Quantitative Evaluation of Preferential Flow Based on Laboratory Breakthrough Experiments of Soil Columns

Because of its critical effect on field-scale soil water flow and transport of contaminants in soils,more and more research concerns are concentrated on preferential flow.However,few reports are found on quantitative evaluation of preferential flow though there are many reports in literature on qualitative descriptions of preferential flow.This paper presents the analysis of the characteristics of preferential transport based on the breakthrough curves obtained from soil columns in the lab and the evaluation of its extent based on the time moment analysis and two-region models by CXTFIT.A conclusion is made that the breakthrough curves(BTCs) exhibit different shapes including some with early breakthrough and increased tailing curves.This qualitatively indicates the presence of preferential flow and different extent of preferential flow in the different soil columns.By time moment analysis,the first normalized moment(μ'1),the second central moment(μ2),and the skewness(S) were used as reference indices to denote the extent of preferential flow.Using transport parameters determined by the program CXTFIT and the time moments of BTCs,an integrated parameter,PFSP,was calculated to ascertain or compare the extent of preferential flow.The calculation results indicate the value of PFSP could be used to quantify the extent of preferential flow when the breakthrough curves could be obtained.The conclusions in the study offer instructive implications in evaluation of preferential flow in the field.