Colorado River

1 Great river of the SW United States, 1,450 mi (2,334 km) long, rising in the Rocky Mts. of N Colo., and flowing generally SW through Colo., Utah, Ariz., between Nev. and Ariz., and Ariz. and Calif., then into Mexico, emptying into the Gulf of California; drains c.244,000 sq mi (631,960 sq km). The Gunnison, Green, San Juan, and Little Colorado are the main tributaries in the upper basin of the Colorado; the Gila is the chief tributary of the lower basin. Silt deposited by the Colorado has formed a great delta across the northern part of the Gulf of California, cutting off the head of the gulf; the Salton Sea is a flooded remnant of the severed part. The mouth of the river was seen by Francisco de Ulloa in 1539; the lower part was explored by Hernando de Alarcón in 1540. The river flows through c.1,000 mi (1,610 km) of canyons, including Arizona's Grand Canyon; many national parks, monuments, and recreational areas lie along its banks. The Colorado's waters are used for power and irrigation, especially by means of the Colorado River storage project, the Colorado–Big Thompson project, Hoover Dam, Davis Dam, Imperial Dam, the All-American Canal, Parker Dam, and Glen Canyon Dam. Controversies over water rights on the Colorado have long raged between the United States and Mexico and among the bordering states (it supplies most of S California's water); treaties and compacts regulate the river's use. California and, to a lesser degree, Nevada have in the past drawn more water than they were designated to receive. A new compact in 2003 gave California 14 years to reduce its water usage to its legal limits. A greater problem, however, is that the 1922 Colorado River Compact that established the division of water use between the upper and lower basins was based on an estimate of the average annual flow that is 10% to 25% higher than long-term data suggest, due to the use of river gauge data from what is now known to be a relatively wet period in the river basin's history.

2 River, 894 mi (1,439 km) long, rising in the Llano Estacado, NW Tex., and flowing SE to Matagorda Bay, an inlet of the Gulf of Mexico; drains c.41,500 sq mi (107,485 sq km). Destructive floods, which prevented private development of the river for power, led the Texas legislature to set up the Lower, Central, and Upper Colorado River authorities to undertake projects for flood control, power plants, and irrigation. The Lower Colorado River Authority, with federal assistance, has been especially active, building five major dams (Buchanan, Roy Inks, Alvin J. Wirtz, Marble Falls, and Mansfield). These projects have benefited a large part of Texas, including the city of Austin. The scenic section of the river above Austin, which includes the lakes formed by the dams, is called Highland Lakes Country. The Central Colorado River Authority has constructed many small irrigation dams and also has jurisdiction over several city reservoirs. The Upper Colorado River Authority regulates the upper Colorado and the several branches of the Concho, a principal tributary.

This article is about the Colorado River which flows through the Grand Canyon. For other rivers named Colorado, see Colorado River (disambiguation).

Colorado River
Map of the Colorado Watershed
Mouth	Gulf of California
Basin countries	United States, Mexico
Length	2,330 km (1,450 mi)
Source elevation	~2700 m (~9000 ft)
Avg. discharge	620 m³/s (22,000 ft³/s)[1]
Basin area	629,100 km² (242,900 mi²)

The Colorado River from the bottom of Marble Canyon, in the Upper Grand Canyon

Colorado River in the Grand Canyon from Desert View

The Colorado River from Laughlin

Horseshoe Bend is a horseshoe-shaped meander of the Colorado River located near the town of Page, Arizona

The Colorado River is a river in the southwestern United States and northwestern Mexico, approximately 1,450 mi (2,330 km) long, draining a part of the arid regions on the western slope of the Rocky Mountains. The natural course of the river flows into the Gulf of California, but the heavy use of the river as an irrigation source for the Imperial Valley has desiccated the lower course of the river in Mexico such that it no longer consistently reaches the sea.

The Colorado River drains 242,900 sq mi (629,100 km²). Total flows of the river range from 4000 cubic feet per second (570 m³/s) in droughts to 1,000,000 ft³/s (28,000 m³/s) in severe floods. With the construction of massive power dams on the lower course of the river, floods of over 70,000 ft³/s (2000 m³/s) are rare. The mean flow of the total river before diversion is 22,000 ft³/s. Historically the flow was much higher before water usage began in the basin.

Course

The Colorado River's source is La Poudre Pass Lake, located high in Rocky Mountain National Park, just west of the Continental Divide. After leaving Rocky Mountain National Park the river flows through the Kawuneeche Valley and is then dammed to create Grand Lake and Shadow Mountain Reservoir. The river then flows into Lake Granby, another reservoir, and finally begins its journey to the Gulf of California where U.S. Highway 40 roughly parallels the river to the town of Kremmling, where it enters Gore Canyon. About a hundred miles later it meets the Eagle River in the town of Dotsero, Colorado and where I-70 parallels the river through Glenwood Canyon. The river then passes through the city of Glenwood Springs where it is joined by the swift flowing Roaring Fork River. West of Glenwood Springs, the Colorado runs through the Grand Valley and is joined by the Gunnison River in Grand Junction. From there it flows westward to the Utah border and Westwater Canyon. The Colorado here ranges from 200 to 1200 feet wide (60 to 370 m) and from 6 to 30 feet in depth (2 to 9 m) with occasional deeper areas.

