Prediction of infiltration from soil hydraulic properties

Abstract

Field and laboratory infiltration measurements using infiltrometers have been the onlymethods of effectively determining the infiltration rates of soils. Infiltration is mainlycontrolled by soil hydraulic properties, especially the hydraulic conductivity. Due to theease with which the saturated hydraulic conductivity can be determined, it is oftenpreferred to the unsaturated hydraulic conductivity in hydrological studies. It is wellknown that, at saturation the steady state infiltrability controls the infiltration process.Thus, it is very clear that the saturated hydraulic conductivity 𝐾𝑠 and steady stateinfiltrability 𝐾𝑜 may be closely related in one way or the other, as suggested in some fewstudies, wherein functions have been developed to relate these two parameters. However,these functions are often site specific and do not always carry out accurately all the time.Determination of 𝐾𝑜 can be tedious and time consuming, whereas 𝐾𝑠 can be easilydetermined in the laboratory. The present study aimed to assess the predictability of amodified Philip’s equation by substituting 𝐾𝑠for 𝐾𝑜. In this study, field infiltrationmeasurements were conducted in two soil types under three different land use systemswith a single ring infiltrometer. Field and laboratory hydraulic and hydrologicexperiments were conducted on soils in a turf grass, an arable land and a pastureland inthe Kwame Nkrumah University of Science and Technology, Kumasi, Ghana. Goodness-offit was used to compare the measured and predicted cumulative infiltration amounts fromboth 𝐾𝑜 and 𝐾𝑠. The results showed that there was a robust relationship between themeasured and predicted cumulative infiltration amount values from the Philip’s andmodified Philip’s equations, respectively for all three fields. However, the use of 𝐾𝑠inplace of 𝐾𝑜 produced the best outcome in all the study areas. Thus, substituting 𝐾𝑠for 𝐾𝑜in the Philip’s infiltration equation can better predict cumulative infiltration amount. Theproposed modified Philip’s infiltration equation and the key parameters (i.e., 𝑆𝜃 and 𝐾𝑠)provide new understanding into the realistic flow processes in soil. Furthermore, the 𝐾𝑠inthe new equation is very close to the measured 𝐾𝑜.