Submitted to: Workshop on Computer Applications in Water Management Proceedings
Publication Type: Proceedings
Publication Acceptance Date: February 10, 1995
Publication Date: N/A
Interpretive Summary: There are increased concern about the adverse impacts of salinity and increased use of lower quality waters for irrigation. These factors combined with increased water use efficiency require that we know the quantities and distribution of salts in the rootzone. We describe the UNSATCHEM model, which is designed to predict the impact of management changes (such as irrigation frequency, amount) and environmental and soil factors on major ion and salinity distributions. The model includes plant water uptake, variably saturated water flow, gas production and transport and a comprehensive chemical routine. We demonstrate the model by simulating the development of sodic soil conditions with time.
Technical Abstract: The UNSATCHEM model is designed as a research/management model for predicting rootzone Chemistry and water and solute movement in the unsaturated zone. The model simulates one-dimensional variably saturated water flow, heat transport, carbon dioxide production and transport, and multicomponent solute transport with major ion equilibrium and kinetic chemistry. The model also considers major ion cation exchange, anion adsorption, both extended Debye-Huckel and Pitzer expressions for single ion activity coefficients at high ionic strength, as well as root development, plant water uptake, and solution chemistry with complexation. Various multicomponent kinetic expressions are used to describe the precipitation-dissolution of calcit and dissolution of dolomite. The model includes a user-friendly interface which operates within a MS Windows 3.1 environment. The user interface includes data pre-processing with the option of selecting from a table of hydraulic parameters based on soil texture, as well as selection of boundary conditions. The data are output in tabular as well as graphical form. Although developed as a research model the addition of the user friendly interface enables use by agricultural specialists.