WS5 Levee Assessment

Workshop Overview

The purpose of this workshop is for students to be able to:

• Evaluate three levee plans (aka. scenarios) for an impact area during analysis of the without-project condition.
• Formulate and evaluate alternative levee sizes for the impact area.
• Compute and review results for the base year and most likely future year
• Specify a recommended levee plan based on the economic and hydraulic performance formulation/evaluation results.
• Determine if the recommended plan (scenario) meets present FEMA floodplain levee certification criteria.

At the conclusion of the workshop the student will be able to perform a conventional levee analysis as required by present USACE guidance and ascertain if the recommended plan, if any, meets Federal Emergency Management Agency (FEMA) criteria for levee certification.

Introduction

Having completed Workshops 1-4, you should have the ability to model an alternative. Provided the inputs, you can produce an estimate of equivalent annual damages for multiple alternatives to compare to the without-project existing conditions. In this workshop, you'll model two different sized levees (a low levee with and without armor and a high levee). You'll be asked to think critically as you compare the results of the three with-project levees against the without-project conditions and consider which levee you might choose if you were so tasked.

A levee alternative is modeled similarly to the way you modeled the without project conditions. To model a levee, you need to:

• Import levee specific Hydraulic Data
• Create Lateral Structure - a lateral structure indicates the levee's system response function, or the relationship between stage and levee failure
• Create new Stage-Discharge Function - with a levee in place, stage for a given discharge increases in the channel
• Create new Scenarios - two new scenarios per levee are required, base and future year
• Create new Alternative - with new base and future year Scenarios, equivalent annual damages can be estimated

The proposed levees have heights that reach elevations of 946 ft and 947.5 ft. The levees are being proposed to benefit the Left-Bank Impact Area and have the exact same footprint, with only the height being different. Only one of the two levee options can be chosen.

Instructions

Task 1 – Open the Starting Workshop 5 Project

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

Alternatively, just reopen your Workshop 4 solution. From the File menu select the top recently opened study (number 1 in the list).

Task 2.1 – Import Low Levee Hydraulic Data

The top of levee for this low levee is 946 ft.

Steps

1. From the Study Tree under Hydraulics right-click on Unsteady HDF, and click Import Hydraulics. The Import Hydraulics dialog opens as a tab.
   

   

   Review the Example Study Data for Version 2 to determine the correct spatial data set type for the Muncie, Indiana Hydraulic study data.

    
2. From the importer enter a name for the hydraulics profile (e.g., LowLevee_Conditions) and enter a description for the profile.
3. From the Source Directory box select the ellipse button to open the Select File browser window.
4. Navigate and select the folder containing the existing conditions hydraulic data (e.g., C:\Workshops\FDA\MuncieData\Hydraulics\Muncie_Low_Levee), and click Select Folder.

5. The importer tab updates with a table displaying the name of the profiles, the annual exceedance probability and the return interval. The Annual Exceedance Probability will need to be corrected. Manually enter the appropriate AEP value for each profile name based on Table 1.

   Table 1
   Name	Annual Exceedance Probability	Return Interval (Return Period)
   50%ACE-LL	0.5	Updates based on the entered AEP using the equation (1/AEP)
   20%ACE-LL	0.2
   10%ACE-LL	0.1
   5%ACE-LL	0.05
   2%ACE-LL	0.02
   1%ACE-LL	0.01
   0.5%ACE-LL	0.005
   0.2%ACE-LL	0.002

   

   Copy and paste is not an option in the import table. Select each cell to type in the appropriate return interval.

6. Note that the Return Interval column updates based on the AEP. Check that the AEP and return interval values are correct and click Save. The hydraulic data is added to the Study Tree.
7. Click Close to close the Import Hydraulics tab.

Task 2.2 – Import High Levee Hydraulic Data

The top of levee for this high levee is 947.5 ft.

Steps

1. From the Study Tree under Hydraulics right-click on Unsteady HDF, and click Import Hydraulics. The Import Hydraulics dialog opens as a tab. 

2. From the importer enter a name for the hydraulics profile (e.g., HighLevee_Conditions) and enter a description for the profile.
3. From the Source File box select the ellipse button to open the Select File browser window.
4. Navigate and select the folder containing the existing conditions hydraulic data (e.g., C:\Workshops\FDA\MuncieData\Hydraulics\Muncie_High_Levee), and click Select Folder.

