CONSTANT HEAD PERMEAMETER FORMULA DEPENDENCE ON ALPHA-PARAMETER

Reliable estimates of saturated hydraulic conductivity are prerequisit es for accurate estimations of waterflow and chemical transport throug h soil profiles. One useful method for evaluating the saturated hydrau lic conductivity in the field (Kfs) is the constant-head well permeame ter (CHWP) method. The governing equation for this test is based upon flow of water from a cylindrical hole and flow theory for unsaturated- saturated steady flow from the hole. By making assumptions concerning the flow from the well, a solution to the equation is derived which in cludes coefficients obtained from measurements taken during the test a nd two parameters related to the soil type being studied. An important parameter in this solution method is the alpha parameter the ratio o f Kfs to the matric flux potential. Relationships are derived and pres ented which describe the sensitivity of the CHWP solution to variation s in alpha. Results show the solution for Kfs is most sensitive to er ror in the estimate of alpha when alpha* < 0.015 mm(-1), correspondin g to fine-textured and compacted clay soils. The error in Kfs introduc ed by poor estimates of alpha is shown to be as large as 210%, for so me cases. Thus, the current classification system used to evaluate alp ha for this test appears to be inadequate to produce reasonable estim ates in Kfs.