The Rio Grande withits fertile valley, along with its tributaries, is a vital water source for seven U.S. and Mexican states, and flows primarily through arid and semi-arid lands. After traversing the length ofNew Mexico, the Rio Grande becomes theMexico–United States border, between the U.S. state ofTexas and the northern Mexican states ofChihuahua andCoahuila,Nuevo León andTamaulipas; a short segment of the Rio Grande is a partial state-boundary between the U.S. states of New Mexico and Texas. Since the mid–twentieth century, only 20 percent of the Rio Grande's water reaches the Gulf of Mexico, because of the voluminous consumption of water required to irrigate farmland (e.g. theMesilla andLower Rio Grande Valleys) and to continually hydrate cities (e.g. Albuquerque); such water usages are additional to the reservoirs of water retained withdiversion dams.[1] 260 miles (418 km) of the river in New Mexico and Texas are designated as theRio Grande Wild and Scenic River.[13]
A riverine islet in the Rio Grande, seen from North Valley, New Mexico.
The segment of the river that forms the international border ranges from 889 to 1,248 miles (1,431 to 2,008 km), depending on how the river is measured.[1] TheRio Conchos is a major tributary of the Rio Grande, with its confluence 310 km. (193 straight air miles) southeast of El Paso nearOjinaga, inChihuahua, Mexico. Downstream, other tributaries include thePecos River andDevils River, both entering the Rio Grande from the north in the vicinity ofAmistad Reservoir in Texas, and theRio Salado andRio San Juan both entering from the south with confluences inTamaulipas, Mexico.
The Rio Grande rises in high mountains and flows for much of its length at high elevation; the valley floor at Albuquerque is 5,312 feet (1,619 m), and El Paso 3,762 feet (1,147 m) abovesea level. In New Mexico, the river flows through theRio Grande rift from onesediment-filled basin to another, cuttingcanyons between the basins and supporting a fragilebosque ecosystem on itsflood plain. From Albuquerque southward, the river flows through desert. Although irrigated agriculture exists throughout most of its stretch, it is particularly extensive in thesubtropicalLower Rio Grande Valley. The river ends in a small, sandydelta at the Gulf of Mexico. During portions of 2001 and 2002, the mouth of the Rio Grande was blocked by a sandbar. In the fall of 2003, the sandbar was cleared by high river flows around 7,063 cubic feet per second (200 m3/s).[2]
The Rio Grande flows through a valley with diverse animal and plants communities. Conservation of the river and the valley is a recurring theme for people who live in the region.[14]
Although the river's greatest depth is 60 feet (18 m), the Rio Grande generally cannot be navigated by passengerriverboats or bycargo barges. Navigation is only possible near the mouth of the river, in rare circumstances up toLaredo, Texas.[15]
Rio Grande in westEl Paso near the New Mexico state line
TheBrownsville & Matamoros International Bridge, a largeswing bridge, dates back to 1910 and is still in use today by automobiles connecting Brownsville withMatamoros, Tamaulipas. The swing mechanism has not been used since the early 1900s, though, when the last of the big steamboats disappeared. At one point, the bridge also had rail traffic. Railroad trains no longer use this bridge. A new rail bridge (West Rail International Crossing) connecting the U.S. and Mexico was built about 15 miles west of the Brownsville & Matamoros International Bridge. It was inaugurated in August 2015. It moved all rail operations out of downtown Brownsville and Matamoros.[17] The West Rail International Crossing is the first new international rail crossing between the U.S. and Mexico in over a century.[18] The Brownsville & Matamoros International Bridge is now operated by the Brownsville and Matamoros Bridge Company, a joint venture between the Mexican government and theUnion Pacific Railroad.
At the mouth of the Rio Grande, on the Mexican side, was the large commercial port ofBagdad, Tamaulipas. During theAmerican Civil War, this was the only legitimate port of the Confederacy. European warships anchored offshore to maintain the port's neutrality, and managed to do so successfully throughout that conflict, despite occasional stare-downs with blockading ships from theUS Navy. It was a shallow-draft river port, with several smaller vessels that hauled cargo to and from the deeper-draft cargo ships anchored off shore. These deeper-draft ships could not cross the shallowsandbar at the mouth of the river. The port's commerce was European military supplies, in exchange for bales of cotton.
