Amistad Dam

Amistad Dam (Spanish: Presa la Amistad) is a major embankment dam across the Rio Grande between Texas, United States, and Coahuila, Mexico. Built to provide irrigation water storage, flood control, and hydropower generation, it is the largest dam along the international boundary reach of the Rio Grande. The dam is over 6 miles (9.7 km) long, lies mostly on the Mexican side of the border, and forms Amistad Reservoir. It supplies water for irrigation in the Rio Grande Valley, 574 miles (924 km) upstream of the Rio Grande's mouth on the Gulf of Mexico at Brownsville, Texas/Matamoros, Tamaulipas. The dam is owned and operated by the International Boundary and Water Commission (IBWC), and facilitates the a border crossing between the US and Mexico. Amistad is derived from the Spanish word for "friendship", representing the two nations' cooperation on the dam.

Because of the Rio Grande's frequent floods and droughts, the sharing of its water between the US and Mexico has been a contentious issue since the 1800s. The 1906 Treaty for Equitable Distribution of the Waters of the Rio Grande enabled the construction of Elephant Butte Dam, the first major Rio Grande dam, in New Mexico. While this benefited water users along the middle Rio Grande, it did little to help the lower Rio Grande Valley, where water flows remained uncontrolled. The 1944 Treaty relating to the utilization of waters of the Colorado and Tijuana Rivers and of the Rio Grande authorized the IBWC to build dams on the uncontrolled border segment of the Rio Grande. The first dam to be completed under the treaty was Falcon Dam in 1953. After the Rio Grande flooded massively in 1954, with a peak flow of 1,158,000 cubic feet per second (32,800 m3/s) recorded at Del Rio, planners realized that a much larger dam would be needed to control the river and two unregulated tributaries, the Pecos and Devils Rivers. The proposed site for the larger dam was about a mile (1.6 km) below the confluence of the Devils River and 12 miles (19 km) upstream of Del Rio. During the initial planning stage, it was known as "Diablo Reservoir", a nod to the name of Devils River (diablo meaning "devil" in Spanish). The final design was approved by the two governments as Minute 207, and authorized by an act of U.S. Congress on July 7, 1960. Work at the dam site began in August 1963 with foundation drilling and grouting in the river bed to support the future concrete section of the dam. Actual construction of the dam itself began in January 1965 and water was first impounded in 1968. U.S. president Richard Nixon and Mexican president Gustavo Díaz Ordaz dedicated the dam in 1969. The construction of the dam required the relocation of 14.3 miles (23.0 km) of the Southern Pacific Railroad tracks, 19 miles (31 km) of highways, and two bridges. When the reservoir filled, it inundated ancient rock art left by Native Americans who once lived in the areas. More than 170 archaeological sites were cataloged during salvage operations between 1958 and 1969, a difficult undertaking due to the arid and remote conditions of the area. The hydroelectric power plants were added later, with the US plant completed in 1983 and the Mexican plant in 1987. Of the dam's roughly US$125 million cost, the US paid about 57% and Mexico 43%, in accordance with the division of water storage rights in the reservoir. In 1993, the dam was determined to be silting up at the rate of 14,000 acre-feet (17,000,000 m3) per year, about 31% greater than had been expected at the time of construction.

Dam data from Wikidata (CC0) plus curated additions. Summary from Wikipedia (CC BY-SA).