A&M study: Irrigation not only factor in groundwater depletion

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It’s no secret groundwater levels have declined across the state over the past eight decades, and that the primary reason was the onset of irrigation in agriculture and population growth. But a recent Texas A&M AgriLife Research study has identified other factors having an impact.

The study was conducted because by 2060 the state’s population is expected to double, increasing the demand for water at a time when the existing water supply is expected to be reduced by about 10 percent.

AgriLife Research scientists wanted to know which areas of the state are more vulnerable to water shortages in order to plan and implement strategies to deal with water level declines.

Scientists at the Vernon AgriLife Research center utilized the boundaries of the Texas Water Development Board’s designated Groundwater Management Areas, or GMAs, for their assessment. The 16 GMAs, with boundaries identified in response to legislation passed in 2001, included all major and minor aquifers in the state. The objective behind GMA identification was to delineate areas considered suitable for management of groundwater resources.

Statewide, the number of counties with deeper median water levels, a water-level depth below 328 feet, increased from two to 13 between 1930s and 2000s. At the same time, there was a decrease in the number of counties, from 134 to 113, having shallower median water-levels or groundwater located within 82 feet of the ground surface.

“We know irrigated agriculture is the major cause of depletion in the Texas Panhandle, as compared to increasing urbanization in North Central Texas,” said Chaudhuri, former post-doctoral research associate at Vernon. “We saw a significant drop in median groundwater levels in irrigation wells from 75 to 180 feet between the 1940s and 1950s in the Texas Panhandle, coinciding with the irrigation of widespread irrigated agricultural practices.”

But he said they knew there was more to the decline than just these uses, because “unused” wells monitored across the state throughout the decades were also showing varying levels of decline. That was when they studied groundwater and surface-water use patterns, soil characteristics, geology and land cover types to better understand the water-level changes in Texas.

For instance, the South Plains and Panhandle were equally involved in agriculture and irrigated crops over the Ogallala Aquifer. However, the sandier soils of the South Plains allow more infiltration and recharge than the tighter clay soils of the Panhandle.

In addition to population growth in North Central Texas, the high clay content in soils coupled with shale/claystone type geology and more land area covered by highways and parking lots have lowered the amount of recharge, thus contributing to the decline in water levels.

There is a brighter note. The trends observed over the decades show the water-level declines are leveling off recently in some parts of the state, including North Central Texas, suggesting a recovery from historical drawdown due to implementation of conservation and regulatory strategies.

The leveling off of the decline has been seen in the past decade after the implementation of the GMAs and the guidelines and regulations that were established with them. Increased use of surface water and assessment of water levels are some measures being utilized to address groundwater depletion issues in the Houston and Dallas areas.

However, these voluntary conservation or regulatory strategies have resulted in a variable pattern of recovery in ambient water-levels, which are still occurring frequently at deeper depths in the hot spots and thus warrant further investigation.

Over the course of the study, the need for more spatially intensive and frequent water-level monitoring has been realized. In addition, further investigation of aquifer-specific influences such as groundwater recharge and flow paths, human dimensions on water-level fluctuations and climate are warranted.

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Missy Hodgin

Missy Hodgin serves as the agriculture extension agent for Clay County, Texas. the mission of the Texas A&M AgriLife Extension Service to serve Texans through community-based education.

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