Managing HEC-HMS Model Alternatives

An HEC-HMS model alternative includes the following components:

• Basin model
• Loss parameters
• Transform parameters
• Zone configurations
• Parameters adjustments for each zone

This guide will teach you how to create and manage HEC-HMS model alternatives in your HEC-RTS watershed.

Build your HEC-HMS model and its associated alternatives within the HEC-HMS software to ensure correct setup before integrating them into your HEC-RTS watershed.

Importing an HEC-HMS Model Alternative

To import an alternative: 

1. Go to the Setup tab.

2. Right-click the HEC-HMS icon in the Watershed Tree and select Import.

3. In the file browser dialog that appears, navigate to and select the desired HEC-HMS project file (.hms extension).

4. Click Select to begin the import process.

5. If the selected model was created using an earlier version of HEC-HMS, a Convert HEC-HMS Project dialog will appear. Click Convert Project to proceed.
   

6. Once the import is complete, the message window will display: HMS: NOTE 16161: Import finished.

7. Save your watershed.

Configuring Zones

After importing HEC-HMS model alternatives, you should define zone configurations for adjusting loss, transform, and baseflow parameters. A zone configuration is a grouping of zones, and each zone contains a set of elements (either subbasins or reaches) within the watershed.

Zones should be created based on hydrologic similarity and the availability of observed flow data for calibration. For example, you might group all headwater subbasins above a reservoir into one zone. This allows you to adjust their loss and baseflow parameters together to better match the modeled reservoir inflows with observed data.

Creating a Zone Configuration

To create a new zone configuration: 

1. Go to the Setup tab.
2. From the Watershed Tree, right-click an HEC-HMS model alternative and choose Zone Configurations.
3. In the Zone Configuration Manager dialog, click New to create a new configuration.
   
   
4. In the Create a New Zone Configuration dialog, enter a Name and optional Description.
   

5. Under Element Type, choose either Subbasins or Reaches.

6. Click Create. The new zone configuration is now listed in the Zone Configuration Manager.

7. Close the Zone Configuration Manager dialog.

Creating Zones

Each zone configuration requires at least one zone.

To create a zone:

1. In the Zone Configuration Manager, select the desired configuration.
2. Click Zones to open the Zones dialog.
   
3. Click New to open the Create a New Zone dialog.
   
4. Enter a required Name and an optional Description.
5. Click Create. The new zone will appear in the list of current zones for that configuration.
6. Repeat these steps to add additional zones as needed.
7. Close the Zones dialog.

Adding Elements to a Zone

Once zones are created, you can assign subbasins or reaches to them.

To assign elements:

1. In the Zone Configuration Manager, select the desired zone configuration.
2. Click Elements to open the Elements dialog.
   
3. From the Zones drop-down, choose the zone you want to modify.
4. In the Unassigned Elements list (left side), select one or more elements to assign:
   1. Click to select a single element
   2. Shift-click for a range
   3. Ctrl-click for multiple individual selections
5. Click Add to assign selected elements to the zone. They will move to the list on the right.
   1. Alternatively, double-click an element to move it to the zone.
6. To remove elements from a zone, select them from the list on the right and click Remove, or double-click to unassign.
7. Close the Elements dialog and then close the Zone Configuration Manager.

Editing an HEC-HMS Model Alternative

The Forecast Alternative Editor allows you to assign zone configurations for loss rate, transform, baseflow, and routing parameters.

To configure an alternative:

1. Go to the Setup tab. 
2. Right-click the HEC-HMS model alternative in the Watershed Tree and select Forecast Configuration.
3. The Forecast Alternative Editor will open.
   
4. In the editor:
   1. Enter a Description.
   2. Set the Start Date, Forecast Date, and End Date.
      (Note: These values will be overwritten each time a new forecast is created.)
   3. From the dropdown menus, select the appropriate zone configurations for:
      1. Loss Rate Config
      2. Transform Config
      3. Baseflow Config
      4. Routing Config
5. Click OK to save and close the editor.

Copying an HEC-HMS Model Alternative

To copy an alternative: 

1. Go to the Setup tab. 
2. From the Models menu, select HMS and click Forecast Alternative Manager.
3. The Forecast Alternative Manager dialog will open.
   
4. In the Current Forecast Alternatives list, select the alternative you want to copy.
5. Click Copy. The Copy Forecast Alternative dialog will appear.
   
6. Enter a new name in the Name field (required) and an optional Description.
7. Click Copy to complete the process.
8. The new alternative will appear in the Current Forecast Alternatives list.
9. Close the Forecast Alternative Manager dialog.
10. The new HEC-HMS model alternative will appear in the Watershed Tree.

Deleting an HEC-HMS Model Alternative

To delete an alternative: 

1. Go to the Setup tab.
2. From the Models menu, select HMS and click Forecast Alternative Manager.
3. The Forecast Alternative Manager dialog will open.

4. In the Current Forecast Alternatives list, select the alternative you want to delete.

5. Click Delete.

6. Click OK to confirm the delete and close the dialog.
   

7. The selected alternative will be removed from the list.

8. Close the Forecast Alternative Manager dialog.

9. The HEC-HMS model alternative will be removed from the Watershed Tree.