An assessment of the single-head analysis for the constant head well permeameter

Abstract

An in-situ constant head well permeameter (CHWP) method employing three or more ponded heads per well was used to establish relationships between field-saturated hydraulic conductivity (Kfs), matric flux potential [Formula: see text], the alpha parameter (α*), soil texture, and soil structure. The relationships were then used to evaluate a single-head CHWP technique which employs representative mean α* values in the determination of Kfs and [Formula: see text]. The measurements were made at several depths on four soils which ranged in texture from loamy sand to silty clay, and in structure from single grain to strong, fine subangular blocky. The Kfs and [Formula: see text] results obtained from the multiple-head CHWP measurements were found to be highly variable within and between soils, yielding within-soil ranges as high as 3.5 orders of magnitude and standard deviation factors (SDF) as high as 5.1. The geometric mean (GM) Kfs and [Formula: see text] values were also highly variable between soils, but they were controlled primarily by soil structure rather than by soil texture or other factors. The α* values, on the other hand, were relatively consistent both within and between soils, yielding an overall SDF of only 1.2 and an overall GM of 11 m−1. Use of α* = 11 m−1 in the single-head CHWP technique yielded Kfs and [Formula: see text] values which were usually accurate to within a factor of 2, and often accurate to within ±25%. These levels of accuracy are within acceptable limits for a field method, considering the many potential sources of error and the extreme range and variability of Kfs and [Formula: see text] normally encountered in the field. Key words: Constant head well permeameter, hydraulic conductivity, matric flux potential, alpha parameter, soil texture, soil structure, single-head analysis