Resultados

Draining an area of over 240,000 square miles, the Colorado River and its main tributary streams originate high within the moun- tains of western Wyoming, central Colorado, and northeastern Utah. With snowpack accumulating as high as 14,000 feet above sea level, the mainstem of the upper Colorado River receives large amounts of snowmelt from several major tributaries: the Green River flowing south out of Wyoming; the Duchesne River in northern Utah; the Dolores, Gunnison, White, and Yampa rivers in Colorado; and the San Juan River flowing northwest through New Mexico. When it reaches the Canyonlands region of southern Utah (site of Lake Pow- ell), the Colorado’s streambed lies hundreds of feet below the sur- rounding mesas and plateaus. After crossing the Utah-Arizona border and passing Lees Ferry, the river flows westward through Grand Can- yon National Park. A further 160 miles downstream—after receiving flows from the Virgin River that drains southwestern Utah and parts of southern Nevada—the Colorado reaches Boulder and Black can- yons (which rim much of Lake Mead) and forms the Arizona-Nevada border. Turning southward, the center of the streambed forms the 200-mile-long border between California and Arizona. Near the southern edge of this border, the Gila River (which, along with its tributary the Salt River, drains most of central and southern Arizona) enters the lower Colorado from the east. Just below its confluence with the Gila, the Colorado River enters the state of Sonora, Mexico. There, most of the Colorado’s remaining flow is consumed by irri- gated agriculture, leaving little water to reach the Gulf of California through the Colorado’s historically expansive delta (USBR, 1947; Waters, 1946).

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 un- matched 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, ranch- ers, government officials, engineers, and, more recently, environ- mental groups and recreational users, all seeking a voice in Colorado River allocation decisions. A root cause of these conflicts is the hy- drologic 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 Colo- rado 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 re- flects 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 ap- propriation could govern apportionment of interstate streams in the arid West. Soon thereafter, the upper basin states succeeded in nego- tiating 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 de- velopment in the four upper basin states. Beginning in 1922, Califor- nia 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

themselves. Once a legal regime (often referred to as “The Law of the River”) was in place governing Colorado River water allocations, Congress supported construction of dams on the mainstem and tribu- taries to support the states’ compact rights and delivery obligations. This regime has permitted the basin and major, nearby urban cen- ters—such as Albuquerque, Denver, Los Angeles, Salt Lake City, and San Diego—to grow, but in recent decades it has become stressed by several factors. These include the accommodation of Indian claims, rapid population growth (especially in Arizona and in southern Ne- vada), the need to control downstream salinity caused by irrigation runoff, disturbances to the Grand Canyon ecosystem caused by the operation of Glen Canyon Dam, and interests in restoring a remnant of the Colorado River Delta in Mexico. These stresses are occurring in the face of the long-standing recognition that the flow estimates on which allocations were negotiated in the 1920 were based upon data drawn from a relatively short and very wet period, and thus turned out to be overly optimistic. Moreover, changes in regional climate condi- tions may further reduce net available water supplies.

Variations in climate and river flows have been an integral part of this history of Colorado River development. The gathering and analysis of hydroclimatic data assume economic significance because, across the basin, hydrology and climate are linked to larger legal con- structs and water development projects. Moreover, the implications of climate and hydrologic studies are related to demographic, water use, and other social and management trends. In reviewing key Colo- rado River legal agreements and treaties, the history of dam and water storage projects, and demographic and other trends affecting the ba- sin, this chapter does not seek to present an exhaustive discourse; rather, it provides a demographic and legal context for appreciating the significance of subsequent discussions involving climate studies, hydrologic records, water use technologies and practices, and adjust- ments to drought. This chapter explores this history of the past 150 years or so of Colorado River water development in greater detail. It divides this period into four broad phases: (1) the 1860s through 1920, (2) 1920 to 1965, (3) 1965 to the mid-1980s, and (4) the mid- 1980s to the present.

EARLY EXPLORATION AND INITIAL FORAYS IN