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TWODAN

TWODAN stands for TWO-Dimensional ANalytic groundwater flow model. Version 5.0 combines advanced analytic elements with an excellent user interface. It is a 32-bit Windows application with a familiar and simple user interface. TWODAN's capabilities, interface quality, and price make it a great value for 2-D flow modeling. It is a good tool for many remediation design, capture zone analysis, and regional modeling problems.

Ground Water Journal Review of TWODAN

In the May-June 1998 issue (Ground Water, v. 36(3), p. 389-390) three independent experts reported on their review of TWODAN. Overall, their rating of TWODAN, on a scale of 1-5, 5 being best, is a follows:

Capability 4, Reliability 4.5, Ease-of-Use 4, Technical support 5

Here are some excerpts of their review:

"TWODAN requires only a moderate investment of money and time to buy and learn, yet it has considerable power and flexibility, resulting in rapid solutions for 2-D flow problems. Used for problem solving or teaching, TWODAN is a valued and handy tool in our hydrogeological software toolbox."

"TWODAN's strengths lie in the ease and speed of model construction, and the ease of model alteration. Using TWODAN, one can arrive at a solution to even relatively complicated 2-D ground water flow problems in an afternoon, compared to the days or weeks commonly required for more sophisticated finite element or finite difference numerical models.

"Even a die-hard MODFLOW user will find TWODAN to be a valuable tool for preliminary 2-D model development..."

"This flexibility and rapid feedback also make TWODAN an excellent teaching tool for introductory hydrogeology courses."

"TWODAN's implementation of the Windows Graphical User Interface (GUI) is robust and gives access to all of the model functions, eliminating the need for the user to formulate input data files."

"One reviewer reported, 'TWODAN was fun to use, and this may be its greatest strength'. We agree that there is substantial gratification provided by the instant feedback to changes in model design and addition of model elements."

"All of our complaints about TWODAN are of a relatively minor nature and easily remedied with minor-level revisions."

About The Analytic Method

The analytic element method described by Strack (1989, Groundwater Mechanics, Prentice-Hall) is the mathematical basis for TWODAN. The principal advantages of this method over conventional numerical methods are its simple input, accuracy, speed, and lack of a fixed grid. With the analytic method, only the boundaries of the domain are discretized, not the domain itself as in finite-difference and finite-element methods. You can model a huge area and still retain great accuracy in small regions of the model. Click here to see an illustration of this point with a TWODAN model. There is no need to arbitrarily define the limits of the model - just model far enough from the area of interest to account for the real boundary conditions on the aquifer. The amount of required inputs is minimal compared to numerical methods.

In this method, large numbers of analytic solutions are superpositioned to solve complex groundwater flow problems. The functions that are superpositioned are associated with particular aquifer features. Some of the functions contain parameters that are unknown when the problem is posed (for example, the discharge of a head-specified linesink). These unknowns are determined by specifying boundary conditions at control points located on or near the aquifer features (for example setting the head at the center of a head-specified linesink). The number of specified boundary conditions equals the number of unknown parameters, yielding a system of linear equations which is solved by standard methods. Once the unknown strengths are solved for, the resulting composite analytic solution satisfies the governing differential equation exactly except at singular points or lines associated with the analytic functions. The specified control point boundary conditions will be met exactly, and boundary conditions will be approximate between control points.

Modeling Capabilities

TWODAN has a suite of advanced analytic modeling features that allow you to model everything from a single well in a uniform flow field on up to complex remediation schemes with numerous wells, barriers, surface waters, and heterogeneities.

Heterogeneous, Layered Aquifers

The aquifer modeled by TWODAN can consist of one or two hydraulically connected layers, it can be confined and/or unconfined, and it can be homogeneous or heterogeneous. Heterogeneities are input as closed polygon regions, each with a distinct set of aquifer properties (base elevation, lower layer K, lower layer thickness, upper layer K, and upper layer thickness). Heterogeneities can be nested inside one another and they can abut one another. Click here to see a model of an aquifer with a variety of heterogeneities and mixed confined/unconfined conditions.

