Colorado River
:''This article is about the river which runs from
Colorado to
California and through the
Grand Canyon. For other rivers named Colorado, see
Colorado River (disambiguation).
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The Colorado River from the bottom of Marble Canyon, in the Upper Grand Canyon |
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Colorado River in the Grand Canyon from Desert View |
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
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 20,000 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 42,600 ft³/s (1206 m³/s). At full flow more runoff volume exists in this river than any other in North America except the Mississippi and Columbia.
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Map of the Colorado Watershed |
The Colorado River's headwaters are located in
Rocky Mountain National Park, just west of the
Continental Divide. (There is some authority for considering the headwaters of the Colorado River, and its main source, to be the Green River which rises in Sublette County, Wyoming. The Green River is practically the same size as the Colorado,formerly known as the "Grand" River at their confluence near Moab, Utah). Following Rocky Mountain National park, the river then follows the Kewuneeche Valley to Shadow Mountain Reservoir, near the town of Granby, then flows into Lake Granby. The river then roughly parallels US Highway 40 to the town of Kremmling, then enters Gore Canyon. Shortly thereafter the river meets the Eagle River and parallels
I-70 through Glenwood Canyon and 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 to
Grand Junction, where it is joined by the
Gunnison River; from there it flows towards 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 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 athwart 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 source, as well as the supplier of most of the water and electricity for the city of
Las Vegas. From Hoover Dam, the river flows south and forms part of the boundary between
Arizona and
Nevada, and the border between Arizona and
California. Along the California-Arizona reach of the river, two additional dams are operated to divert water for agricultural irrigation supplies: 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.
Approximate heights above sea level at several key locations:
Note that the significant difference between the present height 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 long distances, 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.
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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. The river, taking the canal as a new channel, 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.
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,
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 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 and other means of transportation are 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 source of transportation via large steamers.
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List of Colorado River rapids and features*
Bibliography on Water Resources and International Law See
Colorado River. Peace Palace Libray
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Drought Watch Campaign - map of the Colorado River system showing the fill levels of major reservoirs
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Dams on the Lower Colorado River - A look at all the Dams on the Colorado River from Las Vegas Nevada to Mexico
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Grand Canyon North Rim
