WS3 Economic Consequences with Uncertainty

Workshop Overview

The goal of this workshop is to familiarize students with using HEC-FDA Version 2, including navigating the user interface for computing and evaluating stage-damage functions and their associated uncertainties.

• Steps already completed for the students include:
  • Creating the study
  • Setting the study properties
  • Importing the terrain, impact area set and hydraulic data
  • Entering the analytical existing condition flow-frequency functions (exceedance probability functions)
  • Entering the existing condition stage-discharge function with uncertainty
• Students will complete the following steps in this workshop:
  • Import structure occupancy types
  • Import base year (without-project) existing conditions structure inventory data
  • Compute and evaluate stage-damage relationships and associated uncertainties

Introduction

During this workshop, you will bring the economic data into the software and examine the data. You will also compute aggregated stage-damage functions. The economic data consists of a structure inventory sourced from the National Structure Inventory and the related occupancy types. You can read more about the National Structure Inventory by visiting the NSI Technical References. In the below image, the structures are represented by red dots - points in the structure inventory point shapefile. 

Study Damage Categories

The damage categories are those found within the National Structure Inventory (NSI) for Muncie, IN and include Residential, Commercial, Industrial, and Public.

Study Structure Occupancy Types

For each occupancy type, a distribution will be selected, (e.g., normal, triangular) and its parameters, (e.g., mean, standard deviation) will be entered. Uncertain variables include the depth-percent damage relationships for structure and content damage, the content to structure value ratio, the first floor stage in feet, and the structure value. These values will be applied to all structures in the particular structure occupancy type. For instance, the uncertainty in structure value is entered as a percent of the mean value. The mean value for each structure is unique to each structure entered in the structure inventory section. In the calculation procedures in FDA, the percentages are used to calculate a standard deviation or minimum and maximum values, depending on the type distribution.  

Structure Inventory Data

A structure inventory is needed to calculate the consequences - in dollar-denominated terms - of flooding for the range of possible flood events. Modern approaches for putting together a structure inventory include the NSI and/or the use of publicly-available data such as county tax records and Google Earth. The base year (existing conditions) structure inventory used in this workshop was obtained from the NSI database.

Instructions

Task 1 – Open the Starting HEC-FDA Version 2 Study

1. Open the HEC-FDA Version 2 software. 
2. From the File menu, click Open. The Open Study dialog opens as a tab.
3. Click the ellipse button in the Study Path box to open the Select File browser window.
4. Navigate to the Workshop 3 starting project (e.g., C:\Workshops\FDA\Workshops), select the *.sqlite HEC-FDA file and click Open.
5. From the Open Study tab, click OK.

Note which project elements have been entered for you in the starting workshop file.

Task 2 – Import Occupancy Types

1. From the Study Tree, under Economics, right-click on Occupancy Types and select Import Occupancy Types from Tab-Delimited Text File. The importer opens as a tab.
2. From the importer enter a name in the Base Name box (e.g., OccTypes), and enter a description for the relationship (e.g., The Muncie occupancy types are the typical occupancy types referenced in the National Structure Inventory.).
3. From the Tab Delimited File box select the ellipse button to open the Select File browser window.
4. Navigate to the folder containing the occupancy types file (e.g., C:\Workshops\FDA\MuncieData\OccupancyTypes), select the file "MuncieOccTypes20241125.txt" and click Open.

5. From the importer, click Import and view the Import Log.

   Test Your Knowledge - Question 1

   How many occupancy types were imported?

6. Click Close when finished viewing the Import Log.

   Test Your Knowledge - Question 2

   What structures does the RES1-1SNB occupancy type represent and what is the source of the depth-percent damage functions?

   

   Hint

   From the Study Tree, right-click on the imported occupancy types dataset, and select Edit. From the editor, select the RES1-1SNB occupancy type and review the description.

