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Soil‐Macropore and Layer Influences on Saturated Hydraulic Conductivity Measured with Borehole Permeameters
Author(s) -
Wu L.,
Swan J. B.,
Nieber J. L.,
Allmaras R. R.
Publication year - 1993
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1993.03615995005700040006x
Subject(s) - hydraulic conductivity , macropore , borehole , loam , infiltration (hvac) , permeameter , geology , soil science , soil water , silt , geotechnical engineering , sorptivity , mineralogy , materials science , porosity , chemistry , geomorphology , composite material , mesoporous material , biochemistry , catalysis
The borehole permeameter technique can produce erratic saturated hydraulic conductivity ( K sat ) in soils with macropores and abrupt layers because operating theory assumes homogeneous and isotropic conditions. Dye application during an infiltration test demonstrated water movement in macropores and erratic K sat or matric flux potential (ϕ m ). To evaluate the effects of macropores, cracks, and layered soil on K sat and ϕ m , a finite element solution of the Richards equation was used to simulate infiltration from a borehole (0.03‐m radius and 0.50 m deep) with a constant head ( H ) of 0.05 or 0.10 m. Borehole infiltration (for 2 h) was simulated for a Rozetta silt loam (fine‐silty, mixed, mesic Typic Hapludalf) with four configurations: homogeneous, layered, a cylindrical macropore centered at the borehole base, and a crack intersecting the borehole wall. Simulated flow rates were increased by 29% (with H = 0.05 m) and 21% (with H = 0.10 m) when a cylindrical macropore (4 mm by 0.10 m) was located at the borehole base. Respective increases were 25% ( H = 0.05 m) and 20% ( H = 0.10 m) when a crack extending 0.1 m laterally intersected the borehole wall. Three methods were tested for calculating K sat . The simultaneous‐equations approach (SEA) using either the Guelph or the Philip model for a homogeneously configured borehole estimated K sat within a factor of 2 from input K sat , but the Laplace analysis method overestimated input K sat by a factor of 5 to 12. The fixed α value (α = K sat /ϕ m ) method with either the Guelph or Philip model estimated K sat close to input K sat when a proper α value was chosen, but the proper α value differed by soil and model. A negative K sat was computed using the SEA with the Guelph model when macropores intersected the base of a borehole; negative K sat or ϕ m were produced when cylindrical macropores laterally intersected the borehole wall, depending on the vertical locations of the macropores. Soil with layered hydraulic properties also produced unrealistic K sat .