Impermeable and Resistant Boundaries

These features can have irregular shapes consisting of open or closed strings of line segments. The analytic implementation of these elements in TWODAN gives much greater accuracy than is possible with numerical methods. The discharge through resistant boundaries is proportional to a user-specified resistance (thickness/conductivity) and the head difference across the boundary. These elements offer an accurate way to model flow fields containing slurry walls, sheet-pile walls, etc. (see Fitts, C.R., Groundwater, 35(4), 1997). Click here to see models using both the impermeable and resistant elements in remediation simulations.

Wells

Solutions for both steady-state and transient wells are available. TWODAN is also capable of optimizing discharges of steady wells based on specified head and aquifer discharge conditions (see Fitts, C.R., Groundwater, 32(4), 1994.). When transient wells are used, you can write an ASCII file listing head vs. time at a specified location; this file can be imported to a spreadsheet for plotting hydrographs.

Linesinks

Both discharge- and head-specified linesinks are implemented. Head-specified linesinks are typically used to represent constant-head boundaries. Discharge-specified linesinks can be used to model infiltration or pumping trenches.

Infiltration/Leakage

Vertical infiltration or leakage to or from the aquifer can be modeled as uniform or as locally variable. Locally variable infiltration/leakage is modeled using solutions for circular area sources.

Uniform Regional Flow

A uniform cross-flow in the aquifer can be input at any angle and discharge rate.

User Interface

TWODAN 5.0 has a seamless, Windows-standard user interface. It has been designed to be very simple and fast to use. Most common modeling operations are executed at the push of a button on the main screen (see top of this page).

Instead of using tedious data-entry forms, model input data and plot settings data are accessed directly in spreadsheet-like grids. You can quickly edit all aspects of the model input in the model input screen and all the plot settings from the plot settings screen. The input data for a model is stored in one file while the settings for a particular plot are stored in another. This separation is efficient, allowing you to push one button to repeat a plot with the same contours, pathlines, window coordinates, etc.

Digitizing Features

Digitize using the mouse and a DXF basemap overlay. You can also digitize over the top of the previous plot showing contours, pathlines, etc. You can zoom or pan to a different view during the middle of a digitizing operations. You can continuously digitize multiple points, lines, or circles, quickly defining long barrier, heterogeneity, and constant-head boundaries. The digitized coordinates are temporarily stored in the Windows Clipboard. From there, the coordinates can be pasted into the TWODAN data grid or into other editor or spreadsheet files. As a bonus, you can use TWODAN as a general-purpose digitizing program with DXF basemaps.

Graphic Output Options

Your plots can include any of the following:

Contours of head, potential, or stream function
Pathlines can be traced upstream or downstream from single points, a series of points along a line, or a series of points around a circle (useful for defining the capture zone of a well). Arrows along pathlines are spaced at user-defined time intervals.
The DXF basemap.
A layout of model elements.

TWODAN plots can be output to a huge array of devices -- all those supported by the Windows operating system. Graphic plots may directed to the screen, Windows printer devices, bitmap (*.bmp) files, the clipboard, Surfer GRD files, or to DXF files. With all these options, it is now much easier to incorporate TWODAN graphic output into your reports.

Printer plots may be scaled automatically to fit the page, or manually scaled to a specific scale (1 inch = 500 feet, for example). TWODAN automatically centers the plot on the page. You may print a plot with a landscape or portrait orientation, and you may add a border box and up to three lines of title text.

Automatic Contour Labeling

TWODAN labels contours automatically. You elect which contours to label (each contour, every other one, every fifth one, or every tenth one), and how frequently the labels occur along a given contour. Set these parameters once in the plot settings screen, and they will be used each time you press a button to make a plot.

On-Line Help Systems

The on-line help is extensive and well-designed. The following forms of help are available: tips that automatically display when you pause over a control, context-sensitive help (F1 key), and Windows-standard detailed help. The detailed help is indexed, searchable, printable, and it contains embedded jumps to related topics.

Graphic Plotting of Calibration Results

Like many models, TWODAN will compile a list of target heads, model-calculated heads, and differences between these. In addition, TWODAN 5.0 has a very useful feature that plots the spatial distribution of the differences. Click here to see an example of the graphic plotting of calibration results. TWODAN also calculates these summary calibration statistics:

Mean error
Sum of the squared differences.

