Part C: Specify and Compute Scenarios

Transcript for Prerequisites for Scenarios (Video 1)

Welcome to the hydrologic engineering centers, flood damage reduction analysis, version 2.0, training video. My name is Julia Slaughter. And this video identifies the prerequisite conditions and setup considerations necessary for creating and defining scenarios. 

When you get to this point to set up scenarios in your own Watershed, here are a few questions you need to ask yourself. Is flow a variable I can include in my risk assessment? I need to keep in mind that uncertainty in flow is the most important contributor to uncertainty in EAD and it cannot be ignored. Number two, is there flow management occurring such as from a dam or a Detention Reservoir. Number three, are there any modifications to the channel in the with-project condition requiring a modified stage-discharge relationship? Number four, are there levees? Do the levees have probability of failure? And are there situations where a levee can be flanked before being overtopped or situations where a levee can be overtopped without certain failure such that risk is significant in a non-failure scenario? In the case of a non-failure scenario, Total Risk can be modeled in HEC-FDA Version 2.0. Review the Total Risk scenarios video for more information. Number five, are there with-project non-structural actions, requiring modified stage-damage relationships. And lastly, number six, on what basis will I measure my project performance statistics? Will I calculate the default for the without-project condition? Use a levee threshold? Or, for a with-project scenario, identify the corresponding without-project scenario from which we'll identify the threshold?

Let's continue with an overview of the prerequisite conditions for creating scenarios. For our example study, here is an overview of the structure inventories and aggregated stage-damage functions that will be used to create scenarios. The aggregated stage-damage, functions include the base without-project a future without-project, and a base with-project and a future with-project. Which are based on different structure inventories and flood plain conditions, for two analysis years. The scenarios that we will create for our example FDA study include two with-project conditions. One project, is a levee on the Left-Bank impact area; and the second, are non-structural measures. Therefore, in our example study we will have eight scenarios. One for the without-project conditions base year and future year, one for the Levee base year and future year, one for just nonstructural in the base year in future year, and one including the Levee and non-structural for the base year and most likely future year.

Please review the next three scenario videos which focus on how to create and define scenarios, specialization of scenarios in the Scenario Editor including total risk. And the finial scenario video which explains additional compute options and reviewing scenario results.

Transcript for How-to Create Scenarios (Video 2)

Welcome to the hydrologic engineering centers, flood damage reduction analysis, version 2.0, training video. My name is Julia Slaughter. And this video provides instructions for creating and defining scenarios in HEC FDA version 2.0. This tutorial video builds upon the Prerequisites video, so please watch that video before you continue watching this one.

How do we create our scenarios? From the study tree, right-click on scenarios and select the create new command. Let's start with the Without Project Base Year scenario. You'll need to enter the name, description, and the analysis year for the scenario. And set the economic, hydrologic, hydraulic, geotechnical summary relationships required for each impact area. Once the required summary relationships and parameters have been selected, click save and close. Let's repeat this process for the Without Project Future Year. Make sure that you enter the correct analysis year and select the correct stage-DAMAGE function, frequency relationship, and stage-discharge relationship required for the specific scenario for each impact area. Once the without project future year scenario is defined, click Save and Close. 

Now let's create the Levee with-project base year scenario. For our example study, there is one levee located on the Left-bank. Therefore, after identifying the correct analysis year, stage-DAMAGE function, frequency relationship and stage-discharge function, set the appropriate lateral structure dataset for the left-bank impact area. Note that the selected lateral structure dataset sets the Threshold Stage for the left-bank impact area. Now we need to complete the right-bank impact area. 

At this point I'd like you to recall Question #6 from the six focus questions we discussed in the first scenario's video. Specifically, the last part of question six explains the need to identify the threshold value for the right-bank impact area. Let me explain how to identify this threshold value. First, we will need to compute the Without-Project Base Year scenario. To do this, from the study tree, right-click on the Without-Project Base Year scenario and select Compute Scenario. The Compute Log opens to display the compute progress. Once complete, click Yes to view the results. Select the Right-Bank impact area, and the Performance outcomes. Note that the calculated without-project base year Threshold value is displayed for the selected impact area. Return to the Levee Base Year Scenario dialog and enter the identified threshold stage for the right-bank impact area. Now that the required summary relationships and parameters have been selected, click save and close.

Let's also run through the creation of the Levee Future Year scenario. As, with the Levee Base Year scenario, the selected Lateral Structural dataset set's the Threshold Value. However, you must calculate the without-project future year scenario to identify the right-bank threshold value. Again, right-click on the without-project future year scenario and click Compute Scenario. Once computed, review the Performance outcomes results for the right-bank impact area and enter the calculated Threshold value for the Levee Future scenario. Click Save and Close. 

When creating the remaining with-project scenarios. You will need to repeat this process to create each individual scenario. Making sure that you select the correct stage-damage function, frequency relationship, regulated-unregulated flow, stage-discharge function, and any geotechnical relationships required for the specific scenario. Note, that for the with-project scenarios that do not contain a levee on the left-bank impact area you will need to identify the threshold value from the corresponding without-project scenario. 

Please review the next two scenario videos which focus on specialization of the scenarios in the Scenario Editor, explains additional compute options and scenario results.

