A forecast is a simulation that uses current conditions, observed data, and future projections (e.g., precipitation, reservoir operations) to estimate how a watershed or river system will behave over a specified time period. It typically involves integrating multiple models (e.g., meteorological, hydrologic, hydraulic, and consequence models) to predict flows, reservoir levels, potential flooding, and other outcomes to support decision-making for water management, emergency response, or planning.

Before creating and executing a forecast in HEC-RTS, you will need to complete the following steps: 

  1. Create Model Alternatives
  2. Assign Model Alternative Keys
  3. Define the Program Order 
  4. Define Forecast Runs
  5. Configure the Model Linking

Example Forecast Run Configurations

For routine forecasting, a forecast run might include the following model alternatives:

  • No future precipitation (HEC-MetVue), 
  • Normal conditions (HEC-HMS)
  • Normal reservoir operations (HEC-ResSim)
  • Normal river conditions (HEC-RAS)
  • No flooding consequences (HEC-FIA)

In contrast, when a high rainfall event is anticipated, your forecast run might use these model alternatives:

  • 7-day forecasted precipitation (HEC-MetVue)
  • Wet basin conditions (HEC-HMS)
  • Restricted downstream channel capacity (HEC-ResSim)
  • High channel flow (HEC-RAS)
  • Evacuate with warning (HEC-FIA)


In the Modeling tab, you specify a forecast time window, create and manage forecast extract and post lists, extract time-series data for the forecast, create and manage forecast alternatives, edit selected model parameters, and run the models.

The figure below shows the data flow concepts through the five standard analysis applications (HEC-MetVue, HEC-HMS, HEC-ResSim, HEC-RAS, and HEC-FIA). However, you can customize your HEC-RTS watershed by integrating additional applications such as the Ensemble Forecast Processor (EFP), scripts, or RiverWare to meet operational needs. 

Standard Modeling Applications in HEC-RTS

There are five standard modeling applications included in HEC-RTS. 

Meteorological Preprocessor (HEC-MetVue) 

HEC-MetVue combines observed and forecasted hydrometeorological data into a single dataset that can be used by the watershed runoff model, HEC-HMS.

Hydrologic Modeling (HEC-HMS) 

HEC-HMS computes runoff using the observed and future precipitation data, including uncontrolled local flows that are typically used by HEC-ResSim.

Reservoir Simulation (HEC-ResSim) 

After the upstream boundary flows and uncontrolled local flows have been computed by HEC-HMS, you will run the reservoir simulation application HEC-ResSim to operate the reservoirs and compute regulated flows. Reservoir operations might include zones and rules for day-to-day operations, along with zones and rules for extreme events.

River Analysis (HEC-RAS) 

Regulated flows computed by HEC-ResSim are typically used as boundary conditions to the hydraulic routing model, HEC-RAS. Computed flows from HEC-HMS or supplemental models should also be used as input to HEC-RAS. In turn, HEC-RAS computes water surface elevations, which is the input to HEC-FIA.

Flood Impact Analysis (HEC-FIA) 

HEC-FIA analyzes impacts within inundated areas based on computed hydrographs from HEC-ResSim and elevations from HEC-RAS. HEC-FIA calculates flood damage determined by rising stage in a stream, river, lake, or reservoir. HEC-FIA also computes action reports that tell emergency responders what they need to do based on the computed stage values.