Aquaveo & Water Resources Engineering News

How and When to Use Depression Points in WMS

Have you ever wondered what depression points are used for? Should you be including them in your watershed delineation? Depression points can greatly help to improve the accuracy of your model when used correctly.

A depression point is significantly lower than its surrounding elevation, causing a change in flow accumulation and direction. An example of a depression area would be a watershed that contains a mine. TOPAZ is a public domain program that is used in computing flow directions and accumulations for use in basin delineation with DEMs. TOPAZ assumes that all depression points it encounters in its calculations are due to a lack of resolution, and therefore “fills” the depression point in increments until a flow path can be established straight across the low point. In order to view how a natural depression point would affect flow direction and accumulation, it is necessary to define the specified areas as depression points. This causes TOPAZ to read the cell as a NODATA cell, making TOPAZ think it is a DEM boundary instead of raising the elevation in the depression. Comparing a before and after of marking a depression point shows how the flow path is affected by depression points as displayed below.

It is appropriate to use a depression point where a natural depression occurs in the horizon. Typically you would only define depression points for larger areas where the flow path will be significantly affected by the area. It is not always necessary to define a depression point however. You want to use it when you receive straight lines for delineation boundaries for instance. This would most likely be caused by undefined depression points.

Some errors can occur however when defining depression points incorrectly.

  • Sometimes users will mark the bottom elevation that is actually up higher to the side of the depression point and is not exactly the center deepest point. This issue can be avoided by using the Set contour min/max tool in the Terrain Module to correctly identify the absolute bottom elevation. This DEM point is the one which should be marked as a depression point.
  • Another incorrect use of depression points would be to use them to outline where a stream bed is. A stream bed can be identified by using stream arcs in WMS.

Now that we’ve established when and when not to use depression points, you might be wondering how to create depression points in WMS. To create depression points in WMS:

  1. Turn on the Terrain Data Module.
  2. Use the Select DEM points tool to select the cell containing the lowest DEM elevation. If working with an area that has a large natural depression, simply hold down the Shift key to select all of the cells with low elevation at once.
  3. Select DEM | Point Attributes to bring up the DEM Point Attributes dialog.
  4. Turn on Depression point to mark the cell as a depression point.

Now that the depression points are set, you can run TOPAZ to view the new flow paths. TOPAZ will recognize the new depression, and the detention basin calculator can be used to create a stage-storage curve.

Try adding depression points in your WMS model today!

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Creating SRH-2D Pressure Zones with Overtopping

Do you have a location in your SRH-2D project for a box culvert or pressure zone with overtopping?

It is a common feature added to many SRH-2D models. Depending on how the pressure zone is created in SMS, this can be a tricky process for SRH-2D to handle. Here are some steps and tips for creating this feature successfully in SMS.

1 Use Quadrilateral Elements

Create quadrilateral elements between the boundaries of the pressure zone. Using quadrilateral elements tends to increase the stability and reliability of the SRH-2D model run. Quadrilateral elements can be created in one of two ways.

The first is to create the quadrilateral elements when creating the 2D mesh. Create a polygon for the area between and around the pressure zone. Assign this polygon with the Patch mesh type in the 2D Mesh Polygon Properties dialog.

The second method is to create the quadrilateral elements directly in the mesh using the Split/Merge tool and the Switch Element tool. This can be time-consuming, so it is only recommended for small adjustments.

2 Create Voids

Create voids in the mesh on either side of the pressure zone. There are two options for creating these voids, but one option seems to work better.

The first option, and the more stable one, is to create the voids on either side of the pressure zone when generating the mesh. Create the voids as polygons and assign them the None mesh type.

The second option is to generate the mesh then use the Select Elements tool to select and delete the elements where the voids should be. Using this method requires renumbering the mesh nodes. There is a risk that you will not be able to delete all of the nodes related to the elements which can make your mesh unusable to SRH-2D.

3 Assign Boundary Conditions

Two arcs are needed to define the pressure zone. Each arc should be created on an SRH-2D boundary condition coverage. When creating the arcs, make certain all 2D mesh elements between the arcs are quadrilateral elements. Also, it is advisable to have at least one row of quadrilateral elements just past the downstream arc.

Once the arcs have been drawn, select both arcs and open the SRH-2D Linear BC dialog. Set both arcs to the Pressure type and turn on the Overtopping option.

Both the boundary condition coverage and the 2D mesh can be added to your SRH-2D simulation to have a pressure zone with overtopping included in the results.

Try out adding a pressure zone in the community edition of SMS today!

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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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4 New Features in the WMS 11.0 Beta

For the last couple years, we’ve been working hard on the next version of WMS, and the beta for version 11.0 has now been released!

