DIGITIZING COASTAL PLAIN MEANDER BELT SYSTEMS FOR 24K SCALE MAPPING IN THE ROCKY MOUNT 100K SHEET, NORTH CAROLINA

The North Carolina Geological Survey (NCGS) uses high-resolution LiDAR to map landform elements to define Coastal Plain depositional systems, including meander belts, in a relict Quaternary landscape. Quality 2 (QL2), DEMs (3-meter) from 2004 LiDAR were downloaded from the USGS as 15-minute quadrangle tiles and then processed for mapping in the Rocky Mount 100K sheet (30 X 60 quadrangle).

ArcGIS Pro is used to process the LiDAR DEM raster grids for mapping. First, the DEMs are reprojected into an output coordinate system of STATEPLANE NAD 83 Meters. Slope, hillshade, and contour lines (1.0, 0.5, 0.25 m) are then generated from the rasters. When mapping, NCGS uses orthoimagery acquired in 2011 as these provide the most accurate alignment between background imagery and the 2004 LiDAR data. For best display results of the grid and slope, ‘bilinear’ is selected as the resampling type and separate color ramps are applied. The grid is assigned “Elevation #1”, and slope is assigned “Spectrum By Wavelength – Full Bright”; transparencies for both raster layers are set to 50%. Hillshade forms the basal opaque layer and is draped by the slope and elevation grid.

NCGS uses comprehensive landform analysis to develop geologic models for modern and ancient Coastal Plain deposits. Models are based on a combination of LiDAR, contours, and orthoimagery. The Tar River incised valley includes meander belts that are Holocene, Late Pleistocene and Middle Pleistocene in age. Here, the meander belts may include point bars, abandoned channels, wetland flats and Carolina Bays; the meander belts may cut and postdate side valley drainage systems. This dynamic system creates a complexly dissected modern landscape that NCGS divides into component landforms during mapping. In the Rocky Mount 100K, the Tar River incised valley, trends northwest to southeast, is 8-14 km wide, and is inset into Early Pleistocene marine ramps.