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Public Safety Element Table of ContentsLIST OF FIGURES The Public Safety Element is intended to protect the community from unreasonable risks from seismically induced surface rupture, ground shaking, ground failure, tsunami, seiche and dam failure, slope instability leading to mudslides, landslides, subsidence and other known geologic hazards, flooding and fire. It includes maps of known hazards and assesses evacuation routes, water supply needs, road widths, clearances around structures and other items related to potential catastrophic events. The Public Safety Element establishes policies to minimize potential property damage and human injury by reducing the exposure of persons and property to the above hazards and to hazardous materials. Acceptable levels of risk are based upon the nature of each hazard, the frequency of exposure, the number of persons exposed, and the potential damage. The policies in this element are intended to avoid development which would adversely affect future residents and visitors as well as adjacent property and residents. It is also intended that an undue financial burden not be placed on the taxpayer by allowing development which may have unusually high costs for public services and disaster relief. 1.2 RELATIONSHIP TO OTHER ELEMENTS The natural hazards contained in this Element have been considered in the preparation of the Land Use Element. The Land Use Element limits the range of land uses allowed in hazardous areas in order to reduce the number of people and buildings exposed to risk. Public Safety Element policies are also coordinated with the policies of the Open Space, Resource Conservation, Housing, Public Facilities, and Circulation and Transit Elements. This element contains sections on geologic hazards, flood hazards, fire hazards, and hazardous materials. Each section describes the extent of the hazard, the risk of damage and means of protection. An implementation program is also included. 1.4 DETERMINATION OF ACCEPTABLE RISKS The County is not able to guarantee that any particular development will not, at some time in the future, be adversely affected by the hazards identified in this element because such hazards, by their nature, defy precise prediction. In those instances where there is a significant factual question about whether a particular development has mitigated risks from natural hazards to an "acceptable" level and the property owner wishes to proceed in the face of such factual question, the County may require the owner of the property to provide indemnification to the County, insurance or other security and a recorded notice which will protect the interests of the County and provide notice of the potential problem to future purchasers. 2.0 PROTECTION FROM GEOLOGIC HAZARDS 2.1 GEOLOGIC HAZARDS IN SONOMA COUNTY Fault Movement: Earthquakes are usually caused by sudden movement along geologic faults. Sonoma County faults are part of the San Andreas fault system which extends along the California coast. The known geologic faults in Sonoma County are shown on Figures PS-1a through PS-1i (pages 257 through 273). All show evidence of movement during the past 2 million years and are considered to be potentially active. Earthquakes: Since 1855, more than 140 earthquakes have been felt in the Santa Rosa area. The 1906 earthquake caused 61 deaths and major damage in Santa Rosa, Sebastopol, Healdsburg and other communities. The last major earthquake in Sonoma County was the 5.7 magnitude event on the Healdsburg fault in Santa Rosa in 1969. Analysis of seismic data indicates that 8.5 and 7.5 magnitude earthquakes can be expected for the San Andreas and the Healdsburg-Rodgers Creek faults respectively. Earthquakes of 8.0 or more on the San Andreas fault can be expected every 50 to 200 years. Groundshaking: Groundshaking from earthquakes affects the most people and can cause the most damage of any geologic hazard. The amount of ground shaking depends on the magnitude of the earthquake, the distance from the epicenter and the type of earth materials in between. ABAG maps showing the groundshaking hazard in Sonoma County are on file at the Planning Department. Groundshaking similar to that which took place in Santa Rosa during the 1969 earthquake can be expected somewhere in Sonoma County once every 20-30 years. Ground Failure: Damage from groundshaking can be increased by liquefaction and landslides. Liquefaction changes water-saturated soil to a semi-liquid state, removing support from foundations and causing buildings to sink. The most hazardous areas are valleys and tidal marshes with high water tables and sandy soils. Landslides can result from groundshaking and may occur in areas of gentle slopes due to liquefaction of subsurface materials. Ground Displacement Along Fault Traces: During the 1906 earthquake horizontal displacement along the San Andreas fault averaged 15 feet in Sonoma County. The Healdsburg, Rodgers Creek and Maacama faults also show evidence of surface displacement during the past 11,000 years. Tsunamis: Tsunamis are large ocean waves caused by undersea earthquakes or landslides. They travel up to 400 mph and can arrive at a coastline before local warnings can be given. The area covered by a tsunami is determined by water