HomeMy WebLinkAboutChapter 16 - Hazards and SafetyChapter 16: Hazards and Safety
Final Draft August 8, 2005
Butte County General Plan Background Report
1
CHAPTER 16: HAZARDS AND SAFETY
TABLE OF CONTENTS
16.1 INTRODUCTION...............................................................................................................................................3
16.2 HAZARDOUS MATERIALS MANAGEMENT..............................................................................................3
HAZARDOUS WASTE PRODUCTION ............................................................................................................................3
HAZARDOUS WASTE TRANSPORT ..............................................................................................................................3
HAZARDOUS WASTE DISPOSAL .................................................................................................................................4
HAZARDOUS WASTE EMERGENCY RESPONSE ...........................................................................................................5
HAZARDOUS WASTE REGULATION ............................................................................................................................5
16.3 EMERGENCY RESPONSE...............................................................................................................................5
CIVIL DISASTERS .......................................................................................................................................................5
HAZARDOUS MATERIALS EMERGENCY RESPONSE ....................................................................................................5
Regional Response...............................................................................................................................................6
Team Capabilities................................................................................................................................................6
16.4 BUTTE COUNTY EMERGENCY PLAN ........................................................................................................7
MUTUAL AID AGREEMENTS ......................................................................................................................................7
16.5 STRUCTURAL HAZARDS AND CRITICAL FACILITIES.........................................................................7
16.6 FIRE HAZARDS.................................................................................................................................................8
STRUCTURE FIRES .....................................................................................................................................................8
WILDFIRES.................................................................................................................................................................9
HAZARD DESCRIPTION ..............................................................................................................................................9
Influences on Wildfire Impacts.............................................................................................................................9
Weather.............................................................................................................................................................................9
Fuel.................................................................................................................................................................................10
Topography.....................................................................................................................................................................10
Human Actions...............................................................................................................................................................10
Effects of Wildfires.............................................................................................................................................12
HISTORIC WILDFIRES IN BUTTE COUNTY ................................................................................................................12
FIRE HAZARD ANALYSIS .........................................................................................................................................13
Local Wildfire Hazards......................................................................................................................................13
Urban Fire Hazards...........................................................................................................................................13
Effects of the Hazard..........................................................................................................................................14
FIRE PREVENTION AND RESPONSE ...........................................................................................................................14
Uniform Fire Code.............................................................................................................................................17
California Fire Code..........................................................................................................................................17
California Health and Safety Code and the Uniform Building Code.................................................................17
Title 19 of the California Code of Regulations ..................................................................................................17
Title 14 of the Public Resources Code...............................................................................................................17
Assembly Bill 337 (Bates Bill)............................................................................................................................17
FIRE RESPONSE........................................................................................................................................................17
16.7 DRAINAGE AND FLOOD CONTROL..........................................................................................................18
TOPOGRAPHY AND GEOGRAPHY ..............................................................................................................................18
MAJOR DRAINAGE BASINS ......................................................................................................................................19
PRECIPITATION ........................................................................................................................................................19
DRAINAGE AND FLOODING PROBLEM AREAS ..........................................................................................................19
APPRAISAL OF PRINCIPAL FLOOD PROBLEMS ..........................................................................................................21
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Butte County General Plan Background Report
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16.8 FLOOD HAZARDS AND DAM SAFETY......................................................................................................27
FLOOD HAZARDS .....................................................................................................................................................27
DAM SAFETY ...........................................................................................................................................................30
16.9 SEISMIC HAZARDS........................................................................................................................................33
INTRODUCTION ........................................................................................................................................................33
FAULT CLASSIFICATIONS .........................................................................................................................................33
ACTIVE FAULTS .......................................................................................................................................................37
Cleveland Hills Fault.........................................................................................................................................37
San Andreas Fault System..................................................................................................................................37
Midland-Sweitzer Fault......................................................................................................................................37
Eastern Sierra Faults.........................................................................................................................................37
POTENTIALLY ACTIVE FAULTS ................................................................................................................................38
PREDICTED EFFECTS OF EARTHQUAKES ..................................................................................................................39
Ground Shaking.................................................................................................................................................39
Liquefaction Potential........................................................................................................................................40
Seiches ...............................................................................................................................................................42
Landslides..........................................................................................................................................................42
Dam Safety.........................................................................................................................................................42
16.10 GEOLOGIC HAZARDS.................................................................................................................................42
EROSION ..................................................................................................................................................................42
SUBSIDENCE ............................................................................................................................................................45
LANDSLIDES ............................................................................................................................................................47
EXPANSIVE SOILS ....................................................................................................................................................49
VOLCANIC HAZARDS ...............................................................................................................................................51
NATURALLY OCCURRING ASBESTOS .......................................................................................................................51
LIST OF TABLES
TABLE 16-1 LARGE FIRES IN BUTTE COUNTY SINCE 1992...........................................................................................12
TABLE 16-2 FIRE STATIONS IN THE UNINCORPORATED AREA OF BUTTE COUNTY .......................................................16
TABLE 16-3 FLOODS ON BUTTE CREEK AND RECURRENCE INTERVALS .......................................................................23
TABLE 16-4 IDENTIFIED FLOODING PROBLEMS BUTTE COUNTY ..................................................................................26
TABLE 16-5 DAMS UNDER STATE JURISDICTION, BUTTE COUNTY ..............................................................................31
TABLE 16-6 SUMMARY OF MODIFIED MERCALLI INTENSITY SCALE FOR EARTHQUAKES............................................35
LIST OF FIGURES
FIGURE 16-1: FIRE HAZARD SEVERITY ........................................................................................................................11
FIGURE 16-2: FEMA FLOOD HAZARDS .......................................................................................................................22
FIGURE 16-3: ACTIVE AND POTENTIALLY ACTIVE FAULTS .........................................................................................36
FIGURE 16-4: LIQUEFACTION POTENTIAL ....................................................................................................................41
FIGURE 16-5: EROSION HAZARD POTENTIAL ...............................................................................................................44
FIGURE 16-6: SUBSIDENCE POTENTIAL & GAS AND GROUNDWATER WITHDRAWAL ...................................................46
FIGURE 16-7: LANDSLIDE POTENTIAL ..........................................................................................................................48
FIGURE 16-8: EXPANSIVE SOILS ...................................................................................................................................50
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Final Draft August 8, 2005
Butte County General Plan Background Report
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16.1 INTRODUCTION
One important County role is preparing for and responding to various threats to human life,
property, and environmental integrity. This chapter summarizes existing hazardous materials
issues within the county. It also reviews structural hazards and critical facilities, fire hazards,
emergency response, flood hazards, and dam safety.
16.2 HAZARDOUS MATERIALS MANAGEMENT
This section describes the resources in Butte County for managing hazardous materials. In many
instances, a “hazardous material” is simply a commonly used substance, either a gas, liquid, or
solid, that has been improperly used or disposed of. Accidents such as automobile crashes and
airplane crashes often create deposits of such materials, which might include insecticides, waste
motor oil, or cleaning fluids. Managing hazardous materials involves identifying, transporting,
and safely disposing of these materials, in order to prevent hazards to human health and protect
the life of natural systems. It also involves coordinating with State and federal agencies to
regulate hazardous waste production, and to identify and remediate hazardous waste sites.
Hazardous Waste Production
According to Butte County’s Hazardous Waste Management Plan, the county’s hazardous waste
production is about 6,500 tons per year. This amount does not include hazardous wastes treated
on-site. The most recent inventory of Butte County hazardous waste generators, provided by the
California Department of Toxic Substances Control (DTSC), shows a total of 22,036 tons
produced in 2001. The largest percentage is composed of waste oil, with Small Quantity
Generators (SQGs) producing the majority of the amount. Waste oil is the predominant
hazardous waste produced by large and small quantity generators counting for over 84 percent of
the county’s waste production in 2001 (the most recent year for which data is available).
The major generators of this waste in the county are haulers that are licensed to pick up used oil
from locations in other counties. Therefore, the largest sources of hazardous waste important to
Butte County are outside of the county. It is brought in by a licensed hauler and then shipped out
for recycling, treatment, or disposal. Medical wastes are another growing source of hazardous
wastes in the county.
Hazardous Waste Transport
Nearly all of the hazardous materials transported through Butte County are carried by truck on
the State Highway system. Little or none of the hazardous waste is transported through the
county via rail. County roads and city streets are used to transport locally generated wastes from
the source to the regional highway system. The County has not quantified the amount of
hazardous materials which are transported through Butte County en route to adjoining counties
or adjoining states.
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Hazardous Waste Disposal
The Neal Road Landfill, a Class III facility, is not permitted to accept hazardous waste. Class I
landfills are permitted to accept these materials. There are only two remaining Class I landfills in
California permitted to receive untreated hazardous wastes: the Kettleman Hills facility in Kings
County, and the Casmalia Resources Facility in Santa Barbara County.
The county does not have any Class I landfill disposal or treatment facilities. The Butte County
Hazardous Waste Management Plan identified that the amount of hazardous wastes produced or
brought into the county cannot economically support the development of a Class I facility within
Butte County.
In April 2002, Butte County assumed responsibility of a Permanent Household Hazardous Waste
Collection Facility (PHHWCF). The PHHWCF is located adjacent to the Chico Airport and is
operated under contract by A/C Industrial Services, Inc. The PHHWCF provides a controlled
environment for receiving and processing household hazardous waste that originates within
Butte County. The PHHWCF is open to all residents of Butte County. Conditionally Exempt
Small Quantity Generators can also use the facility. In addition, a Mobile Household Hazardous
Waste Program is targeting outlying areas of the county.
Additional household hazardous waste facilities are operated by Norcal Waste Systems in
Oroville, and Waste Management, Inc. in Gridley, for the benefit of their customers.
There is one federally-designated Superfund site in the county that is listed on the National
Priority List (NPL) as of 2003: the Koppers Company, Inc. plant, located south of Oroville. The
investigations and remedial actions at the Koppers plant are substantially complete. Other
previous sites have been de-listed. Investigations by the federal Environmental Protection
Agency (EPA) have found surface and ground water contamination at the Oroville site.
Other sites are being investigated by DTSC and the Regional Water Quality Control Board. The
types of wastes resulting from the cleanups of such sites pose a significant problem for Butte
County’s hazardous waste management planning. Until Remedial/Feasibility Studies are
complete, it is not possible to predict the quantity of clean-up related wastes that will require off-
site treatment or disposal. Therefore, it is possible that additional hazardous waste management
facilities may be needed in the county.
The Humboldt Road Burn Dump in Chico has been the subject of extensive investigation. This
site involves large amounts of burn dump waste, including the primary city disposal area, several
smaller areas historically operated by private companies, and substantial areas of scattered waste.
While the site has been extensively characterized, no final corrective action alternative has yet
been selected. The Regional Water Quality Control Board is the lead agency for this voluntary
cleanup action.
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Butte County General Plan Background Report
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Hazardous Waste Emergency Response
For a full discussion of agencies responsible for emergency responses to hazardous waste
emergencies, please see Section 16.3 below.
Hazardous Waste Regulation
As of 2003, Butte County has not implemented any programs for regulating hazardous wastes,
and only exercises its authority in response to complaints. The local permits required are limited
to those granted by the Butte County Air Quality Management District for hospital incineration .
Additional regulations affecting hazardous wastes originate from the Toxics and Safe Drinking
Water Initiative. Administered by the Environmental Health Division, the County also collects
inventory forms from facilities that store hazardous materials. In order to fulfill legislative
requirements, the County has developed a Hazardous Materials Emergency Response Plan.
The Butte County Division of Environmental Health has submitted an application dated August
31st, 2001, to the California Environmental Protection Agency for certification as a Certified
Unified Program Agency (CUPA). Upon resolution of program funding issues, the Division
hopes to obtain CUPA certification. Additional CUPA program elements include inspection of
hazardous waste generators, “Tiered Permitting” hazardous waste treatment facilities
(conditionally exempt, conditionally authorized, and permit by rule tiers only), and limited
oversight of above ground hazardous material storage tank facilities.
16.3 EMERGENCY RESPONSE
Civil Disasters
Butte County maintains a Civil Disaster Office (CDO) to coordinate interagency and
intergovernmental comprehensive emergency management planning, operations, and disaster
assistance claims management for the county. CDO works with state and local agencies to
develop effective emergency response systems within the county. CDO acts as the requesting
and coordinating agency when situations require the involvement of state and other outside
agencies. Also, substantial amount of the time is spent on public educational activities.
The costs for the emergency services program are shared between the County and the Federal
Emergency Management Agency (FEMA) through its Emergency Management Assistance
Program, which is coordinated in California through the Governor’s Office of Emergency
Services.
Hazardous Materials Emergency Response
In the event of a hazardous material emergency, several agencies are responsible for timely
response, depending on the extent and type of the incident.
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Butte County General Plan Background Report
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The Butte County Hazardous Materials Response Team is the agency which responds to large
scale, emergency hazardous material incidents within the county. This team is made up of
specially trained representatives of the Butte County Fire Department, California Department of
Forestry, and members of the City of Chico, Paradise, Gridley, and Biggs Fire Departments.
