Nearshore bathymetry of the Columbia River littoral cell, Washington and Oregon, 2020

This portion of the USGS data release presents bathymetry data collected during surveys performed in the Columbia River littoral cell, Washington and Oregon, in 2020 (USGS Field Activity Number 2020-622-FA). Bathymetry data were collected using four personal watercraft (PWCs) equipped with single-beam sonar systems and global navigation satellite system (GNSS) receivers. The sonar systems consisted of an Odom Echotrac CV-100 single-beam echosounder and 200 kHz transducer with a 9-degree beam angle. Raw acoustic backscatter returns were digitized by the echosounder with a vertical resolution of 1.25 cm. Depths from the echosounders were computed using sound velocity profiles measured using a YSI CastAway CTD during the survey. Positioning of the survey vessels was determined at 5 to 10 Hz using Trimble R7 GNSS receivers. Output from the GNSS receivers and sonar systems were combined in real time on the PWC by a computer running HYPACK hydrographic survey software. Navigation information was displayed on a video monitor, allowing PWC operators to navigate along survey lines at speeds of 2 to 3 m/s. Survey-grade positions of the PWCs were achieved with a single-base station and differential post-processing. Positioning data from the GNSS receivers were post-processed using Waypoint Grafnav to apply differential corrections from a GNSS base station with known horizontal and vertical coordinates relative to the North American Datum of 1983. Orthometric elevations relative to the NAVD88 vertical datum were computed using National Geodetic Survey Geoid12a offsets. Bathymetric data were merged with post-processed positioning data and spurious soundings were removed using a custom Graphical User Interface (GUI) programmed with the computer program MATLAB. The average estimated vertical uncertainty of the bathymetric measurements is 10 cm. The final point data from the PWCs are provided in a comma-separated text file and are projected in cartesian coordinates using the Washington State Plane South, meters coordinate system. Due to equipment and staffing issues associated with the global pandemic, bathymetric surveys performed at the southern portion of the Clatsop Plains sub-cell (survey lines 71 to 101) and North Beach sub-cell were performed several weeks after the corresponding topographic surveys. The CTD was not available for bathymetric surveys at these locations and an assumed speed of sound of 1,500 and 1,490 m/s was applied to soundings collected in the North Beach sub-cell and southern portion of the Clatsop sub-cell, respectively.

Tags: bathymetry, bathymetry-and-elevation, bathymetry-measurement, clatsop-county, cmhrp, coastal-and-marine-hazards-and-resources-program, columbia-river, echo-sounders, elevation, global-positioning-system-gps-observations, gps-global-positioning-system, gps-measurement, grays-harbor-county, marine-geophysics, pacific-coastal-and-marine-science-center, pacific-county, pacific-ocean, pcmsc, sea-floor-characteristics, single-beam-echo-sounder, u-s-geological-survey, usgs, usgs-613b921bd34e40dd9c0f96e4, water-depth
Organization: Department of the Interior