Aquaveo & Water Resources Engineering News

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!

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!

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!

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.