To help you learn about some of the new features, we’ve compiled this list of four new features in WMS 11.0 Beta.

  1. The first big improvement is a streamlined and updated set of floodplain delineation tools. Due to a lot of under-the-hood work, some of the delineation processes have been sped up by a factor of 10! This can greatly reduce the amount of time you spend on these projects.
  2. WMS 11.0 Beta now supports Amazon Terrain Tiles. These are high resolution digital elevation model (DEM) tiles for every location around the world, and the resolution goes as high as 3 meters per pixel. A digital elevation model is simply a two-dimensional array of elevation points with a constant x and y spacing.These DEM tiles can be accessed through the Import from Web and Get Data tools in WMS.
  3. Through a new dialog, WMS 11.0 Beta now offers better support for managing and editing cross section databases in HEC-RAS models. HEC-RAS is a one-dimensional model for computing water surface profiles for steady state or gradually varied flow. You can select, import, export, manage, and edit cross sections and cross section databases more easily.
  4. The hydraulic modeling module has been updated to be able to import and export LANDXML files for the Storm Water Management Model (SWMM), HY-12 (a storm drain analysis program used for designing inlets, pipes, and general storm drain network layouts), and EPANET (a widely used water distribution model developed by the US Environmental Protection Agency).

These are only some of the many great new and updated features in WMS 11.0 Beta. You can find a bigger list of them here. Try out the beta by downloading it 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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Converting an RMA2 Project to SRH-2D

Do you have an older RMA2 or FESWMS project that you want to convert to an SRH-2D project in SMS? Older model lack the support and many of the features of newer models. In some cases, older models will no longer run with newer operating systems. So converting older projects over helps ensure the accuracy and stability of your results.

Converting projects from an older model is not automatic. Typically, portions of the model will need to be rebuilt. Here is an example of how to convert an older RMA2 model to an SRH-2D model.

Start with creating the SRH-2D mesh.

  1. Load the RMA2 project into the current version of SMS.
  2. Right-click on the RMA2 mesh, and select Duplicate. The duplicated mesh will be used for SRH-2D. The existing RMA2 mesh will be needed, so do not delete it.
  3. Select the duplicated mesh to make it active.
  4. Select the Data | Switch Current Model menu command.
  5. In the Select Current Model dialog, select the Generic Mesh option. The is the mesh type that SRH-2D supports. Be careful to not confuse the Generic Mesh option with the Generic Model option.
  6. Click Yes when warned that there may be data loss.
  7. Click Yes when warned that you are changing from a quadratic mesh to a linear mesh.

Next, you’ll need to define the boundary conditions.

  1. Select the RMA2 mesh to make it active.
  2. Select the Data | Mesh → Map menu command.
  3. In the Mesh → Map dialog, select the Nodestrings → Arc options.
  4. Select the Create New Coverage button.
  5. In the New Coverage dialog, select SRH-2D Boundary Conditions for the Coverage Type.
  6. When done, a new coverage will appear in the Project Explorer with feature arcs in the location of the nodestrings from the RMA2 project.
  7. Select each feature arc in turn and set boundary condition parameters that approximate those in the RMA2 model. Review the RMA2 boundary conditions if needed. Additional boundary conditions can also be added if desired.

You need to define the materials next.

  1. Select the RMA2 mesh to make it active.
  2. Select the Data | Mesh → Map menu command.
  3. In the Mesh → Map dialog, select the Material Regions → Polygons options.
  4. Select the Create New Coverage button.
  5. In the New Coverage dialog, select SRH-2D Materials for the Coverage Type.
  6. When done, a new coverage will appear the Project Explorer with polygons on the assigned materials in the RMA2 project.
  7. Review the material properties and the assigned materials for each polygon to make certain they converted correctly.

Finally, build the SRH-2D model simulation.

  1. Right-click in an empty space in the Project Explorer and select New Simulation | SRH-2D
  2. Link the SRH-2D mesh, boundary condition coverage, and material coverage to the new simulation.
  3. Right-click on the new simulation and select Model Control.
  4. Set the SRH-2D model control to approximate the conditions in the RMA2 model. Review the RMA2 model control if needed.

At this point, the RMA2 mesh could be removed and the SRH-2D model should be ready to run, though some tweaking may be necessary. Refer to the SRH-2D Troubleshooting Guide if needed.

Converting other models, such as FESWMS, follow a similar process to that described above. Try out this conversion process with your older projects today in SMS.

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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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Visualizing Meteorological Data

Do have rainfall data you would like to visualize in WMS? Inside WMS there are a couple tools to make your rainfall data visually interesting.

After you have imported your precipitation data, such as NEXRAD data, you can adjust your display options and/or create an animation.