The team was organized by the Butte County Fire Chiefs' Association beginning in 1989 through
the use of a Joint Powers Agreement (JPA). Team members are provided by the various
departments: cities of Chico, Oroville, Paradise, Biggs, and Gridley; and the County of
Butte/CDF Fire. Funding is provided through the JPA at $.10 per capita (serving 210,000 people
of Butte County), Cal EPA grants, and reimbursements. Annual responses number about 120,
with drug labs and waste being the main cause of incidents. Other significant incidents include
train derailments, tanker overturns, agricultural incidents, and a U-2 which crashed into Oroville.
The team is composed of 33 specialists/technicians and an additional 10 technicians who provide
support. The team trains together monthly, and, with the State-approved hazardous materials
(“haz-mat”) training grounds at Butte College, training includes a variety of hands-on
experiences.
The team is Type 1 and staffs two units. The newer unit, Haz Mat 64, is stationed at the Kelly
Ridge CDF Fire/Butte County Station, and Haz Mat 1 (an older unit) is stationed at Chico
Station 1.
Regional Response
Through a contract with the California Environmental Protection Agency (CalEPA), this team
responds throughout the area from Marysville north to the Oregon border. If approval is granted
by the Department of Toxics duty officer and the incident commander, the unit will be
dispatched by Toxics with no cost to the requesting jurisdiction. CalEPA guarantees covering
team costs if the requesting jurisdiction will help in securing reimbursement from the responsible
party (if possible). This regional concept also involves the Marysville haz-mat team, which
rotates on call with the Butte County team.
Team Capabilities
Each unit carries level A and level B suits, allowing them to enter most toxic atmospheres. They
also carry proximity suits. The units carry chemical analysis kits, air monitoring and gas
detection tools, printed and computer chemical databases, decontamination equipment, and a
variety of hand tools. Special equipment includes: chlorine kits, stinger and air drill for fuel
tankers, underflow and overflow pipes and valves, and a large amount of absorbents.
As of 2003, the team responded to between 60 and 120 calls per year. Approximately 30% of the
calls are from methamphetamine labs and waste dumps. Other significant calls are railroad and
highway related.
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Final Draft August 8, 2005
Butte County General Plan Background Report
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16.4 BUTTE COUNTY EMERGENCY PLAN
The Butte County Emergency Plan is designed to focus on potential large-scale disasters, rather
than daily emergencies that are regularly handled by local law enforcement and protection
agencies. The plan defines the County’s planned response to "extraordinary" emergency
situations associated with natural disasters, technological incidents, and nuclear defense
operations. The plan is activated by the following alarms or incidents:
• an order of the Butte County Board of Supervisors
• a state of emergency proclaimed by the Governor
• a proclaimed state of war emergency
• a Presidential declaration of a National Emergency
• upon receipt of an attack warning
• an indication of a nuclear detonation.
Evacuation routes are determined depending on the location, type, and extent of the emergency
incident.
Mutual Aid Agreements
The Butte County plan states that mutual aid resources will be provided in accordance with the
California Master Mutual Aid Agreement. The plan calls for establishing agreements among
various jurisdictions in order to prepare a coordinated response to a proclaimed emergency. The
agreements are activated when a state of emergency is declared, and the assistance occurs as
prearranged among participating agencies.
16.5 STRUCTURAL HAZARDS AND CRITICAL FACILITIES
The majority of buildings in the unincorporated areas of Butte County are one- and two-story
wood frame structures, most of which are single family dwellings. Concentrations of larger
buildings are found on the campuses of Butte Community College and California State
University, Chico. Adjacent to or in Oroville and Chico are several shopping malls that have
several major structures with large open areas. Concentrations of one to three story unreinforced
masonry structures (primarily brick) are located in the older downtown areas of Chico and
Oroville.
The Board of Supervisors is responsible for adopting codes and standards for the construction,
repair, or alteration of structures. Butte County’s Development Services Department-Building
Inspection Division is the agency responsible for enforcing building regulations in the
unincorporated areas. The Cities of Chico, Gridley, Oroville, and Paradise have their own
building inspection departments.
Critical facilities are generally defined as those providing important health and safety functions
(e.g., hospitals, police and fire stations), having large numbers of occupants (e.g., office
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Butte County General Plan Background Report
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buildings), engaged in large scale industrial processes (e.g., manufacturing plants and mills),
providing large numbers of people with critical services (e.g., electricity, gas, water, and waste
water), involved with the manufacturing, use, storage, or distribution of toxic and hazardous
materials (e.g., refineries, petrochemical plants, and warehouses), having a network character
upon which the community depends heavily (e.g., highways, important main roads, and bridges),
and those whose failure threatens large numbers of people in the nearby and surrounding areas
(e.g., dams, and nuclear power plants).
The performance of a structure during an earthquake varies considerably, depending on the
proximity of the building to an active fault or some other ground hazard, such as erosion or
liquefaction. It also depends on the materials it is built from, the magnitude, intensity, and
duration of the quake, and similar factors. Butte County has experienced two damaging
earthquakes (1940 and 1975). Unreinforced masonry buildings in the older sections of Chico
(1940) and Oroville (1975) suffered moderate to severe damage in these earthquakes.
There is one Earthquake Fault Zone ( Earthquake Fault Zones were called “Special Studies
Zones” prior to January 1, 1994) in the county, the Cleveland Hills Fault south of Oroville, as
depicted Figure 16-3. This Zone was established by the California Division of Mines and
Geology (now the California Geological Survey), pursuant to Public Resources Code Sections
2621-2630 . This law requires that a geologic report be filed as a precondition for building
permit, in order to allow the local building official to judge the damage to the proposed building
in case of a fault rupture.
16.6 FIRE HAZARDS
The public is exposed to fire-related hazards from two potential sources: structural fires and
wildland fires affecting urban and rural residential interface areas. This section will describe
general conditions under which both types of fires may occur, including factors that may
contribute to increased fire hazards within Butte County and its cities.
Structure Fires
Structures in the urban and rural interface areas are at risk of fires from wildland areas as well as
those starting from inside the structures. Such fires can, in turn, spread to wildlands or other
structures, causing additional needs for fire fighting resources. Methods of minimizing the extent
of damages to structures are:
• Automatic sprinkler systems in homes. Required in all new homes built on parcels that
have been created since 1991;
• Defensible space around structures. Public Resource Code 4290, incorporated into Butte
County in 1991, requires that all new dwellings on one acre parcels or larger, must be
setback from property lines at least 30 feet and up to 100 feet where conditions warrant.
Homeowners are responsible to maintain this defensible space to protect their property
from an approaching wildland fire and keep a structure fire from spreading into the
wildland. All new building plans in State Responsibility Areas are reviewed for adequate
fire safety compliance.
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Final Draft August 8, 2005
Butte County General Plan Background Report
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• Non-combustible building materials. Utilizing non-combustible construction on new
dwellings can minimize damages done to buildings.
• Adequate separation or protection of structures to minimize the threat of a conflagration.
Wildfires
The term “wildfire” refers to fires that usually result from the ignition of dry grass, brush, or
timber. Wildfires commonly occur in areas that are characterized by steep, heavily vegetated
hillsides, which make suppression of the fire difficult. Wildfires play an important role in the
ecology of many natural habitats; however, as urban development moves into areas susceptible
to wildfire hazards, risks to human safety and property increase.
To describe an area where urban development has been located in proximity to open space, or
“wildland” areas, the term “urban-wildland interface” is commonly used. The most common type
of urban wildland interface results when development occurs immediately adjacent to wildland
vegetation. Other interface conditions can be created when urban development is intermixed with
wildland vegetation, or when pockets of wildland vegetation occur inside developed areas. The
foothill communities of Kelly Ridge, Bangor, Cohasset, Forest Ranch, Paradise Pines, Concow,
Yankee Hill, Berry Creek, Forbestown, and the town of Paradise are examples of intermixed
urban-wildland interface areas. Fires that occur within the urban-wildland interface areas affect
natural resources as well as life and property. This type of fire is described as “a fire moving
from a wildland environment, consuming vegetation for fuel, to an environment where structures
and buildings are fueling the fire” (California Resources Agency, 1996).
Hazard Description
Influences on Wildfire Impacts
The fire hazard severity assigned to state responsibility lands under BCFD fire protection are
measures of expected fire behavior given the topography, vegetative fuels, and weather
conditions (wind speed, humidity, and temperature). Based on these parameters, the fire hazard
severity is determined to be either very high, high, or moderate. Population density and the
number of structures in a given area are not determinants of an area’s fire hazard severity. The
actions of humans also influence the risk of wildfires. These four factors in Butte County,
weather, fuel, topography and human actions, are described below.
Weather
The climate in Butte County is generally referred to as “Mediterranean” with hot dry summers
and relatively cool, moderately wet winters. Rainfall throughout the county occurs primarily
between October and April, and ranges between 75+ inches per year in the foothill/mountain
areas, to less than 18 inches per year in the valley areas. Because the summer months are
generally hot and dry, the risk of wildfires is greatest in late summer and early fall.
Compounding the severity of fire conditions are north to northeast winds, as well as low relative
humidity in the summer and fall. The community of Yankee Hill/Concow is especially affected
by northeast winds, because the north fork drainage of the Feather River enhances those winds.
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Similar weather-related elements have complex important effects on wildfire intensity and
behavior. Wind is a primary weather factor that influences fire behavior – as wind velocity
increases, the rate of fire spread, intensity and spotting potential also increase. Gust and erratic
wind conditions can cause a fire to spread irregularly, making it difficult to predict its path and
effectively deploy fire suppression forces. Relative humidity is also an important fire-related
weather factor. As humidity levels drop, the dry air causes vegetation moisture levels to
decrease, thereby increasing the likelihood that plant material will readily ignite and burn.
Fuel
A large portion of Butte County is covered by natural vegetation. Fuels have been classified as
grasses, brush, timber, or slash. This vegetation can be further defined into 13 fuel model types,
each of which contributes varying degrees to fire hazard severity. The likely fire hazard severity,
depicted Figure 16-1, can be influenced by many factors, including the age of vegetation, the
amount of accumulated dead plant material, the period of time since a stand of vegetation was
last burned, the climate, and the topography.
The most significant fire hazard severity is posed by communities of mature chaparral and
overstocked stands of mixed conifer with a heavy component of shrub. This type of vegetation
burns with intense heat and high flame, because the amount of fuel readily available to burn can
be very high if the area has not been properly managed or has not recently burned. Controlled
burning is one method that can greatly reduce the fuel loading and hence fire hazard severity for
a given area. Other fuel conditions in addition to fuel loading that can significantly affect fire
behavior include an abundance of dead fuel, live and dead fuel moistures, fuel arrangement, and
in developed areas the addition of some types of ornamental vegetation.
Topography
Steep terrain or slope plays a key role in the rate and direction in which wildfires spread; as fires
will normally burn much faster uphill. Generally, when the gradient of a slope doubles, the rate
of spread of a fire will also double. Steep, rugged topography also channels air-flow, thereby
creating erratic wind patterns. Fire suppression in steep areas is complicated by limited
accessibility, and the effectiveness of firefighters and equipment are hampered by terrain and the
lack of access roads.
Human Actions
Most wildfires are ignited by human action, the result of direct acts of arson, carelessness, or
accidents. Many fires originate in populated areas along roads and around homes, and are often
the result of the careless disposal of cigarettes, use of equipment or debris burning. Recreation
areas that are located in high fire hazard areas also result in increased human activity that can
increase the potential for wildfires to occur.
32
99
70
191
162
70
162
99
32
PARADISE
OROVILLE
BIGGS
GRIDLEY
CHICO
FIRE HAZARD SEVERI TY
Figure 16-1
Butte County
General Plan
Miles02468101
Source: California Department of Forestry and Fire Protection
Date printed: June 6, 2003
Legend
SEVERITY
VERY HIGH
HIGH
MODERATE
NO DATA
NON SRA
Lakes
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Effects of Wildfires
Wildfires affect the natural environment in several ways. Some ecosystems are dependent upon
recurrent fire to survive and have adapted to re-establishing themselves after a fire. These types
of adaptations are common in the chaparral plant community, which typically has a very high
wildfire risk. After a wildfire stops burning, the burned land is laid bare of its protective
vegetation cover and is susceptible to excessive runoff and erosion from winter storms. The
intense heat from the fire can also cause a chemical reaction in the soil that makes it less porous,
and the fire can destroy the root systems of shrubs and grasses that aid in stabilizing slope
material. When the winter rains come, the possibility of severe landslides and debris/mud flows
is greatly increased.
In addition to damaging natural environments, wildfires injure and kill residents and firefighters,
as well as damage or destroy structures and personal property. Wildfires also deplete water
reserves, down power lines, disrupt telephone service, and block roads. They can also indirectly
cause floods, if flood control facilities are inadequate to handle an increase in storm runoff,
sediment, and debris that is likely to be generated from barren, burned-over hillsides.
