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<br />., <br /> <br />e: <br /> <br />. <br /> <br />~ <br />o <br />A <br />(,'0 <br /> <br />PART III. HISTORY OF WATER RESOURCE DEVELOPMENT <br /> <br />A. Irrigation Development <br /> <br />Irrigation development in the Upper Basin took place gradually from <br />the beginning of settlement, about 1860, but was hastened by the purchase <br />of land from the Indians in 1873. About 800,000 acres (320 000 ha) were <br />irrigated by 1905. Between 1905 and 1920 the development of irrigated land <br />continued at a rapid pace, and by 1920 nearly 1.4 million acres (570 000 <br />ha) were irrigated. The development then leveled off and increase since <br />that time has been slow. The average deplet ion from 1971-75 period was <br />approximately 2.2 million acre-feet (2700 x 106m3). <br /> <br />The slow growth in irrigated acreage in the Upper Bas in in the last <br />60 years is ascribed to both physical and economic limitations on the <br />availability of water. By 192D most of the lower cost and more easily <br />constructed developments were in operation, and, although some new develop- <br />ments have taken place since that time, they have been partially offset by <br />other acreage going out of production. <br /> <br />Irrigation development began in the Lower Basin about the same time as <br />in the Upper Basin. Development was slow because of difficult diversions <br />from the Colorado River with its widely fluctuat ing flows. Development of <br />the Gila area began in 1875 and the Palo Verde area in 1879. Construct ion <br />of the Boulder Canyon Project in the 1930's and other downstream projects <br />s ioce that time has provided the means for a cont ioued expans ion of the <br />irrigated area. In 1970 an additional 21,800 acres (B8oo ha) were irri- <br />gated by private pumping either directly from the Colorado River or from <br />wells in the flood plain. In 1974, there were nearly 849,000 ac.res <br />(344 000 ha) in the United States irrigated from Colorado River diversions <br />below Hoover Dam. About 25,500 acres (10 300 ha) of Lower Basin lands in <br />Utah and 12,000 acres (4900 ha) in Nevada are also now under irrigation. <br /> <br />B. Streamflow Depletions <br /> <br />Development and ut i1 izat ion of the bas in I 5 water resources <br />depletions of streamflows. Consumptive use of water by irrigated <br />exports to other basins produce the greatest flow depletions. <br />evaporation and consumptive use of water for municipal and <br />purposes also produce significant depletions. <br /> <br />result in <br />crops and <br />Rese rvo ir <br />indus t ria 1 <br /> <br />The 1978 est imated consumpt ive use of water by irrigated crops and <br />municipal and industrial users in the Upper Basin was approximately 3.3 <br />mill ion acre-feet (2800 x 106m3) in 1978. Deplet ions related to irri- <br />gation such as evaporation from irrigation reservoirs (not CRSP reservoirs) <br />were estimated to be about 120,000 acre-feet (150 x 106m3) per year. <br /> <br />Water exported from the Upper Basin during the period 1941-70 averaged <br />about 360,000 acre-feet (440 x 106m3) per year. Completion of the large <br /> <br />12 <br />