Section 3: Natural Hazard Identification and Risk Assessment Washington County Natural Hazard Mitigation Action Plan Update 2010 Risk assessments provide information about the changes to building codes or development areas where the hazards may occur, the value of regulations, identifying properties or structures existing land and property in those areas, and an appropriate for acquisition or relocation, policies analysis of the potential risk to life, property, and the concerning critical and public facilities, taxation environment that may result from natural hazard strategies for mitigating risk, and informational events. This section identifies and profiles the programs for members of the public who are at risk. location, extent, previous occurrences, and future The third phase, risk analysis, involves probability of natural hazards that can impact estimating the damage, injuries, and costs likely to Washington County, as highlighted in Figure 3.1 be incurred in a geographic area over a period of below. The information in this section was paired time. Risk has two measurable components: (1) the with the information from Section 2: Community magnitude of the harm that may result, defined Profile during the planning process in order to through the vulnerability assessment, and (2) the identify issues and develop actions aimed at likelihood or probability of the harm occurring. An reducing overall risk, or the area of overlap in the example of a product that can assist communities in figure below. completing the risk analysis phase is HAZUS, a risk A risk assessment consists of three phases: assessment software program for analyzing hazard identification, vulnerability assessment, and potential losses from floods, hurricane winds and risk analysis, as illustrated in the following graphic. earthquakes. In the Federal Emergency Management Agency (FEMA) hazard modeling Exhibit 3.1: Risk Assessment summary program HAZUS-MH, current scientific and engineering knowledge is coupled with the latest geographic information systems (GIS) technology to produce estimates of hazard- related damage before, or after a disaster occurs. In 2007, Washington County conducted a Hazard Analysis as part of developing an Emergency Operations Plan. Individual hazards were scored using a formula that incorporated four rating criteria with weight factors and three levels of severity. For every hazard, scores for the four criteria (event history, vulnerability, maximum threat, and Source: USGS - University of Oregon Community Service Center, 2006 probability) were determined by multiplying each criterions severity rating by its weight factor. The The first phase, hazard identification, involves rating criteria scores for each hazard were summed the identification of the geographic extent of a to provide a total score for that hazard. The hazard hazard, its intensity, and its probability of ranking was determined to be: severe weather, occurrence. This level of assessment typically pandemic, flood, earthquake, utility failure, involves producing a map. The outputs from this terrorism / civil disturbance, ash fallout, enemy phase can also be used for land use planning, urban attack, drought / water shortage, hazmat release, growth management, and regulation; public Wildland Urban Interface fire, dam failure, awareness; and defining areas for further study. transportation accident, tornado, and landslide. The The second phase, vulnerability assessment, analysis is included in Appendix B: Hazard combines the information from the hazard Background Information. identification with an inventory of the existing (or This Risk Assessment focuses on natural hazards planned) property and population exposed to a and so will not discuss each of the hazards ranked hazard, and attempts to predict how different types by the County. However, increasing the resiliency of of property and population groups will be affected the County in the face of natural hazards will by the hazard. This step can also assist in justifying contribute to the ability of the County to recover
Washington County Natural Hazard Mitigation Action Plan! 3-1! Section 3: Hazard Identification and Risk Assessment from other kinds of disruptions. Where applicable, we have incorporated information and ranking from the County Hazard Analysis. In describing recent hazard events, it is not always easy to separate causality from occurrence. Severe natural hazard events can alter the environment and trigger other, secondary hazards. For example, winter rain storms often cause flooding and within hours or days over-saturated ground at steep grades can sink or slide. In Washington County, the unique basin-shaped topography can compound the affect of many hazard risks. This section steps through recent hazard events to impact the County, provides an overview of recent scientific data about the hazards and vulnerabilities facing the County, and describes hazard risk in Washington County. More extensive descriptions of each hazard background is provided in Appendix B.
