While few people in Santa Fe think much about what happens at Elephant Butte Reservoir, their water is involved.

An interstate stream compact signed more than 70 years ago, ensuring that Rio Grande water reaches all the way to Texas, affects everyone along the river, especially when there isn't much water to share. About 75 percent of the city's two municipal reservoirs fall under the mandates of the 1938 Rio Grande Compact, according to Santa Fe City Manager Robert Romero.

Battles over Rio Grande water started when New Mexico was still a territory and the prime concern was controlling floods and developing farms. Growing food, not cities, was the big concern.

Dividing a river

Congress in 1902 formed a precursor to the Bureau of Reclamation and charged the agency with developing massive water projects and encouraging Western development. The Rio Grande Project, built a few years later, helped store and deliver river water to 88,000 acres of farmland in New Mexico and 67,000 acres of land around El Paso through Elephant Butte and Caballo reservoirs.

Colorado, New Mexico and Texas were already at odds over how much water each state should get from the Rio Grande. In 1938, the three signed an interstate agreement, the Rio Grande Compact, to divide the water each year. Mexico was added later. A three-person commission meets each year to determine how much water each state will get from the river. In one of those odd twists, under the compact Southern New Mexico farmers answer to the Texas commissioner because they are part of the Rio Grande Project.

In good years, when there's plenty of water, New Mexico can build up a water credit under the compact. In bad years, the state can use these "relinquishment credits" to meet its obligations to Texas and keep some water flowing to New Mexicans.

The water New Mexico has to deliver to Rio Grande Project farmers in Southern New Mexico and Texas under the compact is measured at the Otowi Gauge, between Pojoaque and Santa Fe. The water flowing past that gauge is completely dependent on the snowmelt, streams and springs flowing down from nearby mountains.

Meeting the compact obligations is so important that if the water levels at Elephant Butte fall too low, Santa Fe and other upstream users can't store more water in their reservoirs.

And meeting those obligations to downstream irrigators is increasingly difficult with uncertain water rights still unsettled, endangered species that need water and the still-unfolding impacts of climate change.

Managing a water account

The Rio Grande water for Elephant Butte Irrigation District and El Paso farmers is stored at Elephant Butte until it's needed, like a massive bank account just waiting for drawdowns. When a lot of water flows past the Otowi Gauge and Elephant Butte fills up, New Mexico ends up with a credit in its water account. Only the Rio Grande Compact Commission, which includes New Mexico State Engineer John D'Antonio, can decide how to use that credit.

The Elephant Butte Irrigation District and El Paso farmers get what's left in Elephant Butte after the Rio Grande Compact credit water and a few other water rights are subtracted. Every January, the Bureau of Reclamation tells the farmers how much water is available from Elephant Butte. If they're lucky, which they weren't this year, spring and summer rains help farmers leave water in their Elephant Butte account.

Until the 2008 agreement between irrigators and the Bureau of Reclamation, Elephant Butte Irrigation District farmers received 57 percent of the Rio Grande Project water.
El Paso received 43 percent.

Then the Bureau of Reclamation changed the water accounting through the agreement with the two irrigation districts. Now New Mexico's top water manager, D'Antonio, says Southern New Mexico farmers are getting a lot less water.

Managing a reservoir

Farmers order water for their fields and orchards as they need it, drawing down their water accounts. The Bureau of Reclamation releases the water from Elephant Butte to meet the orders.

For decades, water that the Elephant Butte Irrigation District or El Paso farmers didn't use went into an unused pool to be divided up again the next year. That scheme was good for New Mexico's farmers, who tended to use up all their water each year, said Phil King, associate professor of civil engineering at New Mexico State University and a consultant to the district. It wasn't such a good deal for El Paso farmers.

In addition, the Rio Grande Compact only covers river water, and didn't contemplate the huge growth in irrigation wells and groundwater pumping that's occurred over the last 50 years. Elephant Butte Irrigation District farmers, especially pecan growers, rely on those wells in dry times.

It turns out, pumping groundwater affects river flows. The more aquifers decline, the lower the flows in the Rio Grande and the harder it is for New Mexico to meet its water obligations to Texas.

Under the 2008 agreement, Southern New Mexico farmers can keep pumping their wells when they don't have irrigation water from the reservoirs. But the more they pump, the more it affects flows to the river, contend state engineer staff.

Contact Staci Matlock at 986-3055 or smatlock@sfnewmexican.com.