Interpretation of the Surficial Geology of Lake Mead Based on Sidescan-Sonar Imagery, Topography and Sediment Thickness (LAKEMEAD_INTERP.SHP)

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Frequently anticipated questions:

What does this data set describe?

Title:
Interpretation of the Surficial Geology of Lake Mead Based on Sidescan-Sonar Imagery, Topography and Sediment Thickness (LAKEMEAD_INTERP.SHP)
Abstract:
Lake Mead is a large interstate reservoir located in the Mojave Desert of southeastern Nevada and northwestern Arizona. It was impounded in 1935 by the construction of Hoover Dam and is one of a series of multi-purpose reservoirs on the Colorado River. The lake extends 183 km from the mouth of the Grand Canyon to Black Canyon, the site of Hoover Dam, and provides water for residential, commercial, industrial, recreational, and other non-agricultural users in communities across the southwestern United States. The region covered by the reservoir had been mapped prior to construction of the dam, however there had been little study of how the lake-floor region had changed since impoundment. To address this question, sidescan-sonar imagery and high-resolution seismic-reflection profiles were collected throughout Lake Mead by the U.S. Geological Survey (USGS) in cooperation with researchers from University of Nevada Las Vegas (UNLV). These data allow a detailed mapping of the surficial geology of the lake's floor and the distribution and thickness of sediment that has accumulated in the lake since the completion of Hoover Dam. Results indicate that the accumulation of post-impoundment sediment is primarily restricted to former river and stream beds while alluvial deposits and rock outcrops are still exposed on the lake floor away from the former river beds.
  1. How might this data set be cited?
    Twichell, David C., 2009, Interpretation of the Surficial Geology of Lake Mead Based on Sidescan-Sonar Imagery, Topography and Sediment Thickness (LAKEMEAD_INTERP.SHP): Open-File Report 2009-1150, U.S. Gelogical Survey, Coastal and Marine Geology Program, Woods Hole Coastal and Marine Science Center, Woods Hole, MA.

    Online Links:

    This is part of the following larger work.

    Twichell, David C., and Cross, VeeAnn A., 2009, Surficial Geology of the Floor of Lake Mead (Arizona and Nevada) as Defined by Sidescan-Sonar Imagery, Lake-Floor Topography, and Post-Impoundment Sediment Thickness: Open-File Report 2009-1150, U.S. Geological Survey, Reston, VA.

    Online Links:

