Software FAQ

Visual MODFLOW Flex

What is MODFLOW?

Can I run transport simulations with Visual MODFLOW Flex?

Yes, with Visual MODFLOW Flex 2013.1 and later you can run contaminant transport models with MT3DMS. Click here to learn more.

Can I apply 'Evapotranspiration' to different layers during the simulation?

Similar to Recharge, the Visual MODFLOW Flex interface provides an option to apply “Evapotranspiration” to different layers during the simulation

  • To the top layer
  • To the top-most active layer

What Lake Package (LAK3) capabilities are supported in Visual MODFLOW?

When defining a lake boundary condition, there is now an option to define horizontal leakance explicitly; this is important when there is both horizontal and vertical flow between the lake and aquifer, which is common in quarries or mine tailing ponds that have steep walls.

In the Output, there is a new Lake Budget option for Graphs that allow for showing time series plots of the lake parameters: stage, precipitation, evaporation, runoff, volume changes. You can chart results from a single model or load multiple model results on the same plot, for comparing different model scenarios.

What is MODFLOW -USG?

MODFLOW-USG is a new version of the MODFLOW groundwater flow simulation code developed by the United States Geological Survey (USGS) which uses unstructured grids instead of rectilinear grids to discretize the model domain.

What is an unstructured grid? How is it different than a structure grid used in MODFLOW-2005

An unstructured grid is made up of triangular, rectangular or other polygon shaped geometries individually or in combination to discretize the groundwater model domain. This is in contrast to previous versions of MODFLOW, including MODFLOW-2005 which uses structured, rectilinear grids. Unstructured grids require the use of the finite volume method whereas traditional structured grids are used with the finite difference method.

Structured finite difference MODFLOW-2005 grid (left) and an UnStructured grid with Voronoi Grid (middle) and Quadtree Grid (right) for MODFLOW-USG

What unstructured grid geometrics are supported in Visual MODFLOW Flex?

Although MODFLOW-USG can be used with any grid geometry – triangles, rectangles, polygons – Visual MODFLOW Flex supports unstructured grids made up of polygonal Voronoi Cells or rectangular Quadtree cells.

What are Voroni Cells and Quadtree Grids?

Voronoi Cells

One of the types of unstructured grid supported in Visual MODFLOW Flex. Voronoi Cells are a special type of polygon that honors the Control Volume Finite Difference (CVFD) constraints required by MODFLOW-USG. Using this grid geometry with MODFLOW-USG results in an efficient and robust numerical grid that can handle complex hydrogeological geometries and boundaries with ease – similar to triangles, but with a higher degree of accuracy.
VMODFlex_ImportingVmodProjects_Tutorial

Learn more about Voronoi Cells.

Quadtree Grids

Quadtree Grids are one of the types of unstructured grid supported in Visual MODFLOW Flex. Quadtree grids are based on locally refining rectilinear grids by recursively subdividing cells into four equal quadrants.  This allows you to locally refine the grid around non-linear features such as streams and lakes without having to carry those refinements laterally across the entire model domain as occurs when using fully structured rectilinear grids.

Using this grid geometry with MODFLOW-USG results in an efficient numerical grid that can handle complex hydrogeological geometries and boundaries with ease. However, the use of Quadtrees can introduce some errors as the geometry of Quadtree grids does not adhere to the assumption inherent in the Control Volume Finite Difference approach utilized in MODFLOW-USG that shared cell interfaces occur at the perpendicular bisector of the respective cell centroids (see discussion below on Ghost Node Correction [GNC]).

What is Ghost Node Correction (GNC) and is it used for Voroni Grids or Quadtree Grids?

Ghost Node Correction is a technique that is applied to some unstructured grid types (e.g., Nested or Quadtree Grids), whose geometries do not inherently satisfy the requirements of MODFLOW-USG.   One of the geometric constraints for the Control Volume Finite Difference approach used in MODFLOW-USG is that the line formed by connecting the centroids of two adjacent Finite Volume cells must perpendicularly bisect the shared cell interface. While Voronoi Tessellation by definition fits this criteria, other grid types (such as Delaunay Triangulations and nested or Quadtree Grids) do not strictly conform to this constraint.

