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.

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 into a study using a manually-entered stage-damage function. The best way to track the structure of interest as it relates to its stage-direct damage function is to assign the structure to its own damage category. Stage-direct damage functions will not import into HEC-FDA Version 2.0 from HEC-FDA Version 1.4.3 - they will have to be manually entered. When using HEC-FDA Version 2.0 to compute stage-damage functions, create and manually enter a dedicated damage category for each structure that uses a stage-direct damage function and manually edit the function as needed. 
  • 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

  1. Right-click on Stage-Damage Relationships under Economics within the Study Tree and select Create New Aggregated Stage-Damage Relationship.
  2. Define a useful name and description.
  3. Select Computed.
  4. Optionally, enter the Analysis Year. Analysis Year must be entered correctly if Year In Construction will be used in the structure inventory.
  5. Select the H&H input functions for each impact area, a hydraulics data set, and a structure inventory. 
  6. Optionally, select Write Details to CSV to obtain structure-level stage-damage details (the information found in Version 1.4.3 Fda_StructDetail.out).
  7. Click Compute Curves, Save, and Close. See below for image of finished Aggregated Stage-Damage Functions.