Transmissivity, Hydraulic Conductivity, and Storativity of the Carrizo-Wilcox Aquifer in Texas

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2000

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Transmissivity, hydraulic conductivity, and storativity are crucial parameters for developing local and regional water plans and numerical groundwater flow models to predict the future availability of the water resource. To support this effort, we compiled and analyzed transmissivity, hydraulic conductivity, and storativity values from various sources for the entire Carrizo-Wilcox aquifer in Texas, resulting in a database of 7,402 estimates of hydraulic properties in 4,456 wells. Transmissivity and hydraulic conductivity results for all tests in the Carrizo-Wilcox aquifer follow a log-normal distribution. Transmissivity ranges from about 0.1 to 10,000 ft^2/day and has a geometric mean value of about 300 ft^2/day, while hydraulic conductivity ranges from about 0.01 to 4,000 ft/day and has a geometric mean value of about 6 ft/day. Transmissivity and hydraulic conductivity vary spatially, both vertically and laterally, within the Carrizo-Wilcox aquifer. The Simsboro Formation and Carrizo Sand portions of the aquifer exhibit transmissivity and hydraulic conductivity values that are 2.5 to 11 times higher and 2 to 6 times higher, respectively, than those of the Cypress aquifer, Calvert Bluff Formation, and undivided Wilcox Group.

Semivariograms demonstrate that transmissivity and hydraulic conductivity values in the Carrizo Sand and undivided Wilcox Group are spatially correlated over distances of about 17 and 25 miles, respectively. Large nuggets in the semivariograms suggest local-scale heterogeneity and measurement errors. Kriged maps of transmissivity and hydraulic conductivity reveal the highest values for the Carrizo Sand in the Winter Garden area and the greatest values for the Wilcox Group in the south-central and northeast parts of the aquifer. Storativity and specific storage values exhibit approximately log-normal distributions. Storativity ranges from about 10^-6 to 10^-1 with a geometric mean of 3.0 x 10^-4, while specific storage ranges from about 10^-7 to 10^-3 with a geometric mean of 4.5 x 10^-6. Lower values of storativity and specific storage tend to occur at shallow depths where the aquifer is unconfined.

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