Seismic Preparation at the Wholesale Level:
MWD’S INTEGRATED PROGRAM
By David K. Clark
MWD has invested more than $257 million in seismic resilience projects and plans to spend more
than $163 million over the next 5-7 years at treatment and conveyance facilities after projects.
THE METROPOLITAN WATER DISTRICT OF SOUTHERN CALIFORNIA (MWD) meets about one-half of the
treated and untreated water demands of more than 19 million people living within a 5,200-square mile service
area along the California coastal plain. MWD was created by the California Legislature in 1928 to construct and
operate the Colorado River Aqueduct (CRA) that serves Southern California. MWD’s system includes five regional water
treatment plants, nine reservoirs, 16 hydroelectric plants, 830 miles of large-diameter pipelines and tunnels, and the 242-
mile long CRA. On average, MWD delivers about 1.7 billion gallons a day to 26 member agencies within Los Angeles,
Orange, Riverside, San Bernardino, San Diego, and Ventura counties.
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The seismic risk posed to this infrastructure is significant.
From its inception, MWD has been committed to minimizing
interruptions to water deliveries following major seismic events
through proactive system design, construction, and emergency
preparedness.
In the Beginning
In the 1930s, MWD geologists and engineers took a number
of steps to better understand and mitigate the recognized risks
posed to the CRA from large seismic events on the San Andreas
Fault (SAF). They researched ground shaking and deformation
that occurred along the SAF system during the 1857 Fort Tejon
and 1906 San Francisco earthquakes and improved their under-standing
of the region’s active faults through geologic mapping
and analysis of aerial photographs. Based on their findings, they
designed the aqueduct to cross active faults with inverted siphons
(near the ground surface) and at right angles to the fault trac-es
in order to minimize adverse effects from horizontal ground
movement and simplify access for repairs. In order to minimize
potential damage during seismic events, they also opted for
more flexible designs using siphons to cross the active faults
rather than the rigid, monolithic concrete designs used elsewhere
along the CRA.
The water treatment plants were also designed to incorpo-rate
seismic resilience. MWD’s five water treatment plants are
modular in design and incorporate redundancy of key compo-nents,
are situated strategically to maximize gravity flow, and
have partial to full backup water supplies. All of these steps
improve system flexibility, which helps mitigate the risk of
seismic events impacting the treatment and delivery of water
to MWD’s member agencies.
Continuously Refining MWD’s
Seismic Resilience Strategy
MWD has applied the lessons learned from actual seismic
events to refine its approach to seismic resilience. For example,
after the Joseph Jensen Water Treatment Plant sustained wide-spread
damage from the 1971 San Fernando Earthquake, a com-mittee
of experts was formed to investigate the causes of damage
to the finished water reservoir, wash-water tanks, and connecting
conduits. The committee recommended enhanced seismic design
criteria and site improvements such as stone columns to pre-vent
liquefaction. These modifications contributed to improved
seismic performance of the Jensen Plant in the 1994 Northridge
Earthquake. Except for the rupture of an 84-inch steel pipeline,
only minor structural damage was noted. The Jensen plant was
off-line for less than 72 hours to repair the broken pipeline, and
limited water deliveries continued during the repairs.