THE EFFECT OF DEVELOPMENT AND ENGINEERING ACTIVITIES ON THE EVOLUTION OF A BARRIER-BACKBARRIER SYSTEM: INSIGHTS FROM LONG BEACH ISLAND, NEW JERSEY (Invited Presentation)

Barriers and their associated backbarrier environments protect populated centers and infrastructure from storm impacts, support biodiversity, and provide a number of ecosystem services. Despite their socio-economic and ecological importance, the response of coupled barrier-backbarrier environments to sea-level rise is yet poorly understood. Undeveloped barrier-backbarrier systems typically respond to sea level rise through the process of landward migration, driven by storm overwash, tidal fluxes, and inland marsh upland expansion. Such response, however, can be largely affected by development and engineering activities such as dredging and shoreline stabilization techniques (e.g., seawalls, groins, beach replenishment). To better understand the difference in the response between developed and undeveloped barrier-backbarrier environments to sea-level rise, we extend a morphodynamic model that describes the evolution of a barrier-marsh-lagoon system in terms of five geomorphic boundaries: the ocean shoreline and backbarrier-marsh interface, the seaward and landward lagoon-marsh boundaries, and the upland limit of mainland marsh. We couple this numerical modeling efforts with GIS analysis and historical nautical charts that describe the evolution of Long Beach Island (LBI), New Jersey, over the last ~180 years. We find that between 1840 and 1934 the LBI system experienced landward migration of all five boundaries, including 129 meters of shoreline retreat. Despite its simplicity, the modeling framework can describe the average cross-shore evolution of the barrier-backbarrier system without accounting for human activities, suggesting that natural processes were the key drivers of morphological change during this time period. After the 1930s, however, there was a significant shift in system behavior as frequent beach nourishment, lagoon dredging, and groin construction took place during the following decades. Consequently, between 1934 and 2018 the LBI system experienced ~55 meters of shoreline progradation and a rapid decline in the area of marsh platforms. Overall, these results suggest that anthropogenic changes to overwash fluxes and estuary depths can play a major role in the evolution of barrier-backbarrier environments.