The land–sea coastal border: a quantitative definition by considering the wind and wave conditions in a wave-dominated, micro-tidal environment

A quantitative definition for the land–sea (coastal) transitional area is proposed here for wave-driven areas, based on the variability and isotropy of met-ocean processes. Wind velocity and significant wave height fields are examined for geostatistical anisotropy along four cross-shore transects on the Catalan coast (north-western Mediterranean), illustrating a case of significant changes along the shelf. The variation in the geostatistical anisotropy as a function of distance from the coast and water depth has been analysed through heat maps and scatter plots. The results show how the anisotropy of wind velocity and significant wave height decrease towards the offshore region, suggesting an objective definition for the coastal fringe width. The more viable estimator turns out to be the distance at which the significant wave height anisotropy is equal to the 90th percentile of variance in the anisotropies within a 100 km distance from the coast. Such a definition, when applied to the Spanish Mediterranean coast, determines a fringe width of 2–4 km. Regarding the probabilistic characterization, the inverse of wind velocity anisotropy can be fitted to a log-normal distribution function, while the significant wave height anisotropy can be fitted to a log-logistic distribution function. The joint probability structure of the two anisotropies can be best described by a Gaussian copula, where the dependence parameter denotes a mild to moderate dependence between both anisotropies, reflecting a certain decoupling between wind velocity and significant wave height near the coast. This wind–wave dependence remains stronger in the central baylike part of the study area, where the wave field is being more actively generated by the overlaying wind. Such a pattern controls the spatial variation in the coastal fringe width.Peer ReviewedPostprint (published version

Target Element Sizes For Finite Element Tidal Models From A Domain-wide, Localized Truncation Error Analysis Incorporating Botto

A new methodology for the determination of target element sizes for the construction of finite element meshes applicable to the simulation of tidal flow in coastal and oceanic domains is developed and tested. The methodology is consistent with the discrete physics of tidal flow, and includes the effects of bottom stress. The method enables the estimation of the localized truncation error of the nonconservative momentum equations throughout a triangulated data set of water surface elevation and flow velocity. The method\u27s domain-wide applicability is due in part to the formulation of a new localized truncation error estimator in terms of complex derivatives. More conventional criteria that are often used to determine target element sizes are limited to certain bathymetric conditions. The methodology developed herein is applicable over a broad range of bathymetric conditions, and can be implemented efficiently. Since the methodology permits the determination of target element size at points up to and including the coastal boundary, it is amenable to coastal domain applications including estuaries, embayments, and riverine systems. These applications require consideration of spatially varying bottom stress and advective terms, addressed herein. The new method, called LTEA-CD (localized truncation error analysis with complex derivatives), is applied to model solutions over the Western North Atlantic Tidal model domain (the bodies of water lying west of the 60° W meridian). The convergence properties of LTEACD are also analyzed. It is found that LTEA-CD may be used to build a series of meshes that produce converging solutions of the shallow water equations. An enhanced version of the new methodology, LTEA+CD (which accounts for locally variable bottom stress and Coriolis terms) is used to generate a mesh of the WNAT model domain having 25% fewer nodes and elements than an existing mesh upon which it is based; performance of the two meshes, in an average sense, is indistinguishable when considering elevation tidal signals. Finally, LTEA+CD is applied to the development of a mesh for the Loxahatchee River estuary; it is found that application of LTEA+CD provides a target element size distribution that, when implemented, outperforms a high-resolution semi-uniform mesh as well as a manually constructed, existing, documented mesh

