HEC-FDA Version 2.0

By:  Brennan Beam, P.E., CFM; Taylor Bolt, P.E.; Richard J. Nugent III, Ph.D.; and Julia Slaughter

Introduction

The Flood Damage Reduction Analysis (HEC-FDA) software developed by the U.S. Army Corps of Engineers' (USACE) Hydrologic Engineering Center (CEIWR-HEC) provides the capability to perform an integrated hydrologic engineering and economic analysis during the formulation and evaluation of flood risk management plans. HEC-FDA is designed to assist USACE study members in using risk assessment procedures for formulating and evaluating flood risk management measures (Figure 1) pursuant to pertinent policy and guidance (EM 1110-2-1619, ER 1105-2-101). HEC-FDA is USACE's only tool certified to support inland flood risk assessment recommendations and has supported 49 chief's reports in the last 10 years in which HEC-FDA was used by USACE project delivery teams to identify more than $5 billion in annual benefits that justified nearly $44 billion in flood risk management investment recommendations. 

Software Development Expertise

HEC-FDA Version 2.0 is a modern overhaul of the HEC-FDA software and will be the first major release of the HEC-FDA software program in more than a decade. HEC-FDA Version 2.0 is an open-source software program built with Microsoft's latest .NET software development kit and is largely written in the C# programming language. 

The software program was developed with several important features that enhance the stability of the software over the long-term. Some examples include:

1. Model-View-ViewModel Framework. This software architecture completely separates the computational engine from the user interface code, making software maintenance easier and safer. Read more about the framework in Microsoft's documentation.
2. Open Source. Anyone with internet access can inspect the codebase, evaluate what takes place under the hood, and even submit requests for code changes. The public repository can be accessed on GitHub.
3. DevOps Procedures. The team relies on the Gitflow branching strategy to ensure that the software is in a constantly deliverable state, automated testing upon every code change to prevent unintended consequences, and version control for secure development. Our contributing guide documents these and other software development standards that the HEC-FDA team follows.
4. Team Collaboration. Multiple people can safely and effectively operate in all classes in this codebase now and additional contributors are being onboarded. HEC-FDA will not be exposed to a single point of failure (key person risk) that takes place through reliance on a single person to maintain and develop a codebase or specific parts of a codebase. Contributor activity can be viewed on GitHub.

Team Accomplishment

The completion of HEC-FDA Version 2.0 is a monumental accomplishment for the Hydrologic Engineering Center (CEIWR-HEC) which began more than 10 years ago. Initially, HEC-FDA Version 2.0 was meant to be a new user interface written in Java on top of the existing computational engine. In 2020, Dr. Richard J. Nugent III joined HEC as the new lead of HEC-FDA, and he brought a renewed focus on delivering the first major update of the HEC-FDA software program to the field.  His progressive goal included re-writing the codebase to include critical features such as geospatial data processing and modern software architecture. In 2021, Dr. Nugent stood up a software development team within HEC, which included William Lehman and Brennan Beam, and with support from Lea Adams (current Director of HEC and former Division Chief of the Water Resources Systems Division). The FDA Team quickly began developing the software in earnest; Dr. Nugent and Mr. Beam learned how to develop software whilst adding to USACE capability in parallel computing and user interface development. Many senior software developers at HEC provided assistance to the FDA team; including the consistently generous support provided by Alex Kennedy, a senior computer scientist on the HEC-RAS team. Due to Mr. Beam's dedication and contribution to the development of HEC-FDA Version 2.0, he has earned recognition as a senior software developer at HEC. Under Dr. Nugent's leadership, the team continues to grow and make important contributions towards software development and technology transfer. Notably, Julia Slaughter designed and recorded the popular videos that accompany the HEC-FDA Quick Start Guides. Critical guidance regarding the correct implementation of the underlying theory was provided by Dr. Beth Faber. In addition, Rebecca Augustin, Taylor Bolt, Britt Corley, Audrey Demeaux, Jordan Lucas, Hastings Marek, and Will Shaffer contributed to the development of valuable technology transfer enhancements.  And consequential input on the software was provided by the USACE Flood Risk Management Planning Center of Expertise. 

