Colorado River - Engineering and Development

Engineering and Development

With 36 to 40 million people dependent on its water for both agricultural and domestic needs, the Colorado River is considered one of the "most controlled, controversial and litigated rivers in the world". Over 29 major dams and hundreds of miles of canals serve to supply thirsty cities, provide irrigation water to some four million acres (16,000 km2), and generate more than 12 billion kWh of hydroelectricity each year. Often called "America's Nile", the Colorado is so carefully managed – with basin reservoirs capable of holding four times the river's annual flow – that each drop of its water is used an average of seventeen times in a single year.

One of the earliest water projects in the Colorado River basin was the Grand Ditch, a 16-mile (26 km) diversion canal that sends water from the Never Summer Mountains, which would naturally have drained into the headwaters of the Colorado River, to bolster supplies in Colorado's Front Range Urban Corridor. Constructed primarily by Japanese and Mexican laborers, the ditch was considered an engineering marvel when completed in 1890, delivering 17,700 acre feet (0.0218 km3) across the Continental Divide each year. Because roughly 75 percent of Colorado's precipitation falls west of the Rocky Mountains while 80 percent of the population lives east of them, more of these interbasin water transfers, locally known as transmountain diversions, followed. While first envisioned in the late 19th century, construction on the Colorado-Big Thompson Project (C-BT) did not begin until the 1930s. The C-BT now delivers more than eleven times the flow through the Grand Ditch from the Colorado River watershed to cities along the Front Range.

Meanwhile, large-scale development was also beginning on the opposite end of the Colorado River. In 1900, entrepreneurs of the California Development Company (CDC) looked to the Imperial Valley of southern California as an excellent location to develop agriculture irrigated by the waters of the river. Engineer George Chaffey was hired to design the Alamo Canal, which split off from the Colorado River near Pilot Knob, curved south into Mexico, and dumped into the Alamo River, a dry arroyo which had historically been observed to carry flood flows of the Colorado into the Salton Sink. With a stable year-round flow in the Alamo River, irrigators in the Imperial Valley were able to begin large-scale farming and small towns in the region started to expand with the influx of job-seeking migrants. By 1903, more than 100,000 acres (40,000 ha) in the valley were under cultivation, supporting a growing population of four thousand.

It was not long before the Colorado River began to wreak havoc with its erratic flows. In autumn, the river would drop below the level of the canal inlet and temporary brush diversion dams had to be constructed. In early 1905, heavy floods destroyed the headworks of the canal and water began to flow uncontrolled down the canal towards the Salton Sink. On August 9, the entire flow of the Colorado swerved into the canal and began to flood the bottom of the Imperial Valley. In a desperate gamble to close the breach, crews of the Southern Pacific Railroad, whose tracks ran through the valley, attempted to dam the Colorado above the canal only to see their work demolished by a flash flood. It took seven attempts, over US$3 million and two years for the railroad, the CDC and the federal government to permanently block the breach and send the Colorado on its natural course back to the gulf – but not before part of the Imperial Valley was flooded under a 45-mile-long (72 km) lake, today's Salton Sea. After the immediate flooding threat passed, it was realized that a more permanent solution would be needed to rein in the Colorado.

In 1922, six U.S. states in the Colorado River basin signed the Colorado River Compact, which divided half of the river's flow to both the Upper Basin (the drainage area above Lee's Ferry, comprising parts of Colorado, New Mexico, Utah and Wyoming and a small portion of Arizona) and the Lower Basin (Arizona, California, Nevada, and parts of New Mexico and Utah). Each was given rights to 7,500,000 acre feet (9.3 km3) of water per year, a figure believed to represent half of the river's minimum flow at Lee's Ferry. This was followed by a U.S.–Mexico treaty in 1944, allocating 1,500,000 acre feet (1.9 km3) of Colorado River water to the latter country per annum. In addition, Arizona did not ratify the Colorado River Compact until 1944 because it feared that California would take too much of the lower basin allotment and leave little left over for Arizona's use. These and nine other decisions, compacts, federal acts and agreements made between 1922 and 1973 form what is now known as the Law of the River.

On September 30, 1935, the United States Bureau of Reclamation (USBR) completed Hoover Dam in the Black Canyon of the Colorado River. Behind the dam rose Lake Mead, the largest artificial lake in the U.S, capable of holding more than two years of the Colorado's flow. The construction of Hoover was a major step towards stabilizing the lower channel of the Colorado River, storing water for irrigation in times of drought, and providing much-needed flood control. Hoover was the tallest dam in the world at the time of construction, and also had the world's largest hydroelectric power plant. Flow regulation from Hoover Dam opened the doors for rapid development on the lower Colorado River: Imperial and Parker Dams followed in 1938, and Davis Dam was completed in 1950.

