Aquaveo & Water Resources Engineering News

Assigning Elevations in GMS

GMS offers several options for importing, exporting and manipulating elevation data. With so many options, sometimes it can be confusing when choosing which method to use. If you sometimes struggle with elevation data, you’re in luck, because in this blog post we will be exploring different ways that you can utilize your elevation data to accomplish your goals. Listed below are several ways in which you might be interested in using your elevation data.

  • Assigning elevations in the conceptual model (e.g. to drain nodes)

    Using the Select Points/Nodes Tool , double-click on a point/node such as a drain node. This brings up the Attribute Table dialog. Make sure the Feature Type is set to point/node. Here you can set the type of point/node (such as to a drain or a river) and set the bottom elevation. Things such as river arcs and drain nodes require elevations to run the model in MODFLOW.

  • Interpolating scatter sets/rasters to MODFLOW elevations

    Right-click on the scatter set or raster and select Interpolate To and select MODFLOW layers. This will bring up the Interpolate to MODFLOW Layers dialog. Select the dataset you want to interpolate on the left side of the dialog and the layer you would like to interpolate to on the right-side. With both the dataset and the desired layer selected, click Map. This will add the selection to the Dataset=>MODFLOW data queue. Select Interpolation Options if you want to change the interpolation method. Click OK to exit the dialog and interpolate the scatter set to the layer.

  • Making sure nothing in your conceptual model assigns a polygon elevation that would overwrite the interpolated values

    It is important to note that if you have top and/or bottom elevations assigned as areal properties to a polygon, and you map this coverage to MODFLOW, any scatter points or raster elevations previously interpolated to MODFLOW as the top/bottom elevations that lie within the polygon will be overwritten.

  • Pulling datasets out of MODFLOW (e.g. Layer → 2D Dataset) for manipulation and/or use elsewhere

    Another great feature available in GMS is the ability to pull elevations from a MODFLOW layer to create a 2D dataset. This 2D dataset can then be manipulated and/or used elsewhere for various purposes. This can be done in one of two ways; by using the Layer → 2D Dataset option, or by using the MODFLOW Layers to Scatter option.

  • Layer → 2D Dataset vs. MODFLOW Layers to Scatter (preferred)

    It is possible to create 2D datasets from layer arrays in MODFLOW by going to the Global Options in MODFLOW, and selecting the array you want to create a dataset of (starting heads, top elevations, bottom elevations). In the array dialog box select Layer → 2D Dataset or Grid → 3D Dataset. The dataset that this creates will have ids, i, j, and f values.

    The preferred method for creating datasets from MODFLOW layers is by selecting the layer and then selecting Grid | MODFLOW Layers to 2D Scatter Points. In the MODFLOW Layers → Scatter Points dialog, you can select to create scatter points within a selected coverage and chose the desired coverage. If you use this option, there must be a polygon in the coverage for the points to map to. This dialog also gives many other options that are extremely useful and convenient. When using this method, the 2D scatter set will have x and y coordinates and the f value.

As you can see there are several ways for you to take advantage of the many options available in GMS when working with elevation data. Whether building from a conceptual model, or maybe even building a conceptual model from a MODFLOW simulation, there are many ways to use your elevation data in GMS. Practice using your elevation data in GMS 10.4 today!

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Converting CAD Data to Feature Objects in WMS

CAD data has been around for a long time and it’s one of the most readily available formats for geological data. WMS can make use of the data in a variety of ways. One of these ways is to convert CAD data into feature objects.

When CAD data for an area is available, DWG and DXF file data can be automatically converted to feature objects in WMS. Lines, points, and polygons in the CAD file can be turned into feature objects on a Map coverage for use in your WMS projects. This is done by doing the following:

  1. Import the CAD data into WMS. It will appear in the Project Explorer.
  2. In the Project Explorer, right-click on the CAD file and select CAD to | Feature Objects.
  3. In the CAD → Feature Objects dialog, select the layers to be converted to feature objects.
  4. Next, in the Clean Options dialog, select options to clean up the feature objects such as removing dangling arcs.
  5. Finally, the Properties dialog will appear letting you designate the type of coverage that will hold the new feature objects.

After you have converted your CAD data to feature objects, there are few items to keep in mind.

  • Typically, CAD data will not designate the stream direction. Make certain to check the direction of arcs generated from CAD data. Use the Reorder Streams command to fix this.
  • Polygons will not be automatically generated from polygons in the CAD data. Any enclosed arcs must be converted to polygons using the Build Polygons command.
  • It may be necessary to use the Clean Options dialog again after conversion.
  • Additional adjustments to the arcs may be necessary using the Map module tools.

Generating feature arcs from CAD data can save you a lot of time and frustration when building your watershed model. Try out converting CAD data into feature objects using WMS today!

