CONSTANT HEAD PERMEAMETER FORMULA DEPENDENCE ON ALPHA PARAMETER
Reliable estimates of saturated hydraulic conductivity are prerequisites for accurate estimations of water flow 
and chemical transport through soil profiles. One useful method for evaluating the saturated hydraulic conductivity in the 
field (Kfs) is the constant-head well permeameter (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 includes coefficients obtained 
from measurements taken during the test and two parameters related to the soil type being studied. An important 
parameter in this solution method is the a* parameter, the ratio of Kfs to the matric flux potential. Relationships are 
derived and presented which describe the sensitivity of the CHWP solution to variations in a*. Results show the solution 
for Kfs is most sensitive to error in the estimate of a* when a* < 0.015 mm–1, corresponding to fine-textured and 
compacted clay soils. The error in Kfs introduced by poor estimates of a* is shown to be as large as 210%, for some 
cases. Thus, the current classification system used to evaluate a* for this test appears to be inadequate to produce 
reasonable estimates in Kfs.