HomeMy WebLinkAbout2001-10-23 - AGENDA REPORTS - GP AMEND SEISMIC SECTION (2)CITY OF SANTA CLARITA
AGENDA REPORT
City Manager Approval
Item to be presented by: Enrique Diaz
PUBLIC HEARING
DATE: October 23, 2001
SUBJECT: AMENDMENT TO THE GENERAL PLAN UPDATING
THE SEISMIC SECTION OF THE SAFETY ELEMENT
DEPARTMENT: Planning and Building Services
RECOMMENDED ACTION
Receive staff presentation, conduct the public hearing, and adopt a resolution
approving Master Case No. 01-146 which consists of General Plan Amendment
01-03.
BACKGROUND
Following the Northridge Earthquake on January 17, 1994, damage to the City of
Santa Clarita was estimated to be over $700 million. Through the Disaster Relief
and Emergency Assistance Act of 1988 and State Natural Disaster Assistance
Act, financial assistance was available to public agencies through the Hazard
Mitigation Grant Program (HMGP). The California Office of Emergency Services
approved a grant for the City's seismic update to the Safety Element of the
General Plan on March 10, 1998.
As part of the seismic update to the Safety Element, the proposed project must
meet the HMGP criteria by assuring that the City complies with State Seismic
Hazard Mapping Act and accurately identify safety hazards within the City's
planning area. On August 17, 1998, the State of California Department of
Conservation Division of Mines and Geology developed maps identifying seismic
hazards within the planning area addressing the hazards of liquefaction and
earthquake -induced landslides. The existing General Plan Safety Element,
adopted in June 1991, does not reflect the adopted geologic hazards.
As part of this project the City hired a qualified consultant to prepare a seismic
update to the Safety Element. This revision reflects the new fault maps and other
geologic hazard maps developed by the State since the 1994 Northridge
Earthquake. The proposed amendment will help the City regulate specific
projects within the zones in order to identify and mitigate seismic hazards.
Adopted,. _1/13 Agenda Item : % 9
ANALYSIS
The Safety Element is one of the state -required elements of the General Plan. The
proposed technical background report, map exhibits, tables, and planning goals
and policy changes in the Safety Element of the General Plan are designed to
improve planning for new and existing developments. The proposed amendments
will be helpful to the owner/developer seeking approval of specific development
projects within zones of required seismic investigation and to the engineering
geologist and/or civil engineer who must investigate the site and recommend
mitigation of identified hazards. The proposed amendment will also be helpful to
the lead agency who must complete the technical review, and other lead agency
officials involved in the planning and development approval process.
Text Amendment
The proposed seismic related changes of the technical background will replace the
existing Safety Element pages S-1 through S-6. The proposed changes are
attached to this report and are summarized as follows:
• Introduction — the introduction has been modified to include the specific
hazards which are being evaluated as part of the proposed Safety Element
update which include faults, seismically -induced ground shaking, ground
surface rupture, liquefaction, slope stability and landslides, tsunami, and
seiche. In addition, other hazards being included are ground rupture from
movement of active faults, liquefaction in areas of unconsolidated sediments
and a shallow groundwater table, landslides and other slope movement in
hilly areas, and flooding in the event of dam failure to the Bouquet Canyon or
the Castaic dams.
• Definitions — a new section has been added to include definitions of technical
terms used in the proposed Safety Element update related to seismic issues.
• Geologic Setting — this section has been added and it includes detailed
information about the City's regional geologic setting. In addition, there is a
discussion about important geologic features within the Santa Clarita Valley.
• Seismicity — this section defines the difference between active faults,
potentially active faults, and inactive faults. There is also a description of
how earthquakes are measured and the relationship between magnitude and
intensity. In addition, this section includes Table 1, Modified Mercalli
Intensity Scale of 1931 which describes the intensity of an earthquake's effects
given a location and Table 2, Comparison of Richter Magnitude and Modified
Mercalli Intensity.
