This chapter builds upon the previous chapters by introducing with-project conditions; a levee, nonstructural, and combination plans will be modeled in HEC-FDA 2.0.

Background

The without-project model has been established with uncertainty, flow, and many impact areas. There are several structural and nonstructural plans under consideration, and the team needs those plans to be modeled in HEC-FDA 2.0 to find an estimate of the economic benefits of each plan. 

Nonstructural floodproofing and structure raising will be modeled across the study area for structures with damages at the .01 AEP event or a more frequent event. Floodproofing prevents damages up to 3 feet above the structure's foundation, and structure raising means the depth-percent damage relationship begins at a higher stage.

Learning Objectives

  1. Create a Lateral Structure.
  2. Create a new Occupancy Type.
  3. Create Alternatives.
  4. Create an Alternative Comparison Report.
  5. Model with-project conditions.
  6. Interpret results of with-project conditions.

Model Inputs

Stage-Discharge Function

With a levee in place, the stage-discharge relationship is altered due to the channel being restricted by the levee. For a given flow, stage increases in the channel adjacent to the levee.

Lateral Structure

To model a levee, a system response function must be defined relating stage with a probability of failure. 

Occupancy Types

To model nonstructural floodproofing, an additional occupancy type is needed. This occupancy type is a modification to the existing COM occupancy type that converts all damage estimates at 3 feet and below to zero damage. Floodproofing prevents damages to the structure and other associated assets up to 3 feet above the foundation of the structure. 

Structure Inventory

To model nonstructural floodproofing and structure raising, a new structure inventory must be imported. The new structure inventory must contain two modifications: any structures being floodproofed must have the new occupancy type code (COMFP as shown in this example below), and any structures being raised must have new foundation heights reflecting the elevated height.

Model Development Steps

With the previously described inputs, an HEC-FDA 2.0 model can be developed to provide the team with an estimate of economic damages geospatially.

Enter Stage-Discharge Functions

A new rating curve is needed in the Impact Area with the levee (Impact Area 6), as noted above.

To enter the stage-discharge function:

  1. Right-click Stage-Discharge Functions and select Create New Stage-Discharge Relationship
  2. Enter the name of the function in the Name text box
  3. Enter a brief description of the function in the Description text box
  4. Select Deterministic from the drop-down menu
  5. Enter the X and Y values
  6. Select Save  at the bottom right corner of the window and then Close 

The stage-discharge function utilized in this example is in the image below.

Create a Lateral Structural

To create a Lateral Structure:

  1. Right-click Lateral Structures and select Create New Lateral Structure...
  2. Enter the name of the Lateral Structure in the Name text box
  3. Enter a brief description of the Lateral Structure in the Description text box
  4. Enter the Top of Levee Elevation in the respective box
  5. Select the User Defined radio button next to System Response Curve
  6. Select Deterministic from the Distribution Type dropdown box
  7. Enter the X Values and Y Values in the table
  8. Select Save and select Close 

Add New Occupancy Types

A new occupancy type is needed to model nonstructural measures as mentioned above. Since we're only adding one new occupancy type, and it's based on the COM occupancy type already in this model, the most efficient way to add the occupancy type is to copy the COM occupancy type and modify the depth-percent damage functions.

To copy an occupancy type:

  1. Right-click the occupancy type set in the contents pane and select Edit Occupancy Types...
  2. Highlight the occupancy type from the list of occupancy types and select the Copy Selected Occupancy Type icon 
  3. Enter a name for the new occupancy types
    1. The example image below shows an occupancy type named "COMFP" for "Commercial Floodproof"
  4. Select OK

Now that a new occupancy type has been created, the mean and standard deviation of the depth-percent damage functions need to be reduced to zero for X Values at 3.0 and below for each asset type (ie structures and contents in this example) to reflect the expected performance of floodproofing.

To modify the depth-percent damage functions:

  1. On the Structure Damage tab, highlight each cell in the Mean and Standard Deviation columns in the X Value rows for 3.0 and below and change the values to zero
  2. Within the same occupancy type, select the Content Damage tab and repeat step 1
    1. This can be repeated for Vehicle Damage and Other Damage if those check boxes are selected and those asset types are being utilized in the model - They are not in this model
  3. Select Save and select Close 

Import Structure Inventory

A new structure inventory for the base and future year is required to model nonstructural measures. Modeling floodproofing on non-residential structures requires changing the occupancy type of the selected structures to the COMFP occupancy type discussed above. Modeling elevation of residential structures requires changing the foundation heights of the selected structures to reflect the increased height of the structures.

To import the structure inventory:

  1. Right-click Structure Inventories and select Import from Shapefile
  2. Enter the name of the structure inventory in the Name text box
  3. Enter a brief description of the structure inventory in the Description text box
  4. Select a file path by selecting the ellipsis on the far right side of the Structure Inventory Shapefile text box and navigate to the folder in which you saved the structure inventory
  5. Ensure the Ground Elevation and Foundation Height radio button and From Terrain File radio button are selected
  6. From the dropdown boxes, select the column headers corresponding to the structure ID, occupancy type, foundation height, structure value, and NumberOfStructures respectively
    1. Optionally, select the column headers corresponding to the other attributes listed
  7. Select Next
  8. Ensure the occupancy types from from the occupancy type data are selected in the drop-down menus correspond to the occupancy types indicated in the structure inventory
  9. Select Finish


Generate Aggregated Stage-Damage Function

The nonstructural plan needs a new aggregated stage-damage function for the base and future year.  

