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NMSU Study Shows Multiple Benefits from Acequia Irrigation

ALCALDE?Alfredo Montoya, a grower whose family dates back eight generations in Alcalde, said he feels vindicated by a New Mexico State University study that shows traditional acequia (ditch) irrigation systems provide broad ecological and social benefits to local communities.

Sam Fernald, a New Mexico State University watershed management specialist, measures subsurface water levels and quality near the Alcalde acequia at NMSU's Sustainable Agriculture Science Center. Fernald is studying interaction between surface and groundwater flows along rivers and irrigation canals in northern, central and southern New Mexico. (11/17/2003) (NMSU Agricultural Communications Photo by J. Victor Espinoza)

"The knowledge of how beneficial acequias are has been passed down from generation to generation, but there's been little public recognition of it outside our communities," said Montoya, who is an Alcalde acequia commissioner. "The acequias help keep the countryside lush with vegetation and wildlife, and they help recharge underground water supplies and the Rio Grande. We've always known that, but now there's a scientific study that proves it."

The study, conducted by researchers with NMSU's Agricultural Experiment Station, shows that seepage from acequia irrigation canals replenishes shallow aquifers, contributes to riparian vegetation growth and helps maintain surface water levels downriver, said Sam Fernald, a watershed management specialist directing the research.

"The study is continuing, but we've already confirmed these things," Fernald said. "We now know for sure that acequia seepage creates shallow groundwater flow that benefits aquifers and protects deep groundwater quality while flowing directly back to the river."

The study could have a direct impact on watershed management because state policy-makers and water managers have long discussed lining acequias and other irrigation canals to avoid seepage and channel more water directly to crops, Fernald said.

"There may be benefits to lining some ditches, but if irrigators are getting enough water through their canals, this study suggests it may be better to leave them just the way they are," Fernald said.

The research began in 2001 with funding from NMSU's Water Task Force as part of the Rio Grande Initiative, a joint project with Texas A&M University to study and teach about water conservation and quality along the Rio Grande corridor. The study is documenting interaction between surface and groundwater flows along rivers and irrigation canals in northern, central and southern New Mexico, Fernald said.

The study is most advanced in Alcalde, where Fernald and researchers at NMSU's Sustainable Agriculture Science Center drilled nine wells to measure water flow and quality in three areas: along the acequia, out in the field where crops are and along the river bank. They used 2-inch-wide slotted pipes thrust 20- to 40-feet down. As water ran through the pipes, electronic indicators measured groundwater levels and quality.

"We did find a lot of seepage from the ditches, up to 10 to 12 centimeters per day," Fernald said. "But we also found that the water rapidly seeps into shallow groundwater, and a lot of it flows directly back to the river."

Final measurements are still being analyzed, but over the length of the acequia, about 5 percent of water running through the canals is seeping out and flowing back towards the river, Fernald said. "That doesn't seem like a huge amount a first glance, but add it up over a whole season and that's a lot of water returning to the river," he said.

In addition to recharging aquifers, the shallow subsurface flow from seepage also protects deep groundwater quality by washing away residue from agricultural chemicals, nutrients and salts, Fernald said. And seepage along the acequias provides water for trees, shrubs and pastures to grow in areas far from the river, providing food for wildlife while improving rural aesthetics and land values.

Fernald is now organizing a second research site in Albuquerque, where soil and irrigation systems differ from those in northern New Mexico.

In southern New Mexico, Fernald is studying surface and groundwater flows between the Rio Grande and bosques along the riverbank. Researchers installed 67 wells at a bosque on NMSU's Chihuahuan Desert Rangeland Research Center to measure water level and quality.

"The bosque acts like a riparian sponge that filters and cools the water before flowing back to the river," Fernald said. "That helps downriver users who plan to treat water for drinking, and it benefits fish that need cool water to survive."

In Alcalde, NMSU's Cooperative Extension Service is already disseminating research results.

"This is important, because accurate measurements of return flow to the river and other acequia benefits must be considered when policy-makers evaluate agricultural water use," said Steve Guldan, Alcalde science center superintendent.

Montoya said the research could help growers maintain the traditional acequia system. "It comes at an opportune time when there's fierce competition for water in the state," he said. "It demonstrates that acequias benefit local communities, not just agriculture."