EVALUATION OF TWO MODELS DESCRIBING THE STEADY DISCHARGE FROM A CONSTANT HEAD WELL PERMEAMETER INTO UNSATURATED SOIL

Abstract

This article evaluates two approximate analytical models, viz, model-Philip and model-Guelph, that describe the steady outflow from a constant-head-well permeameter into an unsaturated soil. The two models recognize the existence of a saturated zone around the borehole and consider the combined influence of the saturated-unsaturated soil on the steady outflow from the well. The two models yield an analogous relation between the steady discharge (Qt), the field-saturated hydraulic conductivity (Kfs), and the matric flux potential (φm) or the sorptive number (α), with only the coefficients differing from each other. For a special range of steady discharge ratios, model-Philip yields a larger Kfs value than model-Guelph. The two models yield nearly equal φm values. The lower and upper boundaries of this special discharge ratio range arise from the fact that Kts, and φm are both necessarily positive. Seemingly negative values of Kfs, or φm can be explained by the fact that most soils are heterogeneous and/or anisotropic. Model-Philip leads to somewhat larger errors introduced by disregarding flow in the unsaturated zone than does model-Guelph. For both models these errors decrease as the ponded water level increases or as capillarity decreases. © Williams & Wilkins 1990. All Rights Reserved.