• Seismic Setting — this section includes a description of the City's setting in
relation to local and regional faults. In addition, Exhibit S-1, Recently Active
Faults in the Southern California Region and Table 3, Active Faults near the
City of Santa Clarita.
Active Faults within or near Santa Clarita — this section has information
about the different faults near the City of Santa Clarita. Some of these active
faults include the San Gabriel Fault, Holser Fault, Santa Susana Fault, San
Andreas Fault, Oak Ridge Fault, and San Fernando Fault.
Historic Earthquakes Affecting the City — this section outlines earthquakes
within the City's planning area. Table 4, Significant Historic Earthquakes
Felt within City Limits dates back to the mid 1800's and Exhibit S-3, Major
Earthquakes in the Southern California Region depict the epicenter within or
near the City limits. In addition, there is an evaluation of the 1994
Northridge Earthquake on January 17, 1994 with information about the
damaged structures and total dollar loss due to the earthquake.
• Ground Rupture — this section describes the two (2) types of ground ruptures
which include a Strike -Slip Fault and a Dip -Slip Fault.
• Alquist Priolo Earthquake Fault Zone — this section defines the area within
the Alquist Priolo Zone (500 feet from the fault trace). Alquist Priolo maps are
designed to identify areas of seismically induced ground displacement. State
legislation requires seismic and engineering studies to be conducted for
development projects near earthquake fault zones. Included in this section is
Exhibit S-2, Faults in Planning Area which depicts the Alquist Priolo Special
Study Zone in the planning area.
Ground Acceleration — this section describes both a deterministic approach
and probabilistic approach which are used to calculate seismically induced
ground acceleration.
Landslides — this section describes the factors that influence the stability of
soil which include grain size, moisture content, organic matter content, degree
of slope, and soil type thus causing landslides. The California Department of
Mines and Geology conducted seismic hazard evaluations of the Newhall,
Mint Canyon, Oat Mountain, and San Fernando 7.5 minute quadrangles
which include the City of Santa Clarita limits. This information is included in
Exhibit S-4, Geologic Hazard Zones which identify areas of liquefaction
hazard and earthquake induced landslide hazard.
Liquefaction — there is a description of the liquefaction process with a table
that lists the relationship between liquefaction hazard and groundwater
depth. In addition, the proposed element makes reference to CDMG Special
Publication 117, Guidelines for Evaluating and Mitigating Seismic Hazards,
1997. This report lists recommendations for determining the degree of risk for
liquefaction.
• Tsunami & Seiches — there is a brief analysis of tsunamis and the potential
flooding they can cause, however there is no risk to the City due to the long
distance to the Pacific Ocean. In addition, there is a description of seiche's
and the potential of flooding associated with the Castaic Dam and Bouquet
Canyon Dam that if damaged, released water could potentially flow into the
City.
• Subsidence — there is a section on subsidence which is the lowering of the
ground surface. This generally occurs when fluids such as water, oil, and gas
are withdrawn from the subsurface. The structures most impacted by
subsidence are infrastructure facilities including canals, sewers, and
pipelines.
Map Exhibit Amendments
The existing Safety Element map exhibits will be updated as part of the proposed
amendment. Those map exhibits are attached to this report and are listed as
follows:
• Exhibit S-1, Recently Active Faults in the Southern California Region
• Exhibit S-2, Faults in Planning Area
• Exhibit S-3, Major Earthquakes in the Southern California Region
• Exhibit S-4, Geologic Hazard Zones
Table Amendments
The existing Safety Element tables (Table 1 and Table 2) will be updated and two
(2) new tables will be added to the proposed amendment as follows (see attached
tables):
• Table S-1, Modified Mercalli Intensity Scale of 1931
• Table S-2, Comparison of Richter Magnitude and Modified Mercalli Intensity
• Table S-3, Active Faults Near the City of Santa Clarita (replaces existing
Table S-2)
• Table S-4, Significant Historic Earthquakes Felt within City Limits (replaces
existing Table 9-1)
Goals and Policies
Currently there are five (5) goals with accompanying policies in the existing
Safety Element. Only one (1) goal addresses seismically induced hazards within
the existing Safety Element. This goal has been divided into two (2) separate
goals addressing seismic hazards. Therefore, the Safety Element of the General
Plan will have six (6) goals. The two (2) proposed seismic goals are as follows:
Goal 1 - Minimize risks to life and property associated with fault rupture and
seismically -induced groundshaking.