A High-resolution Storm Surge Model For The Pascagoula Region, Mississippi

The city of Pascagoula and its coastal areas along the United States Gulf Coast have experienced many catastrophic hurricanes and were devastated by high storm surges caused by Hurricane Katrina (August 23 to 30, 2005). The National Hurricane Center reported high water marks exceeding 6 meters near the port of Pascagoula with a near 10-meter high water mark recorded near the Hurricane Katrina landfall location in Waveland, MS. Although the Pascagoula River is located 105 km east of the landfall location of Hurricane Katrina, the area was devastated by storm surge-induced inundation because of its low elevation. Building on a preliminary finite element mesh for the Pascagoula River, the work presented herein is aimed at incorporating the marsh areas lying adjacent to the Lower Pascagoula and Escatawpa Rivers for the purpose of simulating the inland inundation which occurred during Hurricane Katrina. ADCIRC-2DDI (ADvanced CIRCulation Model for Shelves, Coasts and Estuaries, Two-Dimensional Depth Integrated) is employed as the hydrodynamic circulation code. The simulations performed in this study apply high-resolution winds and pressures over the 7-day period associated with Hurricane Katrina. The high resolution of the meteorological inputs to the problem coupled with the highly detailed description of the adjacent inundation areas will provide an appropriate modeling tool for studying storm surge dynamics within the Pascagoula River. All simulation results discussed herein are directed towards providing for a full accounting of the hydrodynamics within the Pascagoula River in support of ongoing flood/river forecasting efforts. In order to better understand the hydrodynamics within the Pascagoula River when driven by an extreme storm surge event, the following tasks were completed as a part of this study: 1) Develop an inlet-based floodplain DEM (Digital Elevation Model) for the Pascagoula River. The model employs topography up to the 1.5-meter contour extracted from the Southern Louisiana Gulf Coast Mesh (SL15 Mesh) developed by the Federal Emergency Management Agency (FEMA). 2) Incorporate the inlet-based floodplain model into the Western North Atlantic Tidal (WNAT) model domain, which consists of the Gulf of Mexico, the Caribbean Sea, and the entire portion of the North Atlantic Ocean found west of the 60 degree West meridian, in order to more fully account for the storm surge dynamics occurring within the Pascagoula River. This large-scale modeling approach will utilize high-resolution wind and pressure fields associated with Hurricane Katrina, so that storm surge hydrographs (elevation variance) at the open-ocean boundary locations associated with the localized domain can be adequately obtained. 3) Understand the importance of the various meteorological forcings that are attributable to the storm surge dynamics that are setup within the Pascagoula River. Different implementations of the two model domains (large-scale, including the WNAT model domain; localized, with its focus concentrated solely on the Pascagoula River) will involve the application of tides, storm surge hydrographs and meteorological forcing (winds and pressures) in isolation (i.e., as the single forcing mechanism) and collectively (i.e., together in combination). The following conclusions are drawn from the research presented in this thesis: 1) Incorporating the marsh areas into the preliminary in-bank mesh provides for significant improvement in the astronomic tide simulation; 2) the large-scale modeling approach (i.e., the localized floodplain mesh incorporated into the WNAT model domain) is shown to be most adequate towards simulating storm surge dynamics within the Pascagoula River. Further, we demonstrate the utility of the large-scale model domain towards providing storm surge hydrographs for the open-ocean boundary of the localized domain. Only when the localized domain is forced with the storm surge hydrograph (generated by the large-scale model domain) does it most adequately capture the full behavior of the storm surge. Finally, we discover that while the floodplain description up to the 1.5-m contour greatly improves the model response by allowing for the overtopping of the river banks, a true recreation of the water levels caused by Hurricane Katrina will require a floodplain description up to the 5-m contour

