WATER-MOVEMENT IN AN UNSATURATED SOIL BENEATH A VELOCITY PERMEAMETER

A computer program was written to solve Richards' model for flow in an unsaturated soil. Finite element analysis was used for the numerical solution and a velocity permeameter defined one boundary condition. Th e program allows for different soil types, some soil anisotropy, and d ifferent velocity permeameter equipment configurations. Changes in soi l water pressure head with time under the velocity permeameter are cal culated. The shape and extent of the wetting and saturated fronts can be determined from the soil water pressure head values. Initial soil p ressure heads of -10, -20, -50, and -100 m were studied. A linear rela tionship between the radial and vertical hydraulic conductivity, K, wa s also examined. The relationship between soil water pressure head and K were modeled for a Pachappa sandy loam, an Indio loam, and a Chino clay soil. Movement of wetting and saturated fonts through the soil un der the velocity permeameter was apparent. Different initial soil wate r content values did not affect the soil water isoheads in position no r extent. Increasing the magnitude of the saturated value of K increas ed the extent of the wetting front both radially and vertically. Choos ing different velocity permeameter equipment (head tube or coring devi ce) affected the volume inflow and, consequently, the time needed to s aturate the soil core, however, isohead position and extent were not c hanged significantly.