Thesedimentary basins forming the modernRio Grande Valley were not integrated into a single river system draining into the Gulf of Mexico until relatively recent geologic time. Instead, the basins formed by the opening of theRio Grande rift were initiallybolsons, with no external drainage and a centralplaya.[19] An axial river existed in the Espanola Basin as early as 13 million years ago, reaching the Santo Domingo Basin by 6.9 million years ago. However, at this time, the river drained into a playa in the southernAlbuquerque Basin where it deposited thePopotosa Formation.[20] The upper reach of this river corresponded to the modernRio Chama, but by 5 million years ago, an ancestral Rio Grande draining the easternSan Juan Mountains had joined the ancestral Rio Chama.[19]
The ancestral Rio Grande progressively integrated basins to the south, reaching theMesilla Basin by 4.5 million years and the Palomas basin by 3.1 million years ago, formingLake Palomas.River capture by a tributary of the Pecos River then occurred, with the Rio Grande flowing to Texas by 2.06 million years, and finally joining the Pecos River 800,000 years ago, which drained into the Gulf of Mexico. Volcanism in the Taos Plateau reduced drainage from the San Luis Basin until a spillover event 440,000 years ago that drainedLake Alamosa, forming theRio Grande Gorge, and fully reintegrated the San Luis Basin into the Rio Grande watershed.[19]
Archeological sites from the earliest human presence in the Rio Grande Valley are scarce, due to traditional Indigenous nomadic culture,Pleistocene andHoloceneriver incision or burial under the Holocene floodplain. However, some early sites are preserved onWest Mesa on the west side of the Rio Grande near Albuquerque. These includeFolsom sites, possibly dating from around 10,800 to 9,700 BCE, that were probably short-term sites such as buffalo kill sites. Preservation is better in flanking basins of the Rio Grande Valley, where numerous Folsom sites and a much smaller number of earlierClovis sites have been identified.[21] LaterPaleo-Indian groups included theBelen andCody cultures, who appear to have taken advantage of the Rio Grande Valley for seasonal migrations and may have settled more permanently in the valley.[22]
The Paleo-Indian cultures gave way to theArchaicOshara tradition beginning around 5450 BCE.[23] The Oshara began cultivation ofmaize between 1750 and 750 BCE, and their settlements became larger and more permanent.[22]
Drought induced the collapse of theAncestral Puebloan culture, atChaco Canyon and elsewhere across the Four Corners region, at around 1130 CE. This led to a mass migration of the Ancestral Puebloans to the Rio Grande and other more fertile valleys of the Southwest, competing with other indigenous communities such as the Apache with territory in the Rio Grande Valley.[24] This led to decades of conflict (the Coalition Period), the eventual merging of cultures, and the establishment of most of theTanoan andKeresanpueblos of the Rio Grande Valley. This was followed by the Classic Period, from about 1325 CE to 1600 CE and the arrival of the Spanish. The upper Rio Grande Valley was characterized by occasional periods of extreme drought, and the human inhabitants make extensive use of gridded gardens and check dams to stretch the uncertain water supply.[25]
Rare first state ofGiovan Battista Nicolosi's four sheet map of North America, the first printed map to accurately depict the course of the Rio Grande (namedRio Escondido) flowing into theGulf of Mexico.
During the late 1830s and early 1840s, the river marked the disputed border between Mexico and the nascentRepublic of Texas; Mexico marked the border at theNueces River. The disagreement provided part of the rationale for theMexican–American War in 1846, after Texas had been admitted as a new state. Since 1848, the Rio Grande has marked the boundary between Mexico and the United States from the twin cities ofEl Paso, Texas, andCiudad Juárez, Chihuahua, to the Gulf of Mexico. As such, crossing the river was the escape route used by some Texanslaves to seek freedom. Mexico had liberal colonization policies and had abolished slavery in 1828.[27]
Railway Bridges and the Great Customs Smelter (postcard,circa 1916)
In 1899, after a gradual change to the river position, a channel was dug for flood control which moved the river, creating what was called Cordova Island, which became the center of theChamizal dispute. Resolving the dispute took many years and resulted in a1909 combined assassination attempt on the American and Mexican presidents.
