Aquaveo & Water Resources Engineering News

Speed Up Edits Using Mesh Subsets

While working with meshes in the Surface-water Modeling System (SMS), you may have noticed that the more elements there are in the mesh, the slower the processing speed gets when making edits. Subset edit mode allows you to edit just one portion of the mesh at a time, which can increase the processing speed considerably. You can access the “Edit Subset” option by selecting the elements on the mesh you want to work with and right-clicking in the Graphics Window.

Using the Edit Subsit mode

Working within the edit subset mode was designed to let you work on a large mesh without overtaxing your machine’s memory and processing power. When you select a section of the mesh and enter subset mode, SMS will stop displaying the parts of the mesh that were not selected. This allows SMS to ignore the elements and data on the parts of the mesh outside of the subset. This can help free up computing power while making changes to the subset mesh. When you are done making your changes, you can exit the subset mode to have SMS include your changes in the full-sized mesh.

While in subset mode, the mesh in the Project Explorer will be tagged with the (subset) suffix. Some of the specific commands that you can use in subset edit mode are:

  • Commit Subset: this command takes you out of subset edit mode, and merges the changes made to the mesh subset with the rest of the mesh.
  • Revert Subset: this command takes you out of subset edit mode, but does not retain any of the changes made to the mesh subset.

You may notice that "Refine" is listed as an option in the right-click menu while subset edit mode is active, however you are not able to refine elements in a subset. If you select "Refine" an error will appear stating "Command not available in subset edit mode."

Some actions that you are not able to perform while in subset edit mode are:

  • Making changes on the border of the mesh subset.
  • Creating a new mesh.
  • Running a numerical model.
  • Changing attributes such as boundary conditions on nodes, nodestrings, and elements.
  • Renumbering node/nodestring/element IDs.

Head over to SMS and see how subset edit mode speeds up the processing time when editing large meshes today!

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Utilizing the Transient Step Function Method

The Groundwater Modeling System (GMS) provides tools for working with transient MODFLOW simulations. When working with transient dataM in a MODFLOW model, it is important to understand stress periods and how GMS calculates their values. There are two different methods you can use to define the values for a stress period: the continuous time series method, and the step function method. This blog post will cover how to input the data for a stress period in the XY Series dialog so that GMS will calculate their values correctly.

Transient MODFLOW simulations use time intervals called stress periods to define the values of transient stresses such as pumping rates, and river stages. The values for stress periods are entered in the XY Series dialog, which is opened from the Attribute Table dialog. For a continuous time series, you need to enter only one data point per time step. When you enter only one value per time step, GMS assumes that the value continues to increase through the stress period, creating a straight line connecting the two points for a smooth transition. But because GMS needs a constant value for each stress period, it will take an average of the starting values of that particular stress period and the starting value of the following stress period.

The step function method tells GMS that there is only one value for each stress period, rather than a continuously increasing value. To input data in the XY Series dialog so that GMS knows that there is only one constant value through the entire stress period, you’ll need to enter both a start value and an end value. The figure below shows an example of the format to use.

Step function in GMS

As you can see in the above figure, you need the end value of a stress period to match the start value of the following stress period. This creates "steps" in the data, telling GMS to read a constant value through the entire stress period, rather than having a gradual increase from beginning to end.

Head over to GMS and try creating a step function for your transient MODFLOW model today!

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Creating Reliable Arc Pairs for SRH-2D

SRH-2D models in the Surface-water Modeling System (SMS) often use pairs of arcs to represent structures like culverts, weirs, bridges, and gates. For some projects, it matters for SRH-2D about how these arc pairs are drawn, and improperly drawn arcs can stand in the way between you and a successfully run model.

Arc pairs in SRH-2D models need to be drawn from left to right as if you are looking from upstream to downstream. This can get quite confusing, so here are a few tips for how to be able to tell which direction your arcs need to go by making use of display settings in the Display Options dialog.

