Peter Dartnell Daniel S. Brothers Brian Sherrod Gerald A. Hatcher Daniel C. Powers Jenna C. Hill Jackson E. Currie Peter Dal Ferro 20250917 GeoTIFF data release DOI:10.5066/P1YKDHGC Pacific Coastal and Marine Science Center, Santa Cruz, California U.S. Geological Survey https://doi.org/10.5066/P1YKDHGC Peter Dartnell Daniel S. Brothers Brian Sherrod Gerald A. Hatcher Daniel C. Powers Jenna C. Hill Jackson E. Currie Peter Dal Ferro 2025 data release DOI:10.5066/P1YKDHGC Pacific Coastal and Marine Science Center, Santa Cruz, CA U.S. Geological Survey Suggested Citation: Dartnell, P., Brothers, D.S., Sherrod, B., Hatcher, G.A., Powers, D.C., Hill, J.C., Currie, J.E., Dal Ferro, P., 2025, Bathymetry and acoustic-backscatter data for Sammamish Lake, Washington collected during USGS field activity 2021-656-FA: U.S. Geological Survey data release, https://doi.org/10.5066/P1YKDHGC. https://doi.org/10.5066/P1YKDHGC Here November 2021 2-m resolution bathymetry data of Lake Sammamish, Washington are provided for the entire lake. Data were collected and processed by the U.S. Geological Survey (USGS), Pacific Coastal and Marine Science Center (PCMSC) with fieldwork activity number 2021-656-FA. Data are provided as a GeoTIFF image. The Pacific Northwest is home to numerous faults that cut through the surrounding crust including the Seattle fault. Over time, frictional stresses accumulate along these faults, building slowly until they exceed the fault's strength, resulting in an earthquake. Evidence of these earthquakes may be found in Pacific Northwest lakes. Past underwater landslides caused by the earthquakes should be well preserved in these relatively undisturbed environments. The lake floor of Lake Sammamish in the Pacific Northwest was mapped to find such evidence of past earthquakes. 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 bathymetric features. These data are not intended to be used for navigation. Additional information about the field activity from which these data were derived is available online at: https://cmgds.marine.usgs.gov/fan_info.php?fan=2021-656-FA Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this Federal Geographic Data Committee-compliant metadata file is intended to document the data set in nonproprietary form, as well as in Esri format, this metadata file may include some Esri-specific terminology. 20211108 20211112 ground condition at time data were collected. Complete None -122.200 -121.966 47.652 47.557 USGS Metadata Identifier USGS:a3e9343c-afd7-415f-982e-8dad99644dc8 ISO 19115 Topic Category geoscientificInformation elevation USGS Thesaurus bathymetry bathymetry measurement lakebed characteristics geospatial datasets marine geophysics sonar methods Data Categories for Marine Planning Bathymetry and Elevation Marine Realms Information Bank (MRIB) Keywords field observation 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) Lake Sammamish State of Washington 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. Please recognize and acknowledge the U.S. Geological Survey as the originators 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 LakeSammamish_USGS_2021_2m_bathymetry_UTM10_NAD83_NAVD88_QV.jpg Preview image of USGS 2021 Lake Sammamish bathymetry JPEG SonarWiz(ver. 6) and ArcMap (ver. 10.3.1) on a Windows 10 computer. Peter Dartnell Daniel S. Brothers Brian Sherrod Gerald A. Hatcher Daniel C. Powers Jenna C. Hill 2025 Dartnell, P., Brothers, D.S., Sherrod, B., Hatcher, G.A., Powers, D.C., and Hill, J.C., 2025, Bathymetric and acoustic-backscatter mapping of Lake Sammamish, Washington, during USGS field activity 2021-656-FA: U.S. Geological Survey Data Report 1207, https://doi.org/10.3133/dr1207 https://doi.org/10.3133/dr1207 The SWATHPlus sonar system (234 kHz) depth standard deviation varies with horizontal range and water depth. The system has an estimated depth standard deviation ranging from about 0.1 m to 0.7 m over a horizontal range of 0 to greater than 100 m (https://doi.org/10.3390/rs14092011). Accuracies of final products may be lower due to total propagated uncertainties of the mapping systems, which include sonar system, position and motion compensation system, and navigation, as well as data processing that includes sounding cleaning, gridding, and datum transformations. Refer to data report, Dartnell and others, 2024, for other accuracy assessments. 