Abstract
Abstract Flow in unsaturated porous media is commonly described by the Richards equation. This equation is strongly nonlinear due to interrelationships between water pressure head (negative in unsaturated conditions), water content and hydraulic conductivity. The accuracy of numerical solution of the Richards equation often depends on the method used to estimate average hydraulic conductivity between neighbouring nodes or cells of the numerical grid. The present paper discusses application of the computer simulation code VS2DI to three test problems concerning infiltration into an initially dry medium, using various methods for inter-cell conductivity calculation (arithmetic mean, geometric mean and upstream weighting). It is shown that the influence of the averaging method can be very large for coarse grid, but that it diminishes as cell size decreases. Overall, the arithmetic average produced the most reliable results for coarse grids. Moreover, the difference between results obtained with various methods is a convenient indicator of the adequacy of grid refinement.
Highlights
Numerical modelling tools often are used to simulate flow and transport processes occurring in the vadose zone
Flow modelling tools are typically based on the Richards equation (Richards 1931), which describes water movement in partially saturated porous media and in extended form is suitable for both unsaturated and saturated conditions
The hydraulic characteristics of unsaturated porous medium are given in the form of water retention curve, which represents the relationship between water content and water pressure, and the relative permeability function, which describes the dependence of the relative hydraulic conductivity on pressure or saturation
Summary
Numerical modelling tools often are used to simulate flow and transport processes occurring in the vadose zone. The package has been developed over a period of nearly 30 years by the US Geological Survey It started as a code for variably saturated flow modelling (Lappala et al 1987), with later extensions covering transport of dissolved substance (Healy 1990) and heat (Healy and Ronan 1996), as well as a graphical user interface (Hsieh et al 1999). The efficiency and accuracy of the solution may strongly depend on the choice of numerical methods and parameters for each stage of solution One of such issues, which is the subject of this work, concerns approximation of the average hydraulic conductivity between two adjacent nodes or gridblocks in a finite-difference type discretization. In this paper we show results of our numerical computations for three problems involving infiltration in sand or loamy sand soils using different grid density and different averaging procedures
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
