RETC, Retention Curve Program for Unsaturated Soils, is a computer program for describing the hydraulic properties of unsaturated soils. The program may be used to fit several analytical models to observed water retention and/or unsaturated hydraulic conductivity data. The model incorporates menu-driven data entry.
Features in RETC include:
- A direct evaluation of the hydraulic functions when the model parameters are known.
- A more flexible choice of hydraulic parameters to be included in the parameter optimization process.
- The possibility of evaluating the model parameters from observed conductivity data rather than only from retention data or simultaneously from measured retention and hydraulic conductivity data.
Although the models used in RETC are intended to describe the unsaturated soil hydraulic properties for monotonic drying or wetting in homogeneous soils, the code can be easily modified to account for more complicated flow processes such as hysteretic two-phase flow.
The soil water retention and hydraulic conductivity are key parameters in any quantitative description of water flow into and through the unsaturated zone. RETC 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 may be used to predict the hydraulic conductivity from observed soil water retention data assuming that one observed conductivity is available. The program also permits one to fit analytical functions simultaneously to observed water retention and hydraulic conductivity data.
RETC uses a nonlinear least-squares optimization approach to estimate the unknown model parameters from observed retention and/or conductivity or diffusivity data.
RETC includes the executable and source codes and technical support.