Morphodynamics of barrier response to sea-level rise

Barrier response to sea-level rise involves a dynamic interplay between the shoreface and the subaerial portion affected by overwashing. Focusing on feedbacks between these two, here we discuss a morphodynamic approach to modeling barrier transgression. In contrast with the steady transgression portrayed by morphokinematic models (which transport mass based on geometric considerations), a simple morphodynamic model predicts two modes of long-term barrier failure: width and height drowning. For barriers that survive sea-level rise, a most likely mode of barrier motion consists of punctuated and abrupt periodic transgression of the shelf, which can arise even from constant driving conditions. These intermittently migrational barriers spend most of their existence staying essentially in place, a stark contrast to the continuous behavior suggested by morphokinematic models of barrier retreat. Even small perturbations to a barrier system traversing the shelf in dynamic equilibrium can kick-start an oscillating retreat. Looking alongshore, shoreline interconnectivity can have a significant effect on shoreline behavior across both space and time. Overall, our morphodynamic modeling results motivate a need to investigate the internal dynamics of barrier systems to understand the full range of past and potential future response of barrier systems to sea-level rise.