FIELD EVALUATION OF THE NEW PHILIP-DUNNE PERMEAMETER FOR MEASURING SATURATED HYDRAULIC CONDUCTIVITY

Abstract

One of the most sensitive parameters in hydrological models, the saturated hydraulic conductivity (K s ), is also one of the most problematic measurements at field scale in regard to variability and uncertainty. The performance of a new type of simple and inexpensive field permeameter, the Philip-Dunne permeameter (PD), is compared with two established alternatives, the laboratory constant head permeameter (LP) and the field Guelph permeameter (GP). A PD prototype, a protocol of usage, and a numerical routine to find K s were developed and tested on a 70-point array laid out on an 850-m 2 volcanic soil plot. A power transformation was applied to the raw data using the three methods, and the transformed data were shown to be normally distributed. The LP and GP data were better described by a log-normal distribution, whereas the PD data could also be approximated with a power-normal distribution. A factor of 3 was found to relate PD, LP, and GP hydraulic conductivity estimates, E[Ks], such that E[K s -PD] ≅ 3 E[K s -LP]; E[K s -LP] ≅ 3 E[K s -GP]. Such differences may be explained by the different water infiltration geometries and sample wetted volume for the three methods. The PD has advantages over the other two methods in terms of personnel involved, preparation time, and ease of operation. Additionally, the PD methodology required a smaller number of samples (41% less than GP and 69% less than LP) to estimate the population mean K s . Both PD and GP also give the suction at the wetting front, an important parameter that characterizes the unsaturated flow properties of the soil.