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United States Department of Agriculture

Agricultural Research Service

Title: Convective-Dispersive Stream Tube Model for Field-Scale Solute Transport: I. Moment Analysis

Authors
item Toride, Nobuo - SAGA UNIV., JAPAN
item Leij, Feike - U.C. RIVERSIDE

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 5, 1997
Publication Date: N/A

Interpretive Summary: Chemical transport in natural fields is typically difficult to model because of the variability of soil properties. The stream tube model is relatively simple for describing chemical movement in the soil for relatively short travel distances. The field is viewed as a series of independent vertical soil columns. In this study the widely-used convection-dispersion equation (CDE) is applied to describe transport in each stream tube. For each tube two transport parameters were random for the following three scenarios: (i) the dispersion coefficient, D, and the pore-water velocity, v; (ii) the distribution coefficient for linear adsorption, Kd, and v; and (iii) the first-order rate coefficient for nonequilibrium adsorption, a, and v. The variability in D has generally a minor effect on solute spreading compared to variability in v. It is important to quantify the correlation between v and Kd. Spreading of reactive solutes increased for negatively correlated v and Kd. A negative correlation between v and a enhanced the asymmetry of the breakthrough curve while spreading was independent of the correlation between a and v.

Technical Abstract: Field-scale solute transport is difficult to model due to the complexity and heterogeneity of flow and transport in natural soils. The stream tube model attempts to stochastically describe transport across the field for relatively short travel distances by viewing the field as a series of independent vertical soil columns. The chemical equilibrium and nonequilibrium convection-dispersion equation (CDE) is used for local-scal transport. A bivariate (joint) lognormal probability density function (pdf) was applied for three pairs of random transport parameters: (i) the dispersion coefficient, D, and the pore-water velocity, v; (ii) the distribution coefficient for linear adsorption, Kd, a v; and (iii) the first-order rate coefficient for nonequilibrium adsorption a, and v. The mean breakthrough time for the field-scale flux-averaged concentration was found to be identical to that for the deterministic CDE. Variability in D has generally a minor effect on solute spreading compared to variability in v. Spreading of reactive solutes increased for negatively correlated v and Kd. A negative correlation between v and a enhanced the skewness of the breakthrough curve.

Last Modified: 4/16/2014
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