Hydrus-2D Review, November 2000
Computer Spotlights in Ground Water (38(1), 10-11, 2000) by David M. Diodato, software editor
Reprinted with the permission of the National Ground Water Association. Copyright 2000
(Unabridged scanned article adapted for web presentation)
Introduction
Hydrus-2D by J. Simunek, M. Sejna, and M.Th. van Genuchten is a numerical modeling environment for simulating one and two-dimensional variably saturated fluid flow and heat, and multiple solute transport in porous media. We reviewed Hydrus-2D for Windows along with Meshgen-2D, an integrated companion mesh generator. The Hydrus-2D/Meshgen-2D combination sells for $1200. (Hydrus-2D is $600 by itself)
How We Tested
Hydrus-2D, version 2.0, was successfully installed on three, platforms: on a Dell workstation with a 450 MHz Pentium processor and 128 MB RAM running Windows 98; a Dell workstation with a 600 MHz Pentium III and 256 MB RAM running Windows N' 4.0 Service Pack 4; and an IBM ThinkPad 390 with a 266 MHz Mobile Pentium II and 128 MB of RAM running Windows NT 4.1 Service Pack 5.
Installation from the vendor-supplied CD was quick and easy. After installation, one file had to be copied separate from the vendor-supplied floppy disk into the install directory to license the software. Reviewers reported hard disk requirement ranging from 46 to 72 MB. Reviewers reported no adverse system reactions to the installation.
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What We Found
Hydrus-2D/Meshgen-2D integrates in a single coherent user interface the SWMS_2D finite element code for solution of the flow and transport equations, Meshgen-2D for generation of the, numerical grids, and a set of post-processing graphical utilities for the display of output data. The code can be run in horizontal, vertical, and vertical axi-symmetric modes. Heterogeneity and anisotropy are supported. Model domains can be rectangular or irregular. The grid generator will generate a default level of refinement, but the user has control on the levels of refinement desired. The software has extensive capabilities for simulating saturated unsaturated water flow and solute transport. The Richards equation is used for simulating unsaturated fluid flow. Three different closed form analytical solutions are included to describe the soil hydraulic properties-Brooks and Corey (1964), van Genuchten (1980), and modified van Genuchten (Vogel and Cislerova 1988). The code also includes the capability of simulating root-zone uptake of soil water
Hydrus-2D supports specification of steady-state and transient boundary conditions, both for Dirichlet and Neumann conditions. The package shows its U.S. Department of Agriculture (USDA) Agricultural Research Station roots with other available specialized boundary conditions including seepage face, free drainage, deep drainage, and "atmospheric"-the land surface boundary. Boundary conditions can be specified and edited inter actively through the graphical interface.
Direct or iterative solvers are used depending on problem size, and forward or inverse solutions may be calculated. The implicitness of the time approximation can also be user-specified
Hydrus-2D has extensive transport capabilities. Heat transport is via conduction and convection with flowing water. Solute transport includes advection-dispersion in the liquid phase and diffusion in the gas phase. Nonlinear nonequilibriurn reactions are supported for interaction between the liquid and solid phases. Also supported are zero-order production, and two first-order degradation reactions-one independent of solute concentration, and one that is incorporated in the calculation of sequential decay of solute species. Linear equilibrium reactions between the gas and liquid phases are included. Further, a two-region, mobile-immobile construct is included for simulating non equilibrium solute transport.
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What We Liked
The integration of the software into the interface is among the most coherent and intuitive that we've seen to date. All elements of the modeling task are visible simultaneously in a "project" environment. This helps to keep the user oriented. Numerical modeling tasks are broadly divided into preprocessing, execution, and post processing tasks in the project. Each of the major elements of these tasks are divided into logical subcategorizes, such as time specification, domain specification, and grid generation. The user can either select each of these subcategorizes individually, enter appropriate data, close the category, and open the next one, or proceed from category to category by using "previous" and "next" buttons.
Meshgen-2D can read lists of data points describing points or lines from simple ASCII flat files. This is useful if the user has digitized geologic or hydrologic boundaries or other geospatial hydrogeologic information.
Heterogeneities are specified by selecting sub regions for each rock or soil type in the domain. Material properties are specified uniquely for each rock or soil type. One handy inclusion for "what if" types of simulations are the tabulated properties of 12 generic soil types. Additionally, Hydrus-2D includes Neural Network Prediction using the ROSETTA program featuring five models based on USDA soil textural classes and texture percentages.