Historic Wildfires in Butte County
During the past decade, Butte County has experienced several large and damaging wildfires in
and around the wildland urban interface areas. In 2000 and 2001 alone, three fires in the Yankee
Hill area burned over 11,874 acres and destroyed 61 residence and three commercial buildings.
A summary of wildfires over 300 acres in size that have occurred in Butte County in the last 10
years is provided in Table 16-1. This table does not list the numerous smaller fires that have
occurred throughout the county.
TABLE 16-1
LARGE FIRES IN BUTTE COUNTY SINCE 1992
Year Fire Name / Community Acreage Burned Structures Destroyed
1992 Dry/Pentz 700 No
1992 Cox/Palermo 700 No
1992 Maidu/Centerville 675 Yes
1992 Burton/Lower Paradise 6,000 No
1992 Villa/Palermo 6,700 Yes
1993 Campbell/West Oroville 693 No
1994 Raulson/Yankee Hill 900 Yes
1994 Table/Oroville 960 No
1995 Hwy 149/Central Butte 2,000 No
1996 Palermo/Palermo 1,200 No
1997 Hwy 149/Central Butte 594 No
1999 Butte Complex/Countywide 35,284 Yes
2000 Concow/Yankee Hill 1,830 Yes
2001 Poe/Yankee Hill 8,333 Yes
2001 Seventy/Yankee Hill 1,711 No
Source: California Department of Forestry and Fire Protection
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Fire Hazard Analysis
Local Wildfire Hazards
CDF has undertaken a program under the California Fire Plan to assess the fuel conditions, asset
vulnerability, weather severity, and level of fire protection services. These assessments are
performed annually and documented in the CDF Butte Unit Fire Management Plan, which
provides the basis and guidance for the Unit’s fire safe planning and hazardous fuel reduction
efforts.
The Fire Hazard Severity Zone classification (see Figure 16-1) assigns ranks (moderate, high and
very high) to given areas based upon expected fire behavior for unique combinations of
topography and vegetative fuels under a given severe weather condition (wind speed, humidity
and temperature). In Butte County, the foothills and mountainous areas of the county, extending
from Cohasset in the north, to Forbestown in the south have been designated as either high or
very high, with the majority of the area in the very high classification. The fact that an area is in
a moderate hazard designation does not mean it cannot experience a damaging fire. The area
likely received the moderate rating due to relatively mild topography or not as frequent severe
fire weather.
Unincorporated communities within the county that are subject to increased wildfire risks are
generally those communities like Forest Ranch, Cohasset, Yankee Hill/Concow, Maglia/Paradise
Pines and Kelly Ridge where development has resulted in the creation of an urban/wildland
interface zone. The Town of Paradise faces the same hazards since it is in the middle of an
urban/wildland area of the county.
The El Medio Fire Protection District covers an area of seven square miles in the South Oroville
area. In 2005, the District included 2,005 single family residences, wildland/urban interface
areas, and other undeveloped areas. According to the Butte County Local Agency Formation
Commission (LAFCO), a Municipal Service Review (MSR) prepared for the El Medio Fire
Protection District indicated that the District did not have the resources to provide an acceptable
level of fire service to either existing or new residents within the District. As of 2005, Butte
County was considering collecting impact fees, although the deficiencies noted within the MSR
cannot be made up with developer impact fees alone – additional revenue is needed to pay for
salaries and buy equipment. Various ballot measures to approve a tax increase to provide the
necessary revenue to address existing deficiencies have been rejected by the voters within the
District in recent years.
Urban Fire Hazards
The risk to life and property that results from fires in urban settings is influenced by many
factors. When assessing the potential for urban fire hazards and the appropriate level of fire
protection that should be provided, the following should be addressed:
• Availability of adequate supplies of water
• On-site fire suppression systems
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• The size and height of the structure
• The “use” occupying the structure
• Flammable or hazardous items that may be stored within the structure
• The type of building construction materials
• Response time by fire suppression personnel
• Adequate emergency ingress and egress
Different types of structures and land uses present their own fire prevention and suppression
characteristics and potential problems. In the developed areas throughout Butte County,
residential structural fires are the predominate urban fire risk.
Effects of the Hazard
The potential for loss of life and property from urban fire hazards is greatest in places where
large groups of people gather, such as offices, stores, hotels, and theaters. Uses which may suffer
large monetary losses due to a major fire include businesses, factories, and shopping areas.
Types of development and conditions that present the most difficult fire-protection problems in
urban areas include:
• Multiple-story, wood frame, high-density apartment development
• Developed areas where structures have little or no setbacks or building-to-building
separation
• The storage, handling, and use of hazardous materials; and
• Natural disasters.
Fire Prevention and Response
The responsibility for the prevention and suppression of wildfires in Butte County belongs to the
California Department of Forestry and Fire Protection (CDF), the Butte County Fire Department
(BCFD), and to individual cities within their incorporated areas.
CDF/BCFD provides fire suppression services to approximately 1677 square miles of Butte
County. As the major fire fighting force in the county, CDF and BCFD maintains 48 fire stations
and support facilities either fully or cooperatively. Fire stations locations in unincorporated areas
of the county that are managed by the CDF/BCFD are shown in Table 16-2. The CDF and BCFD
also maintain a fleet of fire fighting equipment in Butte County, including engines, aircraft,
squads/rescues, bulldozers, water tenders, hazardous materials units and heavy rescue vehicles.
The CDF, United States Forest Service (USFS), and the Bureau of Land Management (BLM)
have entered into a mutual aid agreement for the purpose of wildfire protection in Butte County.
Mutual aid agreements are reciprocal arrangements in which fire protection agencies share
personnel and equipment during emergency situations. The Plumas National Forest, Lassen
National Forest, the cities of Chico, Gridley, Biggs and Oroville and the Town of Paradise are all
signatories to automatic aid agreements with both CDF and BCFD. A mutual aid agreement
exists between BCFD and the El Medio Fire Protection District. CDF and BCFD are also
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participants in the State of California Master Mutual Aid agreement. CDF also has cooperative
agreements with the Cities of Gridley and Biggs for fire protection.
Table 16-2 lists the existing fire stations that are located in the unincorporated areas of the
county and what agency/department is responsible for the station operation.
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TABLE 16-2
FIRE STATIONS IN THE UNINCORPORATED AREA OF BUTTE COUNTY
10 Butte Meadows BC Volunteer
11 Butte Meadows (open during fire season only)CDF/BCFD
12 Stirling City BC Volunteer
13 Stirling City CDF/BCFD
17 Butte Fire Center CDF/CCC
21 Cohasset BC Volunteer
22 Cohasset (open during fire season only)CDF/BCFD
23 Forest Ranch CDF/BCFD
24 Forest Ranch BC Volunteer
25 Butte Valley BC Volunteer
26 Centerville BC Volunteer
27 Centerville BC Volunteer
31 Magalia BC Volunteer
32 Magalia BC Volunteer
33 Upper Ridge CDF/BCFD
35 Paradise CDF/BCFD
36 Jarbo Gap CDF/BCFD
37 Jarbo Gap BC Volunteer
38 Concow BC Volunteer
41 Nord CDF/BCFD
42 North Chico CDF/BCFD
44 South Chico CDF/BCFD
45 Durham CDF/BCFD
51 Feather Falls (open during fire season only)CDF/BCFD
52 Feather Falls BC Volunteer
53 Clipper Mills BC Volunteer
54 Robinson Mills CDF/BCFD
55 Bangor CDF/BCFD
60 Brush Creek BC Volunteer
61 Berry Creek BC Volunteer
62 Berry Creek CDF/BCFD
63 Oroville HQ’s CDF/BCFD
64 Kelly Ridge CDF/BCFD
66 Wyandotte BC Volunteer
67 Cherokee BC Volunteer
71 Richvale CDF/BCFD
72 Palermo CDF/BCFD
73 Biggs CDF/BCFD
74 Gridley CDF/BCFD
76 Gridley BC Volunteer
77 Greylodge BC Volunteer
Source: Butte County Fire Department, 2003
Fire prevention is a primary objective and the major activity of fire departments in urban areas.
After a fire starts, it is the objective of the fire department to minimize the damage to life and
property. To minimize potential fire risks, a variety of legislative and advisory programs have
been developed.
Local ordinances direct fire prevention activities within Butte County. These include 1)
“Improvement Standards for Subdivisions, Parcel Maps and Site Improvements Pursuant to
Chapter 20 of the Butte County Code”; 2) Chapter 38 and 38A of the Butte County Code
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covering Fireworks and Weed Abatement, 3) The Fire Safe Regulations of Public Resource Code
4290 (in State Responsibility Areas) and Public Resource Code 4291.
The following is a list of non-local laws and ordinances that apply to fire hazards:
Uniform Fire Code
This Code provides minimum standards for many aspects of fire prevention and suppression
activities. These standards include provisions for access, water supply, fire protection systems,
and the use of fire resistant building materials.
California Fire Code
The California Fire Code is the Uniform Fire Code with State of California amendments (this is
the official Code for the State and all political subdivisions). It is located in Part 9 of Title 24 of
the California Code of Regulations (Title 24 is commonly referred to as the California Building
Standards Code). The California Fire Code is revised and published every three years by the
California Building Standards Commission. Local jurisdictions have 180 days to make more
restrictive amendments to the Code after it is released. The most recent California Fire Code
became effective as of November 1, 2002.
California Health and Safety Code and the Uniform Building Code
The Heath and Safety Code regulates the abatement of fire-related hazards. It also requires that
local jurisdictions enforce the Uniform Building Code, which provides standards for fire resistive
building and roofing materials, and other fire-related construction methods.
Title 19 of the California Code of Regulations
These regulations pertain to fire prevention and engineering measures for new construction.
Title 14 of the Public Resources Code
These regulations provided additional fire prevention and suppression standards.
Assembly Bill 337 (Bates Bill)
In response to the Oakland Hill fire of 1991, this bill was passed in 1992. It required brush
clearance and fire resistant roof material (Class A or B) to be used on all new construction that is
located in areas designated as being a “Very High Fire Severity Zone”.
Fire Response
The ability of the Fire Department to control both “wildfires” and “structure fires” depends on
several components, one of which is the adequacy and availability of water supply. New
subdivisions and commercial developments are required to install a pressurized water system
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with minimum water flows to meet the requirements of the Uniform Fire Code. This is
accomplished by either connections to an existing water purveyor or establishing a private water
source controlled by a County Service Area (CSA). The CSA systems should be dissolved as
soon as they can be connected to a Community water purveyor or establishment of a Mutual
Water Company. This will assure the Fire Department that adequate water volume and pressure
are readily available in the event of unwanted fires. Access to this water system and the spacing
of the fire hydrants is also determined by the Fire Code.
In areas where no community water system exists, water for fire protection is furnished by the
County’s 17 water tenders. These water tenders are strategically placed around the county to
supplement the fire engines responding to all types of fires. As the population continues to grow
in the urban-wildland areas, additional water tenders will be required to keep up with the growth.
Water tenders are staffed by citizen volunteer firefighters. Because of this, there is no guarantee
that the water tender will respond when needed. Consideration must be given to full time, career
staffing of water tenders to ensure adequate response of this critical resource.
Currently, a mitigation measure is added to all parcel splits that require an automatic fire
sprinkler system be installed in all new dwellings built where a community pressurized water
system does not exist. This fire sprinkler system, installed per the requirements of NFPA 13D,
allows the residents an additional 10 minutes to exit the burning structure. This requirement has
proven to be an effective way to prevent loss of life, reduce fire damages and reduce the time and
personnel needed to control and clean up after the fire. An ordinance mandating that all new
dwellings must have an automatic fire sprinkler system installed should be required in the
county.
16.7 DRAINAGE AND FLOOD CONTROL
This section focuses on western Butte County, where most drainage shortfalls exist. Eastern
Butte County consists primarily of foothills and mountainous areas, with sparse development and
well-defined, deeply incised channels. Drainage issues in the eastern part of the county are
generally not significant, and are therefore not a focus of this report. Most drainage problems
occur either near, or west, of the foothill areas (roughly below an elevation of 300 feet).
Topography and Geography
The western valley topography is mainly flat, with minimal rolling terrain near the base of the
foothills. Drainage within Butte County flows southwesterly from the Cascade and Sierra
Nevada Mountain ranges and foothill areas, toward the Sacramento Valley area in the west.
Ultimately, whether by overland flow, tributary swales (a “swale” is a shallow, vegetated ditch),
or perennial streams such as Butte Creek and Big Chico Creek, all surface drainage ultimately
ends up in the Feather or Sacramento Rivers.
Surface conditions in western Butte County consist primarily of irrigated agricultural land and
non-irrigated pasture. Chico and Oroville are the major urban areas in the west, with many
smaller communities such as Gridley, Biggs, Durham, Palermo, and Richvale.
