FERC Part 12
Vermilion Dam FERC Part 12 Safety Inspection
Devine Tarbell & Associates, Inc.’s (DTA) staff completed the Sixth Five Year
Safety Inspection of Vermilion Dam for Southern California Edison Company (SCE).
The project includes a 165-foot-high, 4,234-foot-long zoned compacted earthfill
dam, an adjacent radial gate service spillway, and an adjacent auxiliary
spillway. The dam is constructed on interbedded glacial outwash and moraine
soils. The area downstream of the dam, generally toward either abutment, has
historically exhibited numerous areas of seepage owing to the fact that the dam
was constructed on the interbedded glacial soils and is crisscrossed by numerous
drainage systems. The seepage history of the dam is documented in the literature
and has been addressed by such noteworthy geotechnical engineers as Dr. Karl
Terzaghi. Because of the proximity of the project to the seismically active
Mammoth Lakes area and Owens Valley, the maximum credible earthquake at the dam
site has been estimated to be 0.32g.
DTA conducted the FERC Part 12 inspections for 21 dams in Southern California
Edison Company's Northern and Eastern hydro systems located in the Sierra Nevada
Mountains near Fresno and Bishop, California. Vermilion Dam is in the Northern
Hydro System, near the town of Big Creek.
The projects in SCE’s systems are a mix of earth, earth and rockfill, timber
faced rockfill, concrete arch and concrete gravity dams. DTA has personnel who
specialize in hydro related civil/structural, geotechnical or
hydraulic/hydrologic engineering and have previously been approved as Part 12
Independent Consultants. This allows DTA to create an inspection team with
skills most applicable to a specific project. For the SCE projects, DTA used a
team of a Civil/Structural Engineer and a Geotechnical Engineer to complete the
on site inspection.
The inspection of the projects began by review of previous five year safety
inspection reports, project design criteria, remediation work reports, project
license drawings, stability calculations, failure analysis, PMF and spillway
adequacy analysis, and geologic and seismology reports.
The field inspection included a review of operational documentation as well as
observation of the water retaining structures and appurtenances of the project.
Following the field inspection, previous structural and slope stability
calculations and hydrologic analyses were reviewed to assess consistency with
accepted FERC procedures and methods. At the conclusion of the work, a summary
report was prepared in accordance with FERC requirements and guidelines.