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The IBWC traces its roots to the 1848 Treaty of Guadalupe Hidalgo and the Gadsden Treaty of 1853, which established temporary joint commissions to survey, map, and demarcate with ground landmarks the new United States (U.S.) – Mexico boundary. The Guadalupe Hidalgo Treaty of February 2, 1848 established the international boundary between the United States and Mexico. The Treaty of December 30, 1853 reestablished the southern boundary of New Mexico and Arizona to enable the United States to construct a railroad to the west coast along a southern route and to resolve a question arising from the 1848 Treaty as to the location of the southern boundary of New Mexico. The Convention of 1882 established another temporary joint commission to resurvey the western land boundary between the Rio Grande and the Pacific Ocean, rebuild the old monuments, and install additional monuments where necessary. U.S. Commissioner John Whitney Barlow and Mexican Commissioner Jacobo Blanco resurveyed the borderline and increased the number of boundary monuments from 52 to 258. This survey started at the El Paso, Texas – Ciudad Juárez, Chihuahua border in 1891, and concluded at the San Diego, California – Tijuana, Baja California border in 1894. Later as border populations increased during the 1900’s, the Commission installed 18 additional boundary monuments for a total of 276.

Border Region

As the settlements grew along the boundary rivers (Rio Grande and Colorado River), settlers began developing adjoining lands for agriculture. In the late Nineteenth Century, questions arose as to the location of the boundary and the jurisdiction of lands when the boundary rivers changed their course and transferred land from one side of the river to the other. As a result, the two Governments adopted certain rules to deal with such questions in the Convention of November 12, 1884.

The U.S. and Mexico established the International Boundary Commission (IBC) on March 1, 1889 as another temporary body to apply the rules that were adopted by the Convention of 1884. The IBC was extended indefinitely in 1900 and is considered the direct predecessor to the modern day International Boundary and Water Commission. The 1884 Convention was modified by the Banco Convention of March 20, 1905 to retain the Rio Grande and the Colorado River as the boundary.

As border populations increased during the early to mid 1900's, the Commission was faced with many new challenges. The U.S. and Mexico used studies developed by the IBC as the basis for the first water distribution treaty between the two countries, the Convention of March 1, 1906, which allocated the waters of the Rio Grande from El Paso to Fort Quitman, an 89-mile (143 km) international boundary reach of the Rio Grande through the El Paso-Juárez Valley. This Convention allotted to Mexico 60,000 acre-feet annually of the waters of the Rio Grande to be delivered in accordance with a monthly schedule at the headgate to Mexico's Acequia Madre just above Juárez, Chihuahua. To facilitate such deliveries, the U.S. constructed, at its expense, the Elephant Butte Dam in its territory. The Convention includes the provision that in case of extraordinary drought or serious accident to the irrigation system in the U.S., the amount of water delivered to the Mexican Canal shall be diminished in the same proportion as the water delivered to lands under the irrigation system in the U.S. downstream of Elephant Butte Dam.

In the Convention of February 1, 1933, the two Governments agreed to jointly construct, operate and maintain, through the IBC, the Rio Grande Rectification Project, which straightened and stabilized the 155-mile (249 km) river boundary through the highly developed El Paso-Juárez Valley. The project further provided for the control of the river's floods through this Valley.

The IBC was also instrumental in developing the second water distribution treaty between the United States and Mexico in 1944, which addressed utilization of the waters of the Colorado River and Rio Grande from Fort Quitman, Texas to the Gulf of Mexico. The Water Treaty of February 3, 1944 expanded the duties and responsibilities of the IBC and renamed it the International Boundary and Water Commission (IBWC). The 1944 Treaty charged the IBWC with the application of the treaty and the exercise of the rights and obligations which the U.S. and Mexican Governments assumed thereunder and with the settlement of all disputes that were to arise under the treaty.

The 1944 Treaty provides that the jurisdiction of the IBWC extends to the limitrophe parts of the Rio Grande and the Colorado River, the land boundary between the U.S. and Mexico and to works located upon the border. Neither Section is to assume jurisdiction or control over works within the limits of the country of the other without the express consent of the Government of the latter. The works constructed, acquired or used in fulfillment of the provisions of the Treaty and located wholly within the territorial limits of either country, although these works may be international in character, they are to remain under the exclusive jurisdiction and control of the Section of the Commission in whose country the works may be situated.

Pursuant to the 1944 Treaty, the IBWC has the status of an international body and consists of a United States Section and a Mexican Section. Each Section is headed by an Engineer Commissioner. Wherever there are provisions for joint action or joint agreement of the two Governments or for the furnishing of reports, studies or plans to the two Governments, it is understood that those matters will be handled by or through the Department of State of the United States and the Ministry of Foreign Relations of Mexico. Each Government affords diplomatic status to the Commissioner, designated by the other Government. The Commission, two principal engineers, a legal adviser, and a secretary, designed by each Government as members of its Section of the Commission are entitled in the territory of the other country to the privileges and immunities appertaining to diplomatic officers. The IBWC and its personnel may freely carry out their observations, studies and field work in the territory of the other country. Each Government bears the expenses of its respective Section; joint expenses which may be incurred as agreed by the IBWC are to be born equally by the two Governments.

