Aquaveo & Water Resources Engineering News

A 2D mesh in SMS has long been the standard geometry for SRH-2D simulations. However, you might have noticed in more recent versions of SMS that SRH-2D simulations can also use 2D unstructured grids (UGrids). Today, we examine what using a 2D UGrid can mean for SMS users who model SRH-2D simulations.

Being able to use a UGrid offers a couple advantages. For one, 2D UGrids don't require the SRH-2D Post-Processor because, unlike 2D meshes, they are already centroid-based. This means the SRH-2D results can be read directly onto the 2D UGrid. Additionally, the same SRH-2D model can be run with a mesh and then run with a 2D UGrid. Since the two geometries differ in how they store data, this practice might be helpful in troubleshooting issues with the geometry design for your model. In most cases where the mesh is well built, there should not be significant differences between the results you get from a UGrid-based SRH-2D simulation and a mesh-based simulation.

The steps for creating a 2D UGrid for an SRH-2D simulation are essentially the same as creating a 2D mesh:

1. Build a mesh generation coverage with polygons.
2. Specify what kind of grid-like structure you want in each.
3. Instead of converting the coverage to a 2D mesh, convert it to a 2D UGrid.

An already-existing 2D mesh can also be converted to a 2D UGrid if so desired.

It's important to note that there are not yet any manual tools for editing 2D UGrids, so any desired adjustments to a 2D UGrid should be made before the UGrid is generated. As with the 2D mesh, this can be done by double-clicking in the polygons in the mesh generation coverage and using the dialogs that appear.

Furthermore, the principles for creating a quality mesh apply to creating a quality 2D UGrid. The quality of a UGrid is just as important to the model outcome as the quality of a mesh. In 2D UGrids for SRH-2D simulations, please keep in mind the following:

• The elements should transition gradually from large to small and vice versa. Adjacent elements should not have enormous variations in size.
• Areas that need more refined results should have finer quality elements.
• For areas that use the patch option, the elements should be fairly even.
• Triangular elements should not be excessively narrow.

These are only some of the considerations.

Much of this can be avoided by making sure that the mesh generator coverage is designed correctly. Again, adjustments to the 2D UGrid can really only be made in the mesh generator coverage before the UGrid has actually been generated.

Try using 2D UGrids in an SRH-2D simulation in SMS today!

Have you imported a DEM into WMS but wanted to trim it down to use only a part of the original data? WMS has tools designed to help you trim DEMs that you have imported into WMS, so you can use only the part of the data that's relevant to your model. In this article, we explore the ways that this can be done in WMS.

Trimming a DEM can help eliminate extra data that is not necessary for your project. Having a DEM that is too large or contains data that is irrelevant to your project can cause your project to operate slower and in some cases can skew the results of your project.

One option for trimming a DEM is when it's part of the GIS Data Module as a raster. To do this, draw a feature object polygon in a map coverage then select it. With the polygon selected, you can right-click on the raster and select the Convert To | Trimmed Raster command. This trims the raster along the border of the polygon. The trimmed raster can be converted, if desired, to a DEM that will show up under the Terrain Data folder.

Of course, there are also tools for trimming files that are already in the Terrain Data Module as DEMs. These tools can be accessed either through the DEM menu when in the Terrain Data Module or through the right-click menu for a DEM item in the Project Explorer. In both places, the tools are found in the Trim submenu.

There are two ways to trim DEMs in the Terrain Data Module: by elevation and by polygon.

When trimming a DEM by elevation, WMS brings up a dialog that lets you specify the maximum elevation that you want the DEM trimmed to. The newly created DEM will have only elevations up to the maximum elevation set in this dialog. The contours will likely change to represent the new range of values in the trimmed DEM.

When trimming a DEM using a polygon, the program turns the mouse into a tool to click out the polygon in the Graphics Window. To finish the polygon, double-click where the last point is desired. Once the polygon is complete, the trimmed DEM is automatically created.

Note that a DEM created this way is still a rectangle. This is part of the definition of a DEM. However, only the points inside the drawn polygon will be active, so the displayed contours will end at the borders of the polygon you drew. The points that were outside the drawn polygon, which make up the rest of the bounding rectangle, are set to NODATA.

