LOUISIANA BARRIER ISLANDS AND THEIR IMPORTANCE IN WETLAND PROTECTION - FORECASTING SHORELINE CHANGE AND SUBSEQUENT RESPONSE OF WAVE CLIMATE

The role that barrier islands play in mitigating the wave climate in l ower energy, bay or lagoonal environments has not yet been addressed i n detail. With the exception of one study in which a shallow water wav e prediction model (HISWA) (LIST et. al., 1992) was applied to idealiz ed barrier-bay configurations, the critical linkages among barriers, w ave energy transmission into bays, regenerated local waves, and subseq uent wave climate have not been made. In Louisiana, barrier disintegra tion is rapid over the short-term (10(2) years) and the mere potential for impacts of barrier loss on the bay wave climate is highly signifi cant. Because of a paucity in scientific data which could be utilized to address this issue, there remains a significant debate as to the va lue of barrier islands in mitigating wave climate in the bays and alon g fringing marshes. In this paper we present historical shoreline chan ge data which are used to predict the rapid disintegration of a sectio n of barrier island coast along central Louisiana (Isles Dernieres) an d resultant forecasted increases in wave energy in the adjacent bays. The methods associated with shoreline, bathymetric and wave energy for ecasting are briefly presented as an example of a larger, ongoing proj ect regarding the feasibility of large-scale barrier island restoratio n in Louisiana. A brief overview of the magnitude and causal mechanism s associated with wetland loss are provided in addition to the implica tions associated with barrier island loss and subsequent detrimental i mpacts on fringing marshes. The example data set presented here indica tes that the role of Louisiana's barrier islands comprising the Isles Dernieres in mitigating the wave climate in their adjacent bays and fr inging marshes appears critical. Considering only fairweather conditio ns, the data indicate that the bays adjacent to the Isles Dernieres co uld experience an increase in wave height of 700% if the barrier chain is reduced to shoals. Although large-scale barrier island restoration will greatly reduce wave energy in Louisiana's bays and along fringin g marshes, additional devices capable of absorbing wave energy around portions of the fringing marshes will likely require construction. Thi s may occur in areas where the fetch permits regeneration of incident waves that have propagated across the Louisiana shelf, or locally gene rated higher frequency waves.