Results for “Surveying and Mapping” — Page 43

USGS2020

Seismic evaluation of shallow-depth structure, faulting, and groundwater variations across the Dos Palmas Preserve, Riverside County, California

Introduction Dos Palmas Preserve is a Colorado Desert oasis and wetland in Riverside County, California, located near the base of the Orocopia Mountains and northeast of the Salton Sea. The original source of water for the oasis was artesian springs that developed at the base of the Orocopia Mountains, but more abundant water supplies were later provided to Dos Palmas Preserve when the Coachella Canal was built and water seeped from unlined parts of the canal. As a result of this abundant water supply in a desert setting, Dos Palmas Preserve, managed by the Bureau of Land Management, is now a wildlife preserve that became home to multiple plants, fowl, insects, rodents, reptiles, and bats, including some endangered and threatened species. More recently, sections of the Coachella Canal have been lined, resulting in a reduction of water seepage and threatening the sustainability of parts of Dos Palmas Preserve. Faults usually act as barriers to groundwater flow and Dos Palmas Preserve is only a few kilometers from the active trace of the San Andreas Fault, where splays of the fault trend through the area. Additionally, numerous closely spaced faults that have been mapped at the surface northwest of Dos Palmas Preserve are believed to extend southward into the Dos Palmas Preserve, where they are covered by alluvium. Thus, evaluation of the subsurface lithology and structure is needed to determine how the current allocation of water from the Coachella Canal affects various parts of Dos Palmas Preserve. To better understand the distribution of the shallow lithology, faulting, and groundwater in Dos Palmas Preserve, the U.S. Geological Survey, in collaboration with the Bureau of Land Management, conducted a seismic survey across the northern part of Dos Palmas Preserve. The seismic survey was designed to “map” the upper part of the aquifer system and to more precisely locate faults that may affect groundwater flow in Dos Palmas Preserve. In this report, we present seismic velocity and reflection images of the shallow subsurface and relate those images to interpretative structures and stratigraphy that may affect groundwater at Dos Palmas Preserve.

California↗

USGS2006

Digital single-channel seismic-reflection data from western Santa Monica basin

During a collaborative project in 1992, Geological Survey of Canada and United States Geological Survey scientists obtained about 850 line-km of high-quality single-channel boomer and sleeve-gun seismic-reflection profiles across Hueneme, Mugu and Dume submarine fans, Santa Monica Basin, off southern California. The goals of this work were to better understand the processes that lead to the formation of sandy submarine fans and the role of sea-level changes in controlling fan development. This report includes a trackline map of the area surveyed, as well as images of the sleeve-gun profiles and the opportunity to download both images and digital data files (SEG-Y) of all the sleeve-gun profiles.

Open-File Report↗

USGS2011

Challenges of using electrical resistivity method to locate karst conduits-A field case in the Inner Bluegrass Region, Kentucky

Conduits serve as major pathways for groundwater flow in karst aquifers. Locating them from the surface, however, is one of the most challenging tasks in karst research. Geophysical methods are often deployed to help locate voids by mapping variations of physical properties of the subsurface. Conduits can cause significant contrasts of some physical properties that can be detected; other subsurface features such as water-bearing fractures often yield similar contrasts, which are difficult to distinguish from the effects of the conduits. This study used electrical resistivity method to search for an unmapped karst conduit that recharges Royal Spring in the Inner Bluegrass karst region, Kentucky, USA. Three types of resistivity techniques (surface 2D survey, quasi-3D survey, and time-lapse survey) were used to map and characterize resistivity anomalies. Some of the major anomalies were selected as drilling targets to verify the existence of the conduits. Drilling near an anomaly identified by an electrical resistivity profile resulted in successful penetration of a major water-filled conduit. The drilling results also suggest that, in this study area, low resistivity anomalies in general are associated with water-bearing features. However, differences in the anomaly signals between the water-filled conduit and other water-bearing features such as water-filled fracture zones were undistinguishable. The electrical resistivity method is useful in conduit detection by providing potential drilling targets. Knowledge of geology and hydrogeology about the site and professional judgment also played important roles in locating the major conduit. ?? 2011 Elsevier B.V.

