Banking Program) and local groundwater, it is unlikely that an outage of both sources would occur simultaneously. A 2015 United States Geological Survey (USGS) study entitled UCERF3: A New Earthquake Forecast for California’s Complex Fault System (2015 UCERF3 Study) indicated that the likelihood of one or more earthquakes of magnitude 7.5 or greater over the next 30 years in Southern California was 36 percent. Local seismic events have the potential to temporarily disrupt service from either the regional facilities or local well fields. A seismic event could also cause damage to the well field that would permanently limit the production capability of one or more wells. A draft white paper evaluating Metropolitan’s emergency storage objective (released at their May 14, 2019 Board meeting) evaluated the expected outages from a large earthquake. Table 1-1 shows the shows the estimated maximum outage durations for two imported water sources for IRWD -- the Colorado River Aqueduct, California Aqueduct East Branch – resulting from a large earthquake. Table 1 ‑ 1: Estimated Maximum Outage for IRWD Imported Water Sources Due to Large Earthquake
Aqueducts
Earthquake (>M 7.8)
Colorado River Aqueduct
6 months 24 months
California Aqueduct East Branch
A major seismic event in the Delta with levee failures would have more significant and longer- term impacts to supplies. It would result in flooding of the Delta with saline waters and disruption of water exports to the SWP. The 2015 UCERF3 Study indicated that the likelihood of one or more earthquakes of magnitude 6.7 or greater over the next 30 years in the San Francisco region (which includes the Delta) was 72 percent. DWR’s 2009 Delta Risk Management Strategy (DMRS) estimated that such an earthquake would result in levee failures and simultaneous flooding of 20 islands with saline waters. For a 20-island breach event, the total cost of levee repair and dewatering was estimated to be $1.8 billion (in 2005 dollars) and require 30 months on average to repair breaches and dewater. In addition, a 20-island breach event was estimated to interrupt SWP freshwater flow from the Delta to Southern California and IRWD for 1.5 years.
Metropolitan’s 2025 Seismic Resilience Report discusses how specific planning, engineering, operations, and reporting efforts are needed to reach their three primary objectives:
• Provide a diversified water supply portfolio, system flexibility, and emergency storage. • Prevent damage to water delivery infrastructure in probable seismic events and limit damage in extreme events. • Minimize water delivery interruptions through a dedicated emergency response and recovery organization.
WSCP - 7
IRWD – 2025 Water Shortage Contingency Plan
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