Running a FDR forecast is nearly the same as running a standard real-time forecast in CWMS, with a few important differences and considerations discussed below.
Forecast Time Window
In an FDR forecast, the focus is on analyzing the lookback period of an event that has already occurred, rather than predicting future conditions (as in a real-time forecast). However, a full forecast time window—including start, forecast, and end dates—is still necessary.
- Start Time/Extract Start: This should be just before the event begins.
- Forecast Time: This should be shortly after the event ends. Depending on your watershed, this might be when the last reservoir starts to recede or when a downstream control point reaches baseflow conditions after the hydrograph has subsided.
- End Time: Set this to allow for full routing from the upstream reservoirs to the watershed outlet.
The forecast time may vary based on the basin characteristics and how well the model calibration matches the recession of the hydrographs.
Computing the Forecast
There are two main approaches for computing the FDR forecast:
- Simple Approach: The FDR forecast is computed just like any other forecast. Once completed, the FDR results can be accessed from the Reports tab or directly within HEC-FIA.
- Complex Approach: Each forecast run is computed separately, and the damage results from each are extracted and post-processed to calculate the final FDR results.
Key Considerations
Regardless of the approach, it's essential to thoroughly review hydrologic and hydraulic (H&H) results as well as consequence outcomes. Errors in model linking or setup are common, so attention to detail is crucial. Additionally, verifying the calibration in HEC-HMS is critical for accurate results. For more guidance on setting up, running, and verifying models, refer to the relevant sections in this document.