Washington County Natural Hazard Mitigation Action Plan! 3-2! Section 3: Hazard Identification and Risk Assessment Known as the “Christmas Flood,” the flood of Flood Hazard December 1964 was rated as a 100-year event by FEMA. The conditions resulting in the floods of 1964 Floodplain maps provide detailed information were similar to the causes of the 1996 floods. Warm, about the location of the flood hazard and can assist prolonged rainfall on a low level snow pack quickly planning jurisdictions in making policy and land filled local streams and rivers. use decisions. Maps of the floodplain provides important data for determining the areas that fall Hazard History: 2004 - 2009 within the floodplain. In Washington County, the Tualatin Basin is a key factor for understanding Severe rain storms significantly impact flood risk. It can amplify the risk of flooding from Washington County and the surrounding region accumulated precipitation or runoff in lakes, rivers, nearly every year. Strong weather systems brought streams, culverts, and throughout low-lying areas. severe storms, flooding, landslides, and mudslides Washington County is prone to two types of from December 2005-January 2006, then again in flooding: riverine and urban flooding. Riverine November and December 2006. These events were flooding occurs when rivers and streams overwhelm declared presidential disasters by FEMA for their banks. Increased development accelerates the counties and communities adjacent to Washington risk of urban flooding. Impervious surfaces such as County. Even though Washington County was not concrete and asphalt collect water at a faster rate included in this declaration, County residents did than an undeveloped landscape and the resulting experience disruption from these events.1 runoff can collect in streets, ditches, and basements, December 2007 again brought torrential rain to impacting County residents on a regular basis. the region that caused flooding, landslides, and mudslides. Highway 26 and 6 were closed due to Hazard History: prior to 2004 trees and debris blocking the roadway. The most Between the 1850’s and the present, human severe impacts of this storm were felt by coastal activity significantly changed the hydrology of the counties, where hurricane force winds knocked out Willamette watershed, including changes to the communications and power lines, and in Columbia Tualatin Basin. Hydroelectric dams and flood County where the town of Vernonia was flooded control systems were constructed throughout the when the Nehalem River breached its banks. In all, drainage basin. Private and public organizations six counties in northwest Oregon, including engaged in the dewatering of wetlands, the draining Washington County, were eligible for federal of floodplains, and diking along some sections of the disaster aid.2 river. More recently, increasing urbanization has contributed to changes in basin hydrology. Prior to human alteration of the river system, rivers in the Since 1978, the National Flood Insurance region flooded larger areas more often. Program (NFIP) has paid over $4.2 million in claims for flood damage to Washington County properties. In February of 1996, an unusually deep, low Exhibit 3.2 shows that, as of May 2009, elevation snow pack in the Cascades and Coast unincorporated Washington County had 64 Range was soaked for four days by precipitation repetitive loss properties, with 14 claims. And as of coming from a subtropical storm off the Pacific March 2010, 904 National Flood Insurance Program Ocean. The four-day rainfall total in Hillsboro was policies in place. A list of repetitive loss properties in 6.70 inches, surpassing the previous record of 5.91 unincorporated Washington County is on file at the inches set in 1974. Washington County suffered Emergency Management and Land Use and almost $10 million in damage from the event; Transportation Offices (This information is protected statewide damages surpassed $280 million. National by the Federal Privacy Act). Also, see Map 3.3. Flood Insurance Program claims from the event surpassed $2.3 million for the County alone.
Washington County Natural Hazard Mitigation Action Plan! 3-3! Section 3: Hazard Identification and Risk Assessment Exhibit 3.2: NFIP Statistics, 1978-2010 ! Total Repetitive Number of Losses / Losses / Policies Paid in full Claims* Payments Beaverton 323 42 / 23 6 / 2 $ 227,607.84 Cornelius 10 1 / 1 $ 3,784.71 Forest Grove 12 5 / 2 $ 75,194.38 Gaston 3 1 / 1 $ 53,293.25 Hillsboro 74 12 / 9 $ 164,213.08 Tigard 136 13 / 10 2 / 2 $ 64,626.88 Tualatin 356 49 / 44 10 / 0 $ 1,390,379.75 Unincorporated Washington County 904 203 / 160 64 / 14 $ 2,277,204.56 Total $ 4,256,304.45 Source: BureauNet, National Flood Insurance Program Reports, Claims information by State and Policy Information by State. Accessed 5/10/2010. <
