Sharing the Rio Grande


The Rio Grande is one long river! It travels 1760 miles through three states and two countries. Starting in the mountains of Colorado, it goes south through New Mexico to El Paso Texas, becomes the border between Mexico and the U.S., and ends its journey at the Gulf of Mexico. On the way, it passes through many communities that use its water for agriculture, and in some cases, for homes or industry. Yet the Rio has always been shallow, and does not carry as much water as many shorter rivers do. It runs through some of the most arid parts of North America, where there is little rainfall to replenish the water and much of it gets lost to evaporation. Finally, the river has historically alternated between flood and drought. Throughout the centuries, the Rio Grande has been an undependable water source for most of its users. Yet the people of the Chihuahuan Desert have always relied on the Rio.

Early Native Americans used the river sparingly, planting crops that were well suited to the climate. They diverted only small amounts of water, and as far as we can tell, had few disagreements about the river. However, from the time of the first Spanish settlements, there were arguments between upstream and downstream users. If an upstream user diverted water from the river for his fields, the downstream user might only get a trickle of water for her crops. During the years between 1600 and 1900, many farmers, both Spanish and Pueblo, brought challenges to the courts, complaining about their upstream neighbors. In addition, the Mexican people were concerned about the small amount of water that was left to them after those to the north had taken what they wanted. A fairer sharing of the Rio Grande waters was needed.


In the early 1900s, many important changes helped to systematize water use. Some of the major events were:

  • 1905: The U.S. Congress passed the first law that directed the allocation of an interstate river. The Rio Grande Project for Southern New Mexico and Texas included the construction of Elephant Butte Dam and Reservoir, and the building or renovation of many diversion dams and ditches.

  • 1906: A treaty was signed that promised Mexico 60,000 acre-feet of water per year from the Rio Grande.

  • 1916: Elephant Butte Dam and Reservoir were completed. The reservoir's capacity is 2,200,000 acre-feet, but it rarely holds that much water. For example, on July 1, 2001, only 1,047,600 acre-feet of water were stored at Elephant Butte. In the 1950s, during the worst drought in recent memory, only 50,000 acre-feet remained in the reservoir!

    Shortly after the project's completion, a survey was taken of the lands that were part of the Rio Grande Project. It was decided that 88,000 acres of farmland in Southern New Mexico and 67,000 acres in Texas would be served by Elephant Butte. The same breakdown is still being used today to allocate the water, although land use has changed dramatically since that time.

  • 1936 -1938: Caballo Dam and Reservoir were completed. Caballo can hold 331,500 acre-feet, but usually contains less. For example, on July 1, 2001, the reservoir held only 72,740 acre-feet of water.

  • 1938: The Rio Grande Compact was signed. It created three regions for water allocation: Colorado, the region of New Mexico above Elephant Butte, and the region below Elephant Butte, including Texas. The same agreement is still in place today.

The Rio Grande Compact was a giant step toward harmony between the river users. Water flows from one area to another are regulated. This is complicated because tributaries are continually adding water to the river, and water is also constantly evaporating. For example, Elephant Butte Reservoir loses between 100,000 and 200,000 acre-feet to evaporation per year; and the Middle Rio Grande Valley actually loses more than it uses for crops!

The Compact attempted to be fair by creating a sliding scale for water allocation, depending on how much water was in the Rio Grande in a given year. The water is measured at gauging stations along its path, with most evaporation being charged to the region in which it occurs. Here are the basics of how the compact works:

  • Water flows are measured at Del Norte in Colorado and at three tributaries. This decides the amount of water to be sent from Colorado to New Mexico.

  • Otowi Station in the Pojoaque Valley of New Mexico has the next measuring gauge. In an average year, 1.1 million acre-feet of water flow by this station. At this flow rate, New Mexico north of Elephant Butte would be allowed to keep 393,000 acre-feet.
However, if the water flow at Otowi were higher or lower than average, the amount to be sent south would be adjusted. New Mexico above Elephant Butte can never keep more than 405,000 acre-feet of this water. But it also gets to use the inflow from tributaries between Otowi and Elephant Butte, which usually amounts to about 100,000 acre-feet.

  • The next gauge is located at San Marcial above Elephant Butte, which measures the flow into Elephant Butte. In an average year, 500,000 acre-feet of water are delivered into Elephant Butte through this station.

  • A maximum of 790,000 acre-feet of water can be released from Elephant Butte and Caballo reservoirs in an irrigation season, to be divided between Texas and Southern New Mexico. If the water in the reservoirs were low, each farmer's quota might be lowered
    .
  • Colorado and New Mexico are allowed to build up water IOUs for years of short supply. But just like your family budget, the amount they can owe is limited.

The Rio Grande Compact has helped to organize the water delivery between the states. However, water shortages are now creating new issues. In the mid 1990s, environmentalists sued to keep enough water in the system for the Rio Grande silvery minnow. Other native fish species had died from poor water conditions in the river, and they wanted to prevent it from happening again. The U.S. Fish and Wildlife Service agreed with the environmentalists, and in 2000 the Bureau of Reclamation released extra water into the Middle Rio Grande to create habitat for the fish. This will continue into the future. In addition, El Paso, Texas wants access to more water for its growing population. And many of the New Mexico Pueblos, who were not included in the negotiations of the original Rio Grande compact, believe they should retain more water rights.

Because almost all the river water is used for agriculture, more efficient irrigation systems, such as drip irrigation, might help relieve some of the water pressure. But ground water and river water are all part of one system, with unused irrigation waters being returned to the ground for municipal use. Therefore, some researchers believe that more efficient irrigation may provide extra flows of river water, but also mean less water under ground. The current problems in the Rio Grande Valley are a reflection of the same issues happening throughout the world. Hydrologists and engineers will likely be working on solutions for a long time to come.