### Ground-water geology of Edwards County, Texas

By: Archie T. Long

                            https://doi.org/10.3133/wsp1619J

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#### Abstract

Edwards County occupies 2,075 square miles of the southern part of the Edwards Plateau in southwest Texas. In 1950 it had a population of 2,908. Its thin limestone soil supports the characteristic flora of a semiarid region. The county is underlain by nearly flat-lying beds of limestone and a few beds of shale and marl.

The Glen Rose limestone of Cretaceous age, the oldest formation tapped by water wells in the county, yields small quantities of rather highly mineralized water. Springs in the Glen Rose discharge water that is generally less mineralized than that from wells. Nearly all the wells and springs tapping the Glen Rose are in the southeastern part of the county, where the Edwards and associated limestones have been removed by erosion or are very thin.

The Comanche Peak, Edwards, and Georgetown limestones, collectively called the Edwards and associated limestones, underlie most of the county and form the principal aquifer. Generally, the water in the Edwards is under water-table conditions, but locally it may be artesian. The Edwards and associated limestones yield small to moderate quantities of water that is hard but otherwise of good chemical quality.

The alluvium in the major stream valleys yields small to moderate quantities of hard water similar in quality to that of the Edwards and associated limestones.

The main ground-water divides in the Edwards and associated limestones follow the topographic divides. Most of the ground water flows southward and either appears as springflow in the Nueces River drainage or flows underground into Kinney or Val Verde County. The remainder flows northward and ultimately appears as springflow in the South Llano River drainage.

About 150,000 acre-feet of water is recharged annually to and discharged from the Edwards and associated limestones in Edwards County. Most of this water is available for additional development inasmuch as only about 900 acre-feet per year is currently being used; however, additional development of ground water will result in a reduction in streamflow.

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