Journal of Applied Geophysics↗

USGS1993

Map showing depth to basement in the deep-sea basins of the Pacific continental margin, Cape Mendocino to Point Conception

The U.S. Geological Survey conducted a series of cruises, EEZSCAN 84 (EEZ-SCAN 84 Scientific Staff, 1986), to collect reconnaissance data on the newly proclaimed Exclusive Economic Zone (EEZ), the area out to 200 nautical miles from the coastline of the United States. The cruises systematically surveyed the entire conterminous United States west coast EEZ using the Geological Long-Range Inclined Asdic (GLORIA) side-scan sonar, a 160-in 3 airgun seismic-reflection profiler, a 3.5-kHz high-resolution seismic-reflection profiler, a 10-kHz echo sounder, and a proton-precession magnetometer. The nominal trackline spacing throughout the survey was 30 km. Derivative maps of sediment thickness (I-2089-A, I-2090-A, I-2091-A) and depth to basement (I-2089-B, I-2090-B, I-2091-B) in the basins of the west coast EEZ were compiled from both the sonar-image dala and the deep-penetration seismic data obtained on these cruises. Only EEZ-SCAN 84 data were used for the map compilations because available data from other cruises in this region are sparsely located, have poor navigational control, or were obtained with seismic systems that were not powerful enough to resolve oceanic basement. For this map series, sediment thickness and depth to basement were determined only in the deep-ocean basin regions because the seismic system used on the EEZ-SCAN 84 cruises could not resolve oceanic basement beneath the thick sediments of the continental slope. All the data used to compile the maps are presented in the "Atlas of the Exclusive Economic Zone, Western Conterminous United States" (EEZ-SCAN 84 Scientific Staff, 1986). Basement Outcrops GLORIA imagery was used to locate areas of basement outcrop throughout the region. Where possible, sediment thickness on and immediately adjacent to basement outcrops was measured from seismic data. Where there was no bathymetric or seismic control, a seamount peak was assumed to have no sediment cover. A pattern is used on the map to indicate all basement outcrops. Data Reduction Acoustic basement in the basins, invariably oceanic Layer 2, was observed on all of the seismic records. One-way traveltime was measured from the sea floor to acoustic basement. Because the trackline spacing of about 30 km is relatively large compared to the data density along track, we chose to measure the sediment thickness every 0.5 hour or at an interval of approximately 7.5 km. Water depth was measured with a 10-kHz profiler. Depth to basement was calculated using the sea surface as the zero datum and adding the corrected water depth (Carter, 1980) to the sediment thickness. Acoustic travel times were converted to depths by first calculating a regression equation from the interval velocity versus depth data of Connard and others (1984). Their data base comprises a compilation of all available Deep Sea Drilling Project data plus wide-angle refraction data, which were collected in Cascadia Basin west of Oregon and represents the best data set available for the United States west coast EEZ. The regression equation was integrated to determine sediment thickness as a function of one-way traveltime . The resulting equation is z = 1400t + 0 .5t 2 where z is sediment thickness in meters, and t is one-way traveltime in seconds. Sediment thicknesses calculated using this equation were compared to values calculated from the general equation of Carlson and others (1986). Values for sediment thickness calculated by the two equations differed by no greater than 10 percent throughout the range of travel times. Bathymetry The bathymetry is from Chase and others (1981). The bathymetric data were compiled from a variety of sources, and data quality is inconsistent. Because of differences in navigational precision and density of coverage, the bathymetric contours of a feature may be at a different location than the corresponding isopleths derived from the EEZ-SCAN 84 data, or a feature may not be indicated on the bathymetry at all. These situations occur because either the feature is poorly located in the bathymetric data set or, especially in the outer EEZ, the bathymetric data are too sparse to have defined the existence of a feature. Acknowledgments Topographic digital data bases were corrected and verified by Christina Lief. Gerald Evenden developed the computer software system MAPGEN, used to compose this map. Reviews, suggestions, and technical contributions from Edward C. Escowitz and Florence Wong and advice about cartographic design from Will Stettner substantially improved the quality of this map. References Cited Carlson, R.L., Gangi, A.F., and Snow, K.R., 1986, Empirical reflection-traveltime/ depth and velocity/depth functions for the deep-sea sediment column: Journal of Geophysical Research, v. 91, no. B8, p. 8249-8266. Carter, D.J.T., 1980, Echo-sounding correction tables: Taunton, United Kingdom, Hydrographic Department, Ministry of Defence, 150 p. Chase, T.E., Wilde, Pat, Normark, W.R, Miller, C.P., Seekins, B.A., and Young, J.D., 1981, Offshore topography of the Western United States between 32° and 49° North latitudes: U.S. Geological Survey Open-File Report 81-443, scale 1:864,518 at 38° latitude, 2 sheets. Connard, G., Couch, R., Keeling , K., Roy, J., and Troseth, S., 1984, Abyssal plain and continental net-objective sedimentary thicknesses, in Kulm, L.D., and others, eds., Western North America continental margin and adjacent ocean floor off Oregon and Washington, Atlas 1 of Regional Atlas Series, Ocean Margin Drilling Program: Woods Hole, Mass., Marine Science International, sheet 7. EEZ-SCAN 84 Scientific Staff, 1986, Atlas of the Exclusive Economic Zone, Western Conterminous United States: U.S. Geological Survey Miscellaneous Investigations Series I-1792, scale 1:500,000, 152 p. See Also "U.S. Pacific West Coast Field Activities" (Paskevich and others, 2011; http://pubs.usgs.gov/of/2010/1332/htmldocs/pc/pc_overview.html). Paskevich, V.F., Wong, F.L., O?Malley, J.J., Stevenson, A.J., and Gutmacher, C.E., 2011, GLORIA sidescan-sonar imagery for parts of the U.S. Exclusive Economic Zone and adjacent areas: U.S. Geological Survey Open-File Report 2010?1332, available at http://pubs.usgs.gov/of/2010/1332/.