  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -114.875584
    East_Bounding_Coordinate: -114.025408
    North_Bounding_Coordinate: 36.485418
    South_Bounding_Coordinate: 36.011239
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
    Beginning_Date: 14-May-1999
    Ending_Date: 26-Apr-2001
    Currentness_Reference:
    Ground condition of the originally collected data. The original data collection was over a span of three years with the following specific dates of collection: May 14, 1999 to May 25, 1999; June 1, 2000 to June 6, 2000; April 1, 2001 to April 26, 2001.
  5. What is the general form of this data set?
    Geospatial_Data_Presentation_Form: vector digital data
  6. How does the data set represent geographic features?
    1. How are geographic features stored in the data set?
      This is a Vector data set. It contains the following vector data types (SDTS terminology):
      • G-polygon (365)
    2. What coordinate system is used to represent geographic features?
      Horizontal positions are specified in geographic coordinates, that is, latitude and longitude. Latitudes are given to the nearest 0.000001. Longitudes are given to the nearest 0.000001. Latitude and longitude values are specified in Decimal degrees. The horizontal datum used is D_WGS_1984.
      The ellipsoid used is WGS_1984.
      The semi-major axis of the ellipsoid used is 6378137.000000.
      The flattening of the ellipsoid used is 1/298.257224.
  7. How does the data set describe geographic features?
    lakemead_interp
    Surficial geology of Lake Mead (Source: USGS)
    FID
    Internal feature number. (Source: ESRI) Sequential unique whole numbers that are automatically generated.
    Shape
    Feature geometry. (Source: ESRI) Coordinates defining the features.
    Id
    Automatically generated feature ID number automatically populated with zeros (Source: ESRI)
    Range of values
    Minimum:0
    Maximum:0
    INTERPRETA
    Bounds of four geologic units mapped on the lake floor. (Source: David C. Twichell)
    ValueDefinition
    alluvialAreas where pre-impoundment alluvial fan deposits are exposed on the lake floor. These deposits show on the sidescan imagery as moderate backscatter areas that are interrupted by thin sinuous bands of low backscatter (dark tones) shaped in a distributary pattern.
    rockAreas where rock is exposed on the lake floor. Rock exposures show as either uniform high backscatter (light tones) or alternating bands of high and moderate backscatter (light and moderate tones) on the sidescan imagery.
    thick sedAreas of the lake floor covered by post-impoundment sediment that is more than 1 m thick. These areas show on the sidescan imagery as low backscatter (dark tones) throughout the lake with the exception of parts of Gregg Basin and the area at the mouth of Las Vegas Wash which are sandy and have a moderate backscatter surface. The thickness of the sediment being greater than 1 m is determined from the seismic-reflection profiles.
    thin sedAreas of the lake floor covered by post-impoundment sediment that is less than 1 m thick. These areas show on the sidescan imagery as low backscatter (dark tones). The sediment thickness for much of these areas was below the resolution of the seismic-reflection system used, and in these areas the presence of post-impoundment sediment is based on the low-backscatter signature on the sidescan imagery alone.
    lake_sect
    The area of the lake in which the polygon falls. (Source: Data interpreter.)
    ValueDefinition
    Boulder BasinThe area of the lake to the west of Boulder Canyon.
    Virgin BasinThe central basin of Lake Mead. Starts at (includes) Boulder Canyon in the west, and extends to the east until it runs into Temple Basin. The northern boundary is marked by the Overton Arm section of the lake.
    Overton ArmThe northernmost portion of Lake Mead, where the Muddy River and Virgin River enter the lake. The southern boundary is marked by the Virgin Basin.
    Temple BasinWestern boundary is marked by Virgin Basin. This area includes Temple Basin as well as the Virgin Canyon area to the east.
    Gregg BasinThe easternmost portion of Lake Mead. The western boundary is at the entrance to Virgin Canyon, and the eastern boundary extends to the limits of the survey. The Colorado River enters Lake Mead to the east.
    utm11_area
    Area of the polygon in meters, UTM Zone 11, WGS84 calculated using XTools Pro version 5.2. (Source: Software calculated.)
    Range of values
    Minimum:0.1357529
    Maximum:24226053.1152
    Units:meters
    utmkm_area
    Area of the polygon in kilometers, UTM Zone 11, WGS84 calculated using XTools Pro version 5.2. (Source: Software calculated.)
    Range of values
    Minimum:0
    Maximum:24.226053
    Units:kilometers

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
    • David C. Twichell
  2. Who also contributed to the data set?
  3. To whom should users address questions about the data?
    David C. Twichell
    U.S. Geological Survey
    Oceanographer
    Woods Hole Coastal and Marine Science Center
    Woods Hole, MA

    (508) 548-8700 x2266 (voice)
    (508) 457-2310 (FAX)
    dtwichell@usgs.gov

Why was the data set created?

This shapefile presents an interpretation of the surficial geology of the floor of Lake Mead based on sidescan-sonar imagery, bathymetry, seismic-reflection data, and geological maps of the areas surrounding the lake.

How was the data set created?

  1. From what previous works were the data drawn?
    OFR-03-320 (source 1 of 1)
    Twichell, David C., Cross, VeeAnn A., and Belew, Stephen D., 2003, Mapping the floor of Lake Mead (Nevada and Arizona): Preliminary discussion and GIS data release: Open-File Report 03-320, U.S. Geological Survey, Reston, VA.

