Streambank topographic lidar survey of the French Broad River near the Interstate 26 bridge located south of Asheville, NC – December 2020, Mid-Construction #1

In January 2020, the North Carolina Department of Transportation (NCDOT) began work on the Interstate 26 (I 26) highway widening project that involves a bridge crossing over the French Broad River (FBR) near Asheville, North Carolina. The U.S Geological Survey (USGS) in cooperation with the NCDOT conducted a pre-construction light detection and ranging (lidar) survey of the streambanks within a one-kilometer reach of the FBR at the bridge construction site in November 2019 (Whaling and others, 2023). In December 2020, a canoe-based repeat streambank lidar survey was collected approximately 11 months after construction began, with the purpose to monitor geomorphological changes to the streambank and inform the NCDOT of potential impacts from construction activities. The survey extended from 300 meters (m) upstream to 700 m downstream from the bridge. Two georeferenced lidar scans were collected; one of the right-descending bank and one of the left-descending bank. Three-dimensional points of the streambanks were collected with a canoe-mounted Velodyne VLP-16 laser scanner integrated with an SBG Systems Ellipse2-D inertial navigation systems (INS), which consists of dual Global Navigation Satellite Systems (GNSS) receivers and an inertial motion unit. The lidar scanner creates a “point cloud” of lidar returns and the INS computes the position and orientation of the points in three-dimensional space. The navigation solution from the INS was further improved in post processing. Ground points were identified in each point cloud with a Cloth Simulation Filter (Zhang and others, 2016) implemented in CloudCompare software (CloudCompare, 2023) and classified with code 2 (ground) according to the American Society for Photogrammetry and Remote Sensing (ASPRS) standard lidar point classes (ASPRS, 2011). Water-surface reflections were identified and classified as code 7 (low noise; ASPRS, 2011). All other points in each point cloud were classified as code 1 (unclassified; ASPRS, 2011). The left and right streambank point clouds are provided as separate LAS files, an industry-standard binary format for storing large point cloud datasets. Each LAS file is provided with position and elevation data in three dimensions in units of meters, 8-bit scaled intensity, and the classification code. The data are projected in Universal Transverse Mercator (UTM) coordinate system, zone 17 north, horizontally referenced to the North American Datum of 1983 (NGS, 2018a), 2011 realization (NAD83 2011), and vertically referenced to the North American Vertical Datum of 1988 (NAVD88; NGS, 2018b).