GEOMORPHIC COASTAL SYSTEM RESPONSES TO SEA-LEVEL RISE SINCE EUROPEAN COLONIZATION: NORTHEASTERN NORTH CAROLINA

Numerous researchers have documented the millennia-scale evolution of the North Carolina coastal system over the past 18,000 years producing detailed sea-level curves. These data suggest that sea level has risen ~0.7 m since the time of European arrival in 1584-85. The geomorphic evolution of the barrier-island and estuarine system during the past 425 years can be summarized as follows. 1) Prior to 1584-85, researchers demonstrated that a major portion of the southern Outer Bank’s barrier islands had broken down (~1000 AD) into a series of broad inlet-shoals that lasted until ~1500 AD. 2) By 1584-85 the barrier islands were in the process of reforming as the broad inlet-shoal systems were systematically closing to form the modern Pamlico Sound. This barrier reformation is documented by historic maps that demonstrate a systematic decrease in both inlet zones of barrier islands from ~45% (of barrier island length) prior to 1584-85 AD to 4% during the 20^th century, and the number of historic inlets from ~8 in the 16^th century to 2 in the 20^th century in the region from Cape Henry to Cape Hatteras. 3) Croatan Creek occurred as the “narrows” within a broad valley of estuarine fill and salt marsh with its head waters in the Roanoke Marshes inter-stream divide. The latter connected Roanoke Island to the mainland until 1817 AD when the last inlet north of Roanoke Island closed. Rising sea level, in combination with the Roanoke River discharge that was now forced to flow seaward through Croatan Creek, overtopped the inter-stream divide at Roanoke Marshes to exit through Pamlico Sound inlets. Since 1817 AD flow from the Roanoke River eroded Croatan Creek both laterally and vertically, to produce the modern Croatan Sound. 4) Rising sea level and storms were eroding the barrier-island and estuarine shorelines resulting in substantial land loss and were forcing wetland ecosystems to evolve and migrate upward and landward. Upstream flooding of low topography left behind offshore landscapes of drowned stumps and stressed cypress, along with changed geomorphic land features such as inland lakes that become open bays. 5) Drowning of land containing cultural remnants, as well as increased ditching and diking of lowland coastal areas demonstrate that sea-level rise and storm dynamics continue to be significant drivers of NC coastal evolution.