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. Extensive research has been conducted on Lake Mead, but a majority of the studies have involved determining levels of anthropogenic contaminants such as synthetic organic compounds, heavy metals and dissolved ions, furans/dioxins, and nutrient loading in lake water, sediment, and biota (Preissler, et al., 1998; Bevans et al, 1996; Bevans et al., 1998; Covay and Leiker, 1998; LaBounty and Horn, 1997; Paulson, 1981). By contrast, little work has focused on the sediments in the lake and the processes of deposition (Gould, 1951). To address these questions, sidescan-sonar imagery and high-resolution seismic-reflection profiles were collected throughout Lake Mead by the USGS in cooperation with researchers from University of Nevada Las Vegas (UNLV). These data allow a detailed mapping of the surficial geology 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 that are now submerged below the lake while the margins of the lake appear to be devoid of post-impoundment sediment. The sediment cover along the original Colorado River bed is continuous and is typically greater than 10 m thick through much of its length. Sediment thickness in some areas exceeds 35 m while the smaller tributary valleys typically are filled with less than 4 m of sediment. Away from the river beds that are now covered with post-impoundment sediment, pre-impoundment alluvial deposits and rock outcrops are still exposed on the lake floor.

Lake Mohave is one of several multi-purpose reservoirs that have been constructed on the Colorado River. The lake was formed upon completion of the Davis Dam in 1953. No mapping of the floor of the lake had been conducted since completion of the Davis Dam. The U.S. Geological Survey, in cooperation with researchers from the University of Nevada Las Vegas, completed a geophysical survey of this lake in April 2002. The survey included collection of sidescan sonar imagery of nearly the entire lake floor, and high-resolution seismic-reflection profiles along widely spaced lines throughout the lake. The detailed mapping of the lake floor was used to determine the amount of sediment that had accumulated in the lake since impoundment, its distribution, and the processes of deposition.

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. Extensive research has been conducted on Lake Mead, but a majority of the studies have involved determining levels of anthropogenic contaminants such as synthetic organic compounds, heavy metals and dissolved ions, furans/dioxins, and nutrient loading in lake water, sediment, and biota (Preissler, et al., 1998; Bevans et al, 1996; Bevans et al., 1998; Covay and Leiker, 1998; LaBounty and Horn, 1997; Paulson, 1981). By contrast, little work has focused on the sediments in the lake and the processes of deposition (Gould, 1951). To address these questions, sidescan-sonar imagery and high-resolution seismic-reflection profiles were collected throughout Lake Mead by the USGS in cooperation with researchers from University of Nevada Las Vegas (UNLV). These data allow a detailed mapping of the surficial geology 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 that are now submerged below the lake while the margins of the lake appear to be devoid of post-impoundment sediment. The sediment cover along the original Colorado River bed is continuous and is typically greater than 10 m thick through much of its length. Sediment thickness in some areas exceeds 35 m while the smaller tributary valleys typically are filled with less than 4 m of sediment. Away from the river beds that are now covered with post-impoundment sediment, pre-impoundment alluvial deposits and rock outcrops are still exposed on the lake floor.

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. Extensive research has been conducted on Lake Mead, but a majority of the studies have involved determining levels of anthropogenic contaminants such as synthetic organic compounds, heavy metals and dissolved ions, furans/dioxins, and nutrient loading in lake water, sediment, and biota (Preissler, et al., 1998; Bevans et al, 1996; Bevans et al., 1998; Covay and Leiker, 1998; LaBounty and Horn, 1997; Paulson, 1981). By contrast, little work has focused on the sediments in the lake and the processes of deposition (Gould, 1951). To address these questions, sidescan-sonar imagery and high-resolution seismic-reflection profiles were collected throughout Lake Mead by the USGS in cooperation with researchers from University of Nevada Las Vegas (UNLV). These data allow a detailed mapping of the surficial geology 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 that are now submerged below the lake while the margins of the lake appear to be devoid of post-impoundment sediment. The sediment cover along the original Colorado River bed is continuous and is typically greater than 10 m thick through much of its length. Sediment thickness in some areas exceeds 35 m while the smaller tributary valleys typically are filled with less than 4 m of sediment. Away from the river beds that are now covered with post-impoundment sediment, pre-impoundment alluvial deposits and rock outcrops are still exposed on the lake floor.

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.

These profiles of suspended-sediment concentration were collected and compiled to characterize suspended sediment in the Colorado River during both average flow conditions and during a controlled flood that occurred in March 2008. The objectives of the study were to measure changes in suspended sediment that occurred during changes in discharge associated with the controlled flood. These data were collected between March 4 and March 10, 2008 in the center of the channel 44.64 river miles downstream from Lees Ferry, Arizona on the Colorado River within Grand Canyon National Park. The sampling location was within a 1-mile study reach beginning 0.14 miles upstream from the sampling location. These data were collected by the USGS Grand Canyon Monitoring and Research Center with cooperators from Northern Arizona University and funding provided by the Glen Canyon Dam Adaptive Management Program. All samples were collected with USGS P-61 point integrating sampler. Samples were processed for silt and clay concentration, sand concentration, and sand grain size using standard methods. These data can be used to study suspended sediment concentration, which can be used in predictions of sediment transport and can be used to develop, calibrate, and verify transport models.

