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<br />were estimated to include approxi- <br />mately 20,000 acres. Ground water has <br />been develope~ to a limited degree. <br />population is predominately rural with <br />St.. George, Utah, being the principal <br />~city in the basin. zion National Park, <br />(')located near Springdale, Utah, attracts <br />~any visitors each year. <br />.... <br /> <br />~Udd:.: River, Nevada: . Th~ Muddy Riv,:,r, <br />a tr1butary of .the V1rg1n R1ver pr10r <br />to the existence of Lake Mead, origin- <br />ates from warm springs in northern <br />Clark County, Nevada, about 10 miles <br />northwest of Glendale. The river flows <br />southeasterly for about 30 miles and <br />terminates at the northwestern extrem- <br />ity of the Overton Arm of Lake Mead <br />near Overton, Nevada. Meadow Valley <br />Wash, the major tributary of Muddy <br />River, originates in northeastern <br />Lincoln County and flows south to <br />join the parent stream at Glendale. <br />The USGS gaging station near Glendale <br />is about 2.4 miles downstream from <br />Meadow Valley Wash. Out flow varies <br />little from year to year. Meadow <br />Va lley Wash, al though perennial in <br />the vicinity of Caliente, is normally <br />dry in the last 50-mile reach above <br />Glendale. Estimated irrigated lands <br />covered approximately lO ,000 acres in <br />1980. The entire basin is sparsely <br />populated. <br /> <br />Bill Williams River, Arizona: The Bill <br />Williams River is formed by the mer- <br />gence of the Big Sandy and Santa Maria <br />Rivers about 7.5 miles above Alamo <br />Dam. The river above Alamo Dam drains <br />an area of about 4,700 square miles <br />from small, rough mountain ranges and <br />intervening valleys in parts of Mohave, <br />Yuma, and Yavapai Counties. Alamo Dam <br />and Reservoir, a flood control struc- <br />ture completed in 1968, was built to <br />protect downstream development along <br />the Colorado River. A minimum pool is' <br />maintained for recreation and game <br />management purposes. Releases up to a <br />maximum of 2,000 cfs from the allocated <br />conservation pool above the minimum <br />pool are coordinated with releases from <br />mainstream reservoirs. Releases from <br /> <br />Alamo Dam and runoff from the inter- <br />vening area flow westerly and enter at <br />the lower end of Lake Havasu just above <br />Parker Dam. Current irrigated lands <br />are estimated to include approxi- <br />mately lO,OOO acres. The limited <br />development. in the basin is dominated <br />by copper mining at the unincorporated <br />town of Bagdad. A large portion of the <br />water supply in the basin is obtained <br />from ground water pumpage. Releases <br />from Alamo Dam during the 1976-80 <br />period varied from l7,350 acre-feet in <br />1977 to 644,500 acre-feet in 1980. <br /> <br />Gila River, Arizona-New Mexico: The <br />Gila River is the largest tributary <br />to the Colorado River in the Lower <br />Colorado River system. The drainage <br />area extends from the Continental <br />Divide in New Mexico to the river's <br />mouth near Yuma, Arizona. Elevations <br />in the basin range from nearly 12,000 <br />feet in the eastern mountains to about <br />150 feet at the mouth. The selected <br />outflow point for the basin is at <br />Painted Rock Dam, a flood control <br />structure located about 20 miles west <br />of Gila Bend, Arizona. The drainage <br />area above Painted Rock Dam is about <br />50,900 square miles, of which 5,600 <br />square miles are in New Mexico and <br />1 ,lOO square miles in Mexico. The dam <br />was constructed to protect agricultural <br />and urban developments downstream. <br />Nearly three-fourths of the popu- <br />lation of the Lower Colorado River <br />system reside in the Gila River Basin <br />in the metropolitan Phoenix and Tucson <br />areas. Industry and recreation playa <br />large part in the economy. About <br />two-thirds of the agricultural develop- <br />ment in the Lower Colorado River system <br />is located in the Gila River Basin. <br />This development is concentrated in the <br />central area of Maricopa, Pinal, and <br />pima Counties and is supported to a <br />large degree by a long-term overdraft <br />of the ground-water resources. Esti- <br />mated irrigated lands in 1980 include <br />approximately 987,000 acres. Nearly <br />all of the sur face water resources in <br />the basin have been developed for <br />decades. Except for maj or flood <br /> <br />8 <br />