The consequences calculations require you to already have entered supporting data. FDA follows the general procedures described in this technical reference manual. Calculations are performed by a plan/analysis year combination, if you select more than one plan/analysis year combination; FDA processes each one independently and loops through all selected combinations.

Stage-aggregated damage functions are one of the three primary functions used in HEC-FDA to construct a damage-probability function. The other two functions are discharge-exceedance probability and stage-discharge. Integration of the damage-probability function produces expected annual damage. The computation of total expected annual damage takes the sum of the individual asset categories of expected annual damages: structure damages, content damages, other damages, and vehicle damages.

The aggregated stage-damage functions must be computed (or directly entered) for each plan, analysis year, stream, damage reach, and asset category. In other words, for a given plan, analysis year, stream, damage reach, and damage category, there is one stage-aggregated total damage function that corresponds. Usually, this function is computed but it may be entered directly if it has been computed using other tools.

The water surface profiles facilitate aggregation of damage from a single structure to the impact area. The structure occupancy types describe depth-damage functions and some global structure parameters. The structure attributes define the parameters necessary for computing stage-damage for each structure. The discharge-exceedance probability and stage-discharge functions are used to determine the span of stages at the impact areas for which aggregated damage is computed.

Once all of the above parameters are defined, you may compute aggregated stage-damage functions for one or more scenario. The computed functions are then used in the computation of expected annual damage. If you change any of the parameters such as a structure's first floor elevation, you must re-compute stage-aggregated damage and then expected annual damage for all plan/analysis year combinations that are dependent upon that structure.

A general overview of what happens when you select a plan/analysis year combination and then calculate stage-damage functions in FDA follows:

  1. For each damage reach, FDA calculates the range of stages for each impact area. The stages represent the range from very frequent to very infrequent events based on the input functions and the uncertainty about those functions. FDA then calculates the interval between stage ordinates. 
  2. FDA processes each of the structures in the structure inventory and impact areas for the selected plan/analysis year. It transforms the tabulation stages that were determined in Step 1 from the impact area to the structure.
  3. FDA determines the damage category, structure occupancy type, and impact area, and then computes stage-damage at each of the tabulation stages for each structure. Damage is computed for the structure, contents, other, and total.
  4. The damage for each tabulation stage is then aggregated to the impact area. During calculations, the stage-aggregated damage functions are stored in memory. After all of the filtered structures are processed, the stage-aggregated damage functions are stored in the FDA study files.