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Water flow and solute spreading in heterogeneous soils with spatially variable water content
Author(s) -
Harter Thomas,
Zhang Dongxiao
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 - 10.1029/1998wr900027
Subject(s) - soil water , water content , soil science , soil texture , spatial variability , pedotransfer function , environmental science , water flow , saturation (graph theory) , field capacity , tortuosity , hydraulic conductivity , hydrology (agriculture) , geology , porosity , mathematics , geotechnical engineering , statistics , combinatorics
Although the spatial variability of water content is expected to be significant in heterogeneous, unsaturated media, its effect on solute transport has been neglected in most stochastic analyses. In this work we develop, evaluate, and numerically verify an analytical model describing the statistical moments of water content, soil water flux, soil water velocity, and solute spreading in the unsaturated zone under conditions of variable soil water content. Results are presented for a wide range of soil conditions. It is shown that soil water content variability increases with soil water tension and decreases with soil textural tortuosity parameter m . As expected, the water content variability also increases with those of soil texture and saturated hydraulic conductivity. However, at or above field capacity (near saturation) the water content variability is generally negligible. The water content variability is very large under dry conditions, even if the soil is relatively homogeneous. In the same soil, longitudinal macrodispersivity is generally smaller when including than when neglecting the variability in water content. Variable water content enhances longitudinal macrodispersivity only in soils with large horizontal anisotropy or soils with m < 2. In this case the enhancement is more significant in drier soils and at the early stages of plume displacement (less than 10 λ ƒ ). With travel distance the longitudinal macrodispersivity in the presence of variable water content converges to that in the absence of it.