Virtual Conference: SIAM Geosciences 2021

JC Dietrich, JL Woodruff, D Wirasaet, AB Kennedy, D Bolster, Z Silver, SD Medlin, RL Kolar. “Sub-Mesh Corrections for Efficient Predictions of Storm-Driven Coastal Flooding.” SIAM Conference on Mathematical & Computational Issues in the Geosciences, Virtual Meeting, 21-24 June, 2021.

Downscaling of Real-Time Coastal Flooding Predictions for Decision Support

During coastal storms, forecasters and researchers use numerical models to predict the magnitude and extent of coastal flooding. These models must represent the large regions that may be affected by a storm, and thus, they can be computationally costly and may not use the highest geospatial resolution. However, predicted flood extents can be downscaled (by increasing resolution) as a post-processing step. Existing downscaling methods use either a static extrapolation of the flooding as a flat surface, or rely on subsequent simulations with nested, full-physics models at higher resolution. This research explores a middle way, in which the downscaling includes simplified physics to improve accuracy. Using results from a state-of-the-art model, we downscale its flood predictions with three methods: (1) static, in which the water surface elevations are extrapolated horizontally until they intersect the ground surface; (2) slopes, in which the gradient of the water surface is used; and (3) head loss, which accounts for energy losses due to land cover characteristics. The downscaling methods are then evaluated for forecasts and hindcasts of Hurricane Florence (2018), which caused widespread flooding in North Carolina. The static and slopes methods tend to over-estimate the flood extents. However, the head loss method generates a downscaled flooding extent that is a close match to the predictions from a higher-resolution, full-physics model. These results are encouraging for the use of these downscaling methods to support decision-making during coastal storms.

CA Rucker, N Tull, JC Dietrich, TE Langan, H Mitasova, BO Blanton, JG Fleming, RA Luettich Jr (2021). “Downscaling of Real-Time Coastal Flooding Predictions for Decision Support.” Natural Hazards, 107, 1341-1369, DOI: 10.1007/s11069-021-04634-8.

Proposal Defense: Johnathan Woodruff

Johnathan Woodruff. “Corrections for Subgrid Flooding Processes in Large-Domain Storm Surge Models.” Department of Civil, Construction and Environmental Engineering, North Carolina State University, Raleigh, North Carolina, 25 May 2021.

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Virtual Conference: EWC Symposium 2021

BA Rumbaugh, JC Dietrich. “Impact of storm events on density stratification in the Pamlico and Albemarle Estuarine System.” Environmental, Water Resources, and Coastal Engineering Research Symposium, North Carolina State University, 26 February 2021.

JL Woodruff, JC Dietrich, AB Kennedy, D Wirasaet, D Bolster, Z Silver, S Medlin, RL Kolar. “Finite Element Shallow Water Flow Model with Subgrid Corrections for Efficient Predictions of Storm-Driven Coastal Flooding.” Environmental, Water Resources, and Coastal Engineering Research Symposium, North Carolina State University, 26 February 2021.

Virtual Conference: ASBPA Coastal Conference 2020

A Gharagozlou, DL Anderson, JF Gorski, JC Dietrich, D Ryan. “Developing an Emulator for Morphodynamic Response of the Nourished Beaches During Future Storm Events Based on XBeach Predictions.” ASBPA 2020 National Coastal Conference, 13-16 October 2020.

JL Woodruff, JC Dietrich, AB Kennedy, D Wirasaet, D Bolster, Z Silver, S Medlin, RL Kolar. “Improving predictions of coastal flooding via sub mesh corrections.” ASBPA 2020 National Coastal Conference, 13-16 October 2020.

Johnathan wins Student Educational Award

Ph.D. student Johnathan Woodruff won the Student Educational Award from the American Shore & Beach Preservation Association. This award is given annually to an undergraduate or graduate student who, through his or her research, is furthering the state of science of coastal systems as it relates to the goals and mission of the ASBPA. The award includes a $500 cash stipend. Johnathan wil attend the ASBPA National Coastal Conference next week to present his findings to the coastal community.

CCHT Ph.D. student Johnathan Woodruff.

Presentation: SECASC Coastal Resilience Working Group

JC Dietrich. “Characterization and Prediction of Coastal Hazards.” SE CASC Climate Resilience Working Group, Virtual Meeting, 30 September 2020.

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