Figure 8 shows transverse cross sections of the reservoir-floor and pre-dam elevation models at each of the seven coring locations (Figure 7). On several of these cross sections the pre-dam surface is above the reservoir-floor surface, indicating apparent net erosion of the valley walls during the post-impoundment period. Similar areas of apparent net erosion are seen along the sides of the reservoir on Figure 5. While the erosion interpretation is possible, these areas may reflect minor inaccuracies in the original datasets (both horizontally and vertically) or problems with the gridding algorithms used. The total volume of apparently eroded material on the isopach map is 990,000 cubic meters (800 acre-feet), and this gives a sense of an upper bound on the size of potential error in the sediment volume calculations (4.5%).

Figure 8. Transverse cross sections of lake floor and pre-dam elevation models at coring locations, from upstream (Site 2) to downstream (Site 1) .

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FUTURE WORK

The USGS is planning to remap the reservoir bathymetry using a phase-discrimination wide-swath sonar system. This mapping produces both continuous swath bathymetry with a lateral resolution of better than 20 cm (8 in), as well as sidescan backscatter images. Another attempt to image the subbottom by seismic reflection profiling using different acoustic sources is also under consideration.

ACKNOWLEDGMENTS

The authors would like to thank: Larry Kooker, Gerald O'Brien, Patrick Hart, Hank Chezar, Tom Reiss, Mike Boyle, and Walt Olson (all of the USGS) for their assistance in conducting the field programs; Brian Haskell (University of Minnesota), the staff of DOSECC Incorporated, and numerous other USGS personnel for their work on the coring project; and Amy Foxgrover, Gerald Hatcher, and Shawn Higgins (all of the USGS) for assistance with ArcGIS. Peter Triezenberg assisted with the preparation of the final web presentation of the report. This report benefitted from reviews by David Rubin and Charles Alpers.

Funding for this study was provided by the CALFED Ecosystem Restoration Program.

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REFERENCES

Chris Ransome & Associates, 1998, Bathymetric, subbottom and sidescan survey in Marysville, California on Narrows Dam for Bookman-Edmonston Engineering, Final Report, May 18, 1998, CRA Job# 98011, unpublished

Snyder, Noah P., Rubin, David M., Alpers, Charles N., Flint, Lorraine E., Curtis, Jennifer A., Childs, Jonathan R., and Haskell, Brian J., 2002, A record of rapid fluvial sedimentation in the Sierra Nevada hydraulic mining region:  preliminary results from the 2002 Englebright Lake coring project; Paper No. 78-2, Geological Society of America 2002 Annual Meeting, Denver, CO
http://gsa.confex.com/gsa/2002AM/finalprogram/abstract_42930.htm

Snyder, Noah P., Childs, Jonathan R., Hampton, Margaret A., Rubin, David M., Alpers, Charles N., Flint, Lorraine E., Curtis, Jennifer A., Wright, Scott A., and Topping, David J., 2003, The history and future of sediment deposition behind Englebright Dam, Yuba River, Northern California; Paper No. 140-5, Geological Society of America 2003 Annual Meeting, Seattle, WA
http://gsa.confex.com/gsa/2003AM/finalprogram/abstract_60291.htm

RELATED LINKS

Upper Yuba River Studies Program
CALFED Bay-Delta Program
Coastal and Marine Geology InfoBank
Flying Eyeball
Didger 3
Geographic Calculator
Generic Mapping Tools

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For questions about the content of this report contact
Jon R. Childs
U.S. Geological Survey Mail Stop 999
345 Middlefield Rd.
Menlo Park, CA 94025-3561
650-329-5195
jchilds@usgs.gov

This report is available only on the Web