Where Is Salvaged Water Going?
Examining the Effects of Saltcedar Control on the Pecos River
By April Smith
The Pecos River Ecosystem Project has consisted of aerial herbicide treatment to more than 10,000 acres of saltcedar. For every acre treated, it is estimated to salvage between three and five acre-feet of water per year. Research is ongoing, and there are still more than 200 river miles to be treated. If the river reclaims much of its water supply, where would all of this water flow?
“We want to find out where the salvaged water is going, and determine the impacts of saltcedar control on the Pecos River,” said Alyson McDonald, a doctorate student at Texas A&M University and a hydrology assistant with Texas Cooperative Extension at Fort Stockton.
In the past year, McDonald has been conducting borehole explorations to examine soil characteristics, which will determine spatial variability in hydrological properties. Six new monitoring wells equipped with water level sensors and loggers have been established near the Pecos River, adjacent to areas where saltcedar was treated and untreated, in order to better understand subsurface flow regimes.
Multiple water releases from Red Bluff Reservoir will be scheduled beginning this summer to detect seasonal changes in the shallow aquifer’s response to saltcedar control. A team including McDonald and Dr. Charles Hart, Associate Professor and Extension Range Specialist, will use data from seepage runs and monitoring wells to calculate a water balance, which includes water inputs and water losses.
These measurements will establish a relationship between ground and surface water. McDonald and the rest of the team will use this data to make a subsurface flow net, a map that shows seepage patterns.
According to McDonald, patterns in water flow and soil stratigraphy are apparent in data collected through 2003. The total water loss, including evapotranspiration, is dependent on the depth to the water table. There is also the presence of a clay layer throughout the area about 10 feet below the soil surface. McDonald said the team should be able to map this clay layer, making water measurement easier if there is limited percolation through this layer.
“We hope to create a model useful for other arid or semiarid regions to evaluate the efficacy of saltcedar control, and whether it can be used to meet their goals,” said McDonald.
McDonald received a grant from TWRI, funded by the U.S. Geological Survey, providing for the purchase of water-monitoring equipment for use in this study.
“The average Texan should view this project as an important component of local water management plans to meet future needs,” said McDonald. “We’re not finding a new source; we’re just manipulating the water balance to meet future needs.”
