Andrew W. Stevens Josh B. Logan Jackson E. Currie Timothy C. Elfers Kai A. Parker 20260604 comma-delimited text data release DOI:10.5066/P1SNSQB9 Pacific Coastal and Marine Science Center, Santa Cruz, California U.S. Geological Survey https://doi.org/10.5066/P1SNSQB9 Andrew W. Stevens Josh B. Logan Jackson E. Currie Timothy Elfers Kai A. Parker 2026 data release DOI:10.5066/P1SNSQB9 Pacific Coastal and Marine Science Center, Santa Cruz, CA U.S. Geological Survey Suggested Citation: Stevens, A.W., Logan, J.B., Currie, J.E., Elfers, T.C., and Parker, K.A., 2026, Beach topography and nearshore bathymetry of Humboldt Bay North and South Spits, California: U.S. Geological Survey data release, https://doi.org/10.5066/P1SNSQB9. https://doi.org/10.5066/P1SNSQB9 Bathymetric data of the nearshore zone were collected along Humboldt Bay North and South Spits, California using personal watercraft (PWCs) equipped with single-beam sonar systems and global navigation satellite system (GNSS) receivers. This data release currently contains bathymetric data from 2 surveys performed between April 2025 and September 2025 and will be updated when additional surveys become available. Data were obtained to quantify changes in coastal morphology and sand volume within an area that extends approximately 12 kilometers (km) north and 8 km south of the Humboldt Bay inlet. Analysis derived from these data were used to inform management of sediment dredged from the bar and entrance channel of Humboldt Bay by the U.S. Army Corps of Engineers. Additional information about the field activities from which these data were derived is available online at: https://cmgds.marine.usgs.gov/fan_info.php?fan=2025-615-FA https://cmgds.marine.usgs.gov/fan_info.php?fan=2025-658-FA Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. 20250429 20250917 Ground condition at time data were collected In work As needed -124.2866575 -124.1677396 40.8666435 40.7000867 USGS Metadata Identifier USGS:34177f4c-ee07-4229-b387-de609d0006a2 ISO 19115 Topic Category elevation Data Categories for Marine Planning Bathymetry and Elevation USGS Thesaurus bathymetry GPS measurement sea-floor characteristics marine geophysics single-beam echo sounder Marine Realms Information Bank (MRIB) keywords Global Positioning System (GPS) observations None U.S. Geological Survey USGS Coastal and Marine Hazards and Resources Program CMHRP Pacific Coastal and Marine Science Center PCMSC Geographic Names Information System (GNIS) Humboldt County North Spit South Spit Humboldt Bay No access constraints USGS-authored or produced data and information are in the public domain from the U.S. Government and are freely redistributable with proper metadata and source attribution. These data are marked with a Creative Commons CC0 1.0 Universal License. Please recognize and acknowledge the U.S. Geological Survey as the originator(s) of the dataset and in products derived from these data. This information is not intended for navigation purposes. U.S. Geological Survey, Pacific Coastal and Marine Science Center PCMSC Science Data Coordinator mailing and physical

