Coastal Waves, Surge and Inundation in the Gulf of Maine

Project Team

Project Leads: Rick Luettich, University of North Carolina at Chapel Hill; Robert Beardsley, Woods Hole Oceanographic Institution

CO-PIs: Joannes Westerink, University of Notre Dame; Changsheng Chen, University of Massachusetts-Dartmouth; Harry Wang, Virginia Institute of Marine Sciences; Will Perrie, Dalhousie University

Collaborators: Bash Toulany, Dalhousie University; Quichan Xu, University of Massachusetts-Dartmouth

Federal Partners: Jesse Feyen, NOAA-CSDL; Jamie Rhome, NOAA-NHC

Project Overview and Results

The goal of this project was to provide guidance on the behavior (e.g., accuracy, robustness, execution speed) and implementation requirements (e.g., resolution, parameterization, computer capacity) of models that are presently in operational use, or that are under consideration for such use, for computing waves, storm surge, and inundation. Models were evaluated for three extratropical storms (May 2005, April 2007, December 2010) and hurricane Bob (1991) in the Gulf of Maine. Skill assessment, sensitivity studies, and intramodel/intermodel comparisons provided a basis for defining model accuracy, implementation requirements, and computational performance. Studies in the Gulf of Maine were conducted at two scales, large-scale (Gulf of Maine/Northwest-Atlantic) and locally in and around Scituate Harbor, MA (using a one-way nested grid that obtained open boundary forcing from a large-scale model).

Sub-Project Descriptions/Data

Hurricane Bob wave-current interaction and stratification

Description: The impacts of wave-current interaction and stratification on the Gulf of Maine coastal response to hurricane Bob were investigated. Wave-current interaction created variations in the surge elevation in both space and time, with the more significant effects occurring over the shelf and open coast rather than inside the inner bays. Sea level change along the coast was mainly driven by barotropic dynamics; the highest vertically integrated water transports were essentially the same for cases with and without vertical stratification. However, wave-current interaction generated strong vertical current shear in some of the stratified areas, leading to a strong offshore transport near the bottom and vertical turbulent mixing over the continental shelf. Stratification could also result in a significant difference in current velocities around islands where the water is not vertically well-mixed.

Publications: Yunfang Sun, Changsheng Chen, Robert C. Beardsley, Quichun Xu, Jianhua Qi, Huichan Lin, 2013. Impact of current-wave interaction on storm surge simulation: A case study for Hurricane Bob, J. Geophys. Res. Oceans, 118, 2685–2701, DOI: 10.1002/jgrc.20207

Model Intercomparisons

Inter-model comparisons around Scituate Harbor, MA, were conducted using three unstructured-grid, fully coupled surge-wave models (ADCIRC+SWAN, FVCOM+SWAVE, SELFE+WWM). For the same unstructured mesh, meteorological forcing and initial/boundary conditions, inter-model comparisons were made for tidal elevation, surface waves, sea surface elevation, coastal inundation, currents, and volume transport. All three models showed comparable tidal accuracy and consistent dynamic responses to storm winds, both with and without the inclusion of wave effects. The three models also showed that wave-current interaction could (1) change the current direction on the shelf to the north of Scituate Harbor from along-shelf to onshore, thereby enlarging onshore water transport and (2) intensify an anticyclonic eddy in the harbor entrance and a cyclonic eddy in the harbor interior, which could push water inside the harbor toward the northern peninsula and the southern end and thus enhance flooding in those areas.

Publications: Changsheng Chen, Robert C. Beardsley, Richard A Luettich Jr., Joannes J. Westerink, Harry Wang, Will Perrie, Qichun Xu, Aaron S. Donahue, Jianhua Qi, Huichan Lin, Liuzhi Zhao, Patrick C. Kerr, Yanqiu Meng, Bash Toulany, 2013. Extratropical storm inundation testbed: Inter-model comparisons in Scituate, Massachusetts, J Geophysical Research, Oceans, 118(10): 5054-5073, DOI: 10.1002/jgrc.20397

Additional studies

Additional studies around Scituate Harbor, MA, used FVCOM+SWAVE on two different resolution grids, with and without wave-current interaction, examined the influence of spatial resolution and model dynamics on predicted flooding. In all simulations, a wind driven coastal current flowed southward across the harbor entrance, with an attached separation eddy forming downstream of the northern breakwater and a rapid decrease of wave energy entering the harbor. With wave-current interaction, the southward coastal current was strongly enhanced and currents within the separation eddy increased to more than 1 m/s, making it highly nonlinear with large lateral shears. Comparisons of the model water elevation time series with harbor tide station measurements showed that wave-current interaction increased the peak model surge by ∼8 cm, in closer agreement with the observed peak. Increased resolution within the harbor produced greater flooding in several shallow areas but did not significantly change the maximum water level in the main harbor

Publications: Robert C. Beardsley, Changsheng Chen, Qichun Xu, 2013. Coastal flooding in Scituate (MA): A FVCOM study of the 27 December 2010 nor'easter, J Geophysical Research, Oceans, 118(110): 6030-6045, DOI: 10.1002/2013JC008862

Published Results