Single-beam bathymetric survey of the French Broad River near the Interstate-26 bridge located South of Asheville, NC – June 2019, Pre-construction

The North Carolina Department of Transportation (NCDOT) began work on a highway widening project on Interstate-26 (I-26) in January 2020. The French Broad River flows adjacent to and under I-26 in the project area, located in Buncombe County of North Carolina. The NCDOT identified channel and streambank morphology as a potential indicator they were interested in monitoring at three focus areas to track impacts from construction activities. The U.S. Geological Survey (USGS) in cooperation with the NCDOT conducted a single-beam bathymetric survey of one of the three focus areas in June of 2019, approximately seven months before construction was to begin. The survey extended from 300 meters (m) upstream to 500 m downstream of the I-26 bridge across the French Broad River located south of Asheville, North Carolina. Depth data were collected using a CEESCOPE (CEE Hydrosystems, 2015a) single-beam echosounder mounted to a canoe. Position and elevation data were collected using Real-Time Kinematic (RTK) global positioning system technology following the single-base RTK approach outlined by Rydlund and Densmore (2012). The final dataset provides position data in three dimensions with units of meters supplied in a “XYZ” file. The data are projected in Universal Transverse Mercator (UTM) coordinate system, zone 17 N, 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). This dataset will be used to construct a digital elevation model (DEM) of the French Broad River bathymetry in the study area to inform the NCDOT’s river monitoring and stewardship plan throughout the duration of the I-26 widening project.