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Soils in western Butte County are comprised primarily of deposits from streams, flood basins,
and mountain runoff. These deposits are called “alluvium.” The low-lying alluvium deposits
consist of sand, gravel, silt and small amounts of clay. The coarser alluvium soils located near
the Sacramento River are more permeable, which means more storm water runoff passes
through. Located primarily in central southern Butte County, the flood basin deposits are
comprised of fine-grained material, principally silts and clays. The permeability of this soil is
low, which provides favorable conditions for rice farming. Alluvial deposits at the bases of
slopes or mountains, called alluvial fan deposits, consist of mixed sediments deposited by
streams. Their infiltration rates are locally variable and have a broad range of permeability.
Major Drainage Basins
Drainage in Butte County can be separated into two major drainage basins that have a number of
tributary basins. The runoff that does not pond in low-lying flat areas ultimately ends up in the
Feather River or the Sacramento River. The Feather River Drainage Basin drains approximately
one-half of Butte County. The Sacramento River drainage includes the extreme western portions
of Butte County, and eventually picks up the Cherokee Canal and Feather River further south in
Sutter County.
Unlike the east portion of the county, western Butte County contains few natural channels for
drainage. Big Chico Creek, Butte Creek, Wyman Ravine, Rock Creek, and Clear Creek are the
major tributaries feeding the Feather and Sacramento Rivers.
Precipitation
A wide range of precipitation has been recorded throughout the county. Precipitation ranges from
less than 20 inches of rainfall annually in the western valley area to over 80 inches of snow and
rain in the eastern Cascades and Sierra Nevada mountains. There is a strong meteorological
dynamic between the low elevation valley areas and the eastern mountains that causes more
precipitation higher in the mountains. The majority of the precipitation falls as rain below the
4,000 foot elevation. Above 4,000 feet, a considerable portion of winter precipitation occurs as
snow.
Drainage and Flooding Problem Areas
Because significant drainage problems exist within the county, various drainage studies have
been performed within the last 47 years to analyze flooding problems and plan for future
drainage needs. Drainage issues in the Chico area, which is the largest developed area in Butte
County, has been studied numerous times. Prior studies conducted by the Federal Emergency
Management Administration (FEMA) excluded all the incorporated areas (City of Biggs, City of
Chico, City of Gridley, City of Oroville and Town of Paradise) from the mapping process since
they did not participate in the program. However, since 1989 FEMA has changed its policy and
all areas within Butte County have been mapped with flood risks and identified SFHAs. They
have been labeled with alpha symbols, such as Zone A, AE, and AO. These are subject to 100
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year flood events on the new FEMA maps Series C, dated June 8, 1998 and Series D, dated April
20, 2000.
Other localities in Butte County flood. Some, however, are not depicted on Federal Flood
Insurance Rate Map (FIRM) panels. Presently, empirical information from personal observations
during storm events by staff of the Public Works Department and the State Department of Water
Resources (DWR) supplement available information provided by FEMA. In order to avoid future
flood problems, the County will apply this knowledge to projects in Butte County even though
FEMA information may not be sufficient to document flooding problems.
Information published by the FEMA Flood Insurance Study (FIS) on June 8, 1998 revises and
supersedes a previous study conducted in 1989. The 1998 and 2000 FIS contains preliminary
flood hazard maps, effective September 29, 1989. These maps are the most accurate and reliable
produced by FEMA to date.
The final 1998 and 2000 FIS combined the previous Flood Insurance Rate Maps (FIRM) and
Flood Insurance Studies of the county and incorporated cities into a consistent countywide
format. Under this new countywide format, FIRM panels have been produced using a single
layout for the entire area within the county. Past FIRM maps depicted separate layout formats for
each community that were difficult to match with adjacent map panels. At times this would raise
questions about the vulnerability to flooding of adjacent panel areas. The 1998 FIS also utilized
digitized mapping data and incorporated road and highway data from the 1990 U.S. Census
TIGER files. Under this new countywide format, the 1998 and 2000 FIS now comprehensively
address flood problems in Butte County identified by FEMA.
The FIRM panels contain flood descriptions of special flood hazard areas. Areas that are subject
to flooding are depicted by alpha symbols, such as A, AE, AH, AO and “shaded X” zones. The
following is a description of these flood symbols:
ZONE “A”: Subject to 100 year flooding with no base flood elevation determined. Identified
as an area that has a one percent chance of being flooded in any given year.
ZONE “AE”: Subject to 100 year flooding with base flood elevations determined.
ZONE “AH”: Subject to 100 year flooding with flood depths between one and three feet
being areas of ponding with based flood elevations determined.
ZONE “AO”: Subject to 100 year flooding with flood depths between one and three feet
being subject to sheet flow on sloping terrain with average depths determined.
“SHADED ZONE X”: Subject to 500 year flooding. Identified as an area that has a .2
percent chance of being flooded in any given year.
Figure 16-2 shows these FEMA flood hazard zones.
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On April 11, 2000, the Butte County Board of Supervisors adopted (through Ordinance No.
3598) the flood insurance study (FIS) produced by the Federal Insurance Administration (FIA)
of the Federal Emergency Management Agency (FEMA), and accompanying flood insurance
rate maps (FIRM) and flood boundary and floodway maps (FBFM) with map index dated June 8,
1998. The ordinance was adopted as Section 21. Article IV, (Flood Hazard Prevention), of
Chapter 26 (Buildings), of the Butte County Code. The April 20, 2000, Series D revisions and
subsequent revision to certain FEMA FIRM panels are automatically included and adopted for
flood hazard prevention requirements.
Appraisal of Principal Flood Problems
As with most Sacramento Valley counties, flooding problems in Butte County occur in the
mountains as well as the poorly-drained valley floor. Butte County’s foothill and upland areas
generally do not have flooding. However, drainage problems in the Paradise and Butte Meadows
areas do exist. Additionally, the runoff from impervious surfaces is also a concern, particularly
because the surface area of impervious cover is increasing. While information on problem areas
in the incorporated areas is available, information on the severity of drainage problems in the
unincorporated areas, which comprise most of the county, is generally not available.
The updated 1998 and 2000 Flood Rate Insurance Maps identify the most recognized flooding
problems in Butte County. As part of the 1989 FEMA map update, special studies were
conducted on the following flooding problem areas: Butte Creek, Wyman Ravine and tributaries,
Mud Creek, Keefer Slough, Ruddy Creek and tributary and Little Chico Creek, additional studies
done for the 1998 FIRM were done on Butte Creek, Big Chico Creek, Little Chico Creek, and
Lindo Channel. For the 2000 FIRM, studies were done on Keefer Slough, Rock Creek, Dead
Horse Slough and Wyman Ravine. These areas were already known to flood; however, they were
not fully evaluated in past FEMA studies.
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The following appraises the principal flood problems in Butte County according to the 1998 FIS.
Butte Creek: Table 16-3 displays seven high discharge events on Butte Creek, as recorded by a
gauge maintained by the U.S. Geological Survey (the gauge location is on right bank side,7/10
mile downstream from Little Butte Creek, 7 ½ miles east of Chico (lat. 39°43’34” long.
121°42’28”, NW quarter of NW quarter of Section 36, Township 22N, Range 2E). The
measurements at this gauge are preferable to measurements taken downstream by the California
Department of Water Resources, because the USGS gauge is placed upstream of all
development.
TABLE 16-3
FLOODS ON BUTTE CREEK AND
RECURRENCE INTERVALS
Water Year Ranked Discharge Annual Exceedance
Probability=Recurrence Interval (1)
1997 35,600 0.0050=200 years USGS; 500 FIS
1986 22,000 0.0040=25 years USGS; 100 FIS
1965 21,200 0.0040=25 years USGS; 50 FIS
1956 18,700 0.0040=25 years USGS
1938 17,000 0.100=10 years USGS
1970 16,500 0.100=10 years USGS
1963 14,200 0.100=10 years USGS; 10+ FIS
Source: U.S. Geological Survey (USGS) data from flow gauge on Butte Creek
Notes:
(1) The reciprocal of annual exceedance probability = the recurrence interval; FIS = Federal Emergency Management Agency (FEMA) Flood
Insurance Study (FIS)
Wyman Ravine and Tributaries: As Wyman Ravine flows out of the steep foothills, its slope
and velocity change downstream of Lincoln Boulevard. Shallow flooding occurs every few years
in the orchards west of the Western Pacific railroad; flood flows over Palermo Road have
extended east of Wyman Ravine almost to Occidental Avenue. Also, Wyman Ravine between
Stimpson Lane and Lone Tree Road experiences annual flooding in most years. Floodways are
defined in the FIRMs.
The area south of Wyman Ravine tributary No. 1, between the Western Pacific Railway
embankment and Melvina Avenue, experiences chronic flooding. The Palermo Tributary floods
during the 10-year and greater storms. Sheet flow across roads and between homes occurs
approximately once in five years.
Keefer Slough: Flooding along Keefer Slough is due to water naturally diverging from Rock
Creek. The frequency of flooding has historically been dependent on the debris and vegetation in
Rock Creek between State Highway 99 and its upstream divergence from Keefer Slough.
Farmers in the vicinity have periodically cleared Rock Creek to improve capacity and flow west
of Highway 99. However, flooding south of Rock Creek depends upon the channel conditions at
the divergence of Keefer Slough from Rock Creek upstream from Highway 99. Notable recent
flooding events occurred in March 1983, January 1995, March 1995, January 1997 and February
1998, when Keefer Slough flooded homes in the vicinity of Keefer Road, Keefer Slough, and the
area southwest of State Highway 99. State Highway 99 was covered with floodwaters for several
hours during each of these events. The floodwaters continued southwest, affecting much of the
area between State Highway 99 and the Southern Pacific Railroad, including the community of
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Nord. Since the 1989 FIS was prepared, floods have also occurred in 1997 and 1998 within the
Rock Creek Keefer Slough area, prompting FEMA to remap this area on the Series D, April 20,
2000 FIRM.
In 1995 flood studies were also conducted within the Keefer Slough watershed as part of the
North Chico Specific Plan (NCSP). According to the NCSP, the capacity of the Keefer Slough
channel between Garner Lane and Highway 99 is estimated at 525 cubic feet per second (cfs)
with the existing capacity of the Highway 99 crossing rated at 600 cfs. The drainage study also
concluded that uncontrolled flooding in Keefer Slough was due to the natural divergence from
Rock Creek.
Flooding in Keefer Slough can be prevented by resolving the Rock Creek divergence problems
as well as improving the flood capacity of Rock Creek. Prior studies have indicated the
possibility of routing the diverted overflow from its beginning point northeast of the Keefer Lane
and Hicks Road intersection in a southerly direction to Mud Creek. However, a Feasibility Study
being prepared by the U.S. Army Corps of Engineers (Corps) found that it was not economically
feasible to divert flows to Mud Creek. Therefore the Rock Creek flood flows must either be
contained in Rock Creek or improvements made to Keefer Slough to accommodate the flows.
The Feasibility Study is leaning toward improvements to Rock Creek. The NCSP also included
other programs to alleviate flooding. However, these will require action by multiple State and
federal agencies in order to implement.
Mud Creek: The Sacramento District Corps of Engineers surveyed project levee crown
elevations along Mud Creek and found that the levees are well maintained, do not have any
known stability or foundation problems, and with the exception of Sycamore creek upstream
from Sheep Hollow Creek, the project will pass design flows for 100 year storm events, provided
maintenance continues.
Sycamore Creek: In March 2002 the California Department of Water Resources prepared a
hydraulic analysis for Sycamore Creek. It found extensive sedimentation and vegetative buildup
along Sycamore Creek between Cohasset Road to Sheep Hollow that reduces the present
capacity below the channel’s design capacity. The analysis recommends the removal of 49,000
cubic yards of sediment, some minor raising of the levee, and keeping vegetation in check.
Ruddy Creek and Ruddy Creek Tributary: Areas of flooding along Ruddy Creek have been
noted throughout the basin. Flood damage was reported after the February 1986, January 1995,
January 1997 and February 1998 storms. Since the 1989 FIS, widespread flooding was observed
in the 1995, 1997, and 1998 winter seasons.
Little Chico Creek: The majority of this area was not depicted on previous FIRM panels as
being subject to 100 year flood events. Flood flows of record measured in Little Chico Creek
occurred in December 1964, March 1974, March 1978, January 1995, and January 1997.
Flooding also occurred with the latest storm in February 1998. On February 3, 1998, the largest
24 hour rainfall total occurred in 82 years in the Chico area. This caused a flood surge which
resulted in flooding at the Alberton Avenue bridge, west of Chico.
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Appraisal of Flood Protection Measures within Special Study Areas: Private levees have
been erected along the banks of a large portion of Wyman Ravine. However, levees along the
lower portions do not contain 10 year storm events (as noted in FEMA FIS, page 7) and their
effectiveness during 100 year floods are negligible. A levee extending approximately 3,500 feet
north of Palermo Road to 2,000 feet upstream of Lincoln Blvd is more significant.
