A winding river and two nations

A portion of the border separating the United States and Mexico is represented on this map of the “relative positions of the Rio Grande near El Paso between 1852 and 1907” created by the International Boundary Commission in 1911.

The Rio Grande, known as the Río Bravo in Mexico, flows through the Chihuahuan Desert dividing what was once one of the oldest non-indigenous cities in the region, El Paso del Norte, into two cities: El Paso, Texas, and Ciudad Juárez, Chihuahua.

The International Boundary Commission, formed by Mexico and the United States in 1889, was tasked with surveying the changes in the river and arbitrating minor disputes. According to the terms of the 1848 Treaty of Guadalupe Hidalgo, which established the river as the border and officially ended the Mexican-American War, the boundary followed the deepest channel of the river and would adjust with any “slow and gradual” changes to the river. If the change in the course of the river was rapid, however, the border would not change with the river and would instead correspond to the 1852 survey—a principle in land law known as accretion versus avulsion.

The Rio Grande, however, running through a relatively flat section of land in this area, wandered constantly. Between the survey in 1852 and the creation of the commission in 1889, the position of the river changed as much as a mile at certain points along the boundary. The shifting banks of the river created two sections of land—the “Chamizal Tract” and “Cordova Island”—which were on both sides of the river at one point after the creation of the border.

Mexican commissioner Fernando Beltram y Puga, a civil engineer, American commissioner Anson Mills, a brigadier general in the U.S. Army, and Canadian commissioner Eugene Lafleur, a retired international law professor, gathered evidence to determine whether the changes in the course of the river were due to avulsion or accretion—that is, whether the changes had happened suddenly or gradually (Schulze 2012).

Based on interviews and documents, Puga determined that the changes in the course of the river were caused by avulsion, and Lafleur found that the evidence supported Mexico’s claim. However, the United States refused to ratify the terms which confirmed that the majority of the disputed territory, including the Chamizal Tract, belonged to Mexico.

The territory remained a source of contention between the two nations until the ratification of the Chamizal Convention in 1964 which returned the Chamizal Tract to Mexico and gave a portion of Cordova Island to the United States in return for equivalent territory along the border.

To prevent any future changes to the section of river between El Paso and Ciudad Juárez, and to fix its location permanently, the International Boundary Commission, which became the International Boundary and Water Commission (IBWC) in the 1940s, created a four-mile cement channel along the line agreed upon in 1964. Like earlier IBWC projects in the 1930s, the project prioritized straightening the river channel. The 1964-1968 channelization project had drastic social and environmental consequences. The concrete eliminated most vegetation, artificially raised the temperature of the water, and increased the speed of the river currents, which threatened many forms of life dependent upon the river (Alvarez 2019).