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Laboratory investigations of effective flow behavior in unsaturated heterogeneous sands
Author(s) -
Wildenschild D.,
Jensen K. H.
Publication year - 1999
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1029/98wr01958
Subject(s) - tortuosity , saturation (graph theory) , degree of saturation , vadose zone , hydraulic conductivity , flow (mathematics) , homogeneous , tracer , suction , geotechnical engineering , flux (metallurgy) , geology , mechanics , soil science , materials science , groundwater , porosity , soil water , thermodynamics , mathematics , physics , combinatorics , nuclear physics , metallurgy
Two‐dimensional unsaturated flow and transport through heterogeneous sand was investigated under controlled laboratory conditions. The unsaturated hydraulic conductivity of five homogeneous sands and three heterogeneous systems composed of these five sands was measured using a steady state flux controlled method. The heterogeneous sand systems were established in a laboratory tank for three realizations of random distributions of the homogeneous sands comprising a system of 207 grid cells. The water flux was controlled at the upper boundary, while a suction was applied at the lower boundary such that on the average a uniform pressure profile was established and gravity flow applied. Solute breakthrough curves measured at discrete points in the tank using time domain reflectometry, as well as dye tracer paths, showed that flow and transport took place in a very tortuous pattern where several grid cells were completely bypassed. The degree of tortuosity appeared to be dependent on the degree of saturation, as the tortuosity increased with decreasing saturation. Despite the tortuous flow patterns, we found that the effective unsaturated hydraulic conductivity as well as the retention curves for the three realizations of the heterogeneous sand were quite similar, thus suggesting that this type of heterogeneous flow system can be treated as an equivalent homogeneous medium characterized by effective parameters.