After a simulation is completed, output files are presented for viewing. The graphical output includes both line graphs and two-dimensional plots. The line graph features include profiles of water content, pressure, and concentration. Users can also quickly display the time evolution of mass balance, number of iterations, Courant and Peclet number, and nine different types of flux. (We think that the Courant and Peclet number data must be the maximum values over the entire domain, although we were not able to locate specific discussions of this in the online or printed documentation.) Two-dimensional plots of fluid pressure head, water content, solute concentrations, temperature, and velocity are included. These can either be filled contours, isolines, or both. Looping animations of these data can be created at the push of a button, or a user can view the output by individual time steps. Also, within the two-dimensional graphing, a user can graphically pick arbitrary lines along which to generate line graphs.
The option to copy this graphical output to the clipboard is presented explicitly. I liked being able to copy the filled contour describing the pressure solution into Paint Shop Pro, and their copying the numerical grid (displayed at the push of a button) into the same Paint Shop Pro image as an overlay layer. The documentation includes a thorough discussion of the analytical and numerical underpinnings of the software. Context sensitive on-line help is complete in some areas, even including equations or filled formats where appropriate. Ten sample problems are supplied with the software installation. One tech support request via e-mail was promptly responded to
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What We Didn't Like
One reviewer (Diodato) was particularly concerned that Hydrus-2D produced nice-looking plots even when there was substantial numerical dispersion in the underlying solution. Even though many sophisticated strategies of time stepping and grid refinement have been coded into Hydrus-2D, it is absolutely necessary for the user to be fairly sophisticated in checking the output files from their runs for numerical dispersion. A good mass balance does not tell the whole story; the user has to decide what is an acceptable level of numerical dispersion for his or her problem. The documentation is an outstanding technical reference. Unfortunately, it is not a very good user's manual. Users deserve both. Maybe the technical reference does not need an index, but the user's manual that we desire does. Furthermore, like so much of the documentation we are subjected to at Software Spotlight, the user's manual that we desire ought to be polished by a technical writer/editor team to improve coherency, order, and relevance. There is a disconnect between some of the labels used in the graphical interface and the FORTRAN variable names used in the hard copy documentation.
Although we found the interface fairly intuitive, and we like, the inclusion of the sample problems, we would like a section of the hard-copy documentation to include tutorials that illustrate the us of progressively more complex features of the software package. Many of us learn by doing, and that holds especially true with software.
While we found the software to be relatively robust and stable we also found that it was possible to cause it to crash on rare occasion. The crashes were local to the instance of the application; no system crashes were reported. It would be nice to be able to import a bitmap, or CAD file into Meshgen-2D to use as an underlay for specifying geologic entities and locations of hydrologic boundaries.
For some publications, we would want to touch up the graphical output a bit or even use a different package.
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Overall
All of the reviewers were favorably impressed by HYDRUS 2D. The capabilities of this sophisticated code are impressive and the interface is well thought out. We have not described all of the capabilities of Hydrus-2D in this column. Some of the things the we didn't get a chance to test include multiple solute transport with coupling via first-order decay reactions and inverse modeling for fitting model parameters.
Meshgen-2D made irregular mesh generation painless. I get the most out of this package, we strongly recommend that Meshgen-2D should also be purchased
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Rating
Reviewers were asked to rate Hydrus-2D/Meshgen-2D on a scale of 1 (worst) to 5 (best). The results reported are the arithmetic means of the three reviewers' responses.
- Capability 5
- Reliability 3.8
- Ease-of-Use 4.7
- Technical Support 5 (one instance)
The Vendor
Hydrus-2D/Meshgen-2D are available from the International Ground Water Modeling Center, Colorado School of Mines, Golden, CO 80401-1887; phone (303) 273-3103; www.mines.edu/research/igwmc/ igwmc@mines.edu
References
- Brooks, R.H., and A.T. Corey. 1964. Hydraulic properties of porous media. Hydrol. Pap. 3. Fort Collins: Colorado: Colorado State University.
- van Genuchten, M.Th. 1980. A closed-form equation for predicting the Hydraulic conductivity of unsaturated soils. Soil Sci. Soc. Am. J. 44,892-898.
- Vogel, T., and M. Cislerova. 1988. On the reliability of unsaturated hydraulic conductivity calculated from the moisture retention curve. Transport in Porous Media 3, 1-15.
The Reviewers
The author would like to extend his thanks and appreciation to the individuals who assisted in reviewing this software. They are: Alden Provost, U.S. Geological Survey, 12201 Sunrise Valley Dr., Reston, VA 20192; and David Ward, Earthward Consulting Inc., 38659 Bolington Rd., Lovettsville, VA 20180, (540) 822-5092, dward@earthwardconsulting.com.
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