East Bay Municipal Utility District’s Aqueduct System in the Sacramento San-Joaquin Delta: Hazard Evaluation

摘要

East Bay Municipal Utility District (EBMUD) is a water utility providing water torn1.3 million people in the Oakland Bay Area. EBMUD’s main source of water is thernMokelumne River watershed in the Sierra foothills, located about 90 miles northeastrnof the San Francisco East Bay Area. The aqueduct system that transports water to thernservice area consists of three large diameter steel pipelines of 65”, 67”, and 87”, builtrnin 1929, 1949, and 1963, respectively. These pipelines are a critical component ofrnEBMUD’s water system and the State of California’s (State) overall waterrninfrastructure. Approximately 15 miles of the aqueduct runs across the fragilernSacramento-San Joaquin Delta (Delta) area through 5 islands that are approximatelyrn5 to 15 feet below mean sea level. This Delta crossing consists of approximatelyrn4.5 miles of buried pipeline, 10 miles of elevated pipeline, and 3 major riverrncrossings with about 0.5 miles of submerged pipeline.rnThe Delta has approximately 1,100 miles of levees, many of significant height (up torn25 feet), which continuously impound sloughs and river waters and protectrnagriculture and urban areas within islands and tracts. The islands’ floor in the centralrnand western Delta is below sea level by up to 20 feet as a result of subsidence fromrnfarming of organic and peaty soils. There have been 166 levee failures leading tornisland inundations since 1900. The State is conducting studies on the Delta region asrnpart of their Delta Risk Management Strategy (DRMS) project. As a part of thernState’s studies, all potential hazards from flooding and seismicity were identified andrnquantified and potential impacts and risks to the Delta levees were evaluated andrnquantified. Both flooding and seismicity fragility curves were developed for thernDelta region on a Delta reach-by-reach basis. Geographic Information Systems werernused to identify the hazard by levee reach.rnThe potential for earthquakes and sea level rise, the presence of highly compressiblernpeat layers and liquefiable soils, potential for internal erosion of levees, and otherrnhazards and resulting flooding all make for a very fragile environment for EBMUD’srnaqueduct infrastructure. This paper provides a discussion of the how EBMUDrnassessed the seismologic, flooding, and geotechnical hazards and their associated