Following the approval of theRio Grande Project by federal lawmakers in 1905, the waters of the Rio Grande were to be divided between the states of New Mexico and Texas based on their respective amount of irrigable land. The project also accorded 60,000acre-feet (74 millioncubic meters) of water annually to Mexico in response to the country's demands. This was meant to put an end to the many years of disagreement concerning rights to the river's flow and the construction of a dam and reservoir at various location on the river between the agricultural interests of theMesilla Valley and those ofEl Paso andJuárez. In the agreement provisions were made to constructElephant Butte dam on public lands. This act was the first occurrence of congressionally directed allocation of an interstate river (although New Mexico would not achieve statehood till 1912).[28]
Bridge of the Americas from El Paso, US to Ciudad Juárez, Mexico (2016).
Following the admittance of New Mexico into the union, the increased settlement of the Rio Grande farther north in Colorado and near Albuquerque, the1938 Rio Grande Compact developed primarily because of the necessary repeal of the Rio Grande embargo among other issues.[29] Though both Colorado and New Mexico were initially eager to begin negotiations, they broke down over whether Texas should be allowed to joinnegotiations in 1928, though it had representatives present. In an effort to avoid litigation of the matter in theSupreme Court a provisional agreement was signed in 1929 which stated that negotiations would resume once a reservoir was built on the New Mexico-Colorado state line. The construction of this was delayed by theMarket Crash of 1929. With negotiations remaining stagnant, Texas sued New Mexico over the issue in 1935, prompting the intervention of thepresident who set up the Rio Grande Joint Investigation the findings of which helped lead to the final agreement.[28] The 1938 Rio Grande Compact provided for the creation of a compact commission, the creation ofgaging stations along the river to ensure flow amounts by Colorado to New Mexico at the state line and by New Mexico toElephant Butte Reservoir, the water once there would fall under the regulation of theRio Grande Project which would guarantee provision to Texas and Mexico. A system ofdebits and credits was created to account for variations in the water provided.[30] The compact remains in effect today, though it has been amended twice.
In 1944, the US and Mexico signed atreaty regarding the river.[31] Due to drought conditions which have prevailed throughout much of the 21st century, calls for a reexamination of this treaty have been made by locals in New Mexico, Mexico, and Texas. Texas, being the state with the least amount of control over the waterway, has routinely seen an under-provision of water since 1992.[32]
Rio Grande southeast of Falcon Reservoir, Municipality of Mier, Tamaulipas, Mexico (August 12, 2007)
In mid-2001, a 328-foot (100 m)-wide sandbar formed at the mouth of the river, marking the first time in recorded history that the Rio Grande failed to empty into the Gulf of Mexico. The sandbar wasdredged, but reformed almost immediately. Spring rains the following year flushed the reformed sandbar out to sea, but it returned in mid-2002. By late 2003, the river once again reached the Gulf.[2]
For much of the time since water rights were introduced in the 1890s, the Rio Grande flowed through Las Cruces from February to October each year, but this is subject to climate change.[33] In 2020, the river flowed only from March to September.[33] As of January 2021, the Elephant Butte Irrigation District (Ebid) expected that water shortages would mean the river only flows through Las Cruces from June through July.[33] The water shortages are affecting the local ecosystem and endangering species includingcottonwood trees and thesouthwestern willow flycatcher.[33]
