Innovative Modification to Improve Resilience of the Los Angeles Aqueduct after the next San Andreas Fault Earthquake

The City of Los Angeles has depended on imported water since 1913 and devotes substantial resources to maintain the Los Angeles Aqueduct and related infrastructure. The 1906 San Francisco earthquake occurred during aqueduct design, and the San Andreas Fault was soon recognized as a major earthquake hazard that could not be avoided. The aqueduct crosses the fault in the middle of the Elizabeth Tunnel section (8-km- (5-mi-) long, concrete-lined, horseshoe-shaped). The current tunnel capacity is 19.6 m 3 /s (310,000 gal/min) or approximately 1.69 billion L/d (446 million gal/d). A major earthquake generated by San Andreas Fault is expected to produce lateral displacement and strong shaking. Displacement of Elizabeth Tunnel at the fault might be 3 m (10 ft) or less over a zone 3 m (10 ft) or more wide. High-density polyethylene (HDPE) pipe in New Zealand proved to be resilient during earthquakes in 2010 and 2011. The City of Los Angeles plans to install an HDPE pipe section across the fault zone to provide a means for some water to pass through the tunnel after the next San Andreas Fault earthquake. The capacity of the tunnel under normal operating conditions will be reduced, but if the HDPE pipe remains open, a 0.91-m- (36-in-) diameter pipe could pass about 18 percent of the current capacity. The Los Angeles Aqueduct is existing infrastructure upon which the City of Los Angeles depends. Conserving water and maintaining infrastructure to extend life cycles are major parts of the City's sustainability program. The planned modifications are an innovative approach that could improve the likelihood that some of the City's water will cross the San Andreas Fault after the next major earthquake. Two other aqueducts bring water to Southern California (Colorado River Aqueduct and California Aqueduct), both of which cross the San Andreas Fault in canal sections.