Of the waters of the Rio Grande, the Treaty allocates to Mexico: (1) all of the waters reaching the main channel of the Rio Grande from the San Juan and Alamo Rivers, including the return flows from the lands irrigated from those two rivers; (2) two-thirds of the flow in the main channel of the Rio Grande from the measured Conchos, San Diego, San Rodrigo, Escondido and Salado Rivers, and the Las Vacas Arroyo, subject to certain provisions; and (3) one-half of all other flows occurring in the main channel of the Rio Grande downstream from Fort Quitman. The Treaty allots to the United States: (1) all of the waters reaching the main channel of the Rio Grande from the Pecos and Devils Rivers, Goodenough Spring and Alamito, Terlingua, San Felipe and Pinto Creeks; (2) one-third of the flow reaching the main channel of the river from the six named measured tributaries from Mexico and provides that this third shall not be less, as an average amount in cycles of five consecutive years, than 350,000 acre-feet annually; and (3) one-half of all other flows occurring in the main channel of the Rio Grande downstream from Fort Quitman.

The 1944 Treaty further provided for the two Governments to jointly construct, operate and maintain on the main channel of the Rio Grande the dams required for the conservation, storage and regulation of the greatest quantity of the annual flow of the river to enable each country to make optimum use of its allotted waters.

The 1944 Treaty provides that of the waters of the Colorado River there are allotted to Mexico: (1) a guaranteed annual quantity of 1.5 million acre-feet to be delivered in accordance with schedules formulated in advance by Mexico within specified limitations; and (2) any other waters arriving at the Mexican points of diversion under certain understandings. To enable diversion of Mexico's allotted waters, the Treaty provided for the construction by Mexico of a main diversion structure in the Colorado River, below the point where the California-Baja California land boundary line intersects the river. It also provided for the construction at Mexico's expense of such works as may be needed in the U.S. to protect its lands from such floods and seepage as might result from the construction and operation of the diversion structure.

In the 1944 Treaty, the two Governments agreed to give preferential attention to the solution of all border sanitation problems.

The Treaty also provides that the IBWC study, investigate and report to the Governments on such hydroelectric facilities as the IBWC finds should be built at the international storage dams and on such flood control works, other than those specified in the Treaty, that the IBWC finds should be built on the boundary rivers, the estimated cost thereof, the part to be built by each Government, and to be operated and maintained by each through its Section of the IBWC.

The IBWC was instrumental in the development of the Chamizal Convention of August 29, 1963, which resolved the nearly 100-year-old boundary problem at El Paso, Texas and Juárez, Chihuahua, known as the Chamizal dispute, involving some 600 acres (243 hectares) of territory which were transferred from the south to the north bank of the Rio Grande by movement of the river during the mid-Nineteenth Century. By this Convention, the two Governments gave effect to a 1911 arbitration award under 1963 conditions. The IBWC relocated and concrete-lined 4.4 miles of the Rio Grande channel and transferred a net amount of 437.18 acres (176.92 hectares) from the north (U.S.) to the south side (Mexico) of the river.

The Treaty of November 23, 1970 resolved all pending boundary differences and provided for maintaining the Rio Grande and the Colorado River as the international boundary. The Rio Grande was reestablished as the boundary throughout its 1,255-mile limitrophe section. The Treaty includes provisions for restoring and preserving the character of the Rio Grande as the international boundary where that character has been lost, to minimize changes in the channel, and to resolve problems of sovereignty that might arise due to future changes in the channel of the Rio Grande. It provides for procedures designed to avoid the loss of territory by either country incident to future changes in the river's course due causes other than lateral movement, incident to eroding one of its banks and depositing alluvium on the opposite bank. This Treaty also charged the IBWC with carrying out its provisions.

The two Governments reached agreement for the solution of another long-standing problem regarding the quality of the Colorado River water allocated to Mexico under the 1944 Treaty, which was incorporated in Minute No. 242 of the IBWC dated August 30, 1973; and the IBWC submitted and the two Governments approved “Recommendations for the Solution of the Border Sanitation Problems,” in Minute No. 261, dated September 24, 1979, which provided that for each border sanitation problem, the IBWC would prepare a Minute that would identify the problem and the course of action for resolution. Pursuant to Minute No. 261, the IBWC subsequently concluded Minutes to address border sanitation problems at Naco, Arizona/Naco Sonora (Minute No. 273), Nogales, Arizona/ Nogales, Sonora (Minute No. 276), Laredo, Texas/Nuevo Laredo, Tamaulipas (Minute No. 279) and San Diego, California/Tijuana, Baja California (Minutes Nos. 283296 and 311), and to address the water quality of the New River at Calexico, California and Mexicali, Baja California (Minute No. 274).