Modeling of Barrier Breaching During Hurricanes Sandy and Matthew. Issue 3 (21st March 2022)

• Record Type: Journal Article
• Authors: Hegermiller, Christie A.; Warner, John C.; Olabarrieta, Maitane; Sherwood, Christopher R.; Kalra, Tarandeep S.
• Is Part Of: Journal of geophysical research. Volume 127:Issue 3(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-03-21
• Subjects: breach -- barrier island -- hurricane; Geomorphology -- Periodicals; 551.3
• DOI: 10.1029/2021JF006307
• Languages: English
• ISSNs: 2169-9003

Abstract

Abstract: Physical processes driving barrier island change during storms are important to understand to mitigate coastal hazards and to evaluate conceptual models for barrier evolution. Spatial variations in barrier island topography, landcover characteristics, and nearshore and back‐barrier hydrodynamics can yield complex morphological change that requires models of increasing resolution and physical complexity to predict. Using the Coupled Ocean‐Atmosphere‐Wave‐Sediment Transport (COAWST) modeling system, we investigated two barrier island breaches that occurred on Fire Island, NY during Hurricane Sandy (2012) and at Matanzas, FL during Hurricane Matthew (2016). The model employed a recently implemented infragravity (IG) wave driver to represent the important effects of IG waves on nearshore water levels and sediment transport. The model simulated breaching and other changes with good skill at both locations, resolving differences in the processes and evolution. The breach simulated at Fire Island was 250 m west of the observed breach, whereas the breach simulated at Matanzas was within 100 m of the observed breach. Implementation of the vegetation module of COAWST to allow three‐dimensional drag over dune vegetation at Fire Island improved model skill by decreasing flows across the back‐barrier, as opposed to varying bottom roughness that did not positively alter model response. Analysis of breach processes at Matanzas indicated that both far‐field and local hydrodynamics influenced breach creation and evolution, including remotely generated waves and surge, but also surge propagation through back‐barrier waterways. This work underscores the importance of resolving the complexity of nearshore and back‐barrier systems when predicting barrier island change during extreme events. Plain Language Summary: Barrier islands are particularly vulnerable to coastal erosion and flooding during extreme storms, such as hurricanes, because they are narrow and low‐lying. Breaching across a barrier, when the ocean becomes connected to a back‐barrier waterway, can result in damage to coastal communities requiring extensive repair efforts, and changes to ocean navigation or water dynamics that sometimes persist for many years. Barrier breaching can be driven by both ocean and back‐barrier waterway processes. However, the conceptual framework describing coastal change during an extreme storm often only considers ocean processes. In this work, we hindcast barrier breaching using a physics‐based numerical model that was recently extended to include infragravity (IG) waves. IG waves are long waves with periods of 25 s to 5 min, which contribute substantially to extreme water levels during hurricanes. The model was able to predict breach formation with good skill, though the modeled breaches did not occur in the exact locations where breaches were observed. Through analyses of modeled water levels, waves, and sand movement, this work demonstrates the importance of resolving the co‐evolution of the beach, the ocean, and the back‐barrier. Key Points: The Coupled Ocean‐Atmosphere‐Wave‐Sediment Transport model was adapted to include infragravity wave dynamics and applied to investigate barrier breaching during two hurricanes Different breaching mechanisms driven by remote to local forcing led to barrier breaches modeled with good skill Ocean‐side processes were as important as back‐barrier processes when breaching occurred from back‐barrier inundation, and vice‐versa