This part of DS 781 presents data for the sediment-thickness map of the Point Conception to Hueneme Canyon, California, region. The raster data file is included in "SedimentThickness_PointConceptionToHuenemeCanyon.zip," which is accessible from https://doi.org/10.5066/F7891424. As part of the USGS's California State Waters Mapping Project, a 50-m grid of sediment thickness for the seafloor within the 3-nautical mile limit between Point Conception and Hueneme Canyon was generated from seismic-reflection data collected in 2014 (USGS activity 2014-632-FA) supplemented with outcrop and geologic structure (fault) information following the methodology of Wong (2012). This sediment thickness layer was merged with a previously published sediment thickness grid for the Santa Barbara Channel region (available at https://pubs.usgs.gov/ds/781/SantaBarbaraChannel/data_catalog_SantaBarbaraChannel.html). Reference Cited: Wong, F. L., Phillips, E.L., Johnson, S.Y., and Sliter, R.W., 2012, Modeling of depth to base of Last Glacial Maximum and seafloor sediment thickness for the California State Waters Map Series, eastern Santa Barbara Channel, California: U.S. Geological Survey Open-File Report 2012-1161, 16 p. (available at https://pubs.usgs.gov/of/2012/1161/)

These spatial data represent alluvial deposits of the Colorado River and tributary deposits adjacent to the Colorado River in Grand Canyon National Park. The map covers the river corridor from Lees Ferry, Arizona to the confluence with Diamond Creek 225 miles (362 km) downstream. The alluvial deposits of the Colorado River are mapped as either sand or gravel based on surface composition and the sand deposits are further subdivided based on sandbar type (Schmidt, 1990; Mueller and others, 2018). The alluvial deposits are also subdivided based on whether they are bare sediment or covered by dense riparian vegetation. The tributary deposits consist primarily of tributary debris fans, which are coarse-grained material transported by tributary flash floods and debris flows (Webb and others, 1989). The source data for creating the alluvial and tributary deposit features were orthorectified, 25-cm resolution, color aerial photographs (described in Davis, 2012). The map units, represented as vector polygon features, were hand digitized on-screen with these images as a background base layer. The map depicts conditions at the time the base images were collected, which was May 2009 while the Colorado River was flowing at a steady flow of approximately 8,000 ft3/s (227 m3/s). In addition to mapping the deposits exposed above the water surface, the wetted channel was also mapped and subdivided based on general hydraulic characteristics. The primary distinction was between portions of the channel with only downstream flow at 8,000 ft3/s and portions of the channel with lateral flow separation zones, or eddies. The alluvial, channel, and tributary fan deposits are also grouped based on the debris-fan eddy complex unit (Schmidt and Rubin, 1995).

In 2012, the U.S. Geological Survey (USGS) in cooperation with Colorado Springs Utilities selected 10 study areas along Fountain Creek between Colorado Springs, Colorado and the confluence of Fountain Creek with the Arkansas River for annual geomorphic monitoring. The purpose of this data release is to present topographic survey data, rasters , and sediment size data collected in 2019 as part of that monitoring effort. Topographic survey points were collected using real-time kinematic Global Navigation Satellite Systems (RTK-GNSS). These point data were interpolated in ArcGIS to generate digital elevation maps (2015 and 2019) and elevation-change maps (from 2015 to 2019) at each study area . In 2019, two types of Unmanned Aerial Survey (UAS) datasets were also collected and processed at one of the study areas (study area three): (1) a UAS Light Detection and Ranging (LiDAR) point cloud collected using the Yellowscan Surveyor payload (Velodyne VLP16 puck and Applanix Inertial Measurement Unit [IMU]) flown at 150 feet (ft) above ground level using the DJI Matrice 600 UAS aircraft, and (2) a photogrammetric survey taken with the Sony a6000 camera at 200 ft above ground level with the DJI Matrice 600 UAS aircraft, which produced an ortho image, a point cloud, and raster surface model (DSM). The USGS is investigating the use of UAS for traditional river surveys of topography. Traditionally, ground-surveying procedures are required to get the level of accuracy and data needed for the annual reporting. The use of UAS could have substantial time and cost savings to supplement the procedures currently used to complete the monitoring. In addition to topographic surveys, pebble-count data were collected in the Spring of 2019 to characterize the size of streambed sediment. Pebble-count surveys included four measurements of grain size at each of 25 equally spaced sampling stations along four separate cross sections across the active channel of each study area. Annual topographic and sediment size data are used to asses geomorphic changes at each study area.

A two-week field operation was conducted in the John Day Reservoir on the Columbia River to image the floor of the pool, to measure the distribution and thickness of post-impoundment sediment, and to verify these geophysical data with video photography and bottom sediment samples. The field program was a cooperative effort between the USGS Coastal and Marine Geology Team of the Geologic Division and the USGS Columbia River Research Laboratory of the Biological Resources Division. The data collection was completed aboard the R/V ESTERO during September 13-27, 2000. The interest in sediment accumulation in the reservoir was two-fold. First, it was unknown how effective this reservoir was as a sediment trap to material that otherwise would have been transported down-river to the estuary and eventually to the ocean. The recent erosion of beaches along the Washington coast has been attributed to a decreased contribution of sediment from the Columbia River to the coastal system due to the damming of the river. Second, sediment accumulation on the floors of reservoirs along the Columbia River has been suggested to be diminishing salmon spawning grounds. The extent of changes in habitat since construction of the John Day Dam, however, had not been documented. Common data sets were needed to address both of these questions, and for these reasons this geophysical and sampling program was undertaken.