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<br />J <br />;~. <br />} <br />, <br /> <br />r <br /> <br />California. Lake Mohave reregu1ates <br />Hoover Dam releases for power produc- <br />tion and for .deliveries to Mexico. <br />Lesser structures downstream include <br />Senator Wash, Laguna, Headgate Rock, <br />Palo Verde, Imperial, and Morelos <br />Dams. Senator Wash and Laguna Dams <br />provide very limited amounts of <br />reregulation capacity while the others <br />are used principally for diversion. <br />Diversions below Lake Mead for <br />agriculture, municipal and industrial, <br />power, export J and other purposes are <br />of the magnitude of 8.5 to 9.5 million <br />acre-feet annually. A portion of these <br />diversions is satisfied from upstream <br />return flows. Yuma and Lake Havasu <br />City in Arizona, and Needles and Blythe <br />in California are the major cities <br />along the mains t ream be 1 ow Lake Mead. <br />Current irrigated lands adjacent to the <br />mainstream are estimated to cover <br />approximately 395,000 acres. There has <br />been a significant annual increase in <br />the diversions for municipal and <br />industrial purposes, particularly from <br />Lake Mead to the metropolitan Las Vegas <br />area in Nevada. <br /> <br />c.., <br />,., <br /> <br />w <br />..... <br />IollIo <br />c...? <br /> <br />Little Colorado River, Arizona-New <br />Mexico: The Little Colorado River <br />drainage area odcupies a large part of <br />northern Arizona and a portion of <br />west-central New Mexico. It origi- <br />nates on the north slopes of the <br />White Mountains about 20 miles above <br />SpringerviUe, Arizona. The river has <br />a mainstream length of about 356 miles <br />and joins the Colorado River on the <br />east boundary of Grand Canyon Nat ional <br />Park about 78 miles downstream from <br />Glen Canyon Dam. <br />A series of saline springs near the <br />mouth produce an estimated l60,OOO <br />acre-feet of water annually. The USGS <br />gaging station near Cameron, Arizona, <br />is located on the Navajo Indian Reser- <br />vation about 45 miles upstream from the <br />mouth. Streamflow is undependable and <br />erratic and is subject to flash floods <br />of considerable magnitude. Flow at the <br />gaging station during the 1976-80 <br />period varied from 69,570 acre-feet in <br />1977 to 472,700 acre-feet in 1979. <br />Only minor development of the ground <br /> <br />water has occurred because of low <br />yields and poor quality. Excessive <br />erosion and sediment deposition plague <br />the area. Agriculture is concentrated <br />along the mainstream in the upper <br />reaches of the river, on Silver Creek, <br />a southern tributary, and on the Zuni <br />River in New Mexico. Current irri- <br />gated lands in the basin are estimated <br />to include approximately 58,000 acres. <br />Irrigated acreage in the basin is <br />subject to variation because of fre- <br />quent water shortages and inadequate <br />storage facilities. Population is <br />predominately rural with a relatively <br />large Indian segment. Principal <br />cities include Flagstaff, Winslow, and <br />Holbrook in Arizona, and Gallup and <br />Zuni Pueblo in New Mexico. Leading <br />industries include tourism, recreation, <br />manufacturing, mining, and forest <br />products. <br /> <br />Virgin River, Arizona-Utah: The Virgin <br />River originates in western Kane <br />County, Utah. It flows southwesterly <br />through the southwest corner of Utah <br />and the northwestern corner of Arizona <br />and empties into the northern extremity <br />of the Overton Arm of Lake Mead in <br />Nevada. The selected outflow point is <br />the long-term USGS gaging station at <br />Littlefield, Arizona, which is about 36 <br />miles upstream from Lake Mead and about <br />lO miles above the Arizona-Nevada State <br />line. The river is fed chiefly from <br />tributaries heading in the southern <br />high plateaus and mountains in Utah. <br />Several springs contribute water to the <br />river at a relatively uniform rate. <br />The two most significant of these <br />springs are located near LaVerkin, <br />Utah, and Littlefield, Arizona, and <br />both are highly saline. Agricultural <br />and municipal developments in Nevada <br />below the selected out flow point are <br />inc luded in "remaining areas, II as shown <br />on the frontispiece map. <br />The major irrigated. areas are <br />located in the LaVerkin-Hurricane-St. <br />George-Santa Clara areas of Washington <br />County, Utah, and in the Littlefield <br />area of Mohave County, Arizona. There <br />are small irrigated areas scattered <br />throughout. Irrigated lands in 1980 <br /> <br />7 <br /> <br />i <br />