The Colorado River is the principal river of the Southwestern United States and northwest Mexico. The one,450-mile (two,330 km) river drains an expansive, arid watershed that encompasses elements of 7 U.S. and two Mexican states. Increasing in the central Rocky Mountains in the U.S., the river flows commonly southwest throughout the Colorado Plateau and by the Grand Canyon just before achieving Lake Mead on the Arizona–Nevada line, in which it turns south toward the worldwide border. Right after moving into Mexico, the Colorado methods the substantial Colorado River Delta in which it naturally emptied into the Gulf of California in between Baja California and Sonora, even though it no for a longer time reaches its delta or the sea.
Recognised for its extraordinary canyons and whitewater rapids, the Colorado is a critical resource of water for agricultural and urban regions in the southwestern desert lands of North America. The river and its tributaries are managed by an in depth procedure of dams, reservoirs, and aqueducts, which divert 90% of its water in the U.S. on your own to furnish irrigation and municipal water provide for almost 40 million people today equally within and outdoors the watershed. The Colorado’s substantial flow and steep gradient are utilised for making hydroelectric ability, and its big dams regulate peaking ability demands in a great deal of the Intermountain West. Because the mid-20th century, intense water consumption has dried the reduced one hundred miles (a hundred and sixty km) of the river these that it has not constantly reached the sea given that the sixties.
Commencing with smaller bands of nomadic hunter-gatherers, Indigenous People in america have inhabited the Colorado River basin for at minimum 8,000 several years. Concerning two,000 and one,000 several years ago, the river and its tributaries fostered substantial agricultural civilizations, which may have been some of the most refined indigenous cultures in North America. These societies are believed to have collapsed since of a mixture of serious drought and bad land use techniques. Most indigenous peoples that inhabit the basin currently are descended from other groups that settled in the area starting about one,000 several years ago. Europeans very first entered the Colorado Basin in the sixteenth century, when explorers from Spain commenced mapping and declaring the space, which later turned portion of Mexico upon its independence in 1821. Early get in touch with in between foreigners and natives was commonly constrained to the fur trade in the headwaters and sporadic trade interactions along the reduced river.
Right after the greater Colorado River basin turned portion of the U.S. in 1846, the bulk of the river’s training course was still largely the subject of myths and speculation. Many expeditions charted the Colorado in the mid-19th century, a single of which, led by John Wesley Powell in 1869, was the very first to run the rapids of the Grand Canyon. American explorers collected precious details that would later be utilised to develop the river for navigation and water provide. Huge-scale settlement of the reduced basin commenced in the mid- to late-19th century, with steamboats giving transportation from the Gulf of California to landings along the Colorado River that linked to wagon roads into the interior of New Mexico Territory. Lesser quantities settled in the higher basin, which was the scene of big gold strikes in Arizona and Nevada in the 1860s and 1870s.
Main engineering of the river basin commenced all over the start off of the 20th century, with lots of recommendations set up in a series of domestic and worldwide treaties regarded as the “Law of the River”. The U.S. federal government was the primary driving pressure driving the building of hydraulic engineering assignments in the river procedure, despite the fact that lots of condition and local water businesses were also associated. Most of the big dams in the river basin were created in between 1910 and 1970, and the procedure keystone, Hoover Dam, was concluded in 1935. The Colorado is now thought of among the the most managed and litigated rivers in the environment, with every drop of its water completely allocated.
The damming and diversion of the Colorado River procedure have been flashpoint troubles for the environmental movement in the American Southwest since of their impacts on the ecology and natural splendor of the river and its tributaries. Through the building of Glen Canyon Dam, environmental organizations vowed to block any even further improvement of the river, and a quantity of later dam and aqueduct proposals were defeated by citizen opposition. As demands for Colorado River water continue on to rise, the amount of human improvement and management of the river carries on to crank out controversy.
