Louisiana Barrier Islands and their Importance in Wetland Protection: Forecasting Shoreline Change and Subsequent Response of Wave Climate

Abstract

The role that barrier islands play in mitigating the wave climate in lower energy, bay or lagoonal environments has not yet been addressed in detail. With the exception of one study in which a shallow water wave prediction model (HISWA) (LIST et. aI., 1992) was applied to idealized barrier-bay configurations, the critical linkages among barriers, wave energy transmission into bays, regenerated local waves, and subsequent wave climate have not been made. In Louisiana, barrier disintegration is rapid over the short-term (10² years) and the mere potential for impacts of barrier loss on the bay wave climate is highly significant. Because of a paucity in scientific data which could be utilized to address this issue, there remains a significant debate as to the value of barrier islands in mitigating wave climate in the bays and along fringing marshes. In this paper we present historical shoreline change data which are used to predict the rapid disintegration of a section of barrier island coast along central Louisiana (Isles Dernieres) and resultant forecasted increase s in wave energy in the adjacent bays. The methods associated with shoreline, bathymetric and wave energy forecasting are briefly presented as an example of a larger, ongoing project regarding the feasibility of large-scale barrier island restoration in Louisiana. A brief overview of the magnitude and causal mechanisms associated with wetland loss are provided in addition to the implications associate d with barrier island loss and subsequent detrimental impacts on fringing marshes. The example data set presented here indicates that the role of Louisiana's barrier islands comprising the Isles Dernieres in mitigating the wave climate in their adjacent bays and fringing marshes appears critical. Considering only fairweather conditions, the data indicate that the bays adjacent to the Isles Dernieres could 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 fringing marshes, additional devices capable of absorbing wave energy around portions of the fringing marshes will likely require construction. This may occur in areas where the fetch permits regeneration of incident waves that have propagated across the Louisiana shelf, or locally genera ted higher frequency waves.