    Online Links:

    Type_of_Source_Media: DVD-ROM
    Source_Contribution:
    Sidescan-sonar mosaics and the sediment isopach grid. These were used as the basis for the lake-floor geology interpretation.
  2. How were the data generated, processed, and modified?
    Date: 22-May-2009 (process 1 of 14)
    Polygon shapefiles created with ArcCatalog (version 9.3) with the projection defined as Geographic, WGS 84. The interpretation was done in five sections and a separate shapefile created for each area. These sections were Boulder Basin, Virgin Basin, Overton Arm, Temple Basin, and Gregg Basin. Person who carried out this activity:
    David C. Twichell
    U.S. Geological Survey
    Oceanographer
    Woods Hole Coastal and Marine Science Center
    Woods Hole, MA

    (508) 548-8700 x2266 (voice)
    (508) 457-2310 (FAX)
    dtwichell@usgs.gov
    Data sources produced in this process:
    • BB_interp_g84.shp
    • VB_interp_g84.shp
    • OVTN_interp_g84.shp
    • TB_interp_g84.shp
    • GB_interp_g84.shp
    Date: 23-May-2009 (process 2 of 14)
    Polygons digitized manually in ArcMap (v. 9.3) at a scale of 1:10,000 or finer using the sidescan-sonar imagery as the base layer. Three different lake floor types were indentified in this process step: alluvial, rock, and sediment. Each polygon was assigned the appropriate name in the INTERPRETA field of the attribute table. Person who carried out this activity:
    David C. Twichell
    U.S. Geological Survey
    Oceanographer
    Woods Hole Coastal and Marine Science Center
    Woods Hole, MA

    (508) 548-8700 x2266 (voice)
    (508) 457-2310 (FAX)
    dtwichell@usgs.gov
    Data sources used in this process:
    • bbasinenh_g.tif
    • lvwash_eng.tif
    • vbasineng_g.tif
    • overtonenh_g.tif
    • tempiceenh_g.tif
    Data sources produced in this process:
    • BB_interp_g84.shp
    • VB_interp_g84.shp
    • OVTN_interp_g84.shp
    • TB_interp_g84.shp
    • GB_interp_g84.shp
    Date: 23-May-2009 (process 3 of 14)
    The surficial geology shapefiles were next overlain on the post-impoundment sediment thickness grid published by Twichell and others (2003) to differentiate the areas of thick sediment (thick sed) and thin sediment (thin sed). The sediment thickness grid was displayed in ArcMap as two categories: areas where sediment was less than 1-m thick and areas where sediment was greater than 1 m thick. The "sediment" polygons were then cut along the boundaries of these two categories and annotated appropriately. Person who carried out this activity:
    David C. Twichell
    U.S. Geological Survey
    Oceanographer
    Woods Hole Coastal and Marine Science Center
    Woods Hole, MA

    (508) 548-8700 x2266 (voice)
    (508) 457-2310 (FAX)
    dtwichell@usgs.gov
    Data sources used in this process:
    • isogrdgeog
    Data sources produced in this process:
    • BB_interp_g84.shp
    • VB_interp_g84.shp
    • OVTN_interp_g84.shp
    • TB_interp_g84.shp
    • GB_interp_g84.shp
    Date: 2009 (process 4 of 14)
    During the interpretation process there were often adjacent polygons created with the same value. In order to eliminate these artificial bounds, the original shapefiles were copies to new files with "merge" in the filename indicating the process to take place. Each new shapefile was opened in ArcMap 9.3 Editor. Adjacent polygons with the same INTERPRA value were selected - and the "merge" option under the edit menu was selected. Person who carried out this activity:
    VeeAnn A. Cross
    U.S. Geological Survey
    Marine Geologist
    Woods Hole Coastal and Marine Science Center
    Woods Hole, MA

    (508) 548-8700 x2251 (voice)
    (508) 457-2310 (FAX)
    vatnipp@usgs.gov
    Data sources used in this process:
    • BB_interp_g84.shp
    • VB_interp_g84.shp
    • OVTN_interp_g84.shp
    • TB_interp_g84.shp
    • GB_interp_g84.shp
    Data sources produced in this process:
    • BB_merge_g84.shp
    • VB_merge_g84.shp
    • OVTN_merge_g84.shp
    • TB_merge_g84.shp
    • GB_merge_g84.shp
    Date: 2009 (process 5 of 14)
    Each of these individual shapefiles was copied to a new file using ArcCatalog 9.2. Once this was done, each of these individual shapefiles needed to be quality checked for sliver polygons and overlaps. To help with the overlap polygons, a tool from the ESRI website (Find overlapping polygons) written by Ken Buja was used within ArcMap 9.2. When overlapping polygons were identified, the shapefile was edited within ArcMap 9.2 to adjust the polygons to remove the overlap. Careful visual inspection identified sliver polygons which were removed during the editing procedure as well. The slivers were usually removed by creating a new polygon using the edit tool Auto Complete Polygon. Then this newly created polygon was merged with the appropriate adjacent polygon. Person who carried out this activity:
    VeeAnn A. Cross
    U.S. Geological Survey
    Marine Geologist
    Woods Hole Coastal and Marine Science Center
    Woods Hole, MA