In order to permit the mathematical solution of the Finite Volume Method certain grids, the USG package employs a technique called Ghost Node Correction (GNC) in which a temporary ‘ghost’ node is created within a cell such that it meets the geometric constraints and the equations may be solved. This solution at the ghost node is then interpolated (corrected) back to the actual cell center point, resulting in a Ghost Node Correction within each cell. (http://pubs.usgs.gov/tm/06/a45/pdf/tm6-A45.pdf)

The ghost node correction package is generally not required when using Voronoi Grids because by definition they satisfy the geometric conditions required for the Control Volume Finite Difference approach used in MODFLOW-USG.

The use of Quadtrees may introduce errors in the simulation results as the geometry of Quadtree grids does not adhere to the assumption inherent in the Control Volume Finite Difference approach utilized in MODFLOW-USG: that shared cell interfaces occur at the perpendicular bisector of the respective cell centroids.  The interfaces between neighboring cells with different degrees of refinement will occur at an angle that departs from perpendicularity and the distance between the centroids will become increasingly asymmetric as the relative degree of refinement between the cells increases. In cases where the model is smooth (that is the model properties, cell elevations/thicknesses, aspect ratio between adjacent cells is small [2:1]) and/or the non-conforming cells are located far from the area of interest, the resulting error may fall within tolerances that are acceptable to the modeler.  For cases where this error may be unacceptable, Visual MODFLOW Flex supports the MODFLOW-USG Ghost Node Correction (GNC) package which corrects for this potential source of error. Note that the use of the GNC package is likely to increase model run times.

What are the benefits of MODFLOW-USG over MODFLOW-2005

Increased Simulation Accuracy

Unstructured grids permit local grid refinement along model features such as wells and boundary conditions, in addition to supporting fully discontinuous layers, both of which deliver high resolution detail and accuracy around areas that matter the most.

Reduced Simulation Runtimes

Traditional MODFLOW grid refinement often results in an excessive number of grid cells outside the areas of interest which leads to an inefficient numerical model with unnecessary long run times. With unstructured grids, the grid refinement is focused only to the areas of interest, resulting in much fewer grid cells, more stable grid structures, and therefore reduced run times.

Further Reading:
Case Study: MODFLOW-USG Yields 90% Reduction in Run Times for Regional Groundwater Model

Superior Modeling of Complex Geology

Unstructured grids are flexible and conform easily to the natural variability found in surface features and subsurface stratigraphy. Unstructured grid layers permit discontinuous layers that pinch-out to zero thickness, providing a more realistic representation of complex hydrogeological conditions, and improved model stability.

Increased Numerical Stability

Unstructured Voronoi grids in Visual MODFLOW Flex are composed of a special type of polygon called Voronoi Cells that are generally superior to other unstructured grid geometries (nested grids, Quadtree grids) as they completely honor the Control Volume Finite Difference (CVFD) constraints, and therefore do not require the Ghost Node Correction (GNC) package. In addition, cell centroids will coincide exactly with conceptual wells and boundary condition feature vertices. This results in an efficient, robust and dependable numerical grid, with improved convergence and accuracy.

What modeling applications are best suited for MODFLOW-USG?

MODFLOW-USG can be used to simulate groundwater flow for virtually any application. However, It’s ability to handle complex geology makes it ideal for applications in mining where steep slope geology is often encountered. Flexible grid refinement capabilities also make it suitable for large regional and watershed scale models.

What process and packages are supported with MODFLOW-USG? And is MODFLOW-USG available in all editions of Visual MODFLOW Flex?

The following processes and packages are supported in MODFLOW-USG:

  • BAS, DIS, BCF, LPF, HFB
  • CHD, FHB
  • WEL, DRN, GHB, RIV
  • STR, SFR, LAK, GAG
  • SUB
  • New Packages: DISU, CLN, GNC, SMS

MODFLOW-USG & Visual MODFLOW Flex

MODFLOW-USG is only available in the Professional and Premium editions of Visual MODFLOW Flex.

Is it possible to convert my MODFLOW-2005 model to a MODFLOW-USG model?

