VADOSE PARAMETER DESCRIPTIONS and use in MODFLOW-SURFACT AND USG-Beta.
F. Kalf 2017.
Frans R. P. Kalf, B.Sc., Cert. Eng. Hyd., M.App.Sc, PhD.
Principal/Director Kalf and Associates Pty Ltd.
e-mail: Tel: +61-2-89190272
Keywords: groundwater. vadose. Van Genuchten. Brooks. Corey. MODFLOW-SURFACT. MODFLOW-USG.
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Vadose parameters in MODFLOW-SURFACT (MS) and MODFLOW-USG-Beta modelling programs determine the relationship between relative permeability of the unsaturated medium when the pressure head converts from saturation (positive pressure head) to increasing desaturation (negative pressure head).
There are a number of functions that have been derived that allow the relative permeability to be calculated depending on the value of negative pressure head. One such function that has become prevalent is the so called Van Genuchten (VG) relationship. The VG method uses the parameters alpha and beta that determines the characteristic shape of the relative permeability Kr versus negative pressure head graphical curve. In addition the US Corey method includes a parameter n to simplify determination of the relative permeability Kr versus negative pressure head curve. The documents plots of the relative permeability Kr determined using the VG method including values of alpha and beta that provide similar graphical curves to those reported for sand, loam and clay respectively and also discusses the consequences of using very large and very small values of VG alpha in Modflow-Surfact and USG-Beta computer codes.