    (508) 548-8700 x2251 (voice)
    (508) 457-2310 (FAX)
    vatnipp@usgs.gov
    Data sources used in this process:
    • BB_merge_g84.shp
    • VB_merge_g84.shp
    • OVTN_merge_g84.shp
    • TB_merge_g84.shp
    • GB_merge_g84.shp
    Data sources produced in this process:
    • BB_merge_g84_vac.shp
    • VB_merge_g84_vac.shp
    • OVTN_merge_g84_vac.shp
    • TB_merge_g84_vac.shp
    • GB_merge_g84_vac.shp
    Date: 2009 (process 6 of 14)
    Once the individual shapefiles were cleaned, then all the individual files were merged into a single shapefile. This was done using ArcMap 92. - ArcToolbox - Data Management Tools - General - Merge. The order of the inputs was as follows: BB_merge_g84_vac.shp, VB_merge_g84_vac.shp, OVTN_merge_g84_vac.shp, TB_merge_g84_vac.shp, GB_merge_g84_vac.shp The field mapping was left to the default since all the individual shapefiles had the same attributes. Person who carried out this activity:
    VeeAnn A. Cross
    U.S. Geological Survey
    Marine Geologist
    Woods Hole Coastal and Marine Science Center
    Woods Hole, MA

    (508) 548-8700 x2251 (voice)
    (508) 457-2310 (FAX)
    vatnipp@usgs.gov
    Data sources used in this process:
    • BB_merge_g84_vac.shp
    • VB_merge_g84_vac.shp
    • OVTN_merge_g84_vac.shp
    • TB_merge_g84_vac.shp
    • GB_merge_g84_vac.shp
    Data sources produced in this process:
    • lakemead_interp_a.shp
    Date: 2009 (process 7 of 14)
    To ensure complete coverage of the interpretation, the individual shapefiles did have some overlap. Now with the shapefiles merged into a single shapefile, these overlaps had to be removed. This was done in ArcMap 9.2 editor by a combination of adjusting boundaries and deleting the overlapping polygon sections. Person who carried out this activity:
    VeeAnn A. Cross
    U.S. Geological Survey
    Marine Geologist
    Woods Hole Coastal and Marine Science Center
    Woods Hole, MA

    (508) 548-8700 x2251 (voice)
    (508) 457-2310 (FAX)
    vatnipp@usgs.gov
    Data sources used in this process:
    • lakemead_interp_a.shp
    Data sources produced in this process:
    • lakemead_interp_a.shp
    Date: 2009 (process 8 of 14)
    In order to divide the interpretation into sections based on areas of Lake Mead, the interpretation polygon was edited in ArcMap 9.2. The area covered by the sections were based on the original individual shapefile interpretations. First, using ArcCatalog 9.2, the shapefile was copied to a shapefile with a new name. Then, in ArcMap 9.2 editor, polygons in the area of the intended boundary were selected. Using the editing option to cut existing polygons, a polyline was drawn splitting the necessary polygons. Person who carried out this activity:
    VeeAnn A. Cross
    U.S. Geological Survey
    Marine Geologist
    Woods Hole Coastal and Marine Science Center
    Woods Hole, MA

