What is an Aggregated Stage-Life Loss Function?

An aggregated stage-life loss function is the relationship between the stage at the location of the hydrologic and hydraulic input relationships and the coinciding level of life loss in the floodplain. The aggregated stage-life loss function is aggregated at the impact area-hazard time level for a given set of hydraulics modeling and H&H input functions (e.g. flow-frequency and stage-flow or just stage-frequency). 

What is the Purpose of an Aggregated Stage-Life Loss Function?

An aggregated stage-life loss function reflects the consequences piece of the risk equation. When an aggregated stage-life loss function is linked to a stage-frequency function, we get a life loss-frequency function, the relationship that is integrated to calculate expected annual life loss.

Where Do I Get an Aggregated Stage-Life Loss Function?

An aggregated stage-life loss function with uncertainty is computed within HEC-FDA using imported LifeSim results, a set of index points, and a hydraulics dataset. In addition, the study must already have an impact area set imported.

Working with Aggregated Stage-Life Loss Relationships in HEC-FDA

You must compute stage-life loss functions within HEC-FDA. You will need to have imported an impact area set, an index point set, and a hydraulics dataset before opening the stage-life loss function importer. In this importer, you will have the option to select LifeSim results from an existing LifeSim study, as well as select the associated hydraulics dataset and index point sets.

Steps to Compute Aggregated Stage-Life Loss Relationships

Impact Area Set Associations

In order for the HEC-FDA stage-life loss functions to compute properly, you must ensure that your study's impact area set matches your LifeSim study's summary polygon set exactly. The easiest way to accomplish this is to export your summary polygons from LifeSim as a shapefile and import that shapefile directly into HEC-FDA using the impact area set importer. Upon import, you must select the unique name attribute that matches your LifeSim summary polygon names for the compute to function properly. 

Index Point Set Associations

The index point set that you import into HEC-FDA and use for computing aggregated stage-life loss functions must contain a one-to-one (1:1) mapping of index points to impact areas. This means that each impact area contains exactly one index point, and each index point is contained within exactly one impact area. Any malformed inputs will be rejected by the compute.

Hydraulics Dataset Associations

Your selected hydraulic profile names must exactly match your LifeSim study's hydraulic profile names. Similarly, the easiest way to accomplish this is to copy your hydraulic profiles directly from LifeSim and import them into HEC-FDA. Be sure that the profile names match your hydraulic profile names in LifeSim.

To create a new aggregated stage-life loss function:

  1. Right-click on Aggregated Stage-Life Loss Functions under Consequences within the Study Tree and click Import LifeSim Database.
  2. Define a useful Name and Description.
  3. Under Configure and Compute, open the LifeSim Database file explorer dialog by clicking the three dots on the far right of the row. Locate your LifeSim study's .fia file and select it. LifeSim Simulations, Alternatives, and Hazard Times should populate automatically.
  4. Next, select your appropriate Hydraulics datsaset and Index Points.
  5. Next, select your desired LifeSim Simulation. This will repopulate the LifeSim Alternatives.
  6. By default, all of the LifeSim Alternatives, which have associated hydraulic profiles, will be selected as part of the compute. This results in the highest definition compute, but you may elect to only include a subset of these profiles by unchecking the checkbox next to profiles you wish to exclude from the compute.
  7. By default, two Hazard Times will also be selected. Their default weights are 0.55 and 0.45. While FDA computes aggregated stage-life loss functions for both selected times, only one final function will be included in the eventual scenario compute. Thus, the two times must be combined, and their relative weighting in that final combination is determined by weights that you may adjust. For example, if you would like the final combination function to weight 0200 less heavily than 1400, you may enter weights such as 0.4 and 0.6, respectively. Weights must always sum to 1.
  8. Finally, click Compute Curve. You will see a compute log and progress bar advance as the compute proceeds. When it completes, plots of the functions will populate below in the Generated Curves section.
  9. Click Save and Close.