Barrier Islands as coupled human-landscape systems

Abstract

In recent decades, coastal development has transformed barrier systems around the world. The longest, most intensively developed chain of barriers extends along the Atlantic and Gulf Coasts of the U.S., where mean population density is the highest in the country. There are nearly 300 barrier islands between Maine and Texas, and of these, at least 70 are intensively built-up. Concentrated development exists and continues despite the fact that barrier islands are transient landscapes, not only over geologic time scales of millennia, but also within human and economic time scales of centuries to decades. Populated barrier islands are inherently vulnerable to natural hazards such as sea-level rise, cumulative erosion, and storm events; this vulnerability drives humans to actively modify barrier geometry and environments. The most common manipulations are beach nourishment, to mitigate shoreline erosion, and increases to dune height or seawall construction to prevent flooding and damage from overwash during storm events. Over time scales of years to decades, hazard-mitigation actions impact natural, spatio-temporal barrier processes such as washover deposition and planform transgression, which in turn affect future efforts to manage, control, or prevent changes to barrier morphology. Through their maintenance and persistence, interventions against coastal hazards represent a significant dynamical component of developed barrier-island system evolution, such that, within the past century, human actions and natural barrier-island processes have become dynamically coupled. This coupling leads to steady-state barrier-island behaviors that are new. A fundamental way to understand how developed barrier islands will respond to climate change over decadal time scales is to treat these settings as strongly coupled human-natural systems. Dynamical demonstration of coupled-system behavior suggests new avenues for less reactionary and more holistic coastal management perspectives for barrier systems and raises questions about whether and how society may adapt to coastal change. Over time scales longer than centuries, human interventions may be coupled only weakly to long-term barrier dynamics. Short of major technological advancements or sweeping decisions to transform these environments into comprehensively geoengineered terrains, high-density development on U.S. barrier islands will eventually have to change-perhaps radically-from its current configuration.