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Coring to Study Sediment Dispersal in Lake Mead, Nevada By Dave Twichell July 2002 in this issue:  previous story | next story Anchors aweigh: Launching of the barge used during the USGS/UNLV coring program in Lake Mead. USGS scientists and their colleagues completed 10 days of coring at Lake Mead, NV, in early June 2002. This coring program is part of a cooperative research effort between the USGS and the University of Nevada, Las Vegas (UNLV), to understand the processes of sediment dispersal in this large manmade reservoir, which lies behind Hoover Dam on the Colorado River. Sediment and sediment-hosted pollutant dispersal in the lake are of interest to several State and Federal agencies responsible for its management. Interest is peaking owing to a significant drop (more than 40 ft) in lake level over the past 2 years, causing shallow-water deltaic deposits to be remobilized and distributed deeper into the lake. Although some of the classic work on density flows and turbidities was already done in Lake Mead, systematic geophysical mapping and companion ground-truth sampling had not been conducted before this cooperative program. Participants in the fieldwork included Ken Parolski, VeeAnn Cross, and Dave Twichell (USGS, Woods Hole, MA), Keith Ludwig (USGS, St. Petersburg, FL), Mark Rudin, Brenda Buck, and Robyn Howley (UNLV), and Tom Hixon (St. Thomas University, Minneapolis, MN). The field program was conducted during a reportedly cool spring, when daily high temperatures reached only 98-112° F. Deployment: (From left to right) Dave Twichell (USGS), Mark Rudin (UNLV), Tom Hixon (St. Thomas University), and Brenda Buck (UNLV) deploying the vibracorer during the coring program in Lake Mead. Ken oversaw the completion of a coring barge that UNLV and the National Park Service put together, and he provided technical support during the cruise. VeeAnn interfaced the seagoing GIS (geographic information system) with the navigation system and then spent much of her time with the GIS group at the Bureau of Reclamation, integrating our geophysical data with their multibeam bathymetric data. The collaborative effort to pool data and research results between these two agencies is leading to a central, publicly available GIS for research on Lake Mead. Keith oversaw the Rossfleder vibracoring system brought from St. Petersburg, FL, and trained the rest of us in its operation. Dave delivered a presentation to officials from the Bureau of Reclamation and the National Park Service before the cruise, and served as the program's chief scientist. Cores were collected only in the western part of Lake Mead, with the primary focus on Las Vegas Bay. Runoff from the city of Las Vegas enters Las Vegas Bay, and geophysical data suggest that sediment associated with runoff is transported down the axial valley of this bay (as density flows) to the deep part of the lake. Some of the cores were split before the end of the field program. All of these cores penetrated the post-impoundment sediment (deposited after the lake was created) and as much as 1 m of the underlying pre-impoundment gravel. Post-impoundment sediment thickness in the cores closely matched the thickness inferred from seismic data. Graded silt and sand beds in the post-impoundment sediment indicate that density flows are actively transporting sandy sediment beyond the delta and significant distances into the lake. Lake Mead Group Travels to Las Vegas, NV March 2002 Lake Mead Mapping Completed June 2001 Seismic and Sidescan Sonar Survey in Lake Mead, Nevada July 2000 Lake Mead: UNLV Cooperative Cruise July 1999 Sediment Studies in Lake Mead U.S. Geological Survey (USGS) in this issue:  previous story | next story

July 2002 Mailing List: Sign up to receive monthly email updates: print this issue in this issue: cover story: Sea Otter Numbers Slide for Second Straight Year Lake Mead Sediment Study Salmon & Trout Habitat Students Tour M/V Auriga Williams' Presentation on Videotape Benthic-Habitat Symposium Caribbean Climate Change Conference Regional Syntheses Scientists Speak in Reston & D.C. Remote-Sensing Conference Sea-Survival Course Regional Geologist Visits WHFC New WHFC Employees New Student Interns WHFC Labs Pass Audit Award-Winning Student Volunteer Contaminated Sediment - Special Issue of Continental Shelf Research July Publications List

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