Amistad 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. 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. 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 per year, about 31% greater than had been expected at the time of construction. ==Specifications==

Dam and spillways The dam has a total length of , almost 6 miles (10 km), of which are in Mexico and in the United States. The center section at the Rio Grande is a concrete gravity dam long, with the remainder being earthen embankment. In total, the dam contains 13.5 million cubic yards (10,300,000 m3) of earth, 1.8 million cubic yards (1,400,000 m3) of concrete, 1.76 million cubic yards (1,300,000 m3) of riprap, and 12,500 tons (11,300 metric tons) of steel. The maximum height above the riverbed is , and the elevation at the dam crest is above sea level. The embankments are protected on both sides by riprap to reduce erosion. The riprap is thick on the upstream (reservoir) side and thick on the downstream side. During extreme flood events, however, this may still be a cause for concern. Flood waters are released through a concrete ogee crest spillway with 16 tainter gates. The gates measure and can spill up to . The reservoir levels fluctuate greatly due to the region's highly variable annual precipitation as well as heavy water use. The record high level was on September 22, 1974. It reached a record low level of on May 23, 2013, or below normal levels, after several consecutive years of drought. The average annual inflow to Amistad Reservoir is about . Power generation The dam has two hydroelectric power stations, one on either side of the border, with a capacity of 66 megawatts (MW) each. The maximum hydraulic head is , with a minimum of required to run the plants. The four generators have a capacity of 33 MW each and are powered by a 42,300-hp (31.54-MW) Francis turbine. The maximum combined water flow through the power plants is . In 2009, the Amistad Dam plants produced a total of 296,734,000 kilowatt hours. ==Border crossing==

The Amistad Dam Port of Entry was built when Amistad Dam was completed in 1969. The Dam was a bi-national effort to establish flood control on the Rio Grande and provide sources of water. Although US Department of Transportation statistics combine traffic counts with Del Rio Texas Port of Entry, approximately 65,000 vehicles crossed the dam into the US in 2005. The border station was rebuilt by the US Army Corps of Engineers in 2012. ==Recreation==

The dam and reservoir are part of the Amistad National Recreation Area. ==See also==

• Archival film footage of the Amistad Dam and Reservoir from the Texas Archive of the Moving Image