In Washington County, the Army Corps of flood hazard is included as Map 3.1: Washington Engineers, the Federal Emergency Management County 100-Year Floodplain. Agency (FEMA), Clean Water Services, the Oregon The Oregon Department of Water Resources also Department of Water Resources, and the maintains the hydrography database of rivers, Washington County Department of Land Use and streams, and lakes in the County. These represent Transportation all collect and maintain various the 25-year floodplain data for Tualatin River aspects of flood data. tributaries. Though this data has not been updated In 1974, the Army Corps of Engineers mapped since 2004, it is included as Map 3.2: Washington the 100-year floodplain for the Tualatin River Basin. County Drainage Hazard Area to identify the In 1980, FEMA mapped the 100-year and 500-year location and extent of the hazard. floodplain in Washington County. Since then, the County has updated portions of the Corps and Vulnerability Assessment FEMA maps with smaller drainage studies Flooding can occur every year depending on throughout the County. rainfall, snowmelt, or how runoff from development In 2008, the County updated the floodplain impacts streams and river. Surveys by the model. Modifications included: including areas Department of Geology & Mineral Industries outside of the Urban Growth Boundary that may (DOGAMI), the County, and FEMA have established experience development in the future; more accurate the 100-year floodplain and the County has modeling of the hydrology and stream hydraulics; designated some areas to be “special flood hazard and accounting for increased impervious areas due areas” at a 25-year level. to population growth and other changes to the Changes to development patterns since 2004 surface conditions. While these additions and have the potential to incur increased risk of clarifications do result in a significant increase in the flooding. However, Metro and County development number of acres located within the floodplain, this regulations restrict new development in areas does not necessarily represent increased identified as floodplain. This reduces the impact of development in flood prone areas. In fact, a more flooding on future buildings. As new land has been accurate definition of the floodplain will assist the brought into the regional Urban Growth Boundary, County as it continues to implement the as with the areas of North Bethany and development ordinances that restrict and monitor development code has been written to prevent the development within the floodplain.!This expanded siting of new structures in flood prone areas.3 data that identifies the location and extent of the
Washington County Natural Hazard Mitigation Action Plan! 3-4! Section 3: Hazard Identification and Risk Assessment Risk Assessment accurate and extensive modeling of the flood hazard area. In 2007, the County revised the floodplain The floodplains in Washington County are model to include potential development areas generally located along the Tualatin River and its (including portions of the Urban and Rural reserves) tributaries. Exhibits 3.3 and 3.4 display changes in and conducted new mapping that clarifies previous the hazard areas from 2004 and estimate potential floodplain analysis. Due to the expanded flood losses. GIS analysis of the tax lot information model, the updated floodplain data reveals a determined that there are now approximately 42,402 significant increase in the amount of property — acres within the 100-year floodplain boundaries in both land and buildings — in the floodplain. the County jurisdiction and approximately 60,978 acres within the County Drainage Hazard Areas. These numbers have increased so dramatically not because of rapid development in flood hazard areas or a significant shift in the geology and hydrology of the County, but are due to more
Exhibit 3.3: Flood Hazard Assessment
!Source: Washington County GIS data; analysis by ECONorthwest, 2010
Exhibit 3.4: Drainage Hazard Area Assessment
Source:! Washington County GIS data; analysis by ECONorthwest, 2010
Washington County Natural Hazard Mitigation Action Plan! 3-5! Section 3: Hazard Identification and Risk Assessment This page intentionally left blank.
