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<br /> <br />Chapter 2 <br /> <br />I' , <br />,;r <br /> <br />DESCRIPTION OF BASIN <br /> <br />"':> <br /> <br />The construction and filling of the mainslem reservoirs of the Colorado River Basin (figure 1) have <br />brought about significant changes in the now patterns of the river. The Colorado River Basin <br />encompasses portions of seven Basin States: Wyoming. Utah. Colorado. Nevada. New Mexico. <br />Arizona. and California. The river flows more than I.~OO miles from its headwaters in Colorado. <br />It joins with Iributaries from Wyoming. Utah. and New Mexico. flows through the Grand Canyon: <br />provides State boundaries for Nevada. Arizona. and CalIfornia: flows through the Republic of <br />Mexico: and discharges in the Gulf of California. The Colorado River and its Iributaries provide <br />municipal and mdumial (M&I) water for more than 20 million people and irrlgalion waler to <br />nearly 3 million acres in the Umted Stales. <br /> <br />CLIMATE <br /> <br />E.-.;,uemes of temperature in the Colorado River Basin range from ~50 to 130 degrees Fahrenheit. <br />The northern portion of the Colorado River Basin is characterized by shon. warm summers and <br />long. cold winters. and many mountain areas are blanketed by deep snow all winter. Much of the <br />area consists of high basms or valleys with cold winters and hot. dry summers. The southern <br />desert portion of the Colorado River Basin has long, hot summers. practically continuous sunshine, <br />and almost complcote absence of freezing temperatures. Rainfall averages ~.5 inches per year in the <br />southern end of the Colorado River Basin. while [olal precipitation in the mountam.<i reaches <br />~O to 60 mches annually. <br /> <br />HYDROLOGY <br /> <br />The Colorado River begins where peaks rise more than I~,OOO feet in the northwest portion oflhe <br />Rocky Moumain National Park. 70 miles northwesl of Denver. Colorado. It meanders southwest <br />for MO miles through the Upper Colorado Rivcor Basin to Lee Ferry. {he dividing point for [he <br />upper and lov.er portions of the Colorado River Basin. <br /> <br />The Green River. the major trihulary to the Colorado River. rises in western Wyoming and <br />discharges into the fiver in southeastern Utah-730 river miles south of Its origin and 2.:!0 miles <br />above Lee Ferry. The Green RIver drains 70 percent more area than [he Colorado River above <br />their junction bUI produces only ahout three-fourths as much water. The Gunnison and San Juan <br />Rivers are the mher principallributaries of the Upper Colorado River Basin. <br /> <br />The Colorado River Basin has a total area of approximately 24-;.000 square miles, carrying an <br />a'..erage annual narural flow of about 15 million acre-feet (maf) at Lee Ferry. Oflhis flow, more <br />than 5 maf per year are e:o;:poned 10 (he Arkansas and Missouri River basins. the RIO Grande basin. <br />the Great Basin, and southern California. <br /> <br />5 <br />