depth, underwater topography, and shape of the coastline. A tsunami expected once in 200 years would flood the coast and bay shoreline up to 20 feet above sea level. Secondary Effects of Earthquakes: Earthquake damage to utilities and other public facilities can produce disastrous secondary effects. Much of the destruction from the 1906 earthquake was from fires which could not be put out due to broken water lines, damaged roads and lack of communications. These secondary effects can be reduced by various methods but larger facilities and population growth increase the potential damage. Downstream flooding may result from dam failure. Warm Springs Dam is located on a medium-sized fault but was designed to absorb the maximum expected displacement and groundshaking from any fault in the region. The most common type of ground failure in Sonoma County is landslides, the downslope movements of soil and/or rock materials. Extensive land areas of the county are subject to this hazard and are shown on Figures PS-1a through PS-1i (pages 257 through 273). Landslides can be triggered by heavy rainfall, earthquakes or human activities such as road cuts, grading, construction, removal of vegetation, and changes in drainage. Buildings, utilities and roads can be damaged by clay-rich soils which swell each winter and shrink each summer depending upon the rainfall. This is a less obvious hazard than earthquakes or landslides, but the gradual cracking, settling and weakening of older buildings is significant in total. Soils with high clay content are found in many valley areas which are planned for development. 2.2.1 Assessment of Hazards and Risks Figures PS-1a through PS-1i show data from detailed maps on file in the Planning Department. The large file maps are to be used in the review of projects and are incorporated by reference herein. State law requires a geologic report for projects along known active faults. "Special Studies" zones have been designated along four faults in Sonoma County where surface movement has taken place during the past 11,000 years. 2.2.2 Development Planning and Regulation Reducing risks of damage and injury to acceptable levels requires special permit review procedures and construction standards. Construction must meet the standards of the Uniform Building Code for seismic resistance, site stability, grading and geologic studies. Dams, schools, hospitals and power plants are specially regulated by state and federal agencies for protection against such hazards. Land uses vary in their sensitivity to geologic hazards. Agriculture and timber management are considered appropriate in areas subject to geologic hazards because such uses require few occupied structures. Structures should not be placed on known landslides or faults and, when located close to these features, may need special design to withstand damage. Schools, utility structures, hospitals, and powerplants are especially sensitive to geologic hazards. 2.3 REDUCTION OF POTENTIAL DAMAGE FROM GEOLOGIC HAZARDS Goal PS-1 Prevent unnecessary exposure of people and property to risks of damage or injury from earthquakes, landslides and other geologic hazards. Objective PS-1.1 Continue to utilize available data on geologic hazards and associated risks. Objective PS-1.2 Regulate new development to reduce the risks of damage and injury from known geologic hazards to acceptable levels. The County shall use the following policies, in addition to those in the Land Use Element, to achieve these objectives:
3.0 PROTECTION FROM FLOOD HAZARDS 3.1 FLOOD HAZARDS IN SONOMA COUNTY Streams overflow banks when runoff from the watershed exceeds the capacity of the stream channel to carry it. Floods on small streams usually peak and recede quickly, while floods on the lower Russian River may not peak for two days or more after the start of a storm and may exceed floodstage for four days or more. Flood hazards are estimated by the area flooded by the maximum storm event expected over a 100 year period, a 10 year period or some other frequency. Figures PS-1a through PS-1i (pages 257 through 273) show the general extent of peak flooding expected during a 100 year flood for those streams which have been studied. Flooding can move or destroy buildings and wash away soil, crops, and loose objects. Floating debris is a very dangerous hazard. Flood damage may weaken building materials and increase mildew, dust, bacteria and other disease vectors. Public facilities, roads and services may also be affected. A particular concern is the disruption of sewage treatment facilities and resulting water quality impacts. 3.2.1 Assessment of Hazards and Risks The Federal Emergency Management Agency (FEMA) and Federal Insurance Administration have assessed flood hazards for most major streams in the county. They have prepared maps showing the areas with at least a one percent (1%) chance of being flooded in any year. The approximate boundaries of these areas are shown on Figures PS-1a through PS-1i. The FEMA maps are being revised for the Russian River and Dry Creek due to Warm Springs Dam. The Sonoma County Water Agency has prepared drainage plans for some urbanized areas in the county. 