Stochastic analysis of simulated vadose zone solute transport in a vertical cross section of heterogeneous soil during nonsteady water flow
1991
Russo, D.
The problem of transport of a conservative nonreactive solute in a vertical cross section of a hypothetical partially saturated, scale-heterogeneous soil under transient water flow was analyzed here. It was assumed that locally the water flow and the solute transport can be described by the Richards' equation and by the one-component convection dispersion equation, respectively. The simulated water content and the solute concentration distributions in the vertical cross section of the soil at different elapsed times were quantified in terms of space averages and two-point autocorrelation functions. The time evolution of the solute plume was quantified in terms of its first two normalized spatial moments, from which the time dependence of the longitudinal and the transverse components of the solute velocity vector, and the spatial covariance tensor, were estimated. The results of this study, which are relevant to solute transport at the local or the plume scale, demonstrated the considerable variability in the solute concentration in space and time, due to the complex heterogeneity of the soil hydraulic properties in both the vertical and the horizontal directions. Consequently, the movement of the solute plume was characterized by a compression-expansion phenomenon, attributed to the decrease in the effective solute velocity through the zones of relatively fine-textured soil material. It was concluded that existing stochastic vadose zone transport models may be applicable to shallow depths but may fail to describe the actual spread of a solute plume when the transport takes place at relatively large depths, mainly because of the neglect of the significant vertical heterogeneity in the soil hydraulic properties.
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