Mapping the floor of Lake Mead (Nevada and Arizona): Preliminary discussion and GIS data release U.S. Geological Survey Open-File Report 03-320 By 1David C. Twichell, 1VeeAnn A. Cross, and 2Stephen D. Belew 1U.S. Geological Survey, Woods Hole, MA 2Bureau of Reclamation, Boulder City, NV Introduction The U.S. Geological Survey in cooperation with the Lake Mead/Mohave Research Institute, University of Nevada, Las Vegas completed a detailed geophysical mapping of the floor of Lake Mead during 1999, 2000, and 2001. The 1999 survey covered the Boulder Basin section of the lake, the 2000 survey focused on the northwestern portion of Las Vegas Bay, and the 2001 survey covered the eastern part of the lake (Fig. 1). Results from these surveys have been presented in several reports (Cross and Twichell, 2003a; 2003b; 2003c; Twichell and others, 1999; 2001); however, here the three data sets have been integrated and are presented as a composite of the entire lake. In this section we provide a brief geologic overview of floor of Lake Mead, and summarize some of the findings that have resulted from these surveys to provide a geologic perspective for the GIS that is the main body of this report. Lake Mead started to fill following the completion of Hoover Dam in 1935, and since then has supplied water to agricultural, industrial, and municipal users. The multiple uses of the lake have led to a high degree of interest in the lake. Although much of the interest is in the quality of water within the lake, there also is interest in the geology of the lake floor. Water managers are interested in the distribution and amount of sediment that has accumulated in the lake since impoundment to understand changes in the holding capacity of the reservoir. For these reasons, this geophysical mapping program was designed to create a near-complete coverage of the lake floor using sidescan-sonar in water depth greater than about 5-10 m, and to map the distribution and thickness of post-impoundment sediment throughout the lake as derived from high-resolution seismic-reflection profiles. The map and data products derived from these datasets are intended to serve as base maps for other geological and geochemical studies of the lake. Getting Started Two Environmental Systems Research Institute (ESRI) ArcView 3.2 Geographic Information System (GIS) project files, data_sa.apr and data_nosa.apr, reside in the top-level directory of this DVD. All associated GIS files are contained within the data directory. The user must have a copy of ESRI ArcView 3.2 in order to view the project files. Visit the ESRI website (http://www.esri.com) for information concerning this, and other software. Each project file contains a startup script that prompts the user for the drive letter of the DVD-ROM drive. This information is needed in order to establish "hotlinks" found within the project file. Extensions: These projects use raster image files compressed with Mr. Sid Geospatial Encoder version 1.4. In order to load and view these files, the MrSid Image Support extension must be loaded. This extension will be loaded by default within both project files. The data_sa.apr utilizes gridded data sets. As such, the Spatial Analyst extension must be loaded in order to view and manipulate these grids. This extension is loaded by default within the data_sa.apr. For users who do not have the Spatial Analyst extension, data_nosa.apr utilizes TIFF or MrSid images of the grid datasets. The necessary extensions will be loaded by default within the project file. Projection: All of the shapefiles are in the Geographic NAD83 coordinate system. Most of the grids and images are available in both the Geographic NAD83 coordinate system, as well as UTM, Zone 11, NAD83 projection. Within the project files, the data loaded into the project views are all in the Geographic NAD83 coordinate system. Hotlinking: The seismic trackline data presented within the project files are "hotlinked" to HTML files containing the interpreted and uninterpreted JPEG images of the seismic reflection profiles. To view these HTML documents, click on the lightning bolt within the project tool bar, and click on an individual trackline within an active trackline theme. The user's default WWW browser will be activated to view the document. System Requirements WWW Browsers: The data and information on this DVD-ROM are formatted for access and download by use of WWW information browsers (e.g., Internet Explorer, Netscape, Opera). Hyperlink references in this report to additional Internet-resident information will not function if your computer is not actively connected to the Internet (WWW) via ISP or online LAN. These web links are functional at publication, but there can be no guarantee that they will not change or be discontinued. The disk has been tested on systems utilizing the following operating systems: Windows 2000/XP, Macintosh and UNIX. GIS: An Environmental Systems Research Institute (ESRI) ArcView 3.2 Geographic Information System (GIS) project files, data_sa.apr and data_nosa.apr, reside