Once inside of Utah, the river turns south partially forming the southern border of Arches National Park near Moab, Utah, then passes by Dead Horse Point State Park and through Canyonlands National Park where it is met by one of its primary tributaries, the Green River. The river then flows into Lake Powell, formed by the Glen Canyon Dam. Below the dam, water released from the bottom of Lake Powell makes the river clear, clean, and cold. Just south of the town of Page, Arizona, the river forms the dramatic Horseshoe Bend, then at Lees Ferry is joined by another tributary, the warm, shallow, muddy Paria River, and begins its course through Marble Canyon. Here, the Colorado ranges from 300 to 2000 feet in width (90 to 610 m) and 9 to 130 feet in depth (3 to 40 m).

At the southern end of Marble Canyon, the river is joined by another tributary, the Little Colorado, and the river then turns abruptly west directly across the folds and fault line of the plateau, through the Grand Canyon, which is 217 miles long (349 km) and from 4 to 20 miles wide (6 to 30 km) between the upper cliffs. The walls, 4000 to 6000 feet high (1200 to 1800 m), drop in successive escarpments of 500 to 1600 feet (150 to 490 m), banded in splendid colours toward the narrow gorge of the present river.

Below the confluence of the Virgin River of Nevada the Colorado abruptly turns southward. Hoover Dam, built during the Great Depression, forms Lake Mead, a popular recreation site as well as the supplier of most of the water for the city of Las Vegas. From Hoover Dam, the river flows south and forms part of the boundary between Arizona and Nevada and between Arizona and California. Along the California-Arizona reach of the river, four additional dams are operated to divert water for agricultural irrigation and for recreation. Lake Mohave, formed by Davis Dam, lies in the southern portion of the Lake Mead National Recreation Area. Lake Havasu, formed by Parker Dam, provides recreation as well as the home of the retired New London Bridge. The two remaining dams supply irrigation water: Palo Verde Diversion Dam and Imperial Dam. Here, the Colorado River ranges in width from 700 to 2500 feet (210 to 760 m) and from 8 to 100 feet in depth (2 to 30 m).

Below the Black Canyon the river lessens in gradient and in its lower course flows in a broad sedimentary valley's distinct estuarine plain upriver from Yuma, where it is joined by the Gila River. The channel through much of this region is bedded in a dike-like embankment lying above the floodplain over which the escaping water spills in time of flood. This dike cuts off the flow of the river to the remarkable low area in southern California known as the Salton Sink, Coachella Valley, or Imperial Valley. The Salton Sink is located below sea level; therefore, the descent from the river near Yuma is very much greater than the descent from Yuma to the gulf.

The lower course of the river, which forms the border between Baja California and Sonora, is essentially a trickle or a dry stream today due to use of the river as Imperial Valley's irrigation source. Prior to the mid 20th century, the Colorado River Delta provided a rich estuarine marshland that is now essentially desiccated, but nonetheless is an important ecological resource.

Elevation summary

Approximate heights above sea level at several key locations:

Note that the significant difference between the present height of the rim of the Grand Canyon (about 8000 ft; 2440 m) and the levels at which the river enters/exits it gives rise to the geologic theory that its upheaval must have begun around the same time the river began flowing through it and eroding it (since rivers do not run uphill, it would have followed some other path around the upheaval). Estimates for the beginning of this erosion/upheaval process range from 5 to 70 million years ago.

Engineering

Glen Canyon Dam and Lake Powell

In the autumn of 1904, the river's waters escaped into a diversion canal a few miles below Yuma, Arizona, creating the New River and Alamo River. The rivers re-created in California a great inland sea in an area that it had frequently inundated before, for example, in 1884 and 1891, when it had for a time practically abandoned its former course through Mexican territory to the Sea of Cortez. But it was effectively dammed in the early part of 1907 and returned to its normal course, from which, however, there was still much leakage to the Salton Sea. In July 1907, the permanent dam was completed. From the Black Canyon towards the sea the Colorado normally flows through a desert-like basin.