The Colorado starts at La Poudre Move in the Southern Rocky Mountains of Colorado, at far more than two miles (three km) earlier mentioned sea amount. Right after a short run south, the river turns west below Grand Lake, the biggest natural lake in the condition. For the very first 250 miles (four hundred km) of its training course, the Colorado carves its way by the mountainous Western Slope, a sparsely populated area defined by the portion of the condition west of the Continental Divide. As it flows southwest, it gains energy from lots of smaller tributaries, as perfectly as larger ones like the Blue, Eagle and Roaring Fork rivers. Right after passing by De Beque Canyon, the Colorado emerges from the Rockies into the Grand Valley, a big farming and ranching area in which it fulfills a single of its biggest tributaries, the Gunnison River, at Grand Junction. Most of the higher river is a swift whitewater stream ranging from 200 to 500 ft (sixty to one hundred fifty m) broad, the depth ranging from 6 to thirty ft (two to 9 m), with a several notable exceptions, these as the Blackrocks achieve in which the river is practically one hundred ft (thirty m) deep. In a several regions, these as the marshy Kawuneeche Valley close to the headwaters and the Grand Valley, it reveals braided features.
Arcing northwest, the Colorado starts to reduce throughout the eponymous Colorado Plateau, a broad space of significant desert centered at the Four Corners of the southwestern United States. Listed here, the local weather results in being noticeably drier than that in the Rocky Mountains, and the river results in being entrenched in progressively deeper gorges of bare rock, starting with Ruby Canyon and then Westwater Canyon as it enters Utah, now the moment once again heading southwest. Farther downstream it receives the Dolores River and defines the southern border of Arches National Park, just before passing Moab and flowing by “The Portal”, in which it exits the Moab Valley in between a pair of one,000-foot (300 m) sandstone cliffs.
In Utah the Colorado flows mostly by the “slickrock” state characterized by its narrow canyons and special “folds” produced by the tilting of sedimentary rock layers along faults, this is a single of the most inaccessible regions of the continental United States. Underneath the confluence with the Eco-friendly River, its biggest tributary, in Canyonlands National Park, the Colorado enters Cataract Canyon, named for its risky rapids, and then Glen Canyon, regarded for its arches and erosion-sculpted Navajo sandstone formations. Listed here, the San Juan River, carrying runoff from the southern slope of Colorado’s San Juan Mountains, joins the Colorado from the east. The Colorado then enters northern Arizona, in which given that the sixties Glen Canyon Dam close to Page has flooded the Glen Canyon achieve of the river, forming Lake Powell for water provide and hydroelectricity generation.
A narrow river flows by a narrow gorge flanked by significant rocky bluffs
In Arizona, the river passes Lee’s Ferry, an crucial crossing for early explorers and settlers and given that the early 20th century the principal place in which Colorado River flows are calculated for apportionment to the 7 U.S. and two Mexican states in the basin. Downstream, the river enters Marble Canyon, the starting of the Grand Canyon, passing below the Navajo Bridges on a now southward training course. Underneath the confluence with the Little Colorado River, the river swings west into Granite Gorge, the most extraordinary portion of the Grand Canyon, in which the river cuts up to a single mile (one.6 km) into the Colorado Plateau, exposing some of the oldest visible rocks on Earth, relationship as prolonged ago as two billion several years. The 277 miles (446 km) of the river that flow by the Grand Canyon are largely encompassed by Grand Canyon National Park and are regarded for their hard whitewater, divided by swimming pools that achieve up to a hundred and ten ft (34 m) in depth.
At the reduced stop of Grand Canyon, the Colorado widens into Lake Mead, the biggest reservoir in the continental United States, formed by Hoover Dam on the border of Arizona and Nevada. Positioned southeast of metropolitan Las Vegas, the dam is an integral element for administration of the Colorado River, managing floods and storing water for farms and cities in the reduced Colorado River basin. Underneath the dam the river passes below the Mike O’Callaghan–Pat Tillman Memorial Bridge – which at practically 900 ft (270 m) earlier mentioned the water is the optimum concrete arch bridge in the Western Hemisphere – and then turns due south in direction of Mexico, defining the Arizona–Nevada and Arizona–California borders.
