Seismic Mitigation - Mokelumne Aqueduct No. 3 East Bay Municipal Utility District

Abstract

The East Bay Municipal Utility District (EBMUD) is located in the east portion of the San Francisco Bay Area, serving water to over 1.3 million people. The water system includes a network of reservoirs, aqueducts, treatment plants, and other distribution facilities stretching from the Sierra foothills to the Bay Area. The main source of water is the Mokelumne River watershed in the Sierra foothills located about 90 miles northeast of the Bay Area. Mokelumne River water is collected in the Pardee Reservoir and flows from Pardee to the Bay Area via the Mokelumne aqueduct system consisting of three large diameter steel pipelines. The Bay Area has high seismic risk, with numerous earthquake faults throughout the region. EBMUD's Water Supply Management Plan completed in 1993 identified that the aqueduct system is vulnerable to damage in a 14-mile reach located in the San Joaquin-Sacramento River Delta Area, possibly causing unacceptable outage duration. Recognizing this danger, EBMUD has undertaken a $39 million project to upgrade Aqueduct No. 3 and increase its seismic reliability. The EBMUD upgrade performance goal is to limit damage such that it can be repaired within six months following a 500-year return period earthquake, with terminal storage located within the service area being used to provide water to customers during the six month repair period. The project was executed in two phases. Phase 1 was completed in 1999 and consisted of upgrading three river crossings and 5 miles of buried pipeline. Phase 2 is currently under construction, and consists of a 9-mile elevated portion of the aqueduct. Both phases meet the EBMUD seismic performance goal based on a 500-year return period event. However, the entire project included consideration of the >2000 year design earthquake. Phase 2 implementation of performance-based design led to innovative use of elastomeric seismic isolation bearings to mitigate ground-shaking effects. This paper describes the Phase 2 project.