IMAP↗

USGS2006

Map showing geology, oil and gas fields, and geologic provinces of the Gulf of Mexico region

This map was created as part of a worldwide series of geologic maps for the U.S. Geological Survey’s World Energy Project, available on CD-ROM and through the Internet. The goal of the project is to assess the undiscovered, technically recoverable oil and gas resources of the world. Geologic provinces were created for ranking purposes in the World Petroleum Assessment 2000 (U.S. Geological Survey World Energy Assessment Team, 2000). A modified subset of these provinces are shown on the map, based on new bathymetric data and geologic knowledge. Geologic province boundaries are not intended to be taken for country boundaries or exclusive economic zone (EEZ) boundaries. The USGS World Petroleum Assessment 2000 - Description and Results can be found online at: http://pubs.usgs.gov/dds/dds-060 . Oil and gas fields are represented by a single geographic point in the center of the field and displays field type (oil or gas) only. The map includes three surface geology datasets, which were modified for display purposes.

Open-File Report↗

USGS2020

A system design for implementing advanced feature descriptions for a map knowledge base

A prototype system to explore Linked Data that semantically integrates geospatial data in various formats from different publication sources with data from The National Map of the U.S. Geological Survey is presented. The focus is on accessing advanced feature descriptions for data from The National Map with data coreferenced from other sources. The prototype uses Geoserver to access The National Map data, which are converted to Resource Description Framework triples using Karma and stored in the Marmotta triplestore. Marmotta uses a Postgres relational database as a backend for the project and queries to the Marmotta triplestore are converted to structured query language and executed by Postgres. Triples retrieved are linked with same_as relationships to external data sources. The links to these sources provide additional attributes and relationships of the data from The National Map. Visualization of the results is provided using Leaflet and workflows for all parts of the system are defined. A use case for the system is provided to access structures and names information from The National Map for the Washington, D.C., area and link these to Geonames data, with visualization of the graphical and tabular results.