    (508) 548-8700 x2251 (voice)
    (508) 457-2310 (FAX)
    vatnipp@usgs.gov
    Data sources used in this process:
    • lakemead_interp_a.shp
    Data sources produced in this process:
    • lakemead_interp.shp
    Date: 2009 (process 9 of 14)
    In ArcMap 9.2, the text attribute "lake_sect" was added to the attribute table using the attribute table - options - add field. By selecting the polygons in each of the defined areas, this attribute was then edited to reflect the appropriate value. The five defined areas are: Boulder Basin, Virgin Basin, Overton Arm, Temple Basin, and Gregg Basin. Person who carried out this activity:
    VeeAnn A. Cross
    U.S. Geological Survey
    Marine Geologist
    Woods Hole Coastal and Marine Science Center
    Woods Hole, MA

    (508) 548-8700 x2251 (voice)
    (508) 457-2310 (FAX)
    vatnipp@usgs.gov
    Data sources used in this process:
    • lakemead_interp.shp
    Data sources produced in this process:
    • lakemead_interp.shp
    Date: 2009 (process 10 of 14)
    Using XTools Pro, version 5.2, the area of each polygon was calculated. This procedure was performed twice. Once to calculate the area in meters based on the UTM, Zone 11, WGS84 projection. This information populates the utm11_area attribute. The area was also calculated in kilometers based on the UTM, Zone 11, WGS84 projection. This information populates the utmkm_area attribute. Person who carried out this activity:
    VeeAnn A. Cross
    U.S. Geological Survey
    Marine Geologist
    Woods Hole Coastal and Marine Science Center
    Woods Hole, MA

    (508) 548-8700 x2251 (voice)
    (508) 457-2310 (FAX)
    vatnipp@usgs.gov
    Data sources used in this process:
    • lakemead_interp.shp
    Data sources produced in this process:
    • lakemead_interp.shp
    Date: 09-Nov-2016 (process 11 of 14)
    Edits to the metadata were made to fix any errors that MP v 2.9.34 flagged. This is necessary to enable the metadata to be successfully harvested for various data catalogs. In some cases, this meant adding text "Information unavailable" or "Information unavailable from original metadata" for those required fields that were left blank. Other minor edits were probably performed (title, publisher, publication place, etc.). Added online link to the data in the distribution section. The distribution format name was modified in an attempt to be more consistent with other metadata files of the same data format. The metadata date (but not the metadata creator) was edited to reflect the date of these changes. The metadata available from a harvester may supersede metadata bundled within a download file. Compare the metadata dates to determine which metadata file is most recent. Person who carried out this activity:
    U.S. Geological Survey
    Attn: VeeAnn A. Cross
    Marine Geologist
    384 Woods Hole Road
    Woods Hole, MA

    508-548-8700 x2251 (voice)
    508-457-2310 (FAX)
    vatnipp@usgs.gov
    Date: 20-Jul-2018 (process 12 of 14)
    USGS Thesaurus keywords added to the keyword section. Person who carried out this activity:
    U.S. Geological Survey
    Attn: VeeAnn A. Cross
    Marine Geologist
    384 Woods Hole Road
    Woods Hole, MA

    508-548-8700 x2251 (voice)
    508-457-2310 (FAX)
    vatnipp@usgs.gov
    Date: 18-Nov-2019 (process 13 of 14)
    Crossref DOI link was added as the first link in the metadata. Person who carried out this activity:
    U.S. Geological Survey
    Attn: VeeAnn A. Cross
    Marine Geologist
    384 Woods Hole Road
    Woods Hole, MA

    508-548-8700 x2251 (voice)
    508-457-2310 (FAX)
    vatnipp@usgs.gov
    Date: 08-Sep-2020 (process 14 of 14)
    Added keywords section with USGS persistent identifier as theme keyword. Person who carried out this activity:
    U.S. Geological Survey
    Attn: VeeAnn A. Cross
    Marine Geologist
    384 Woods Hole Road
    Woods Hole, MA

    508-548-8700 x2251 (voice)
    508-457-2310 (FAX)
    vatnipp@usgs.gov
  3. What similar or related data should the user be aware of?
    Twichell, David C., Cross, VeeAnn A., and Belew, Stephen D., 2003, Mapping the floor of Lake Mead (Nevada and Arizona): Preliminary discussion and GIS data release: Open-File Report 03-320, U.S. Geological Survey, Reston, VA.