Finite Element Modeling Of Tides And Currents Of The Pascagoula River

This thesis focuses on the simulation of astronomic tides of the Pascagoula River. The work is comprised of five steps: 1) Production of a digital elevation model describing the entire Pascagoula River system; 2) Development of an inlet-based, unstructured mesh for inbank flow to better understand the basis of the hydrodynamics within the Pascagoula riverine system. In order to assist in the mesh development, a toolbox was constructed to implement one-dimensional river cross sections into the two-dimensional model; 3) Implementation of a sensitivity analysis of the Pascagoula River two inlet system to examine the inlet effects on tidal propagation; 4) Improvement of the inlet-based model by performing a preliminary assessment of a spatially varied bottom friction; 5) Implementation of an advection analysis to reveal its influence on the flow velocity and water elevation within the domain. The hydrodynamic model employed for calculating tides is ADCIRC-2DDI (ADvanced CIRCulation Model for Shelves, Coasts and Estuaries, Two-Dimensional Depth Integrated). This finite element based model solves the shallow water equations in their full nonlinear form. Boundary conditions including water surface elevation at the off-shore boundary and tidal potential terms allow the full simulation of astronomic tides. The improved astronomic tide model showed strong agreement with the historical data at seven water level monitoring gauge stations. The main conclusions of this research are: 1) The western inlet of the Pascagoula River is more dominant than the eastern inlet; however, it is necessary to include both inlets in the model. 2) Although advection plays a significant role in velocity simulation, water elevations are insensitive to advection. 3) The astronomic model is sensitive to bottom friction (both global and spatial variations); therefore, a spatially varied bottom friction coefficient is suggested. As a result of this successful effort to produce an astronomic tide model of the Pascagoula River, a comprehensive storm surge model can be developed. With the addition of inundation areas the surge model can be expected to accurately predict storm tides generated by hurricanes along the Gulf Coast

U.S. IOOS coastal and ocean modeling testbed: Evaluation of tide, wave, and hurricane surge response sensitivities to mesh resolution and friction in the Gulf of Mexico: IOOS TESTBED-RESOLUTION AND FRICTION

This paper investigates model response sensitivities to mesh resolution, topographical details, bottom friction formulations, the interaction of wind waves and circulation, and nonlinear advection on tidal and hurricane surge and wave processes at the basin, shelf, wetland, and coastal channel scales within the Gulf of Mexico. Tides in the Gulf of Mexico are modestly energetic processes, whereas hurricane surge and waves are highly energetic. The unstructured-mesh, coupled wind-wave and circulation modeling system, SWAN+ ADCIRC, is implemented to generate modeled tidal harmonic constituents and hurricane waves and surge for a Hurricane Ike (2008) hindcast. In the open ocean, mesh resolution requirements are less stringent in achieving accurate tidal signals or matching hurricane surge and wave responses; however, coarser resolution or the absence of intertidal zones decreases accuracy along protected nearshore and inland coastal areas due to improper conveyance and/or lateral attenuation. Bottom friction formulations are shown to have little impact on tidal signal accuracy, but hurricane surge is much more sensitive, especially in shelf waters, where development of a strong shore-parallel current is essential to the development of Ike's geostrophic setup. The spatial and temporal contributions of wave radiation stress gradients and nonlinear advection were charted for Ike. Nonlinear advection improves model performance by capturing an additional 10―20 cm of geostrophic setup and increasing resonant cross-shelf waves by 30―40 cm. Wave radiation stress gradients improve performance at coastal stations by adding an extra 20―40 cm to water levels

A global unstructured, coupled, high-resolution hindcast of waves and storm surge

Accurate information on waves and storm surges is essential to understand coastal hazards that are expected to increase in view of global warming and rising sea levels. Despite the recent advancement in development and application of large-scale coastal models, nearshore processes are still not sufficiently resolved due to coarse resolutions, transferring errors to coastal risk assessments and other large-scale applications. Here we developed a 50-year hindcast of waves and storm surges on an unstructured mesh of >650,000 nodes with an unprecedented resolution of 2-4 km at the global coast. Our modelling system is based on the circulation model SCHISM that is fully coupled with the WWM-V (WindWaveModel) and is forced by surface winds, pressure, and ice coverage from the ERA5 reanalysis. Results are compared with observations from satellite altimeters, tidal gauges and buoys, and show good skill for both Sea Surface Height (SSH) and Significant Wave Height (Hs), and a much-improved ability to reproduce the nearshore dynamics compared with previous, lower-resolution studies. Besides SSH, the modelling system also produces a range of other wave-related fields at each node of the mesh with a time step of 3 hours, including the spectral parameters of the first three largest energy peaks. This dataset offers the potential for more accurate global-scale applications on coastal hazard and ris

