Aquaveo & Water Resources Engineering News

Obtaining Nonstandard Data for Curve Numbers

Calculating curve numbers is a necessary process for many WMS projects. WMS contains a number of tables with suggested soil and land use data for use in calculating the curve number. These are not comprehensive lists of every possible soil data resource, however. These are, only those that are readily downloadable through WMS.

So what do you do if you need to use soil or land use data from a location without data readily available in WMS? You can use nonstandard soil or land use data by creating a file with the data formatted as a table. The format of those land table files can be applied to create a table for any soil data source, such as local shapefiles developed for specific projects.

Example of a land use shapefile

The format for these files is a set of columns as follows:

  1. Soil ID number
  2. Category Label
  3. Hydrologic soil group A
  4. Hydrologic soil group B
  5. Hydrologic soil group C
  6. Hydrologic soil group D

Once you have created a text file with your soil or land use data, import it into WMS as you would any other soil or land use data.

If you’re building your own table for your soil data, there are sources for the tables and charts to help facilitate estimating the curve numbers to put into the table.

For an explanation of or introduction to SCS or runoff curve numbers, a good source is the National Conservation District Employees Association. Their guidance may help clarify the process of creating your own curve numbers.

Additional sources can also be found for soil or land use data. Use whichever data source you feel is appropriate for your project. As long as the data is formatted correctly, WMS should be able to import it.

Try out importing soil and land use data from locations around the world using WMS today!

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Using STL Files in SMS

Starting in SMS 13.0, SMS can now make use of STL files.

STL files use tessellation, the process of mimicking a surface by assigning surface coordinates to a repeated pattern of polygons. In the case of STL files, triangles are used to make a 3D mesh that can effectively be rendered into any shape needed including landscapes.

STL files are typically used for 3D printing. They also can be used for the modeling landscapes. There are several methods for creating these files. This post will not attempt to cover the specifics of those methods as other places cover how do this.

Uploading and Using STL Files

In SMS, STL files are used to model terrain. Once you have created an STL file, importing it by using the File | Open command or dragging-and-dropping the file into SMS.

When uploaded, the file is automatically transformed into a Ugrid and adjusted for the associated z values. This UGrid can then be used for all the normal uses of such in SMS.

Example of an STL file loaded into SMS

It is important to mention that the z values may or may not be representative of the elevation depending on the source of the STL file used. Fortunately, there is a way to handle such cases in SMS. After import, the Ugrid can be converted into a 2D scatter dataset. The scatter can then be interpolated to a mesh or modified with the data calculator. If desired, tim and dim files representing that data can then be created as usual.

Exporting STL Files

To create an STL file, you must have a UGrid with the corresponding elevation data attached. This UGrid must consist of only triangular elements.

Export the STL file by:

  1. Right-click on the UGrid and select the Export command.
  2. Then select a (*.stl) file type before saving the file.

There are two STL file type available for export. The binary option is often used since it requires less memory. The ASCII file is more user friendly if the file needs to be inspected. Both save data by recording the coordinates of the vertices associated with each triangle. If unaccompanied by other files, the Ugrid will also have to be manually associated with the correct projection after uploading.

We hope to add more functionality for STL files in the future. Try using STL files with your SMS projects today!

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Exploring MODFLOW Head Boundary Packages

GMS allows using a number of different MODFLOW head boundary packages (GHB, RIV, STR, SFR, etc.) to indicate flow in or out of your model. These packages often appear to be similar. To the differences between them, here we discuss a few of these packages.

Example of MODFLOW head boundary packages available in GMS
General Head

The General Head Boundary (GHB) is, conceptually, a fixed head far from the model where it is assumed to be a fixed head with time (i.e., the river or head will not be affected by the model stresses over time). The purpose of using this boundary condition is to avoid unnecessarily extending the model domain outward to meet the element influencing the head in the model. As a result, the general head condition is usually assigned along the outside edge of the model domain.

General head cells are often used to simulate lakes. General head conditions are specified by assigning a head and a conductance to a selected set of cells. If the water table elevation rises above the specified head, water flows out of the aquifer. If the water table elevation falls below the specified head, water flows into the aquifer. In both cases, the flow rate is proportional to the head difference, and the constant of proportionality is the conductance.

River

The MODFLOW River (RIV) package only tracks flow between the aquifer and the river. With the River Package, once water has entered the river, it is lost to the model.

