Defining Elevation and Storage Capacity of Detention Basins

Did you know that the Watershed Modeling System (WMS) has a calculator that can define the relationship between the elevation and storage capacity of a detention basin? This is a useful tool for any WMS project with detention basins. The detention basins calculator is a simple tool that can quickly get the storage calculations you need for your model.

WMS uses the Hydraulic Toolbox to perform these calculations for the detention basin calculator. To open the detention basin calculator, first you need to make the Hydrologic Modeling Module active and select an outlet. Detention basins… is one of the options under the Calculator menu. After selecting Detention basins… a dialog named Detention Basin Hydrograph Routing will appear. Clicking the Define… button opens the Storage Capacity Input dialog, which is where you can enter the data that is needed for the calculations.

Basin Calculator in WMS

There are four data input options you can use to calculate storage capacity in the Storage Capacity Input dialog. Only one of the four input options is needed in order to perform the calculations. Which one you use will depend on what data is readily available for your model.

It is important to note that regardless of what measurement the general display projection is set to, the detention basin calculator will measure the elevation in feet and the storage volume in acres per foot.

After you exit the Storage Capacity Input dialog, a plot will be automatically generated in the Detention Basin hydrograph Routing dialog. This plot displays the relationship between the elevation and the amount of storage, as well as discharge if there is any. This plot functions the same way as any other plot window in WMS. You can learn more about plot windows by following this link to our wiki.

Head over to WMS to check out the detention basin calculator and see how you can use it to calculate the storage versus elevation for your detention basins today!

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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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ASCII Grid Files for GSSHA in WMS

The Watershed Modeling System (WMS) offers powerful tools for managing and analyzing spatial data using ASCII files. In this blog post, we will explore WMS ASCII files, discuss specific file formats like the *.dep (DEPTH) and *.gfl (FLOOD_GRID) outputs as well as the possibility of exporting ASCII gridded files for GSSHA.

WMS utilizes ASCII files to store and exchange spatial data, such as boundaries, elevation data, and model outputs. To extract information from these files, it is helpful to understand their formatting. The WMS ASCII file contains coordinates representing the boundary limits of the data. However, a common question arises regarding whether these coordinates represent the corner or center of the boundary cells. The coordinates provided in a file header can represent the lower left corner of the cells rather than their center. This information is for accurately defining the spatial coverage of the data.

ASCII Gridded Files Format

WMS is capable of outputting files containing spatial information as grid files, such as the DEP and GFL files. These files store multidimensional data (time, x, y) in a single column format. In the DEP and GFL files, as well as other GSSHA files, the data is organized by cell ID. The introductory information in the file provides details such as the type of information, geometry type, number of cells and values, and dataset name. Each time step is indicated by the TS field, followed by the corresponding data. The dataset file concludes with a flag indicating the end of the data.

ASCII gridded file properties in WMS
Exporting ASCII Gridded Files with GSSHA

While discussing GSSHA, it is important to note that it employs cell-centered Cartesian grids. It is also important to note that GSSHA does not offer alternative export formats for gridded files, apart from the ASCII-based output options provided in WMS. These options can be found by doing the following:

  1. Select GSSHA | Job Control command to open the GSSHA Job Control Parameters dialog.
  2. Click the Output Control button to open the GSSHA to Output Options dialog.
  3. In this dialog, make certain that the ASCII option is selected for output.

ASCII gridded files are one of the many options you can use with GSSHA in WMS. Try out ASCII files and other formats in WMS today!

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Combining Runoff in Watershed Basins with WMS

The Watershed Modelling System (WMS) includes use of the Rational Method, which enables the calculation of peak flows for small watersheds in urban and rural areas. This feature can combine runoff from multiple basins to find the values.

The Rational Method requires a couple specific components to calculate the runoff coefficient for an area. The required inputs are soil data, along with either a table relating soil IDs to runoff coefficients, or a runoff coefficient coverage. Composite runoff coefficients use an area-weighted average of all runoff coefficients that overlay each basin for computation. The inputs chosen will depend on what method you choose to calculate runoff in the Rational Method module. The two primary methods to calculate runoff are first, to assign coefficients to polygons within a coverage, and second, to import a table with all of the coefficients already assigned to a land or soil use ID.

Example of Land Use in WMS Example of Soil Group in WMS

There are two ways to assign runoff coefficients to a polygon. The first way is to enter the coefficients polygon by polygon, and the second is to assign the coefficients through the Soil type mapping dialog.

To assign runoff coefficients polygon by polygon, do the following:

  1. Start with a Runoff Coefficient coverage.
  2. Select one of the polygons that intersects the drainage basin.
  3. Enter the runoff coefficient that matches the soil or land type for that polygon in the Runoff Coefficient dialog window that appears.
  4. After entering the data for each polygon that intersects the basin, activate the Hydrologic Modeling Module and go to Calculators | Compute GIS Attributes.
  5. In the Compute GIS Attributes dialog, make sure the following options are active:
    • “WMS Coverages” is selected as the data type.
    • Under Computation, Runoff coefficients is selected on the dropdown menu.
    • The “Use” dropdown is set to runoff coefficient coverage.
    • The “coverage name” dropdown is set to your new coverage.

To assign runoff coefficients to polygons by soil mapping, do the following:

  1. Start with a “Soil Type” coverage.
  2. Select one of the polygons that intersects the drainage basin.
  3. On the bottom left of the Soil type mapping dialog that appears, turn off the "SCS Soil Type" checkbox and turn on the "Runoff Coefficient" checkbox.
  4. You will now have a list of soil IDs and names with a field for runoff coefficients. Enter a coefficient value for each of these fields according to the material type.
  5. Open the Compute GIS Attributes dialog as described above.
  6. Set everything the same as are in the last set of steps, except change the "Use" dropdown to Coverage.

There are multiple ways to create runoff coefficient tables to import into a project. One of the ways is to create a table from scratch. If you choose this route, you can view the structure requirements on the Aquaveo wiki to make sure it includes everything you need. To import a table with the runoff coefficients, do the following:

  1. With the “Soil Type” coverage active, double-click on a polygon that intersects the drainage basin.
  2. Select “Import file” under Import soil attribute file.

You can also import a table in the Compute GIS Attributes dialog.

Head over to WMS and try out the different ways to assign runoff coefficients to your watershed project today!

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