A 5-mile stretch of the river ran dry inAlbuquerque in 2022
The water of the Rio Grande is over-appropriated: that is, more users for the water exist than water in the river. Because of both drought and overuse, the section from Las Cruces downstream through Ojinaga frequently runs dry and was recently tagged "The Forgotten River" by those wishing to bring attention to the river's deteriorated condition.[34]
In 2022, due to increasing drought and water use, the water debt owed to Texas increased from 31,000 acre-feet to over 130,000 acre-feet since 2021, despite "very significant efforts that were done on the river this year to keep water flowing downstream."[35] In response, New Mexico increased its program offering to subsidize farmers who fallow their fields rather than planting crops, which uses additional water;[36] the city of Albuquerque shut off its domestic supply diversion and switched to full groundwater pumping in 2021.[37]
Additionally, in 2022, work began onEl Vado Dam, during which it is unavailable for storage, reducing system capacity by about 180,000 acre-feet. MRGCD has requested storage of "native water" downstream atAbiquiu Reservoir, which normally only stores waters imported into the Rio Grande watershed from theColorado River watershed via theSan Juan–Chama Project.[38]
Elephant Butte Reservoir, the main storage reservoir on the Rio Grande, was reported at 13.1% of capacity as of May 1, 2022,[39] further decreasing to only 5.9% full by November 2021.[39] Nearly a year later, in October 2022, the reservoir had made only insignificant rebounds, resting at 6.4% of capacity.[39]
In late July 2022, due to extreme drought, the Rio Grande ran dry for about 50 miles in the middleRio Grande Valley, including five miles in Albuquerque, the first time it had done so in over 40 years.[40] The following winter, the basin experienced above-average snowfall, leading to very high flows in the river in spring of 2023[41] and flooding of some of its tributaries, including theJemez andPecos Rivers.[42][43] By that summer, after the spring runoff had concluded and due to a failedNew Mexico monsoon season and record high temperatures, the river went dry in Albuquerque for a second consecutive year.[44]
The United States and Mexico share the water of the river under a series of agreements administered by theInternational Boundary and Water Commission (IBWC), US–Mexico. The most notable of these treaties were signed in 1906 and 1944.[45][46] The IBWC traces its institutional roots to 1889, when the International Boundary Committee was established to maintain the border. The IBWC today also allocates river waters between the two nations and provides for flood control and water sanitation. Use of that water belonging to the United States is regulated by theRio Grande Compact, an interstate pact between Colorado, New Mexico, and Texas.
TheUpper Colorado River Basin Compact allots 62,780 acre-feet (77,440,000 m3) of water from the upperColorado River basin per year to municipalities in New Mexico. Albuquerque owns 48,200 acre-feet (59,500,000 m3), about three-quarters of the total amount. The water is delivered to the Rio Grande via theSan Juan–Chama Project. The project's construction was initiated by legislation signed by PresidentJohn F. Kennedy in 1962, and was completed in 1971. This diversion project transports water under thecontinental divide from tributaries of the San Juan River (the Navajo, the Little Navajo, and Blanco Rivers) to Heron Reservoir, which empties into theRio Chama before this connects to the Rio Grande.[47] Although it held rights to San Juan-Chama water for many years, it was only as of 2008 that Albuquerque began using it as part of its municipal supply, with the completion of San Juan-Chama Drinking Water Project (SJCDWP) by the Albuquerque Bernalillo County Water Utility Authority.[48]
Treatment plant, San Juan-Chama Drinking Water Project, Albuquerque.