Stream

Unlike the River package, the Stream (STR) package routes flow through the stream. The water can travel downstream and possibly re-enter the aquifer at another point. The Stream package also allow periodic drying. However, there are more restrictions than in the River package.

Also unlike the River package, the Stream package calculates the water depth based on the flow rather than it being manually entered. There are several different options available for calculating water depth, including using Manning’s equation or a depth versus flow table.

The Stream package divides streams into reaches and segments. It models effects of rivers on aquifers while tracking flow in river. Interaction between surficial streams and the groundwater for the Stream package uses Manning’s equation and simple channel hydraulics to compute the stage in the stream.

Streamflow Routing

This Streamflow Routing (SFR2) package is similar to the Stream package. Though it has more restrictions than STR, it has more sophisticated hydraulics and routing options.

These are just the most commonly-used of over a dozen different MODFLOW head boundary packages that can be used with GMS. Go ahead and explore the different MODFLOW packages available in GMS today!

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Downloading NLCD Data

One of the crucial elements of any project is having data. WMS makes use of a large number of data sources. One type of data that we find frequently used is National Land Cover Database (NLCD) data. NLCD is provided by the MRLC (Multi-Resolution Land Characteristics Consortium) as a large collection of raster datasets.

Here are three ways this data can be imported into WMS.

Direct Download

NLCD data can be downloaded from the MRLC site. Much of the other data available on the MRLC site can also be used with WMS.

Downloaded NLCD data can be opened in WMS by selecting the Open macro, browsing to the folder containing the downloaded data, and selecting the desired raster. WMS should be able to recognize the data file and bring it into your project.

Using the Modeling Wizard

NLCD data can also be downloaded while using the Hydrologic Modeling Wizard or the HY-8 Modeling Wizard. To do this:

  1. Start the Hydrologic Modeling Wizard or the HY-8 Modeling Wizard
  2. Create the project in the first step
  3. Define your project bounds and set the project projection
  4. In the Watershed Data step, turn on the Use web services option
  5. In the Download Data (Web Services) step, select one of the NLCD data types
  6. Click the Download Data From Web button to download and import your NLCD data
  7. Enter a raster cell size for the data
  8. Save the data as a file
Using the Get Data Tool

Downloading NLCD data can also be obtained by using the Get Data tool. To use this tool, your project must have a projection already defined. When you have a projection set, do the following:

  1. Using the Get Data tool, click-and-drag a box in the Graphics Window that covers the area where you want NLCD data
  2. Save a file with the NLCD data
  3. Enter the raster cell size for the data
Downloading NLCD data

You might also notice that a lot of other data sources are available through the Modeling Wizard and Get Data tool. Feel free to try downloading data from these sources for your WMS projects.

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Using the Plot Data Coverage

Have you generated a plot in SMS and found it was difficult to see where a bridge, culvert, or other structure location matched up with the plot? The Plot Data coverage helps make them more visible, making an observation coverage more meaningful in a profile plot.

Typically, a profile shows some desired value such as water surface elevation or the riverbed elevation. This data can be more useful in many cases if structures are displayed on the plot as well. A Plot Data coverage allows creating polygons over structures that then helps display the location of the structure on the plot profile.

To use the Plot Data coverage, do the following:

  1. In the Map Module, create a new coverage with the Plot Data type.
  2. In this new Plot Data coverage, create a polygon over the area of interest.
  3. Double-click on the Polygon to assign attributes in the Plot Data dialog.
  4. Create an observation arc that includes the area of interest.
  5. Create an observation profile plot.
  6. In the Plot Data Options, turn on the Plot Data coverage.

The profile plot will now show where the polygon on the Plot Data coverage aligns with the profile.

Example of a Plot Data coverage used in a plot profile

For example, if you want to consider the impact of a new bridge placement on the flow of a river, you could create a polygon representing the bridge location. When included in the profile, this could help you visualize placing a bridge at that location along the river and at the indicated height. If water elevation data is available, such as from an SRH 2D simulation, the height of the bridge can be easily compared with elevation profile of the water surface. This could be helpful in considering if the bridge would be washed out or flooded during periods of heavy rain when the river swells.

Culverts can similarly be shown on the profile by using the Plot Data coverage. Likewise, obstructions or structures of any shape could also be shown in the profile using the Plot Data coverage. Multiple plot data coverages could be used when there is a desire to layer structures such as a hypothetical bridge and the supporting abutments or columns.