Goal 2 - Minimize risks to life and property associated with geologic hazards,
including but not limited to, landsliding, liquefaction, debris flows, mudslides,
rockfalls, and expansive soils.
ENVIRONMENTAL STATUS
As part of the project review, an environmental assessment was made to evaluate
the impacts of the project. It was determined that the proposed project could not
have a significant impact on the environment. As such, a Draft Negative
Declaration and Initial Study was prepared by staff and circulated for public
review and comment on August 28, 2001. As of the date of preparing this report,
staff has not received any feedback from members of the public.
FISCAL IMPACT
The cost of preparing an update to the seismic section of the Safety Element is
$12,000. Funding for this project has been budgeted in account 3120-8110 FY
2001-2002. Upon completion of the project the City will receive $7,500 from the
HMGP grant.
ATTACHMENTS
Resolution No.
Draft Safety Element Amendment (Exhibit A)
Draft Negative Declaration and Initial Study
JJL:VPB:ED
s:pbs \advance\ safetyel \ 01-146 \ council\report
CITY OF SANTA CLARITA
PLANNING & BUILDING SERVICES DEPARTMENT
NOTICE OF PUBLIC HEARING
APPLICATION: MASTER CASE NUMBER 01-146
(General Plan Amendment 01-003)
PROJECT APPLICANT: City of Santa Clarita, Planning and Building Services
PROJECT
DESCRIPTION: Amend the City's General Plan to modify the background technical
section, the goals and policies, and the map exhibits for the seismic
and geology section of the Safety Element. The proposed Amendment
will not result in development, but will affect future development
proposals within the Santa Clarita Valley.
PROJECT LOCATION: Citywide
A DRAFT NEGATIVE DECLARATION has been prepared for this proposed project and is available for
public review beginning at 12:00 p.m. on August 28, 2001 at:
City Hall
Planning & Building Services Department
23920 Valencia Boulevard, Suite 302
Santa Clarita, CA 91355
A public hearing on this matter will be conducted by the City of Santa Clarita Planning Commission
on:
DATE: October 2, 2001
TIME: 7:00 p.m.
LOCATION: Council Chamber, City Hall
23920 Valencia Blvd. First Floor
Santa Clarita, CA 91355
A public hearing on this matter will be conducted by the City of Santa Clarita City Council on:
DATE: October 23, 2001
TIME: 7:00 p.m.
LOCATION: Council Chamber, City Hall
23920 Valencia Blvd. First Floor
Santa Clarita, CA 91355
If you wish to challenge the action taken on this matter in court, you may be limited to raising only
those issues you or someone else raised at the public hearing described in this notice, or written
correspondence delivered to the City of Santa Clarita at, or prior to, the public hearing. If you wish
to have written comments included in the materials the Planning Commission receives prior to the
public hearing, it must be submitted to the Planning & Building Services Department by 12:00 P.M.
on Tuesday, September 25, 2001.
For further information regarding this proposal, you may contact the City of Santa Clarita,
Department of Planning & Building Services, 23920 Valencia Blvd., Third Floor, Santa Clarita, CA
91355; Telephone: (661) 255-4330, Enrique Diaz or Wendy Deats, Project Planners.
Vincent P. Bertom Jeffrey Lambert
Planning Manager Director of Planning & Building Services
Posted: Santa Clarita City Hall Published: The Newhall Signal
Los Angeles County Library, Valencia Branch August 14, 2001