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December Bulletin 2023

Hindcasting compound pluvial, fluvial and coastal flooding during Hurricane Harvey (2017) using Delft3D-FMWonhyun Lee1, Alexander Y. Sun1, Bridget R. Scanlon1 & Clint Dawson21Bureau of Economic Geology, Jackson School of Geoscience, The University of Texas at Austin, Austin, USA2 Oden Institute for Computational Engineering and Sciences, The University of Texas at Austin, Austin, USAAbstractHurricane Harvey (2017) resulted in unprecedented damage from flooding in the Houston–Galveston area of the U.S. Gulf Coast. The objective of this study was to better quantify the impacts of compound flooding and to assess the relative contributions of storm surge, pluvial (rainfall) and fluvial (riverine) flooding using Hurricane Harvey as a case study. Here we developed a comprehensive numerical modeling framework to simulate flood extents and levels during Hurricane Harvey using Delft3D Flexible Mesh and validated results against observed water levels, waves, winds, hydrographs and high water marks. Results show that pluvial flooding dominated from widespread heavy rainfall during Harvey, accounting for ~ 60–65% of flooding. Pluvial flooding occurred mostly in watersheds and floodplains in West and South Bays (≤ ~ 1.5 m), upper Galveston Bay (Trinity River Basin, 2–3 m) and Harris County (≤ ~ 2.5 m). River runoff led to local ~ 1–2 m flooding. Significant storm surge levels were simulated northwest of the main Bay (2–2.5 m) and Galveston Bay (1–2 m) and in several watersheds in West/East of Galveston Bay. Wave action caused flood depth and water levels to rise by about 0.3–0.5 m in nearshore areas. Maximum flooding extent developed around August 29, 2017, which compared well to FEMA flood depth data. Nonlinear effects of compound flooding are greater than the sum of individual components. Results from this large-scale coupled modeling analysis provide a useful basis for coastal risk management and hazard mitigation. Our integrated framework is general and can be readily applied to other coastal compound flooding analyses.

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