    Online Links:

    Twichell, D.C., Cross, V.A., Rudin, M.J., and Parolski, K.F., 2000, Surficial geology and distribution of post-impoundment sediment of the western part of Lake Mead based on a sidescan sonar and high-resolution seismic-reflection survey: Open-File Report 99-581, U.S. Geological Survey, Reston, VA.

    Online Links:

    Twichell, D.C., Cross, V.A., Rudin, M.J., Parolski, K.F., and Rendigs, R.R., 2001, Surficial geology and distribution of post-impoundment sediment in Las Vegas Bay, Lake Mead: Open-File Report 01-070, U.S. Geological Survey, Reston, VA.

    Online Links:

How reliable are the data; what problems remain in the data set?

  1. How well have the observations been checked?
  2. How accurate are the geographic locations?
    The horizontal accuracy is a function of the originally collected sidescan-sonar imagery. Those data were navigated with a P-Code Global Positioning System. In 1999 and 2001 the sidescan-sonar towfish was deployed at approximately the same depth each day, with little variation during the course of the survey. Therefore range-to-fish values were assumed to be consistent and accurate. In 2000, the navigation antenna was placed at the approximate layback position of the towfish, therefore range-to-fish errors were negligible. In all cases, based on the navigation system and towfish configuration, the data are assumed to be accurate to within 20 meters. The interpretation is based on these data and completed at map scales less than 1:10,000.
  3. How accurate are the heights or depths?
  4. Where are the gaps in the data? What is missing?
    This interpretation reflects the complete coverage of the lake floor by the sidescan-sonar imagery.
  5. How consistent are the relationships among the observations, including topology?
    The interpretation was carried out by a single person and is consistent throughout the study area.

How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?
Access_Constraints none
Use_Constraints The interpretation was completed at map scales less than 1:10,000, and is not intended for use smaller map scales. Public domain data from the U.S. Government are freely redistributable with proper metadata and source attribution. Please recognize the U.S. Geological Survey (USGS) as the source of this information.
  1. Who distributes the data set? (Distributor 1 of 1)
    David C. Twichell
    U.S. Geological Survey
    Oceanographer
    Woods Hole Coastal and Marine Science Center
    Woods Hole, MA

    (508) 548-8700 x2266 (voice)
    (508) 457-2310 (FAX)
    dtwichell@usgs.gov
  2. What's the catalog number I need to order this data set? Downloadable Data
  3. What legal disclaimers am I supposed to read?
    Neither the U.S. Government, the Department of the Interior, nor the USGS, nor any of their employees, contractors, or subcontractors, make any warranty, express or implied, nor assume any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, nor represent that its use would not infringe on privately owned rights. The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the USGS in the use of these data or related materials. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
  4. How can I download or order the data?
    • Availability in digital form:
      Data format: The WinZip (version 9.0) file contains the shapefile for the lake floor interpretation, as well as FGDC compliant metadata. in format Shapefile (version ArcGIS 9.2) Size: 0.629
      Network links: http://pubs.usgs.gov/of/2009/1150/gis/interpretation/lakemead_interp.zip
      Media you can order: CD-ROM (Density 650 Mbytes) (format UDF)
    • Cost to order the data: None.

  5. What hardware or software do I need in order to use the data set?
    The user must be capable of uncompressing WinZip files. Once uncompressed, the user must have software capable of displaying ESRI shapefile format.

Who wrote the metadata?

Dates:
Last modified: 18-Mar-2024
Metadata author:
VeeAnn A. Cross
U.S. Geological Survey
Marine Geologist
Woods Hole Coastal and Marine Science Center
Woods Hole, MA

(508) 548-8700 x2251 (voice)
(508) 457-2310 (FAX)
whsc_data_contact@usgs.gov
Contact_Instructions:
The metadata contact email address is a generic address in the event the person is no longer with USGS. (updated on 20240318)
Metadata standard:
FGDC Content Standards for Digital Geospatial Metadata (FGDC-STD-001-1998)
This page is <https://cmgds.marine.usgs.gov/catalog/whcmsc/open_file_report/ofr2009-1150/lakemead_interp.shp.faq.html>
Generated by mp version 2.9.51 on Mon Mar 25 16:05:29 2024