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Section 3: Hazard Identification and Risk Assessment Vulnerability Assessment • On or close to steep hills including steep road- cuts or excavations into steep slopes; Landslides can affect utility services, • Existing landslides or places of known historic transportation systems, and critical lifelines. landslides (such sites often have tilted power Communities may suffer immediate damages and lines, trees tilted in various directions, cracks in loss of service. Disruption of infrastructure, roads, the ground, and irregular-surfaced ground); and critical facilities may also have a long-term effect on the economy. Utilities, including potable • Steep areas where surface runoff is channeled, water, wastewater, telecommunications, natural gas, such as below culverts, V-shaped valleys, and electric power are all essential to service canyon bottoms, and steep stream channels; community needs. Loss of electricity has the most • Fan-shaped areas of sediment and boulder widespread impact on other utilities and on the accumulation at the outlets of canyons, large whole community. Natural gas pipes may also be at boulders (2 to 20 feet diameter) perched on soil risk of breakage from landslide movements as small near fans or adjacent to creeks; and as an inch or two. • Occurrences of logjams in streams Roads and bridges are subject to closure during landslide events. Because many Washington County Risk Assessment residents are dependent on roads and bridges for Maps 3.4, Slope, show that the western areas of travel to work, delays and detours are likely to have the County have steep slopes which put any resou- an economic impact on county residents and rces – private development or public infrastructure – businesses. To evaluate landslide mitigation for at risk of damage from landslides in those areas. roads, the community can assess the number of vehicle trips per day, detour time around a road Map 3.5, Landslide Inventory, highlights the closure, and road use for commercial traffic or areas where landslides have occurred. There are 90 emergency access. landslide instances within the Washington County border (some straddle the border). The slides were Lifelines and critical facilities should remain documented in: 1967(13), 1973(2) 1983(2), 1995(60), accessible if possible during a natural hazard event. 1996(10), 1997(2), and 2001 (1). The impact of closed transportation arteries may be increased if the closed road or bridge is a critical Map 3.6, Landslide Hazard Areas shows that lifeline to hospitals or other emergency facilities. there are 143 acres of the urban unincorporated Therefore, inspection and repair of critical areas within the landslide hazard zone. transportation facilities and routes is essential and Together, these three maps identify the location should receive high priority. Losses of power and and extent of the landslide hazard in Washington phone service are also potential consequences of County. The majority of areas that have the most landslide events. Due to heavy rains, soil erosion in dense urban development are in the bowl of hillside areas can be accelerated, resulting in loss of Tualatin River basin. However, in these areas even soil support beneath high voltage transmission moderate slopes can become unstable and trigger a towers in hillsides and remote areas. Flood events landslide if rain or runoff oversaturates the soil. can also cause landslides, which can have serious impacts on gas lines. In addition to these maps, DOGAMI conducted a number of in-depth inventories of landslide At the time of this update, sufficient data was hazards in portions of Washington County in 2008 not available to determine the landslide and 2009. These included a landslide hazard map vulnerability in terms of the types and numbers of series, report, and Light Detection and Ranging existing and future buildings, infrastructure, or (LIDAR) data of the Southwest Quarter of the critical infrastructure. However, locations vulnerable Beaverton quadrangle (West Bull Mountain to landslides or debris flows include areas with one planning Area) and (Report and map series) and or more of the following conditions: LIDAR data for the Forest Grove area.4 These maps are included in Appendix F. Washington County Natural Hazard Mitigation Action Plan! 3-8! 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Severe Weather Hazard Windstorm The most common type of wind pattern affecting Winter Storm Washington County is straight-line winds, which originate as a downdraft of rain-cooled air, and A severe winter storm is generally a prolonged reach the ground and spread out rapidly. Straight- event involving snow or ice. The characteristics of line winds can produce gusts of up to 100 mph. The severe winter storms are determined by a number of valley floor in Washington County generally does meteorological factors including the amount and not feel severe effects of the east winds and storms extent of snow or ice, air temperature, wind speed, because it is somewhat protected by the Tualatin and event duration, and can affect the county from Mountains in the eastern part of the County. the northwest and southeast, and from the Mountainous terrain slows down wind movement, Columbia River Gorge. Severe winter storms which is why Oregon’s sheltered valley areas have affecting Washington County typically originate in the slowest wind speed in the state. However, in the the Gulf of Alaska and in the central Pacific Ocean foothills, the wind speeds may increase due to and are most common from October through March. down-sloping winds from