Andrew W. Stevens Joshua 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 Joshua 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., Parker, K.A., 2026, Beach topography and nearshore bathymetry of Humboldt Bay North Spit and South Spit, California: U.S. Geological Survey data release, https://doi.org/10.5066/P1SNSQB9. https://doi.org/10.5066/P1SNSQB9 Topographic data were collected along the beaches and dunes of Humboldt Bay North Spit and South Spit, California using global navigation satellite system (GNSS) receivers mounted to backpacks. Additional topographic data were collected between transects in some areas with an all-terrain vehicles equipped with GNSS receivers. This data release currently contains topographic 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. 20250428 20250919 Ground condition at time data were collected In work As needed -124.2768441 -124.1651965 40.8627511 40.6969119 USGS Metadata Identifier USGS:2b7206ab-ff8c-4bb1-8bce-6b5df8ba3726 ISO 19115 Topic Category elevation Data Categories for Marine Planning Bathymetry and Elevation USGS Thesaurus GPS measurement 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 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 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 variable posture of the topographic surveyors during data collection is unknown. Uncertainty in the vertical positions of the topographic 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. Uncertainty in the vertical positions associated with variable posture of the surveyors, changes in antenna height due to weight distribution of the all-terrain vehicle, or sinking into the substrate during acquisition 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 Topographic profiles were primarily collected on foot with GNSS receivers mounted on backpacks. Hand-held data collectors were used to log raw data and display navigational information allowing surveyors to navigate survey lines. Topographic profiles were surveyed from the landward edge of the study area (either the base of a bluff, engineering structure, or just landward of the primary dune) over the beach foreshore, to wading depth on the same series of transects as nearshore bathymetric surveys. Additional topographic data were collected between survey lines with an all-terrain vehicle (ATV) to constrain the elevations and alongshore extent of major morphological features. 20250919 Precise positioning of the topographic platforms was achieved with a single GNSS base station transmitting differential corrections in real time via UHF radio modem at 1-Hz intervals. Trimble Business Center software was used to apply differential corrections to topographic data collected in autonomous mode when radio communication between the GNSS base station and rover failed. Orthometric elevations relative to the NAVD88 vertical datum were computed using the National Geodetic Survey Geoid18 geoid model. The final point data are projected in cartesian coordinates using the Universal Transverse Mercator (UTM), Zone 10N meters coordinate system. 20250923 All available topographic data from the surveys were compiled into a comma-delimited text files (one file for each survey) for distribution 20250925 Point Point 151949 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]_topo.csv Table containing attribute information associated with the topography 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-28 13:44:39.000 2025-Sep-19 15:04:13.000 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 -124.2768441 -124.1651965 Decimal degrees latitude Latitude coordinate of data point relative to the North American Datum of 1983 (EPSG: 4269) Producer defined 40.6969119 40.8627511 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 392125.55 401800.09 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 4505894.79 4524177.27 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 783.58 2070.53 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 -2.99 2.99 meters ellipsoid_ht_m Height in meters of data point with reference to the reference ellipsoid Producer defined -32.83 -18.55 meters ortho_ht_m Height in meters relative to the NAVD88 vertical datum, computed assuming National Geodetic Survey Geoid18. Producer defined -1.75 12.29 meters This dataset contains one comma separated values (csv) topography file for each field activity. Data files are named hb[yy]_[mmm]_topo.csv, in which [yy]_[mmm] indicates the year and month of the survey. 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 Topographic 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 14.1 https://doi.org/10.5066/P1SNSQB9 Topographic data may be accessed and downloaded via the Internet by using the first Network_Resource_Name link and scrolling to the Location-Elevation 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