Yes. If you currently use Visual MODFLOW Flex, you will already have a 3D conceptual model that defines the geologic layers, properties and boundary conditions independent of the grid. To run your model with MODFLOW-USG, simply auto-generate the unstructured grid and then run the simulation. Visual MODFLOW Flex’s multi-model environment allows you to manage both your MODFLOW-2005 and MODFLOW-USG models within the same project, and both models can be easily compared side-by-side.

If your model currently exists in Visual MODFLOW Classic, you will need to import your model into Visual MODFLOW Flex before you can run the model using MODFLOW-USG.

Hydro GeoAnalyst

How can I complete water quality analyses using Hydro GeoAnalyst and AquaChem?

In order to use the water quality analysis feature within Hydro GeoAnalyst, you must first have AquaChem installed on the local machine.

  • With your project open in Hydro GeoAnalyst, select Modules > AquaChem (or select the AquaChem icon from the toolbar).
  • Hydro GeoAnalyst will check the current project database to see if the Geochemistry Extension has been added – if this has not been added you will be prompted to add this extension.
  • Once the Geochemistry Extension has been added to the project database, AquaChem will launch displaying the selected data.

Please view the online help documentation for additional details on using the AquaChem (Water Quality Analysis) feature, or feel free to view a short video on this process available on our YouTube channel.

How can I complete pumping test analyses with my Hydro GeoAnalyst data?

In order to use the Aquifer Test analysis feature, you must first have Aquifer Test 4.1 or later installed on the local machine.

  • With your project open in Hydro Geo Analyst, select Modules > Aquifer Test (or select the Aquifer Test icon from the toolbar). This will launch the Pumping Test Analysis window.

For additional information on completing the Pumping Test Analysis please view the online help documentation. Once all the required fields have been defined, click the Analyze button to send the data to Aquifer Test.

How can I use my Hydro GeoAnalyst data in Visual MODFLOW Flex?

Hydro GeoAnalyst can be used to build the conceptual model layers for a Visual MODFLOW Flex model. You may also use the data in Hydro GeoAnalyst to import observation wells into Visual MODFLOW’s Classic Interface.

Creating Conceptual Model Layers:

In Hydro GeoAnalyst, you can query the database to determine layers with different lithology and export this data for use in Visual MODFLOW Flex.

For example, the HGA demonstration database can be queried to determine the bedrock elevation. To query the bedrock surface, we will need to do the following calculation:

  • Ground Surface (station.elevation) – Top of Bedrock (depth to shale or limestone). In the Query Builder this would be represented by:
  • Select Max Function and expression, station.name= lithology.from_ with the Alias name Top of Bedrock
  • A condition may then be applied for soil_type = limestone
  • You may need to adjust the query according to your project fields/data. You may then execute the query. Once the database has been queried to determine the bedrock elevation, a gridded surface can be created and used in Visual MODFLOW. In HGA, load the query into the Map Manager and create a gridded surface of the data (.grd file). For additional information on creating gridded data please view the online help documentation.
  • Export Model Layers. You can choose which layers to export and from which cross sections. The more cross sections you define, the more points you have for defining the layer interfaces. The model layers will be exported as a text file with x, y and z values. For additional details on creating your geological layer interpretations, please view the online help documentation.

In Hydro GeoAnalyst, you can create a calibration point file by creating a query with the following columns, for example, to import observation wells:

Name X Y Screen Measure Point Elevation Stop Time Head
BH0902 2438 6556 1 580.1 1 602.55

Once you have created the appropriate query, you may export the data to an .xls or .txt file to import into the Visual MODFLOW Classic Interface.

In Visual MODFLOW, you will need to set up the model with the appropriate model or world coordinates so that the files imported from HGA will correspond with these coordinates. Create the model and import the model layers and calibration points from HGA into Visual MODFLOW.

How do I restore from location of the project? (*.VBH or *.HGA)?

If you are restoring your database from a backup, or are opening a project for the first time you will need to ensure that you have the entire project directory on your local machine along with a copy of the Backup File (*.BAK).