5. The importer tab updates with a table displaying the name of the profiles, the annual exceedance probability and the return interval. The Annual Exceedance Probability will need to be corrected. Manually enter the appropriate AEP value for each profile name based on Table 2.

   Table 2
   Name	Annual Exceedance Probability	Return Interval (Return Period)
   50%ACE-HL	0.5	Updates based on the entered AEP using the equation (1/AEP)
   20%ACE-HL	0.2
   10%ACE-HL	0.1
   5%ACE-HL	0.05
   2%ACE-HL	0.02
   1%ACE-HL	0.01
   0.5%ACE-HL	0.005
   0.2%ACE-HL	0.002

   

   Copy and paste is not an option in the import table. Select each cell to type in the appropriate return interval.

6. Note that the Return Interval column updates based on the AEP. Check that the AEP and return interval values are correct and click Save. The hydraulic data is added to the Study Tree.
7. Click Close to close the Import Hydraulics tab. 

Task 3.1 – Enter Stage-Discharge Functions for Low Levee

The top of levee for this low levee is 946 ft.

Steps

1. From the Study Tree, right-click on Stage-Discharge Functions and select Create New Stage-Discharge Relationship. The Create New Stage-Discharge Relationship opens as a tab.

2. Enter a name for the relationship in the Name box (e.g., LowLeveeTOL946), and enter a description for the relationship (e.g., The stage-discharge function below represents the with-project condition for a low levee. Observe that some stages are higher for a given discharge.).

3. For Distribution Type, select Triangular and use the information in Table 3 to create the new stage-discharge relationships for the with-project condition.

   Table 3

   {"name":"MuncieData.xlsx","sheet":"LowLevee_TOL_946","page":"Example Study Data","type":"xlsx","pageID":"152636670","space":"FDAUM"}

   Loading

4. Click Save. 

Task 3.2 – Enter Stage-Discharge Functions for High Levee

The top of levee for this high levee is 947.5 ft.

Steps

1. From the Study Tree, right-click on Stage-Discharge Functions and select Create New Stage-Discharge Relationship. The Create New Stage-Discharge Relationship opens as a tab.

2. Enter a name for the relationship in the Name box (e.g., HighLeveeTOL947.5), and enter a description for the relationship (e.g., The stage-discharge function below represents the with-project condition for a high levee. Observe that some stages are lower for a given discharge.).

3. For Distribution Type, select Triangular and use the information in Table 4 to create the new stage-discharge relationships for the with-project condition.

   Table 4

   {"name":"MuncieData.xlsx","sheet":"HighLevee_TOL_947.5","page":"Example Study Data","type":"xlsx","pageID":"152636670","space":"FDAUM"}

   Loading

4. Click Save.

Task 4 – Enter the Three Lateral Structures

For each levee, follow the instructions below to create two new lateral structures.

Note

The user defined system response curves have less data than the default curve. After you select User Defined you will need to delete the extra rows. To delete extra rows, highlight the extra rows, right-click inside a highlighted cell, and click Delete Row(s). Then copy the provided system response curve into the table.

• From the Study Tree, right-click on Lateral Structures and select, Create New Lateral Structure. The Create New Lateral Structure dialog opens as a tab. Enter the appropriate levee system name, description, top of levee elevation, and system response curve, and Save each levee.

• Use the Create New Lateral Structure dialog to add the following two levees:
  1. Name: LowLevee-noArmor; Description: With-project scenario for proposed low levee without armor for the left-bank with a top elevation of 946 feet.
     1. Top of Levee Elevation: 946
     2. System Response Curve:
        {"name":"MuncieData.xlsx","sheet":"LowLevee_noArmor","page":"Example Study Data","type":"xlsx","pageID":"152636670","space":"FDAUM"}

        Loading

     3. Click Save and Close to close the dialog.
  2. Name: LowLevee-Armored; Description: With-project scenario for proposed low levee with armor for the left-bank with a top elevation of 946 feet.
     1. Top of Levee Elevation: 946
     2. System Response Curve:
        {"name":"MuncieData.xlsx","sheet":"LowLevee_wArmor","page":"Example Study Data","type":"xlsx","pageID":"152636670","space":"FDAUM"}

