Success Dam is located on the Tule River, about five miles east and upstream of the town of Porterville, Tulare County, California. Success is an earthen dam 145 feet (44 meters) tall and 3,490 feet (1,060 meters) long. The dam and reservoir were authorized as part of the Tule River Project under the Flood Control Act of 1944 and construction was completed in 1961. The reservoir provides flood risk management, water storage and recreation benefits to the local area.
The dam was built using design standards that were current at the time of construction, and built well. Seismic reanalysis that began in 1992 indicated that the alluvial (loose soil or sediment) foundation underlying the dam is susceptible to liquefaction, which in a major earthquake could cause the dam to fail.
In 1999, Congress authorized the U.S. Army Corps of Engineers to study how to address seismic risk to the dam. The study revealed additional concerns about seepage and overtopping, requiring further study and funding authorizations. In late 2006, the Corps began limiting the amount of water stored in Success Lake to minimize flood risk to the public while the Corps studied the dam and developed a solution.
New requirements and modifications to the Corps’ dam evaluation process since 2004 required additional analysis and a new type of report. Upon completion of this report in 2010, the Corps’ national dam safety program required the district to perform a baseline risk assessment - a comprehensive analysis of all the dam’s safety risks using the same methods now being applied to Corps dams throughout the nation. This re-evaluation demonstrated that the risk associated with liquefaction (dam failure during an earthquake) and seepage is significantly less than early study results indicated, and the Corps approved April 11, 2014, raising the operating restriction of the reservoir behind Success Dam to the maximum authorized storage capacity of 82,291 acre-feet, or a storage elevation of 652.5 feet.
The baseline risk assessment for Success Dam is currently being reviewed and is scheduled to be completed in summer 2014. At that time, the determination will be made as to whether the dam needs a significant fix or not.