Unsaturated Flow in a Centrifugal Field

For measuring hydraulic properties, and for investigating transport phenomena at low water contents, we have developed the theory of unsaturated flow in a centrifugal field. The first step in this was to predict and the nature of soil moisture profiles that can develop from steady unsaturated flow at centrifugal forces much greater than gravity (Nimmo and others, 1987). This development was used in inventing the SSC method for unsaturated K measurement and testing Darcy’s law for unsaturated flow. We further developed this theory for use in predicting the choice of experimental settings (centrifuge speed, applied flow rate, etc.) most likely to produce reliable K data from the SSC method (Nimmo and others, 1994). We developed a numerical solution of Richards' equation reformulated for centrifugal force (Nimmo, 1990) and used it in testing the applicability of Richards' equation at low water contents. We formulated the dynamics of saturated flow in a centrifugal field under conditions practical for measurement of saturated K (Nimmo and Mello, 1991). We have conducted an extensive analysis of the commercialized version of the SSC, the UFA apparatus, which we have presented in meetings with its developers as well as in a manuscript to be published in the third edition of the Methods of Soil Analysis monograph of the Soil Science Society of America.