The Rio Grande is an important source of internationally regulated irrigation, a use it has long been put to. Pueblos were thriving on its banks N of Las Cruces, N.Mex., and the Native Americans were practicing irrigation of the arid country, when Spanish explorer Francisco Vásquez de Coronado arrived (1540). Today, dams on the Rio Grande are used for irrigation, flood control, and regulation of the river flow. Elephant Butte Dam (completed 1916) and Caballo Dam (completed 1938) in New Mexico create reservoirs that serve large areas. Further downstream N of Del Rio, Tex., is the Amistad Dam (completed 1969); it is 6 mi (9.7 km) long and impounds a huge reservoir; Amistad National Recreation Area is there. Below Laredo are Falcon Dam (completed 1954) and its large reservoir. Near the mouth of the Rio Grande is the irrigation-dependent citrus-fruit and truck-farm region commonly called the Rio Grande Valley and developed principally in the 1920s. An agreement between the United States and Mexico in 1944 provided for future distribution of the river's water, but in drought years the amount reaching the United States is often less than what is called for under the treaty, and upper portions of the river in the United States can also be reduced to a trickle in drought years.
Shifts in the river's channel have led to border disputes between the United States and Mexico. Parts of its bed have been stabilized by canalization, and an international border commission mediates disputes. The 114-year controversy over the location of the border at El Paso was finally settled in 1968 when the water of the Rio Grande was diverted into a concrete channel. A 191-mi (307-km) section of the river on the American shore below Big Bend National Park is protected as the
See R. E. Riecker, Rio Grande Rift (1979); P. Horgan, Great River: The Rio Grande in North American History (2 vol., 1984).
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