        Loading

     3. Click Save and Close to close the dialog.
  3. Name: HighLevee; Description: With-project scenario for proposed high levee for the left-bank with a top elevation of 947.5 feet.
     1. Top of Levee Elevation: 947.5
     2. System Response Curve:
        {"name":"MuncieData.xlsx","sheet":"HighLevee_ProbOfFailure","page":"Example Study Data","type":"xlsx","pageID":"152636670","space":"FDAUM"}

        Loading

     3. Click Save and Close to close the dialog. 

Task 5.1 – Compute With-Project (Low Levee) Aggregated Stage-Damage Functions

For both analysis years create the aggregated stage-damage functions for the Low Levee:

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 an appropriate name for the new function (e.g., Base-WP-LL and Future-WP-LL for the base year and future year, respectfully) in the Name box and a description for the relationship.
3. Enter the appropriate Analysis Year: (base year is 2031, future year is 2080)
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. Scroll through the list of computed curves (you should generate 28 curves). 
6. Click Save and the created stage-damage function displays in the Study Tree. 
7. Click Close to close the dialog.

Task 5.2 – Compute With-Project (High Levee) Aggregated Stage-Damage Functions

For both analysis years create the aggregated stage-damage functions for the High Levee:

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 an appropriate name for the new function (e.g., Base-WP-HL and Future-WP-HL for the base year and future year, respectfully) in the Name box and a description for the relationship.
3. Enter the appropriate Analysis Year: (base year is 2031, future year is 2080)
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. Scroll through the list of computed curves (you should generate 28 curves). 
6. Click Save and the created stage-damage function displays in the Study Tree. 
7. Click Close to close the dialog.

Task 6.1 – Create Scenarios for the Three Proposed Levees

The Without Base Year and Without Future Year scenarios have been created for you, but now you need to create new scenarios for the three proposed levees for both analysis years. Table 4 provides an overview table of the new base year and future year with-project scenarios. 

Steps to Create With-Project Scenarios

Use these instructions and Table 4 to create the three new base year scenarios and three new future year scenarios:

1. From the Study Tree, right-click on Scenarios and select Create New Scenario. The Create New Scenario dialog opens as a tab.
2. Enter a name for the new scenario in the Name box (e.g., see Table 4), and enter a description.
3. Enter the Year: (base year is 2031 and future year is 2080).
4. From the Stage-Damage list use Table 4 to select the appropriate stage-damage function. 
5. From the Left-Bank Impact Area tab: 
   1. Recall that the left-bank impact area contains the proposed levee, so you need to select the appropriate levee created in Task 4 for each scenario (as identified in Table 4) and the appropriate stage-discharge function that you created in Task 3.  

   2. Select the following for the Left-Bank impact area:

      Click here to expand and view an example for the base year, low levee (without armor) the left-bank setup...

      

6. From the Right-Bank Impact Area tab:
7. The right-bank impact area does not contain the levee; therefore, do not add a lateral structure. However, the right-bank still requires the with-project condition stage-discharge function imported in Task 3.
   

   1. Select the following for the Right-Bank impact area:

      Click here to expand and view an example for the right-bank base year low levee (without armor)setup...

      

   2. Now you must enter the Threshold Stage manually. Uncheck the Calculate Default Threshold checkbox and enter the project performance threshold in the Threshold Stage box and in HEC-FDA Version 2.0.
      
      
      

      Threshold Stage (Right-Bank)

      Review the Target Threshold section of the Scenarios page in HEC-FDA User Manual. As explained in this section, for impact areas without levees, and for scenarios that reflects with-project conditions, then the user must enter the threshold stage as the default threshold stage from the without-project condition (for the specific analysis year). With-project system performance then reflects the stage at which significant damage begins in the without-project condition.

      Click here to expand and view a quick How-to GIF...

      

      Warning!

      This quick how-to does not show you the value you should enter for your study, instead it just shows you how-to find the value. Please use your own Without Base Year scenario to determine the appropriate Threshold Stage value to set for the Right-Bank impact area.