the mountains. Severe winter storms pose a significant risk to Windstorms have the ability to cause damage life and property in Washington County by creating over 100 miles from the center of storm activity. conditions that disrupt essential regional systems Isolated wind phenomena in the mountainous such as public utilities, telecommunications, and regions have more localized effects. Winds near the transportation routes. Severe winter storms can earth’s surface and associated pressure effects on produce rain, freezing rain, ice, snow, cold walls, doors, windows, and roofs, may cause temperatures, and wind. Ice storms accompanied by structural components, the elements that provide high winds can have destructive impacts, especially the buildings structure, to fail. to trees, power lines, and utility services. Severe ice storms occur more frequently in areas exposed to The effects of wind speed are shown in Exhibit east winds blowing out of the Columbia River 3.5: Gorge. Severe freezes, where high temperatures Exhibit 3.5: The Damage Effect of Wind Speed remain below freezing for five or more days, occur every three to five years in Washington County. WIND SPEED WIND EFFECTS Severe or prolonged snow events occur less (MPH) frequently, but have widespread impacts on people 25-31 Large branches will be in motion. and property in the County. 32-38 Whole trees in motion; inconvenience felt Ice storms occasionally occur in northern areas walking against the wind. of Oregon, resulting from cold air flowing westward 39-54 Twigs and small branches may break off of through the Columbia Gorge. Freezing rain can be trees; wind generally impedes progress the most damaging of ice formations. While sleet when walking; high profile vehicles such and hail can create hazards for motorists when it as trucks and motor homes may be accumulates, freezing rain can cause the most difficult to control. dangerous conditions within a community. Ice 55-74 Potential damage to TV antennas; may buildup can bring down trees, communication push over shallow rooted trees especially towers, and wires creating hazards for property if the soil is saturated. owners, motorists, and pedestrians alike. The most 75-95 Potential for minimal structural damage, common freezing rain problems occur near the particularly to unanchored mobile homes; Columbia Gorge. The Gorge is the most significant power lines, signs, and tree branches may east-west air passage through the Cascades. Rain be blown down. arriving from the west can fall on frozen streets, cars, and other sub-freezing surfaces, creating dangerous conditions. Washington County Natural Hazard Mitigation Action Plan! 3-9! Section 3: Hazard Identification and Risk Assessment WIND SPEED WIND EFFECTS occurred. Hillsboro reported 42.4 inches of snowfall (MPH) during this event. 96-110 Moderate structural damage to walls, The Columbus Day wind storm in 1962 was the roofs and windows; large signs and tree most destructive storm to ever occur in Oregon in branches blown down; moving vehicles recorded history, both in loss of life and property pushed off roads. damage. The storm killed thirty-eight people and 111-130 Extensive structural damage to walls, did upwards of $200 million in damage. Hundreds roofs, and windows; trees blown down; of thousands of homes were without power for mobile homes may be destroyed. short periods of time, while others were without 131-155 Extreme damage to structures and roofs; power for two to three weeks. More than 50,000 trees uprooted or snapped. homes were seriously damaged, and nearly 100 Greater than 155 Catastrophic damage; structures were completely destroyed. Entire fruit and nut destroyed. orchards were destroyed and livestock killed as barns and trees blew over onto animals. Intense Source: National Oceanic and Atmospheric Administration, Estimating Wind Speed. Accessed 5/9/2010. wind speeds were recorded in the metropolitan << http://www.wrh.noaa.gov/pqr/info/wind.php>> areas with gusts of 116 mph on the Portland Morrison Bridge and peak gusts in Hillsboro of When severe windstorms strike a community, 90mph. downed trees, power lines, and damaged property can be major hindrances to emergency response and November 1981 saw two successive windstorms disaster recovery. Debris carried along by extreme on November 13 and 14. Wind gusts in Portland winds can directly contribute to loss of life and were recorded at 71 mph on the first day and 57 indirectly to the failure of protective building mph on the second day. Eleven people were killed envelopes, siding, or walls of buildings. Storm and $50 million in damages, were reported as a winds can damage buildings, power lines, and other result of the two storms. Estimates indicated that property and infrastructure by means of falling trees nearly 500,000 homes were without power for at and branches. During wet winters, saturated soils least a short time during the weekend. Many cause trees to become less stable and more airports across Oregon and Washington suffered vulnerable to uprooting from high winds. damage. The December 8, 1993 tornado near Newberg Hazard History: prior to 2004 was the most powerful tornado in Oregon in many There were three severe winter storms in years. A dairy farm was damaged, roofs were blown January 1950, with very little time separating them. off some small buildings, and many trees were Their net effect was a nearly continuous storm. The broken. People reported that the funnel was sucking storm had severe effects on infrastructure, residents, water from the Willamette River as it moved and businesses across the state. Deep snow drifts northeast