UNSATURATED ZONE PARAMETER ESTIMATION USING THE HYDRUS AND ROSETTA SOFTWARE PACKAGES

Authors: Van Genuchten, Martinus; SIMUNEK, JIRKA - UC RIVERSIDE,CA; SCHAAP, MARCEL - USSL,RIVERSIDE, CA; Skaggs, Todd

Submitted to: Proceedings of the International Workshop on Uncertainty, Sensitivity, and Parameter Estimation for Multimedia Environmental Modeling
Publication Type: Proceedings
Publication Acceptance Date: 3/10/2003
Publication Date: 8/10/2003
Citation: Van Genuchten, M.T., Simunek, J., Schaap, M.G., Skaggs, T.H. 2003. Unsaturated zone parameter estimation using the hydrus and rosetta software packages. Proceedings of the International Workshop on Uncertainty, Sensitivity, and Parameter Estimation for Multimedia Environmental Modeling. Publisher: U.S. Nuclear Regulatory Commission, pp. 41-43.

Interpretive Summary: The past several decades have seen much effort in developing analytical and numerical models for application to existing or anticipated soil and groundwater pollution problems. Computer models are now increasingly used to predict the movement of water and dissolved agricultural and other contaminants in the subsurface. Such models often require a large number of parameters, some of which may be very difficult to measure directly. For these reasons parameter estimation (inverse) techniques have been developed that estimate these parameters from more easily measured input and output information related a particular experiment. The Salinity Laboratory has long developed and used such parameters estimation codes. Much of our earlier work focused on parameters in analytical solute transport models. Recently a windows-based version (STANMOD) of the different one- and multidimensional analytical transport models became available. We also developed the HYDRUS codes for estimating the unsaturated soil hydraulic properties (i.e., water retention and hydraulic conductivity parameters) from laboratory and/or field data. The HYDRUS codes require numerical solutions of the governing Richards equation for one or two-dimensional unsaturated flow. In this paper we briefly review the main features of the HYDRUS codes and their utility for estimating soil hydraulic and solute transport parameters. Also, as an alternative to using HYDRUS for site-specific parameter estimation studies, we briefly summarize the Rosetta code for estimating the unsaturated soil hydraulic parameters and their uncertainty in a more generic manner from soil texture and related surrogate data that are often available. Details of these and other models discussed in this paper can be found at the Web Site of the Salinity Laboratory (www.ussl.ars.usda.gov/models/models.htm).

Technical Abstract: Parameter optimization techniques are becoming increasingly popular for estimating a variety of subsurface flow and transport parameters. The Salinity Laboratory has long developed and used parameters estimation codes to estimate such parameters from laboratory and/or field experimental data. Much of our earlier work focused on parameters in analytical solute transport models. Recently a windows-based version (STANMOD) of the different one- and multidimensional analytical transport models became available. Using parameter optimization techniques for estimating the unsaturated soil hydraulic properties became popular in the mid 1980s, initially in conjunction with mostly one- and multi-step outflow experiments. Such optimizations require numerical solutions of the governing Richards equation for variably-saturated flow because of the highly nonlinear relationships between the water content, the hydraulic conductivity and the pressure head. As more flexible and comprehensive numerical programs such as the HYDRUS codes became available, these studies were extended to analyses of upward flux or head-controlled infiltration experiments (including tension infiltrometry), evaporation methods, or any other experiment involving some appropriate combination of water flow and solute transport data. In this paper we briefly review the main features of the HYDRUS codes and their utility for estimating soil hydraulic and solute transport parameters. Also, as an alternative to using HYDRUS for site-specific parameter estimation studies, we briefly summarize the Rosetta code for estimating the unsaturated soil hydraulic parameters and their uncertainty in a more generic manner from soil texture and related surrogate data that are often available. Details of these and other models discussed in this paper can be found at the Web Site of the Salinity Laboratory (www.ussl.ars.usda.gov/models/models.htm).