      

   3. The default Damage Category selection is RES and Asset Category selection is Structure. Click Preview Compute.

8. Click Save, and click Close.
9. Repeat these steps until you've created three new base year with-project scenarios and three new future year with-project scenarios (as outlined in Table 4).

Task 6.2 – Compute All Scenarios

Compute the new Levee scenarios:

1. From the Study Tree, right-click on Scenarios and click Compute Scenarios.
2. From the Compute Scenarios tab, click the checkbox to select the new scenarios, and then click Compute. A message box opens asking if you'd like to view the results. Click Yes.
3. The Summary Results tab opens. Close the Compute Log tab.

Task 7 – Create and Compute Three Alternatives for the Three Proposed Levees

Create and Compute Three Alternatives

Use the instructions below to create the three alternatives, one for each of the three proposed levees. 

1. From the Study Tree, right-click on Alternative and select Create New Alternative. The Create New Alternative dialog opens as a tab.

2. Enter a name (see example names below) and a description for the new alternative.

   1. Low Levee without Armor: LowLevee_noArmor
   2. Low Levee with Armor: LowLevee_Armored
   3. High Levee: HighLevee
3. From the Base Year Scenario box, select the appropriate base year scenario you created in Task 6; and from the Year box, enter: 2031.
   1. Low Levee without Armor, select: Base-LLnoA
   2. Low Levee with Armor, select: Base-LLwA
   3. High Levee, select: Base-HL
4. From the Future Year Scenario box, select the Future Year Levee 1 scenario you created in Task 6; and from the Year box, enter 2080.
   1. Low Levee without Armor, select: Future-LLnoA
   2. Low Levee with Armor, select: Future-LLwA
   3. High Levee, select: Future-HL
5. Click Save and Close.

6. From the Study Tree, right-click on the created alternative, and click View Results. Close the Compute Log.

7. Repeat these steps until you've created three new with-project alternatives. 

Task 8 – Create and Compute an Alternative Comparison Report

1. From the Study Tree, right-click on Alternative Comparison Report and select Create New Alternative Comparison Report. The Create New Alternative Comparison Report dialog opens as a tab.
2. Enter a name for the new alternative comparison report in the Name box (e.g., Comparison), and enter a description (e.g., alternative comparison report to provide damage reduced between the without-project condition and with-project conditions).
3. From the Without Project list select: Without Project.
4. From the With Project list select (if you use the same naming convention described in Task 7): LowLevee_noArmor.
5. Click Add Comparison. From the newly added With Project list select: LowLevee_Armored.
6. Click Add Comparison. From the newly added With Project list select: HighLevee.
   Click here to expand and see the Create New Alternative Comparison Report ...

   

7. Click Save. Click Close. The new comparison report is added to the Study Tree.
8. From the Study Tree, right-click on the created comparison report, and click View Results. Close the Compute Log.

Workshop Discussion Questions

Project Performance

Review the Project Performance reports to answer the following questions.

Test Your Knowledge - Question 3

What is the probability that High Levee will experience overtopping in the next 30 years?

Hint: Look for the Long-Term Exceedance Probability in the Base_HL Scenario results.

Test Your Knowledge - Question 4

What is the fifty percent exceedance probability average annual equivalent (AAEQ) damage reduced value for low levee no armor for the Left-Bank?

Hint: Take a look at the Alternative Comparison Report results tables.

Test Your Knowledge - Question 5

Is it always correct to assume that the without-project conditions and with-project conditions stage-discharge (rating) function is the same for a levee project?  Why?  How would you account for a difference using HEC-FDA.

Hint: For a flood-level volume of water, if the water cannot spread out into the floodplain, what does it do? 

Conclusion

Download the solution project below to compare to your project:

• Muncie_WS5.7z
• Muncie_WS5.zip

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

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Best Answers to Test Your FDA Knowledge Questions

Click here to review answers...

Note: Your results may not exactly match the results shown here. That's a product of variation in the software since this workshop was created and does not indicate that you did something wrong. Your results should follow the same trends and the values should be somewhat close to the ones shown below.

Test Your Knowledge - Question 1

Pursuant to ECB 2019-11 (hold Ctrl while clicking to open in another tab), do any of the levee plans meet FEMA’s criteria for NFIP levee accreditation?