  • From the Project Menu, select Open from Backup, this will launch the Restore Database dialogue.
  • Specify the desired SQL Server, and the location of the Project (*.VBH) and Backup file to be restored and press the OK button to open the project.

Additional information on backing up your database can be found in the online help documentation.

AquaChem

Opening a project in a previous version and running a saved Summary Statistics Report in the parameters tab, I see headers don't match up to the data and receive an error message saying 'Error when reading data for numeric fields." How do I resolved this problem?

Delete the listed parameters and then re-enter/re-select the parameters. You will notice the column contents now match the headers and the report should be able to run.

Using PHREEQC, some of the saturation indices or complexes are not calculated. How should the parameters be defined?

PHREEQC will calculate saturation indices and activities for those parameters which are defined in your database. Also, the saturation indices will require that the PHREEQC component be mapped exactly as it is shown within AquaChem.

Where can I find the thermodynamic database files?

The PHREEQC database files distributed with the program are installed under My Documents AquaChem PHREEQC.

Can I use AquaChem features in Hydro GeoAnalyst (HGA)?

Yes, with AquaChem 2012.1 and later you can run the program completely on a Hydro GeoAnalyst (HGA) SQL database.

I cannot get the PHREEQC program to run. Where can I find the installer?

You can find the most up to date versions of the PHREEQC Graphical User Interface from the USGS website by selecting File>Preferences> PHREEQC, and clicking on the PHREEQC Website button.

When trying to load a database, I get the "ActiveX component can't create object" error. How can I resolve this issue?

MS Access 2007 is a prerequisite for the installation of AquaChem (version 2011.1 and higher).
If this dependency is missing, you will receive the template message and a “[Warning!] ActiveX component can’t create object” error will occur. To correct this issue you will need to install the MS Access 2007 Runtime Engine directly from Microsoft Website: http://www.microsoft.com/download/en/details.aspx?id=4438

I am not able to open a project created in a previous version in AquaChem 2012 - I am receiving error messages stating there is an error in executing sqi statements. How can these warnings be corrected?

The issue can be due to a missing system table in the database if the project was created using the advanced template. This can be fixed by following these steps:

  • Create a new project in AquaChem.
  • Open the project in MS Access.
  • Copy (ctrl+C) the table M_LinkedObjects from the list of tables.
  • Open the client project in MS Access.
  • Paste (ctrl+V) the table into the list of tables.
  • Save the changes in MS Access and open the project in AquaChem.

How can I input custom water quality standard ranges into AquaChem?

To create a new water quality standard, follow the steps below:

  • Open the Database options dialogue (File > Preferences), and select the Standards-Import tab.
  • Click the [+] Add button to create a new standard.
  • A blank Water Quality Standards dialog will load. Here you can: enter the name for this new set of standards, enter a reference for the new set of standards, enter a URL for the set of standards, enter the year that the standards were approved, and enter guideline levels for the new set of standards.
  • There are two ways to enter parameters and assign guideline levels: the values can be entered manually or the data can be imported from a file. Either way, data is entered for one guideline at a time.
  • Once finished, click the [Close] button.

I am trying to create Durov plots but the data does not appear on the plots. Why is this happening?

To display the data on these plots, values must be present for all of the ions that you are trying to show on the plot. If even one of the ions does not have any values then your information will not be plotted. Right click on you parameter from the Sample Details screen, and double check if all parameters are available.

I am trying to plot Box and Whisker (multiple stations) but the plot tells me that there are no data points? How can the plot be arranged so that it displays the box and whisker for each of the stations?

Please ensure that the plot symbols have been assigned correctly. This means that a separate symbol will represent each station in the project.

  • You can confirm how the symbols are assigned by selecting Plots>Define Symbol or Line from the top toolbar. Ensure that Station is selected as the symbol grouping.
  • If this is not available, you can add a new grouping for station id by selecting the […] button and adding a new grouping. Select this new grouping as the Symbol Group and then select Auto to automatically assign a symbol based on the station id.
  • Alternatively, you can add only the stations you would like to view on a plot to the symbol grouping list.
  • Once the symbol grouping has been selected and applied to the project, recreate your plot and select the stations you wish to view on the plot.

