Uncertainty in Long-Term Projections of Barrier Island Morphology Considering Impacts of Coastal Restoration Practices

Abstract:

Barrier island systems provide a wide range of benefits to coastal communities, including the reduction of backbarrier surge during storm events. However, these low-lying, dynamic land masses are particularly vulnerable to sea level rise (SLR), an imminent threat according to current SLR projections. As sea levels rise, overwash, breaching, and backbarrier flooding are more prone to occur. As such, various coastal restoration practices are implemented in order to mitigate these negative storm impacts. However, the long-term implications of such practices are poorly understood. To address this gap, the authors simulate the long-term evolution of a representative barrier island system (i.e., shoreface, barrier, and backbarrier marsh/lagoon environment) using a 1D morphodynamic model (Lorenzo-Trueba and Mariotti 2017, Chasing boundaries and cascade effects in a coupled barrier-marsh-lagoon system). Three common coastal restoration practices (e.g., beach/dune nourishment, created marsh, seawalls) are modeled via sediment flux reductions, geometric manipulation of the barrier profile, and volume adjustments according to current literature for each practice. To account for uncertainties in SLR projection, wind condition, and overwash potential, a Monte Carlo framework is employed with 10,000 simulations for each coastal restoration practice, producing a distribution of potential barrier morphology (e.g., Fig. 1). Results indicate that barrier widening and height reduction occur as overwash values decrease through year 2100 from coastal restoration practices. For each coastal restoration scenario, results are presented in the context of recent findings in the scientific literature (e.g., Rogers et al. 2015, Anthropogenic controls on overwash deposition: Evidence and consequences; Miselis and Lorenzo-Trueba 2017, Natural and Human-Induced Variability in Barrier-Island Response to Sea Level Rise) and compared to baseline scenarios with no human intervention. Additionally, sensitivity analysis results are presented which indicate the parameters most influential in the long-term evolution of the modeled barrier system.