Scientific Investigations Report↗

USGS2015

Potential application of radiogenic isotopes and geophysical methods to understand the hydrothermal dystem of the Upper Geyser Basin, Yellowstone National Park

Numerous geochemical and geophysical studies have been conducted at Yellowstone National Park to better understand the hydrogeologic processes supporting the thermal features of the Park. This report provides the first 87Sr/86Sr and 234U/238U data for thermal water from the Upper Geyser Basin (UGB) intended to evaluate whether heavy radiogenic isotopes might provide insight to sources of groundwater supply and how they interact over time and space. In addition, this report summarizes previous geophysical studies made at Yellowstone National Park and provides suggestions for applying non-invasive ground and airborne studies to better understand groundwater flow in the subsurface of the UGB. Multiple samples from Old Faithful, Aurum, Grand, Oblong, and Daisy geysers characterized previously for major-ion concentrations and isotopes of water (δ2H, δ18O, and 3H) were analyzed for Sr and U isotopes. Concentrations of dissolved Sr and U are low (4.3–128 ng g-1 Sr and 0.026–0.0008 ng g-1 U); consequently only 87Sr/86Sr data are reported for most samples. Values of 87Sr/86Sr for most geysers remained uniform between April and September 2007, but show large increases in all five geysers between late October 2007 and early April, 2008. By late summer of 2008, 87Sr/86Sr values returned to values similar to those observed a year earlier. Similar patterns are not present in major-ion data measured on the same samples. Furthermore, large geochemical differences documented between geysers are not observed in 87Sr/86Sr data, although smaller differences between sites may be present. Sr-isotope data are consistent with a stratified hydrologic system where water erupted in spring and summer of 2007 and summer of 2008 equilibrated with local intracaldera rhyolite flows at shallower depths. Water erupted between October 2007 and April 2008 includes greater amounts of groundwater that circulated deep enough to acquire a radiogenic 87Sr/86Sr, most likely from Archean basement rocks. Details of how the shallow and deep components interact and mechanisms causing these interactions remain unknown, but the data demonstrate the usefulness of obtaining Sr-isotope data from future sample campaigns. Geophysical methods that would be useful for characterization of the UGB subsurface properties and geothermal system include electromagnetic (EM), gravity, and ambient seismic. A suite of ground-based EM methods could be used in a synergistic combination together with airborne EM surveys to provide data for a range of spatial scales and resolutions. Existing thermal data for the shallow subsurface could be used to relate ground and airborne EM survey data to locations of geothermal fluids near the surface. Gravity surveys would be useful for mapping subsurface density anomalies and possibly monitoring changes in degree of saturation with groundwater. Ambient seismic surveys would be useful for estimating the thickness of unconsolidated deposits that contain the shallow groundwater system. A study that combines radiogenic isotope tracers with geophysical methods has the potential to better characterize the geothermal workings in the UGB. Insights gained could lead to a better understanding of the geothermal system and how Park infrastructure may cause perturbations. Measurements of radiogenic isotopes from multiple geysers and pools in localized areas within the UGB that are coupled with data from geophysical surveys would help refine conceptual models of mixing between deep- and shallow-derived subsurface fluids.

Wyoming↗

USGS2021

Elevation and elevation-change maps of Fountain Creek, southeastern Colorado, 2015-20

The U.S. Geological Survey, in cooperation with Colorado Springs Utilities, has collected topographic data annually since 2012 at 10 study areas along Fountain Creek, southeastern Colorado. The 10 study areas were located between Colorado Springs and the terminus of Fountain Creek at the Arkansas River in Pueblo. The purpose of this report is to present elevation maps based on topographic surveys collected in 2020 and to present maps of elevation change that occurred between 2015 and 2020 at all 10 study areas. Elevation and elevation-change maps were developed in Global Mapper, R, and ArcGIS from topographic surveys collected at each study area during the winters of 2015 and 2020. Topographic surveys in 2015 were completed using real-time kinematic Global Navigation Satellite Systems. Topographic surveys in 2020 were completed using both real-time kinematic Global Navigation Satellite Systems and light detection and ranging. Elevation-change maps were created using propagated uncertainties associated with the 95-percent confidence limit. Study areas along Fountain Creek underwent a range of geomorphic responses between 2015 and 2020 that were often related to the dominant channel planform pattern of the study area. The results of this ongoing monitoring effort can be used to assess long-term changes in land-surface elevation and to advance understanding of the geomorphic response to possible changes in flow conditions on Fountain Creek.

