GEOLOGIC EVOLUTION OF THE LOWER ROANOKE RIVER DRAINAGE SYSTEM IN RESPONSE TO GLACIAL AND POST-GLACIAL CLIMATIC AND SEA-LEVEL CHANGES

The Roanoke River, largest of North Carolina rivers, has headwaters in the Appalachian Province of VA and flows SE for about 400 miles. The lower Roanoke River (LRR) watershed is that portion E of the Fall Line where the river flows across the coastal plain and discharges into Albemarle Sound. The geomorphic evolution of the LRR is based upon field mapping in concert with aerial photograph and LiDAR analysis. The LRR valley consists of an extremely complex, cut and fill mixture of geomorphic units, most are relict and formed during very different climatic and hydraulic conditions. Three types of riverine deposits are preserved within the LRR valley and reflect major fluctuations in the earth's climate regime. Paleo-braid plains reflect the extremes of the last glacial period when boreal conditions existed in NC. Paleo-meander plains reflect cool temperate or transitional climatic conditions that existed between the glacial and interglacial conditions. NC's warm temperate climate of the ongoing interglacial period has resulted in an incised riverine system dominated and bound by vegetation. Laterally, the LRR valley displays prominent basin asymmetry with the S and W portion containing the active valley that is generally deepest and incised into Cretaceous and Cenozoic sediment units. The valley floor is gently terraced to the N and E and is dominated by paleo-meander and paleo-braid plains. A topographic profile down the channel of the LRR consists of five main Roanoke River zones (RRZ) as it flows off the Piedmont Province and approaches sea level to become Albemarle Sound. RRZ 1: Fall Zone; RRZ 2: Riverine Zone; RRZ 3: Supra-Tidal Riverine Zone; RRZ 4: Embayed Riverine Zone; and RRZ 5: Drowned River Estuary. These five RRZs form the basis for the discussion of the different geomorphic components of the river and future influence of rising sea level upon ecosystem evolution.