MODELING PAST AND FUTURE COASTAL REORGANIZATION IN RESPONSE TO TIDAL REGIME CHANGE: NORTHEASTERN NORTH CAROLINA COASTAL SYSTEM

There is much concern about coastal erosion in response to scenarios of future sea-level rise and increased tropical cyclone intensities. A typical mapping exercise to try to forecast the effects of sea-level rise is to superimpose increasing sea-level elevations on an existing topographic model to illustrate possible shoreline locations in the future. These models are inaccurate as they do not account for any of the multiple factors that control erosion, sediment transport, and deposition such as the geologic framework, biological factors, and physical oceanographic processes. We are using observations of coastal stratigraphy, paleo-bathymetric models, and tidal models in northeastern North Carolina to understand past changes of the coastal system in response to storms and sea-level change. The modeling approach is based upon geologic observations of late Pleistocene and Holocene facies within and surrounding the Albemarle-Pamlico Estuarine System (APES), derived from seismic data, cores, and microfossil assemblages, temporally constrained by radiocarbon and optically-stimulated luminescence ages. The modern APES has a microtidal range of approximately 0.1 m, due in part to the existence of the Outer Banks barrier islands. The late Pleistocene facies are dominated by extensive tidal flat deposits, and tidalites are also locally evident in Holocene strata. These data indicate that during the late Pleistocene and earlier Holocene, the APES had an astronomical tidal component significantly in excess of the modern system. We hypothesize that major coastal reorganization accompanied transitions in the tidal regime in response to sea-level rise and the degree of barrier island continuity. To further understand this transitional behavior, we are modeling the tidal effects using various representations of barrier island morphology, which are constrained by our geologic observations. The ADCIRC model is being used to investigate the degree of tidal change that corresponds to the geologic observations. These data will enable an understanding of the potential for a threshold response of the barriers and estuaries to future sea-level rise and storms, and evaluate the potential for future reorganization to a tidally-dominated system.