Several levee systems have been constructed along Butte Creek, Cherokee Canal, Big Chico
Creek, Hamlin Slough, Little Chico Creek-Butte Creek Diversion Channel, Comanche Creek,
and Little Chico Creek. An evaluation of these levees found that they do not provide protection
from 100 year flood events. Inadequate levees and/or channel capacities were found on portions
of the following streams: Butte Creek downstream of the Skyway, Hamlin Slough, the Little
Chico-Creek downstream of the Butte Creek Diversion Channel, Comanche Creek, and
Cherokee Canal. During intense storms, water would typically over-top these levees and break
out of the channel, usually not returning for several thousand feet, if at all. Therefore, they have
been shown on the 1998 and 2000 FIRMs as not containing the base flood.
Table 16-4 below contains information on known flooding problems and planned drainage
improvements as identified by the referenced studies. This table indicates the drainage problem
or issue, the reference source, and the status of identified drainage problems.
Countywide drainage impact fees are presently nonexistent. However, adopting drainage fees for
specifically studied projects may help fund upcoming projects.
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TABLE 16-4
IDENTIFIED FLOODING PROBLEMS
BUTTE COUNTY
Study Location
Description of problems
identified Suggested Improvements if any Status (1)
Thermalito Many existing conduits found to
be inadequate to accommodate
existing and near future flows.
Many areas undrained due to lack
of facilities.
Utilize natural drainage courses in
conjunction with additional well-
placed drainage improvements. Such
improvements include new trunk
lines, and several additional culverts
and improvement of natural
channels.
Little progress in
implementation due to
lack of projects to spur
development interest.
North Chico Specific Plan
Area
Few existing drainage facilities to
off-set increasing development
resulting in increasing land
divisions creating many small
parcels.
Improvement of existing storm drain
facilities, and addition of new
facilities to serve ultimate urban
development. New improvements
include on-site detention to reduce
peak runoff, a trunk facility with
collector lines to areas without
facilities and pump stations to
Sycamore or Mud Creek.
Improvements to be
constructed in
accordance with North
Chico Specific Plan
and approved County
drainage design
criteria.
South-East Chico,
Chapman Area
Little existing street
improvements such as curbs,
gutters, and sidewalks. No
existing storm drain facilities in
many areas.
Construction of storm drain facilities
such as curbs and gutters and
conduit. Adoption of drainage plan
for area.
A portion has been
implemented
Northern Butte County,
North-West of City of
Chico
Area plagued by recurrent
flooding due to contributing
upstream drainage area, a broad
natural floodplain and poor
channel alignment.
Install diversion/detention facilities
to reduce/rechannel excess
floodwaters to improvements
constructed by Army Corps of
Engineers south of area.
Status unknown or no
action taken
South East of City of
Oroville area called
Wyman Ravine
Existing facilities are inadequate
to handle existing and future
flows.
Replace a series of undersized
culverts and other drainage
structures.
Shown on
FEMA/FIRM maps.
City of Chico A need to evaluate current
facilities and plan for future
development, by way of outlining
planning criteria.
Create planning/design criteria
which designates new facilities to
meet future needs across
jurisdictional boundaries.
City improvements to
original Plan being
reviewed by County.
Not subject to
jurisdiction of the
County unless they are
connecting to County
maintained facilities.
Town of Paradise Field inventory of existing
drainage facilities shows that past
adopted policies were many
times ignored either through lack
of knowledge or indifference.
Create planning criteria designating
more strict and controlled regulation
of development. Master plan
provides developmental guidelines
and a schedule of improvements for
the planned area.
An incorporated area,
not included in County
General Plan. Not
subject to Jurisdiction
by Butte County.
City of Chico and
Surrounding Area
Environmental impact report
addressing the adoption of the
Chico Urban Area Draft Storm
Drainage Master Plan relating to
a 5000 ac. Annexation.
EIR references prior City Master
Plan in 1997 for future
improvements of areas lacking in
storm drain systems and strategies
for improving areas with existing
storm drain systems.
Currently under County
Review.
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North of the City of
Chico, Rock Creek-
Keefer Slough Area
Location experiences flooding
problems during periods of high
intensity storms.
Overland flow from approx. 50
sq. mile upstream tributary area
causing significant flooding
problems coupled with old
channels within district
boundaries and undersized
culverts.
An U.S. Army Corps of Engineers
(Corps) Feasibility Study will
provide cost-of-solution data for the
proposed improvements, such as
setback levees, floodwalls, channels
and drainage structures. Study will
enable local property owners to
make a determination on funding
projects.
Complete the Rock Creek Keefer
Slough Flood Plain Study and
implement appropriate actions to
reduce flooding.
The County, in
cooperation with Corps
and DWR, is
undergoing a
Feasibility Study to
determine the most
appropriate method to
mitigate flooding
problems related to
Rock Creek and Keefer
Slough. Study currently
in hiatus and awaiting
funding.
East Chico Area: 1978
Rolls, Anderson and Rolls
Study Area.
Only two areas were identified
within the study area as having
existing underground drainage
facilities. Runoff calculations
indicated the storm drains for
both areas are undersized
compared to the area being
drained.
Study of drainage patterns shows the
size and location for eight additional
storm drains to drain the study area
for both existing and future
development.
The Chico Parks and
Playgrounds
Commission has a
policy to review and
minimize all additional
storm drains into Big
Chico Creek above One
Mile Recreation Area.
Notes: (1) Status information provided by County of Butte Staff
16.8 FLOOD HAZARDS AND DAM SAFETY
Flood Hazards
In Butte County, several storms have been responsible for significant flood damage, notably
storms in March 1983, January-March 1995, December 1996, January 1997, and February
1998.Therefore, flood hazards in the county have been evaluated in an effort to develop effective
flood policies and implementation measures to aid in reducing adverse impacts resulting from
flood events. This section summarizes the flood hazards present in the county, along with the
flood control methods being used to manage them.
The National Flood Insurance Program (NFIP) encourages state and local governments to adopt
responsible floodplain management programs and flood measures. The NFIP also provides
floodplain and floodway boundaries which are shown on the Flood Insurance Rate Maps
(FIRM). In some instances the FIRM delineates 100-year flood elevations to assist communities
in developing floodplain management measures. The delineation of flood boundaries and
adoption of County Ordinances regulating development within identified flood plains/floodways
are the basic flood management tools that the County uses to identify flood hazards and
implement its own flood management program.
The larger streams in Butte County are subject to heavy runoff, and a number of smaller streams
have caused considerable flood damage in the past. Corrective flood control projects have
alleviated most of the dangerous and life threatening flooding problems in the county. The most
notable of these projects was the construction of the Oroville Dam and related flood control
projects. Also, the streams designated for flood control projects by the Flood Control Act of
1944 corrected many serious flood problems along the Sacramento River and its tributaries,
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including Mud Creek, Sandy Gulch, Big and Little Chico Creeks, Butte Creek, and Cherokee
Canal.
However, while significant steps have been taken to control the most serious flood hazards,
many areas of Butte County remain vulnerableto flooding. The seriousness of flooding in these
areas has grown in the last twenty years because development continued in areas that were
previously thought to be out of exposed floodplains. Now, many of these areas are known to be
prone to flooding.
As the Sacramento River meanders within the floodplain, its channel in the Butte Basin area,
upstream from the project levees, is largely uncontrolled. The river’s action plays a key role in
shaping the topography and determining land uses within the area. Within the floodplain the
lands are low and flat, characterized by meandering channels, natural levee terraces, swales, and
associated wetlands, swamps, and ponds. Over time, the alluvial fans of the stream modify the
floodplain and eventually rework the entire valley floor.
Soil types in the flood basin correspond to flow and inundation patterns of the river. As the river
moves back and forth, its waters deposit silt, sand, and gravel that form gravel points and bars.
The river banks, or natural levees, consist of deposits of sandy loams. Beyond the levees, fine
clays and alkaline soils are carried into the floodplain. While flooding occurs across much of the
overflow area, deposited clays and soils on the floodplain primarily affect lands adjacent to the
river. Waterways within the floodplain provide valuable wetland areas and wildlife habitat.
The most frequently used flood control technique in the county is retention or detention of peak
runoff to, at, or below predevelopment levels. Another approach to flood control involves
comprehensive watershed management (CWM). CWM does not solely focus on flood control –
it focuses on management of the floodplain by providing wider areas for flooding using a
combination of setback levies, floodwalls, and other structural and non-structural designs. The
CWM design concept allows for the natural development of riparian habitat within the flood
plain, reduction in flood velocities, and reduction in the normal maintenance requirements. This
approach to flood management has been gaining national and statewide consideration, and
significant grant funding has been provided to foster the development of CWM plans. Within
Butte County, CWM plans are being developed for the watersheds of Butte Creek, Big Chico
Creek, and Little Chico Creek.
Humans usually intervene in a watershed for a wide variety of purposes: to bring water to
residences, irrigate, generate electricity, dispose of waste, mine, manage timber, recreate,
enhance wildlife, and control floods. Science has discovered that the cumulative effects of these
activities over time can make flooding problems worse. This is attributed to the alteration of the
watershed’s “dynamic equilibrium.”
As human activities within the watershed alter its natural balance, the flood volumes for various
frequency storms within the watershed of a stream or river are also changed. Often flood heights
and velocities increase, necessitating higher levies, greater blank stabilization, channelization,
and methods of reducing runoff through on-site detention or retention.
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One alternative is to allow the river and floodplain to revert back to its natural system. Because
this precludes all development within the floodplain, and may also require the removal of
existing development from the floodplain, such an alternative tends to be unpopular. Even so,
some communities are attempting to correct poor watershed policy by restoring their watershed’s
“dynamic equilibrium.” For example, in 1998 Napa County approved an innovative ½ cent sales
tax for flood control improvements. This will raise $6 million per year for 20 years for flood
control improvements along the Napa River. The project is innovative because it disfavors
traditional methods of flood control, such as creating concrete channels to control floodwaters.
Instead, the monies would be spent to “restore” the floodplain and create “meander belts” for the
Napa River. Probably the most significant aspect of this measure is that funding will be provided
to pay for the removal of homes and businesses in areas that flood frequently.
Locally, Butte County is working with the various watershed groups as a part of its overall flood
management program. The County has also prepared a Flood Hazard Mitigation Plan which the
Butte County Office of Emergency Services administers. A County Ordinance adopted in March
1983 enforced flood hazard prevention establishing Article IV in Chapter 26 of the Butte County
Code. Through this County Code, the floodplain administrator, in this case the Director of
Development Services, has the authority to enforce County flood hazard prevention policy. This
County Code relies upon FEMA and FIS data, though other studies may supplement this data if
the Floodplain Administrator recommends it and the Board of Supervisors approves it. The
Flood Hazard Prevention Ordinance appoints the Department of Development Services to review
all applications for new construction or subdivisions within flood hazard areas. The Ordinance’s
basic requirement, in order to reduce flood hazards, is that the lowest floor of any new
construction or substantial improvement within Flood Zones A, AE, AH and shaded Zone X be
elevated one foot or more above the regulatory flood elevation, and that it can be shown that
development within the floodplain will not raise the existing flood level. There are other criteria
for building within flood hazard areas, which include flood proofing nonresidential structures
and designing structures to withstand hydrostatic pressures and hydrodynamic loads.
Within areas subject to flooding that are proposed for subdivision, the County is required to
ensure the following:
a) All such proposed developments are consistent with the need to minimize flood damage.
b) Subdivisions and parcel maps shall, as a condition of approval, establish regulatory flood
elevations and note same on final maps prior to recordation of the final map.
c) Adequate drainage is provided to reduce exposure to flood hazards.
d) All public utilities and facilities are located so as to minimize or eliminate flood damage.
Impervious surfaces, sloped contours, and drainage infrastructure make urban areas very
efficient at channeling and diverting storm water into a floodplain. Sometimes this efficiency
creates a storm “surge,” in which urban storm waters overtax the ability of natural river channels
to drain floodwaters. A high 24-hour storm event can overload a drainage system if the area
sheds water quickly. As the surge reaches critical height, flooding occurs downstream, because
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30
runoff from other areas accumulates in the natural drainage system. In an alternative scenario,
storm waters flood the city because they do not drain as quickly. Therefore, another approach to
floodplain management involves slowing and reducing peak storm flows from urban areas.
The approach to managing this type of floodplain problem involves utilizing on-site detention or
retention basins or other holding facilities designed to reduce the peak runoff from the site to, at,
or below pre-development levels. Such holding facilities include leach trenches, detention basins,
retention basins, and open drainage ditches. Open ditches and detention basins slow the
movement of storm water into the drainage systems and provide sediment areas for pollutants
Clustering homes together and building narrower paved streets are also floodplain management
practices, because they decrease the amount of impervious surface.
The State Department of Water Resources Division of Flood Management has established the
Sacramento River Flood Control Project to implement flood control projects for the entire
Sacramento River system, including its tributaries. Two components of this project that fall
within Butte County are the Chico Landing to Red Bluff Project and the Sacramento River Bank
Protection Program.