Right after leaving the confines of the Black Canyon, the river emerges from the Colorado Plateau into the Lessen Colorado River Valley (LCRV), a desert area dependent on irrigation agriculture and tourism and also residence to numerous big Indian reservations. The river widens right here to a broad, moderately deep waterway averaging 500 to one,000 ft (one hundred fifty to 300 m) broad and achieving up to 1⁄4 mile (four hundred m) throughout, with depths ranging from 8 to sixty ft (two to twenty m). Prior to channelization of the Colorado in the 20th century, the reduced river was subject to frequent training course alterations induced by seasonal flow versions. Joseph C. Ives, who surveyed the reduced river in 1861, wrote that “the shifting of the channel, the banking companies, the islands, the bars is so continuous and quick that a comprehensive description, derived from the encounters of a single journey, would be observed incorrect, not only throughout the subsequent year, but most likely in the training course of a 7 days, or even a day.”
The LCRV is a single of the most densely populated regions along the river, and there are a lot of cities like Bullhead City, Arizona, Needles, California, and Lake Havasu City, Arizona. Listed here, lots of diversions draw from the river, giving water for equally local employs and distant regions like the Salt River Valley of Arizona and metropolitan Southern California. The previous big U.S. diversion is at Imperial Dam, in which over 90 percent of the river’s remaining flow is moved into the All-American Canal to irrigate California’s Imperial Valley, the most effective winter agricultural area in the United States.
Underneath Imperial Dam, only a smaller portion of the Colorado River helps make it further than Yuma, Arizona, and the confluence with the intermittent Gila River – which carries runoff from western New Mexico and most of Arizona – just before defining about 24 miles (39 km) of the Mexico–United States border. At Morelos Dam, the whole remaining flow of the Colorado is diverted to irrigate the Mexicali Valley, among the Mexico’s most fertile agricultural lands. Underneath San Luis Río Colorado, the Colorado passes totally into Mexico, defining the Baja California–Sonora border in most several years, the extend of the Colorado in between right here and the Gulf of California is dry or a trickle formed by irrigation return flows. The Hardy River gives most of the flow into the Colorado River Delta, a broad alluvial floodplain covering about three,000 sq. miles (seven,800 km2) of northwestern Mexico. A substantial estuary is formed right here just before the Colorado empties into the Gulf about seventy five miles (a hundred and twenty km) south of Yuma. Prior to 20th-century improvement dewatered the reduced Colorado, a big tidal bore was existing in the delta and estuary the very first historic record was manufactured by the Croatian missionary in Spanish services Father Ferdinand Konščak on July 18, 1746. Through spring tide conditions, the tidal bore – locally termed El Burro – formed in the estuary about Montague Island in Baja California and propagated upstream.
The Colorado is joined by over 25 sizeable tributaries, of which the Eco-friendly River is the biggest by equally length and discharge. The Eco-friendly takes drainage from the Wind River Range of west-central Wyoming, from Utah’s Uinta Mountains, and from the Rockies of northwestern Colorado. The Gila River is the next longest and drains a greater space than the Eco-friendly, but has a noticeably reduced flow since of a far more arid local weather and larger diversions for irrigation and cities. Both equally the Gunnison and San Juan rivers, which derive most of their water from Rocky Mountains snowmelt, lead far more water than the Gila did naturally.
