HYDRUS Unsatchem Module
The geochemical UNSATCHEM module (Šimůnek and Suarez, 1994; Šimůnek et al., 1996) has been implemented into one-, two-, and three-dimensional computational modules of the HYDRUS-1D and HYDRUS (2D/3D) software packages. The geochemical UNSATCHEM module simulates the transport of major ions in variably-saturated porous media, including major ion equilibrium and kinetic non-equilibrium chemistry. The resulting code is intended for predictions of major ion chemistry, along with water and solute fluxes in soils during transient flow. The major variables of the chemical system in UNSATCHEM-2D are Ca, Mg, Na, K, SO4, Cl, NO3, H4SiO4, alkalinity, and CO2. The model accounts for various equilibrium chemical reactions between these components, such as complexation, cation exchange and precipitation-dissolution. For the precipitation-dissolution of calcite and dissolution of dolomite, either equilibrium or multicomponent kinetic expressions can be used, which includes both forward and back reactions. Other dissolution-precipitation reactions considered include gypsum, hydromagnesite, nesquehonite, and sepiolite. Since the ionic strength of soil solutions can vary considerably in time and space and often reach high values, both the modified Debye-Hückel and the Pitzer expressions are incorporated into the model to calculate single ion activities. The effect of solution chemistry on the hydraulic conductivity is also considered. Water flow and heat transport modules are similar (almost identical) as in regular HYDRUS. Possible applications include studies of the salinization/reclamation of agricultural soils, sustainability of various irrigation systems, and the disposal of brine waters in mining operations. Applications of the UNSATCHEM module are demonstrated on several examples.
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Unsatchem Examples
Unsatchem-Related References
- Šimůnek, J., and D. L. Suarez, Modeling of carbon dioxide transport and production in soil: 1. Model development, Water Resour. Res., 29(2), 487-497, 1993.
- Suarez, D. L., and J. Šimůnek, Modeling of carbon dioxide transport and production in soil: 2. Parameter selection, sensitivity analysis and comparison of model predictions to field data, Water Resour. Res., 29(2), 499-513, 1993.
- Šimůnek, J., and D. L. Suarez, Two-dimensional transport model for variably saturated porous media with major ion chemistry, Water Resour. Res., 30(4), 1115-1133, 1994.
- Suarez, D. L., and J. Šimůnek, UNSATCHEM: Unsaturated water and solute transport model with equilibrium and kinetic chemistry, Soil Sci. Soc. Am. J., 61, 1633-1646, 1997.
- Šimůnek, J., and D. L. Suarez, Sodic soil reclamation using multicomponent transport modeling, ASCE J. Irrig. and Drain. Engineering, 123(5), 367-376, 1997.
- Šimůnek, J., D. L. Suarez, and M. Šejna, The UNSATCHEM software package for simulating one-dimensional variably saturated water flow, heat transport, carbon dioxide production and transport, and multicomponent solute transport with major ion equilibrium and kinetic chemistry, Version 2.0, Research Report No. 141, U.S. Salinity Laboratory, USDA, ARS, Riverside, California, 186 pp., 1996. (Download PDF, 3.5Mb)
- Šimůnek, J., M. Šejna, and M. Th. van Genuchten, The UNSATCHEM Module for HYDRUS (2D/3D) Simulating Two-Dimensional Movement of and Reactions Between Major Ions in Soils, Version 1.0, PC Progress, Prague, Czech Republic, 54 pp., 2012. (pdf 1.1MB)
- Šimůnek, J., M. Šejna, and M. Th. van Genuchten, The UNSATCHEM Module for HYDRUS (2D/3D) Simulating Two- and Three-Dimensional Movement of and Reactions Between Major Ions in Soils, Version 2.0, PC Progress, Prague, Czech Republic, 54 pp., 2021. (pdf 1.1MB)
Tutorials for the Two-Dimensional Unsatchem Module
A furrow irrigation problem is used in this tutorial to simulate two-dimensional infiltration of gypsum saturated water into a sodic soil. The simulation of sodic soil reclamation demonstrates the cation exchange feature of the UNSATCHEM module. Several variants (such as using different irrigation water, effects of solution composition on hydraulic conductivity, etc) of the basic simulations (done first) are discussed in the second part of the tutorial.
- Furrow irrigation with gypsum-saturated water.
- The effects of the solution composition on the hydraulic conductivity.
- Furrow irrigation with high quality water
- Furrow irrigation with high quality water and assuming presence of calcite in the profile (and either instantaneous or kinetic dissolution)
- Furrow irrigation with water of different qualities
Download tutorial document: Unsatchem Tutorials (0.7 MB)
Download tutorial projects: Unsatchem_Tutorial.zip (4.8 MB)
Recent Applications of the Unsatchem Module
- Ramos, T. B., H. Darouich, J. Šimůnek, M. C. Gonçalves, and J. C. Martins, Soil salinization in very high-density olive orchards grown in southern Portugal: current risks and possible trends, Agricultural Water Management, 217, 265-281, doi: 10.1016/j.agwat.2019.02.047, 2019.
- Rasouli, F., A. K. Pouya, and J. Šimůnek, Modeling the effects of saline water use in wheat-cultivated lands using the UNSATCHEM model, Irrigation Science, 31(5), 1009-1024, doi:10.1007/s00271-012-0383-8, 2013.
- Ramos, T. B., J. Šimůnek, M. C. Gonçalves, J. C. Martins, A. Prazeres, and L. S. Pereira, Two-dimensional modeling of water and nitrogen fate from sweet sorghum irrigated with fresh and blended saline waters, Agricultural Water Management, 111, 87-104, 2012.
- Ramos, T. B., J. Šimůnek, M. C. Gonçalves, J. C. Martins, A. Prazeres, N. L. Castanheira, and L. S. Pereira, Field evaluation of a multicomponent solute transport model in soils irrigated with saline waters, J. of Hydrology, 407(1-4), 129-144, 2011.
- Gonçalves, M. C., J. Šimůnek, T. B. Ramos, J. C. Martins, M. J. Neves, and F. P. Pires, Multicomponent solute transport in soil lysimeters irrigated with waters of different quality, Water Resour. Res., 42, W08401, doi:10.1029/2006WR004802, 17 pp., 2006.
- Phogat, V., D. Mallants, J. W. Cox, J. Šimůnek, D. P. Oliver, T. Pitt, and P. Petrie, Impact of long-term recycled water irrigation on crop yield and soil chemical properties, Agricultural Water Management, 237, 106167, 14 p., doi: 10.1016/j.agwat.2020.106167, 2020.
- Raij-Hoffman, I., D. Jacques, and N. Lazarovitch, Suction cup system-dependent variable boundary condition: Transient water flow and multicomponent solute transport, Vadose Zone Journal, 19, e20030, p. 13, doi: 10.1002/vzj2.20030, 2020.