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Moving SRH-2D Material Attributes to Another Project

After setting your SRH-2D material attributes in one SMS project, have you ever wanted to transfer those attributes to another SMS project? Doing this can save you from having to reenter the same material attributes into a separate project. You can even transfer multiple material coverages at once.

There are three project files referred to here: the original project, the project with the saved material coverage attributes, and the third project to which you want to add the saved material attributes. To make sure these instructions are clear, we'll call them Project A, Project B, and Project C, respectively.

To save time on other projects that use the same material attributes, you can use the following steps to export them for later use:

  1. Outside SMS, create a copy (Project B) of your project directory. This prevents you from accidentally damaging the original project (Project A) during the process.
  2. In Project B (the copy), delete any geometric data that isn’t going to be transferred, such as meshes, grids, GIS data, and scatter sets.
  3. Also remove any coverages and material data you do not want transferred.
  4. On the SRH-2D material coverages, remove any polygons and feature objects that you do not want transferred. This is assuming that the project receiving the new material parameters will be assigning the material properties to different polygons.
  5. This is the tricky part. You have to have at least one Map object for a map file to be saved in SMS. Therefore, create a new coverage of any type as a placeholder. Create a single feature point in this placeholder coverage.
  6. Use the Save command to save Project B that only contains the SRH-2D material coverages with your material properties, and one one other coverage with a single feature object.
  7. In another instance of SMS, open Project C.
  8. Use the Open command to open Project B.
  9. SMS should ask if you want to delete this data. If this happens, respond "No". The coverages from Project B (and its material lists and attributes) will be loaded into Project C.
  10. Now to add the material lists from the Project B into the material lists in Project C by right-clicking on the transferred coverage and selecting the Assign Materials to menu command. SMS will bring up the Assign Materials dialog where you can add materials from one coverage to another. You can either add the materials to the list of this coverage or replace the materials list in this coverage.

Now that you know how to transfer material parameters from one project to another, try it out in the SMS today!

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Incorporating Geology into a MODFLOW Model

Have you created a MODFLOW model and would like to incorporate geological features in between the MODFLOW layers?

The first step is to create the solid to be used. In GMS, solids are representations of stratigraphy used for site characterization and visualization. Solids can be created in any one of three ways:

  1. Convert horizons to a solid.
  2. Convert one or more TINs to a solid.
  3. Manually create a solid by right-clicking in the Project Explorer and selecting the desired type of solid from the New | Solid menu.

Using the first two methods will allow the solid material composition (what the solid is made of) to be automatically interpolated from the horizon or TIN information. Using the third method will allow you to select the material for each solid reated. The third method also requires knowledge of the XYZ coordinates and other attributes, depending on the type of solid being created (cube, cylinder, sphere, or prism).

Once you’ve created your solids, these steps will integrate the solids into the MODFLOW model:

  1. Right-click on the grid and select Classify Material Zones… to bring up the Classify Material Zones dialog.
  2. Select the solids folder you just created.
  3. Select the Classify algorithm you want to use.
  4. Enter the name of the material set being created.

The Centroid algorithm assigns the solid to the cell if it passes over the centroid of the cell. The predominant material algorithm assigns the solid to the cell if it is the predominant material in the cell (the material making up the highest percentage of the cell). This method maintains your grid, while interpolating the materials to the grid, so that you can have multiple materials within a layer.

Try adding solids to your MODFLOW models in GMS today!

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Working with Rain Gages in GSSHA

Are you needing to add rain gages to your GSSHA model? Using rain gages to define your precipitation in GSSHA is extremely useful due to its ability to spatially model precipitation over a watershed. Combining spatially varying rainfall with the distributed parameters of GSSHA is a great way to create a fairly realistic model for your watershed.

One of the bigger challenges when simulating a storm event is finding reliable data. Although it is important to investigate the most accurate source for your particular watershed, there are websites containing NOAA and GLDAS data for not only the United States, but globally. Having many sources of compiled data all on one site makes Cuahsi’s HydroClient a very useful resource. For those using our software internationally, another possibly useful resource when gathering storm data from the Global Precipitation Climatology Centre. This gives monthly values from 1901-2013, with newer data being added frequently.

Now that you have solid data for your watershed, it is time to define your gages. To use rain gages as your precipitation input:

  1. Create a rain gage coverage.
  2. Create rain gages in their proper locations.
  3. Using the Select tool, double-click on the gage to bring up the Rain Gage Properties dialog.
    1. Set the gage type to GSSHA.
    2. Define the precipitation using either a cumulative or an incremental distribution.
    3. Beneath the Show drop-down, choose GAGES if your data is incremental, and ACCUM if your data is accumulative.
  4. Return to the 2D-Grid module and select GSSHA | Precipitation.
    1. Select Gage as the rainfall event, select Rain Gage, and choose your preferred interpolation method (Inverse distance weighted or Thiessen polygons).

