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Rapid deterioration of the barrier coast in coastal Louisiana is resulting in a transformation of low-energy, semiprotected hays into high-energy, open marine environments. Numerical models (ADCIRC and SWAN) are used to hindcast, nowcast, and forecast wave conditions along south-central coastal Louisiana. Measurements from across the shelf, nearshore, and hays are also used to shed light on the mitigative ability of harriers on the wave and .surge field during tropical cyclones. Along western Louisiana the coast is fronted by a muddy shelf, supplied by sediment from the Atchafalaya River. The cohesive nature of this material results in significant damping of waves, particularly during storm events. East of this area the coast is characterized by shell reefs that have historically been dredged for commercial use. Numerical modeling demonstrates that with the reduction in reefs over time, wave energy in the adjacent Acadiana Bays has increased considerably and is likely responsible in part for erosion along marshes fringing the bays. [ABSTRACT FROM AUTHOR]

Data are presented indicating the complexity and highly variable response of beaches to cold front passages along the northern Gulf of Mexico, in addition to the impacts of tropical cyclones and winter storms. Within the past decade, an increase in the frequency of tropical storms and hurricanes impacting the northern Gulf has dramatically altered the long-term equilibrium of a large portion of this coast. A time series of net sediment flux for subaerial and nearshore environments has been established for a section of this coast in Florida, and to a lesser extent, Mississippi. The data incorporate the morphological signature of six tropical storms/hurricanes and more than 200 frontal passages.Data indicate that (1) barrier islands can conserve mass during catastrophic hurricanes (e.g., Hurricane Opal, a strong category 4 hurricane near landfall); (2) less severe hurricanes and tropical storms can promote rapid dune aggradation and can contribute sediment to the entire barrier system; (3) cold fronts play a critical role in the poststorm adjustment of the barrier by deflating the subaerial portion of the overwash terrace and eroding its marginal lobe along the bayside beach through locally generated, high frequency, steep waves; and (4) barrier systems along the northern Gulf do not necessarily enter an immediate poststorm recovery phase, although nested in sediment-rich nearshore environments. While high wave energy conditions associated with cold fronts play an integral role in the evolution and maintenance of barriers along the northern Gulf, these events are more effective in reworking sediment after the occurrence of extreme events such as hurricanes. This relationship is even more apparent during the clustering of tropical cyclones.It is anticipated that these findings will have important implications for the longer term evolution of barrier systems in midlatitude, microtidal settings where the clustering of storms is apparent, and winter storms are significant in intensity and frequency along the coast. [Copyright &y& Elsevier]