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RETC is a computer program which may be used to analyze the soil water retention and hydraulic conductivity functions of unsaturated soils. These hydraulic properties are key parameters in any quantitative description of water flow into and through the unsaturated zone of soils. The program uses the parametric models of Brooks-Corey and van Genuchten to represent the soil water retention curve, and the theoretical pore-size distribution models of Mualem and Burdine to predict the unsaturated hydraulic conductivity function from observed soil water retention data. The program comes with a manual which gives a detailed discussion of the different analytical expressions used for quantifying the soil water retention and hydraulic conductivity functions. A brief review is also given of the nonlinear least-squares parameter optimization method used for estimating the unknown coefficients in the hydraulic models. The RETC program may be used to predict the hydraulic conductivity from observed soil water retention data assuming that one observed conductivity value (not necessarily at saturation) is available.

The program also permits one to fit analytical functions simultaneously to observed water retention and hydraulic conductivity data. Several examples are presented to illustrate a variety of program options.

The program comes with a user manual giving detailed information about the computer program along with instructions for data input preparation and listings of sample input and output files. A listing of the source code is also provided.

Dataset Info

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U.S. Salinity Laboratory
Product Type
United States Department of Agriculture
Contact Name
Skaggs, Todd
Contact Email
Public Access Level
Primary Article

van Genuchten, M. Th., F.J. Leij, & Yates, S.R. (1991). The RETC Code for Quantifying the Hydraulic Functions of Unsaturated Soils, Version 1.0. EPA Report 600/2-91/065, U.S. Salinity Laboratory, USDA-ARS, Riverside, California.

Related Article

Price, J., Whittington, P., Elrick, D., Strack, M., Brunet, N., & Faux, E. (2008). A Method to Determine Unsaturated Hydraulic Conductivity in Living and Undecomposed Moss. Soil Science Society Of America Journal, 72(2), 487.

AgID: 723411
Funding Source(s)
Agricultural Research Service
Program Code
005:037 - Department of Agriculture - Research and Education
Bureau Code
005:18 - Agricultural Research Service
Modified Date
Release Date
Ag Data Commons Keywords: 
  • Agroecosystems & Environment
  • Water
  • Agroecosystems & Environment
ISO Topic(s):