Model of Tidal Inlet and Barrier Island Dynamics in a Regime of Accelerated Sea Level Rise

The latest report of the IPCC predicts that based on global warming and other factors, future sealevel rise during this century could range from 25 to 90 cm ( , 2001)(Fig. 2). The average Holocene rate of ~55 cm per century may serve as a reasonable estimate on which to base future predictions. Changes in sea level are linked to global climate, and are primarily controlled by the volume of continental ice masses (polar and alpine), global sea surface temperatures, and deep ocean temperatures. Average global surface temperatures are expected to continue to rise, although predictions vary concerning the rate and magnitude of the change. The IPCC estimates that surface temperature increases up to 5.5 °C may occur over the next 50 years if the concentration of CO in the atmosphere increases at ~1% ( , 2001). The apparent historic acceleration in melting of polar ice has increased debate about the stability of major ice sheets, particularly the West Antarctic sheet, and predictions of future sea-level rise vary widely in part due to this uncertainty. In addition, warming and subsequent expansion of sea surface water will cause increases in future global sea level. If deep ocean waters also increase in average temperature, the expansion effect could be still greater. During the past century, thermal expansion of ocean water has contributed up to 7 cm of sea level rise . , 2001). The impacts of rising sea level and its rate of acceleration will vary dramatically along world's coastlines due to differing local effects that change the vertical position of the land such as compaction due to dewatering, subsidence, isostatic rebound, and tectonic uplift 1991). For barrier coasts having limited supplies of new sand, rising sea level will result in When most coastal scientists consider the effects of rising sea-level, they focus on shoreline erosion, inundation of wetlands, changes to the backbarrier, and consequences to water supplies ( , 1990). Few researchers have looked at the impact of accelerated sea-level rise on tidal inlets and how changes to sand reservoirs of tidal deltas may influence future erosional-depositional patterns on adjacent barrier shorelines. It has been shown along mixed energy coasts that the sand contained in ebb-tidal deltas may be comparable in volume to that of the adjacent barriers ( , 1988). Many of the barrier island chains in the world occur in mixed energy settings, including large sections of the East Coast of the United States (northern New England, southern New Jersey, Virginia, South Carolina and Georgia), Friesian Islands in the North Sea, Copper River Delta coast in the Gulf of Alaska, among others. These coasts are characterized by short stubby barriers, numerous tidal inlets, well developed ebb-tidal deltas, and a backbarrier that consists of expansive marsh and/or tidal flats that are incised by tidal creeks (Fig. 1). Much of the salt marsh in these settings exists at a high tide to supratidal elevation. If sea level rises at a rate faster than the marsh surface can accrete vertically, then the supratidal marsh will be converted to an intertidal saltmarsh and ultimately intertidal marshes will become open-water (subtidal) areas. This process will increase the tidal exchange between the backbarrier and the ocean. This paper presents a conceptual model of how a barrier coast will respond in a regime of accelerated sea-level rise. The model illustrates that a dramatic increase in tidal prism will ultimately produce a retrogradational barrier coast. TITUS