In an average precipitation year when the irrigator receives about 18 inches of precipitation of which 10.62 inches is effective, he would need 9.38 inches of irrigation water to produce his yield goal. More than 10,000 center pivot systems are in operation in the Water District. Surge valves are used on almost every farm which does not have a center pivot system. There are 20,000 to 30,000 miles of underground pipe used to convey the water from the wells to the fields being irrigated. Irrigation application efficiency in the district averages 80 percent or better on about 70 percent of the irrigated farms in the district.
Water use efficiency translates into less water being removed from the aquifer.
From 1988 to 1998, the net depletion in the original 5.5 million acre area averaged 866,250 acre-feet per year. In 1997, the region received about 22 inches of precipitation, which is about 4 inches above average. Consequently, the net depletion of the aquifer dropped to 280,500 acre-feet. From 1988 to 1998, the net depletion in the 6.9 million acre service area averaged 1,086,750 acre-feet. The net change in the volume of water in storage during calendar year 1997 was 350,365 acre-feet in the 6.9 million acre service area.