AquiferTest

There's a lot of 'noise' in my data. How can I minimize that?

New feature in Pro: Use derivative “smoothing” to reduce noise in the dataset. AquiferTest provides three methods for derivative smoothing: Bourdet Derviate (BOURDET 1989), Standard (HORNE 1995) and Regressive (SPANE & WURSTNER 1993). For more information on these methods, please refer to the original texts.

  • To open the Derivative Setting dialogue,go to the Analysis tab, and select Analysis> Derivative… , from the main menu. You can apply derivative smoothing to all datasets in the analysis by selecting the Use sample setting for all data option.
  • To assign different methods to different data sets, select the ‘Set’ each data set separately option.

The Neuman method is taking a long time to run. How can I speed it up?

New Feature: Neuman analysis now has an option to use tabular interpolation which provides a much faster solution. Currently this is only available in the dimensionless display. The new feature is located in >Main Menu, >Tools, > Options, General tab. Using the tabular interpretation will provide a faster, however slightly less accurate, Neuman solution.

I've used the parameter control buttons to get a 'better' fit but my curves are still not matching?

New feature: Click on the curve, generated from your data, and drag it to your desired best fit location using your mouse. This method provides more flexibility and improved accuracy.

I'm performing a slug test in a high conductivity aquifer. Are there any solution methods suited for this type of aquifer?

The Butler High-K method (Butler et al., 2003) is appropriate for the analysis of slug tests performed in partially penetrating wells in formations of high hydraulic conductivity and those that exhibit inertial effects and oscillatory response.

We have a few lateral drains so we can enhance our recovery. Can AquiferTest handle horizontal drains or only vertical wells?

New feature in Pro: The Clonts & Ramey solution is suited for determining hydraulic properties, i.e., transmissivity, storativity and conductivity anisotropy ratio, from horizontal well pumping test data from confined aquifers.

When I click on the 'automatic' fit button I receive the following error: Warning automatic fit did not succeed". What does this mean and how do I resolve it?

This message indicates that given the data set, the automatic fit was unable to match to the data points. If the automatic fit did not succeed you may consider adjusting the starting parameters by using the Parameter Controls.

  • Select the parameter control icon above the analysis graph and use the slider bars to modify the parameter values and to provide a better starting point for the automatic fit.
  • Once these values have been adjusted you can perform the automatic fit.

Additionally, if you continue to experience difficulties with the automatic fit, you may consider increasing the number of iterations used for the fit by selecting Tools>Options and browsing to the Constants tab. The automatic fit options are available under this tab.

It appears that AquiferTest assigned random colors to my curves. Can I change the color scheme?

Once in reports, please go to >Maine menu, >Tools from the top menu bar and choose “Options”. In the Appearance tab, you can modify the colors and symbols used.

Can I open AquiferTest projects from older versions in the current AquiferTest version?

Please note that currently only projects created in AquiferTest 4.x onward can be opened in the current version of AquiferTest . To open 3.x AquiferTest projects in the new version please follow these steps:

  • Using version 4.x of AquiferTest, open your project and save. Then, using the current AquiferTest version, open your desired project, creating a back up if prompted.
  • It is recommended that you ALWAYS create a backup copy of any project files before you open them in the new version. Specifically, ensure that you back up your original MS Access database (.MDB), which contains all project data.

I am unable to print any of my reports in AquiferTest. Please help?

Your printing issue could be the result of a number of settings within AquiferTest Pro that have not been selected. Please consider the following:

Printer Setup

  • Click File and select Printer Setup from the main menu
  • Select the appropriate printer from the drop down menu since the default may not always be correct.
  • Click OK and attempt to print the reports again

*This option will also allow you to select PDFCreator as your printer which will export your reports as PDF documents. You could then open each .pdf file and print them from there.

Printout Selection

  • From the Reports tab ensure there is a check mark in the boxes beside each printout you wish to be generated. AquiferTest will allow you to view your reports by highlighting each name, however they will only print when the check mark is showing.

Printer Drivers

  • Be sure to update the drivers on your printer, this can be done by selecting your desired printer from the Control Panel on your computer.