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Soil Science Society of America Journal Abstract -

Soil-Macropore and Layer Influences on Saturated Hydraulic Conductivity Measured with Borehole Permeameters


This article in SSSAJ

  1. Vol. 57 No. 4, p. 917-923
    Received: Jan 14, 1992

    * Corresponding author(s):
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  1. L. Wu ,
  2. J. B. Swan,
  3. J. L. Nieber and
  4. R. R. Allmaras
  1. Soil Science Dep., Univ. of Minnesota, St. Paul, MN 55108
    Dep. of Agronomy, Iowa State Univ., Ames, IA 50011
    Dep. of Agricultural Engineering, Univ. of Minnesota, St. Paul, MN 55108
    USDA-ARS, Soil Science Dep., Univ. of Minnesota, St. Paul, MN 55108



The borehole permeameter technique can produce erratic saturated hydraulic conductivity (Ksat) 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 Ksat or matric flux potential (ϕm). To evaluate the effects of macropores, cracks, and layered soil on Ksat and ϕm, 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 Ksat. The simultaneous-equations approach (SEA) using either the Guelph or the Philip model for a homogeneously configured borehole estimated Ksat within a factor of 2 from input Ksat, but the Laplace analysis method overestimated input Ksat by a factor of 5 to 12. The fixed α value (α = Ksatm) method with either the Guelph or Philip model estimated Ksat close to input Ksat when a proper α value was chosen, but the proper α value differed by soil and model. A negative Ksat was computed using the SEA with the Guelph model when macropores intersected the base of a borehole; negative Ksat or ϕm 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 Ksat.

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