WWRC 96-02
An Analytical Solution of Macrodispersivity for Adsorbing Solute Transport in Unsaturated Soils
Abstract
An analytical solution of macrodispersivity was derived for the adsorbing solute
transport in physically and chemically heterogeneous unsaturated soils under the condition
of gravity-dominated flow. The unsaturated hydraulic conductivity and water content were
treated as spatial random functions. The chemical adsorption was described by a linear
equilibrium isotherm, and the adsorption coefficient was represented as a spatial random
function with specified correlation structures. The closed-form expression for
macrodispersivity was expressed as a function of the hydraulic and adsorbing statistical
properties of the unsaturated soil. For a short solute travel distance the macrodispersivity
linearly increased with the increase of the solute plume travel distance. The
macrodispersivity approached an asymptotic value when the center of the solute plume
moved a long distance. The general solution quantified the effects of various factors, such
as variabilities of the water content and unsaturated hydraulic conductivity, mean water
content, and the retardation factor, on the macrodispersivity.
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