Basic Concepts and Theory
Most hydrogeologists and engineers concerned about the vadose zone are typically faced with some aspect of characterizing or monitoring it. Any rationale for characterizing and monitoring in the vadose zone must be based upon fundamental concepts governing vadose zone processes and theory of flow and transport. In many instances, the motivation for vadose zone characterization is to provide quantitative information and parameters to make predictions with mathematical models. The osmotic component takes account of the chemical concentration differences that may influence the energy state of the water. Examples of semipermeable membranes include the air-water interfaces within porewater and the Casparian strip in plant roots. Gradients in the temperature potential also cause soil water to move from areas of high temperature to areas of low temperature. The hydraulic gradient in the vadose zone exhibits interesting characteristics that contrast markedly with those that hydrogeologists are accustomed to in aquifers.