Effects of degree of water saturation on dispersivity and immobile water in sandy soil columns

Munjed A. Maraqa, Roger B. Wallace, Thomas C. Voice

Research output: Contribution to journalArticlepeer-review

86 Citations (Scopus)


Three natural nonaggregated soil samples, with similar grain-size distributions, have been used to determine the dispersive behavior of porous media under steady, saturated and unsaturated flow conditions. Tritium was used as a tracer and was found to have no sorption on the solid matrix. Generated breakthrough curves (BTCs) for the unsaturated experiments were symmetrical with no evidence of tailing. The unsaturated experiments for two of the soils were adequately described by considering all the water in the pore volume as mobile. However, about 10% of the pore water, independent of the degree of saturation, was found to be immobile in the case of the third soil during unsaturated flow. For this soil, there was no mass transfer between the two water regions, indicating that the immobile water is essentially isolated from the flowing water fraction. For all three soils, dispersivity under unsaturated conditions was found to be higher, independent of the degree of water saturation, than the value determined for the saturated experiments. This is inconsistent with what would be expected from the simple bundle-of-capillary-tubes model and does not agree well with a more sophisticated conceptualization of the porous medium. The data, however, clearly indicate a wider range in pore-water velocities when these soils are desaturated.

Original languageEnglish
Pages (from-to)199-218
Number of pages20
JournalJournal of contaminant hydrology
Issue number3-4
Publication statusPublished - Mar 1997
Externally publishedYes


  • Hydrodynamic dispersion
  • Physical nonequilibrium
  • Transport model
  • Tritium
  • Unsaturated flow

ASJC Scopus subject areas

  • Environmental Chemistry
  • Water Science and Technology


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