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Human-Made Hazards
Natural Hazards
This chapter provides a discussion of the public health and safety hazards in Napa County. The chapter describes the methods used to analyze hazard potential for human-made hazards, including vehicular accidents, crime, and hazardous materials spills; as well as natural hazards, including seismically related hazards, wildland fires, and flooding.
HUMAN-MADE HAZARDS
Traffic
To assess traffic hazards, five law enforcement agencies, including the California Highway Patrol, were contacted. Napa County is below average compared to adjoining counties in the total numbers of persons killed and injured from auto and motorcycle accidents. From 1993 to 2003, the total number of accidents in Napa County has increased by 30%. The City of Napa experienced approximately 60% of the total accidents in the County in 2003, although only 1 of the 20 deaths occurred in the City. Overall, the total number of traffic accident-related deaths within the County remained relatively constant from 1993 to 2003 despite increases in population; this may be due in part to safer vehicles and improved enforcement of seatbelt laws.
Crime
The Office of the Attorney General at the California Department of Justice (CDJ) and the Napa County Sheriff’s Department were contacted to collect information on crime rates and trends. Napa County has a lower crime rate than the state as a whole. Solano, Yolo, and Lake Counties report higher crime rates than Napa County, but Napa County reported more incidents of crime than Sonoma and Marin Counties. From 1993 to 2003, the total reported crimes (per 100,000 people) in Napa County decreased 27%, from 4,230 to 3,074 (CDJ 2004). The highest population-adjusted crime rate occurred in the year 1994 and the lowest in 2000.
Reported crimes fall into four general categories: violent crimes (homicide, rape, robbery, and aggravated assault); property crimes (burglary and motor vehicle theft); larceny/theft; and arson. Larceny/theft is the most common type of reported crime in Napa County, followed by property crimes, violent crimes, and arson. Of the four types of violent crimes, aggravated assault is the most prevalent.
Hazardous and Contaminated Sites
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Napa County is known for its agricultural production. Due to the use of fuel, pesticides, and other chemicals, agricultural production is a major source of hazardous wastes and contaminated sites. However, due to increasing population in all Bay Area counties, including Napa, hazardous materials are also becoming more widely used throughout the urban centers, including in Napa County. Potential human exposure, magnitude of risk associated with contaminated sites, chemical spills, and polluted groundwater within Napa County are all public health and safety issues. Existing data provided by Napa County regarding hazardous sites included contaminated site listings from the many databases identified in this chapter. The database search described in the methods section identified hundreds of sites, each with varying levels of information and detail. From this information, a hazardous sites map was developed and divides the hazardous site locations into four different classes (red, orange, yellow, and white) based on the potential risk to human health.
NATURAL HAZARDS
Earthquakes, Seismicity, and Other Geologic Hazards
Napa County, similar to the San Francisco Bay region, is subject to primary and secondary seismic hazards (resulting from earthquake activity) and other non-seismic geologic hazards. As stated in the geological resources chapter, a number of faults have been mapped within the County, but only three have been designated active by the California Geological Survey in accordance with the Alquist Priolo Earthquake Fault Zoning Act. The primary seismic hazard generated from earthquakes on these faults is surface rupture. Secondary seismically induced hazards, which could be generated from faults within the County or regionally, include groundshaking, landslides, liquefaction, lateral spreading, lurching, differential settlement, and failure of levees and dams.
Non-seismically induced geologic hazards include ground subsidence/settlement, landslides and soil creep, and erosion. These hazards have the potential to cause injury to people or damage to property. GIS maps created for these hazards are provided in this chapter to identify the potential for occurrence in the County.
Fire Hazard Severity
Most of Northern California, with its cool wet winters and long dry summers, is considered a high fire hazard environment. Wildfire is a natural and integral component of California’s landscape that has sculpted the geology, soil, and vegetation of the region. Napa County is characterized by narrow valley floors surrounded by steep, hilly terrain and fire-evolved vegetation, which, combined with the plentiful wildland recreational opportunities, leads to the high wildland fire rates experienced in the County.
Wildland fires are so frequent that in the last 30 years wildfires have burned 232,000 acres of land in or directly adjacent to Napa County, a county of approximately 482,000 acres.
Fire hazard zoning is one of the first steps in comprehensive land use planning. To determine the fire hazard severity in the County, a GIS-based model was developed. This model uses digital mapping of parameters that affect wildfire hazards such as landscape characteristics, historical data, weather, and structural value, to rank areas within the County from low to high on a fire hazard severity scale. The model analyzed and ranked the risk, hazard, and value for each evaluation area. Based on results of the model, Napa County has 47,441 acres of severe high fire hazard land, which represents about 10% of the County. The Napa Valley floor, eastern mountains and Cameros areas, which comprise 16,358, 12,645, and 3,587 acres respectively, had the greatest amount of high fire hazard severity land. The Angwin area has the highest percentage, with 41.8% of its area characterized as high hazard. With 0.72%, the Knoxville area has the lowest percentage of high fire hazard land. The fire hazard severity model and data used will be given to the County upon completion of the BDR analysis, which will allow the California Department of Forestry and Fire (CDF) and Napa County Fire to easily make adjustments when more data become available in the future.
Flooding
Napa County is a flood-prone region because it has a Mediterranean climate of wet winters and dry summers and a landscape of steep hills and a wide valley floor. Recent population and development pressures have also increased the flood hazard potential in the County. The Napa River flows through the Napa Valley Floor past Calistoga, St. Helena, Yountville, and Napa. The City of Napa, located where the Napa River flattens into the San Pablo Bay estuary, is the most flood-prone populated area in the County and the fifth most flood-prone community in California in terms of flood damage payments from the Federal Emergency Management Agency (FEMA). To assess flooding hazards, FEMA flood zone maps for the 100- and 500-year floods were analyzed. Specific areas subject to flooding in City of Napa are generally from Trancas Street in the north to Imola Avenue in the south, Coombs Street to the west and Silverado Trail to the east. Between 1862 and 1997, the City of Napa experienced 27 floods, the largest of which occurred on February 18, 1986 (Wadsworth 1998).
During a 100-year flood, more than 325,000 gallons of floodwater per second would flow through the City of Napa, or five times the volume of Lake Hennessey, over the span of the flood. More than 3,500 people and 2 million square feet of business and office space would be inundated.
