 1, 15 January 1959, Page 33

Storage Dam for Pump Irrigation Water

TO reduce irrigation costs by pumping water when the cheaper night rates for electricity apply, Mr J. Kinney, of Hyde, Central Otago, has made use of a circular dam on a hilltop to store irrigation water which is later used for daylight irrigation, as described in this article by W. A. Lunn, Fields Instructor, Department of Agriculture, Ranfurly. This type of dam was widely used by early miners throughout the goldfields and has recently been developed in Australia as a "turkey nest" dam for lowcost water storage or "water harvesting" during heavy rainfall and subsequent use through irrigation sprinklers.

THIS type of dam can often be placed in a more favourable position to command a larger area for irrigation than can a gully dam, provided the soil contains a reasonable percentage of clay to assist consolidation and to prevent leakage.

The dam on Mr Kinney’s property is 90 yds. in diameter and was constructed entirely by a bulldozer pushing spoil outward to form a circular dam. The cost of bulldozing was £l7O.

Water is pumped 170 vertical feet from the Taieri River through 750 ft. of pipeline. The pipeline comprises 130 ft. of 10 in. and 11 in. steel pipe which raises the water 80 ft. in one stage, 320 ft. of 9 in. high-pressure concrete pipe which raises the water to the 150 ft. level, and 300 ft. of 9 in.

low-pressure concrete pipe which raises the water through the remaining 20 ft. A 40 h.p. 3-phase electric induction motor operates a 4 in. high-lift pump capable of delivering 400 gallons per minute to a height of 250 ft. A time switch operates the pump from 10 p.m. to 7 a.m., during which period electricity charges are lower. The dam has a capacity of 1| million gallons and is filled after 7 nights’ pumping. Daylight irrigation uses about 2 cusecs of water, a proportion of which is replaced each night by the pump. At this rate the dam can supply sufficient water for 10 days’ irrigation.

Details of irrigation labour and operating costs are not given here, as these would be different for each irrigation scheme. Eventually an area of up to 250 acres could be irrigated, with an estimated increase of 500 ewes, which would double the previous carrying capacity. . Because of the high lift and the' nature of the country, the scheme has been made possible only by the construction of the hilltop dam to take advantage of the cheap night rates for electricity. Mr Kinney and his two sons have done all the work except the bulldoz-

ing of the dam and the electrical installations. In the immediate future the area irrigated will be 150 acres. The .cost of installation for the 150 acres, including the pump, motor, pipeline, the electrical equipment, and the dam, has been £8 10s. per acre. This figure would be considerably higher if the work had been done by hired labour or by contract, and the scheme is a good example of what can be achieved in reducing costs by sound planning and initiative.