Numerical Model Study of Breakwaters at Grand Isle, Louisiana

Abstract

Abstract : This report presents the results of a numerical shoreline response investigation of a proposed segmented detached breakwater project offshore of Grand Isle, Louisiana. Functional shore protection characteristics of the recommended breakwater design alternative are further evaluated using empirical methods together with comparison to a recently constructed breakwater project between Holly Beach and Ocean View Beach in Cameron Parish, LA. The investigation involved the following three technical tasks: (a) conducting a nearshore wave transformation study, (b) numerical modeling of shoreline response, and (c) comparison of proposed breakwater design with empirical functional design guidance and similar projects. Results of this investigation indicate good agreement between the numerically-generated (GENESIS) estimates of shoreline change in the vicinity of the proposed breakwater project at Grand Isle and the observed shoreline response at the Cameron Parish projects. Empirical relationships for functional breakwater design provided a relatively poor indication of actual beach response to breakwaters along the Louisiana coast. Because of the environmental similarities (mild beach slope, wave climate, tide range, etc.) between Grand Isle and Cameron Parish it is recommended that the Cameron Parish breakwater project together with the GENESIS results be used for designing the Grand Isle breakwater project. Beach erosion, Grand Isle, Coastal processes, Louisiana, Detached breakwaters, Shoreline change.