Nearshore bathymetry data from the Elwha River delta, Washington, July 2016
Dates
Publication Date
2016
Start Date
2016-07-17
End Date
2016-07-20
Citation
Stevens, A.W., Gelfenbaum, G., Warrick, J.A., Miller, I.M., and Weiner, H.M., 2016, Bathymetry, topography, and sediment grain-size data from the Elwha River delta, Washington, July 2016: U.S. Geological Survey data release, http://dx.doi.org/10.5066/F7GQ6VXX.
Summary
This portion of the USGS data release presents bathymetry data collected during surveys performed on the Elwha River delta, Washington in July 2016 (USGS Field Activity Number 2016-658-FA). Bathymetry data were collected using two personal watercraft (PWCs) and a kayak, all equipped with single-beam sonar systems and global navigation satellite system (GNSS) receivers. The PWC sonar systems consisted of an Odom Echotrac CV-100 single-beam echosounder and 200 kHz transducer with a 9° 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 [...]
Summary
This portion of the USGS data release presents bathymetry data collected during surveys performed on the Elwha River delta, Washington in July 2016 (USGS Field Activity Number 2016-658-FA). Bathymetry data were collected using two personal watercraft (PWCs) and a kayak, all equipped with single-beam sonar systems and global navigation satellite system (GNSS) receivers. The PWC sonar systems consisted of an Odom Echotrac CV-100 single-beam echosounder and 200 kHz transducer with a 9° 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 10-Hz using Trimble R7 GNSS receivers with Trimble Zephyr Model 2 antennas operating primarily in real-time kinematic (RTK) mode. Differential corrections were transmitted by a VHF radio to the PWC GNSS receivers at 1-Hz from a base station placed on a benchmark with known horizontal and vertical coordinates relative to the North American Datum of 1983 (CORS96 realization) and North American Vertical Datum of 1988. Output from the GNSS and sonar systems were combined in real time on the PWC by a computer running HYPACK® (version 13.0.0.6) hydrographic survey software. Navigation information was displayed on a video monitor, allowing PWC operators to navigate along predefined survey lines spaced at 25-50 m intervals alongshore at speeds of 2-3 m/s.
Bathymetry data were merged with GNSS positions and quality control was applied using the computer program transectViewer, a Graphical User Interface (GUI) programmed with the computer program MATLAB. Raw data were post-processed to remove spurious soundings, and the GUI was used to digitize the bottom by hand where the echosounder signal processing failed, which typically occurred in areas with submerged aquatic vegetation. After the raw depths were adjusted, a running mean with a window length of 5 points (approximately 1 m distance) was used to remove high-frequency vertical fluctuations, such as those caused by pitch and roll of the survey vessels.
Additional bathymetry data were collected in the river channel and portions of the estuary using a kayak equipped with a SonarMite single-beam echosounder and 200 kHz transducer with a 4° beam angle. Depths from the kayak sonar were computed assuming a sound velocity of 1,460 m/s. Positioning of the kayak was determined at 1-Hz using a Trimble R7 GNSS receiver and Trimble Zephyr Model 2 antenna operating in real-time kinematic (RTK) mode. Bathymetric soundings and positioning data were recorded on a Trimble TSC2 data collector. Raw data were reviewed and quality control was applied using Trimble Business Center software.
The estimated vertical uncertainty of the bathymetric measurements is 12 cm. The final point data from the PWCs and kayak are provided in comma-separated text formats and are projected in Cartesian coordinates using the Washington State Plane North, meters coordinate system.
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Purpose
Data were obtained to assess the coastal geomorphic response following the removal of two dams on the Elwha River. These data are intended for science researchers, students, policy makers, and the general public. These data can be used with geographic information systems or other software to identify topographic and shallow-water bathymetric features.
