Now that the quality of the time-series data has been validated, you are ready to create an HEC-RTS forecast. An HEC-RTS forecast is a simulation of watershed processes and consequences of potential flooding from various software applications configured in HEC-RTS. The meteorological data processor, MFP, combines observed and forecasted meteorological data into gridded datasets for use in HEC-HMS. The hydrologic software application, HEC-HMS, computes flow from forecasted and observed meteorological time-series. The reservoir operation software application, HEC-ResSim, computes flow and release schedules. The hydraulic software application, HEC-RAS, computes stage and inundation maps. The impact analysis software application, HEC-FIA, computes flood consequences and action reports. Prior to creating an HEC-RTS forecast, you will have already configured an HEC-RTS watershed. Specifically, Model Alternatives will have been configured, Model Alternative Keys (Model Alternatives and Forecast Runs) assigned, Program Order and Forecast Runs defined, and Model Linking (Model Linking Editor) configured.

An HEC-RTS forecast might be configured using a typical forecast run that includes something similar to the following model alternatives: Winter Nextrad QPF (for MFP), normal conditions (for HEC-HMS), normal reservoir operations (for HEC-ResSim), normal river conditions (for HEC-RAS), and no flooding consequences (for HEC-FIA). If a high rainfall event is forecasted, an HEC-RTS forecast might be created using a forecast run with model alternatives similar to the following: HRRR QPF (for MFP), wet basin conditions (for HEC-HMS), restricted downstream channel capacity (for HEC-ResSim), high channel flow (for HEC-RAS), and evacuate with warning (for HEC-FIA).

In the Modeling module, the user will specify a forecast time window, create and manage forecast extract and post lists, extract time-series data for the forecast, create and manage forecast runs, edit model parameters, and run the models. Figure 1 displays the data flow concepts through the five standard HEC-RTS analysis applications (MFP, HEC-HMS, HEC-ResSim, HEC-RAS, and HEC-FIA).

Hydrologic Modeling (MFP, HEC-HMS) 

The meteorological preprocessor MFP will be used to combine observed precipitation data and future precipitation information into a single precipitation dataset that can be used by the watershed runoff model, HEC-HMS. Using the observed and future precipitation data, HEC-HMS computes runoff, including uncontrolled local flows that are typically used by HEC-ResSim. The types of data typical that need to be changed for a forecast are loss rates and baseflow.

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 use those flows during the operation of the reservoirs to compute regulated flows. Reservoir operations might include zones and rules for day-to-day operations, along with zones and rules for extreme events.
The types of data that might typically be changed for a forecast are the starting conditions for reservoirs. As long as the reservoir starting conditions are linked to real-time data (starting elevations or storages, reservoir or outlet releases, and any other boundary conditions needed by the model), then the user shouldn't have to make any revisions to the HEC-ResSim model in order to run routine HEC-RTS forecasts.

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 can also be used as input to HEC-RAS. In turn, HEC-RAS computes stage, which is input to HEC-FIA. The types of data that might typically be changed for a forecast are n values at selected cross sections to match profile information better throughout the lookback period.

Impact Analysis (HEC-FIA) 

HEC-FIA analyzes impacts within inundated areas based on computed hydrographs from HEC-ResSim and stages 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 responders what actions need to done based on the computed stage values. The types of data that might typically be changed for a forecast are adjustments to the levee failure stages to see the associated damage and impacts during an event.