HR: 14:25h
AN: H23I-04    [Abstracts]
TI: Calculation of Aquifer Parameter and Sensitivity Values Using Both Analytical and Numerical Solutions in an Aquifer Test in Duval County, Florida
AU: * Sepulveda, N
EM: nsepul@usgs.gov
AF: U. S. Geological Survey, 224 W. Central Parkway Suite 1006, Altamonte Springs, FL 32714-2545 United States
AB: An aquifer test conducted in Duval County, Florida in 2004 was analyzed by using both numerical and analytical solutions. Analytical expressions for the drawdown in the Upper Floridan aquifer and confining units were developed for the aquifer-well configuration where the production well of finite diameter discharges at a constant rate and fully penetrates the aquifer. The aquifer is overlain and underlain by confining units having uniform values of vertical hydraulic conductivity, thickness, and specific storage, both spatially and temporally. Drawdowns calculated from the analytical expressions were verified with a solution by Moench (1985, Water Resources Research, vol. 21, no. 8, p. 1121-1131) based on the numerical inversion of the appropriate Laplace transforms. Hydraulic properties of the Upper Floridan aquifer and adjacent confining units were estimated by the inverse solution of analytical and numerical solutions. Numerical solutions were calculated by using a finite-difference solution of the ground-water flow equation (MODFLOW). Unweighted differences between predicted and measured drawdown were squared and summed in the objective function, which was minimized with a Levenberg-Marquardt algorithm. Hydraulic parameter sensitivity values were calculated by using both analytical and numerical methods. No meaningful changes in optimal values between numerical and analytical models were noted for hydraulic parameters with large relative sensitivities. Relative sensitivities of the overlying confining unit, computed from MODFLOW, were about half the values calculated from the analytical expressions. Optimal parameter values derived for the overlying confining unit from the numerical model were off by a factor of about two when compared to the values derived from the analytical model.
DE: 1828 Groundwater hydraulics
DE: 1829 Groundwater hydrology
DE: 1846 Model calibration (3333)
DE: 1849 Numerical approximations and analysis
SC: Hydrology [H]
MN: Fall Meeting 2005