Using vectors to find stream direction

If you’re not sure which direction is upstream and which is downstream, select 2D Mesh from the list on the left of the Display Options dialog and turn on Vectors. This requires having a dataset associated with the mesh that contains vector values. The vectors will display the direction the water is flowing, which makes it easy to be able to tell where upstream is. Now, to draw the arcs in the correct direction, imagine you are standing upstream and looking downstream. Then start the arc on your left and end it on your right. Both arcs need to be drawn in the same direction.

What do you do if you’ve already drawn the arcs and then you try to run your simulation and it fails? If the failure is caused by misdrawn arcs, the error will read "Program stopped due to the following: Linked Pair nodestring direction is wrong; please reverse them". The fix is simple if you have only one pair of arcs on your mesh: select both arcs in the Graphics Window, right-click, and select Reverse Arc Direction.

The Reverse Arc Direction command

However, the existence of more than one arc pair can make solving this error a little more complicated. Rather than going around and either redrawing or reversing all the arcs, here's what you can do to pinpoint the problematic pair. First, open the Display Options dialog. On the Map tab check the box next to Annotations and click the Options button. In the Arc Annotation Options dialog, turn on Show arc direction arrow. Doing this will add arrows to the arc, pointing toward the end. This makes it easy to look at the arcs and see which ones are facing the wrong direction, at which point you can use the same steps as above to reverse the arc direction.

Head over to SMS and use this guide to help your SRH-2D model run more smoothly today!

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Using Mesh Auto-Backup

Needing to save and reload older versions of your 2D mesh in the Surface-water Modeling System (SMS)? SMS 13.3 has a new set of tools that let you do just that. The Auto-Backup folder included in the Toolbox contains the Mesh Backup and the Mesh Reload tools. These tools let you save past versions of a 2D mesh while you are editing the mesh. If you discover a change to the mesh was undesirable, you can load a version of the mesh before the change was made.

SMS uses 2D meshes for a wide variety of models including, but not limited to, ADCIRC and SRH-2D, as well as generic models. Using the new Auto-Backup tools, you are free to make as many edits to the mesh as you need knowing you can recover the previous versions. This blog post reviews how the Auto-Backup tools work.

Mesh Backup Tool
The auto-backup tools

The Mesh Backup tool creates a series of backups at specified intervals for a specified number of iterations. Both the interval and the number of backups are determined by the user in the tool’s dialog. The default values are a mesh backup every 20 seconds, 10 times. These values can be changed to whatever works best for your project, however, it is recommended that you limit the amount of backups to roughly 200 or less.

When you run the tool, a dialog labeled Turn on/off auto mesh backup will appear. This dialog means that the tool is on, and will run in the background while you work on your mesh. This dialog is intended to stay open while you work on your mesh. Clicking Cancel will turn off the tool. While the tool is running, SMS checks to see whether or not a change has been made to the mesh every time the specified time interval has elapsed, and then creates a backup copy.

Running the mesh backup

The log portion of the Turn on/off auto mesh backup dialog keeps track of how many backups have been made for the mesh. It will also tell you if there was an interval where no changes were made to the mesh. In cases where no changes were detected, a backup copy of the mesh during that period will not be stored.

Mesh Reload Tool

The Mesh Reload tool is where you can access the mesh backups. Naturally, this means that you have to run the Mesh Backup tool before anything will be available to reload. The Mesh Reload tool dialog contains a dropdown menu with all the backup meshes labeled by timestamp. The dropdown menu will often not contain every single time stamp, because there will likely be some time stamps where no changes to the mesh have been made.

Using the Mesh Reload tool does not erase the current mesh, or backtrack any changes that you’ve made. It will simply add a copy of what the mesh looked like at that time stamp under the "Mesh Data" folder in the Project Explorer. Try out the new Auto-Backup tools in SMS 13.3 today!

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Solution for Overlapping Points in MODFLOW

When using the Groundwater Modeling System (GMS), it is important to understand how cells work in MODFLOW models, especially with conceptual models. Conceptual MODFLOW models are defined using feature objects such as points, arcs, and polygons on a grid. GMS processes each feature object separately, and occasionally there may be more than one feature object in a cell. MODFLOW is able to handle more than one boundary condition in a cell simultaneously, however, there are some things you should note.