New in HEC-FDA Version 2.0

The latest version of HEC-FDA comes with a completely new user interface that provides modern software functionality (Figure 2). That's right folks, you can now copy and paste. The figure below of the Create Frequency Function editor displays a typical table with standard copy and paste functionality and a plot to facilitate inspection of the input data. Review the Differences Between Version 1.4.3 and Version 2.x page of the HEC-FDA User Manual for more information.

As illustrated in Figure 3, the HEC-FDA Version 2.0 user interface is structured with a Menu Bar (top), a Study Tree (left-hand side), and a Display Window (right-hand side). To learn more, navigate to the section on the HEC-FDA User Interface in our user documentation. Users can obtain detailed risk reporting by right-clicking on compute configurations (e.g., Muncie Without - 2025) from the Study Tree, or by viewing summary results tables that are formatted for direct use in decision documents. The risk reporting includes expected annual damage with uncertainty, project performance statistics, and damage reduced with uncertainty. Further, the figure below displays the system performance statistics open in the Display Window for an example scenario compute (Muncie Without - 2025). A scenario is a new concept in the HEC-FDA Version 2.0 software, which reflects the study configuration at the project condition and analysis year level. Further, the system performance statistics are one of the outputs from the scenario compute algorithms. Review the HEC-FDA User Manual for more information regarding scenarios.

The HEC-FDA consequences engine has been dramatically modernized. The consequences engine produces aggregated stage-damage functions with uncertainty, and the calculation of these functions now relies on georeferenced hydraulic modeling. No extra work is required on behalf of economists to take advantage of two-dimensional hydraulic modeling results, which are now the most common type of hydraulic data thanks to advances in HEC-RAS. HEC-FDA uses the RasMapper library to read georeferenced hydraulic modeling, and is able to read the dynamic results stored in HEC-RAS output files.

In addition, the modernized consequences engine now uses a histogram as an approach for modeling uncertainty in damage for a given stage. This method is more effective than the approach used in HEC-FDA Version 1.4.3, which was to fit normal distributions to the resulting samples of damage. In other words, HEC-FDA now uses an uncertainty distribution that can flexibly match the result of any given Monte Carlo simulation instead of changing the result of the Monte Carlo simulation to match a normal distribution. 

Figure 4 provides a visualization of the change in methodology for an example study (Greenbrook). In Version 1.4.3, HEC-FDA fit a normal distribution to the result of the Monte Carlo distribution to represent the uncertainty in damage for a given stage, as plotted in orange below. The result of the Monte Carlo simulation captured in a histogram is plotted in blue. The histogram demonstrates much stronger convexity than a Normal distribution would allow, which means that fitting a normal distribution to the Monte Carlo results would cause significant bias in the risk with uncertainty compute. In other words, HEC-FDA Version 2.0 does a much better job at modeling the uncertainty in damage for a given flood. 

User Support 

HEC-FDA Version 2.0 is being released alongside a wealth of new user documentation and other resources. This user documentation includes engaging video tutorials, self-paced training, and hands-on workshops. These resources have been developed with the support of USACE Flood and Coastal Systems (FCS) R&D (funded through GI R&D) in response to Statements of Need 1498, 1507, and 1534. 

1. HEC-FDA Quick Start Guides with video tutorials to get you up and running quickly.
2. Version 1.4.3 to Version 2.0 Study Conversion tutorial for easy conversion reference. 
3. HEC-FDA User Manual for thorough descriptions of software functionality. 
4. HEC-FDA Technical Reference for detailed information about how the computational engine works. 
5. PROSPECT #209 Course Materials Using HEC-FDA Version 2.0 Software. We recorded lectures and hands-on workshops. 
6. Discourse FDA user group for issue reporting, troubleshooting questions, and opportunities to share lessons learned. 

What's Next

The future of HEC-FDA is bright. An effort is currently underway to bring a map window to HEC-FDA and add complete geospatial functionality so that economists can carry out all plan formulation and evaluation steps within one software and using one consistent workflow. This work is funded with the support of USACE FCS R&D in response to Statement of Need 2002. Research and development have been proposed to improve the way that empirical hazard uncertainty is incorporated into expected annual damage, to calculate benefits at the structure level and aggregate logically, to automate nonstructural plan formulation and evaluation, and to improve reporting and data visualization on intermediate calculations. This work is proposed in response to USACE FCS R&D Statement of Need 2195. Meanwhile, the HEC-FDA team is poised to fix bugs as they are reported and deliver new versions to the field quickly and safely.