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<br />melons. Multiple cropping 1/ occurs on approximately 32 percent of <br />the irrigated land. Border and furrow irrigation are the predominant <br />methods used, and app 1 i cat ion is usually controlled to prevent tail- <br />water from fields. Overall onfarm irrigation efficiency on valley <br />lands was found to be 54.7 percent, with a variation among subareas of <br />the District of from 42 percent to 64 percent. <br />Drainage is provided by a 150-mile system of open drains, most of <br />which discharge into the Palo Verde Outfall Drain, which runs in a <br />southerly direction through the center of the District. The outfall <br />drain discharges into an old channel of the Colorado River and enters <br />the present river channel approximately 10 miles south of the <br />District. The flow in the outfall drain ranges from a low of approxi- <br />mately 350 ft3/s to a high of approximately 800 ft3/s. <br />The District's entitlement to Colorado River water has the first <br />priority among the agricultural water users in California. As speci- <br />fied in the Seven-Party Priorities Agreement, the District is entitled <br />~------ ---.- <br />to ". . . such waters as may be required . . . for beneficial use <br />exclusively on lands aggregating a gross area of 104,500 acres. . ." <br />[3J. For purposes of water accounting, the District's use of river <br />water is cons i dered to be di versi ons 1 ess measured returns to the <br />river. During the period 1970-1974, the average annual District <br />diversion was 914,000 acre-feet, and the average measured return flow <br />was 454,668 acre-feet. The District water charge to irrigators is <br />based on the number of irrigable acres and not on the amount of water <br />delivered. <br /> <br />Geology <br />Irrigated lands of the District are located mainly on the valley <br />floor adjacent to the river. The topography of the valley floor may <br />be characteri zed as fl at, wi th a mil d slope to the south of about 2 <br />feet per mile. Its elevation ranges from 220 feet to 270 feet above <br />sea level. It is bounded on the east by the Colorado River and on the <br />west by a steep escarpment 80 to 120 feet high. There are also some <br />agricultural lands on the Palo Verde Mesa to the west of the valley. <br /> <br />C.- f":'t)".., <br />.... I..} '1 \J <br /> <br />1/ Including livestock grazing after harvest. <br /> <br />7 <br />