An official website of the United States government.

This is not the current EPA website. To navigate to the current EPA website, please go to This website is historical material reflecting the EPA website as it existed on January 19, 2021. This website is no longer updated and links to external websites and some internal pages may not work. More information »

Retention Curve (RETC) Computer Program

RETC is a program for analyzing the hydraulic conductivity properties of unsaturated soils. The parametric models of Brooks-Corey and van Genuchten are used to represent the soil water retention curve. The theoretical pore-size distribution models of Mualem and Burdine predict the unsaturated hydraulic conductivity function. The simulation can be generated from observed soil water retention data, assuming that one observed conductivity value (not necessarily at saturation) is available. The program also permits users to fit analytical functions simultaneously to observed water retention and hydraulic conductivity data.

Version 1.1
Release Date November 1994
Operating System DOS

Minimum System Requirements

To run RETC, you will need the following:

  • IBM PC/AT or compatible
  • DOS version 2.0 (or higher)
  • Color graphic adapter (CGA) board
  • 640 KB of RAM


RETC Program Files (ZIP)(70 K)

"The RETC Code for Quantifying the Hydraulic Functions of Unsaturated Soils." Publication No. 600/2-91/065.

Installation Instructions

  1. Go to Windows Explorer and create a directory named RETC.
  2. Download the program files and user's manual to the new directory.
  3. Unzip the program files to the RETC directory.
  4. Review the user’s manual for instruction on running the model.