Dam Seismic Retrofit

Crane Valley Dam

Crane Valley Dam is located about 40 miles northeast of Fresno in Madera County, California on the North Fork of Willow Creek, a tributary of the San Joaquin River. The dam was built between 1902 and 1911 when very little was known about seismic activity. The dam is a 145-foot high, hydraulic earth and rock fill embankment, with a thin central concrete core wall. The dam is 1,880 feet long, and the crest of the dam is at 3,380 feet elevation.

Crane Valley Dam consists of two distinct dams separated by a rock knoll. The Main Dam is located in the main channel of the creek, and has earth fill on the upstream side of the core wall and rock fill on the downstream side. The West Dam is located adjacent to the main dam in a smaller side channel west of the creek, and has earth fill on both sides of the core wall. The spillway is located on a saddle about 500 feet to the east of the dam.

Rock Fill Qualities Detail

Seismic Retrofit Project History

There are two main regulatory agencies involved with the Crane Valley Dam:

  • The Federal Energy Regulatory Commission (FERC)
  • The Department of Water Resources (DWR), Division of Safety of Dams (DSOD)

Division of Safety of Dams is responsible to review the stability of all dams in California. In light of improved design approaches as well as new findings regarding earthquake hazards and hydrologic estimates, DSOD periodically establishes new requirements for dams. In 2002, DSOD requested that PG&E revise previous seismic stability analysis of Crane Valley Dam (BassLake). After completing studies on the dam stability, the results indicated that modifications to the dam were necessary to meet current standards for seismic stability. Since 2002, PG&E has worked in concert with DSOD and the FERC to conduct further analysis of the seismic stability and coordinate the development of a seismic retrofit plan for Crane Valley Dam. Analysis showed that in the event of an earthquake, the dam could slump and allow water to flow over the top, causing flooding downstream.

Since then, PG&E has developed a retrofit design to modify the Crane Valley Dam to increase the stability of the dam structures to meet state and federal safety guidelines. The dam modification would consist of the addition of approximately 253,000 cubic yards of rock fill to selected areas on the upstream and downstream faces of the dam.

In summary, the seismic retrofit project will include the following measures:

  • Installation of rockfill buttresses on the sections of the dam that have hydraulic fill on both the upstream and downstream sides of the concrete core wall
  • Tying back the top of the concrete core wall in the section of the dam where the downstream shell consists of a massive rockfill embankment
  • Raising and re-grading the crest to elevation 3387, about 7 feet above present minimum crest elevation, to provide more freeboard

Status of the Seismic Retrofit Project

PG&E has applied to Federal Energy Regulatory Commission (FERC) for modification of the project under 18 C.F.R., Part 12 (Safety of Water Power Projects and Project Works). All work would be done in accordance with all conditions set forth in FERC License No.1354 re-issued on September 16, 2003. FERC actions are also subject to the National Environmental Policy Act (NEPA). FERC has reviewing the project and prepared an Environmental Assessment to comply with NEPA requirements. Click here to view or download the Final Project Environmental Assessment.

In California, environmental review is performed under the California Environmental Quality Act (CEQA). The lead agency for the state CEQA process is the Department of Water Resources (DWR), Division of Safety of Dams (DSOD). DWR issued and approved the Final Environmental Impact Report for the project. Click here to download the FEIR .

PG&E secured permits to begin construction on the retrofit project. Construction activities began in mid-October 2010 and the project is anticipated to be completed in 2012.

Project Plan Overview