MODELING THE EVOLUTION OF A COUPLED BARRIER-MARSH-LAGOON SYSTEM: INSIGHTS FROM THE NEW JERSEY COASTLINE

Much of the New Jersey coastline is fronted by barrier islands which have various degrees of human development. Often these barriers have been fixed in place, disconnecting them from the natural processes that would normally modify them. Such processes include overwash, which cause barriers to migrate inland through storm-driven transport of sediment from the shoreface to the backbarrier. Deposition on marsh platforms help them expand/compete against erosional forces in the lagoon, maintaining barrier ecosystem services and backbarrier marsh health. Development along barrier islands, however, significantly reduces overwash fluxes, which generally results in fixed (or even progradational) ocean shorelines and erosion of the marsh platforms. To gain a better quantitative understanding of this dynamic, we combine GIS analysis, historical nautical charts, and numerical modeling to study the evolution of Long Beach Island (LBI), New Jersey, over the last ~180 years. Between 1840 and 1934, we find that the LBI system experienced 129 meters of shoreline retreat and moderate marsh platform loss. 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.

We use our numerical model to then recreate LBI’s historical past by further testing input parameters. Utilizing the morphological changes of LBI in phase 1 to constrain all input parameter values in our cross-shore numerical model, maximum overwash flux, and the initial lagoon geometry, which controls the wave regime in the lagoon. The set of parameters that produces the best fit yields a minimum least square error of ~6%. Using the same set of parameter values, and extending the model to account for beach nourishment practices, we model the evolution of LBI between 1934 and 2018. We find good agreement between model results and field observations. These results could provide us with the tools to investigate how development may impact the future evolution of LBI and other heavily managed coastal barriers.