Modeling Coastal Flooding and Sand Transport in the Gulf of Maine during Severe Storms in a Changing Climate

Elevated water level and large waves cause extensive damage and economic loss to coastal communities. An integrated atmosphere-ocean-coast modeling system that links physical processes with scales ranging from the open ocean to the surf zone has been developed for the Gulf of Maine. The modeling system includes a hydrodynamic model, a wave overtopping model and a sediment transport model. It is then applied to investigate and gain a comprehensive understanding of the following coastal processes: (1) the interaction between tide-surge, waves and bathymetry, (2) coastal flooding due to wave overtopping, and (3) sand transport. Both coastal flooding and sand transport rely on the accurate prediction of water level, waves, and currents at the coast. This work has demonstrated that the interactions between tide-surge, waves and bathymetry have a significant impact on coastal waves, circulation and water level; and the interactions exhibit strong temporal and spatial variability along the coast. The inclusion and appropriate representation of the interaction processes in numerical modeling is important for coastlines with complex configurations. The integrated modeling system has been applied to predict coastal flooding due to wave overtopping at the seawall in Scituate, Massachusetts. The capacity of the seawalls to protect coastal communities against flooding as sea level rises is investigated. It has been shown that seawalls will have to be elevated much more than the projected sea level rise to cope with future storms due to the presence of larger waves approaching the coast as depth increases. Sand transport and its response to different storm characteristics are closely linked to waves and currents. Local bathymetry and winds are the two most important factors determining waves, currents and sand transport. The role of wind-driven and wave-induced current for sand transport varies depending on water depth and coastline geometry. The wind-driven current dominates in shallow water, while the wave-induced current is more significant at headlands and around coastal structures and islands. Differences in net sand transport mainly result from different flow patterns due to the counterbalance between wind-driven and wave-induced currents

Analysis, Modeling, And Simulation Of The Tides In The Loxahatchee River Estuary (Southeastern Florida).

Recent cooperative efforts between the University of Central Florida, the Florida Department of Environmental Protection, and the South Florida Water Management District explore the development of a two-dimensional, depth-integrated tidal model for the Loxahatchee River estuary (Southeastern Florida). Employing a large-domain approach (i.e., the Western North Atlantic Tidal model domain), two-dimensional tidal flows within the Loxahatchee River estuary are reproduced to provide: 1) recommendations for the domain extent of an integrated, surface/groundwater, three-dimensional model; 2) nearshore, harmonically decomposed, tidal elevation boundary conditions. Tidal simulations are performed using a two-dimensional, depth-integrated, finite element-based code for coastal and ocean circulation, ADCIRC-2DDI. Multiple variations of an unstructured, finite element mesh are applied to encompass the Loxahatchee River estuary and different spatial extents of the Atlantic Intracoastal Waterway (AIW). Phase and amplitude errors between model output and historical data are quantified at five locations within the Loxahatchee River estuary to emphasize the importance of including the AIW in the computational domain. In addition, velocity residuals are computed globally to reveal significantly different net circulation patterns within the Loxahatchee River estuary, as depending on the spatial coverage of the AIW

Influence Of Topographic Elevation Error On Modeled Storm Surge

The following presents a method for determining topographic elevation error for overland unstructured finite element meshes derived from bare earth LiDAR for use in a shallow water equations model. This thesis investigates the development of an optimal interpolation method to produce minimal error for a given element size. In hydrodynamic studies, it is vital to represent the floodplain as accurately as possible since terrain is a critical factor that influences water flow. An essential step in the development of a coastal inundation model is processing and resampling dense bare earth LiDAR to a DEM and ultimately to the mesh nodes; however, it is crucial that the correct DEM grid size and interpolation method be employed for an accurate representation of the terrain. The following research serves two purposes: 1) to assess the resolution and interpolation scheme of bare earth LiDAR data points in terms of its ability to describe the bare earth topography and its subsequent performance during relevant tide and storm surge simulation