TWODAN - 2-D analytic ground-water flow model for Windows - remediation design, capture zone analysis, and regional modeling problems
TWODAN Categories: flow models - pathlines/capture zones, flow models - saturated zone
Introduction to TWODAN
Looking for software that can quickly perform a wide range of flow and advective transport analyses?
Look carefully at TWODAN. You will find many powerful capabilities that other 2-D models lack: heterogeneities, impermeable barriers, resistant barriers, and transient solutions, to name a few. Modeling doesn't get any easier than this! The analytic method demands minimal input, and the new seamless Windows interface can be quickly mastered. As hundreds of users attest, TWODAN is a great choice for modeling remedial design alternatives, wellhead capture zones, and regional aquifer flow.
With this new version, TWODAN combines advanced analytic elements with an excellent user interface. Compare TWODAN's capabilities, interface quality, and price to any competing 2-D modeling software; TWODAN is a great value! It is the right tool for many remediation design, capture zone analysis, and regional modeling problems.
The analytic method described by Strack (1989, Groundwater Mechanics, Prentice-Hall) is the mathematical basis for TWODAN. The principle 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. 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. See below an illustration of this point with a TWODAN model.
The plot above is at a regional scale showing all elements in the model. The elements are in green. Head-specified linesinks form constant head boundaries at streams, ponds, and wetlands. A high conductivity glacial outwash valley aquifer is represented by a heterogeneity in the upper right area. A well with a U-shaped resistant (leaky) barrier is within this heterogeneity.
The plot above is the same model and solution - just a different, smaller window chosen for the plot. It shows the heterogeneity and barrier area in more detail.
The plot above is still the same model but even closer up on the well and barrier. Note the accuracy of the solution near the well and barrier, despite the large extent of the entire model. This level of accuracy and flexibility with model boundaries is not found in finite-difference or finite-element numerical methods.
In this method, large numbers of analytic solutions are superpositioned to solve complex ground-water 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.
TWODAN has a suite of advanced analytic modeling features that allow you to model everything from a single well in a uniform flow field to complex remediation schemes with numerous wells, barriers, surface waters, and heterogeneities.
Heterogeneous, Layered Aquifers
Impermeable and Resistant Boundaries
This plot shows three heterogeneities in a TWODAN model. Counting the outside aquifer, there are four zones, each with unique definitions of base elevation, upper and lower layer elevations, and upper and lower layer conductivities. The two larger ones that abut are more conductive and have lower base elevations than the regional aquifer outside. The small heterogeneity nested inside of the biggest heterogeneity has a conductivity much lower than its surroundings.
Uniform Regional Flow
TWODAN has a seamless, Windows-standard user interface. TWODAN 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. 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. See below for these three main screens in TWODAN.
TWODAN Main Screen
The plot above shows two open-ended impermeable barriers in a simulation of a funnel and gate remediation. There is a high conductivity heterogeneity in the region to the left of the gate.
The plot above is of a closed, resistant boundary with a well pumping inside it. This type of remediation is sometimes used to isolate the contamination zone and reduce the amount of clean water pumped.
TWODAN Model Input Screen
TWODAN Plot Settings Screen
Digitizing Features in TWODAN
Graphic Output Options in TWODAN
TWODAN plots can be output to a huge array of devices - all supported by the Windows operating system. Graphic plots may be directed to the screen, Windows printer devices, bitmap (*.bmp) files, the clipboard, Surfer GRD files, and 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 in TWODAN
TWODAN On-Line Help Systems
Graphic Plotting of Calibration Results in TWODAN
Plotted Calibration Results
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:
32-bit Windows operating system (Windows 95/98/2000 or Windows NT)
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, noncommercial purposes. Purchase of either license includes unlimited support to make sure that TWODAN operates properly on your system.
Scientific Software Group
P.O Box 708188 Sandy, Utah 84070
Phone (801) 208-3011 or Toll Free (U.S.) 1-866-620-9214 Fax (801) 302-1160 E-mail email@example.com
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