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This article in SSSAJ

  1. Vol. 48 No. 4, p. 703-708
     
    Received: Nov 10, 1983


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doi:10.2136/sssaj1984.03615995004800040002x

Boundary Conditions for Displacement Experiments through Short Laboratory Soil Columns1

  1. M. Th. van Genuchten and
  2. J. C. Parker2

Abstract

Abstract

This paper presents a discussion of the physical and mathematical significance of various boundary conditions applicable to one-dimensional solute transport through relatively short laboratory soil columns. Based on mass balance considerations, it is shown that a first-type or concentration-type condition at the inlet boundary incorrectly predicts the volume-averaged or resident concentration inside both semi-infinite and finite systems. A third-type or flux-type inlet boundary condition preserves mass in semi-infinite systems, but underpredicts effluent concentrations from finite columns unless a local transformation is used to convert volume-averaged concentrations into flux-averaged concentrations. This transformation leads to an expression for the effluent concentration that is identical to the solution for the semi-infinite system using a concentration-type boundary condition. For column Peclet numbers greater than about five, the resulting analytical expression for the effluent curve is shown to be nearly identical to the analytical solution for a finite system based on a flux-type inlet boundary condition and a zero-concentration gradient at the exit boundary. Both solutions correctly preserve mass in the system; other solutions of the convective-dispersive transport equation are shown to be inappropriate for analyzing column effluent data.

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