and greatly damaged a mobile home park. closed all highways west of the Cascades and On December 12, 1995 a large low pressure through the Columbia River Gorge. Sleet that turned storm hit Washington County. Gusts of over 100 to freezing rain caused unsafe conditions on mph occurred along the coast while gusts in the highways and damaged trees and power lines. Willamette Valley exceeded 60 mph. Hundreds of During a severe sleet event on January 18, hundreds thousands of people in the state lost power, and of motorists were stranded in the Columbia River there was widespread damage to homes, buildings, Gorge. The stranded motorists had to be rescued by and boats. The damage resulted in a presidential train, even though all rail traffic had considerable disaster declaration. Four Oregonians lost their lives difficulty and many delays in getting through the during the storm. Gorge. Freezing rain downed many trees and power lines, creating widespread power outages across northwestern Oregon. Hundreds of thousands of dollars in damage to public and private property Washington County Natural Hazard Mitigation Action Plan! 3-10! Section 3: Hazard Identification and Risk Assessment Hazard History: 2004 - 2009 from severe weather related to both physical damages and interrupted services. A severe winter storm hit Washington County and the region in December 2008 with record Damage to infrastructure resulting from severe snowfall of 18.9 inches that paralyzed transportation weather events include collapsed or damaged and the economy for days. As the storms peaked, buildings, damaged or blocked roads and bridges, roughly 14,300 households and businesses lost damaged traffic signals, streetlights, and parks, power and severe weather shelters for the homeless among others. Roads blocked by fallen trees during operated for 15 days throughout the County. Three a windstorm or ice / snow event may have severe state highways (US 26, OR 4, and OR 6) were closed consequences to people who need access to at different times over the course of the storm emergency services. Historically, falling trees have despite the fact that transportation crews sanded been the major cause of power outages. and plowed county roads for nearly 15 days.5 Additionally, emergency response operations can be Washington County and its neighbors were declared complicated when roads are blocked or when power a presidential disaster and FEMA provided supplies are interrupted. assistance for emergency protective measures for a Rising population growth and new period of 48 hours in addition to both Public infrastructure in the county creates a higher Assistance and Individual Assistance.6 probability for damage to occur from severe weather as more life and property are exposed to risk. As Data Sources both an industry best practice and hazard mitigation Unlike most other hazards, it is not simple to action, Washington County’s electric infrastructure systematically map winter and wind storm hazard is increasingly being built, or retrofitted, zones. The entire County is susceptible to damaging underground which lessens the risk from severe severe weather. Exhibit 3.5, above, identifies the weather. extent of the wind storm hazard. Winter storms that At the time of this update, sufficient data was bring snow and ice can impact infrastructure, not available to determine severe weather business, and individuals. Those resources that exist vulnerability in terms of explicit types and numbers at higher elevations will experience more risk of of existing and future buildings, infrastructure, or snow and ice, but the entire County can face critical infrastructure. damage from winter storms and, for example, the hail or life threateningly cold temperatures that Risk Assessment winter storms bring. Inventorying the structural integrity of County infrastructure that is exposed to Given current available data, no quantitative high winds and cataloguing the health and maturity assessment of the risk of severe weather was of trees near to that infrastructure will assist the possible at the time of this NHMAP update. County in focusing mitigation actions on areas that However, assessing the risk to the County from may incur the most damage due to windstorms. winter and wind storms should remain an ongoing process determined by community characteristics Vulnerability Assessment and physical vulnerabilities. Weather forecasting can give County resources (emergency vehicles, Washington County is susceptible to direct warming shelters) time to prepare for an impending impacts on infrastructure and property, and indirect storm, but the changing character of the County costs stemming from business closures and lost population and resources will determine the impact work time resulting from severe weather. Industry of winter and wind storms on life and property in and commerce can suffer losses from interruptions Washington County. in electric service and from extended road closures. They can also sustain direct losses to buildings, personnel, and other vital equipment. There are direct consequences to the local economy resulting Washington County Natural Hazard Mitigation Action Plan! 3-11! Section 3: Hazard Identification and Risk Assessment This page intentionally left blank. Washington County Natural Hazard Mitigation Action Plan! 3-12! Section 3: Hazard Identification and Risk Assessment out. These factors, combined with the annual easterly Wildfire Hazard wind events typically in September and October, drastically increase the chance a fire start will grow Even though wildfires are a natural part of the rapidly and resist