A modified upward infiltration method for characterizing soil hydraulic properties

Abstract

This note describes a modified upward infiltration method (UIM), which combines laboratory experiments and inverse parameter estimation for determining soil hydraulic properties in the wetting direction. The laboratory method used a Mariotte system to impose a constant head boundary condition on the bottom of a soil column, allowing water to be taken up by the soil material under negative pressure head. Tensiometers installed along the column measured the change in soil pressure head before and after wetting front arrival. The HYDRUS-1D code was used to obtain an optimal set of van Genuchten parameters, using pressure head and cumulative flux data as auxiliary variables in the objective function. Two soil types (a fine sand and a sandy loam) were tested in triplicate in uniformly-packed soil columns. The results of the uniform column experiments were repeatable, and showed excellent fits between observed and predicted data. Fitted parameters were used in forward simulations to independently predict water flow behavior in layered columns of the same soil material. The forward simulations successfully predicted water flow for sand-over-loam and loam-over-sand combinations in layered columns. The relative simplicity of the experimental procedure and the availability of appropriate numerical models renders the modified upward infiltration method an alternative for determining wetting hydraulic properties of soils.