A simple method for correcting the effects of initial soil moisture on Modified Philip-Dunne Infiltrometer drawdown curves

Abstract

The effect of varying initial soil moisture (θin) of a given soil on the drawdown curve measured using the Modified Philip-Dunne Infiltrometer (MPDI) and consequently on the estimated saturated hydraulic conductivity (Κs) value, was investigated. The laboratory tests completed using three different types of soil show that the drawdown curve was sensitive to θin for all three soils. This resulted in yielding Κs values that are sensitive to the values of θin. The lowest value of Κs was observed when the MPDI was used under wet conditions. To obtain a consistent estimate of Κs, a new correction factor was developed. This factor can be multiplied with the geometrical coefficient used in the governing equations of the MPDI to make appropriate corrections. After employing the correction factor, the variations in Κs values for all three tested soils decreased from 66%, 61% and 59%, to 26%, 16% and 26%, respectively. In situ experimental tests also show similar results and the coefficient of variation decreased from 81% to 61% after applying the correction factor. The performance was further validated by testing the relative performance of the MPDI against the results obtained using Minidisk Infiltrometer (MDI) under varying θin values. Results from the MDI show that the coefficient of variation for the Κs values of the three soils were 20%, 28%, and 32%, which are similar to the variations obtained after applying the correction factor in the MPDI model calculations. The aforementioned results indicate that the correction method proposed in this study is a useful method for improving the overall performance of MPDI.