Ž . Journal of Contaminant Hydrology 51 2001 131–144 www.elsevier.comrlocaterjconhyd Characterization of preferential flow in undisturbed, structured soil columns using a vertical TDR probe J. Lee a , R. Horton b, ) , K. Noborio c , D.B. Jaynes d a Biosystems Engineering and EnÕironmental Science, The UniÕersity of Tennessee, KnoxÕille, TN 37901, USA b Department of Agronomy, Iowa State UniÕersity, Ames, IA 50011, USA c Department of Agricultural Engineering, Iwate UniÕersity, Morioka, Iwate 020-8550, Japan d USDA-ARS, National Soil Tilth Laboratory, 2150 Pammel DriÕe, Ames, IA 50011, USA Received 29 September 2000; received in revised form 4 April 2001; accepted 18 April 2001 Abstract Rapid movement of agricultural chemicals through soil to groundwater via preferential flow pathways is one cause of water contamination. Previous studies have shown that time domain Ž . reflectometry TDR could be used to characterize solute transport in soil. However, previous studies have only scarcely addressed preferential flow. This study presents an extended application of TDR for determining preferential flow properties. A TDR method was tested in carefully controlled laboratory experiments using 20-cm long and 12-cm diameter undisturbed, structured soil columns. The method used a vertically installed TDR probe and a short pulse of tracer Ž . Ž . application to obtain residual mass RM breakthrough curves BTC . The RM BTC obtained from Ž . TDR were used to estimate mobilerimmobile model MIM parameters that were compared to the Ž . parameter estimates from effluent data. A conventional inverse curve fitting method CXTFIT was used to estimate parameters. The TDR-determined parameters were then used to generate calculated effluent BTC for comparison with observed effluent BTC for the same soil columns. Time moments of the calculated and observed BTC were calculated to quantitatively evaluate the calculated BTC. Overall, the RM BTC obtained from TDR were similar to the RM BTC obtained from effluent data. The TDR-determined parameters corresponded well to the parameters obtained from the effluent data, although they were not within the 95% confidence intervals. Correlation coefficients between the parameters obtained from TDR and from effluent data for the immobile Ž . Ž . Ž . water fraction u ru , mass exchange coefficient a , and dispersion coefficient D were im m 0.95, 0.95, and 0.99, respectively. For three of the four soil cores, u ru ranged from 0.42 to im 0.82, indicating considerable preferential flow. The TDR-calculated effluent BTC also were ) Corresponding author. Fax: q 1-515-294-3163. Ž . E-mail address: rhorton@iastate.edu R. Horton . 0169-7722r01r$ - see front matter q 2001 Elsevier Science B.V. All rights reserved. Ž . PII: S0169-7722 01 00131-0