For more information and specifics on working with gages in GSSHA, please take a look at the GSSHA user’s manual. WMS provides a useful and helpful resource when creating a GSSHA model, analyzing and viewing the results. Practice using rain gages as your precipitation source in WMS 11.0 today!

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New Bridge Scour Tool in SMS 13.0

You are probably aware of the potential destruction caused by bridge scour. Up to 60 percent of bridge failures in the United States from 1950 to 1989 were caused by scour. Bridge scour occurs when the stream bed material around bridge piers is eroded. This can leave the pier unsupported by the stream bed, causing it to collapse.

Recent news has shown bridges of all sizes all around the world collapsing or in danger of collapsing due to scour. Such failures can have a huge negative impact on the economy and also pose a danger to the lives of those who use the bridge regularly. The Federal Highway Administration (FWHA) advised that it is far less expensive to take measures to prevent scour than to replace a bridge that fails due to scour.

Part of the scour mitigation process is evaluating countermeasures that can be taken to prevent such failures. These include onsite surveys and inspections, physical modeling such as that done at the FWHA Hydraulics Laboratory at the Turner-Fairbank Highway Research Center in McLean, Virginia, and computer modeling using tools such as the Surface-water Modeling System (SMS) from Aquaveo.

SMS 13.0 adds powerful new post-processing Bridge Scour tools that can be used to quickly test the scour effect of different pier arrangements, pile sizes and shapes, and vessel impact protection structures such as dolphins and fender rings. The Bridge Scour feature in SMS 13.0 can be used with the FWHA Hydraulic Toolbox to take advantage of its various bridge scour calculators and mapping tools.

One of the most exciting features of Bridge Scour is how it saves time. When creating the contracted section, approach, centerline, bank, abutment toe, and pier arcs, SMS 13.0 automatically assigns the arc type if they are created in order. This translates into saved time and cost, allowing you to be more productive.

Check out the Bridge Scour tool in the SMS 13.0 beta.

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Troubleshooting MODFLOW

Are you experiencing issues with your MODFLOW simulation? Unable to get your model to converge? Even after properly constructing a model in GMS, you might still find that your model won’t converge or it terminated with an error. Below are some hopefully helpful suggestions on why the model might not be converging and what you can do about it.

To begin, look at what might be causing the convergence issues to occur. The model might have improper aquifer properties which should be reviewed and adjusted if needed.

Another possibility is that there is an unbalanced flow budget. An unbalanced flow budget can manifest itself in two ways. One way is when the inflow is greater than the outflow, then the model can experience sometimes extreme flooding, and the model in turn will not converge. The other way in which there can be an unbalanced flow budget is if the outflow is greater than the inflow. If all the cells in a model are caused to go dry, then the model will not converge. A high outflow may be caused by things such as high conductivity and high pumping rates.

Another possible issue that might cause MODFLOW to have some issues is if you have a specified head for all grid cells in the model. This is because when all cells are Specified Head boundaries, then there is nothing for MODFLOW to compute and the model will terminate with an error.

Some other common issues include: improper initial conditions, improper boundary conditions, wetting and drying issues (as mentioned above) and a highly sensitive model. If the area is known to be highly sensitive, this might cause MODFLOW to not converge due to the speed at which flow can be affected.

Now that we know of some issues which might cause MODFLOW to struggle, we can take a look at three basic troubleshooting steps.

Basic Troubleshooting Steps:

  1. Review the command line output from MODFLOW, and check to see where the issue began to arise. This will enable you to better pinpoint the cause of the error.
  2. Before running MODFLOW, make sure you always run the model checker to see if there are any errors that will prevent convergence. Immediately repair the errors found in the Model Checker. The Model Checker can be found by clicking MODFLOW | Check Simulation…
  3. Look in the MODFLOW output file (*.out) to search for missing values.

Further detail for some specific issues is also given below.

  • If the head is going to drop below the cell, use the MODFLOW-NWT solver.
  • Cells usually go dry due to a low recharge or a high conductivity. Adjust these parameters to better calibrate the model.
  • A transient water table will cause a fluctuation in the heads and the cells may go dry. In this case it is best to use the rewetting option which is available in all flow packages. However when possible MODFLOW-NWT is still the best solution to this problem.
  • Relax the maximum residual or head change criteria. It is best to not increase these values beyond about 1% of the value.

Hopefully with these troubleshooting tips, you can get your MODFLOW simulation up and running in no time. Additional information can be found in the Frequently Asked Questions section of the MODFLOW user manual under the question "My model hasn’t converged. What can I do?" If you are still struggling to get your model to work, consider using Aquaveo's consulting services for expert assistance.