Colorado↗

USGS2003

Location and age database for selected foraminifer samples collected by Exxon Petroleum geologists in California

Most of the geologic maps published for central California before 1960 were made without the benefit of age determinations from microfossils. The ages of Cretaceous and Tertiary rocks in the mostly poorly exposed and structurally complex sedimentary rocks represented in the Coast Ranges are critical in determining stratigraphic succession or lack of it, and in determining whether the juxtaposition of similar appearing but different age formations means a fault is present. Since the 1930’s, at least, oil company geologists have used microfossils to assist them in geologic mapping and in determining the environments of deposition of the sediment containing the microfossils. This information has been so confidential that some companies even coded the names of foraminifers to prevent disclosure. In the past 20 years, however, the attitude of petroleum companies about this information has changed, and many of the formerly confidential materials and reports are now available. We report here on 1,964 Exxon foraminifer samples mostly from surface localities in the San Francisco Bay region, and elsewhere in California. Most but not all the samples were plotted on U. S. Geological Survey (USGS) 7.5’ topographic maps or on obsolete USGS 15’ maps. The information from the slides can be used to update geologic maps prepared without the benefit of microfossil data, to analyze the depth and temperature of ocean water covering parts of California during the Mesozoic and Cenozoic Eras, and for solving nomenclature and other scientific problems. A similar report on more than 30,000 slides for surface samples collected by Chevron geologists has been released (Brabb and Parker, 2003), and another report provides information on slides for more than 2000 oil test wells in Northern California (Brabb, Powell, and Brocher, 2001).

California↗

USGS2020

Assessing geohazards to the Denali National Park road with geologic mapping

Denali National Park (DENA) is home to iconic and breathtaking landscapes surrounding the tallest mountain range in North America, the Alaska Range. The park, which covers 6 million acres, is a major draw for tourism and recreation, making it an important economic engine for central Alaska. However, the geologic forces that created the beautiful, steep landscape of DENA also make it prone to geologic hazards (geohazards) like landslides, debris flows, and earthquakes. DENA has only one major road, called the Park Road, that serves nearly all of its infrastructure. The success of DENA as a visitor destination, an economic engine, and a safe environment for visitors, residents, and staff relies on the resilience of this road, making it a major transportation lifeline for the region. Since 2017, the National Park Service and the U.S. Geological Survey National Cooperative Geologic Mapping Program have partnered to produce a new high-resolution geologic map of the Park Road corridor to identify and address ongoing geohazards affecting DENA infrastructure. In the area of Polychrome Overlook, this map is being used to guide a new route for the Park Road around an area of landslide-prone slopes, where ongoing slumping is costing National Park Service millions of dollars in annual road maintenance costs. Beyond this area, the map serves as a park resource to assess geohazard risk in future infrastructure and management decisions. Geologic mapping is also fueling new research in understanding the geologic and tectonic history of DENA, while training a new generation of geologic mappers through the USGS EDMAP program.

Alaksa↗

USGS1989

Alaska Interim Land Cover Mapping Program; final report

In 1985, the U.S. Geological Survey initiated a research project to develop an interim land cover data base for Alaska as an alternative to the nationwide Land Use and Land Cover Mapping Program. The Alaska Interim Land Cover Mapping Program was subsequently created to develop methods for producing a series of land cover maps that utilized the existing Landsat digital land cover classifications produced by and for the major land management agencies for mapping the vegetation of Alaska. The program was successful in producing digital land cover classifications and statistical summaries using a common statewide classification and in reformatting these data to produce l:250,000-scale quadrangle-based maps directly from the Scitex laser plotter. A Federal and State agency review of these products found considerable user support for the maps. Presently the Geological Survey is committed to digital processing of six to eight quadrangles each year.

Open-File Report↗

USGS1998

Combining satellite data with ancillary data to produce a refined land-use/land-cover map

As part of the U.S. Geological Survey's National Water-Quality Assessment Program in the Western Lake Michigan Drainages Study Unit, a current map of land use and land cover is needed to gain a better understanding of how land use and land cover may influence water quality. Satellite data from the Landsat Thematic Mapper provides a means to map and measure the type and amount of various land-cover types across the Study Unit and can be easily updated as changes occur in the landscape or in water quality. Translating these land cover categories to land use, however, requires the use of other thematic maps or ancillary data layers, such as wetland inventories, population data, or road networks. This report describes a process of (1) using satellite imagery to produce a land-cover map for the Fox/Wolf River basin, a portion of the Western Lake Michigan Drainages NAWQA Study Unit and (2) improving the satellite-derived land-cover map by using other thematic maps. The multiple data layers are processed in a geographic information system (GIS), and the combination provides more information than individual sources alone.

