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<br />~ <br />;... <br />'.] <br />1'.;, <br /> <br />Chapter 2 <br /> <br />Description of Basin <br /> <br />The Colorado River Basin encompasses POrtions <br />of seven States: Wyoming, Utah, Colorado, <br />Nevada, New Mexico, Arizona, and California. <br />The river flow8 over 1,400 miles from its <br />headwaters in Wyoming and Colorado. It join. <br />....'ith tributaries from Utah and New Mexico; <br />flows through the Grand Canyon; provides State <br />boundaries for Nevada, Arizona, and California; <br />flow8 through the Republic of Mexico; and <br />tenninat.es in the GulfofCalifornia. The <br />Colorado River provides municipal and <br />industrial water for more than 18 million people <br />and irrigation water to 1.7 million acres in the <br />United States. <br /> <br />CLIMATE <br /> <br />Extremes of temperature in the Colorado River <br />Basin range from -50 to 130 OF. The northern <br />portion of the basin is characterized by short, <br />warm summers and long, cold winters; and <br />many mountain areas are blanketed by deep <br />snow all winter. Much of the area consists of <br />high basins or valley, with cold winters and hot, <br />dry summers. The southern desert POrtion of <br />the basin has long, hot summers, practically <br />continuous sunshine, and almost complete <br />absence offreezing temperatures. Rainfall <br />averages 2.5 inches per year in the southern end <br />of the basin, while total precipitation in the <br />mountains reaches 40 to 60 inches annually. <br /> <br />HYDROLOGY <br /> <br />The Colorado River begins where peaks rise <br />more than 14,000 feet in the northwest portion <br />of Rocky Mountain National Park in Colorado, <br />70 miles northwest of Denver. It meanders <br />southwest for 640 miles through the Upper <br />Basin to Lee Ferry. <br /> <br />The Green River, the major tributary of the <br />Colorado Rh'er, rises in western Wyoming and <br />discharges into the river in southeastern <br /> <br />Utah-730 river miles south of its origin and <br />220 miles above Lee Ferry. The Green River <br />drains 70 percent more area than the Colorado <br />River abo\'e their junction, but produces only <br />about three.fourths as much water. The <br />Gunnison and San Juan Rivers are the other <br />principal tributaries of the Colorado River in the <br />Upper Basin. <br /> <br />The Colorado River Basin has a total area of <br />approximately 244,000 square miles, carrying an <br />average annual virgin flow of 13 to 15 million <br />acre.feet at Lee Ferry. Of this flow, more than <br />6 million acre. feet per year are exported to the <br />Arkansas and Missouri River basins, the Great <br />Basin, southern California, and the Rio Grande <br />basin. <br /> <br />The Colorado River Basin is an arid or semiarid <br />basin. Compared to others, such as the <br />Columbia River Basin, which drains <br />approximately the same area, it carries a <br />smaller flow, as shown in table 1. While the <br />Colorado River Basin is one of the major <br />drainage basins in the continental United <br />States, its runoff is about equal to that of the <br />Delaware River which drains a much smaller <br />area. <br /> <br />Table 1.-COmparison 01 <br />river basin dtainage and runoff <br /> <br /> ..,.. Runoff Runoff per <br /> (1.000 (million unit at/ila <br /> square acre.'eel ind1ell <br />River basin miles) per year per year <br />Colorado 244 15 1.2 <br />MIssissippi 1,234 440 6.7 <br />Columbia 256 180 13.1 <br />Delaware 12 ,. 20.9 <br /> <br />The flow at various points in the Colorado Ri\'er <br />Basin for the 1941.89 period is given in tables 1 <br />through 20 at the end of this report. The records <br />