Aquaveo & Water Resources Engineering News

The conceptual model approach in GMS is a very useful way to assign specific attributes to a MODFLOW model without having to manually input them cell by cell. One particularly helpful tool available in a GMS coverage is the "Layer Range" option.

Layer range can be used in addition to other coverage choices—such as streams, wells, rivers, head boundary, etc.—allowing you to be as precise as you need to be when applying your model attributes.

In the past, we have mentioned this tool in a blog post about assigning Ugrid attributes to specific layers, but that is only one of many helpful ways to use it. Here, we will go over each of the options available with the Layer Range, and exactly how they work.

First, turn on this option by selecting "Layer Range" in the sources/sinks column of the coverage setup dialog. At the bottom of this dialog, make sure that the default layer range for the coverage covers all the parts of your grid that you wish to use.

Second, apply feature objects to your coverage. In our example, we have created a Time-Variant Specified Head arc.

Once your feature objects are in place, you can assign values to them in the attribute table. This is where the Layer Range settings will come into play.

• Use Layer Range: This option applies your feature objects to a specific range of layers. That range is selected in the attribute table under "From Layer" and "To Layer". A feature point assigned a layer range of 2–6 will be applied to every cell in that vertical column from layer 2 to layer 6.
  Similarly, a polygon or arc will apply its attributes to the whole assigned layer range for every vertical column that it intersects.
• Auto-Assign BC to One Cell: Any time you want only one cell per column, you can choose "Auto-Assign BC to One Cell". This setting is especially useful when mapping an object type that can't or shouldn't be applied to more than one vertical cell at a time. Stream arcs are one example.
  Auto-assigning to one cell will use the elevation inputs from your feature object to choose the most applicable cell in that vertical column to receive the assigned attributes.
• Auto-Assign BC Including Lower Cells: This setting allows the coverage to automatically calculate which initial layer the object is applicable to, similar to the "One Cell" option. It then applies the object to that cell, and to everything below it within the range of the coverage.
  Including the lower cells is very useful when you do want more than one vertical cell to be assigned, but need different layer ranges for different parts of the same feature object.

Once you have selected the Layer Range option that best suits your model, you can map the coverage to your simulation. The results can be viewed in the MODFLOW | Optional Packages dialogs, as well as the Sources/Sinks table in the right-click menu for the grid cells.

The Layer Range tool is a great way to get your model attributes as specific as you need them to be without any laborious manual editing. Try it out in your GMS model today.

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!