Michigan, Wisconsin↗

USGS1998

High-resolution multibeam bathymetry of East and West Flower Gardens and Stetson Banks, Gulf of Mexico

The 1990s have seen rapid advances in seafloor mapping technology. Multibeam sonars are now capable of mapping a wide range of water depths with beams as narrow as 1°, and provide up to a 150° swath. When these multibeam sonars are coupled with an extremely accurate vehicle motion sensor and very precise navigation, they are capable of producing unprecedented images of the seafloor. This technology was used in December 1997 to map the East and West Flower Gardens and Stetson Banks, Gulf of Mexico. The results from this survey provide the most accurate maps of these areas yet produced and reveal features at submeter resolution never mapped in these areas before. The digital data provide a database that should become the fundamental base maps for all subsequent work in this recently established National Marine Sanctuary.

Gulf of Mexico Science↗

USGS2000

Geologic map database of the El Mirage Lake area, San Bernardino and Los Angeles Counties, California

This geologic map database for the El Mirage Lake area describes geologic materials for the dry lake, parts of the adjacent Shadow Mountains and Adobe Mountain, and much of the piedmont extending south from the lake upward toward the San Gabriel Mountains. This area lies within the western Mojave Desert of San Bernardino and Los Angeles Counties, southeastern California. The area is traversed by a few paved highways that service the community of El Mirage, and by numerous dirt roads that lead to outlying properties. An off-highway vehicle area established by the Bureau of Land Management encompasses the dry lake and much of the land north and east of the lake. The physiography of the area consists of the dry lake, flanking mud and sand flats and alluvial piedmonts, and a few sharp craggy mountains. This digital geologic map database, intended for use at 1:24,000-scale, describes and portrays the rock units and surficial deposits of the El Mirage Lake area. The map database was prepared to aid in a water-resource assessment of the area by providing surface geologic information with which deepergroundwater-bearing units may be understood. The area mapped covers the Shadow Mountains SE and parts of the Shadow Mountains, Adobe Mountain, and El Mirage 7.5-minute quadrangles. The map includes detailed geology of surface and bedrock deposits, which represent a significant update from previous bedrock geologic maps by Dibblee (1960) and Troxel and Gunderson (1970), and the surficial geologic map of Ponti and Burke (1980); it incorporates a fringe of the detailed bedrock mapping in the Shadow Mountains by Martin (1992). The map data were assembled as a digital database using ARC/INFO to enable wider applications than traditional paper-product geologic maps and to provide for efficient meshing with other digital data bases prepared by the U.S. Geological Survey's Southern California Areal Mapping Project.

California↗

USGS2020

Elevation and elevation-change maps of Fountain Creek, southeastern Colorado, 2015–19

The U.S. Geological Survey, in cooperation with Colorado Springs Utilities, has been collecting topographic data at 10 study areas along Fountain Creek, Colorado, annually since 2012. The 10 study areas are located between Colorado Springs and the terminus of Fountain Creek at the Arkansas River in Pueblo. The purpose of this report is to present elevation maps based on topographic surveys collected in 2015 and 2019 and to present maps of elevation change that occurred between 2015 and 2019 at all 10 study areas. Elevation and elevation-change maps were developed in ArcGIS from topographic surveys collected at each study area using real-time kinematic Global Navigation Satellite Systems during the winter months (January through April) of 2015 and 2019. Elevation-change maps were created using statistically defined minimum levels of change detection asso-ciated with the 68-percent confidence limit and the 95-percent confidence limit. Study areas along Fountain Creek underwent a range of geomorphic responses between 2015 and 2019 that often depended on the dominant channel pattern of the study area. The results of this ongoing monitoring effort can be used to assess long-term changes in land-surface elevation and to advance understanding of the geomorphic response to possible alterations in flow conditions on Fountain Creek.

