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A recent study reveals that more than 60,000 miles (>96,500 km) of coastal roadways are in the 100-year floodplain in the United States and vulnerable to the attacks of water surges and storm waves generated by hurricanes. Mitigating the effects of coastal flooding requires accurate predictions of the destructive hydrodynamic forces. This study demonstrates a methodology for integrating state-of-the-art storm surge and wave prediction models as an effective tool for engineering design of coastal infrastructure and facilitation of hurricane emergency management. The methodology has the capability of resolving complex geometry and topography typical of coastal road flooding. The surge model incorporates moving shoreline conditions associated with flooding and allows for nonlinear interactions among astronomical tide, storm surge, and wave setup. The wave model takes into account the unsteadiness of wind forcing, currents, and water levels. A historical hurricane event is simulated for the landfall of Hurricane Georges (1998) on the north coast of the Gulf of Mexico. Good agreement between the modeled and measured surge hydrographs in Mobile Bay, Alabama, has been found. The advanced surge model (ADCIRC), coupled with the wave model, successfully simulates the inundation and measured high water marks along two highways adjacent to the bay. The third- generation wind wave model (SWAN) coupled with the hydrodynamic model reveals the temporal and spatial variability of wave heights and wave periods in the Mobile Bay estuary and on the flooded highways. Numerical experiments were carried out to examine the response of the estuary to various forcing agents, including the offshore surge hydrograph, local wind forcing, and wave thrust. [ABSTRACT FROM AUTHOR]

In comparison with wave modeling on an open coast, the complex geometry and bathymetry of estuaries, the unsteady conditions associated with estuarine circulation generated by tides and winds, and the relatively inadequate field data present a unique challenge. This study utilizes an unsteady, curvilinear spectral wave model that has the flexibility to resolve large geometric and bathymetric gradients and allows for consideration of unsteady forcing and currents to predict wind waves in Mobile Bay, Alabama. First, a laboratory data set on wave transformation over a circular shoal is chosen to test the curvilinear wave model. Excellent agreement is found between the numerical results and the laboratory measurements with a directional wave input and fine spatial resolution. Second, a three-dimensional circulation model is used to predict the varying current field and water levels that serve as the input to the wave model. The predictions of the wave model under unsteady forcing and ambient currents are then compared with the existing field measurement of wind waves in Mobile Bay. Numerical experiments are carried out to examine the effects of estuarine circulation and grid resolution on the model result. The study shows that the technique of linking a spectral wave model to a hydrodynamic model on curvilinear grids is an effective tool for wave prediction in estuaries. [ABSTRACT FROM AUTHOR]

The initial establishment and survival ofa salt marsh is regulated by a variety of factors, including salinity, sediment type, elevation, nutrient levels, and wave climate. Despite the obvious importance of wave climate on the existence or nonexistence of wetlands along shorelines of water bodies, there are currently few methods for its evaluation at wetland locations. This study used an existing wind-wave hindcast method to estimate wave climate at sites with and without Spartina alterniflora, along the shoreline in coastal Alabama. The sites with vegetation along the shoreline had lower wave levels than nearby sites without vegetation. Other sites with eroding stands of vegetation bad wave levels intermediate between the no-vegetation and vegetation sites. The upper limit of wave energy for (noneroding) salt marsh existence was a median significant wave height of about H = 0.1 meter and a corresponding 80 percentile (less than this level 80% of the time) significant wave height of H = 0.2 meter. Sites with less wave energy had vegetation along the shoreline. The results indicate that wave height frequency distribution based on wind-wave modeling hindcasts is an appropriate methodology for wave climate evaluation at wetland sites. The results can be used to minimize the size of breakwaters used in constructed wetlands. [ABSTRACT FROM AUTHOR]

A model for the migration of submerged mounds constructed offshore of the day-to-day surf zone but within the depths disturbed by waves during storm events is developed. The model considers net shoreward sand transport due to the velocity asymmetry of finite-amplitude waves, and is based on Bagnold's bed-load–sand transport equation with Stokes' second-order wave theory. Conservation of sand considerations lead to an equation that indicates mounds will behave according to a nonlinear convection-diffusion model. The “convection coefficient”–like parameter, which is based on the wave and sand-transport models only, is proposed as an estimate of the migration rate for submerged mounds. The expected value of mound movement in different depths can be estimated with site-specific wave-climate data. The full sediment-transport equations successfully simulate the migration of a mound at Silver Strand State Park, California, in 1989. The expected value of the mound-movement parameter gives results that agree reasonably well with measured migration rates both at Silver Strand and offshore of Mobile, Alabama. [ABSTRACT FROM AUTHOR]