You will have to identify the computed assurance of the 1% AEP event using the Annual Exceedance Probability report under Performance outcomes for all levees.  The following ranges of assurance determine the accreditation recommendation:

Assurance for the 1% AEP	Recommendation
Assurance < 65%	Do not accredit
Assurance > 85%	Accredit
65% ≤ Assurance ≤ 85%	More evidence is needed to accredit

Answer: No. None of the levees demonstrate assurance of the 1% AEP in ranges in the above table.

Test Your Knowledge - Question 2

Nonfederal sponsors and members of the vertical team are often interested in knowing what a levee's level of risk reduction is in terms of return interval years.  If the criteria for this statement is having 90% assurance that the event would not exceed the levee height, what statement could be said about the high levee?

Answer: The annual exceedance probability (AEP) with 90% assurance has been computed as 0.0534.

The policy-compliant simplified communication (per paragraph 8j(5) of ER 1105-2-101) would be : “Given irreducible uncertainties inherent in flood frequency analysis, the Levee 3 Plan will pass the 5.3% event with 90% assurance.”

Test Your Knowledge - Question 3

What is the probability that the high levee will experience overtopping in the next 30 years?

Hint: Look for the Long-Term Exceedance Probability in the Scenario results.

Answer: .6369, or ~64%

Test Your Knowledge - Question 4

What is the fifty percent exceedance probability equivalent annual damages reduced value for low levee no armor for the Left-Bank? 

Hint: Take a look at the Alternative Comparison Report results tables.

Answer: $917,010.16

Test Your Knowledge - Question 5

Why is there a with-project condition rating curve?

Answer: A levee restricts water to the channel that would have otherwise spread out in the area now kept dry by the levee, so the stages increase for a given level of flow.

Related Topics

For the list of resources below, either select a specific page to view the related information, or click on a page label to see all the pages for a specific topic (e.g., fda_help_resources).

• Page:
  Alternative Results (HEC-FDA User Manual)

  • fda_alternatives
  • fda_advanced_topics
• Page:
  Alternatives (HEC-FDA User Manual)

  • fda_v1_v2_diff
  • fda_impactareaset
  • fda_alternatives
  • fda_advanced_topics
• Page:
  Consequences Methodology (HEC-FDA Technical Reference)

  • fda_consequences
• Page:
  Expected Annual Damage (HEC-FDA Technical Reference)

  • fda_scenarios
• Page:
  Flood Risk Assessment and HEC-FDA (HEC-FDA User Manual)

  • floodriskequ-um
  • fda_help_resources
• Page:
  Functions (HEC-FDA Technical Reference)

  • fda_scenarios
• Page:
  Getting Help and Additional Resources (HEC-FDA User Manual)

  • fda_help_resources
  • fda_advanced_topics
• Page:
  Glossary (HEC-FDA User Manual)

  • fda_help_resources
• Page:
  Known Issues (HEC-FDA User Manual)

  • scroll-help-center-news-page
  • fda_help_resources
• Page:
  Lateral Structures (HEC-FDA User Manual)

  • fda_impactareaset
  • fda_lateralstruc
• Page:
  Part C Specify and Compute Scenarios (HEC-FDA Quick Start Guides)

  • fda_scenarios
• Page:
  Part D Specify Alternatives and an Alternative Comparison Report (HEC-FDA Quick Start Guides)

  • fda_alternatives
  • fda_alt-comp-report
• Page:
  Scenario Results (HEC-FDA User Manual)

  • fda_scenarios
  • fda_advanced_topics
• Page:
  Scenarios (HEC-FDA User Manual)

  • fda_v1_v2_diff
  • fda_impactareaset
  • fda_scenarios
  • fda_advanced_topics
• Page:
  Study Dimensions and Compute Configuration and Results (HEC-FDA User Manual)

  • fda_impactareaset
  • fda_help_resources
  • fda_advanced_topics
• Page:
  Version 2.0 Certification Report (HEC-FDA User Manual)

  • fda_help_resources
• Page:
  Version 2.1 Certification Report (HEC-FDA User Manual)

  • fda_help_resources