Vadose Zone Permeability Tests: Steady State Results

Free surface and saturated-unsaturated flow models are applied to the problem of constant head borehole infiltrat1on tests for determining saturated hydraulic conductivity above a water table. The free surface model follows the same general approach employed to develop analytical solutions, but this model does not suffer from some of the many simplifying assumptions regarding boundary conditions. Nonetheless, the results of steady state simulations with the free surface model agree rather well with the analytical solutions. The free surface approach provides a distorted view of the infiltration process. Saturated-unsaturated models used to simulate quasi-steady state conditions indicated that only a small volume of soil in the vicinity of the borehole is completely saturated with water. Based on saturated-unsaturated simulations in four different homogeneous, isotropic soils, an empirical solution is developed for deep water table conditions to estimate saturated hydraulic conductivity with improved accuracy. Due to the effects of borehole geometry unsaturated soil characteristics, water table depth, heterogeneity, and anisotropy, it is extremely difficult to develop a completely general formula.