The use of coordinates is essential to GMS as a whole, but not to MODFLOW. GMS uses coordinates to keep track of the exact location of feature objects relative to each other, as well as relative to the grid and other model data. Because the cell is the smallest unit of measurement in MODFLOW models, it only cares about the contents of the cell and not the specific location within it. All feature objects within the cell are mapped to the cell center and used for the cell calculations simultaneously.

When importing MODFLOW data that wasn't created in GMS, there are no coordinates tied to that data, so GMS uses the cell center as a reference and places all points there. This poses a problem as GMS requires that all points are assigned to unique coordinates, so GMS will generate an error message if any two or more points share an x, y, and z location. The way to fix this is pretty straightforward, although it can become tedious depending on the number of points on your grid. To solve this problem, follow these steps:

  1. Open the Attribute Table dialog by double-clicking on a point in the Graphics Window.
  2. Make sure the Feature type is set to "Points", and the Show dropdown is set to "All".
  3. Check the box next to Show coordinates.
Overlapping points in MODFLOW

Now you can identify which points share the same coordinates and make the necessary changes. GMS only cares if more than one point has exactly the same coordinates in the x, y, and z directions. Offsetting a point even slightly in one of the three directions is enough for GMS to no longer have a problem, and the calculations will come out the exact same as long as the point remains within the original cell.

Head over to GMS and use these tips to make sure your MODFLOW simulation runs smoothly!

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How to Turn on Hydrographs for GSSHA Outlets

Are you needing to enable hydrographs in your GSSHA model in the Watershed Modeling System (WMS)? Hydrographs are a valuable tool included in WMS for understanding water dynamics in your model. In this blog post, we will learn about the process of enabling them within your GSSHA model.

The Gridded Surface Subsurface Hydrologic Analysis (GSSHA) model is a two-dimensional finite difference rainfall/runoff model. GSSHA uses a grid to establish the computational domain and parameters for surface runoff. The GSSHA model is fully coupled with hydraulic stream flow/routing models. After building a GSSHA model in WMS, you can create hydrographs to analyze the results.

Select a Sub-Basin Outlet Point within your GSSHA model, and identify one of the points where you want to monitor water flow and drainage closely. When using a GSSHA type coverage, the hydrographs can be turned on or off in the point attributes dialog. To access this dialog:

  1. Select one of the sub-basin outlet points, and right-click it and choose Attributes.
  2. In the Properties dialog that appears, turn on the checkbox labeled Hydrograph Output.
  3. Click out and this will turn on the hydrograph for that particular point.
  4. Next, re-run GSSHA. This is a crucial step because new GSSHA results will be needed to access the hydrograph.
Example of Hydrograph for GSSHA

After the new solution is loaded, you should see the hydrograph icon next to that point. From there, you can select and view it. Now, you can read the data and gain valuable insights into water flow dynamics at that location.

It is important to note that if you do not see the hydrograph icon then it is likely that WMS did not register you turning on the hydrograph option for the location. Check the properties for the model to see if the hydrograph output options were correctly saved.

Turning on Hydrographs for different outlets is one of the many options you can use with GSSHA in WMS. Try out turning on Hydrographs for different outlets and other options for GSSHA in WMS today!

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Using the Hydraulic Toolbox with SMS

You may have already used the Hydraulic Toolbox to define a culvert for an SRH-2D model, but did you know its suite of calculators can assist you in many ways when creating a simulation in the Surface-water Modeling System (SMS)? The Hydraulic Toolbox is a software developed for the FHWA by Aquaveo, and there are many uses for the calculators, but today we’ll go over one example today to give you an idea of what you can do.

The Hydraulic Toolbox can assist you with calculations for other simulations, such as an SHR-2D urban hydraulics project in SMS. One of the main calculators that can be used for urban modeling with SRH-2D is the Curb and Gutter flow analysis.This calculator examines flow across storm drain inlets for various curb and gutter openings.

