MWD has implemented further seis-mic
resilience enhancements in the de-cades
following the 1989 Loma Prieta and
1994 Northridge earthquakes. Engineers
adopted a fault-crossing strategy for new
pipelines in the distribution system that
utilized steel pipelines with welded joints,
crossing of fault zones at right angles, and
burying the pipes relatively shallow to
enable easy access for repair. MWD also
increased its emergency storage supplies
and completed numerous capital projects
to harden facilities and enhance system
flexibility.
Current Seismic
Resilience Strategy
Recently, MWD reassessed its Seismic
Resilience Strategy to identify and close
any existing gaps. The resulting approach
is built upon improved collaboration
between in-house planning, engineering,
and operations groups and formal
collaboration with external agencies that
also import water to Southern California,
specifically the Los Angeles Department
of Water and Power (LADWP) and
the California Department of Water
Resources (DWR). MWD’s current
Seismic Resilience Strategy consists of
five complementary components:
• Planning
• Engineering
• Operations
• Inter-Agency Collaboration
• Formal Reporting
Planning. In 1999 proactive plan-ning
resulted in design and construction
of Southern California’s largest surface
water reservoir, Diamond Valley Lake
(DVL). In addition to increasing seasonal
storage, DVL was purposefully construct-ed
on the coastal side of the SAF and the
San Jacinto Fault Zone (SJFZ) in order to
supply the region in case CRA deliveries
are interrupted. In conjunction with local
production and conservation, DVL and
other local reservoirs can provide the re-gion
with six months of emergency water
supply. MWD will continue to evaluate
emergency storage needs as they relate to
seismic risks and incorporate seismic re-silience
into its integrated water resource
planning.
Engineering. The engineering com-ponent
of seismic resilience addresses
MWD’s Diamond Valley Lake was constructed on the coastal side of the SAF to protect water supplies
in case CRA deliveries are interrupted.
infrastructure and system vulnerabilities
through a formal Seismic Upgrade Pro-gram
and periodic vulnerability assess-ments.
The Seismic Upgrade Program
assesses existing structures on a cyclical
basis and upgrades those identified with
seismic deficiencies. The assessment crite-ria
is based on current applicable building
codes, industry standards, and the most
up-to-date seismological and geotechni-cal
information. Upgrades can include
adding new structural components such
as shear walls and braces, strengthen-ing
existing components with fiber-rein-forced
polymer or carbon wrapping, con-crete
jacketing, reinforcing the anchorage
of water storage tanks, and addressing
slope stability issues. In general, an exist-ing
structure is upgraded to be compara-ble
with the seismic performance of a new
facility. The Seismic Upgrade Program is
primarily focused on above-ground facil-ities
and structures, including dams and
reservoirs. An additional program ad-dresses
the assessment and mitigation of
geotechnical hazards.
Periodic vulnerability assessments
are performed to evaluate the potential
impacts of credible earthquake scenarios
on the ability to deliver water to specif-ic
regions of MWD’s distribution system
and to evaluate non-structural elements
of facilities. Such assessments can lead to
capital improvements to strengthen facil-ities,
enhance system flexibility, and im-prove
emergency response planning. For
example, a vulnerability assessment was
conducted on the Mills Water Treatment
Plant, which is supplied by water from
Silverwood Lake and currently has only
limited backup supply from Lake Perris.
As a result of this evaluation, a project
was developed to also allow water from
DVL to be delivered to Mills in the future
for improved backup capability. Another
assessment conducted on all five water
treatment plants has led to installation of
additional bracing of process piping and
equipment anchorage improvements at
each facility.
Over the past two decades, MWD
has invested more than $257 million in
seismic resilience projects. More than 300
high-risk (pre-1990) structures have been
evaluated and the facilities most critical
for water deliveries have been upgraded
or are currently in the design/construction
process. These include pumping plants
along the CRA, the outlet towers at Lake
Mathews, treatment plant buildings, and
treatment plant wash-water tanks. MWD
plans to invest an additional $163 million
in seismic resilience projects over the next
five to seven years.
MWD is also currently launching
an effort to further improve the seismic
resilience of its distribution system over
time. This involves detailed assessment of
risks and application of modern mitigation
measures at active fault crossings, areas of
known permanent ground deformation,
and areas of significant ground shaking.
This refined approach, which includes
state-of-the-art computing methods and
use of seismic-resistant pipelines and
joints, is being implemented as part of
MWD maintains a dedicated Emergency
Operations Center and conducts regular
emergency response exercises.
26 SOURCE fall 2017