The only state-maintained flood control system, for the Sacramento River, in the county is
located south of Chico on the Sacramento River, within the Butte Basin overflow facilities. The
M&T weir and Goose Lake weir are maintained by the Department of Water Resources, the 3B’s
overflow is an earthen weir prone to erosion, currently maintained by private parties. These
structures regulate floodwaters associated with the Sacramento River at the Butte Basin overflow
area. The project levees are designed to control the floodwater overflowing into Butte Basin, by
containing excess flow until the Sacramento River subsides. The Department of Water
Resources, as an affiliate of the Sacramento River Bank Protection Program, maintains these
facilities.
Dam Safety
As of 2003, there are 24 dams in Butte County under the jurisdiction of the California
Department of Water Resources Division of Safety of Dams (DSD). Table 16-5 summarizes this
information. A majority of these dams (15) are earthfill embankments. The remaining dams can
be categorized as follows: three gravity concrete dams, three variable radius concrete arch dams,
two rock embankment dams, and one hydraulic fill dam. These dams function in a variety of
service capacities for the county, including irrigation, recreation, stock watering, power
production, and municipal water supply. The reservoirs contained by these dams range in size
from 85 acre feet to 3,537,377 acre feet.
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TABLE 16-5
DAMS UNDER STATE JURISDICTION, BUTTE COUNTY
Dam No.Dam Name
State Dam
No.Owner
Inundation
Map Status
Construction
Type
Storage
Capacity
(acre-feet)
Year
Comple
ted
1 A L Chaffin 346-000
George
Chaffin X Earth 450 1957
2
California
Park 1340-000 E M West X Earth 446 1966
3 Cannon Ranch 345-000
Spring Valley
Minerals X Earth 217 1870
4 Concow 67-000
Nevada
Irrigation
District X Var. Radius Arch 8,600 1925
5.
Desabla
Forebay 97-005
Pacific Gas &
Electric Co.F Earth 280 1903
6
Feather river
Hatch 1-047
Dept. Of
Water
Resources No Gravity 580 1964
7
Forbestown
Divers.63-007
Oroville-
Wyandotte Irr.
Dist.F Var. Radius Arch 358 1962
8 Grizzly Creek 349-000
Ronald T.
Dreisbach X Earth 76 1964
9 Kunkle 97-007
Pacific Gas &
Electric Co.Yes Earth 253 1907
10 Lake Madrone 1004-000
Lake Madrone
Water District X Earth 200 1931
11
Lake
Wyandotte 63-000
Oroville-
Wyandotte Irr.
Dist.Yes Earth 200 1931
12 Lost Creek 63-002
Oroville-
Wyandotte Irr.
Dist.F Var. Radius Arch 5,680 1924
13 Magalia 73-000
Paradise Irr.
District Yes Hydraulic Fill 2,900 1918
14 Miners Ranch 63-009
Oroville-
Wyandotte Irr.
Dist.Yes Earth and Rock 912 1962
15 Oroville 1-048
State Dept.
Water
Resources Yes (FERC)Earth 3,537,377 1965
16 Paradise 73-002
Paradise
Irrigation
District Yes Earth 11,500 1957
17 Philbrook 97-008
Pacific Gas &
Electric Yes Earth 5,180 1926
18 Poe 93-005
Pacific Gas &
Electric Yes Gravity 1,150 1959
19
Ponderosa
Diversion 63-008
Oroville-
Wyandotte Irr.
Dist F Earth 4,750 1962
20 Round Valley 97-009
Pacific Gas &
Electric X Earth and Rock 85 1895
21 Sly Creek 63-006
Oroville-
Wandotte Irr.
Dist.X Earth 65,050 1961
22
Thermalito
Afterbay 1-055
State Dept.
Water
Resources Yes Earth 57,041 1967
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32
Dam No.Dam Name
State Dam
No.Owner
Inundation
Map Status
Construction
Type
Storage
Capacity
(acre-feet)
Year
Comple
ted
23
Thermalito
Diversion 1-049
State Dept.
Water
Resources Yes Gravity 13,328 1967
24
Thermalito
Forebay 1-054
State Dept.
Water
Resources Yes Earth 11,768 1967
X: No Current Map; in 1992 California Office of Emergency Services (OES) requested maps to be made.
F: Regulated by the Federal Energy Regulatory Commission;
Source: Department of Water Resources, State of California, Dams Within the Jurisdiction of the State of California, Bulletin 17-88, October
1988.
Division personnel inspect DSD jurisdiction dams each year. The DSD has also evaluated the
seismic safety of the dams at Lake Wyandotte, Lost Creek, and Round Valley. As a result of the
study done for Lake Wyandotte, the spillway has been lowered to contain the reservoir in the
event of dam lowering in an earthquake. Lost Creek dam personnel submitted their study and are
in the process of studying several faults of special concern. Round Valley has also submitted a
study which found the dam in compliance with earthquake standards. The main focus of this
study was correcting seepage. According to the area engineer for the Division of Dam Safety,
this problem has been corrected.
In 1992 Harlan Tate Associates studied Magalia Dam and concluded that the upstream slope of
the dam was found to have inadequate stability under seismic loading conditions. As of 2003 the
water level in the reservoir was lowered, due to seismic stability concerns. The County is doing
preliminary engineering on a project to widen the Skyway across Magalia Dam. The Paradise
Irrigation District’s preferred alternative for the widening project involves stabilizing the dam
and would permit the restoration of the design water level behind Magalia Dam.
The DSD also identified an additional safety hazard at the Lake Madrone dam. The spillway is
below the minimum design standard. It has been certified as safe for a 1:500 year flood, whereas
the normal minimum level is 1:1,000 years. However, minimum levels differ in various locations
and depends on construction type, terrain, seismic features in the area, and habitat (human and
otherwise) in the downstream flood zone. This facility is under court order to increase dam
spillway capacity. According to the DSD area engineer, Lake Madrone continues to defy a court
order to correct its deficiencies. DSD is seeking further legal remedies to obtain compliance and
correct this problem. Of the remaining dams, Kunkle is typical of several dams whose use has
been restricted to a particular storage level. The DSD believes these dams are safe at a particular
fill level and has restricted their use to that level or lower.
Inundation maps have been required since 1972, following the 1971 San Fernando Earthquake
and near failure of the Lower Van Norman Dam. 11 maps for Butte County are on file with the
State Office of Emergency Services (OES). Eight dams do not have maps on file, and they have
been requested beginning in 1992. Four are regulated by the Federal Energy Regulatory
Commission (FERC), but maps are assumed to exist for these. Only one dam (Hatchery) is not
required to have an inundation map.
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33
16.9 SEISMIC HAZARDS
Introduction
The Seismic Hazards Mapping Program of the California Geological Survey categorizes Butte
County as a “seismic hazard zone.” This section characterizes these seismic hazards in Butte
County and assesses the potentially hazardous effects of earthquakes. This section also contains
information on other geologic hazards, including erosion potential, subsidence, landslides,
expansive soils and volcanic hazards.
Fault Classifications
Seismic risk in Butte County results from earthquake faults within the county, as well as from
faults outside the county whose seismic activity would cause potentially damaging ground
motion in the county. The Sierra foothills contain literally hundreds of mapped faults, dozens of
which are located within Butte County. Many of these faults occur within the Cenozoic era, or
within the past 66 million years. Others are Mesozoic and thus are older than 66 million years.
Most of these faults are not now considered active. Furthermore, most of these faults are very
short and thus are probably not capable of producing severely damaging earthquakes.
The California Mining and Geology Board has defined active faults as those for which there is
evidence of surface displacement within the Holocene epoch, that is, within about the last 11,000
years. Some faults are characterized as active based on surface displacements within historic
time, about the last 200 years, while others are characterized as active based on surface
displacements in rocks or sediments that occurred within the last 11,000 years. This definition of
“active fault” does not mean, however, that all faults for which there is no evidence of surface
displacement during the Holocene are inactive. Some faults may have been active in this time
period, but they did not result in changes to the surface that are easily identifiable. Meanwhile,
other faults may still be active although they have not been active during the Holocene. Many
damaging California earthquakes, including the 1975 Oroville earthquake, the 1983 Coalinga
earthquake, and the 1987 Whittier Narrows earthquake occurred on faults not previously
recognized as active.
The Mining and Geology Board has defined potentially active faults as those for which there is
evidence of surface displacement within the Quaternary period, that is, within about the last 1.6
million years. Faults classified as potentially active faults show no evidence of surface
displacements within the past 11,000 years, but this period of time is short geologically and thus
such faults are considered potentially active. It is important to keep in mind, however, that faults
that do not meet the Mining and Geology Board’s criteria are not necessarily permanently
inactive. Moreover, seismic risk is not limited to faults that have been identified.
In fact, a significant fraction of small to moderately large earthquakes occur on faults that were
not previously recognized. Such earthquakes are characterized as “background seismicity” or
“floating earthquakes,” terms that indicate that the expected sources and locations of such
earthquakes are often unknown. Based on this concept, the general geologic setting of Butte
County, and earthquake experience elsewhere in the Sierra foothills and central valley, it appears
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34
reasonable to assume that background seismicity could produce earthquakes as large as Richter
magnitude 6.0 or 6.5 virtually anywhere in Butte County.
In 1998 the State Legislature adopted AB6x which expanded Civil Code Section 1102.6
regarding disclosure of earthquake hazards. Beginning in June, 1998, the sellers of residential
property must give prospective buyers a new “Natural Hazard Disclosure Statement” if the
residential property lies within an earthquake fault zone or a seismic hazard zone. The new law is
intended to warn prospective real estate buyers that local earthquake or seismic hazards may
limit their ability to develop the property or obtain insurance and may affect their ability to
obtain assistance after a disaster.
The disclosure requirement is consistent with the Alquist-Priolo Earthquake Fault Zoning Act
and its associated legislation, which requires the State Geologist to map areas of potential surface
rupture along active earthquake faults. The State Geologist has mapped and studied the
Cleveland Hills Fault since 1977.
In addition, all of Butte County has been identified as a “seismic hazard zone” by the Seismic
Hazards Mapping Program of the California Geological Survey, since the entire county is subject
to earthquakes of Modified Mercalli Intensity (MMI) scale VIII. The Oroville earthquake of
1975 is the only earthquake of this intensity recorded in Butte County. In 1984 a study published
by the California Geological Survey correlated this seismic activity with the filling and emptying
of Lake Oroville. The study, titled Open File Report 84-25, concluded that other earthquakes of
the same or greater intensities are unlikely in Butte County.
Earthquake “magnitude” is a measure of the total amount of energy released in an earthquake.
With increasing magnitude (i.e., larger earthquakes) ground motions are stronger, last longer,
and are felt over larger areas. Earthquake “intensity” refers to the effects of earthquake ground
motions on people and buildings. Earthquake intensity is often more useful than magnitude when
discussing the damaging effects of earthquakes. The most common intensity scale is the
Modified Mercalli Intensity scale, which ranges from I to XII. A summary of the observed
effects corresponding to the various MMI levels is given in Table 16-6.
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35
TABLE 16-6
SUMMARY OF MODIFIED MERCALLI INTENSITY SCALE FOR EARTHQUAKES
I. Not felt except by a very few under especially favorable circumstances.
II. Felt only by a few persons, especially on upper floors of buildings. Delicately suspended objects may swing.
III. Felt noticeably indoors, especially on upper floors of buildings, but many people do not recognize it as an earthquake.
Standing motor cars may rock slightly. Vibration like passing of truck. Duration estimated.
IV. During the day felt by many, felt outdoors by few. At night some awakened. Dishes, windows, doors disturbed; walls make
creaking sound. Sensation like heavy truck striking building. Standing motor cars rocked noticeably.
V. Felt by nearly everyone; many awakened. Some dishes, windows, etc. broken; a few instances of cracked plaster. Unstable
objects overturned. Disturbance of trees, poles, and other tall objects sometimes noticed. Pendulum clocks may stop.
VI. Felt by all; many frightened and run outdoors. Some heavy furniture moved; a few instances of fallen plaster or damaged
chimneys. Damage slight.
VII. Everybody runs outdoor. Damage negligible in buildings of good design and construction; slight to moderate in well-built
ordinary structures; considerable in poorly built or badly designed structures; some chimneys broken. Noticed by persons driving
motor cars.
VIII.Damage slight in specially designed structures; considerable in ordinary substantial buildings with partial collapse; great in
poorly built structures. Panel walls thrown out of frame structures. Fall of chimneys, factory stacks, columns, monuments, walls.
Heavy furniture overturned. Sand and mud ejected in small amount. Changes in well water. Disturbs persons driving motor cars.
IX. Damage considerable in specially designed structures; well designed frame structures thrown out of plumb; damage great in
substantial buildings, with partial collapse. Buildings shifted off foundations. Ground cracked conspicuously. Underground pipes
broken.
X. Some well-built wooden structures destroyed; most masonry and frame structures destroyed with foundations; ground badly
cracked. Rails bent. Landslides considerable from river banks and steep slopes. Shifted sand and mud. Water splashed (slopped)
over banks.
XI. Few, if any (masonry) structures remain standing. Bridges destroyed. Broad fissures in ground. Underground pipe lines
completely out of service. Earth slumps and land slips in soft ground. Rails bent greatly.
