GMS

Creating a Raster from MODFLOW Contours

You’ve just finished successfully running a MODFLOW simulation in GMS and you are viewing the results in lovely contours on your screen. Now you would like to save those results as a raster file you can import into another application.

In order to save the MODFLOW contours as a raster, the MODFLOW results will first need to be converted to a scatter point set, then the scatter point set can be made into a raster.

Converting MODFLOW Layers to Scatter Points

To convert MODFLOW data to scatter point data, do the following:

  1. Select the MODFLOW simulation.
  2. Use the Grid | MODFLOW Layers → Scatter Points menu command.
  3. In the MODFLOW Layers → Scatter Points dialog, you can select the Computed Heads option.
  4. With the Computed Heads option active, you can select the MODFLOW solution datasets and time steps to convert into a scatter point.

Once done, you will have a scatter point set in the Project Explorer containing dataset generated from your MODFLOW results.

Converting Scatter Points to Rasters

Now that you have your MODFLOW solution datasets as scatter point data, you can do the following to convert them into a raster file.

  1. In the Project Explorer under the scatter point set, select the dataset created from the MODFLOW solutions.
  2. Right-click on the scatter point set in the Project Explorer, and select Convert To | New Raster.
  3. In the Scatter → Raster dialog, set the interpolation option you wish to use and specify the extents of the raster.
  4. Finally, save your raster file with a name and raster file type.

The raster file will be loaded into GMS, so you can compare it to the contours in your MODFLOW solution datasets. The raster file contains elevation data that was in the MODLOW solution.

Now that you know how to generate a raster file from MODFLOW contours, try it in out in GMS today!

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Converting Units

Seeing which units are being used in a project or for a particular object within the project is fairly easy. Converting the units from, for example, U.S. feet to meters, can introduce problems into a project if you do not do it in the correct way.

Reproject

Reprojecting the data involves moving the data from one coordinate system to another. So if your data is in a UTM coordinate system in meters and the rest of your project is in a State Plane projection that uses U.S. survey feet, reprojecting can change the data to match. Conceptually, the data will remain in the same location, but the data will be adjusted to the new units.

To reproject a dataset:

  1. Right-click on the dataset in the Project Explorer and select Reproject.
  2. In the Reproject dialog, the current projection is shown on the left. On the right side, set the new projection and units.

When converting units through reprojection, keep in mind that Z values (elevations) don’t always convert correctly. Round off errors sometimes occur when reprojecting data. In general, reproject does well in changing the X and Y units. The Z value, if it has been set as the bathymetry, typically also converts units well using the reproject option. Other datasets often do not convert between units using the reproject method.

When converting from rasters to scatter sets, the elevation is usually recognized and converted correctly.

Dataset Calculator

Datasets units can be converted using the Dataset Calculator. This is often necessary when the data has been reprojected, but not all of the datasets can be converted using that method. For example, a velocity dataset or conductivity data.

To convert a dataset with the Dataset Calculator:

  1. Select the desired dataset in the Project Explorer.
  2. Select the Data Calculator macro, or the Data Calculator command or the Dataset Toolbox command in the Data menu.
  3. Select the dataset to convert, then multiple or divide the dataset by the conversion value.

There are a few numbers it is useful to have when doing these conversions:

  • 0.304800609601 meters is equal to one U.S. Survey foot
  • 3.28083333333 U.S. Survey feet are equal to one meter
  • 0.3048 meters is equal to one International foot
  • 3.28083989501 International feet are equal to one meter

Note that there are many datasets that will not work with the Data Calculator.

In the end, make certain all the data being used in your model is in the correct units. Having mismatched units will typically create model errors and generate inaccurate results.

Try reprojecting data or using the Data Calculator to convert units in GMS, SMS, or WMS today!
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Using Mass Flux Computations

Are you wanting to compute the mass flux for a group of MODFLOW boundary conditions? The mass flux is the rate of mass flow per unit area, or mass per time per area. Computing this can quantify the strength of contaminants at a particular location in your model.

Use the MT3DMS or MT3D-USGS model to compute the mass flux at specific location. To do this:

  1. First create and run a MODFLOW model.
  2. Then create an MT3DMS or MT3D-USGS simulation with all relevant parameters set and contaminant species defined.
  3. Make certain the Transportation Observation Package is turned on in the MT3DMS/RT3D Packages dialog.
  4. If it is not already in the model, create a conceptual model with the MT3DMS/MT3D-USGS defined species.
  5. Create a map coverage with the observation point option for the species turned on.
  6. Create points on the coverage at the locations where you want to to observe mass flux.
  7. Assign these points as observation points and enter attributes as needed.
  8. Access the Transport Observation Package dialog through the MT3DMS or MT3D-USGS menu.
  9. Turn on the Compute mass flux at source/sinks option.
  10. Run the model.

MT3MDS/MT3D-USGS will compute the mass flux at each observation point. The computation is done using the units set for the input concentration. Typically, these are the units used for the display projection in GMS. So if your project is using U.S. survey feet, then your mass flux will be calculated as ft^3*mg/L. If varying units are used in the concentrations, then conversions must be done before calculating the mass flux.

The mass flux will be contained in a dataset file with the “.mfx” file extension. This file can be opened using any text editor. The file will show the calculated mass flux for each time step and for each source or sink included in the model.

Hopefully, you now understand a little more about calculating mass flux in GMS. Try out mass flux calculations and other features in GMS today!

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5 Ways to Select Arcs in GMS

Everyone knows you can select an arc in GMS by using the Select Arcs tool and clicking on the desired arc. But did you know there are five different ways to select one or more arcs? Here’s a quick rundown of all of them:

  1. Use the Select Arcs tool to click on a single arc. This is the most common way to select an arc, but it only allows you to select one at a time. If you have multiple arcs you need selected, there are better, more efficient ways to select them.
  2. Use the Select Arcs tool while pressing the Shift or Ctrl key to select multiple specific arcs. This allows you to select only the desired arcs for whatever purpose you wish. This method includes all of the precision of the first method, but can take a long time if you have many different arcs to select. The next three methods allow you to more quickly select larger numbers of arcs.
  3. Use the Select Arcs tool to drag a box around multiple arcs to select them. All arcs where both nodes of the arc are contained within the box wil be selected. Arcs where one node is outside of the box will not be selected. The click and drag method provides a quick method for selecting multiple arcs, but is not as accurate.
  4. Use the Select All command in the Edit menu to select all the arcs in the project. Just make sure to have the Select Arcs tool selected first so GMS knows what to select. The Unselect All command can be used to deselect everything when you’re done, if desired.
  5. The Select With Poly command in the Edit menu lets you draw out a polygon around the arcs you want selected. Keep in mind that both ends of an arc must be within the polygon in order for it to be selected.

Try out these options today in the GMS Community Edition.

Edit: This post was updated on 7/20/2018 to correct information in methods 2 and 3.

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