in the top-level directory of this DVD. All associated GIS files are contained within the data directory. The user must have a copy of ESRI ArcView 3.2 in order to view the project files. Visit the ESRI website (http://www.esri.com) for information concerning this, and other software. Additionally, the user must also have the ESRI Spatial Analyst extension in order to view the data_sa.apr project file. For those users who do not have ArcView 3.2 or later, the individual GIS data files can still be viewed with a compatible GIS viewer, or a free GIS viewer - ArcExplorer. This GIS data viewer is available from ESRI (http://www.esri.com). Please note that the ArcExplorer software is limited to the Microsoft Windows operating systems and some UNIX operating systems. PDF: A PDF version of the document is available in the htmldocs/pdf directory. PDF versions of the data acquisition logbooks are contained in the data/pdflogs directory. In order to view the files in the PDF format, a free copy of Adobe Acrobat Reader can be downloaded from http://www.adobe.com. ZIP files: This DVD contains several files compressed using the Windows program WINZIP v8.0. For those users who do not have software capable of uncompressing files of this format, software may be obtained from www.winzip.com or www.pkzip.com. DVD Contents Top level directory: disc_acc.htm - This file is the disclaimer for this DVD and describes USGS accessibility requirements. index.htm - This file is intended to be the starting point for the DVD-ROM access. It is written in the Hypertext Markup Language utilized by the World Wide Web (WWW) project and must be opened with a WWW browser. Once opened, the user may browse the DVD-ROM's contents as they would browse pages from the WWW. readme.txt - ASCII text file containing a description of this DVD-ROM. This file may be viewed or printed with any system program capable of opening ASCII text files. data_sa.apr - ArcView project file created with ArcView 3.2a on a Windows2000 computer. This ArcView project contains grids and requires the ArcView extension Spatial Analyst. data_nosa.apr - ArcView project file created with ArcView 3.2a on a Windows2000 computer. This ArcView project uses TIFF or MrSid images with associated world files instead of ESRI formatted grids. This removes the dependency on the Spatial Analyst extension such that any user with ArcView version 3.2 or a later version can view the project. Directories: Directory data - What follows is a brief description of the data contained in the underlying directories. For a more complete description of the data, refer to the metadata associated with each data file. This directory contains the following directories: bounds - contains basic boundary files of the study area including the lake bounds, extent of post-impoundment sediment, and the paleo-thalweg of the Colorado River. doq - contains mosaicked DOQ images of the study area downsampled to 4m/pixel. These images are available in Mr. Sid image format, in both geographic and UTM, Zone 11, NAD83 coordinate systems. htmlseis - html documents containing the uninterpreted and interpreted seismic reflection profiles for all the seismic reflection profiles collected as a part of this study. The data are separated by collection year in the following subdirectories: 1999, 2000, and 2001. isopach - contains the isopach (sediment thickness) data from Lake Mead in both grid and TIFF image format. nav - contains navigation separated by year of collection in the following subdirectories: 1999, 2000, and 2001. pdflogs - contains the PDF versions of the field logbooks maintained during each year of data collection. The logbooks are stored in the following subdirectories based on year of collection: 1999, 2000, and 2001. seisimages - contains JPEG images of all the seismic reflection profiles (both uninterpreted and interpreted) collected as a part of this study. The data are stored in the following subdirectories based on year of collection: 1999, 2000, and 2001. sscanimgs - contains sidescan-sonar mosaics. The initial directory division is based upon projection: geographic or UTM, Zone 11, NAD83. Each of the directories contains enhanced and unehenhanced mosaics in Mr. Sid and TIFF formats. The mosaics are divided into 5 areas so that the final mosaic is not unmanageably large. Las Vegas Wash is mapped at 1 m/pixel, while the remaining mosaics are 2 m/pixel. In the eastern portion of the lake (east of Boulder Canyon), one set of enhanced images attempts to tone-match the mosaics. These files reside in data/sscanimgs/utm11/dctenh. surfaces - contains grids and images (TIFF and Mr. Sid formats) representing the present day surface of the study area. These data combine the on land DEM with the lakefloor bathymetry. This data are stored in the following subdirectories: utm11 and geographic. Directory htmldocs: contains the HTML pages accessed within this Open-File Report (excluding the seismic HTML pages accessible from the ArcView projects). This directory contains the following subdirectories: icons - contains all the images files and icons utilized in constructing the Open-File Report HTML pages. pdf - contains the PDF version of the Open-File Report. This PDF document does not maintain all the links found on the GIS metadata and data catalog page. Directory metadata: contains the HTML and ASCII text versions of the metadata files for all the data contained in this Open-File Report. This directory has the following subdirectories: bounds, doq, htmlseis, isopach, nav, pdflogs, seisimages, sscanimgs, and surfaces. References: Barry, R.M., Cavers, D.A., and Kneale, C.W., 1975, Recommended standards for digital tape formats, Geophysics, v. 40, p. 344-352. Cross, V.A., and Twichell, D.C., 2003a, Archive of seismic-reflection data collected during USGS cruise Lake Mead 01007 in Lake Mead - Nevada and Arizona, 1-28 April, 2001: U.S. Geological Survey Open-File Report 02-478 - 1 DVD-ROM. Cross, V.A., and Twichell, D.C., 2003b, Archive of seismic-reflection data collected during USGS cruise Lake Mead 99014 in Lake Mead - Nevada and Arizona, 14-25 May, 1999: U.S. Geological Survey Open-File Report 03-3 - 1 DVD-ROM. Cross, V.A., and Twichell, D.C., 2003c, Archive of seismic-reflection data collected during USGS cruise Lake Mead 00027 in Lake Mead - Nevada, 1-6 June, 2000: U.S. Geological Survey Open-File Report 03-4 - 1 DVD-ROM. Danforth, W.W., O'Brien, T.F., Schwab, W.C., 1991, USGS image processing system: near realtime mosaicking of high resolution sidescan-sonar data: Sea Technology, Jan. 1991, p. 54-59. Gould, H.R., 1951, Some quantitative aspects of Lake Mead turbidity currents: SEPM Special Publication 2, p. 34-52. Gould, H.R., 1960a, Character of the accumulated sediment: in Smith, W.O., Vetter, C.P., and Cummings, G.B., eds., 1960, Comprehensive survey of sedimentation in Lake Mead, 1948-1949, US Geological Survey Professional Paper 295, p 149-186. Leifson, G., 1960, Survey of the lake: in Smith, W.O., Vetter, C.P., and Cummings, G.B., eds., 1960, Comprehensive survey of sedimentation in Lake Mead, 1948-1949, US Geological Survey Professional Paper 295, p.39-102. Longwell, C.R., 1936, Geology of the Boulder Reservoir floor: Geological Society of America Bulletin, v. 47, p. 1393-1476. Longwell, C.R., 1960, Geologic setting of Lake Mead: in Smith, W.O., Vetter, C.P., and Cummings, G.B., eds., 1960, Comprehensive survey of sedimentation in Lake Mead, 1948-1949, US Geological Survey Professional Paper 295, p. 11-20. Paskevich, V.F., 1992, Digital mapping of sidescan sonar data with the Woods Hole Image Processing System software: U.S. Geological Survey Open-File Report 92-536, 87 p. Paskevich, V.F., 1996, MAPIT: An improved method for mapping digital sidescan sonar data using the Woods Hole Image Processing System (WHIPS) Software: U.S. Geological Survey Open-File Report 96-281, 73 p. Smith, W.O., Vetter, C.P., and Cummings, G.B. (eds.), 1960, Comprehensive survey of sedimentation in Lake Mead, 1948-1949: US Geological Survey Professional Paper 295, 254 p. Twichell, D.C., Cross, V.A., Rudin, M. and Parolski, K.F., 1999, 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: U.S. Geological Survey Open-File Report 99-581, 27 p (ONLINE - http://pubs.usgs.gov/openfile/of99-581/). Twichell, D.C., Cross, V.A., Rudin, M.J., and Parolski, K.F., 2001, Surficial geology and distribution of postimpoundment sediment in Las Vegas Bay, Lake Mead: U.S. Geological Survey Open-File Report 01-70, 27 p (ONLINE - http://pubs.usgs.gov/openfile/of01-070/). Twichell, D.C., Cross, V.A., and Rudin, M., 2002, Mapping turbidites in Lake Mead from source to sink: American Association of Petroleum Geologists Abstracts with Programs, v. 11, p. A179-A180. Twichell, D.C., Cross, V., Buck, B., Hanson, A., Hickson, T., Rudin, M., and Zybala, J., 2003, Seismic architecture of turbidites in Lake Mead: American Association of Petroleum Geologists Abstracts with Programs, v. 12, p. A173. Disclaimer This Compact Disc-Read Only Memory (DVD-ROM) publication was prepared by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, make any warranty, expressed or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed in this report, or represents that its use would not infringe privately owned rights. Reference therein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. Any views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. Although all data published on this DVD-ROM have been used by the USGS, no warranty, expressed or implied, is made by the USGS as to the accuracy of the data and related materials and/or the functioning of the software. The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the USGS in the use of this data, software, or related materials. Contact Information: David C. Twichell U.S. Geological Survey 384 Woods Hole Rd. Woods Hole, MA 02543-1598 508-548-8700 x2266 dtwichell@usgs.gov VeeAnn A. Cross U.S. Geological Survey 384 Woods Hole Rd. Woods Hole, MA 02543-1598 508-548-8700 x2251 vatnipp@usgs.gov Stephen D. Belew Bureau of Reclamation P.O. Box 61470 Boulder City, NV 89006-1470 702-292-8150 sbelew@lc.usbr.gov