Task 3 – Import the Without-project Base Structure Inventory

1. From the Study Tree, under Economics, right-click on Structure Inventories and select Import From Shapefile. The Import Structure Inventory opens as a tab.
2. From the importer, enter a name in the Name box (e.g., Base Year WOP), and enter a description for the relationship (e.g., base year inventory for the Existing Conditions (without-project inventory)).
3. From the Structure Inventory Shapefile box, select the ellipse button to open the Select File browser window.
4. Navigate to the folder containing the structure inventory file (e.g., C:\Workshops\FDA\MuncieData\StructureInventories\base-year_without-project), select the file "BaseMuncieStructsFinal.shp" and click Open.
5. The importer is a two part import wizard. From the first window, select the following in the Required Attributes:
   1. Select the Ground Elevation and Foundation Height radio button. The wizard updates to provide options for defining the ground elevation.
   2. Set the Ground Elevation Source by selecting the From Terrain File radio button.
   3. Make the following selections for the Import Attributes:
      

      Name	Import Attributes Selection
      Structure ID	TARGET_FID
      Occupancy Type	occtype
      Foundation Height	found_ht
      Structure Value	val_struct
      Content Value	val_cont
      Vehicle Value	val_vehic

   4. Click Next to access the next window in the import wizard.
      
      

      GUI Known Issue: The attribute selection dropdown lists do not contain a blank. Therefore, if you happen to select an attribute for something by accident (e.g., OtherValue) you cannot unselect the attribute. To fix this you will have to click Cancel and start over.

6. The import wizard updates to display selection criteria for assigning the occupancy types for the structure inventory. When an HEC-FDA project contains multiple occupancy types, the Load Occupancy Types from the Following Sets panel contains a list of the imported occupancy types. You imported one in Task 2; therefore, there is only one option to select in this panel.
7. The second import wizard window also displays a Default Occupancy Type Assignments section. Review the default selections and confirm that the default selection matches the Occupancy Types imported in Task 2. 
   For example, RES3A should be assigned to "OccTypes MuncieOccTypes20241125 | RES3A" (if you named your imported occupancy types the same as identified in Task 2).
8. When finished reviewing the default assignments, click Finish. The import wizard closes and the imported structure inventory displays in the Study Tree.

Task 4 – Set Study Properties

1. From the File menu, click Properties. The Study Properties dialog opens as a tab.

2. From the Study Properties dialog, enter the correct discount rate for the current Fiscal Year.

   Test Your Knowledge - Question 3

   What is the default discount rate in the software?

   

   Please note that the discount rate should be in decimal form, not percentage.

3. Click Save to save your edits and then click Close.

Task 5 – Create and Compute Existing Stage-Damage Functions

1. From the Study Tree, under Economics, right-click on Aggregated Stage-Damage Functions and select Create New Stage-Damage Functions. The Create New Stage-Damage Functions opens as a tab.
2. Enter a name for the new function in the Name box (e.g., Base Year Without Project), and enter a description for the relationship (e.g., Base Year HEC-FDA Version 2 Workshops Existing Conditions Function).
3. In the Analysis Year box enter "2031" for our base year.
4. Select the Computed radio button and enter the information identified below (if you've been following the naming convention identified in the workshops your options should be the same).
   
5. After you complete the configuration, click Compute Curves. Wait until HEC-FDA generates the curves and click OK when the compute is complete.
   
   

   There is no progress bar for the stage-damage computes. Just be patient - FDA is working.

6. Scroll through the list of computed curves (you should generate 28 curves, 16 for the Left-Bank and 12 for the Right-Bank). 
7. Click Save and the created stage-damage functions for the without-project (existing) base conditions displays in the Study Tree.
8. Click Close to close the dialog.

Conclusion

Download the solution project below to compare to your project:

• Muncie_WS3.zip
• Muncie_WS3.7z

Review the best answers to test your FDA knowledge questions and compare with yours to see how you did!

Return to top of page.

Best Answers to Test Your FDA Knowledge Questions

Click here to review answers...

Test Your Knowledge - Question 1

How many occupancy types were imported?