In its natural condition, the Colorado River poured about sixteen.three million acre ft (twenty.one km3) into the Gulf of California every single year, amounting to an regular flow fee of 22,500 cubic ft for every next (640 m3/s). Its flow regime was not at all regular – indeed, “prior to the building of federal dams and reservoirs, the Colorado was a river of extremes like no other in the United States.” The moment, the river reached peaks of far more than one hundred,000 cubic ft for every next (two,800 m3/s) in the summertime and very low flows of considerably less than two,500 cubic ft for every next (seventy one m3/s) in the winter yearly. At Topock, Arizona, about 300 miles (480 km) upstream from the Gulf, a most historic discharge of 384,000 cubic ft for every next (ten,900 m3/s) was recorded in 1884 and a minimal of 422 cubic ft for every next (eleven.9 m3/s) was recorded in 1935. In contrast, the controlled discharge costs on the reduced Colorado below Hoover Dam almost never exceed 35,000 cubic ft for every next (990 m3/s) or drop below four,000 cubic ft for every next (a hundred and ten m3/s). Annual runoff quantity has ranged from a significant of 22.two million acre ft (27.four km3) in 1984 to a very low of three.8 million acre ft (four.seven km3) in 2002, despite the fact that in most several years only a smaller portion of this flow, if any, reaches the Gulf.
The regular yearly discharge of the Colorado River has proven a slight but visible reducing development in between 1895 and 2004.
Annual Colorado River discharge volumes at Lee’s Ferry in between 1895 and 2004
Concerning eighty five and 90 percent of the Colorado River’s discharge originates in snowmelt, typically from the Rocky Mountains of Colorado and Wyoming. The a few big higher tributaries of the Colorado – the Gunnison, Eco-friendly, and San Juan – on your own produce almost 9 million acre ft (eleven km3) for every year to the primary stem, typically from snowmelt. The remaining ten to 15 percent comes from a range of resources, principally groundwater foundation flow and summertime monsoon storms. The latter usually creates heavy, remarkably localized floods on reduced tributaries of the river, but does not usually lead sizeable volumes of runoff. Most of the yearly runoff in the basin occurs with the melting of Rocky Mountains snowpack, which starts in April and peaks throughout May perhaps and June just before exhausting in late July or early August.
Flows at the mouth have steadily declined given that the starting of the 20th century, and in most several years immediately after 1960 the Colorado River has run dry just before achieving the sea. Irrigation, industrial, and municipal diversions, evaporation from reservoirs, natural runoff, and likely local weather adjust have all contributed to this considerable reduction in flow, threatening the foreseeable future water provide. For case in point, the Gila River – formerly a single of the Colorado’s biggest tributaries – contributes little far more than a trickle in most several years due to use of its water by cities and farms in central Arizona. The regular flow fee of the Colorado at the northernmost place of the Mexico–United States border (NIB, or Northerly International Boundary) is about two,060 cubic ft for every next (fifty eight m3/s), one.forty nine million acre ft (one.84 km3) for every year – considerably less than a 10th of the natural flow – due to upstream water use. Underneath right here, all of the remaining flow is diverted to irrigate the Mexicali Valley, leaving a dry riverbed from Morelos Dam to the sea that is supplemented by intermittent flows of irrigation drainage water. There have been exceptions, on the other hand, specifically in the early to mid-nineteen eighties, when the Colorado the moment once again reached the sea throughout numerous consecutive several years of record-breaking precipitation and snowmelt. In 1984, so a great deal excessive runoff happened that some sixteen.5 million acre ft (twenty.four km3), or 22,860 cubic ft for every next (647 m3/s), poured into the sea.
The United States Geological Study (USGS) operates or has operated forty six stream gauges to evaluate the discharge of the Colorado River, ranging from the headwaters close to Grand Lake to the Mexico–U.S. border. The tables at correct listing information connected with eight of these gauges. River flows as gauged at Lee’s Ferry, Arizona, about midway along the length of the Colorado and sixteen miles (26 km) below Glen Canyon Dam, are utilised to determine water allocations in the Colorado River basin. The regular discharge recorded there was somewhere around fourteen,800 cubic ft for every next (420 m3/s), ten.seventy two million acre ft (thirteen.22 km3) for every year, from 1921 to 2010. This figure has been heavily influenced by upstream diversions and reservoir evaporation, specifically immediately after the completion of the Colorado River Storage Job in the seventies. Prior to the completion of Glen Canyon Dam in 1964, the regular discharge recorded in between 1912 and 1962 was seventeen,850 cubic ft for every next (505 m3/s), 12.ninety three million acre ft (15.ninety five km3) for every year.