Take advantage of DEM trimming tools in WMS today!

If you are using MODFLOW 6 in GMS, you may notice that it uses a different workflow than other versions of MODFLOW in GMS. These changes were made to improve flexibility and performance for groundwater modeling in GMS. One difference is the process of mapping data from the conceptual model to the MODFLOW simulation. In all versions of MODFLOW in GMS, mapping involves taking data input in the conceptual model and "mapping" that data to the grid or mesh being used by the MODFLOW simulation. With every other version of MODFLOW, this is accomplished using the Map to MODFLOW command. However, in MODFLOW 6, mapping is accomplished using the Map from Coverage command.

Now, why this change? It mostly has to do with differences in how GMS handles these different kinds of MODFLOW. A GMS project can only hold one older MODFLOW simulation, but GMS was improved to allow multiple MODFLOW 6 simulations in a project. For handling multiple models and simulations, the Map to MODFLOW command is insufficient. There might be multiple simulations in your project, and you might not want the coverage or conceptual model you are pulling data from to map to all of these MODFLOW 6 simulations.

So how does the new command work? For a MODFLOW 6 package in GMS, do the following:

1. Right-click on the simulation package and select the Map from Coverage command.
2. Select a coverage for GMS to map over the package.

GMS will then map the data from the coverage into the MODFLOW 6 package. It's important to note that only some of the MODFLOW 6 packages can be mapped from coverages. This means some packages must be manually set up in their package dialog. This new workflow can have some important effects on how you build your MODFLOW 6 simulation. In MODFLOW 6 it’s especially important that you map over the correct coverage. Since the data isn’t generically mapped over to MODFLOW, it’s especially necessary to know which coverage will be used to define each MODFLOW 6 package.

Try out the Map from Coverage process for MODFLOW 6 in GMS today!

Have you been wanting to export the contour lines in your SMS project as a shapefile so they can be opened in a different application? SMS allows exporting contour lines as a shapefile. This post will explain how to export contour lines as shapefiles.

Saving your contours as a shapefile requires your project to be set up correctly. Save the contours as a shapefile by doing the following:

1. Make sure the contours you want to convert to a shapefile are set to Linear in the Display Options. To do so, open Display Options and click on the page for the geometry that has the contoured dataset loaded (e.g. mesh, UGrid, etc.). First, make sure that contours are turned on. Then, click on the Contours tab. In the Contour Method in the top left, make certain the first dropdown is set to "Linear".
2. Make sure the desired dataset is active in SMS. This can be done by clicking on the dataset in the Project Explorer.
In the File menu, select the Save As command. In the Save as type drop-down menu, select Shapes Files (*.shp). Then navigate to the desired directory. Make sure it's somewhere you will know how to find it. Then click Save.
3. Once you’ve clicked Save, a dialog opens that gives you options for converting project information to a shapefile. Select one of the contour options. The “Mesh Contours → Arc Shapefile” option is usually best.
4. Now open your shapefile in the appropriate GIS software. The contour lines will appear as arc lines.

If you encounter issues with the shapefile, start by checking the folder where you saved the file. Make certain that all of the necessary files for the shapefile are there, including a projection file.

Another item to check is that everything you want in the shapefile is displayed correctly in the Graphics Window before you export. Try using the Uncheck All command in the Project Explorer and then checking only the desired geometry. This could allow you to more clearly see the contours as they will appear in the shapefile. You might also consider using the display options to turn off the geometry elements. This would also allow for clearer visualization of the contours. Once you can see the contour lines clearly, use the display options to adjust the contour lines if needed. Finally, there may be some differences between how SMS displays a shapefile and how other GIS applications display the shapefile. Opening the shapefile in SMS can help you determine if this is the case.

Be aware that selecting the Mesh Contours → Polygon Shapefile option when exporting the shapefile causes SMS to create a shapefile with only polygons. This might not accurately reflect the linear contours displayed in SMS since some of them might be only line segments.

Try out exporting contour lines as shapefiles in SMS today!