Colorado River
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- For other uses, see Colorado River (disambiguation).
Image:Canyon midday.jpg Image:Colorado River from Desert View-1000px.jpeg 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.
There are other rivers with the name Colorado River, but this one is the longest and the largest by volume. 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.
Spanish explorer Melchior Diaz was one of the first to explore the river, in 1540.
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Course
Image:Colorado watershed.png 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). The river's course then follows the Kewuneeche Valley to Shadow Mountain Reservoir, near the town of Granby, then flows into Lake Granby. Most of the river's first tributaries are small. However there are exceptions, such as the Green River (the largest), Roaring Fork and Gunnison Rivers, in which massive amounts of water flow. The river then roughly parallels US Highway 40 to the town of Kremling, then enters Gore Canyon. Shortly thereafter, the river roughly parallels I-70 through Glenwood Canyon and the city of Glenwood Springs, where it is joined by the swift flowing Roaring Fork River. Below Glenwood, the Colorado runs through the Grand Valley to Grand Junction, where it is joined by the Gunnison River; from there it flows on to the Utah border. 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, and goes through Arches National Park, then Dead Horse Point State Park and 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 gloomy 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, formed Lake Mead, a popular recreation source, 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 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 dry stream today due to use of the river as a water 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:
| Feet | Meters | Location |
| 9000 | 2750 | Colorado headwaters (Rocky Mountains) |
| 6100 | 1850 | midway to Colorado-Utah border |
| 4300 | 1300 | Colorado-Utah border |
| 3850 | 1170 | midway to Utah-Arizona border |
| 3700 | 1130 | Utah-Arizona border (Wahweap Bay) |
| 3000 | 900 | midway to Grand Canyon (Rider Point) |
| 2800 | 850 | Grand Canyon North Rim |
| 2500 | 760 | Grand Canyon South Rim |
| 1200 | 365 | Lake Mead |
| 600 | 183 | after Hoover Dam |
| 485 | 150 | California-Nevada-Arizona border |
| 100 | 30 | California-Arizona-Mexico border |
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.
Engineering
Image:Glen Canyon Dam & Lake Powell.jpg 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.
Image:HooverDamColorado.jpg 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.
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.
This article incorporates text from the Encyclopædia Britannica Eleventh Edition{{#if:{{{article|}}}| article {{#if:{{{url|}}}|[{{{url|}}}}} "{{{article}}}"{{#if:{{{url|}}}|]}}{{#if:{{{author|}}}| by {{{author}}}}}}}, a publication now in the public domain.
See also
External links
- Drought Watch Campaign - map of the Colorado River system showing the fill levels of major reservoirs
- Dams on the Lower Colorado River - A look at all the Dams on the Colorado River from Las Vegas Nevada to Mexico
- Grand Canyon North Rimda:Colorado River
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