| A regional equivalent porous medium (EPM) model was developed using available hydrogeologic data for the steeply-dipping karst aquifer of the Northern Shenandoah Valley of West Virginia and Virginia. The model employed uniform recharge and variable hydraulic conductivity (K) distributed at the formation level based on published field-test estimates. Three independent procedures were used for calibration, with the most acceptable approach using calibration to heads at wells and specified fluxes for springs. Although this procedure produced a reasonable regional head distribution and acceptable calibration statistics (mean error = 0.58 m, mean absolute error = 8.61 m), the use of specified fluxes at springs and 100-m grid cells induced unrealistic potentiometric depressions around springs. This model was used in subsequent simulations of anisotropy with the Ky/Kx (strike-parallel/perpendicular) ratio ranging from 2 to 10. Increasing Ky generally reduced regional head gradients and softened the anomalous drawdown at specified flux spring cells. These results suggest that the model could be improved by additional model layers, heterogeneity, and/or anisotropy. |
