Rehabilitation of Railroad Canyon Dam

Railroad Canyon Dam is a variable-radius concrete arch structure, with an original maximum height of 75 feet, retaining a 12,000 acre-foot reservoir. The dam was built in 1928 to provide irrigation and domestic water supply. In response to safety concerns, the dam was modified in 1965 by enlarging and strengthening the thrust blocks at each end of the arch. Subsequent to the National Dam Safety Inspection program in the late 1970's, the seismic safety and spillway capacity was evaluated. The dam was found to be stable under seismic loads, but subject to overtopping during the Probable Maximum Flood. Due to concern that flood overtopping of the dam could lead to erosion of weak rock from the abutments, which could undermine the dam, the California Division of Safety of Dams directed preparation of plans to protect the abutments. The final design concept included lowering the arch portion of the dam to widen the overflow spillway, raising the thrust blocks and wing walls by about 13 feet, and constructing concrete armoring slabs and training walls on the abutments and channel bottom. The rehabilitation project was completed over a period from early 1995 to early 1996 with the reservoir only drawn down several feet below the existing overflow spillway crest, and with no diversion other than the City's nearby water intakes. The total construction cost for the entire project was about $6 million, of which about $1 million was for the post-tensioned anchor work, including drilling the holes, furnishing the tendon bundles, and installing, stressing, and testing the anchors. [Also presented at Dam Safety 1997] 11 pp.