Completed in 1938 some 20 miles (32 km) above Yuma, Imperial Dam diverts nearly all of the Colorado's flow into two irrigation canals. The All-American Canal, built as a permanent replacement for the Alamo Canal, is so named because it lies completely within the U.S., unlike its ill–fated predecessor. With a capacity of over 26,000 cu ft/s (740 m3/s), the All-American is the largest irrigation canal in the world, supplying water to 500,000 acres (2,000 km2) of California's Imperial Valley. Because the valley's warm and sunny climate lends to a year-round growing season in addition to the large water supply furnished by the Colorado, the Imperial Valley is now one of the most productive agricultural regions in North America. In 1957, the USBR completed a second canal, the Gila Gravity Main Canal, to irrigate about 110,000 acres (450 km2) in southwestern Arizona with Colorado River water as part of the Gila Project.

The Lower Basin states also sought to develop the Colorado for municipal supplies. Providing water for up to 10 million people each year, the Colorado River Aqueduct, which delivers water nearly 250 miles (400 km) from near Parker Dam to California's Los Angeles metropolitan area, was completed in 1941. The San Diego Aqueduct branch, whose initial phase was complete by 1947, furnishes water to nearly three million people in San Diego and its suburbs. The Las Vegas Valley of Nevada experienced rapid growth in part due to Hoover Dam construction, and tapped a pipeline into Lake Mead by 1937. Nevadan officials, believing that groundwater resources in the southern part of the state were sufficient for future growth, were more concerned with securing a large amount of the dam's power supply than water from the Colorado; thus they settled for the smallest allocation of all the states in the Colorado River Compact.

Central Arizona initially relied on the Gila River and its tributaries through projects such as the Theodore Roosevelt and Coolidge Dams – completed in 1924 and 1928, respectively. Roosevelt was the first large dam constructed by the USBR, and provided the initial water supplies needed to start off large-scale agricultural and urban development in the region. Agricultural and urban growth in Arizona eventually outstripped the capacity of local rivers, leading to the inception of the Central Arizona Project in 1968, which now irrigates more than 830,000 acres (3,400 km2) and provides municipal supplies to over five million people from Phoenix to Tucson using water from the Colorado River.

Through the early decades of the 20th century, the Upper Basin states with the exception of Colorado remained relatively undeveloped and utilized little of the water allowed to them under the Colorado River Compact. However, water use had increased significantly by the 1950s, and more water was being diverted out of the Colorado River basin to the Front Range corridor, the Salt Lake City area in Utah, and the Rio Grande basin in New Mexico. Such projects included the Roberts Tunnel, completed in 1956, which diverts 63,000 acre feet (0.078 km3) per year from the Blue River to the city of Denver, and the Fryingpan-Arkansas Project, which delivers 69,200 acre feet (0.0854 km3) from the Fryingpan River to the Arkansas River basin each year. Without the addition of surface water storage in the upper basin, there was no guarantee that the upper basin states would be able to utilize the full amount of water given to them by the compact. There was also the concern that drought could impair the upper basin's ability to deliver the required 7,500,000 acre feet (9.3 km3) past Lee's Ferry per year as stipulated by the compact. A 1956 act of Congress cleared the way for the USBR's Colorado River Storage Project (CRSP), which entailed the construction of large dams on the Colorado, Green, Gunnison and San Juan Rivers.

The initial blueprints for the CRSP included two dams on the Green River within Dinosaur National Monument's Echo Park Canyon, a move criticized by both the U.S. National Park Service and environmentalist groups such as the Sierra Club. Controversy reached a nationwide scale, and the USBR dropped its plans for the Dinosaur dams in exchange for a dam at Flaming Gorge and a raise to an already-proposed dam at Glen Canyon. The famed opposition to Glen Canyon Dam, the primary feature of the CRSP, did not build momentum until construction was well underway. This was primarily because of Glen Canyon's remote location and the result that most of the American public did not even know of the existence of the impressive gorge; the few who had, however, contended that it had much greater scenic value than Echo Park. Sierra Club leader David Brower fought the dam both during the construction and for many years afterwards until his death in 2000. Brower strongly believed that he was personally responsible for the failure to prevent Glen Canyon's flooding, calling it his "greatest mistake, greatest sin".