The Yuba River is located on the eastern border of the Tahoe National Forest and is a critical watershed in northern California that provides for irrigation, drinking water and hydroelectric power generation. The New Bullards Bar Dam is a 645-foot-high double curvature concrete arch dam across the North Yuba River. It is located in Yuba County, California, about 12 miles northwest of the City of Grass Valley.
Our House Dam is a 70-foot-high concrete gravity structure located in Nevada County, California, about 17 miles north of the City of Grass Valley. Log Cabin Dam is a 49-foot-high concrete gravity dam located in Yuba County, about 15 miles north of the City of Grass Valley. As an outcome of the recent Federal Energy Regulatory Commission (FERC) safety inspections of the three dams, it was recommended that the seismic stability of the dams be evaluated using updated ground motions at the dam sites.
SAGE seismic geologists and geotechnical earthquake engineers performed ground motion studies to update the seismic input motions.
Our scope of services included:
- Reviewing updated seismotectonic studies, updating the seismicity, and identifying the seismic sources in the vicinity of the dams;
- Characterizing the seismic sources in terms of maximum earthquake magnitudes, style of faulting, slip rates, and other fault parameters;
- Developing deterministic response spectra for the controlling seismic sources at statistical (median or 84th percentile) levels commensurate with the Division of Safety of Dams (DSOD) Consequence Hazard Matrix;
- Selecting sets of three-component (two-horizontal and one vertical) recorded acceleration time histories from earthquakes of magnitudes and at distance ranges similar to those postulated for the controlling seismic sources; and modifying the selected time histories such that their response spectra will match the evaluation spectra; and
- Preparing technical Memos to be submitted for review and approval by the DSOD and FERC.