What is an Aggregated Stage-Damage Function?

An aggregated stage-damage function is the relationship between the stage at the location of the hydrologic and hydraulic input relationships and the coinciding level of damage in the floodplain. The aggregated stage-damage function is aggregated at the impact area-damage category-asset category 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-Damage Function?

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

Where Do I Get an Aggregated Stage-Damage Function?

An aggregated stage-damage function with uncertainty is computed within HEC-FDA using the structure inventory, a set of hydraulic profiles, and H&H input functions (flow-frequency and stage-flow or just stage-frequency). Alternatively, for unique situations, an aggregated stage-damage relationship may be manually entered.

Working with Aggregated Stage-Damage Relationships in HEC-FDA

Typically, you will compute aggregated stage-damage relationships in HEC-FDA. You will need to have imported a set of hydraulics and a structure inventory as well as have defined for each impact area the flow-frequency and stage-flow functions or just stage-frequency function to compute the aggregated stage-damage relationships.

Stage-Damage H&H Data

  • There are three types of engineering data required for a stage-damage compute: a frequency function, a stage-discharge function if frequency reflects flows, and a hydraulics data set. Double-check that the project conditions are the same across the three items. The computed stage-damage function will not make sense if: (1) with-project conditions are unique from without-project conditions, and (2) with-project data is used along with without-project data for the without-project set of stage damage functions. 
  • Ensure that the coordinate reference system is either set to be the same across all geospatial data sets, or that the study coordinate reference system is set by selecting the study projection from the study properties editor under the File menu. 

Differences Between HEC-FDA Versions 1 and 2

  • In HEC-FDA Version 1.4.3, stage-direct damage functions were entered into study data through the structure inventory, and were saved, imported from/exported to tab delimited within the occupancy types. In HEC-FDA Version 2.0, a stage-direct damage function for a particular structure should be entered using a dedicated occupancy type that has a reverse-engineered depth-percent damage function that replicates the stage-direct damage function. An alternative is to develop a separate set of aggregated aggregated-stage damage functions which are manually entered rather than computed internally. A separate scenario will need to be generated. Please note that stage-direct damage functions will not import into HEC-FDA Version 2.0 from HEC-FDA Version 1.4.3.
  • Index points are no longer required for a stage-damage compute. The aggregation stages are identified using the H&H input functions. 

Steps to Compute Aggregated Stage-Damage Relationships

The following items must be selected for configuration of an aggregated stage-damage compute: 

  1. Discharge-frequency function and discharge-stage function or just a stage-frequency function 
  2. Hydraulic data set
  3. Structure inventory 
  4. Occupancy types 

To create a new aggregated stage-damage function:

  1. Right-click on Aggregated Stage-Damage Functions under Economics within the Study Tree and select the create new option.
    Aggregated Stage-Damage Functions - Create and Import shortcut menu commands.
  2. Define a useful Name and Description.
  3. Select Computed.
  4. Enter the Analysis Year (e.g., base year is 2024 in the example).
  5. In the Configure and Compute panel, select the the appropriate hydraulic dataset (e.g., Steady-State_RASdata) and structure inventory (e.g., BaseWO). Then for each impact area select the appropriate Frequency and Stage Discharge functions. 
  6. Optionally, select Write Details to CSV to obtain structure-level stage-damage details (selected by default). The CSV file for the created function will be saved to you study directory in a new folder named StuctureStageDamageDetails.
  7. Click Compute Curves.

    Aggregated Stage-Damage Function FDA icon An aggregated stage-damage function is computed for each impact area, damage category, asset category combination.

     
    Example Aggregated Stage-Damage Functions dialog.
  8. Click Save, and Close.