With an annual mean discharge of about 15 million acre-feet, the Colorado River is not a giant among the world’s rivers. The Colorado River traverses one of North America’s driest regions, however, thus offering opportunities for economic development and growth unmatched by any other water source in this arid region. For the past 100 years these possibilities have spurred myriad political contests among irrigators, businesses, civic boosters, politicians, tribes, ranchers, government officials, engineers, and, more recently, environmental groups and recreational users, all seeking a voice in Colorado River allocation decisions. A root cause of these conflicts is the hydrologic reality that, although roughly 90 percent of the river’s flow originates in the upper basin states of Colorado, New Mexico, Utah, and Wyoming, much of the demand for the river’s water emanates from the lower basin states of Arizona, California, and Nevada (Hundley, 1966, 1975; Martin, 1989; Moeller, 1971; Pearson, 2002; USBR, 1947).

The story of the development, management, and use of the Colorado River was initially one where concerns over unreliable water supplies were resolved by technological advances, accompanied by legal and administrative arrangements. More recently, this story reflects the concerns of the federal government, the basin states, tribes, municipalities, and other major water users adapting to conditions not fully anticipated when the legal regime and the major dams were put in place.

In the early 20th century, the sparsely populated and largely rural upper basin states watched Southern California’s rapid agricultural and urban growth with trepidation. Trepidation turned to fear in 1922 when the Supreme Court held that the western doctrine of prior appropriation could govern apportionment of interstate streams in the arid West. Soon thereafter, the upper basin states succeeded in negotiating the first interstate compact to allocate flows in an interstate stream. The 1922 Colorado River Compact divided the river between the upper and lower basins and reserved unused water for future development in the four upper basin states. Beginning in 1922, California led the fight for the construction of a multipurpose dam on the lower Colorado (decades later they found that the price for having Hoover Dam constructed was a federal apportionment of the river among the three lower basin states). During World War II, political considerations led to a treaty that guaranteed Mexico a supply and in 1948 the upper basin states agreed to an allocation formula among

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