Vadose zone

About: Vadose zone is a research topic. Over the lifetime, 5781 publications have been published within this topic receiving 130825 citations. The topic is also known as: unsaturated zone.

Using groundwater levels to estimate recharge

Abstract: Accurate estimation of groundwater recharge is extremely important for proper management of groundwater systems. Many different approaches exist for estimating recharge. This paper presents a review of methods that are based on groundwater-level data. The water-table fluctuation method may be the most widely used technique for estimating recharge; it requires knowledge of specific yield and changes in water levels over time. Advantages of this approach include its simplicity and an insensitivity to the mechanism by which water moves through the unsaturated zone. Uncertainty in estimates generated by this method relate to the limited accuracy with which specific yield can be determined and to the extent to which assumptions inherent in the method are valid. Other methods that use water levels (mostly based on the Darcy equation) are also described. The theory underlying the methods is explained. Examples from the literature are used to illustrate applications of the different methods.

Review and comparison of models for describing non-equilibrium and preferential flow and transport in the vadose zone

Abstract: In this paper, we review various approaches for modeling preferential and non-equilibrium flow and transport in the vadose zone. Existing approaches differ in terms of their underlying assumptions and complexity. They range from relatively simplistic models to more complex physically based dual-porosity, dual-permeability, and multi-region type models. A relatively simple dual-porosity flow model results when the Richards equation is combined with composite (double-hump type) equations for the hydraulic properties to account for both soil textural (matrix) and soil structural (fractures, macropores, peds) effects on flow. The simplest non-equilibrium flow model, a single-porosity model which distinguishes between actual and equilibrium water contents, is based on a formulation by Ross and Smettem [Soil Sci. Soc. Am. J. 64 (2000) 1926] that requires only one additional parameter to account for non-equilibrium. A more complex dual-porosity, mobile–immobile water flow model results when the Richards or kinematic wave equations are used for flow in the fractures, and immobile water is assumed to exist in the matrix. We also discuss various dual-permeability models, including the formulation of Gerke and van Genuchten [Water Resour. Res. 29 (1993a) 305] and the kinematic wave approach as used in the MACRO model of Jarvis [Technical Description and Sample Simulations, Department of Soil Science, Swedish University of Agricultural Science, Uppsala, Sweden (1994) 51]. Both of these models invoke terms accounting for the exchange of water and solutes between the matrix and the fractures. Advantages and disadvantages of the different models are discussed, and the need for inter-code comparison is stressed, especially against field data that are sufficiently comprehensive to allow calibration/validation of the more complex models and to distinguish between alternative modeling concepts. Several examples and comparisons of equilibrium and various non-equilibrium flow and transport models are also provided.

Drastic: A Standardized System to Evaluate Groundwater Pollution Potential using Hydrogeologic Setting

Abstract: DRASTIC is a methodology which allows the pollution potential of any area to be systematically evaluated. The system optimizes the use of existing data and has two major portions: the designation of mappable units, termed hydrogeologic settings, and the superposition of a relative ranking system called DRASTIC. Hydrogeologic settings incorporate the major hydrogeologic factors which are used to infer the potential for to enter groundwater. These factors form the acronym DRASTIC and include depth to water, net recharge, aquifer media, soil media, topography, impact of the vadose zone and hydraulic conductivity of the aquifer. The relative ranking scheme uses a combination of weights and ratings to produce a numerical value, called the DRASTIC Index which helps prioritize areas with respect to pollution potential.

Applied contaminant transport modeling

Abstract: Preface. Preface to the First Edition. 1. Introduction. PART 1: CONCEPTS AND TECHNIQUES. 2. Darcy's Law and Advective Transport. 3. Dispersive Transport and Mass Transfer. 4. Transport with Chemical Reactions. 5. Mathematical Model and Analytical Solutions. 6. Simulation of Advective Transport. 7. Simulation of Advective-Dispersive Transport. 8. Simulation of Nonequilibrium Processes and Reactive Transport. PART 2: FIELD APPLICATIONS. 9. A Framework for Model Applications. 10. Building a Contaminant Transport Model. 11. Model Input Parameters. 12. Model Calibration and Sensitivity Analysis. 13. Dealing with Uncertainty. 14. Contaminant Transport Modeling: Case Studies. PART 3: ADVANCED TOPICS. 15. Simulation of Density-Dependent Flow and Transport. 16. Simulation of Flow and Transport in the Vadose Zone. 17. Optimal Management of Groundwater Quality. Appendix A: Darcy's Law and the Variable-Density Flow Equation. Appendix B: Application of Stream Functions to Groundwater Flows. Appendix C: Information on Groundwater Modeling Software. References. Index.