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July 2009 cover image Hamilton Pool

Rio Grande Watermaster

Divvying up the river’s water for homes, farms and many other interests requires a careful balancing act.

By Eileen Mattei

Unlike the rest of Texas, water rights holders downstream of Amistad Reservoir on the Rio Grande are not assured of water based on the seniority of their rights, the longevity of their claim. Instead, a watermaster controls water allocations along the river from Amistad Dam, north of Del Rio, to the Gulf of Mexico under a complex system that is designed to apportion water first for municipal uses. While other uses, such as industry and mining, get a share of the remaining water, irrigation districts and agricultural users consume most of it. How much they can take in any given year is subject to water availability.

Rio Grande Watermaster Erasmo Yarrito Jr. explains that the Rio Grande’s volume of 1.3 million acre-feet (the average annual yield) is divvied up between 1,600 water rights holders in Texas along the 1,172 river miles under his jurisdiction. International politics complicate the situation: A 1944 Mexico-U.S. treaty apportioned water rights along the international boundary. While the U.S. has legal rights to 58 percent of the river, Mexican watershed dams sometimes retain water destined for American use.

Now a division of the Texas Commission on Environmental Quality, the Rio Grande Watermaster Program evolved after the 1950s droughts resulted in people with “older” rights at the east end of the Rio Grande receiving no water once upstream holders had legally diverted their water. The program, which began operating in 1971, covers 17 counties and extends west to Ft. Quitman, although rights upstream of Amistad follow seniority. No unclaimed water rights exist on the river.

Each month the watermaster re-establishes a municipal reserve of U.S. waters in Amistad and Falcon reservoirs of 225,000 acre-feet, the equivalent of one year’s average diversions for all municipal demands downstream from Amistad Dam. If the reservoirs have more than that amount, the watermaster divides the surplus among the non-municipal claimants. This quantity is called storage balance and accumulates up to the amount of the assigned water rights. Rights holders withdraw from their usable balance, which is their storage account water allotted the previous year.

“The usable balance is much like a checking account: if you have it, it’s your decision when to use it,” Yarrito said. Along the Rio Grande, though, it’s more complicated than starting up a pump. Water has to be booked days in advance to give the ordered volume time to travel downstream to its destination.

“Folks realize that this is a unique situation. The watermaster system protects everybody’s water rights,” Yarrito explained. To assure compliance, six watermaster specialists perform 24,000 yearly inspections from Ft. Quitman to Boca Chica Beach.

With reservoirs full this year, Yarrito foresees no immediate restrictions on water use, unlike extreme drought years when some farms and ranches were left high and dry. The program has proven itself a workable method for managing a finite resource, but does not consider environmental flow needs.

A separate watermaster program monitors rights on the Guadalupe, Lavaca, San Antonio, Concho and Nueces rivers but does not control water use. Other functions of the program include sequencing diversions, answering complaints, and following up with enforcement actions, if needed.

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