Sensitivity analysis of aquifer parameter estimations based on the Laplace equation with linearized boundary conditions

Abstract

Estimates of aquifer parameters, saturated hydraulic conductivity, and drainable porosity were obtained by an analytical solution of the two-dimensional Laplace equation with linearized boundary conditions and were compared to prescribed parameters in a finite element model that simulated drainage of a coupled system of unsaturated/saturated flow. Boundary conditions prerequisite for the analytical solution were systematically relaxed during numerical experiments to see how the resulting aquifer-parameter estimates deteriorate if (1) correct aquifer geometry values are used and (2) aquifer geometry is imprecisely estimated. Sensitivity of aquifer parameter estimation to imprecise saturated thickness and groundwater profile information was also performed at the watershed scale. The analysis supports the robustness of the saturated hydraulic conductivity and drainable porosity estimates in all cases considered, at both field and catchment scales, with the only exception being the drainable porosity for sand where a significant flux-exchange between the vadose and phreatic zones during drawdown results in both modeled and estimated effective drainable porosities significantly larger than traditionally expected.