Eelgrass distributions and bathymetry derived from an acoustic survey of the Nisqually River delta, Washington, 2012
Dates
Publication Date
2020-07-21
Start Date
2012-02-15
End Date
2012-02-19
Citation
Stevens, A.W., Takesue, R.K., and Grossman, E.E., 2020, Eelgrass distributions and bathymetry of the Nisqually River delta, Washington: U.S. Geological Survey data release, https://doi.org/10.5066/P9N9K2I1.
Summary
This portion of the USGS data release presents eelgrass distribution and bathymetry data derived from acoustic surveys of the Nisqually River delta, Washington in 2012 (USGS Field Activity Number D-01-12-PS). Eelgrass and bathymetry data were collected from the R/V George Davidson equipped with a single-beam sonar system and global navigation satellite system (GNSS) receiver. The sonar system consisted of a Biosonics DT-X single-beam echosounder and 420 kHz transducer with a 6-degree beam angle. Depths from the echosounder were computed using sound velocity assuming a salinity of 30 psu and temperature of 10 degrees Celcius. Positioning of the survey vessel was determined at 5 to 10 Hz using a Trimble R7 GNSS receiver and Trimble Zephyr [...]
Summary
This portion of the USGS data release presents eelgrass distribution and bathymetry data derived from acoustic surveys of the Nisqually River delta, Washington in 2012 (USGS Field Activity Number D-01-12-PS). Eelgrass and bathymetry data were collected from the R/V George Davidson equipped with a single-beam sonar system and global navigation satellite system (GNSS) receiver. The sonar system consisted of a Biosonics DT-X single-beam echosounder and 420 kHz transducer with a 6-degree beam angle. Depths from the echosounder were computed using sound velocity assuming a salinity of 30 psu and temperature of 10 degrees Celcius. Positioning of the survey vessel was determined at 5 to 10 Hz using a Trimble R7 GNSS receiver and Trimble Zephyr Model 2 antenna operating in real time kinematic (RTK) mode. Differential corrections were transmitted by a VHF radio to the GNSS receiver on the survey vessel at 1-Hz from a GNSS base station placed on a nearby benchmark with known horizontal and vertical coordinates relative to the North American Datum of 1983 (CORS96 realization). Output from the GNSS and sonar systems were combined in real time by the Biosonics DT-X deck unit and output to a computer running HYPACK hydrographic survey software. Navigation information was displayed on a video monitor, allowing the vessel operator to navigate along predefined survey lines spaced at 25-50 m intervals alongshore at speeds of 2 to 3 m/s.
Acoustic backscatter data were analyzed using a custom graphical user interface that implements a signal processing algorithm applied to each sonar sounding that differentiates and extracts the location of the seafloor apart from the presence of vegetation. Individual acoustic returns along a survey line were grouped into packets of ten, and eelgrass percent cover was calculated as the fractional percent of acoustic returns that were classified as vegetated within each group, resulting in an estimate of percent cover every 4 to 5 m (depending on the vessel speed).
Orthometric elevations relative to the NAVD88 vertical datum were computed using National Geodetic Survey Geoid12a offsets. The average estimated vertical uncertainty of the bathymetric measurements is 12 cm. The final point data are provided in a comma-separated text file and are projected in Cartesian coordinates using the Universal Transverse Mercator (UTM), Zone 10 north, meters coordinate system.
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nq12_bathy_eelgrass_metadata.xml Original FGDC Metadata
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nq12_bathy_eelgrass.csv
47 MB
text/csv
nq12_bathy_eelgrass_tracklines.png
2.76 MB
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Related External Resources
Type: Browse Image
Top: map showing bathymetry data along 2012 survey tracklines; Bottom: map showing eelgrass distribution and percent coverage along 2012 survey tracklines.
Data were obtained to document interannual changes in eelgrass distributions and coastal morphology following the removal of a dike that restored tidal processes to over 300 ha of former freshwater wetlands on the Nisqually River delta in 2009. 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 the distributions of eelgrass and shallow-water bathymetric features.
Preview Image
Top: map showing bathymetry data along 2012 survey tracklines; Bottom: map showing eelgrass distribution and percent coverage along 2012 survey tracklines.