Hydraulic Properties of the Carrizo-Wilcox Aquifer in Texas...

Use of groundwater-flow models for prediction of future availability of water resources is standard practice. Having accurate hydraulic parameters for input into groundwater-flow models is critical to the generation of realistic local and regional water-resource management plans. Transmissivity, hydraulic conductivity, and storativity are some of the important parameters needed for developing numerical groundwater-flow models. These hydraulic parameters provide information on how easily water flows through an aquifer, how much water is stored in an aquifer, and how rapidly an aquifer responds to pumping and recharge. The Carrizo-Wilcox aquifer is a major Texas aquifer that is utilized widely by domestic and industrial users in 60 Texas counties between the Rio Grande and the Sabine River. The entire aquifer occurs along a 50- to 100-mi-wide band, which lies inland approximately 100 mi and parallel to the Gulf of Mexico in Texas, Arkansas, and Louisiana. To date, references to Carrizo-Wilcox aquifer hydraulic properties are scattered among various State and public documents, including those of the Texas Water Development Board (TWDB), the Texas Commission on Environmental Quality (TCEQ), and the Railroad Commission of Texas (RRC), among others. Herein we have compiled and statistically analyzed transmissivity, hydraulic-conductivity, and storativity values from numerous sources of data for the entire Carrizo-Wilcox aquifer in Texas. Results include a database of 7,402 estimates of hydraulic properties in 4,456 wells. The database shows that transmissivity of the Carrizo-Wilcox aquifer ranges from 0.1 to 10,000 ft2/d and has a geometric mean value of 300 ft2/d and that hydraulic conductivity ranges from 0.01 to 4,000 ft/d and has a geometric mean value of 6 ft/d. Transmissivity and hydraulic conductivity results for all hydraulic tests in the Carrizo-Wilcox aquifer are lognormally distributed. Transmissivity and hydraulic conductivity vary spatially, both vertically and areally, in the Carrizo-Wilcox aquifer. Geologic units composing the aquifer are the Simsboro and Calvert Bluff Formations of the Wilcox Group and the unconformably overlying Carrizo Sand. The Simsboro Formation and Carrizo Sand portions of the Carrizo-Wilcox aquifer have transmissivity and hydraulic-conductivity values that are 2.5 to 11 times higher and 2 to 6 times higher, respectively, than those of lower permeability units of the aquifer. Semivariograms show that transmissivity and hydraulic-conductivity values in the Carrizo Sand and undivided Wilcox Group are spatially correlated over about 17 and 25 mi, respectively. Large nuggets in the semivariograms suggest local-scale heterogeneity and measurement errors. Kriged maps of transmissivity and hydraulic conductivity show the greatest values for the Carrizo Sand in the Winter Garden area of South Texas. Highest values of transmissivity and hydraulic conductivity for the undivided Wilcox Group occur in the south-central and northeast parts of the aquifer. Storativity and specific storage values approximate lognormal distributions. Storativity ranges from about 10-6 to 10-1, with a geometric mean of 3.0 x 10-4. Specific storage ranges from about 10-7 to 10-3 ft-1, with a geometric mean of 4.5 x 10-6 ft-1. Higher values of storativity and specific storage tend to occur at shallow depths, where the aquifer is unconfined.
Robert E. Mace
Rebecca C. Smyth

Mace, R. E., and Smyth, R. C., 2003, Hydraulic Properties of the Carrizo-Wilcox Aquifer in Texas: Information for Groundwater Modeling, Planning, and Management: The University of Texas at Austin, Bureau of Economic Geology, Report of Investigations No. 269, 40 p.

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The University of Texas at Austin, Bureau of Economic Geology
Report of Investigation

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