XII. Damage total. Waves seen on ground surfaces. Lines of sight and level distorted. Objects thrown upward into the air.
Source: K.V. Steinbrugge, 1982, Earthquakes, Volcanoes, and Tsunamis, and Anatomy of Hazards.
!.
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UV32
UV99
UV70
UV191
UV162
UV70
UV162
UV99
UV32
PARADISE
OROVILLE
BIGGS
GRIDLEY
CHICO
ACTIVE AND POTENTIALLY
ACTIVE FAULTS
Figure 16-3
Butte County
General Plan
®Miles02468101
Source: California Division of Mines and Geology
Legend
SEISMIC MAGNITUDE
!.0.1 to 3.9 Richter Magnitude
!.4.0 to 4.9 Richter Magnitude
!.5.0 to 5.9 Richter Magnitude
!.6.0 and Greater Richter Magnitude
FAULTS
Activity Unknown
Concealed
Inferred
Possible (Lineation)
Active (Cleveland Hills)
Lakes
EPICENTER REGION
After Shock Epicenter Region
Not in Aftershock Area
Date printed: June 17, 2003
Tehama County
Glenn County
Colusa County
Sutter County
Yuba County
Nevada County
Plumas County
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Active Faults
Cleveland Hills Fault
As of 2003 there is only one identified active fault located within Butte County, the Cleveland
Hills fault. The State Geologist has mapped and studied it since 1977. It is subject to the Alquist-
Priolo Act and is identified pursuant to AB6x as an “earthquake fault zone.” This fault was
responsible for the 1975 Oroville earthquake of Richter magnitude 5.7, an event that produced
surface displacement along about 2.2 miles of the fault. Ground motions corresponding to
Modified Mercalli Intensity VIII were experienced at Gridley and Oroville. Significant structural
damage occurred to unreinforced masonry buildings in Oroville. Geologic studies indicate that
the total length of the Cleveland Hills fault is probably 11 to 15 miles. The maximum credible
earthquake on this fault is probably about magnitude 6.5 to 6.7. An event of this magnitude
would cause substantially more damage than the 1975 event.
The official map of the State Geologist for the Cleveland Hills “earthquake fault zone” may be
consulted at the Development Services Department.
San Andreas Fault System
The San Andreas fault, along with related faults such as the Hayward and Calaveras faults, is one
of the most active faults in California. Total displacement along this fault has been at least 450
miles and could possibly be as much as 750 miles. This fault system was responsible for the
magnitude 8 San Francisco earthquake of 1906 as well as numerous other damaging earthquakes,
including the 1989 Loma Prieta earthquake. At its nearest point, the San Andreas fault is about
95 miles west of Butte County. The 1906 earthquake was strongly felt in Butte County, at
approximately MMI V, but there was little damage.
Midland-Sweitzer Fault
The 80-long Midland-Sweitzer fault lies approximately 40 miles southwest of Butte County.
Historically, earthquakes of Richter magnitudes between 6 and 6.9 have occurred on or near this
fault, including two strong earthquakes in 1892. Based on the fault length and the historic
activity, this fault is capable of producing a magnitude 7 earthquake which would be experienced
in Butte County with MMI as high as VIII or IX.
Eastern Sierra Faults
The eastern Sierra contain a number of active faults including the Russell Valley fault, which
produced the 1966 Truckee earthquake of magnitude approximately 6, and several faults in the
Last Chance and Honey Lake fault zones, which have produced several magnitude 5 to 5.9
earthquakes. These fault zones are approximately 50 miles east of Butte County. Earthquakes on
these faults could be experienced in Butte County with MMIs as high as VII or VIII.
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Potentially Active Faults
There are a number of faults within Butte County and a large number of relatively nearby faults
that could be considered potentially active, based either on the fairly restrictive criteria
developed by the California Mining and Geology Board or on more conservative criteria. Figure
16-3 shows these potentially active faults (based on 1977 data from the Division of Mines and
Geology (now the California Geological Survey.
Some geologists consider the Big Bend fault zone potentially active. This fault could produce a
magnitude 7 earthquake with Modified Mercalli Intensity of IX or X in Butte County. Intensities
this high would result in major damage. The Foothills shear zone extends into southern Butte
County. A possible magnitude 7 earthquake in this zone would result in intensities as high as IX
in Butte County. Finally, the Chico Monocline fault which extends northwesterly from Chico
was considered potentially active in an unpublished 1988 report by the California Division of
Mines and Geology (now the California Geological Survey). Based on its length, this fault could
produce at least a magnitude 7 earthquake which would cause major damage in Chico and
elsewhere in Butte County.
South of Butte County is a series of small faults around the Sutter Buttes and an 18-mile long
fault near Dunnigan. Earthquakes on these faults would produce only moderate ground motion in
Butte County, probably not exceeding Modified Mercalli Intensity VI, with little or no damage.
West of Butte County is the 40-mile long Willows fault which could produce a magnitude 7
earthquake and could yield a Modified Mercalli intensity as high as VIII in Butte County
(comparable to the intensity experienced during the 1975 Oroville earthquake). The Coast
Ranges Thrust Zone is approximately 35 miles west of Butte County. This fault zone could
potentially produce a magnitude 8 earthquake which could be experienced in Butte County as
Modified Mercalli Intensity IX or X. An event of this magnitude would cause major damage to
Butte County.
East and Southeast of Butte County there are numerous faults in the Sierra Foothills, including
the Foothills Shear Zone (which extends into Butte County), the Camel’s Peak fault, the
Hawkins Valley fault, the Melones-Dogwood Peak fault system, the Bear Mountain fault, and
many others. Potential activity on these faults cannot be excluded from consideration, although
geologists disagree on how active or inactive these faults are.
After the 1975 Oroville earthquake, geologists reevaluated the earthquake hazard in the Sierra
foothills region, including Butte County. It is now generally accepted that earthquakes of
magnitude 6 or 6.5 are possible anywhere in the foothills and near the margins of the Sacramento
Valley, including Butte County. Opinions differ on the possibility of larger earthquakes of
magnitude 7 or higher. The possibility of such earthquakes along the Chico Monocline fault, in
the Coast Ranges thrust zone, and along several faults in the Sierra foothills cannot be excluded
from consideration. Earthquakes as large as magnitude 7 in these areas would produce major
damage in Butte County. Such events would probably result in MMIs of IX or X in Butte County
and could result in collapses of unreinforced masonry buildings, with substantial numbers of
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casualties.
The earthquake performance of structures varies considerably due to a number of factors. These
include their location across active faults or in poor ground areas (e.g., landslide and
liquefaction), type of construction (e.g., wood frame, unreinforced masonry, and nonductile
concrete frame), magnitude and intensity of the earthquake and duration of strong ground
shaking, distance from the causative faults, and similar factors. In recent history, Butte County
has experienced two damaging earthquakes (1940 and 1975). Unreinforced masonry buildings in
the older sections of Chico (1940) and Oroville (1975) suffered moderate to severe damage in
these earthquakes.
There is one Earthquake Fault Zone ( Earthquake Fault Zones were called “Special Studies
Zones” prior to January 1, 1994) in the county (the Cleveland Hills Fault south of Oroville, see
Figure 16-3), established by the California Division of Mines and Geology (now the California
Geological Survey), pursuant to Public Resources Code Sections 2621-2630. Except for single
family dwellings, this law requires that a geologic report be filed as a condition of any building
permit so the local building official can judge the risk of fault rupture damaging the proposed
building.
In general, evidence from past earthquakes shows that wood frame structures properly tied to
their foundations perform very well, or if badly damaged cause few injuries and life loss even if
located in poor ground areas. Older wood frame structures that have stone, brick, or cripple wall
foundations, or that are not bolted to their foundations, do not perform well. Unreinforced
masonry structures, on the other hand, perform poorly under almost all earthquake conditions,
and especially if located on poor ground areas. Nearby relatively small earthquakes can be very
damaging because of the sharp motions they generate. Distant events, while more damaging to
taller buildings, can also damage unreinforced masonry buildings because of the stresses caused
by long-period motions. Mobile homes generally perform very well because of their lightness,
but failures of their weak foundation supports (usually flimsy metal stands or concrete blocks)
can produce serious damage and economic losses. Older mobile homes are also considered
serious fire hazards because of the non-fire resistant wall paneling and other materials. The
performance of other structures depends on their specific characteristics, quality of construction,
and other factors discussed above.
Predicted Effects of Earthquakes
Ground Shaking
Based on the known active faults and on the large number of potentially active faults, all parts of
Butte County are potentially subject to moderately strong ground shaking. The intensity of
ground shaking at any specific site depends on the characteristics of the earthquake, the distance
from the earthquake, and on the local geologic and soils conditions. There are insufficient data to
predict accurately the expected ground motions at various locations within Butte County.
Conservatively, ground motions as strong as those observed in Oroville during the 1975
earthquake (Modified Mercalli Intensity VIII) can be expected anywhere in Butte County. More
conservatively, ground motions with Intensities as high as X (ten)could occur from magnitude 7
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earthquakes on the Chico Monocline Fault, the Big Bend Fault, or the Foothills Shear zone.
Similar intensities could be experienced in Butte County from larger earthquakes on more distant
faults such as the Coast Ranges thrust zone or Melones fault zone.
Liquefaction Potential
Liquefaction, which may occur under strong ground shaking during earthquakes, is the
transformation of a granular sediment or fill material from a solid state to a temporarily liquid
state. Liquefaction is a serious hazard because buildings on ground which undergoes liquefaction
may sink or suffer major structural damage. Liquefaction during an earthquake requires strong
shaking continuing for a relatively long time period and loose, clean granular materials
(particularly sands) that may settle and compact because of the shaking.
Areas paralleling the Sacramento River that contain clean sand layers with low relative densities
are estimated to have generally high liquefaction potential. Granular layers underlying most of
the remaining Sacramento Valley area of Butte County have higher relative densities and thus
have moderate liquefaction potential. Clean layers of granular materials older than Holocene are
of higher relative densities and are thus of low liquefaction potential. Areas of bedrock, including
most of eastern Butte County have no liquefaction potential, although localized areas of valley
fill alluvium can have moderate to high liquefaction potential. Figure 16-4 shows areas of
liquefaction potential in Butte County.
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LIQUIFACTION POTENTIAL
Figure 16-4
Butte County
General Plan
®Miles02468101
Source: California Division of Mines and Geology, 1995
LIQUEFACTION POTENTIAL OF GRANULAR SEDIMENTS
GENERALLY HIGH - Recent Sacramento Valley Sediments Bordering River - Alluvium
GENERALLY MODERATE - Recent Valley Sediments - Alluvium
LOCALLY HIGH - where loose, clean granular layers are present
GENERALLY LOW except along stream channels where it may be
LOCALLY HIGH in recent alluvium
Legend
LIQUIFACTION POTENTIAL
GENERALLY HIGH
GENERALLY MODERATE
GENERALLY LOW
LakesDate printed: June 17, 2003
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Seiches
A seiche is a periodic oscillation of a body of water such as a reservoir, river, lake, harbor or bay
resulting from seismic shaking or other causes such as landslides into a body of water. The
period of the oscillation varies depending on the size of the body of water and may be several
minutes to several hours. Depending on the magnitude of the oscillations, seiches can cause
considerable damage to dams, levees, and shoreline facilities. Seiches have not been recorded in
any of the reservoirs in Butte County that are within the jurisdiction of the California Division of
Dam Safety. However, the potential for seiches does exist in Butte County, either from
landslides or from stronger earthquakes than have been experienced in historical times.
Landslides
The general potential for landslides in Butte County is discussed in the Hazards section of this
document.
Earthquakes may initiate landslides, particularly during the wet season, in areas of high ground
water or saturated soils. The most likely areas for earthquake-induced landslides are the same
areas of high landslide potential discussed in the Geologic Hazards section.
Dam Safety
Earthquakes can endanger dams in several ways, including failure of the foundations or dams
themselves due to ground failures, or through secondary effects such as seiches and landslides in
the reservoir. Dam safety, including seismic safety, is discussed under the Flooding and Dam
Safety section.
16.10 GEOLOGIC HAZARDS
Erosion
Erosion is a two-step process by which soils and rocks are broken down or fragmented and then
transported. Rocks can rub against each other, fall apart, or be exposed to weather, but water
causes most erosion. Wind may also be an important erosion agent. The rate of erosion depends
on many variables including the soil or rock texture and composition, the permeability of the
soil, the slope, the extent of vegetative cover, and precipitation amounts and patterns.
Erosion increases with increasing slope, increasing precipitation, and decreasing vegetative
cover. Erosion may be extremely high in areas where protective vegetation has been removed by
fire, construction, or cultivation. High rates of erosion may have several negative impacts
including degradation and loss of agricultural land, degradation of streams and other water
habitats, and rapid silting of reservoirs.
There are five general classes of potential erosion hazard:
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• None: Slopes less than two percent, with moderately rapid to rapid subsoil permeability.
• Slight: Slopes of two to nine percent with permeability at least moderate with weak soil
profile development.