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How to Calculate Riprap Using the Hydraulic Toolbox

Are you needing to determine the size of stones needed for riprap? Having stones that are too small will reduce the effectiveness of the riprap which could be disastrous. On the other side, having stones that are too large could cause unnecessary expense.

After defining drainage data in WMS, it is possible to calculate the riprap needed for your model using the FHWA Hydraulic Toolbox. To do this:

  1. Define your drainage data in WMS.
  2. Assign each basin attribute to an analysis method by double-clicking on the feature, and then selecting Edit Attributes…. This will give you the opportunity to link your drainage data to the Hydraulic Toolbox.
  3. Click on the Hydraulic Toolbox macro in WMS to bring up the Hydraulic Toolbox.
  4. You can calculate riprap using one of two methods:
    • Channel Lining Design Analysis Tool. Keep in mind when using this tool that a filter material must be separately designed.
    • Riprap Analysis Tool. This tool will calculate the filter material along with riprap size.

Once in the Hydraulic Toolbox, locate the name of the analysis method chosen and double-click to open the analysis dialog for the chosen parameter and method. You will notice that all of the data you input into WMS is now filled in the analysis tool. After you specify blank parameters, the tool will calculate and display the results at the bottom of the screen under “Minimum Riprap Thickness”.

Using the Hydraulic Toolbox to calculate riprap can help your project move forward. The toolbox also contains many other features worth exploring. Try using the Hydraulic Toolbox today!

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Aquaveo Visits Namibia

From November 6-9, Aquaveo had the privilege of traveling to Windhoek, Namibia to conduct a training and provide consulting sponsored by BGR for several employees of MWAF. The Ministry graciously provided space in its building for the training classes. During the training classes, Alan Lemon helped them refine a MODFLOW model of the Ohangwena II aquifer.

Northern Namibia has a long history of droughts, and Namibia is the driest country in sub-Saharan Africa. Surface water is not a reliable source for potable water in the area due to the infrequency of rain storms to replenish the watershed. Because of this, the Namibian government—through its Ministry of Agriculture, Water, and Forestry (MWAF)—partnered in 2012 with the German Federal Institute for Geosciences and Natural Resources (Bundesanstalt für Geowissenschaften und Rohstoffe, or BGR) to research and develop an aquifer discovered near the northern border with Angola.

The Ohangwena II aquifer is found below an area about 75 km by 40 km, and has nearly 20 billion cubic meters of fresh water. This is enough to last for well over 400 years at current usage levels, and some think there may be even more water there. This kind of resource would be invaluable to the Namibian people.

Creating a valid working model of the aquifer will help the government of Namibia and BGR to come up with a solid groundwater management plan. Such a plan will help them better manage this amazing resource so that the people living in northern Namibia will have the water they need while also preventing needless wasting of hundreds of years of water located in the precious aquifer.

During the trip, Alan had the chance to visit the Okaukuejo Waterhole in Etosha National Park, where he saw a number of different animals, including rhinoceroses, crocodiles, and springbok. The watering hole is visited by tens of thousands of animals each year, from small birds and mammals to some of the largest and most dangerous animals in Africa. The national park is near the area covered by the Ohangwena II aquifer.

We want to thank BGR and MAWF for inviting us to their facility, and for the opportunity to work on such an important project. If you are interested in having Aquaveo assist with your projects, check out our consulting services.

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New Floodway Delineation Tool in SMS 13.0

City planners, developers, and others have a great interest in using available land. Sometimes that land is close to areas that flood, so precautions need to be taken so the build site is not too close to (or directly in) the potential flood area. Failure to properly plan and delineate a floodway can potentially cause millions of dollars in flood damage as well as potential losses in property values. Hurricanes Harvey and Florence, with their extreme rainfall amounts, are prime example of why floodway delineation is so important.

In addition to the guidance provided by the Federal Emergency Management Agency (FEMA), the new Floodway tool in SMS allows the extents of a floodway area to be more clearly defined. This tool allows planners, developers, and others to run multiple simulations to determine the safest places to build as well as the places which may be most impacted during a significant flooding incident.

To use the Floodway tool in SMS, a project must have a either a Cartesian grid, a 2D mesh, or a 2D scatter set that has simulation result datasets for at least water depth and velocity. Two coverages are also required: a 1D hydraulic centerline coverage and a 1D hydraulic cross section coverage.

The way the Floodway tool works is by calculating how far in from both sides of a river or stream that vertical walls can be placed and raise the center of flow by the targeted maximum rise. FEMA suggests this rise should be no more than 1 foot. These calculations use the input provided by the water depth dataset, the velocity dataset, and the two hydraulic coverages to define the floodway extents along the entire length of the study area.

Once these extents are known, the data can be used when making area planning and development decisions at all levels of government and businesses. You can try out this feature in SMS 13.0 beta today.

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