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Santa Cruz CA 95060 831-427-4747 pcmsc_data@usgs.gov MATLAB Version: 25.2.0.2998904 (R2025a) No formal attribute accuracy tests were conducted. No formal logical accuracy tests were conducted. Dataset is considered complete for the information presented, as described in the abstract. Users are advised to read the rest of the metadata record carefully for additional details. Manufacturer reported accuracy for the differentially corrected horizontal positions for both bathymetric and topographic measurements is 0.8 cm + 0.5 ppm, where ppm refers to baseline distances between GNSS rovers and base stations in parts per million. Mean and maximum baselines from the GNSS base station during the survey were 3.1 km and 6.3 km, respectively suggesting a mean and maximum horizontal accuracy of bathymetric and topographic positions to be between 0.67 centimeters (cm) and 0.82 cm relative to the base station coordinate. Uncertainty in the horizontal positions associated with pitch and roll of the survey vessels during data collection is unknown. Uncertainty in the vertical positions of the GNSS measurements was estimated based on the accuracy of the Trimble GNSS rovers used in the survey. Manufacturer reported accuracy for the differentially corrected vertical positions for the GNSS rover trajectories is 1.5 cm + 1 ppm. The maximum baseline from the GNSS base station during the survey was 6.3 km, suggesting a minimum vertical accuracy of 2.76 cm relative to the base station coordinate. The bathymetric measurements include additional sources of vertical uncertainty associated with the CEEHydrosystems CEESCOPE single beam echosounder systems used in this survey. The manufacturer of the single beam echosounders reports a vertical uncertainty of 1 cm + 1 percent of water depth. Based on a mean (7 m) and maximum water depth (23.7 m) measured during the survey, the mean and maximum vertical uncertainty for the bathymetric soundings is estimated to be 8 and 24 cm, respectively. Combining the uncertainty related to the GNSS positions and bathymetric soundings in quadrature yields a total mean and max vertical uncertainty of 8.5 and 24.2 cm respectively for the final bathymetric elevations. Uncertainty in the vertical positions associated with pitch and roll of the survey vessels is unknown. Geodetic control for the project was established using simultaneous static GNSS network surveys on four benchmarks installed near the study area. Static GNSS occupations were conducted on these benchmarks during February, April, and May 2025. Observation data from each session were processed using the National Geodetic Survey’s Online Positioning User Service (OPUS) Projects. All static observations used in the network adjustment met USGS Level I quality standards for single-base OPUS-S surveys. The resulting geodetic control is aligned to the National Spatial Reference System (NSRS) through the North American Datum of 1983, National Adjustment of 2011 (NAD83(2011)), at epoch 2010.00. Elevations are referenced to the North American Vertical Datum of 1988 (NAVD88), with orthometric heights computed using NGS GEOID18. 2025 Bathymetric data were acquired using single-beam sonar systems and global navigation satellite systems (GNSS) receivers mounted on personal watercraft (PWC). Depths from the echosounders were computed using sound velocity profiles measured using a CTD during the survey. Positioning of the survey vessels was determined at 10 Hz using dual frequency GNSS receivers. Output from the GNSS receivers and sonar systems were combined in real time by a computer running HYPACK hydrographic survey software. Navigation information was displayed on a video monitor, allowing vessel operators to navigate along planned survey lines. 20250917 Precise positioning of the bathymetric platforms was achieved with a single GNSS base station transmitting differential corrections in real time via UHF radio modem at 1-Hz intervals. Positioning data from the bathymetric survey platforms were later post-processed using Waypoint Grafnav to apply differential corrections from the GNSS base station. These post-processed positions superseded those that were recorded in the field. Orthometric elevations relative to the NAVD88 vertical datum were computed using the National Geodetic Survey Geoid18 geoid model. 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 final point data are projected in cartesian coordinates using the Universal Transverse Mercator (UTM), Zone 10N meters coordinate system. 20250923 All available bathymetric data from the surveys were compiled into a comma-delimited text files (one file for each survey) for distribution 20250925 Point Point 808183 0.0000001 0.0000001 Decimal degrees North American Datum of 1983 GRS_1980 6378137.0 298.257222101 North American Vertical Datum of 1988 0.01 meters Explicit elevation coordinate included with horizontal coordinates hb[yy]_[mmm]_bathy.csv Table containing attribute information associated with the bathymetry dataset, where [yy]_[mmm] in the file name is the year and month in which the data were collected. Producer defined line_number Numeric code identifying the number of the survey line. Data that were not collected along a survey line are labeled "None". Producer defined 001 104 datetime_utc The date and time of data collection in Coordinated Universal Time (UTC). Producer defined 2025-Apr-29 18:27:28.627 2025-Sep-17 20:21:53.164 date and time in yyyy-mmm-dd HH:MM:SS.FFF format longitude Longitude coordinate of data point relative to the North American Datum of 1983 (EPSG: 4269) Producer defined -124.2866575 -124.1677396 Decimal degrees latitude Latitude coordinate of data point relative to the North American Datum of 1983 (EPSG: 4269) Producer defined 40.7000867 40.8666435 Decimal degrees easting_m East coordinate of data point relative to the North American Datum of 1983, projected in the Universal Transverse Mercator Zone 10N, meters, coordinate system (EPSG: 6339) Producer defined 391307.19 401586.93 meters northing_m North coordinate of data point relative to the North American Datum of 1983, projected in the Universal Transverse Mercator Zone 10N, meters, coordinate system (EPSG: 6339) Producer defined 4506247.93 4524622.45 meters distance_m Distance from reference point along planned survey line. Distances are relative to an arbitrary reference point. Depending on the orientation of the target line and position of the reference point, the along-line distance can be positive or negative in any direction. NaN=not a number, because the data were not collected along a pre-defined survey line. Producer defined -244.27 1930.91 meters offline_m Horizontal distance from planned survey line. Depending on the orientation of the target line and position of the reference point, the offline distance can be positive or negative in any direction. NaN=not a number, because the data were not collected along a pre-defined survey line. Producer defined -20.00 19.99 meters ellipsoid_ht_m Height in meters of data point with reference to the reference ellipsoid Producer defined -54.35 -30.25 meters ortho_ht_m Height in meters relative to the NAVD88 vertical datum, computed assuming National Geodetic Survey Geoid18. Producer defined -23.53 0.62 meters [MA3.1]This dataset contains one comma separated values (csv) bathymetry data file for each field activity. Data files are named hb[yy]_[mmm]_bathy.csv, in which [yy]_[mmm] indicate the year and month of the survey. The first line of the csv file is a header line. U.S. Geological Survey U.S. Geological Survey - Coastal and Marine Geoscience Data System Mailing and Physical Address

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Santa Cruz CA 95060 USA 831-427-4747 pcmsc_data@usgs.gov Bathymetric data from each survey are available as separate comma-delimited text files, along with associated FGDC-compliant metadata. Unless otherwise stated, all data, metadata and related materials are considered to satisfy the quality standards relative to the purpose for which the data were collected. Although these data and associated metadata have been reviewed for accuracy and completeness and approved for release by the U.S. Geological Survey (USGS), no warranty expressed or implied is made regarding the display or utility of the data on any other system or for general or scientific purposes, nor shall the act of distribution constitute any such warranty. comma-delimited text MATLAB Version: 25.2.0.2998904 (R2025b) comma-delimited text file No compression applied 77.8 https://doi.org/10.5066/P1SNSQB9 Bathymetric data may be accessed and downloaded via the Internet by using the first Network_Resource_Name link and scrolling to the Sonar Data section. None 20260604 U.S. Geological Survey, Pacific Coastal and Marine Science Center PCMSC Science Data Coordinator mailing and physical

2885 Mission Street

Santa Cruz CA 95060 831-427-4747 pcmsc_data@usgs.gov Content Standard for Digital Geospatial Metadata FGDC-STD-001-1998