Abstract
Three-dimensional fingers caused by gravity driven, wetting front instability in unsaturated porous media were explored through laboratory experimentation. Two sets of experiments were conducted using initially dry sand in large 30 cm diameter columns to guide analytical development for finger velocity and diameter. The first set consisted of ponding water on a two-layer sand system with a fine sand overlying a coarse sand. Here, a complicated pattern of interaction among fingers was found to occur. In the second set, water was applied directly to the coarse layer as 2 cm diameter area sources, enabling systematic study of individual finger structure. Based on dimensional analysis and the experimental results, general relationships were found for finger velocity and cross-sectional area as a function of both the flux through the finger and hydraulic properties of the coarse layer represented by the sorptivity, saturated conductivity, and initial and saturated moisture contents. Unlike the two-dimensional case, air entrapment was an important factor in explaining the experimental results.
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Glass, R.J., Cann, S., King, J. et al. Wetting front instability in unsaturated porous media: A three-dimensional study in initially dry sand. Transp Porous Med 5, 247–268 (1990). https://doi.org/10.1007/BF00140015
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DOI: https://doi.org/10.1007/BF00140015