Example of the Hydraulic Toolbox with SMS

The Hydraulic Toolbox includes a macro that opens the Curb and Gutter Analysis calculator, or you can access it through the Calculators menu at the top of the window. This adds it to the Project Explorer under a “Project” folder. Once it has been added to the Project Explorer, double-click on the tool to open the calculator’s dialog. There are three main parts to the calculator: Gutter, Inlet, and a Parameters table. The Gutter section contains values for the gutter dimensions. This includes, but is not limited to, the gutter width, design flow, width of spread, etc.. The Inlet section is where factors defining the inlet location, inlet type, grate type, etc. are included. The Parameters table displays all the inlet data after it has been calculated by using the “Compute Inlet Data” button.

The Hydraulic Toolbox is separate from SMS, so as of SMS 13.3, data from the calculator will need to be entered manually into the relevant portions of SMS. The calculated data can easily be viewed from the calculator dialog itself, or you can export a document that contains a list of all of the data from the calculator. The Create Report function can be performed by right-clicking on the project folder in the Project Explorer, clicking the “Create Report” macro, or finding the Create Report option under the Calculators menu.

You can also attach notes to the project in the Hydraulic Toolbox. The options that allow you to create notes are found in the same three locations as the Create Report function, detailed above.

More in depth information about how the Curb and Gutter calculator, as well as the Hydraulic Toolbox in general, works can be found in the User’s Manual, which is accessed through the Help menu in the Hydraulic Toolbox. The Hydraulic Toolbox can be downloaded from this link.

The Curb and Gutter analysis calculator is just one example of how you can use the Hydraulic Toolbox with SMS. Head over to SMS and the Hydraulic Toolbox to explore the variety of calculators and how they can help you with your project today!

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How to Refine an Unstructured Grid

When working with a multi-layer unstructured grid (UGrid) in the Ground-water Modeling System (GMS), your project may require different levels of refinement in each layer to introduce complexity to the stratigraphy. GMS currently offers a limited number of ways to achieve this in a 3D UGrid module. Mapping coverage directly to a 3D grid simplifies vertical refinement considerably, but it results in all layers being of uniform size. This blog post will cover the most straightforward way to create a complex stratigraphy, as well as some things that may be useful to know about how refining grids works and what the limitations are.

The type of grid that will often get you the closest to where you want to be is a Quadtree grid. These are the steps you’ll want to follow:

Using the Refine command to refine a quadtree
  1. Use the TINs/Horizons to UGrid approach to generate a grid that incorporates the desired pinchouts and ensures an appropriate level of refinement for the least refined layer.
  2. Right-click on the Quadtree UGrid in the Project Explorer and scroll to the bottom of the UGrid Properties dialog window.
  3. Make sure the Constraint dropdown is set to "None". If the constraint is set to "3D", you will not be able to refine the UGrid cells.
  4. Note that you can’t change the constraint back to "3D" after changing to "None", so you may want to duplicate the UGrid and make changes to that one to preserve the original.
  5. In the toolbar above the Graphics Window, check the box for Single Layer to isolate a layer of the grid for refinement. Highlight the cells you wish to refine using the Select Cells tool.
  6. Right-click on the selected cells and choose Refine.

The newly generated UGrid maintains the original level of refinement on all layers except for the one where you just refined some of the cells. You can repeat this process as many times as needed to achieve the desired level of refinement.

Currently, there is no automated process for this kind of complex refinement, so while it is possible to use this process on a larger project, it may not be practical. If you have a limited number of areas to work on, this workflow lets you produce a grid that features your desired TIN pinchouts, with varying levels of refinement for different layers. It is also not possible to un-refine a grid, so you’ll always need to start with the least refined layer and work your way to the most refined.

Head over to GMS and try this method to refine your 3D grid today!

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Tips for Locating the Correct Projection

It is crucial that data brought into GMS, SMS, or WMS contain the correct coordinate system. The coordinate systems are designated through the use of projections. But what do you do if you import data and it doesn’t have the correct projection information or is missing projection information all together?