Answer: 41.

Test Your Knowledge - Question 2

What structures does the RES1-1SNB occupancy type represent and what is the source of the depth-percent damage functions?

Hint

From the Study Tree, right-click on the imported occupancy types dataset, and select Edit. From the editor, select the RES1-1SNB occupancy type and review the description.

Answer: One Story No Basement Residential Structures according to Economic Guidance Memorandum (EGM) 01-03.

Test Your Knowledge - Question 3

What is the default discount rate in the software?

Answer: 3%.

Test Your Knowledge - Question 4

Why are the frequency functions, stage-discharge functions, and regulated-unregulated functions required for the aggregated stage-damage compute?

Answer: The summary relationships identify the stage in the channel at the index location for each frequency. The damage in the floodplain for each frequency in the hydraulics dataset is concorded to the stage in the channel by frequency. 

Test Your Knowledge - Question 5

What is the shape of a typical aggregated stage-damage function?

Answer: Most aggregated stage-damage functions reflect convexity as marginal damage accelerates with increasing stage, then concavity with marginal damage approaching zero with increasing stage.

Test Your Knowledge - Question 6

Do you notice a problem with the left-bank commercial structure aggregated stage-damage function?

Answer: There is non-monotonicity between the stages of 945 and 946 feet. This is the result of idiosyncrasies in the hydraulic modeling. If dig into your StructureStageDamageDetails.csv (located in your study directory), you'll notice that for that coordinate, which maps back to ~5%ACE event, we're calculating no damage for a handful of structures, even though they showed damage at a more frequent event. If we track that event back to the hydraulics in HEC-RAS, we'll find the hydraulic model results are suspect. RAS Users may recognize this pattern as the result of poorly correlated grid cell size and computational timestep for this area of steep terrain, and shallow flow. 

Test Your Knowledge - Question 7

Describe the symmetry of the uncertainty in damage reflected in the computed base year without-project left-bank industrial structure aggregated stage-damage function. 

Answer: The uncertainty is skewed right, and the skew lessens as stage increases. Observe that the central tendency is closer to the 5th percentile than the 95th percentile, reflecting the long right tail. 

Test Your Knowledge - Question 8

Identify the mean residential content damage that has a 0.01 probability of being exceeded for the left-bank.

Hint

Pop open the flow-frequency, stage-flow, and stage-damage windows, identify the median flow at 0.01 AEP, the stage for that flow, and the damage for that stage. 

Answer: $4,770,266.03. 

Test Your Knowledge - Question 9

What are some approaches that can be used to estimate the uncertainty in structure value and first floor elevation?

Answer: Approaches include estimating the magnitude of natural variability as a proxy for model uncertainty, or estimating the measurement error, by surveying a sample of inventoried structures.

Related Topics

• Page:
  Aggregated Stage-Damage Functions (HEC-FDA User Manual)
• Page:
  Consequences Methodology (HEC-FDA Technical Reference)
• Page:
  Continuous Distributions (HEC-FDA Technical Reference)
• Page:
  Economic Data (HEC-FDA User Manual)
• Page:
  Flood Risk Assessment and HEC-FDA (HEC-FDA User Manual)
• Page:
  Getting Help and Additional Resources (HEC-FDA User Manual)
• Page:
  Glossary (HEC-FDA User Manual)
• Page:
  Known Issues (HEC-FDA User Manual)
• Page:
  Occupancy Types (HEC-FDA User Manual)
• Page:
  Part A Create Study then Import or Specify Study Data (HEC-FDA Quick Start Guides)
• Page:
  Part B Compute Aggregated Stage-Damage Functions (HEC-FDA Quick Start Guides)
• Page:
  Structure Inventory (HEC-FDA User Manual)
• Page:
  Study Dimensions and Compute Configuration and Results (HEC-FDA User Manual)
• Page:
  Version 2.0 Certification Report (HEC-FDA User Manual)
• Page:
  Version 2.1 Certification Report (HEC-FDA User Manual)