• Moderate: Slopes of 9-30 percent with soils of no profile development to weak profile
development and slopes of 9-15 percent with moderate profile development.
• High: Slopes of 30-50 percent in soils with no profile development to weak profile
development and slopes of 15-30 degrees in soils with moderate to strong profile
development.
• Very High: Slopes above 50 percent on soils with no profile development and slopes
above 30 percent with moderate to strong soil profile development.
Erosion hazard in Butte County is shown in Figure 16-5. This figure shows the degree of erosion
that may be expected when protective vegetation is removed, as well as the level of erosion
hazard according to underlying geology and rainfall.
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EROSION HAZARD POTENTIAL
Figure 16-5
Butte County
General Plan
®Miles02468101
Source: California Division of Mines and Geology, 1995
Legend
Lakes
EROSION POTENTIAL
VERY HIGH HAZARD
HIGH HAZARD
MODERATE HAZARD
SLIGHT HAZARD
NO HAZARD
HIGH - Slopes of 30 to > 50%, on soils with no to weak profile development and
15 to 30% slopes on soils with moderate to strong profiles.
MODERATE - Slopes of 9 to 30%, on soils with no to weak profile development,
and slopes of 9 to 15% with moderate profile development.
SLIGHT - Slopes of 2 to 9%, moderate to moderately rapid subsoil permeability,
weak profile development.
NONE - Slopes less than 2%, subsoil permeability moderately rapid and rapid.Date printed: June 17, 2003
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Subsidence
Subsidence is the sinking of a large area of ground surface in which the material is displaced
vertically downward, with little or no horizontal movement. The California Department of Water
Resources installed two devices for measuring subsidence in 1989 and plans to install three more
in 2003. These devices are called “extensometers,” and essentially are metal rods fixed into a
deep well. A gauge on the rod measures how much the soil declines at the edges of the well.
There has been no subsidence in Butte County since the extensometers were installed.
Subsidence, usually as a direct result of groundwater withdrawal or oil and gas withdrawal, is
common in several areas of California, including parts of the Sacramento Valley and in large
areas of the San Joaquin Valley. Subsidence is a greater hazard in areas where the subsurface
geology includes compressible layers of silt and clay. Subsidence due to ground-water
withdrawal generally affects larger areas and presents a more serious hazard than does
subsidence due to oil and gas withdrawal.
However, localized subsidence due to oil and gas withdrawal has been observed at numerous
locations in California, primarily in the Los Angeles basin. In portions of the San Joaquin Valley,
subsidence has exceeded 20 feet over the past 50 years. In the Sacramento Valley, preliminary
studies suggest that much smaller levels of subsidence, ranging from half a foot to two feet, may
have occurred. In most of the valley, elevation data are inadequate to determine positively if
subsidence has occurred. However, ground water pumpage in the Sacramento Valley has been
increasing and groundwater levels have declined in some areas.
The amount of subsidence caused by groundwater withdrawal depends on several factors,
including: 1) the extent of water level decline, 2) the thickness of the water-bearing strata tapped,
3) the thickness and compressibility of silt-clay layers within the vertical sections where ground-
water withdrawal occurs, 4) the duration of maintained ground water level decline, 5) the number
and magnitude of water withdrawals in a given area, and 6) the general geology and geologic
structure of the groundwater basin.
The damaging effects of subsidence include gradient changes in roads, streams, canals, drains,
sewers, and dikes. Many such systems are constructed with slight gradients and may be
significantly damaged by even small elevation changes. Other damaging effects include damage
to water wells resulting from sediment compaction and increased likelihood of flooding of low-
lying areas.
Land subsidence is a potential hazard for the portions of Butte County located within the
Sacramento Valley. Areas of potentially significant subsidence are shown in Figure 16-6. The
greatest potential subsidence areas are those where heavy ground water withdrawal is occurring
and in gas-producing areas. According to investigations by the U.S. Geological Survey, the areas
of heaviest groundwater withdrawal extend about two miles north and south of Chico and in a
one mile radius around Gridley. The amount of subsidence that could take place in the county
depends primarily on the amount of groundwater withdrawal. The possibility of subsidence
resulting from large groundwater drawdowns during prolonged droughts is a serious concern.
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Landslides
Landslides are downward and outward movements of slope-forming materials which may be
rock, soil, artificial fill, or combinations of such materials. The size of landslides varies
enormously, from tiny slides containing less than a cubic yard of material to massive slides
containing millions of cubic yards. Large landslides may move downslope for hundreds of yards,
or even several miles. A landslide may move rapidly as in a soil or rock avalanche or it may
move slowly for hours or even weeks. A similar but much slower movement is called creep.
The susceptibility of a given area to landslides depends on a great many variables. However, the
general characteristics which influence landslide hazards are well understood and thus it is
possible to map areas in terms of general susceptibility to landslides. Among the important
factors which govern the formation of landslides are:
• Steepness of slope: Landslides usually occur on moderate to steep slopes.
• Type of slope material: Loose, unconsolidated soils and soft, weak rocks are more
hazardous than are firm, consolidated soils or hard bedrock.
• Structure and physical properties of materials: The orientation of layering and zones of
weakness relative to slope direction strongly affect landslide potential.
• Water content: Increasing water content increases landslide hazard because water
decreases resistance to sliding and adds weight to the materials on a slope.
• Amount of vegetation: Abundant vegetation with deep roots increases slope stability.
• Proximity to areas undergoing rapid erosion or man-made cuts: Undercutting slopes
may greatly increase landslide potential.
• Earthquake ground motions: Strong ground motion may trigger landslides in marginally
stable slopes or loosen slope materials and thus increase the risk of future landslides.
Landslides do occur in Butte County, but they are not common. Because of differences in the
physical characteristics of slope materials which markedly influence landslide potential, some
superficially similar areas may differ strongly in landslide hazards. Furthermore, a detailed
assessment of potential landslide hazards at any specific site requires a detailed geotechnical
analysis of the specific site under consideration.
Most landslides in Butte County occur on slopes greater than 15 percent, and most new
landslides occur in areas that have experienced previous landslides. The areas of highest
landslide potential are in the mountainous central area of the county where well-developed soils
overly impervious bedrock on steep slopes which at times undergo heavy rainfall. The slopes
around flat uplands, such as Table Mountain, are also highly susceptible to landslides. Most of
the rest of Butte County has moderate to low landslide potential. The areas of lowest landslide
potential are the flat lands of the Sacramento Valley. There may, however, be some landslide
hazard due to possible liquefaction of soils bordering the Sacramento River and its tributaries.
Areas of potential landslides are shown in Figure 16-7.
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Figure 16-7
Butte County
General Plan
®Miles02468101
Source: California Division of Mines and Geology
Date printed: June 17, 2003
Legend
LANDSLIDE RISK
High
Moderate to High
Moderate
Low to Moderate
Low to None
Lakes
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Expansive Soils
Expansive soils have a potential to undergo significant changes in volume, either shrinking or
swelling, with changes in moisture content. Periodic shrinking and swelling of expansive soils
can cause extensive damage to buildings, other structures and roads. Moisture content and the
percentage and type of clay minerals present in the soil determine the potential volume change of
an expansive soil. Soils composed only of sand and gravel have no potential for volume change
due to moisture change. Soils containing clays have variable potential for volume changes. Such
soils are generally classified into three expansive soils classes with low, moderate, and high
potential for volume changes:
• Low: This soils class includes sands and silts with relatively low amounts of clay minerals.
Sandy clays may also have low expansion potential, if the clay is kaolinite. Kaolinite is a
common clay mineral.
• Moderate: This class includes silty clay and clay textured soils if the clay is kaolinitic and
also includes heavy silts, light sandy clays, and silty clays with mixed clay minerals.
• High: This class includes clays and clay with mixed monmorillonite, a clay mineral which
expands and contracts more than kaolinite.
More technically, expansive soils are classified on a numerical shrink-swell classification index
which varies from zero (no potential volume changes) to 10 (maximum potential volume
changes). In this classification, soils with a shrinkage index below five are considered to have
low expansion potential. Soils with an index between five and seven have moderate expansion
potential, and soils with indices above seven have high expensive potential.
Figure 16-8 shows the distribution of expansive soils within Butte County, grouping soils with
no expansive potential with the low expansion potential soils. Soils with no or low expansion
potential occur along stream and river valleys and on steep mountain slopes. Soils of high
expansion potential occur in the level areas of the Sacramento Valley, including around the
population centers of Chico, Oroville, Biggs, and Gridley.
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Figure 16-8
Butte County
General Plan
®Miles02468101
Source: California Division of Mines and Geology, 1995Legend
Lakes
SOIL EXPANSIVITY
LOW
MODERATE
HIGH
LOW - Those soils range from sands to silt loams with any clay material and include sandy clay loams if the
clay is kaolmitic. The Unified Soil Class can be ML, SM, CL or SC and the shrinkage index is less than 5.
MODERATE - This class includes the silty clay loam to clay textures if the clay is kaolinite, and heavy silt
loams, light sandy clays and silty clay loams with mixed clay minerals. The Unified Soil Class is CH if the clay
is kaolmitic or CL or ML if the clay minerals are mixed. The shrinkage index is between 5 and 7.
HIGH - This class includes clay loams to clays with mixed or montmorillonitic clays. The Unified Soil Class
is CH with mixed or montmorillonitic clays, and the shrinkage index is greater than 7.Date printed: June 17, 2003
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Volcanic Hazards
Some of the most striking topographic features of Butte County, including Table Mountain north
of Oroville, are volcanic in origin. The lava flows which now cap Table Mountain and most of
the other volcanic features in the county are, however, tens of millions of years old. The geologic
activity producing this volcanism has long since ceased and thus there are virtually no volcanic
hazards in most of Butte County. However, extreme northern Butte County is an exception to
this generalization because Mt. Lassen, an active volcano, is only about 25 miles north of the
Butte County line.
Mount Lassen is the southernmost volcano in the Cascade Range. There are numerous active
volcanoes in the Cascades, including Mount Shasta in California and several others in Oregon
and Washington. Mount Lassen last erupted in the period between 1914 and 1921; this period of
volcanic activity included steam and ash eruptions as well as a small lava flow. Like the other
volcanoes in the Cascades, Mount Lassen is considered dormant, which means that it is not
currently erupting but is expected to erupt again in the future. Mount Lassen has erupted at least
seven times within the past 1,200 years.
There are four main hazards that may accompany volcanic eruptions: 1) ash and cinder falls, 2)
explosive blasts, 3) lava flows, and 4) mud flows. Despite the general severity of volcanic
hazards, potential volcanic hazards for Butte County are limited to the northernmost portions of
the county. Even here, the hazards are relatively modest because of the distance between Butte
County and Mount Lassen. In historic times, there are no records of significant ash falls,
explosive effects, lava flows or mud flows reaching Butte County. Furthermore, impending
volcanic eruptions generally give numerous advance warning signs and thus it is usually possible
to evacuate residents in areas subject to volcanic hazards.
Naturally Occurring Asbestos
Within California, naturally occurring asbestos (NOA) is known to exist in serpentine rock.
Serpentine rock, and it’s parent material, ultramafic rock, is abundant in the Sierra foothills, the
Klamath Mountains, and Coast Ranges. Within Butte County, serpentine rock is found within the
foothill and montane regions.
NOA is commonly found in ultramafic rock, including serpentine, and near fault zones. The
amount of asbestos that is typically present in these rocks ranges from less than 1 percent up to
25 percent and more. Asbestos is released from ultramafic and serpentine rock when it is broken
or crushed. This can happen when cars drive over unpaved roads or driveways which are
surfaced with these rocks, when land is graded for building purposes, or at quarrying operations.
Asbestos is also released naturally through weathering and erosion. Once released from the rock,
asbestos can become airborne and may stay in the air for long periods of time.
Asbestos is a known carcinogen and inhalation of asbestos may result in the development of lung
cancer or mesothelioma. The asbestos contents of many manufactured products have been
regulated in the U.S. for a number of years. The California Air Resources Board (CARB) has
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regulated the amount of asbestos in crushed serpentinite used in surfacing applications, such as
for gravel on unpaved roads, since 1990. In 1998, new concerns were raised about possible
health hazards from activities that disturb rocks and soil containing asbestos and may result in
the generation of asbestos-laden dust. These concerns lead to CARB to revise their asbestos limit
for crushed serpentinite and ultramafic rock in surfacing applications from 5 percent to less than
0.25 percent, and to adopt a new rule requiring best practices dust control measures for activities
that disturb rock and soil containing naturally occurring asbestos.
Serpentine soils are an important natural resource of Butte County. Over 200 species of native
California flora are restricted wholly or in large part to serpentine soils, and an estimated 90 to
100 taxa are endemic to serpentine and related soil types in the northern coast ranges of
California. Taking simple and common sense precautions will ensure that residents and soils can
safely exist together. Serpentine soils or rock should be left undisturbed and stabilized to reduce
exposing or releasing asbestos fibers into the environment. As long as fibers remain bound in
rock or soil, they pose very little health threat.