Part B: Compute Aggregated Stage-Damage Functions

Transcript for Aggregated Stage-Damage Functions video

Hello and welcome to the Hydrologic Engineering Center's Flood Damage Reduction Analysis version 2.0, training video. My name is Julia Slaughter, and this video provides instructions for creating aggregated stage damage functions in HEC-FDA version, 2.0. This video builds upon the Occupancy Types and Structure Inventories videos. So, please review the other economic videos before you continue viewing this one. 

Before you can create aggregated stage damage functions, you must have imported all the required and relevant study data. For this example study, the following data has been imported, a terrain file, Impact area set, hydraulic data, Stage discharge functions, a lateral structure, occupancy types, and a base year without project structure inventory. Oh no, the example data set is missing a required function, which is the existing conditions or without project conditions flow frequency function, and it must be added before the aggregated stage damage functions can be created. Now that all the required study data has been imported for this example study, the Aggregated Stage Damage function for the Without project condition, or existing conditions, can be created.
First, let's take a look at the study property for this tutorial video. We will keep the convergence criteria at defaults. 

Now, let's create our new Aggregated Stage Damage function and compute. From the study tree, under economics, right-click on Aggregated Stage Damage Functions and select the Create New option. A set of stage damage functions is specific to the alternative plan and analysis year. For example, the Without Project conditions and Base year. We're going to keep the editor as a tab, but you can pop it out by selecting this icon. Now we need to enter a name and description for a new stage damage function. Computed is already selected for you by default. We'll need to enter an analysis year for a new function and from the configure and compute box, we'll have to select our water surface elevations, our structure inventory, the frequency function for each of our impact areas and the stage discharge function. If your study has a regulated and unregulated function, select it at this time as well. For example, study, there's only one water surface elevation, so it's already selected for us. And the structure inventory is our base without project. With the frequency functions for both our impact areas, it's the existing conditions function. And from the stage discharge function, it’s our without project function. The right details to CSV is already selected by default. The details will show up in the subdirectory within the study directory named structure-stage damage details. We're ready, so let's hit compute. Depending on the size of your inventory and study data, this may take a while.

So, while we're waiting for FDA to generate the stage damage curves, let's briefly review why we need these curves. If you've watched the occupancy types and structure inventory videos, this illustration and equation should look familiar. We're looking at the simplified flood risk equation, where risk is a function of consequences. And a set of stage damage functions is the calculated consequences of exposure, which is the structure inventory. And vulnerability which comes from the occupancy types. Recall, that I mentioned earlier that a set of stage damage functions is specific to the alternative plan and analysis year. For the example of the without project conditions and base year. Therefore, it is imperative that the selected hydraulics data set correctly represents the conditions in the floodplain because the generated curves represent the relationship between stage in the river and damage in the floodplain and are the economic summary relationship that is used to calculate the expected annual damage or EAD. 

Now that we've discussed the importance of the stage damage compute, let's take a look at the links from water to structure and content value to damage. The distribution of the 1st floor elevations for a given structure determine a distribution of depth of water above the 1st floor for a given water surface elevation. This distribution of depth of water above the 1st floor translates into a distribution of percent of structure value and content value damaged, which are each linked with the respective structure and content value distributions to produce a distribution of structure damage and content damage for a given water surface elevation. Summing the two distributions, we get the stage damage relationship.

Now that we've discussed the stage damage compute algorithm in FDA, let's see if FDA has finished computing our base year without project conditions, Stage damage functions. Indeed, you may need to pop out the Stage Damage Functions window to review the generated curves. Let's do that now so we can examine the resulting functions for the without project base year. The generated curves are ordered first by impact area name, then by damage category, and last by asset category. One function was produced for each Damage Category, Asset Category, Impact Area combination. The stage-damage relationship describes the level, or distribution, of damage measured in dollars for a given elevation, or stage, of flooding. In other words, the damage for a given stage is collected in a histogram so that the distribution of damage displayed in the plot window is the 5th percentile, mean, and 95th percentile for the generated empirical distribution. Once you're done reviewing the curves, click Save and Close. The new aggregated stage damage function that you've created will be added to the Study Tree. Note, FDA will also display the last time it was edited or computed. Created curves can be Edited, Removed or Renamed.