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Texas Agriculture Archive

March 7, 2003

Salvaging the Pecos

By Jorge A. Ramirez

Texas Cooperative Extension Service

The Pecos River stretches more than 300 river miles, starting near the New Mexico border and slowly meandering south and east to empty into the Rio Grande. It is the source of water for agricultural producers all along its basin and around the Amistad Dam area of the Rio Grande.

Recent droughts have taken their toll on the Pecos, a main water source for the lower Rio Grande. But it's also the water-thirsty saltcedar trees along its banks that are drinking the Pecos down, diminishing groundwater supplies and increasing the salinity of both water and soil.

Introduced as an ornamental in the early 1900s and planted for stream bank stabilization in 1925, the saltcedar dominates all native vegetation and has earned a reputation as the most water-hungry plant in Texas. The tree, found across the western half of the United States, is a fixture along all Texas rivers and their tributaries west of Interstate 35.

Dr. Charles R. Hart in Fort Stockton and Dr. Larry White at Texas A&M University, range specialists with Texas Cooperative Extension, are leading efforts to control the saltcedar invasion and restore the potential of the Pecos River.

What kind of difference could eliminating saltcedar make?

After three years' work along 120 miles of the river, Hart estimates that saltcedar control has salvaged more than 36,000 acre-feet of water, just under 12 billion gallons, or roughly enough water to serve a city the size of Lubbock for a year.

And that could be just the beginning. Because each year more saltcedar is controlled, Hart explained, potential water savings in 2003 are estimated to increase to 48,000 acre-feet, or 16 billion gallons per year.

Using helicopters, satellite guidance and other technology to minimize drift, Hart's crews apply a slow-acting herbicide annually in September, and, by the following spring, more than 90 percent of the saltcedar trees die of root kill. The chemical, Arsenal, is a herbicide that is not toxic to animals.

Approximately 6,300 acres of saltcedar have been treated. The entire spray project encompasses nearly one-third of the river's length in Texas plus the Red Bluff Lake area on the New Mexico border and portions of some Pecos tributaries.

The research team has been able to estimate water consumption of saltcedar trees by measuring hourly groundwater levels taken from shallow wells dug close to the river bank in the cedar zone.

Readings are taken with precision data loggers that record the tiny fluctuations in the water level every minute. Typically, water levels drop during the day as trees use water.

Each river mile averages 30 acres of saltcedar, with a density of about 200 plants of different sizes per acre.

"Our research shows that when you add it up, conservatively, one acre of saltcedar uses about 7.7 acre-feet of water annually, or 2.5 million gallons," Hart said. "Each tree along the Pecos uses about 14,000 gallons annually, or 78 gallons per tree per day over the tree's 180-day growing season."

After three years of spray treatments, no major reinvasion has been seen. Assuming a mere three-year treatment life, the project has cost $8 per acre-foot of water salvaged. This approaches one-tenth the cost of comparable untreated water sold by two Central Texas water authorities.

Saltcedar also pumps salts from the ground, through the plant, and deposits them on the soil surface. These salts contaminate the soil and eventually move into the river.

To monitor changes in salinity, 10 river water samples are taken annually over 120 miles starting around Red Bluff Lake near the New Mexico border.

"Before the treatments," Hart said, "we found that salinity doubles by the time the river travels that 120 miles. But after three years of treatment, the salinity is controlled and no longer doubles."

One of the benefits is that salts are flushed from the river banks, and native grasses start recovering the second year. By the third year, the river banks are awash in a sea of green grasses, forbs and shrubs, the original flora of the area.

J.W. Thrasher, Texas commissioner for the Pecos River Compact Commission, which governs water use along the river, said the treatment program has been very successful.

"Water will be more available for irrigation," he said, "and cattle will have more access to the river with better vegetation for grazing."

Tom Nance, a Ward County farmer active on water improvement and irrigation district boards, said he was most impressed with the high kill rate of saltcedar. He noted that because of the drought of the past 10 to 12 years, it has been difficult to see an effect on water availability yet.

Hart and White work with the Pecos River Ecosystem Project group, composed of state and federal agencies, irrigation districts and water systems in the region. It was organized in 1997 to address ways to control saltcedar.

Funding for the project, administered locally by the Upper Pecos Soil and Water Conservation District, has been provided by area water and irrigation districts and a $1 million grant from the Texas Department of Agriculture.

Additional research funds are provided through the federally funded Rio Grande Basin Initiative, administered by the Texas Water Resources Institute.

The initial phase of the treatment is targeted for a 2004 finish, with a second phase starting in 2006-07 dedicated to pretreatment debris removal.

Until recently, Texas was the only state dealing with saltcedar issues through spraying. But new spraying technology, know-how borrowed from the forest industry, has sparked interest in similar programs, Hart said.

"Now New Mexico has invested $2.5 million into treatment as a result of our work, and other states are interested," he said.

Also in the works are plans to treat the Rio Grande and Colorado rivers in Texas. Monitoring wells are already in place to estimate the potential for water salvage in both river systems.

If funding is approved, Hart said, the first target area on the Rio Grande is from Fort Quitman to Presidio.

The Colorado River has an estimated 21,000 acres of saltcedar that, if treated, he said, could mean a savings of 128,000 acre-feet of water every year.

But it's difficult to estimate the water savings potential if saltcedar were removed from most Texas rivers and tributaries.

"We don't know the total acreage involved," Hart said. "This is a moving target, because saltcedar establishes itself in new areas along rivers several miles downstream each year.

"Controlling the waste of water by the invasive saltcedar plant is an important part of meeting Texas's water needs in the future," he added. "It may be a small part of the overall water plan for the state, but every drop counts."