Barrier islands are an important part of the natural, economic, and recreational landscape of the North American coast. These elongated and detached bodies of unconsolidated sand or gravel lie above the high-tide level and are separated from the mainland by a lagoon, a marsh, or a sound. The islands are most prominent on wide and gently sloped trailing edge coasts, although they can form on collision coasts where there is an adequate supply of sediment. The islands typically occur in chains separated from neighboring islands by inlets, which are spaced depending on the relative strength of wave and tide forces. Long (wave-dominated) barriers tend to form where tidal range is small, and waves are able to close breaches that form during storms (e.g., from Southern ...