CS19A - Concurrent Session 19A: New Calaveras Dam – Performance After Five Years

Construction work on the 220-foot-high earth and rockfill dam, spillway, and outlet works for the Calaveras Dam Replacement Project began in August 2011 after eight years of geotechnical investigations, design, environmental review, and regulatory review. The dam replaced a nearly 100-year-old hydraulic fill dam, constructed in 1925. The new dam and appurtenant works were designed to remain functional after the design earthquake, a moment magnitude 7¼ maximum credible earthquake (MCE) on the Calaveras Fault located 0.3 miles west of the dam. Construction of the new dam was completed in November 2018 and initial reservoir filling began in January 2019.

Monitoring dam performance is critical, especially during initial filling, requiring an integrated effort between the Owner, the Engineer of Record, jurisdictional dam safety agency and construction team. To coordinate this effort, an Initial Reservoir Fill Plan was developed to cover roles and responsibilities between these entities, and inspection and monitoring protocols during initial filling until the reservoir spills for the first time. Instrumentation of the structure included an array of vibrating wire piezometers, standpipe piezometers, seepage weir, inclinometers, survey monuments, accelerographs, and reservoir level sensors.

Instrumentation data and observations from regular visual inspections were used to evaluate the behavior of the dam during the first filling of the reservoir and to confirm that conditions are consistent with the design assumptions. As data were compiled, trends and thresholds under normal operation were established, and the significance of variations under unusual events or loads, such as earthquakes, were evaluated.
Initial reservoir filling and monitoring over the several seasons needed to fill the reservoir are discussed. The reservoir received minimal net inflow for several years, then filled rapidly due to very heavy rainfall from a series of atmospheric river events during December 2022 - January 2023, when the reservoir spilled for the first time. Over the past five years, the dam has performed, and is continuing to perform, as intended. Continued monitoring is necessary to confirm adequate dam safety, especially following large earthquakes and heavy rainfall events that can be expected due to climate change.