3.2.2 Flood Prevention and Control Construction of dams and other improvements is one way to reduce flood hazards. Flood levels in the Russian River basin have been reduced by Coyote Dam and Warm Springs Dam. Flooding in Santa Rosa Creek and its branches has been reduced by five small dams. However, dams and structural improvements are costly, take a long time to complete, increase sediment buildup and give a false sense of security to floodplain residents. Future flood control activities may include improvements to drainage channels and removal of excess sediments from stream beds. Flooding may also be reduced by proper siting of development, watershed management, retention basins, and similar measures to decrease runoff. These methods reduce the needs for costly construction projects and disaster relief. Land uses which can sustain periodic flooding and which decrease flood hazards downstream are encouraged in floodplains. On the other hand, floodplains are attractive for development because of the availability of water, soil, transportation and visual amenities. Unincorporated communities with development in designated floodplains include Guerneville, Monte Rio, Windsor, Penngrove, Geyserville, Glen Ellen and Cazadero. Floodplain management is required by federal and state law. Various incentives such as flood insurance, loans and state funding of control projects are offered if flood management practices are followed. A local "hazard mitigation plan" is required by the federal government after aid is requested for a flood disaster. Sonoma County has adopted an ordinance requiring permits for construction in 100 year floodplains. Floodplain management suggests limits on land uses to agriculture, recreation and other low intensity activities without permanent residences or other occupied structures. However, there may be public benefit from allowing additional development in existing communities in floodplains. 3.3 REDUCTION OF POTENTIAL DAMAGE FROM FLOODING Goal PS-2.1 Prevent unnecessary exposure of people and property to risks of damage or injury from flooding. Objective PS-2.1 Maintain complete data on flood hazards. Objective PS-2.2 Regulate new development to reduce the risks of damage and injury from known flooding hazards to acceptable levels. The County shall use the following policies, in addition to those in the Land Use Element, to achieve these objectives:
4.0 PROTECTION FROM FIRE HAZARDS 4.1 WILDLAND FIRE HAZARDS IN SONOMA COUNTY The combination of highly flammable fuel, long dry summers and steep slopes creates a significant natural hazard of large wildland fires in many areas of Sonoma County. Wildland fire results in death, injury, economic losses and a large public investment in fire fighting efforts. Woodlands and other natural vegetation are destroyed resulting in the loss of timber, wildlife habitat, scenic quality and recreation. Soil erosion, sedimentation of fisheries and reservoirs, and downstream flooding can also result. Most damage results from a few large fires in the dry weather months. There were 42 wildland fires of 100 acres or more in the county between 1965 and 1984. Fire hazard severity has been mapped by the California Department of Forestry (CDF). Areas with a high or very high risk are shown in Figures PS-1a through PS-1i on pages 257 through 273 and include over half of the county. The highest hazard is found in mountainous areas with dry summers, plenty of fuel, and steep slopes. Residences have increased the number of fires in hazardous rural areas. Human activities now account for 9 out of 10 wildland fires. Residences in rural areas cause fire suppression agencies to devote limited resources to structural protection while the wildfire spreads. The probability of large damaging fires in urban areas is affected by weather conditions and the spread of fires in surrounding wildland areas. The type of construction, preventive measures, and the extent of fire suppression services are the chief factors which determine how far these fires spread. 4.2.1 Assessment of Hazards and Risks Fire hazards shown on Figures PS-1a through PS-1i are only a general picture of the actual hazard because of the size of the areas and differences in vegetation and slope. The maps show the fire hazards only in unincorporated areas which are classified as "wildlands" and are therefore within the "State Responsibility Area" served by CDF. Project review should include an assessment of wildlife fire potential and needed mitigation measures. This assessment is important for residential uses, public facilities multi-story and contiguous buildings, mobile homes, and uses of flammable substances or explosives. In order to reduce the risk of fire damage in rural areas, the types and intensities of land uses should be limited. Wildland fire hazards may be reduced by mitigation measures including the removal of vegetation and installation of dependable water systems, but cannot be eliminated entirely. Rural development should be most restricted where natural fire hazards are high, fire protection is limited, and road access prevents timely response by firefighting personnel and rapid evacuation by residents. Fire hazard regulations are intended to minimize on-site property damage and personal injury, avoid damage to adjacent properties and reduce the cost of fire suppression services. Increasing "built-in" fire protection in new construction is the most cost effective