Simulating Compound Flooding: A Comparison between HEC-RAS and ADCIRC

Compound flooding is a relatively new term to describe when two or more flood events occur simultaneously or consecutively; for instance, hurricane storm surge combined with heavy rainfall and high tides. In recent years, possibly due to climate change, the number of compound flooding events is on the rise. Among the existing state-of-the-art models, Hydrologic Engineering Center-River Analysis System (HEC-RAS) and Advanced Circulation (ADCIRC) are the most common and reliable ones to simulate inland and storm surge flooding, respectively. In this study, for the first time, we compared ADCIRC and HEC-RAS models in simulating compound flooding. New tools were developed and added to ADCIRC to include riverine flows. Although the mesh structure and resolutions were different, the bottom friction coefficients, bathymetry, and land elevation were set identical in these two models. The results showed very similar water surface elevation (WSE) within the study area despite the fact that these two models are solving different sets of equations and handle the boundary conditions differently. While both models require upstream flow boundaries, the use of ADCIRC is superior as by expanding the domain size, and including the larger water bodies, it could simulate the storm surge using the wind field data. In contrast, the HEC-RAS model could not simulate the storm surge independently and requires downstream boundary conditions. Thus, ADCIRC's more extensive range of capabilities provides the opportunity to model compound flooding by running ADCIRC as the primary forward model and couple it with inland flooding models such as HEC-RAS.