From the Hoover Dam

The Colorado River is a major and in some cases life-sustaining source of water for irrigation, drinking, and other uses by people living in the arid American southwest. Allocation of the river's water is governed by the Colorado River Compact. Several dams have been built along the Colorado River, beginning with Glen Canyon Dam near the Utah-Arizona border. Other dams include Hoover Dam, Parker Dam, Davis Dam, Palo Verde Diversion Dam, and Imperial Dam. Since the completion of the dams, the majority of the river in normal hydrologic years is diverted for agricultural and municipal water supply. The Colorado's last drops evaporate in the Sonoran Desert, miles before the river reaches the Gulf of California. Almost 90% of all water diverted from the river is for irrigation purposes. The All-American Canal is the largest irrigation canal in the world and carries a volume of water from 15,000 to 30,000 ft³/s (420 to 850 m³/s), making it larger in volume than New York's Hudson River. The canal's waters are used to irrigate the parched but fertile Imperial Valley, where several years can pass between measurable rainfalls. Hydrology transport models are used to assess management of the river's flow and water quality.

Hoover Dam (originally Boulder Dam, and the first dam of its type) was completed in 1936. Its impoundment of the river in the Mojave Desert creates Lake Mead, which provides water for irrigation and the generation of hydroelectric power.

Several cities such as Los Angeles, Las Vegas, San Diego, Phoenix, and Tucson have aqueducts leading all the way back to the Colorado River. One such aqueduct is the Central Arizona Project ("CAP") canal, which was begun in the 1970s and finished in the 1990s. The canal begins at Parker Dam and runs all the way to Phoenix and then Tucson to supplement those cities' water needs.

The Colorado is navigable by moderate to large sized craft throughout most of its length. The lower river from Davis Dam to Yuma is navigable by large paddlewheel boats and river barges, but commercial navigation on the river is unimportant because the river is cut off from the sea, making other means of transportation more efficient in the region. Before the railroads arrived, the Lower Colorado River from the Sea to near present day Laughlin, Nevada was an important means of transportation via large steamers.

Colorado River

Wildlife

The Colorado River basin is home to fourteen native species of fish. Four are endemic and endangered: Colorado pikeminnow (formerly Colorado squawfish), razorback sucker, bonytail chub, and humpback chub. The Upper Colorado River Endangered Fish Recovery Program is a controversial effort by the US Fish and Wildlife Service, in conjunction with the Arizona Game and Fish Department, the Colorado Division Of Wildlife, and the Utah Department Of Wildlife to recover these endangered fish.

Moab, Utah uranium tailings

Main article: Moab Tailings

Atlas Corporation operated a uranium mine in the area of Moab, Utah, just under three miles from downtown Moab. As a byproduct of mining activities, a ten-million-ton pile of radioactive tailings exists. The pile is located about 700-800 feet from the Colorado River. Although no pollution has been detected, proximity of the material to the watershed has been a concern. The Senate has authorized the U.S. Department of Energy to budget $22.8 million in 2007 to begin the project of moving the uranium tailings further from the river. The plan is to move the pile 15-20 miles north and away from the river. The project is expected to be completed by 2017.

The Colorado in James M. Robb Colorado River State Park as the Morning Sun rises

References

This article incorporates text from the Encyclopædia Britannica Eleventh Edition, a publication now in the public domain.

See also

• List of Colorado River rapids and features
• Colorado River Delta
• Colorado River Compact
• List of Flora of the Lower Colorado River Valley

External links

Wikimedia Commons has media related to:

Colorado River

• Federal Department of Energy site on uranium mine tailing site.
• State of Utah site on uranium mine tailings.
• Bibliography on Water Resources and International Law See Colorado River. Peace Palace Libray
• Drought Watch Campaign - map of the Colorado River system showing the fill levels of major reservoirs. Last updated April 2004.

Colorado River system
Dams and aqueducts (see US Bureau of Reclamation)	Shadow Mountain Dam • Granby Dam • Glen Canyon Dam • Hoover Dam • Davis Dam • Parker Dam • Palo Verde Diversion Dam • Imperial Dam • Laguna Dam • Morelos Dam • Colorado River Aqueduct • San Diego Aqueduct • Central Arizona Project Aqueduct • All-American Canal • Coachella Canal • Redwall Dam
Natural features	Colorado River • Rocky Mountains • Colorado River Basin • Grand Lake • Sonoran desert • Mojave desert • Imperial Valley • Colorado Plateau • Grand Canyon • Black Canyon • Glen Canyon • Marble Canyon • New River • Paria Canyon • Gulf of California/Sea of Cortez • Salton Sea
Tributaries	Dirty Devil River • Dolores River • Escalante River • Gila River • Green River • Gunnison River • Kanab Creek • Little Colorado River • Paria River • San Juan River • Virgin River
Major reservoirs	Fontenelle Reservoir • Flaming Gorge Reservoir • Taylor Park Reservoir • Navajo Reservoir • Lake Powell • Lake Mead • Lake Mohave • Lake Havasu
Dependent states	Arizona • California • Colorado • Nevada • New Mexico • Utah (See: Colorado River Compact)
Designated areas	Glen Canyon National Recreation Area • Lake Mead National Recreation Area

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