To generate an aggregated stage-damage function:

  1. Right-click Aggregated Stage-Damage Functions and select Create New Stage-Damage Functions...
  2. Enter the name of the aggregated stage-damage function in the Name text box
  3. Enter a brief description of the aggregated stage-damage function in the Description text box
  4. Ensure the Computed radio button is selected
  5. Enter the appropriate analysis year in the Analysis Year text box
  6. Select the Water Surface Elevations and Structures from the respective drop-down boxes
  7. Select the generated Frequency Function from the drop-down box
  8. Ensure the Write Details to CSV radio button is selected
  9. Select Compute Curve
  10. Wait for the aggregated stage-damage function to generate as indicated by functions being displayed at the bottom of the window and then select Save and select Close 
  11. Complete these steps for the base year nonstructural plan and the future year nonstructural plan 

Create a New Scenario

A new Scenario is needed to model the nonstructural plan, levee plan, and combination plan.

To create a new scenario:

  1. Right-click on Scenarios and select Create New Scenario...
  2. Enter a name and description for the scenario in the respective text boxes.
  3. Enter the appropriate analysis year in the Year(s) text box
  4. Select the stage-damage function from the Stage-Damage drop-down box
    1. For the nonstructural and combination plans, select the nonstructural stage-damage function
    2. For the levee plan, select the without-project stage-damage function
  5. Select the frequency functions from the Frequency Relationship drop-down box and assign them to the appropriate impact areas
  6. Select the stage-discharge function from the Stage-Discharge drop-down box
    1. For the levee and combination plans, select the new with-levee rating curve for Impact Area 6
    2. For the nonstructural plan, select the original rating curve for Impact Area 6
  7. For the levee and combination plan, select the lateral structure from the Lateral Structure dropdown box for Impact Area 6
  8. Ensure the Calculate Default Threshold radio button is selected
  9. Select save  and select Close 

When all scenarios have been created, right-click on Scenarios in the contents pane and select Compute Scenarios... Check the boxes of all the new Scenarios and select Compute .


Create a New Alternative

For each plan, an Alternative needs to be created.

To create a new Alternative:

  1. Right-click on Alternatives and select Create New Alternative...
  2. Enter a name and description for the Alternative in the respective text boxes
  3. Select the base year Scenario for the subject Alternative from the Base Year Scenario dropdown box
  4. Enter the base year in the Year text box
  5. Select the future year Scenario for the subject Alternative from the Future Year Scenario dropdown box
  6. Enter the future year in the Year text box
  7. Select save  and select Close 
  8. Complete Steps 1-7 for the without-project, levee, nonstructural, and combination plans

Create a New Alternative Comparison Reports

To create a new Alternative Comparison Report:

  1. Right-click on Alternatives Comparison Reports and select Create New Alternative Comparison Report...
  2. Enter a name and description for the Alternative Comparison Report in the respective text boxes
  3. Select Add Comparison two times to create a total of three With Project dropdown boxes
  4. Select the without-project Alternative from the Without Project dropdown box
  5. Select the levee, NS, and combination plans from the With Project dropdown boxes
  6. Select save  and select Close 

Results

Performance

To view performance results pertaining to the levee Scenario, right-click on the future year levee Scenario and select View Results... and select Performance from the Outcomes dropdown box. Ensure Impact Area 6 is selected in the top dropdown box.

Performance statistics can be viewed for three different Reports: AEP, Long-Term Exceedance Probability, and Assurance of Threshold. The Threshold defaults to the top of levee elevation entered in the Lateral Structure input.

The target stage in this example is 83, the top of the levee. The Assurance of AEP is the percent chance that the target stage will not be exceeded given the occurrence of a specific flood event. As such, the inverse of the values provided can be considered the chance that the target stage will be exceeded given the occurrence of a specific flood event.  An AEP With 90% Assurance of .038 means there's a 90% chance that the stage of 83 (top of levee) will not be exceeded for a .038 AEP event. There's a 29.57% chance that the stage of 83 (top of levee) will not be exceeded for a .01 AEP event.   

Long-term Exceedance Probability is the percent chance that the target stage is exceeded once in 10, 30, or 50 years. There's a 44.33% chance the target stage is exceeded at least once in 30 years.

View Alternative Summary Results

To view the results for the Alternatives, right-click Alternatives in the contents pane and select View Alternative Summary Results... Check one or all of the checkboxes and select View .

Alternative Summary Results include study property information and uncertainty around Average Annual Equivalent Damage values by alternative and damage category.

To view results for a single alternative with options to view Damage with Uncertainty, Damage by Impact Area, or Damage by Damage Category, right-click on the alternative and select View Results...The three reports can be toggled by the Report dropdown box.

View Alternative Comparison Report Results

To view the results for the Alternatives Comparison Report, right-click the Alternative Comparison Report and select View Results... 

From the With-Project Alternative dropdown box, each of the with-project alternatives can be selected to view AAEQ or EAD reduced in the base or future year from among three report types: Damage with Uncertainty, Damage by Impact Area, or Damage by Damage Category.

By selecting Summary from the With-Project Alternative dropdown box, the interface displays without and with-project EAD and AAEQ for all alternatives, as well as the mean and quartiles of EAD and AAEQ reduced for each of the alternatives.