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

Conference: ADCIRC 2020

Posters: EWC Symposium 2020

A Poisson, JC Dietrich “Improving ‘sub-grid’ representation in the SLOSH model. Environmental, Water Resources, and Coastal Engineering Research Symposium , North Carolina State University, 6 March 2020.

Improving ‘sub-grid’ representation in the SLOSH model.

CA Rucker, N Tull, JC Dietrich, R Luettich, R Cyriac. “Improving the accuracy of a real-time ADCIRC storm surge downscaling model. Environmental, Water Resources, and Coastal Engineering Research Symposium , North Carolina State University, 6 March 2020.

Improving the accuracy of a real-time ADCIRC storm surge downscaling model.

JL Woodruff, JC Dietrich, AB Kennedy, D Wirasaet, D Bolster, Z Silver, RL Kolar. “Improving predictions of coastal flooding via sub-mesh corrections.Environmental, Water Resources, and Coastal Engineering Research Symposium, North Carolina State University, 6 March 2020.

Improving predictions of coastal flooding via sub-mesh corrections.

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Subgrid Theory for Storm Surge Modelling

Averaging techniques are used to generate upscaled forms of the shallow water equations for storm surge including subgrid corrections. These systems are structurally similar to the standard shallow water equations but have additional terms related to integral properties of the fine-scale bathymetry, topography, and flow. As the system only operates with coarse-scale variables (such as averaged fluid velocity) relating to flow, these fine-scale integrals require closures to relate them to the coarsened variables. Closures with different levels of complexity are identified and tested for accuracy against high resolution solutions of the standard shallow water equations. Results show that, for coarse grids in complex geometries, inclusion of subgrid closure terms greatly improves model accuracy when compared to standard solutions, and will thereby enable new classes of storm surge models.

AB Kennedy, D Wirasaet, A Begmohammadi, T Sherman, D Bolster, JC Dietrich (2019). “Subgrid Theory for Storm Surge Modelling.” Ocean Modelling, 144, 101491, DOI: 10.1016/ocemod.2019.101491.

Posters: ASBPA Coastal Conference 2019

CA Rucker, N Tull, JC Dietrich, R Luettich, R Cyriac. “Improving the accuracy of a real-time ADCIRC storm surge downscaling model.ASBPA 2019 National Coastal Conference, Myrtle Beach SC, 23 October 2019.

Improving the accuracy of a real-time ADCIRC storm surge downscaling model.

JL Woodruff, JC Dietrich, AB Kennedy, D Wirasaet, D Bolster, Z Silver, RL Kolar. “Improving predictions of coastal flooding via sub-mesh corrections.ASBPA 2019 National Coastal Conference, Myrtle Beach SC, 23 October 2019.

Improving predictions of coastal flooding via sub-mesh corrections.

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Presentation: ASCE NC Fall Conference

PREEVENTS Project Meeting in Chicago

Several CCHT members visited Chicago to meet with collaborators from Notre Dame on our NSF PREEVENTS project. The meeting was held in the Chicago campus of the Notre Dame College of Business, located on Michigan Avenue in downtown. Despite the great views from the venue, we had a productive meeting!

Johnathan Woodruff, Zachariah Silver, Casey Dietrich, Autumn Poisson, Andrew Kennedy, Amirhosein Begmohammadi, Thomas Sherman, and Dam Wirasaet.

Conference: ADCIRC 2019