Model Alternatives

Model Alternative refers to a specific configuration of the model, including a defined set of inputs and parameters. Models and their alternatives are typically created and configured using the native modeling software (such as HEC-HMS or HEC-ResSim) and then imported into the HEC-RTS watershed through the import commands found under the File menu in the Setup module. Once imported, model alternatives can be further configured and edited within HEC-RTS.

HEC-MetVue Model Alternatives

A HEC-MetVue Project provides the foundation for creating model alternatives in HEC-RTS. Each project follows this hierarchy:

• Project: Contains global settings for the watershed.
• Sessions: Represent model alternatives in HEC-RTS (each session is treated as a model alternative).
• Map Windows: Contain settings for input data and basin average maps.

An HEC-RTS watershed uses a single HEC-MetVue project, which may include multiple Sessions. Every Session should have at least one Map Window. These Map Windows process data for Lookback and Forecast time windows, typically requiring separate windows for each.

For step-by-step instructions, refer to the video Setting up a MetVue Project on YouTube or the Creating an HEC-MetVue Project tutorial.

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

In HEC-RTS, you can adjust parameters in the basin model to calibrate the model outputs against observed flow data from the lookback period. You can also blend modeled results with observed flows at specific locations where such data is available. 

If your HEC-HMS project contains multiple basin models (e.g., for summer and winter conditions), you can create separate model alternatives for each one.

HEC-ResSim Model Alternatives

An HEC-ResSim model alternative includes:

• A watershed schematic
• A stream and reservoir network
• Operational rules for each reservoir

Within HEC-RTS, you can override forecasted releases to replicate desired operations during the forecast period.

If your HEC-ResSim project contains multiple network alternatives (e.g., summer vs. winter conditions), you can create separate model alternatives for each network.

HEC-RAS Model Alternatives

A HEC-RAS model alternative includes three key components:

• one Geometry File
• one Flow File
• one Plan File that links a geometry file to a flow file

In HEC-RTS, you can adjust parameters in the geometry file to calibrate the model outputs against observed flow data from the lookback period.

If your HEC-RAS project includes multiple plans (e.g., one for steady flow and another for unsteady flow), each plan will be imported as a separate model alternative in HEC-RTS.

HEC-FIA Model Alternatives

An HEC-FIA model alternative includes the following components:

• Emergency Planning Zones
• Inundation Configuration
• Structure Inventory
• Critical Infrastructure
• Impact Response Information
• Agricultural Data
• Computation Settings

You can create multiple alternatives within a single HEC-FIA project - for example, one for summer crop conditions and another for winter crops.

For detailed guidance on defining an HEC-FIA alternative, refer to the HEC-FIA User's Manual.

EFP Alternatives

An Ensemble Forecast Processor (EFP) alternative includes:

• Input settings for the lookback and forecast time windows to control:
  • Locations to add observed data
  • Locations to add ensemble forecasts
• Output settings to control:
  • Locations to compute metrics 
  • Cumulative volume scalar decision metrics based on the ensemble forecasts
  • Ability to return the ensemble member with the closest volume to a given metric

Unlike other applications (HEC-HMS, HEC-RAS) an Ensemble Forecast Processor alternative is only available within HEC-RTS. More information on the EFP can be found here. 

Model Alternative Keys

Each model alternative must have a Model Alternative Key assigned to it in HEC-RTS. This key is an alphanumeric identifier that must be unique within a specific model, but can be reused across different models. For example, you might use N to represent “no future rain” in an HEC-MetVue model alternative and also use N for “normal conditions” in an HEC-HMS model alternative. However, you cannot assign N to two different HEC-MetVue model alternatives. Refer to the table below for some examples.

Example Model Alternative Keys

Additional Resources

Refer to this guide to learn how to import and edit model alternatives within you HEC-RTS watershed.