Storm-Driven Erosion and Inundation of Barrier Islands from Dune- to Region-Scales

Barrier islands are susceptible to erosion, overwash, and breaching during intense storms. However, these processes are not represented typically in large-domain models for storm surge and coastal inundation. In this study, we explore the requirements for bridging the gap between dune-scale morphodynamic and region-scale flooding models. A high-resolution XBeach model is developed to represent the morphodynamics during Hurricane Isabel (2003) in the North Carolina (NC) Outer Banks. The model domain is extended to more than 30 km of Hatteras Island and is thus larger than in previous studies. The predicted dune erosion is in good agreement with post-storm observed topography, and an ‘‘excellent’’ Skill Score of 0.59 is obtained on this large domain. Sensitivity studies show the morphodynamic model accuracy is decreased as the mesh spacing is coarsened in the cross-shore direction, but the results are less sensitive to the alongshore resolution. A new metric to assess model skill, Water Overpassing Area (WOA), is introduced to account for the available flow pathway over the dune crest. Together, these findings allow for upscaled parameterizations of erosion in larger-domain models. The updated topography, obtained from XBeach prediction, is applied in a region-scale flooding model, thus allowing for enhanced flooding predictions in communities along the Outer Banks. It is found that, even using a fixed topography in region-scale model, the flooding predictions are improved significantly when post-storm topography from XBeach is implemented. These findings can be generalized to similar barrier island systems, which are common along the U.S. Gulf and Atlantic coasts.

A Gharagozlou, JC Dietrich, A Karanci, RA Luettich, MF Overton (2020). “Storm-driven erosion and inundation of barrier islands from dune- to region-scales.” Coastal Engineering, 158, 103674, DOI: 10.1016/j.coastaleng.2020.103674

Seminar: UNC Wilmington

News: Connecting Erosion to Flooding

2019/09/26 – NC Sea Grant Coastwatch
XBeach Model Predicts Storm Impacts on Beaches and Dunes

Alireza Gharagozlou (below) is a doctoral student in the Department of Civil, Construction, and Environmental Engineering at NC State University. He studies how to connect predictions of beach and dune erosion to community-wide flooding and serves with Casey Dietrich on NC State’s Coastal & Computational Hydraulics Team. North Carolina Sea Grant has supported their work.

Alireza surveying the beach profile near Hatteras, NC, with RTK-GPS after Hurricane Florence.

2019/04/26 – NC Sea Grant Coastwatch Currents
Model Predicts Storm Impacts on Beaches and Dunes

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During storms, strong waves and currents can erode beaches and dunes and create low-lying areas vulnerable to flooding. We use field surveys and a computer model called XBeach to predict this erosion, as well as to understand its interactions with storm-driven flooding of larger regions.

Computer models allow us to see how the storm surge and waves impact the beach over time, and which locations are vulnerable to large-scale damage. Good predictions of such storm impacts help emergency managers take better-informed measures to protect coastal areas. Understanding vulnerabilities also instructs highway access design and residential area planning.

We used the XBeach computer model on more than 30 kilometers of Hatteras Island between Avon and Rodanthe to explore how to connect erosion predictions to larger areas. Could XBeach cover more of the island, yet still provide good erosion predictions at beach and dune scales? And how could we connect erosion predictions to other models for storm surge and flooding?

Presentation: ASCE NC Fall Conference

Conference: ADCIRC 2019

Alireza Gharagozlou wins Student Educational Award

Ph.D. student Alireza Gharagozlou won the Student Educational Award at the ASBPA National Coastal Conference 2018. This award is given annually to an undergraduate or graduate student who, through his or her research, is furthering the state of the science of coastal systems as it relates to the goals and mission of the ASBPA. Congrats to Alireza!

Alireza accepts the Student Educational Award during the awards luncheon at the ASBPA National Coastal Conference.