USING LIDAR AND GIS TO MAP FLOODPLAINS, COASTAL PLAIN TERRACES AND RECONNAISSANCE-LEVEL STRATIGRAPHIC UNITS, NEUSE RIVER BASIN, NORTH CAROLINA

LIDAR (Light Detection and Ranging) is a remote sensing technique that provides high resolution elevation data with a vertical accuracy of +/- 25 cm per 1 m x 1 m tile. This paper demonstrates the use of LIDAR to map geomorphic features associated with floodplains and terraces in the middle Coastal Plain that border the Neuse River and its tributaries in eastern North Carolina. The results of this analysis provide a template for reconnaissance-level correlation between geomorphic features and an established stratigraphic model for southeastern Virginia (see Mixon and others, 1989; Johnson and Berquist, 1989). The results are then compared with geomorphic features and map units interpreted from georeferenced digital raster graphic images (DRGs) of scanned 7.5 minute topographic quadrangles with 2 m contour intervals.

LIDAR data was downloaded from the North Carolina Floodplain Mapping Program’s website (http://www.ncfloodmaps.com/) using a cell size of 20 ft X 20 ft. Downloaded ASCII tiles (10,000 ft X 10,000 ft) were converted to raster grids in ArcGIS^TM, mosaiced in ArcInfo^TM, and clipped to watershed boundaries in ArcMap^TM. The ArcGIS^TM extension, Spatial Analyst^TM, created hillshade and slope data sets that were combined with ramped elevation colors to produce maps of watershed geomorphology displayed in 3D relief. Creation of contour lines in Spatial Analyst and topographic profiles in the ArcGIS^TM extension 3D Analyst^TM assists in the geomorphic interpretation of map units.

High resolution LIDAR shows that floodplains and terraces are geomorphically complex. Lidar resolves features such as Carolina Bays, (fluvial) point bar ridges and swales, and subtle beach ridge accretion complexes that are commonly unresolvable on DRGs. Stratigraphically, the terraces that border the Neuse River and its tributaries likely correlate with the middle Pleistocene and younger Chuckatuck, Charles City and Tabb Formations (3 members) in southeast Virginia. These might be associated with highstand positions of 20 m, 16 m, and 9 m. These interpretations and regional correlations await subsurface confirmation.