A comprehensive performance assessment of the modified Philip-Dunne infiltrometer

Abstract

This study aims at furthering our understanding of the Modified Philip-Dunne Infiltrometer (MPDI), which is used to determine the saturated hydraulic conductivity Ks and the Green-Ampt suction head Ψ at the wetting front. We have developed a forward-modeling algorithm that can be used to simulate water level changes inside the infiltrometer with time when the soil hydraulic properties Ks and Ψ are known. The forward model was used to generate 30,000 water level datasets using randomly generated values of Ks and Ψ values. These model data were then compared against field-measured water level drawdown data collected for three types of soil. The Nash-Sutcliffe efficiency (NSE) was used to assess the quality of the fit. Results show that multiple sets of the model parameters Ks and Ψ can yield drawdown curves that can fit the fieldmeasured data equally well. Interestingly, all the successful sets of parameters (delineated by NSE ≥ the threshold value) give Ks values converged to a valid range that is fully consistent with the tested soil texture class. However, Ψ values varied significantly and did not converge to a valid range. Based on these results, we conclude that the MPDI is a useful field method to estimate Ks values, but it is not a robust method to estimate Ψ values. Further studies are needed to improve the experimental procedures that can yield more sensitive data that can help uniquely identify Ks and Ψ values.