490 - Hydrodynamic Modeling of Coastal Flooding: Joint Impact Assessment of Fluvial and Storm Surge Flood Drivers in St. Augustine, Florida

As climate change accelerates and sea levels rise, coastal cities are facing an increasingly urgent and complex challenge. The dynamic interplay of these climate-based risks exerts growing pressure on the frequency and intensity of storm surges and high-precipitation events, exacerbating the risks of flooding caused by their combined effects. In response to these imminent threats, this study assesses the capability of recent advancements in two-dimensional (2D) hydrodynamic modeling to provide a qualitative and quantitative understanding of spatial and temporal distribution of compound flooding in coastal regions by integrating the combined impact of precipitation, riverine flow, and storm surge. The Hydrologic Engineering Center's River Analysis System (HEC-RAS) was employed to analyze the compounding effects of fluvial and coastal flooding. By considering multiple Annual Exceedance Probabilities (AEP) for various flood drivers, the model was applied to characterize compound flooding scenarios in the City of St. Augustine, Florida. The compound flooding model used data from the National Oceanic and Atmospheric Administration (NOAA) Atlas 14 Precipitation-Frequency, and storm surge time series from the Coastal Hazard System (CHS). The 2D modeling approach comprehensively depicted flooding in coastal areas, facilitating interactions with more fluvially influenced inland regions to produce flood simulations. While storm surge was the primary driver of flooding, combined events exacerbated both the extent and depth of flooding, particularly in cases of low-frequency precipitation events. This integration of multiple drivers in coastal regions provides a more realistic representation of spatial and temporal patterns of compound flooding, often the most destructive aspect of coastal inundation.