Barrier islands face a gradual path toward drowning under most sea level rise scenarios

Abstract

The expected increase in rates of sea level rise during the 21st century and beyond may cause tidal inlets to expand and barrier islands to drown. However, timescales involved in the drowning process are difficult to predict due to lack of observations. Here we present results obtained with an adapted version of a barrier island model to study inlet morphodynamics under sea level rise. Our new model (BRIE-D) allows for changes in the alongshore extent of the barrier lying below sea level. These concern reductions in barrier width, barrier height, as well as lateral expansion of tidal inlets. Model results show that the evolution of barrier islands is mostly susceptible to the wave height and the rate of sea level rise that they experience. It turns out that it takes hundreds of years for barrier islands to drown in response to high rates of sea level rise (more than 15 mm/yr). Furthermore, increasing rates of sea level rise cause an earlier and more severe barrier drowning in environments with low waves. Barrier systems that face higher waves can undergo more frequent inlet closures (due to a larger amount of sediment imported into the inlets), but also the degree of barrier drowning might increase (due to a deepening of the toe of the shoreface). Whether one process dominates over the other depends on the rate of sea level rise.