Other Nifty Utilities

Some other interface features deserve at least a brief mention:

Report-ready ASCII text output file summarizing the model inputs.
Sum the aquifer discharge across a polyline. Digitize a multi-segment polyline, and TWODAN will calculate the discharge across this line. Handy for remediation design.
Sum well or linesink discharges. Quickly sum the discharge of a wellfield or of a surface water defined by constant-head linesinks.
Examine the analytic solution at a point. You digitize a point, and TWODAN calculates head, gradient, transmissivity, aquifer discharge, potential, and stream function at a point.
Create a hydrograph of head vs. time at a point. Useful for models using transient well solutions. The output file is a comma-delimited list of head, time that can be imported into spreadsheet and other graphics programs for nice plotting.

Documentation

Most of the information about how to use the software is in the on-line help system. The TWODAN Manual is a 7 x 9 inch spiral bound booklet containing the following sections.

Introduction
Tutorial - a step-by-step development of a complex TWODAN model, showing screens as they appear in the process.
Method Employed - a detailed section describing the analytic methods and equations employed.
Program Checks - 14 separate checks of the method and solutions implemented in TWODAN. One check of a complex model against the equivalent Modflow model. The model input and plot settings files for the check models are included on the software diskettes.
References

System Requirements

32-bit Windows operating system (Windows 95 or Windows NT as of this writing)
4 MB of hard disk space
8 MB of memory

Partial List of Users

There are over 350 licensed TWODAN users. What follows is a representative partial list of users.

Domestic Consultants

Dames and Moore, Dow Environmental, ENSR, Environ, ERM, Geomatrix Consultants, GeoTrans, Golder Associates, Harding-Lawson, Martin Marietta Energy Systems (Oak Ridge National Lab), O'Brien and Gere, Rust Environment and Infrastructure, Shannon and Wilson, Woodward and Clyde.

Foreign Consultants

Trading Port SRL (Argentina), Groundsearch Australia Pty Ltd. (Australia), IF Technology (Netherlands), Aqua-Dyne Technological Services (Philippines), Geoestudios Ltda. (Chile), Electrowatt Engineering Services (Switzerland), Kemakta Konsult (Sweden), Brandt-Gerdes-Sitzmann (Germany), Woodward Clyde (Australia), Grundwasser Cnslt Ingen (Germany), Aquifirma (New Zealand), Geotherma Batiment le Continental (France).

Domestic Government Agencies

Maine Dept. of Env. Protection, U.S. EPA Environmental Response Team, Wright-Patterson Air Force Base, Illinois EPA, US EPA R.S. Kerr Research Lab, Minnesota Geological Survey, US Bureau of Land Management, San Gabriel Basin Water Quality Authority, St Johns Water Management District, Washington Department of Ecology, California Regional Water Quality Control Board, US Dept. Agriculture, Grassland Soil and Water Research Lab.

Foreign Government Agencies

Geological Survey of Denmark, Geological Survey of Sweden, Republic of Botswana Geological Survey, Geological Survey of Finland.

Domestic Universities

North Carolina State Univ., New Mexico State University, Utah State University, Ohio University, Calif. State Univ. at Chico, University of Hawaii, Temple University, LaSalle University, University of Texas, University of Oklahoma, University of Texas at San Antonio.

Foreign Universities

Christian-Albrechts-University (Germany), Seoul National University (Korea), Freie Universitat Berlin (Germany), Eberhard-Karls University (Germany), University of Toronto (Canada), University of the Witwatersrand (South Africa), Indian Institute of Technology (India), Institute of Geoscience (Japan).

Licenses and Support

The commercial TWODAN license is a typical software license; one license allows installation on one computer at a time.

The academic license is a site license available for qualified educational institutions, and is restricted to academic, non-commercial purposes.

Purchase of either license includes unlimited support to make sure that TWODAN operates properly on your system.

Downloading a Demo

The demo version of TWODAN is contained in one self-extracting installation file setuptd.exe. This file is just less than 3MB in size, so depending on your system, it may take a while to download. Instructions for running the demo version are given during the setup process. The demo is the same as the full TWODAN software, except printing and saving features are disabled.

Click here to download the demo installation file.