The SJCDWP uses an adjustable-height diversion dam to skim imported San Juan-Chama water from the Rio Grande, then pumps this water to a treatment plant on Albuquerque's north side. From there it is added to a municipal drinking water distribution system serving Albuquerque's metro area. Diversions are restricted during periods of low river flow in order to protect the riparian ecosystem and mitigate effects on endangered species like theRio Grande silvery minnow.Treated effluent water is recycled into the Rio Grande south of the city. Surface water from the SJCDWP comprises a significant percentage of Albuquerque's drinking water supply, withgroundwater constituting the remainder; annual percentages vary according to runoff and climate conditions. Acquisition of native pre-1907 water rights is not part of the Water Authority's long-term resource management plan, dubbed WATER 2120.[49]
Dams on the Rio Grande includeRio Grande Dam,Cochiti Dam,Elephant Butte Dam,Caballo Dam,Amistad Dam,Falcon Dam,Anzalduas Dam, andRetamal Dam. In southern New Mexico and the upper portion of the Texas border segment, the river'sdischarge dwindles. Diversions, mainly for agricultural irrigation, have increased the natural decrease in flow such that by the time the river reachesPresidio, little or no water is left. Below Presidio, the Rio Conchos restores the flow of water.[1] Near Presidio, the river's discharge is frequently zero. Its average discharge is 178 cubic feet per second (5 m3/s), down from 945 cubic feet per second (27 m3/s) at Elephant Butte Dam. Supplemented by other tributaries, the Rio Grande's discharge increases to its maximum annual average of 3,504 cubic feet per second (99 m3/s) near Rio Grande City. Large diversions for irrigation below Rio Grande City reduce the river's average flow to 889 cubic feet per second (25 m3/s) at Brownsville and Matamoros.[2]
Río Grande is Spanish for "Big River" andRío Grande del Norte means "Big River of the North". In English, Rio Grande is pronounced either/ˈriːoʊˈɡrænd/ or/ˈriːoʊˈɡrɑːndeɪ/.
In Mexico, it is known asRío Bravo orRío Bravo del Norte,bravo meaning (among other things) "furious", "agitated" or "wild".
Historically, thePueblo and Navajo peoples also have had names for the Rio Grande/Rio Bravo:
The four Pueblo names likely antedated theSpanishentrada by several centuries.[50]
Tó Baʼáadi,Navajo, "Female River" (the direction south is female in Navajo cosmology)[51]
Rio del Norte was most commonly used for the upper Rio Grande (roughly, within the present-day borders of New Mexico) fromSpanish colonial times to the end of the Mexican period in the mid-19th century. This use was first documented by the Spanish in 1582. Early American settlers inSouth Texas began to use the modern 'English' name Rio Grande. By the late 19th century, in the United States, the name Rio Grande had become standard in being applied to the entire river, fromColorado to the sea.[50]
By 1602,Río Bravo had become the standard Spanish name for the lower river, below its confluence with the Rio Conchos.[50]
The largesttributary of the Rio Grande bydischarge is the Rio Conchos, which contributes almost twice as much water as any other. In terms ofdrainage basin size, the Pecos River is the largest.
^"Rio Grande River".Encyclopædia Britannica. RetrievedMay 18, 2016.In some places the depth of the river has varied from nearly 60 feet (18 metres) to a bare trickle or nothing.
^Tom Lea (1957)The King Ranch writes that Richard King made his fortune as a riverman on the Rio Grande before he proposed marriage to Henrietta and started his cattle ranch.
^Ballenger, Jesse; Holliday, Vance; Sanchez, Guadelupe (2017). Mills, Barbara; Fowles, Severin (eds.).The Earliest People in the Southwest. Vol. 1.doi:10.1093/oxfordhb/9780199978427.013.11.
^abVierra, B.J.; Jodry, M.A.; Shackley, M.S.; Dilley, M.J.; Bousman, C.B.; Vierra, B.J. (2012). "Late Paleoindian and early archaic foragers in the Northern Southwest".From the Pleistocene to the Holocene: Human organization and cultural transformations in prehistoric North America. Vol. 17. Texas A&M University Press. p. 171.ISBN978-1603447782.
^Gibbon, Guy E.; Ames, Kenneth M. (1998).Archaeology of Prehistoric Native America: An Encyclopedia. New York: Taylor and Francis. p. 798.ISBN081530725X.
Coker, Caleb (1992).The News from Brownsville: Helen Chapman's Letters from the Texas Military Frontier, 1848–1852. Austin: Texas State Historical Association.ISBN0876111150.
Diaz, George T. (2015).Border Contraband: A History of Smuggling across the Rio Grande. University of Texas Press.[ISBN missing]
Kearney, Milo; Knopp, Anthony K. (1995).Boom and Bust: The Historical Cycles of Matamoros and Brownsville. Austin, Texas: Eakin Press.ISBN978-0890158159.
Kelley, Pat (1986).River of Lost Dreams: Navigation on the Rio Grande. Lincoln: University of Nebraska Press.ISBN978-0803227125.
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