Colorado↗

USGS1971

Mapping from space

Remote sensing of the earth promises to become an operational tool of the engineer and the scientist within the next few years. There are no real technical limits on the uses of data from space sensors. However, it is not practical to fly special missions, particularly in space, for each specific use. General-purpose, earth-sensing missions aimed at meeting a wide variety of requirements must be defined. Engineers must help define earth-sensing missions, based on the concepts of repetitive coverage, multispectral response, and spatial correlation.

Journal of the Surveying and Mapping Division↗

USGS2002

Fifty-year flood-inundation maps for La Lima, Honduras

After the devastating floods caused by Hurricane Mitch in 1998, maps of the areas and depths of the 50-year-flood inundation at 15 municipalities in Honduras were prepared as a tool for agencies involved in reconstruction and planning. This report, which is one in a series of 15, presents maps of areas in the municipality of La Lima that would be inundated by Rio Chamelecon with a discharge of 500 cubic meters per second, the approximate capacity of the river channel through the city of La Lima. The 50-year flood (2,400 cubic meters per second), the original design flow to be mapped, would inundate the entire area surveyed for this municipality. Because water-surface elevations of the 50-year flood could not be mapped properly without substantially expanding the area of the survey, the available data were used instead to estimate the channel capacity of Rio Chamelecon in La Lima by trial-and-error runs of different flows in a numerical model and to estimate the increase in height of levees needed to contain flows of 1,000 and 2,400 cubic meters per second. Geographic Information System (GIS) coverages of the flood inundation are available on a computer in the municipality of La Lima as part of the Municipal GIS project and on the Internet at the Flood Hazard Mapping Web page (http://mitchnts1.cr.usgs.gov/projects/floodhazard.html). These coverages allow users to view the flood inundation in much more detail than is possible using the maps in this report. Water-surface elevations for various discharges on Rio Chamelecon at La Lima were determined using HEC-RAS, a one-dimensional, steady-flow, step-backwater computer program. The channel and floodplain cross sections used in HEC-RAS were developed from an airborne light-detection-and-ranging (LIDAR) topographic survey of the area and ground surveys at three bridges. Top-of-levee or top-of-channel-bank elevations and locations at the cross sections were critical to estimating the channel capacity of Rio Chamelecon. These elevations and locations are provided along with the water-surface elevations for the 500-cubic-meter-per-second flow of Rio Chamelecon. Also, water-surface elevations of the 1,000 and 2,400 cubic-meter-per-second flows are provided, assuming that the existing levees are raised to contained the flows.

La Lima↗

USGS1993

Map showing sediment isopachs in the deep-sea basins of the Pacific Continental Margin, Strait of Juan de Fuca to Cape Mendocino

