GMS

Using Top Elevation Data for Starting Head Values for MODLOW 6

By aquaveo on May 28, 2024

The Ground-water Modeling System (GMS) includes multiple methods of setting the starting heads in the Initial Conditions (IC) package for MODFLOW 6. Starting with GMS 10.8, you can use the top elevation data already entered in the Discretization by Vertices package (DISV) for your starting head values without any extra steps.

When you open the Initial Conditions (IC) dialog, it shows several options for setting the starting heads. For simple models you can set a constant value for starting heads across the entire grid. But for more complex models, you'll want values to better represent the test area. This often means you have to either manually enter, copy and paste, or import from another data file.

However, doing this sometimes involves duplicated work you might have already completed in the DISV package. To eliminate this inefficiency, GMS 10.8 has added a new method that allows you to use the DISV top elevation data as your starting head values. This can be done using the following steps:

Open the Initial Conditions (IC) dialog.
Check on the box that says "Set starting heads equal to cell top elevations."

Starting head equal to cell top elevation option

Turning on this option will match the starting heads to the elevation data already imported or entered in the DISV package and grays out all other parts of the dialog.

Using this option, the top elevation data will be used as the starting head values during the MODFLOW 6 simulation run. Setting the starting heads equal to the top elevations in GMS offers some benefits:

It provides an additional option for inputting the starting heads data.
It can save you time by using data already in the model.

As always, it is best to review the data before running the simulation and after running the simulation to verify that the values were incorporated correctly.

Now head over to GMS 10.8 and check out using your top elevation data as your starting heading values in your MODFLOW 6 projects today!

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Utilizing MODFLOW Symbols Display Options

By aquaveo on May 7, 2024

The Groundwater Modeling System (GMS) has many different options for customizing the display of your project. One display feature created for MODFLOW in GMS is the ability to use symbols to represent the properties of individual cells. This can be quite useful especially for more complicated MODFLOW models. You can use the MODFLOW symbols in the Display Options dialog to represent things like rivers, lakes, wells, drains, and more.

You can find the MODFLOW display options as their own tab by selecting the corresponding grid from the list on the left side of the Display Options dialog. The MODFLOW symbols all have a default shape, size, and color. The shape, size, and color of the symbols can all be customized by clicking the button to the left of the checkbox. The ability to customize the MODFLOW symbols is a useful feature for everyone, but especially our users who are visually impaired or color blind. For the best results, the symbols should be set to something different enough from each other that it is easy to tell which is which at a glance.

If you use the MODFLOW symbols in your project, you should consider turning on the display symbol legend. The legend shows a list in the corner of the Graphics Window of all of the MODFLOW cell properties contained within the current project, making it easier to keep track of what everything means. Only symbols that exist in the layer being viewed will appear in the legend.

There are a few additional symbol display options for MODFLOW on the Map Data section of the Display Options dialog. A list of the symbols appears when MODFLOW is selected from the Coverage dropdown. These symbols are specific to properties on the coverages in your project, and they can be customized in the same way as the symbols under the MODFLOW tab of the grid in the Display Options dialog.

Open GMS and use the MODFLOW symbols in the display options to help you keep track of the properties of your MODFLOW project today!

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Defining Constant Concentration for Multiple Species in MT3DMS

By aquaveo on April 16, 2024

Are you struggling to define separate constant concentrations for different chemicals in your MT3DMS model areas? MT3DMS is an invaluable tool for groundwater modeling, but like any software, it has its limitations. The Groundwater Modeling System (GMS) incorporates MT3DMS into its interface, which includes both the benefits and limitations of MT3DMS. The inability of MT3DMS to define separate constant concentrations for different chemicals in the same area can be a hindrance for modelers aiming for precision and accuracy in their simulations. So what should you do if your MT3DMS model requires defining constant concentration for two or more chemicals in separate areas?

There's a workaround provided by the MT3DMS developers for defining multispecies simulations. By using negative values in the table for species that need to be left undefined, you can effectively overcome this constraint and tailor your model to your specific needs. In GMS, this value is entered on the Source/Sink Mixing Package dialog for MT3DMS.

Example of the Constant Concentration Settings for MT3DMS

Note that it may seem as though a value of zero would have the same result when defining concentration. However, this is not the case. Entering a value of zero will be recognized as the same as entering a positive value. Therefore, it is important to enter a negative value for species that need to be left undefined when working with a multispecies simulation.

When running MT3DMS, cells that have negative values entered for a species will not have constant concentration for that species applied to that cell. Concentration, constant or varying, will be applied to all cells where the value is positive. As always, it is important to review the entered species values before running the model to ensure accuracy.

Now with more understanding of how to work with constant concentration values for multiple species in MT3DMS, see if you can use it in your GMS project today!

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New MODFLOW-USG 3D Dataset to Array

By aquaveo on March 26, 2024

While most groundwater projects typically only need a 2D dataset to define arrays, 3D datasets are becoming more available. There’s a new feature in the Ground-water Modeling System (GMS) version 10.8 for MODFLOW-USG and MODFLOW-USG Transport models. MODFLOW-USG and MODFLOW-USG Transport are MODFLOW models that were designed specifically to be used with unstructured grids, or UGrids. The Recharge (RCH), Evapotranspiration (EVT), and EvapoTranspiration Segments (ETS) packages in MODFLOW-USG now have the option to use a 3D dataset to define the input arrays. Previous versions of GMS only had the option to use a 2D dataset with a matching 2D structured grid.

Example of the 3D Dataset to Array option

You can find the 3D Dataset → Array button in the properties dialog of the Recharge (RCH), Evapotranspiration (EVT), or EvapoTranspiration Segments (ETS) package. In order to use the 3D Dataset → Array button, the 3D dataset in the MODFLOW-USG model has to have the same number of rows and columns as the 3D grid. If the rows and columns don’t match the 3D grid, then the button will be grayed out and you won’t be able to use it.

Clicking the 3D Dataset → Array button will bring up a Select Dataset dialog with a list of all the datasets associated with the current 3D grid. You can then select the relevant dataset to assign values to the MODFLOW-USG package. 3D datasets are often created using the 3D Scatter Point tool, which can help you interpolate rainfall data to the cells on your grid. If you are using a transient dataset, then the dataset values will be interpolated linearly to each stress period when they are copied to the array. You can learn more about using the 3D Scatter Point tool on this page of our wiki.

Now head over to GMS 10.8 and try using the new 3D Dataset → Array button in your MODFLOW-USG or MODFLOW-USG Transport project today!

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