Aquaveo & Water Resources Engineering News

Both TOPAZ and TauDEM make computing flow directions and accumulations for basin delineation easier. One of these two programs is typically used during the process of delineating a watershed. During this process, it is not unusual to run into some issues. Below are some common issues and how to resolve them.

Missing DEM

DEM data is required to run TOPAZ or TauDEM. A DEM can be imported from a file or downloaded from a web service. If you get an error stating that no DEM exists after you have imported the DEM data, this is typically because the DEM was not imported correctly.

Often, the DEM has been imported as a raster file and is in the GIS data module. In order for TOPAZ or TauDEM to use this as a DEM it will need to be converted from a raster to a DEM using the Convert to | DEM right-click command in the GIS module.

Not Enough Data

In order for TOPAZ or TauDEM to work properly, a DEM is needed that has enough data to work with. When working on modeling very small areas, TOPAZ or TauDEM may fail to execute correctly because there is not enough data available to complete the process.

In order to fix this issue, it is recommended that you slightly expand the size of the area you are modeling. In particular, the resolution of the DEM being used may need to be increased. Use your best judgement as to how much additional data to add.

Too Much Data

The opposite of having too little data would be to have too much data which causes TOPAZ or TauDEM to slow down or stop running altogether. This typically happens when attempting to model a very large watershed. In this case, the issue typically isn’t related to problems with TOPAZ or TauDEM but is more likely related to the available processing power of the computer being used.

With many projects that have too much data, often much of that data is unnecessary. Often a lower resolution DEM can be used. When modeling a large watershed area, you should use your engineering judgement to find areas of greatest interest and then focus on those areas. If that is not possible, then you will need to find a way to increase your computer's processing power.

TOPAZ and TauDEM tools for delineating a basin. Try them out in WMS today!

Have you tried dewatering a mine model using MODFLOW-NWT? MODFLOW-NWT is a version of MODFLOW provided by the USGS that uses a method to solve MODFLOW models that are non-linear due to unconfined cells or non-linear boundary conditions, creating an asymmetric results matrix. Because mines that need to be dewatered sit below the water table, cells within the simulation will become dry at times due to the removal of the water from the mine. MODFLOW-NWT is great for such situations as it handles dry cells well.

Mine dewatering models are often used when estimating the required flow capacity for the pumps used in the field. You can create a regional model to establish a baseline, then create one or more models with various pit depths to establish the best approach for the mine in question. While elevations cannot be set to transition during a MODFLOW run, multiple conceptual models can be created within the same project in order to keep all of the data together.

It’s important to remember the difference between wells and drains when creating the dewatering model. Drains only subtract water when the head is above the elevation of the drain. Therefore, drains can be used to represent the seepage face around the edges of the pit, and the drain elevations should be set to equal the ground surface elevations. The amount of water removed by a drain is related to the conductance of the material of the seepage face. Drains are generally used at the bottom and side seepage faces of the mine.

Wells remove a specific amount of flow, and can therefore dewater the cell they are in prior to dewatering the rest of the mine. MODFLOW-NWT, as mentioned previously, handles these dry cells very well, keeping them active in case they become wet again.

Because MODFLOW-NWT uses 3D grids, you should make sure the cells inside the pits are inactive. You do this by creating the boundary polygon, and then removing a "donut hole" of cells within the pit area. Use the Activate Cell(s) in Coverages tool to inactivate the cells. You’ll have to do this for each layer, and each layer should be on its own coverage.

Finally, always use the Model Check to make sure there aren't any obvious errors or missing values in any of the inputs. After MODFLOW-NWT finishes running, you should review the water table by looking at the drawdown output contours. You can also do this by switching to Ortho view and reviewing the head in the appropriate rows or columns.

Try out making a mine dewatering model using MODFLOW-NWT in GMS today!

SMS allows using HY-8 to create culverts in SRH-2D models. HY-8 was created to model culvert profiles. When SRH-2D was being developed, structure boundary conditions were allowed to be linked HY-8 culverts to SRH-2D. Doing this permits SMS to make use of the more robust tools of HY-8 when designing culverts.

When designing a culvert for an SRH-2D model in SMS 13.0:

1. Right-click on the SRH-2D BC coverage and open the HY-8 Options dialog.
2. From the dialog, create the HY-8 file for the project.
3. On the SRH-2D BC coverage, create two arcs for the culvert: one for the inlet side of the culvert and one for the outlet side.
4. Select both arcs and open the SRH-2D Linear BC dialog.
5. In the dialog, select the Culvert HY-8 option and launch HY-8 to connect the HY-8 file.
6. In HY-8 design your culvert.

There are a few items to keep in mind when creating your culvert:

• Pay attention to where the culvert is located and how it snaps to the mesh in SMS. Designing your culvert for a location that doesn’t match up with your culvert is designed in HY-8 can cause discrepancies. Also, it helps to have the inflow entering the culvert at as close to a 90 degree angle as possible.
• Note that the crest length for constant elevation roadway profiles is the length between embankments.
• After the initial model run, the inflow values to the culvert may need to be adjusted and calibrated. If SRH-2D is showing lower or higher flow values, adjust the values in HY-8 as needed.
• Using a monitor line at the inlet or outlet side of the culvert. The results of the monitor lines may be different than what HY-8 reports. Use this difference to calibrate the model.
• 2D mesh elements are disabled between the culvert arcs during the model run.

HY-8 makes a great addition to SRH-2D in SMS. HY-8 is shipped with SMS, so feel free to try it out with your models today!

Have you needed to obtain land use or soil type data for your WMS project? Land use, or land cover, data is used to define the land use or cover of areas in the watershed such as urban, forested, farm, etc. Soil type data is typically used to control the movement of water in a watershed model. Data for land use or soil type can be added to your watershed project in WMS by using files on your computer or by downloading the data from a database.

Import a File

Files containing land use or soil type data are often contained in a shapefile, though other formats are possible. This file can be imported from your computer using the File | Open command. Once imported, the shapefile will appear in the GIS Module. It will likely need to be converted to the map coverage before being used in your watershed model.

Import From Web

Land use or soil type data can be obtained from online web services. To access these services, do the following:

1. Select File | Add Data | Get Data from Map.
2. In the Virtual Earth Map Locator, select the location of your project. If your project already has a set projection, then the location of your project should already be visible.
3. In the Data Service Options dialog, select one of the web services containing land use or soil type data such as the Land Use Shapefile, Statsgo Soil Type Shapefile, or Harmonized World Soil Database.
4. Save the land use or soil type data to your computer. The data will automatically be imported into your project as a shapefile in the GIS Module.

Moving Land Use and Soil Type Data

In most cases, having land use or soil type data on a shapefile will not include the data in your watershed model. Most often the data will need to be moved from the shapefile to the Map module. To do this:

1. Create a map coverage with the Land Use or Soil Type property. Land use data should be placed on a land use coverage and soil type data should be placed on a soil type coverage. Data may be lost if the wrong coverage type is used.
2. After creating the correct map coverage, select the land use or soil type shapefile in the GIS module then select the Mapping | Shape to Feature Object command.
3. When using the GIS to Feature Objects Wizard, select correct map coverage and make certain all of the attributes are correctly assigned.

Once you have imported land use or soil type data and it has been correctly converted to the Map module, it is ready to be used in your watershed model. Try out using land use and soil type data in WMS today!