Adjusting the Display Options

  1. Use the Display | Display Options command to open the Display Options dialog.
  2. Adjust your display options to show the data you want captured. It is recommended to turn on the Contours options.
  3. If using the Contours option, right-click on your rainfall dataset under 2D Grid Data and select Contour Options to open the Contour Options dialog.
  4. Adjust the contour method and interval to best display your rainfall data.
  5. With the down arrow key on the keyboard, step through the time steps in the properties window on the right sidebar to see how the precipitation varies.

Creating an Animation Loop

  1. Select your rainfall dataset in the 2-D Grid Module. The selected dataset will be used to create the film loop and can be cumulative or incremental. View incremental rainfall datasets in the same way as cumulative datasets.
  2. Select the Data | Film Loop command to open the Film Loop Setup Wizard. This wizard needs to be opened with the 2-D Grid Module active in order to have access to the meteorological data options.
  3. The first step in the Film Loop Setup wizard is essentially the same as creating any other animation through WMS. Select the location where the animation file will be saved and the type of film loop to generate.
  4. The second step of the Film Loop Setup wizard is to set the desired time step options for the rainfall data.
  5. The final step is where you will finalize the display options of the animation, and click Finish.
  6. WMS will take a few moments to create and save the animation file. The animation will start playing as soon as the saving process is complete.

When all is done, you can view your animation using the AVI play provided with the WMS installation, or you can use another application, such as GoogleEarth. The animation will display the movement of the storm through the selected time steps.

Try visualizing meteorological data in WMS today!

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5 Ways to Make Projects Work Faster

Have you ever noticed your SMS project taking a long time to open or running slow when you’re working in it? Does the project seem to lag when zooming or panning? Perhaps it is time to clean up your project so it runs faster.

While not every project can be made to load or work faster, there are some items that can be done to speed things up. In general, a project that takes a long time to open or operates slowly is usually a larger project with many large components. Having a detailed mesh or large raster files will often slow down SMS on many machines.

To get things going faster, here are five tips for making your project work faster.

1. Change Display Options

Having more objects visible in the Graphics Window will impact how quickly SMS can operate. When SMS is trying to display a lot of data, it will slow down. By reducing the amount of visual information in the Graphics Window, SMS can process faster. This can be done in two ways.

The first method is to hide items in the Project Explorer, such as images or map coverages that are not being currently used. Having several images and rasters showing can particularly slow down a project.

The second method is to open the Display Options dialog and turn off options that are not needed. Contours and vector displays and displaying mesh elements can particularly slow down SMS. Keeping the total number of active display options to a minimum when working with large projects can speed things up for you.

Finally, when opening a large project or file, turning off all or nearly all of the display options can reduce the time it takes to open.

2. Remove Unnecessary Files

Does your project have a lot of data in it? There is a chance that this is slowing things down. Removing files that are no longer needed from the project can help.

If you have already interpolated your elevation data to your mesh or grid, then that data can be removed. If you have a dynamic image in your project, SMS will update the image every time you zoom or pan. Replacing the dynamic image with a static image and removing the dynamic image will speed things up. Shapefiles can also be removed from the project once you’ve interpolated or converted their data.

3. Resample Rasters

Having a large raster or lidar file is not really that unusual. However, having a 10 gigabyte (or larger) file loaded into your project will make SMS run slower. In many cases, all of the data contained in these large files isn’t necessary for the model to run and obtain accurate results.

Resampling the raster to a lower resolution can help. If the raster has already been loaded into SMS, right-click on the raster in the Project Explorer and select Export to resample it. When done resampling and adding the resampled image, remember to remove the original file from the project.

SMS uses a simple resample process. For more controlled application of rasters, other software can be used.

4. Refine the Mesh or Grid

Are you working with a detailed mesh or grid with a lot of elements? While fine detailed meshes and grids are sometimes needed, only certain parts of the mesh or grid may need those details. The rest of the mesh or grid can have larger elements without affecting the accuracy of the project.

For example, when using a mesh for a riverine model, fine elements are generally only needed around the channel and structures. The mesh will often still be suitable using larger elements further away from these key areas.

5. Keep the Number of Simulations Small

Having a lot of simulations in one project file is tempting. For models that use the simulation process, such as SRH-2D, there is no limit to the number you can create.

However, for each simulation in your project file, SMS has to load that instance of the simulation. While all of your simulations may use the same geometry, items such as the model parameters will have been duplicated and increase the file size.

Therefore, when possible, it is best to limit the number of simulations in the project. You may want to create copies of your project then only include simulations in each project that share a particular variable. For example, one project file might have simulations with 10 year predictions while another project file has simulations with 100 year predictions.

Try out any of these tips with your SMS projects 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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