Evolution of the morphology surrounding deteriorating shore-parallel protection structures on sandy estuarine beaches

Coastal armoring has historically been the preferred method for the protection of coastal infrastructure threatened by inundation. With sea level expected to accelerate in the future, the use of shore protection structures is anticipated to increase along with the likelihood that pre-existing structures will be at risk for overtopping and deterioration. While pre-existing structures may be upgraded, maintained, or removed, abandonment and deterioration is the most likely scenario for structures not protecting important cultural, historical, or recreational resources due to the lack of cost and effort involved. This study aims to understand and characterize the morphological changes that take place surrounding shore-parallel structures on sandy estuarine beaches as they deteriorate and remain within the landscape past their useful lifetime. Four sites containing wood sheet pile bulkheads, four sites containing stone riprap revetments, and one natural site in Gateway National Recreation Area were evaluated based on topography and landcover as case studies, in conjunction with comprehensive shore protection structure inventories. Results reveal that changes in the landscape over the course of a structure’s lifetime are predictable and can be described by four distinct morphological stages, where stage is a period in the lifetime of a structure characterized by the effectiveness of the protection structure and manifest in indicative features in the surrounding landscape. As the condition or effectiveness of a structure decreases over time and stage increases, the amount of open water or bare sand landward of the structure increases along with sediment mobility. Shoreline irregularity peaks during the deterioration process, before it returns to a more natural, linear state. Successful renovations or improvements on existing structures should consider the pattern of deterioration during the planning process, and weigh the benefits of protection provided by the structure versus increased ecosystem resiliency of a natural beach. A protection structure life stage model is presented as a tool to aid in the decision-making process. The most critical stage to make a decision regarding the improvement, repair, removal, or abandonment of a structure is Stage 2, which can be determined by managers via site visits or remote imagery using the key features described in this study.Ph.D.Includes bibliographical referencesby Katherine Korotk