Fact Sheet: The Rio Grande Compact of 1938 by Water Education Colorado

JULY 2022

In the San Luis Valley’s Rio Grande Basin, where irrigators rely heavily on groundwater, groundwater management plans of the Rio Grande Water Conservation District serve as an alternative way to protect senior surface rights from injury by tributary groundwater pumping. Photo by Christi Bode Skeie

FACT SHEET

The Rio Grande Compact of 1938

The Rio Grande begins high in the San Juan Mountains above Creede, Colo. From there it flows down through the San Luis Valley, into New Mexico, then Texas, eventually reaching Mexico and terminating in the Gulf of Mexico. As early as prehistoric times it was used for irrigation by Native Americans and centuries later, when Spanish settlers began farming in the San Luis Valley and New Mexico, water shortages began occurring downstream. By 1896, water supplies were so short that the U.S. Secretary of the Interior barred development of any new reservoirs in Colorado and New Mexico. In 1929, Congress authorized a federal study tracking the river’s flows. It would form the basis for what became The Rio Grande Compact of 1938. Unlike other river compacts in Colorado, the Rio Grande agreement divides the water among the basin states annually, based on how much water is generated by the river system for the current calendar year. Other compacts say a fixed amount of water must be delivered during each specified period. For example, in the Colorado River Compact, the upper basin states must deliver 75 million acre-feet to lower basin states each rolling 10-year period. In years where more water flows, Colorado is required to deliver a higher percentage of the water to New Mexico, and the same is true for New Mexico in its obligations to Texas. (Texas does not have any obligation to Mexico but the U.S. does.)

In years where flows are lower, a lower percentage of the water is legally required to be delivered to the downstream states. In addition, if Elephant Butte and Caballo Reservoirs have very low storage amounts, Colorado and New Mexico cannot store water in their own reservoirs that were constructed after the date of the compact negotiations, a condition that exists until Elephant Butte and Caballo Reservoirs refill above the restriction level. The Rio Grande Compact apportions water based upon how the river was utilized during the compact study period, 1928 to 1937. A varying percentage of annual volumes of water flowing into the Rio Grande and

Conejos rivers in Colorado must be delivered by Colorado to the New Mexico state line. And New Mexico, in turn, has flow and delivery requirements that determine how much water it must deliver to the downstream Rio Grande Project at Elephant Butte Reservoir. The compact envisions a “normal release” of 790,000 acre-feet per year from Elephant Butte Reservoir, near Truth or Consequences, New Mexico. That water is delivered to Rio Grande Project lands to irrigate about 160,000 acres in New Mexico and Texas. It also includes 60,000 acre-feet for Mexico. More than 80 years post-compact, the states continue to work within and rely on the compact to inform other operations. CONTINUED

New Mexico and Texas successfully sued Colorado in 1966, causing Colorado to reexamine the way it delivered water and to carefully manage diversions. Decades later, in 2013, Texas sued New Mexico, alleging that New Mexico’s groundwater pumping in the southern portion of the state was harming Texas’ own Rio Grande supplies. Colorado is also named in the suit, where settlement talks are now underway. One major issue has been the impact of

Rio Grande Basin

groundwater use in Colorado’s San Luis Valley, where models have shown that heavy pumping on big potato farms and elsewhere has hurt flows in the Rio Grande and Conejos, which is the largest tributary to the Rio Grande in Colorado. As a result, in 2015, Colorado approved a community-based program where growers tax themselves and pay fees to use the groundwater. Revenues from taxes and fees are used to retire farmland and reduce pumping. Colorado and New Mexico are in compliance with the compact.

Five things to know about the Rio Grande

1 The river serves Colorado, New Mexico, Texas and Mexico and begins in the San Juan Mountains above Creede, Colo.

2 The river’s waters were first used for irrigation by Native Americans in prehistoric times

Now provides water to some 6 million people

4 Irrigates 200,000 acres of farmland, which produces alfalfa, cotton, vegetables, pecans and grain, for municipalities, tribes, and industry

5 Climate challenges include rising temperatures of 5 to 6 degrees Fahrenheit in the 21st century, highly variable precipitation and decreasing snowpack and runoff from April–July RESOURCES Citizen’s Guide to Colorado’s Interstate Water Compacts https://bit.ly/3i7ShPi U.S. Bureau of Reclamation Rio Grande Basin Fact Sheet https://on.doi.gov/3nIc2zv Rio Grande Compact and Commission Report https://on.doi.gov/3nK5AHZ

Produced by Water Education Colorado, an independent and nonpartisan nonprofit working to ensure Coloradans are informed on water issues, in collaboration with its news initiative, Fresh Water News.