Try out using the Plot Data coverage in SMS today!

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Troubleshooting Observations in GMS

After creating your observation points in GMS, have you ever reviewed the results from the observation wells and thought they didn't look right? It can sometimes happen that observation wells give back the wrong values or are missing altogether. This can happen for a number of reasons.

Here are a few tips to help ensure that your observation points give back accurate information:

Point Outside Grid
  1. Review the location of the observation points/wells. Make certain the point is located on the grid. A common issue is that the elevation of the point causes it to be above or below the grid, so be certain to review this.
  2. Make certain the observation points have correctly mapped over to the grid. If the point is outside of the grid area, then it will not be included in the model run.
  3. After being mapped over, check that the observation wells are in the correct layer of the grid. If the observation point is meant to be on more than one layer, make certain it shows up on each layer.
  4. Well Screen Equals Zero
  5. When using a well screen, check the length of the point. If the length is 0, then the observation point will not be able to record any results. Check that the top screen elevation is higher (greater) than the bottom screen elevation by a positive, non-zero amount.
  6. Check that the observation point is in cells that are active. If there are no head values, or the cell is dry, then it is unlikely that the observation point will provide any useful information.

These are just some of the items to look for when using observation points in GMS. For most of these issues, when you save the file, a warning message should appear.

If you have a current license of GMS with paid maintenance, you may contact technical support for additional help in using observations. For project specific troubleshooting, contact Aquaveo's consulting team.

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Using Advanced Data Services Options

In the current versions of GMS, SMS, and WMS, the data service options for importing online maps has changed. It was noted by some of our users that the Advanced option for the Data Services Options dialog was removed.

We are happy to say that the advanced options for the Data Services Options dialog has been restored. The new advanced options are only available when using the Import from Web command in the release of GMS, SMS, and WMS that went out at the beginning of May 2019.

To access the Advanced options from the Data Services Options dialog, click the Advanced button, just as before, to bring up the Select Online Source dialog. This dialog allows users to bring in new data sources for downloading data.

Select Online Source Dialog

Adding new data sources to the Select Online Source dialog can be done in any of three ways:

    Add New Source Dialog
  1. The Select Online Source dialog contains a list of all of the data sources currently available. You can select one of these sources and click the Duplicate Source button to create a copy of the data source. Then, with the copy selected, click the Edit Source button to reach a dialog where you can make modifications to the source such as limiting the layers downloaded from the source or changing the image format downloaded from the source.
  2. You can click the Add New Source button to reach a dialog where you can specify the url of a new data source along with any modifications.
  3. Finally, if you have an Online Source File with the information needed to reach a source, you can click the Add Sources from File to add the source to the available list.

Sources can be deleted from the available list by selecting a source in the list and clicking the Remove Source button. Only sources that have been manually added can be removed or edited.

To get access to the new advanced options for the Data Services Options dialog, visit our downloads page today.

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What Makes a Good Quality Mesh?

Several models in SMS rely on using a 2D mesh. The quality of this mesh can greatly impact your model run and overall results, so here are some tips for making a good quality mesh.

Start with a Good Mesh Generator Coverage

A lot of how well a mesh turns out begins with the mesh generator coverage. Generally, when a poor mesh has been generated, it is because the arcs, vertices, and polygons on the mesh generator coverage did not clearly define a good quality mesh.

When defining the mesh parameters in the coverage, there are few items to keep in mind:

  • Make certain the polygons accurately reflect the work area. Do not draw polygons outside of your elevation data.
  • Vertices along the arcs determines the size and spacing of elements in the mesh. Adding too few or too many vertices along an arc can cause poor spacing. Using the Redistribute Vertices tool can help with getting the correct number of vertices, and making sure they are evenly spaced along each arc.
  • Keep individual arcs smooth and rounded to avoid interior acute angles.
  • Use the 2D Mesh Polygon Properties dialog to preview how the final mesh will appear.
Mesh generation coverage example
Check the Size Transition of the Elements

How elements transition in size can greatly impact how a model uses the mesh. In general, a gradual change in element size functions makes for a better mesh for most models. A poor mesh will have a quick change in elements size, acute interior angles, and thin triangles.

Mesh with incorrect spacing

The solution for smoothing out the element transition is to adjust the spacing of the arc vertices in the mesh generator coverage and to examine the proximity of the arcs. In general, arcs that are close to each other should have a similar number of vertices. Arcs that are further apart can have a greater disparity of vertices.

