Automatic irrigation system

Press, Volume CXII, Issue 32862, 10 March 1972, Page 12

Automatic irrigation system

A new Australian continuous automatic spray irrigation system can supply an inch of water to a 50-acre field each week with almost no labour costs, minimum power costs, and great economy of water.

The system has already been commercially installed on a beef cattle property and is working successfully. The system, Cablerain, consists of a flexible irrigation pipeline anchored to an outlet pipe at the centre of the field. The sprayline is mounted on wheel bogies. An endless cable round the perimeter of the field slowly pulls the outer end of the sprayline until it makes a full circle of the field. A hydraulic winch at one side of the perimeter hauls the cable at variable speeds. Different - sized spray nozzles along the pipeline give the field an even cover of water. The company which developed the system is McPherson’s, Ltd, an Australian engineers’ supply firm. It was the brainchild of a retired employee, Mr R. Mitchell. McPherson’s, aided by an Australian Government research grant, spent $A30,000 developing the system, including prototype testing at a farm run by the University of Sydney. The first commercial installation was made on a fat cattle property at Scone in the fertile Hunter River Valley in New South Wales. The installation, on Mr N. B. D. Smith’s property “St Aubin’s Without,” cost SA22O an acre, but McPherson’s, Ltd, is confident of reducing this to SAISO an acre in future installations. The system supplies an inch of water to each acre of ground at a cost of 34.4 c an acre. The pump delivers a constant flow of water and by varying the cable speed the sprayline can make a full circle in three days and a half to spray half an inch on the field, seven days to spray one inch, or 14 days to spray two inches. At Scone, water is supplied to the system from a well, and is pumped a distance of 3000 ft with a 75ft rise to the central pipe of the system. It then goes out along a 980 ft spray line

made up of 20ft lengths of aluminium pipe, emerging through spray nozzles every 20ft. The nozzle sizes vary and have matched flow control valves to ensure equal water distribution along the sprayline. All but the outside nozzle are straight nozzles, set at a 20 degree angle to direct the water to the rear of the pipeline and avoid dampening the earth in front of the system’s wheel bogies. The end nozzle is a part-circle sprinkler. The sprayline is mounted on a simple girder and undercarriage, with galvanised steel wheels 14in in diameter and three inches wide mounted on nylon bushes and castors. The big wheels and the flexibility of the pipeline allow the system to traverse undulating ground and thick pasture growth without trouble. The sales engineer of McPherson’s pump division, Mr C. Thompson, said the system over-watered only at the centre —2 per cent of the area being irrigated was overwatered by about 300 per cent, but this was considered acceptable. At Scone the system used 7000 gallons of water an hour, or 1,250,000 gallons a week. t The pump unit was the greatest user of power, at a cost of 29c an acre-inch of irrigation. Power used by the hydraulic winch cost only 5.4 c an acre-inch. Labour costs were very small. Once operating, the Cablerain system could be left virtually untended, Mr Thompson said. Casual, visual observation was sufficient to check its progress. After making a complete circuit of a field over three days and a half, seven or 14 days, the installation turned itself off automatically. The cable was attached to the pipeline by a gooseneck, and on returning' to the winch the gooseneck tripped a switch and stopped the system.

To begin a new cycle, workmen simply had to knock a wedge from the gooseneck, attach the gooseneck to the cable emerging from the winch, and secure it again with a wedge. A pushbutton then started the system for a new cycle. At the Scone installation, the winch trip-switch will be linked to the well pump 3000 ft away by a radio transmitter. This will ensure that both pump and winch are switched on and off together.