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United States Department of Agriculture

Agricultural Research Service

Title: Discrepancies Between Analytical Solutions of Two Borehole Permeameters for Estimating Field–saturated Hydraulic Conductivity

Authors
item JABRO, JALAL "JAY"
item Evans, Robert

Submitted to: Applied Engineering in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 23, 2006
Publication Date: July 24, 2006
Repository URL: http://handle.nal.usda.gov/10113/1920
Citation: Jabro, J.D., Evans, R.G. 2006. Discrepancies between analytical solutions of two borehole permeameters for estimating field–saturated hydraulic conductivity. Applied Engineering in Agriculture. 22(4): 549-554.

Interpretive Summary: The Richards’ solution of the GP and the Glover’s solution of the CCHP were compared for their ability to estimate Kfs in a Duffield silt loam soil. Steady-state flow rates at a single constant-head infiltration from a borehole measured by the Guelph permeameter were made. The following conclusions were drawn from the results of this study: 1) The estimation of Kfs by the Glover’s solution was significantly higher than Kfs values estimated by the Richards’ solution. These discrepancies between the two solutions exist because Glover’s solution excludes the effect of the water flow due to capillarity of the unsaturated soil surrounding the borehole; 2) The Glover’s and Laplace’s solution produces Kfs values larger (1.5- 2) than Kfs estimated with the Richards’ solution for a Duffield silt loam soil; 3) A significant difference in Kfs values was found between the Glover’s and Richards’ solutions by comparing their mean values using both paired and unpaired student t-test approaches; 4) The variability and magnitude of Kfs results are influenced by the type of analytical solution used in Kfs calculations, and 5) Selecting analytical methods or solutions for calculating Kfs that are capable of producing invariable estimates of Kfs in soils continues to be uncertain and further work appears warranted for developing appropriate Kfs estimation methods for borehole permeameters. Despite the uncertainty of selecting an appropriate solution for calculating Kfs and discrepancies between the analytical solutions’ results, both GP and CCHP methods are currently considered common, simple and convenient methods for measuring Kfs and no one method was found to be superior over the other.

Technical Abstract: Field-saturated hydraulic conductivity (Kfs) is considered the most important parameter for water flow and chemical transport phenomena in soils. The Richards’ and Laplace’s solutions of the Guelph Permeameter (GP) and the Glover’s solution of the Compact Constant Head Permeameter (CCHP) for estimating Kfs were compared. Steady-state flow rates of water into soil at a single constant head infiltration from a borehole measured with the Guelph permeameter method were used to estimate Kfs values using these solutions. The mean values of Kfs calculated using Richards’, Laplace’s and Glover’s solutions were 0.192, 0.272, and 0.385 cm h1, respectively, for the Duffield silt loam soil. The Glover’s and Laplace's solutions, neither of which take into account the effect of unsaturated capillary flow, produce Kfs values approximately 1.5-2 times larger than the Kfs values calculated using Richards’ solution. The student t-test showed significant differences in Kfs results between Richards’ and Glover’s water flow solutions by comparing their arithmetic means. Further, a paired student’s test showed that the mean difference (Md) between the two solutions was significantly different from zero (Md = 0.114 cm h-1, t = 7.22, pr < 0001). Thus, statistical analyses indicated that the three analytical methods result in dissimilar estimates of Kfs values. This indicates that the variability and high inconsistency in Kfs estimates depend not only on soil structure, texture, and other soil characteristics but also on method of estimation imposed by the borehole analytical solution.

Last Modified: 7/28/2014
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