With the completion in 1916 of Elephant Butte Dam near Truth or Consequences, New Mexico, 120 miles north of El Paso, the Mesilla valley in southern New Mexico and the Ciudad Juárez-El Paso valley in Chihuahua and Texas were assured of water for irrigation. However, since the dam tamed the river, the stream stopped flooding and could not clean its own channel. The bed filled with silt, and uncontrolled wanderings not only wasted water but destroyed crops, increased scrub vegetation, and shifted the international boundary. When little water flowed through the river the channel still marked the border, but that line was becoming more and more difficult to find.
An analysis called for straightening and trenching the Rio Grande from the lower limit of Cordova Island downstream to Box Canyon, below Fort Quitman. International bridges would be installed. Bancos would be divided. On February 1, 1933, the United States and Mexico signed the Rio Grande Rectification Treaty, which called for construction of a floodway 590 feet wide and a normal flow channel with a bottom width of sixty-six feet between parallel levees averaging 7½ feet in height. The levees doubled as maintenance roadways and fences against future floods. The middle of the deepest channel of the Rio Grande within the rectified channel was made the international boundary, and each nation yielded about 3,500 acres to the other. The original plan was completed in 1938 at a cost of $5 million, 88 percent of which the United States paid. The International Boundary Commission, later renamed the International Boundary and Water Commission, was given responsibility for the construction and maintenance of the rectified channel.
Engineers removed the curves from the river, shortening the segment from 155.2 miles to 85.6 miles, and divided the bancos in accord with the 1905 banco treaty. Toll-free bridges were erected between Ysleta, Texas, and Zaragoza, Chihuahua; between Fabens, Texas, and Guadalupe, Chihuahua; and between Fort Hancock, Texas, and El Porvenir, Chihuahua.
The treaty also called for the construction of Caballo Dam, twenty-two miles south of Elephant Butte Dam. It captured water released to generate electricity (but wasted for irrigation) from Elephant Butte and trapped rainwater that fell between the two reservoirs. A subsequent Rio Grande Canalization Project straightened the Rio Grande in New Mexico between Caballo Dam and El Paso. See also CHAMIZAL DISPUTE.