The U.S. Geological Survey conducted a series of cruises, EEZSCAN 84 (EEZ-SCAN 84 Scientific Staff, 1986), to collect reconnaissance data on the newly proclaimed Exclusive Economic Zone (EEZ), the area out to 200 nautical miles from the coastline of the United States. The cruises systematically surveyed the entire conterminous United States west coast EEZ using the Geological Long-Range Inclined Asdic (GLORIA) side-scan sonar, a 160-in 3 airgun seismic-reflection profiler, a 3.5-kHz high-resolution seismic-reflection profiler, a 10-kHz echo sounder, and a proton-precession magnetometer. The nominal trackline spacing throughout the survey was 30 km. Derivative maps of sediment thickness (I-2089-A, I-2090-A, I-2091-A) and depth to basement (I-2089-B, I-2090-B, I-2091-B) in the basins of the west coast EEZ were compiled from both the sonar-image dala and the deep-penetration seismic data obtained on these cruises. Only EEZ-SCAN 84 data were used for the map compilations because available data from other cruises in this region are sparsely located, have poor navigational control, or were obtained with seismic systems that were not powerful enough to resolve oceanic basement. For this map series, sediment thickness and depth to basement were determined only in the deep-ocean basin regions because the seismic system used on the EEZ-SCAN 84 cruises could not resolve oceanic basement beneath the thick sediments of the continental slope. All the data used to compile the maps are presented in the "Atlas of the Exclusive Economic Zone, Western Conterminous United States" (EEZ-SCAN 84 Scientific Staff, 1986). Basement Outcrops GLORIA imagery was used to locate areas of basement outcrop throughout the region. Where possible, sediment thickness on and immediately adjacent to basement outcrops was measured from seismic data. Where there was no bathymetric or seismic control, a seamount peak was assumed to have no sediment cover. A pattern is used on the map to indicate all basement outcrops. Data Reduction Acoustic basement in the basins, invariably oceanic Layer 2, was observed on all of the seismic records. One-way traveltime was measured from the sea floor to acoustic basement. Because the trackline spacing of about 30 km is relatively large compared to the data density along track, we chose to measure the sediment thickness every 0.5 hour or at an interval of approximately 7.5 km. Water depth was measured with a 10-kHz profiler. Depth to basement was calculated using the sea surface as the zero datum and adding the corrected water depth (Carter, 1980) to the sediment thickness. Acoustic travel times were converted to depths by first calculating a regression equation from the interval velocity versus depth data of Connard and others (1984). Their data base comprises a compilation of all available Deep Sea Drilling Project data plus wide-angle refraction data, which were collected in Cascadia Basin west of Oregon and represents the best data set available for the United States west coast EEZ. The regression equation was integrated to determine sediment thickness as a function of one-way traveltime . The resulting equation is z = 1400t + 0 .5t 2 where z is sediment thickness in meters, and t is one-way traveltime in seconds. Sediment thicknesses calculated using this equation were compared to values calculated from the general equation of Carlson and others (1986). Values for sediment thickness calculated by the two equations differed by no greater than 10 percent throughout the range of travel times. Bathymetry The bathymetry is from Chase and others (1981). The bathymetric data were compiled from a variety of sources, and data quality is inconsistent. Because of differences in navigational precision and density of coverage, the bathymetric contours of a feature may be at a different location than the corresponding isopleths derived from the EEZ-SCAN 84 data, or a feature may not be indicated on the bathymetry at all. These situations occur because either the feature is poorly located in the bathymetric data set or, especially in the outer EEZ, the bathymetric data are too sparse to have defined the existence of a feature. Acknowledgments Topographic digital data bases were corrected and verified by Christina Lief. Gerald Evenden developed the computer software system MAPGEN, used to compose this map. Reviews, suggestions, and technical contributions from Edward C. Escowitz and Florence Wong and advice about cartographic design from Will Stettner substantially improved the quality of this map. References Cited Carlson, R.L., Gangi, A.F., and Snow, K.R., 1986, Empirical reflection-traveltime/ depth and velocity/depth functions for the deep-sea sediment column: Journal of Geophysical Research, v. 91, no. B8, p. 8249-8266. Carter, D.J.T., 1980, Echo-sounding correction tables: Taunton, United Kingdom, Hydrographic Department, Ministry of Defence, 150 p. Chase, T.E., Wilde, Pat, Normark, W.R, Miller, C.P., Seekins, B.A., and Young, J.D., 1981, Offshore topography of the Western United States between 32° and 49° North latitudes: U.S. Geological Survey Open-File Report 81-443, scale 1:864,518 at 38° latitude, 2 sheets. Connard, G., Couch, R., Keeling , K., Roy, J., and Troseth, S., 1984, Abyssal plain and continental net-objective sedimentary thicknesses, in Kulm, L.D., and others, eds., Western North America continental margin and adjacent ocean floor off Oregon and Washington, Atlas 1 of Regional Atlas Series, Ocean Margin Drilling Program: Woods Hole, Mass., Marine Science International, sheet 7. EEZ-SCAN 84 Scientific Staff, 1986, Atlas of the Exclusive Economic Zone, Western Conterminous United States: U.S. Geological Survey Miscellaneous Investigations Series I-1792, scale 1:500,000, 152 p. See Also "U.S. Pacific West Coast Field Activities" (Paskevich and others, 2011; http://pubs.usgs.gov/of/2010/1332/htmldocs/pc/pc_overview.html). Paskevich, V.F., Wong, F.L., O?Malley, J.J., Stevenson, A.J., and Gutmacher, C.E., 2011, GLORIA sidescan-sonar imagery for parts of the U.S. Exclusive Economic Zone and adjacent areas: U.S. Geological Survey Open-File Report 2010?1332, available at http://pubs.usgs.gov/of/2010/1332/.

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