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. The Applanix POS-MV post-processed horizontal positional accuracy is about 0.1 m with roll and pitch accuracies of about 0.02 degrees (https://www.applanix.com/downloads/products/specs/posmv/POS-MV-WaveMaster-II.pdf). Accuracies of final products may be lower due to total propagated uncertainties of the mapping systems, which include sonar system, position and motion compensation system, and navigation, as well as data processing that includes sounding cleaning, gridding, and datum transformations. The Applanix POS-MV post-processed vertical positional accuracy is about 0.2 m (https://www.applanix.com/downloads/products/specs/posmv/POS-MV-WaveMaster-II.pdf). Accuracies of final products may be lower due to total propagated uncertainties of the mapping systems, which include sonar system, position and motion compensation system, and navigation, as well as data processing that includes sounding cleaning, gridding, and datum transformations. The data were collected with a SWATHplus-M 234-kHz interferometric side-scan sonar system pole-mounted on the U.S. Geological Survey (USGS) R/V San Lorenzo. During the mapping mission, an Applanix POS-MV (Position and Orientation System for Marine Vessels) was used to position the vessel during data collection, and it also accounted for vessel motion such as heave, pitch, and roll. The POS-MV also recorded position and vessel motion parameters for later post-processing. Sound-velocity profiles were collected throughout the survey days with a Castaway sound velocimeter. Post-processed POS-MV Smoothed Best Estimate of Trajectory (SBET) files were merged with the survey line files using BathySwath software and then the line files were imported into SonarWiz software. Soundings were cleaned for obvious errors and gridded into a 2-m base surface. The base surface was exported as an Erdas Imagine file in UTM-10, WGS-84 coordinates vertically referenced to the WGS84 ellipsoid. The data were transformed from WGS-84 to NAD-83 horizontal coordinates using ArcGIS Pro ArcTool raster projection command WGS_1984_(ITRF08)_To_NAD_1983_2011. NOAA's on-line VDATUM transformation tool states there is a +23.688m difference between WGS-84 and NAVD-88 elevations (vertical uncertainty of 0.06m) at a point in the center of the lake. A value of 23.688m was added to the original bathymetry grid to transform from WGS-84 elevations to NAVD-88 elevations. The NAVD-88 bathymetry grid was then exported as a GeoTIFF file in UTM zone 10, NAD-83(2011) coordinates, relative to NAVD88. 2022 Raster Grid Cell 5380 8710 1 Universal Transverse Mercator 10 0.9996 -123.00000 0.00000 500000.0 0.00 coordinate pair 1.0 1.0 Meters North American Datum of 1983, 2011 realization (NAD83(2011)) GRS80 6378137.00 298.257222101 North America Vertical Datum 1988 0.1 meters Explicit elevation coordinate included with horizontal coordinates value elevation in meters relative to NAVD-88 Producer defined The complete 2-m resolution grid "LakeSammamish_USGS_2021_2m_bathymetry_UTM10_NAD83_NAVD88.tif" was originally archived as a TIFF image with the following attributes. >Cell size = 2.0 >Number of rows = 5380 >Number of columns = 8710 > >Data type = floating point > >Boundary >Xmin = 560211 >Xmax = 577634 >Ymin = 5267349 >Ymax = 5278111 > >Statistics >Minimum value = -25.03 >Maximum value = 9.86 >Mean = -10.76 >Standard deviation = 5.96 > >Coordinate system description >Projection: UTM >Zone: 10 >Datum: NAD83(2011) >Vertical Reference: NAVD88 >Units: meter U.S. Geological Survey U.S. Geological Survey - CMGDS Mailing and Physical

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Santa Cruz CA 95060 831-427-4747 pcmsc_data@usgs.gov These data are available in GeoTIFF format, including a tif world file (.tfw), accompanied by CSDGM 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. GeoTIFF ArcMap (version 10.3.1) Downloadable zip file contains the TIFF (.tif) version of the bathymetry data and a projection file (.tfw). WinZip 14.4 https://doi.org/10.5066/P1YKDHGC Data and metadata can be downloaded using the Network_Resource_Name link and scrolling down to the sonar data section. None. The downloadable data file has been compressed with the "zip" command and can be unzipped with Winzip (or other tool) on Windows systems. To utilize these data, the user must have software capable of uncompressing the WinZip file and importing and viewing a GeoTIFF file. 20250917 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