Mesh with corrected spacing
Check For an Even Patch

When creating quadrilateral elements in a mesh using a patch, it is important that the spacing of the vertices be precise. Parallel arcs need to have the same number of vertices when creating a patch or the result will be an uneven patch.

Example of an uneven patch

It is recommended to always preview the mesh when using the patch option, then adjust the number of vertices to make certain the patch is even.

Remove Unnecessary Elements

Cleaning up a mesh after it has been generated is sometimes necessary. When generating a mesh from a scatter set or other source, more of the mesh may need to be reviewed and cleaned. Using the Select Thin Triangles command and the Clean command can help with getting rid of unnecessary elements that could cause problems during the model run. It is also recommended to use a mesh with the fewest number of elements needed for your project.

These are only some of the recommended guidelines for generating a good quality mesh. We hope this helps you in your projects.

If you have questions about how to make a better mesh in SMS, contact our technical support for general questions, or contact our consulting services for project-specific inquiries.

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Splitting UGrid Layers

Have you been working with a project in GMS only to discover that the project’s 3D unstructured grid (UGrid) needs to include another layer? Fortunately, it’s rare that a UGrid needs to have another layer, but every once in a while a layer needs to be added to an existing UGrid. GMS provides a way to divide UGrid layers quickly.

One thing to note: whenever a UGrid is changed—such as with adding a new layer—the existing MODFLOW simulation attached to the UGrid will be removed. It is therefore best to make certain the UGrid is correct—including having the necessary number of layers—before building the MODFLOW simulation.

In order to add a new layer to an existing Ugrid, do the following:

  1. Using the Select Cell tool, select a cell on the layer you want to split.
  2. Right-click on the selected cell and select the Split Layer command to start the process of dividing the UGrid layer.
UGrid layer before and after being split

When GMS finishes processing, it creates a new UGrid with the additional layer, leaving the original UGrid intact. The layer to which the selected cell belonged is divided into two layers on the new UGrid. GMS averages the distance between the top and bottom of the layer, then divides the layer equally to create the two new layers. It is recommended to carefully review the new UGrid to check for any unintended anomalies.

As mentioned above, any MODFLOW simulations contained in the original UGrid are not copied to the new UGrid. A new MODFLOW simulation must be created for the new UGrid.

Another option is to create a new UGrid with the additional layer and leave the existing UGrid as is. This option is best if you need to finely control the layer elevations.

For adding layers to complicated UGrids, you may want to consider using Aquaveo’s consulting services.

Now that you’ve seen the basics of splitting a UGrid layer, try it out in GMS today!

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Modeling a Dam in GSSHA

Do you have a project that requires modeling a dam, or similar structure, in GSSHA? WMS can make this process smoother with tools designed to help define the structure quickly and efficiently.

In order to create a simulation that includes modeling the dam in WMS and analyzing the dam’s effects using GSSHA, the workflow is as follows:

  1. Import an existing GSSHA base model.
  2. In the GSSHA map coverage, use the Shift key to select the node where you want the dam to be and the node immediately downstream from it.
  3. Right-click on the selected nodes and select Attributes to open a Properties dialog.
  4. Select Output Hydrographs at those nodes.
  5. Run GSSHA.
  6. Using the results from the GSSHA run, size your embankment based on the necessary storage.
  7. Using the Create Feature Arc tool, create an arc to represent your dam.
  8. Double-click on the arc to bring up the Attributes dialog.
  9. Set the type of arc to be an Embankment, then click the ... button next to it to open the Embankment Arc Profile Editor dialog.
    1. Set the PVI Elevation to be the height of the dam.
    2. Click Compute Vertical Curve to compute the Curve Length.
  10. Double-click the node in the stream where your structures will be defined to open the Properties dialog.
  11. Click the button under Hydraulic structures to open the GSSHA Hydraulic Structures dialog.
    1. Add a Detention Basin, Weir and Culvert.
    2. Define the attributes for each of these structures.
  12. Run GSSHA again to see the effects of the dam you have created.
GSSHA Dam Modeled in WMS

If needed, adjust the display options when reviewing the results to get a better idea of how the dam structure affected the results. Try different various options to get a better feel of how the dam affected the simulation results.

Now that you know how to add a dam to GSSHA, try out modeling dam structures and other applications in WMS today!
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