way of achieving these objectives. All development must have adequate water available for fire suppression, whether from a hydrant and community system or from an on-site storage tank. Where development is permitted near wildlands and natural vegetation, the fire hazard must be further mitigated by other measures. The locations of subdivision lots and building envelopes can maximize access by emergency vehicles and minimize construction in steep or wooded areas. Fire retardant roof materials are now required in high hazard areas. Preventing the spread of wildland fires to and from structures also requires removal of surrounding vegetation and clearing of fuel breaks. Fire safety standards adopted by the County include the Uniform Fire Code, National Fire Code, Uniform Building Code and companion codes, and the subdivision and zoning ordinances. Differences in code requirements, staffing and training among local fire districts prompted the formation of the Sonoma County Department of Fire Services in 1985. The Department's Fire Marshal reviews projects and assists local fire districts in adoption and enforcement of fire safety codes. Improvements in standards for road design, water supply and sprinkler systems could increase the effectiveness of local fire protection services. CDF enforces requirements for fire fighting and prevention, works with landowners on controlled burns, and advises rural residents on fire prevention methods. Minimum fire safety standards for wildland areas are now being prepared. 4.3 REDUCTION OF POTENTIAL DAMAGE FROM WILDLAND FIRE HAZARDS GOAL PS-3.1 Prevent unnecessary exposure of people and property to risks of damage or injury from wildland and structural fires. Objective PS-3.1 Continue to utilize complete data on wildland and urban fire hazards. Objective PS-3.2 Regulate new development to reduce the risks of damage and injury from known fire hazards to acceptable levels. The County shall use the following policies, in addition to those in the Land Use Element, to achieve the above objectives:
5.0 PROTECTION FROM HAZARDOUS MATERIALS 5.1 HAZARDOUS MATERIALS IN SONOMA COUNTY Many man-made substances can be hazardous to health. The increased use of such materials has increased potential hazards and actual damage. Public concerns have led to tighter controls on the production, transport, storage, sale and use of hazardous materials and, particularly, on the handling and disposal of concentrated residues and wastes produced by power plants and other industrial operations. Hazardous materials are found at many locations in Sonoma County. The electrical generating plants in the Geysers geothermal area use and produce hazardous materials hauled on winding mountain roads. Spills and releases of such materials have occurred. Petroleum fuels get into ground water and surface water, particularly from underground tanks. Prevention of hazardous materials in the County's solid waste landfills and transfer stations and industrial operations is important because these materials could affect water quality. The management of hazardous materials is included in this element because it has become a major public safety issue requiring significant resources and attention by local agencies. While different agencies have different responsibilities in the regulation of hazardous materials, the Health Department has been designated as the lead agency for preparation of a comprehensive hazardous materials management plan, including the County Hazardous Waste Management Plan now in the draft stage. 5.3 REDUCTION OF POTENTIAL DAMAGE FROM HAZARDOUS MATERIALS Goal PS-4 Prevent unnecessary exposure of people and property to risks of damage or injury from hazardous materials. Objective PS-4.1 Maintain complete documentation and assessments of data on hazardous materials. Objective PS-4.2 Regulate the transport, storage, use and disposal of hazardous materials in order to reduce the risks of damage and injury from hazardous materials to acceptable levels. The County shall use the following policies to achieve these objectives.
6.0 PUBLIC SAFETY IMPLEMENTATION PROGRAM: Public Safety Program 1: Safety Hazards Information System/Related Plan and Zoning Amendments Program Description: Log and maintain records of all mapping and reports regarding geologic and flood hazards information prepared for project applications and by other sources. Use the information in assessing constraints. Revise plans and zoning as appropriate. Public Safety Program 2: "Floodplain" and "Geologic Hazard Area" Zoning Combining Districts Program Description: Prepare amendments to Chapter 26 of the Sonoma County code to: 1) revise flood plain zoning restrictions in conformance with Chapter 7 of the Sonoma County Code and 2) include a "geologic hazard area" combining district which establishes regulations for permissible types of uses and their intensities and appropriate development standards. Public Safety Program 3: Drainage, Erosion, and Fire Safety Standards for Subdivisions Program Description: Prepare amendments to Chapter 25 of the Sonoma County Code to clarify standards for drainage, erosion control and fire safety. Figure PS-1a Figure PS-1b Figure PS-1c Figure PS-1d Figure PS-1e Figure PS-1f Figure PS-1g Figure PS-1h
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