Example of The Display Projections dialog

If you know what projection the data is supposed to be set to, use either the Display Projection dialog to set the projection for the project or right-click on the data in the Project Explorer to set the object projection. It is recommended that all data in a project use the same projection. To set the projection using the Projection dialog, do the following:

  1. Go to the Display menu at the top of the window and select Display Projection. This will bring up the Display Projection dialog.
  2. Under the Horizontal section, if “No projection” is selected, change it to “Global projection”. If “Global projection” is already selected and you want to change the projection, select the Set Projection… button.
  3. /From the dialog that opens, you can search through the provided database for the correct projection, or you can import a projection (*.prj) file from outside the application.

More information about the Display Projection dialog can be found here [2]. The object projection is set through the Project Explorer right-click menus, but otherwise follows a similar workflow.

If you already have data imported into the project that has the correct projection, see if you can reproject the data with the incorrect or missing projection. In general, you can reproject the data by right-clicking on a specific data object in the Project Explorer. With SMS, you can also go to the Display menu at the top of the window and select Reproject All… to reproject the data all at once.

If you don’t have a projection, use the Online Maps tool to locate the correct area in the world, then download the data using Online Maps to obtain coordinate data. Set your data to use this projection. Make certain the data lines up correctly with the downloaded data.

Rarely, the project information is included in the data but XMS fails to read the projection. This is often the result of a formatting issue. Try opening the file in a text editor to see what projection information is there. Then either adjust the formatting so XMS can read the projection information, or set the projection for the data after importing.

Head over to any of the XMS products and see how projections work today!

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Using SRH-2D Initial Conditions

Are you wondering which initial hydraulic condition to use for your SRH-2D model in the Surface-water Modeling System (SMS)? Setting the initial condition for how each cell is to be treated in an SRH-2D simulation is an integral part of the model. This blog post will explore each of the five options for the initial conditions of a simulation that SMS provides. The settings for the initial conditions are found in the SRH-2D Model Control of the simulation on the General tab.

Example of SRH-2D initial conditions in SMS

The "Dry" initial condition is the default in SMS. This condition means that there is no water in any of the elements. This selection works well for almost any simulation and is recommended as a good option for the base of an SRH-2D project if you are not certain which condition will suit your project best. The dry condition is also commonly used to create a restart file, which will be covered later.

The "Automatic" condition begins the simulation with water at the outflow depth specified in the boundary condition coverage, which fills the domain. The outflow depth is assumed to be anything lower in elevation than the elements marked as containing backwater. Anything above the backwater elements are marked as dry. Dry and automatic are the best options to use to prepare a restart file condition.

The "Initial Water Surface Elevation" condition takes a water surface elevation dataset and applies one elevation value to all elements. If the starting elevation of an element is higher than the assigned water surface elevation, SMS automatically marks that element as dry. The Initial Water Surface Elevation condition is similar to Automatic in this way, but it can be useful if the water surface elevation value you want to use for your project is different from the elevation at the outflow boundary.

The "Water Surface Elevation Dataset" condition takes the values from a dataset at a single time step to determine the water surface elevation value for each element at the start of the simulation. Unlike the Initial Water Surface Elevation condition, the elevation value at each element will vary. In order to use a water surface elevation dataset condition, a simulation will need to have already been run.

The "Restart File" condition allows you to upload a file from a previous run that contains the initial conditions. This is a quick way to split a particularly long simulation into smaller chunks, which will cut down on run time. Each time SRH-2D runs with any of the initial conditions listed above, a restart file is written and saved to the data files folder outside of SMS. It should be noted that a restart file has to have been generated from a mesh that exactly matches the mesh in the simulation, otherwise it will not work. The slightest difference in the restart file mesh and the simulation mesh will generate an error during the model run.

When a restart file is used to denote the initial conditions, the hydraulic conditions that were computed during the run that created the restart file will always be applied starting at the very first time step in the simulation. More in depth information on the usage of a restart file in SRH-2D can be found in this blog post.

Head on over to SMS and explore the different ways these initial condition options can help you with your SRH-2D project today!

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