Seasonal water-level perturbations beneath the high plains of the Llano Estacado

• Published in: Journal of hydrology. Regional studies 2018-08, Vol.18, p.1-14
• Main Author: Stout, John E.
• Format: Article
• Language: English
• Subjects: Depth to water; Groundwater; Ogallala Aquifer; Saturated thickness; Water table
• ISSN: 2214-5818; 2214-5818
• DOI: 10.1016/j.ejrh.2018.04.009

•A method for computing water-level perturbation curves was developed.•Water-level perturbations are defined as deviations from a nonstationary mean water level.•Perturbation curves follow seasonal patterns of high water levels in winter and low levels during the growing season.•This technique provides insight into how the collective actions of farmers affect the Ogallala Aquifer. The Llano Estacado is a vast elevated plain located at the southern end of the Great Plains of North America. The Llano Estacado region is favorably situated above the southernmost extension of the Ogallala Aquifer, which provides groundwater for a highly productive irrigated agricultural system. A method was developed to compute the average deviation of the groundwater level from a nonstationary annual-average water level. Groundwater is pumped from the Ogallala Aquifer during each growing season, which induces seasonal and long-term changes in observed groundwater levels. Recorder wells, maintained by the Texas Water Development Board, track these changes and provide a wealth of hydrologic data. Of special interest here are seasonal water-level perturbations induced by nearby actively pumped wells. Groundwater levels are observed to follow a regular pattern of declining water levels during the growing season followed by a recovery after irrigation systems are shut down. In areas with limited groundwater, farmers may shut off irrigation systems when soil moisture is adequate or when the supply of available water becomes critically low. As a result, one can often detect periods during the growing season when irrigation is paused and the water table is allowed time to partially recover. Such hydrographic deviations appear to correlate closely with periods of abundant rainfall. In areas where groundwater supplies are more plentiful, irrigation breaks are less evident. This suggests that farmers with adequate groundwater may be less inclined to shutdown irrigation systems to conserve water despite adequate rainfall.