Search

The influence of including the dynamic effects of future shoreline changes associated with sea level rise into hydrodynamic modeling is evaluated for the coast of the Northern Gulf of Mexico from Mobile Bay, AL to St. Andrew Bay, FL. A two-dimensional, depth-integrated hydrodynamic model forced by astronomic tides and hurricane winds and pressures representative of Hurricanes Ivan (2004), Dennis (2005) and Katrina (2005) is used to simulate present conditions, 2050 projected sea level (0.46 m rise) with present-day shorelines, and 2050 sea level with projected 2050 shorelines. The 2050 shoreline and nearshore morphology are projected using Coastal Vulnerability Index shoreline change rates to determine the position of the new Gulf and bay shorelines, while the active beach profile is shifted horizontally according to the amount of erosion or accretion, and vertically to keep pace with rising seas. Hydrodynamic model results show that taking a dynamic approach to modeling sea level rise (as opposed to a static, or 'bathtub' approach) increases tidal ranges and tidal prisms within the bay systems. Incorporating the projected shoreline changes does not alter tidal ranges, but some bays experience changes in tidal prisms depending on whether the planform area of the bay increases or decreases with the projected erosion or accretion. Barrier islands with projected erosion are vulnerable to increased overtopping from storm surge inundation, which impels more water into the back-bays and increases the inland inundation extent and magnitude. Inundation along barrier islands with projected accretion remains relatively the same as inundation under present-day shorelines, which prevents additional overtopping and limits more water from entering back-bays. Results demonstrate that although modeling sea level rise as a dynamic process is necessary, the incorporation of shoreline changes has variable impacts when evaluating future hydrodynamics and the response of the coastal system to sea level rise. [ABSTRACT FROM AUTHOR]

This paper demonstrates a practical application of coupling a hydrodynamic model with a wave model for the calculation of storm tide elevations in the St. Johns River (Northeastern Florida). Hurricane Floyd (1999) is chosen as the storm of interest due to its track which paralleled the northeast coast of Florida without making a direct landfall on the St. Johns River. The advanced circulation (ADCIRC) numerical code is applied as the hydrodynamic model for the computation of two-dimensional circulation resulting from astronomic tides and meteorologically induced storm surge. The simulating waves nearshore (SWAN) numerical code is applied as the wave model for the computation of wind-induced waves. Two model implementations are considered in order to investigate the effect of short wave contributions on the overall storm tide water level: (1) a one-way coupling procedure that transfers gradient of wave radiation stresses from SWAN to ADCIRC; and (2) a two-way coupling procedure that builds on the former to include feedback of water levels and currents from ADCIRC to SWAN. Simulated storm tide elevations are compared to historical National Ocean Service data to result in two major conclusions: (1) wind-induced waves play a significant role in the storm tide (contributing 10–15% of the peak water level), namely with respect to the transfer of momentum from the dissipation of short waves to the long-wave motion of the storm surge; and (2) a local-scale hydrodynamic model requires the application of a hydrograph boundary condition in order to account for the remote effects of the storm surge response. [ABSTRACT FROM AUTHOR]

The storm surge generated by Hurricane Hugo (1989) is reproduced for the purposes of (1) evaluating the significance of including inland flooding areas and corresponding levels of spatial resolution and (2) assessing the spatial variability of near-inlet boundary forcings with respect to storm surge hydrographs. The study focuses on the coastal regions of South Carolina, incorporating inundation areas between Charleston and Shallotte Inlet and including Winyah Bay and the Waccamaw River. The region of interest is modeled with five variations of an unstructured, finite-element mesh, including a localized coarse grid with and without floodplains, a localized fine grid with and without floodplains, and a large-domain approach that includes floodplains and the continental shelf and deep ocean. Simulation results demonstrate that the inclusion of inland flooding areas significantly improves the description of storm surge generation within coastal regions. While the large-domain approach is shown to be beneficial, it is determined that the coarse mesh resolution of the floodplains is sufficient. Computed water surface elevations at specific locations surrounding Winyah Bay Inlet indicate that storm surge hydrographs are highly spatially dependent near inlets, as opposed to the astronomical tides, which exhibit minimal variance in space around the inlet environment. [ABSTRACT FROM AUTHOR]

A previously developed research-grade (e.g. high-resolution) unstructured mesh of the northern Gulf of Mexico (named NGOM3) is optimized to produce a computationally efficient forecast-grade mesh for deployment in a real-time hurricane storm surge early warning system. The real-time mesh is developed from a mesh decimation scheme with focus on the coastal floodplain. The mesh decimation scheme reduces mesh nodes and elements from the research-grade mesh while preserving the representation of the bare-earth topography. The resulting real-time unstructured mesh (named NGOM-RT) contains 64% less mesh nodes than the research-grade mesh. Comparison of (ADCIRC + SWAN) simulated times-series and peak water levels to observations between the research-grade and real-time-grade meshes for Hurricanes Ivan (2004), Dennis (2005), Katrina (2005), and Isaac (2012) show virtually no difference. Model simulations with the NGOM-RT mesh are 1.5–2.0 times faster than using NGOM3 on the same number of compute cores. [ABSTRACT FROM AUTHOR]

Summary: Water surface elevations in the St. Johns River (Northeastern Florida) are simulated over a 122-day time period spanning June 1–September 30, 2005, which relates to a particularly active hurricane season for the Atlantic basin, and includes Hurricane Ophelia that significantly impacted the St. Johns River. The hydrodynamic model employed for calculating two-dimensional flows is the ADCIRC (Advanced Circulation Model for Oceanic, Coastal, and Estuarine Waters) numerical code. The region of interest is modeled using three variations of an unstructured, finite element mesh: (1) a large-scale computational domain that hones in on the St. Johns River from the Western North Atlantic Ocean, Gulf of Mexico, and Caribbean Sea; (2) a shelf-based subset of the large domain; (3) an inlet-based subset of the large domain. Numerical experiments are then conducted in order to examine the relative importance of three long-wave forcing mechanisms for the St. Johns River: (1) astronomic tides; (2) freshwater river inflows; (3) winds and pressure variations. Two major findings result from the various modeling approaches considered in this study, and are applicable in general (e.g., over the entire 122-day time period) and even more so for extreme storm events (e.g., Hurricane Ophelia): (1) meteorological forcing for the St. Johns River is equal to or greater than that of astronomic tides and generally supersedes the impact of freshwater river inflows, while pressure variations provide minimal impact; (2) water surface elevations in the St. Johns River are dependent upon the remote effects caused by winds occurring in the deep ocean, in addition to local wind effects. During periods of calm weather through the 122-day time period, water surface elevations in the St. Johns River were generally tidal in response, with amplitudes exceeding 1m at the mouth and diminishing to less than 10cm 150km upriver. Considering an extreme storm event, the timing of Hurricane Ophelia occurred during the neap phase of the tidal cycle and at the mouth of the St. Johns River, the wind-driven storm surge was near equal to the tidal component, each contributing about 0.5m to the overall water surface elevation. However, 150km upriver, meteorological forcing dominated, as over 90% of the total water surface elevation was driven by winds and pressures. The simulation results replicate these behaviors well. As a supplement, it is shown that applying a hydrograph boundary condition, generated by a large domain, to a localized domain is highly beneficial towards accounting for the remote wind forcing. [Copyright &y& Elsevier]