THE EFFECT OF ACCELERATING SEA LEVELS ON BARRIER ISLAND STABILITY

Narrow coastal barriers are sandy deposits that run parallel to and protect the mainland coast. Although barrier islands are geologically ephemeral features, thriving and established communities depend on their survival as they are home to tourism economies, fishing and shipping industries, and other infrastructure. Barrier islands naturally migrate landward with sea level rise through overwash deposition. Overwash deposits result from barriers flooding, causing a flow of water and sediment to wash over and behind the island, removing sediment from the ocean side of the barrier and depositing it on top of and behind the barrier. When sea level rise is too rapid, barriers can drown either by not growing tall or wide enough for overwash to maintain a subaerial landform. Existing numerical models of barrier island evolution have typically tested scenarios of drowning using different constant rates of sea level rise. However, anthropogenically driven climate change is expected to make sea level rise at an increasing rate, which means that barriers will be experiencing constantly changing driving conditions. Here, we model barrier stability using a simple, morphodynamic cross shore barrier island evolution model to predict barrier stability under variable wave conditions and, most importantly, different scenarios of accelerating sea level (RCP2.5, RCP4.5, and RCP8.5). We then couple these experiments with a myopic economic model for beach nourishment to explore the stability of coastal communities under increasing rates of sea level rise. Results from these model experiments demonstrate the importance of considering future increases in sea level rise rates when predicting the resilience of barrier islands to climate change.