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Lynn J. Torak

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A MODular, Finite-Element digital-computer program (MODFE) was developed to simulate steady or unsteady-state, two-dimensional or axisymmetric ground-water flow. Geometric- and hydrologic-aquifer characteristics in two spatial dimensions are represented by triangular finite elements and linear basis functions; one-dimensional finite elements and linear basis functions represent time. Finite-element matrix equations are solved by the direct symmetric-Doolittle method or the iterative modified, incomplete-Cholesky, conjugate-gradient method. Physical processes that can be represented by the model include (1) confined flow, unconfined flow (using the Dupuit approximation), or a combination of both; (2) leakage through...
Categories: Publication; Types: Citation; Tags: Open-File Report
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Descriptions of the geohydrology, flow-system conceptualization, and stream-aquifer relations are presented based on digital-model analysis. Simulation results are used to assess the basin's water resources for the historical drought of 1986. Potential effects of increased ground-water pumpage on the stream-aquifer system are described and illustrated using detailed water budgets and maps showing the ground-water-level surface and water-level changes caused by simulated pumpage increases during drought conditions.
Categories: Publication; Types: Citation; Tags: Water Supply Paper
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Hydrogeologic data and water-chemistry analyses indicate that Lake Seminole leaks into the Upper Floridan aquifer near Jim Woodruff Lock and Dam, southwestern Georgia and northwestern Florida, and that ground water enters Lake Seminole along upstream reaches of the lake's four impoundment arms (Chattahoochee and Flint Rivers, Spring Creek, and Fishpond Drain). Written accounts by U.S. Army Corps of Engineers geologists during dam construction in the late 1940s and early 1950s, and construction-era photographs, document karst-solution features in the limestone that comprise the lake bottom and foundation rock to the dam, and confirm the hydraulic connection of the lake and aquifer. More than 250 karst features having...
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To determine the effects of seasonal ground-water pumpage for irrigation, a finite-element ground-water flow model was developed for the Upper Floridan aquifer in the lower Flint River Basin area, including adjacent parts of the Chattahoochee and Apalachicola River Basins. The model simulates withdrawal from the aquifer at 3,280 irrigation, municipal, and industrial wells; stream-aquifer flow between the aquifer and 36 area streams; leakage to and from the overlying upper semiconfining unit; regional ground-water flow at the lateral boundaries of the model; and water-table recharge in areas where the aquifer is at or near land surface. Steady-state calibration to drought conditions of October 1999 indicated that...
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Simulation results indicate that ground-water withdrawal in the lower Apalachicola-Chattahoochee-Flint River basin during times of drought could reduce stream-aquifer flow and cause specific stream reaches to go dry. Of the 37 reaches that were studied, 8 reaches ranked highly sensitive to pumpage, 13 reaches ranked medium, and 16 reaches ranked low. Of the eight reaches that ranked high, seven contain at least one federally protected mussel species. Small tributary streams such as Gum, Jones, Muckalee, Spring, and Cooleewahee Creeks would go dry at lower pumping rates than needed to dry up larger streams. Other streams that were ranked high may go dry depending on the amount of upstream flow entering the reach;...
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