Unsaturated Flow Modeling—Exact Solution to Approximate Problem?

Abstract

Unsaturated flow models are increasingly being used in ground‐water quantity/quality studies to predict recharges due to rainfall. This paper presents a critical examination of the current practice of using numerical models in light of the approximate nature of problem identification. Three issues are addressed: (1) Sophistication of models; (2) specification of boundary conditions; and (3) selection of hydrogeological properties. To systematically study these issues, two ground‐water models are used, a simple lumped parameter model and the numerical model, UNSAT1. The models are applied to two hypothetical unsaturated domains as well as to a field site where extensive monitoring of ground‐water conditions is reported in literature. The results indicate that, in the case of spatially homogeneous soil profiles, errors in recharge predictions due to improper problem identification are more significant than those due to model simplification. The study exemplifies the importance of problem identification in modeling studies.