Transcript for Special Considerations and Total Risk (Scenarios Video 3)

Welcome to the hydrologic engineering center's, flood damage reduction analysis, version 2.0, training video. My name is Julia Slaughter. And this video covers special considerations when creating scenarios and total risk in HEC-FDA Version 2.0. This tutorial video builds upon the Prerequisites video, and How-to Create Scenarios video. So, please watch those videos before you continue watching this one.

Now that you've created your scenarios  let's go through a few neat tricks that the Scenario Editor provides. Right-click on one of your scenarios and select Edit. Let's, pop out the window and select the Preview Compute button. Notice the bottom of the scenario editor updates with a series of plots. What your viewing right now is the deterministic estimate for EAD and the summary input relationships. The series of plots are very helpful and you should inspect these plots, starting in the top right, and moving counter-clockwise, to verify that there's substantial overlap between the dependent variable in the first plot,  and the independent variable in the next plot. If not, there might be a flaw in the modeling and information is being lost. 

Another option in the scenario editor is the ability to add additional thresholds.  Additional thresholds could be handy for nonstructural alternatives to be able to report performance for differentially elevated structures. To add thresholds, click the Additional Thresholds button and from the System Performance Thresholds dialog click Add to add new rows to the thresholds table and enter a stage value. Repeat this process to add more thresholds. To remove an entered threshold, select the row you want to delete and click Remove. Once finished, click OK.

New in Version 2.0 is the added functionality to calculate Total Risk. Total risk is the sum of failure risk and non-failure risk. Traditionally, when there is a levee assigned to an impact area, HEC-FDA would calculate failure risk only, which is appropriate when there is no interior flooding expected if the levee does not fail. However, if there is any type of significant interior flooding despite the levee performing correctly, we need to include that non-fail risk.

Let's review the setup requirements and parameters necessary for calculating a non-failure scenario using our example study. First, two sets of hydraulics will be required to compute two sets of stage-damage functions. One set reflects the damage that would occur in the floodplain if the levee fails. And the second reflects the damage that would occur in the floodplain if the levee did not fail. Therefore, to illustrate these setup requirements, a second hydraulic dataset and corresponding aggregated stage-damage functions have been added to our example FDA study. Now, we can create our hypothetical non-failure scenario where damaging inundation is expected even when the levee behaves as expected.

Let's walk through how to create a scenario that models non-failure for the base year and most likely future year. From the Study Tree, right-click on Scenarios and select the create new option. From the dialog enter the name for the Base Year Total Risk scenario, and a description. Enter the analysis year for the scenario. Next, check the "Non-Failure Scenario Modeled" option and select the correct Failure Stage-Damage and Non-Failure Stage Damage Functions. Now, you can complete the Base Year Total Risk scenario as you normally would by making sure you select the correct hydrologic, hydraulic and geotechnical summary relationships required for each impact area. In our example study the levee is located on the left-bank impact area, which sets the Threshold stage. At this point I'd like you to recall the process for identifying the threshold value from the corresponding without project scenario which was covered in the second scenarios video. Please review the How-to create scenarios with thresholds video for more information. Once the required summary relationships and parameters have been selected for each impact area, click save and close.

Let's repeat this process for the Future Year Total Risk scenario. Enter a name, a description and the analysis year. Next, turn on the "Non-Failure Scenario Modeled" option and select the correct Failure Stage-Damage and Non-Failure Stage Damage Functions for the future year, and select the correct hydrologic, hydraulic, and geotechnical summary relationships required for each impact area. Once the required summary relationships and parameters have been selected, click save and close.

You may now calculate the total risk scenarios and view the results. Please watch the final scenarios video which explains additional compute options and scenario results.

Transcript for Compute Options and Scenario Results (Video 4)

Welcome to the hydrologic engineering centers, flood damage reduction analysis, version 2.0, training video. My name is Julia Slaughter. And this video provides instructions for computing and reviewing scenario results in HEC-FDA Version 2.0. This tutorial video builds upon the three proceeding videos about Scenario Prerequisites, How-to Create Scenarios, and Special Considerations which includes Total Risk. So, please watch those videos before continuing to watch this one. 

There’s a simple way to calculate all of the scenarios at once from the study tree. Right-click on Scenarios and select Compute Scenarios. This opens a dialog that allows you to select specific scenarios or all of them and compute. Once the compute has been completed, you can open the summary results.  Let’s look at the summary results in greater detail now. You can pop out the window to take a closer look. The top table provides the total expected annual damage. I want to emphasize that we're looking at the expected annual damage. Not the average annual equivalent damage, because these measures do not consider time and value of money. These damage measures cannot be compared with costs. The top table displays the mean and the quartiles. One way of reading the first quartile is that this is the level of damage that has a 75 percent chance of being exceeded. 

Assurance of threshold, where the threshold is either a stage or a levee, this is the chance that a threshold will not be exceeded for a specific flood event. This is typically calculated based on a distribution of stages. The long term exceeds probability is the chance that a threshold is passed at least once within a given time frame. This is calculated using the binomial theorem and the average AEP. The Assurance of AEP or annual exceedance probability of 0.01. This is the chance that the frequency with which the threshold is passed is less than 0.01. This is the measure of assurance that considers the entire range of flooding. It is calculated based upon the distribution of AEP. 

As well as a summary results. Users can review results for a specific scenario. If you review the results for a specific scenario, you can select the specific impact area to look at the damages or the performance. When you have damage selected, you can also look at damage by damage category. After you've finished reviewing the results, you can close the window.