suppression activities. Furthermore, Pacific Northwest ecosystem, they can present a grain harvest is also occurring at this time. Occasionally, substantial hazard when threatening life and harvesting equipment causes an ignition that can spread property, especially along the Wildland Urban into populated areas and timberlands.8 Interface area. The Community Wildfire Protection Plan adopted in 2007 (see Appendix H) charts the Vulnerability Assessment number of fire incidents in Washington County and their ignition sources. The Oregon Office of State Wildfire hazard areas are commonly identified Fire Marshal Annual Report for 2009 reports that, in regions of the Wildland Urban Interface. The statewide, the number of fire incidents is at a ten- interface is the urban-rural fringe where homes and year low.7 other structures are built into a densely forested or natural landscape. If left unchecked, it is likely that Certain conditions must be present for fires in these areas will threaten lives and property. significant interface fires to occur. The most One challenge Washington County faces is from the common are hot, dry, and windy weather; the increasing number of houses being built in the inability of fire protection forces to contain or urban/rural fringe as compared to twenty years suppress the fire; the occurrence of multiple fires ago. The “interface” between urban or suburban that overwhelm committed resources; and a large areas and the resource lands has significantly fuel load (dense vegetation). Once a fire has started, increased the threat to life and property from fires. several conditions influence its behavior, including Responding to fires in the expanding Wildland fuel, topography, weather, drought, and Urban Interface area may tax existing fire protection development. systems beyond original design or current In 2007 Washington County developed and capability. adopted a Community Wildfire Protection Plan. Ranges of the wildfire hazard are further (CWPP). The CWPP describes Washington County’s determined by the ease of fire ignition due to fire hazard profile this way: natural or human conditions and the difficulty of The three major physical components that determine fire suppression. The wildfire hazard is also fire behavior are the fuels supporting the fire, the magnified by several factors related to fire topography in which the fire is burning, and the weather suppression/control, such as the surrounding fuel and atmospheric conditions during a fire event. At the load, weather, topography, and property landscape level, both topography and weather are beyond characteristics. our control. We are powerless to control winds, temperature, relative humidity, atmospheric instability, Risk Assessment slope, aspect, elevation, and landforms. It is beyond our The CWPP development process included an control to alter these conditions, and thus impossible to analysis of Washington County’s fire hazard risk. alter fire behavior through their manipulation. When we Field visits and discussions with area residents and attempt to alter how fires burn, we are left with fire control specialists provided insights into forest manipulating the third component of the fire health issues and treatment options. This environment; fuels which support the fire. By altering information was mapped and evaluated to develop fuel loading and fuel continuity across the landscape, we an assessment of wildland fire risk in the region. have the best opportunity to control or affect how fires Exhibits 3.6 and 3.7 from the CWPP inventory the burn. fire prone landscapes in the County to identify the The severity of a fire season can usually be location and extent of the wildfire hazard. determined in the spring by how much precipitation is The CWPP provides an extensive Fire Hazard received, which in turn, determines how much fine fuel risk assessment and it is included as Appendix H of growth there is and how long it takes this growth to cure this NHMAP. Washington County Natural Hazard Mitigation Action Plan! 3-13! Section 3: Hazard Identification and Risk Assessment Exhibit 3.6: Fire Prone Landscape acres in each The risk category values developed in this Category for Washington County analysis should be considered ordinal data, that is, while the values presented have a meaningful ranking, they neither have a true zero point nor scale between numbers. Rating in the “40” range is not necessarily twice as “risky” as rating in the “20” range. These category values also do not correspond to a rate of fire spread, a fuel loading indicator, or measurable potential fire intensity. Each of those scales is greatly influenced by weather, seasonal and daily variations in moisture (relative humidity), solar radiation, and other factors. The risk rating presented here serves to identify where certain constant variables are present, aiding in identifying where fires typically spread into the largest fires across the landscape.9 Source: Washington County Community Wildfire Protection Plan, 2007 Exhibit 3.7: Distribution of Fire Prone Landscapes by ranking scale Source: Washington County Community Wildfire Protection Plan, 2007 Washington County Natural Hazard Mitigation Action Plan! 3-14! Section 3: Hazard Identification and Risk Assessment Figure 4.7. Wildland Urban Interface Map in Washington County, Oregon. Map 3.7 Washington County Wildland Urban Interface Map Data source: Washington County Community Wildfire Protection Plan, 2007 A map of the Wildland-Urban Interface in Washington County as defined by the Community Wildfire Protection Planning committee is also included in Appendix I. 4.4.1 Potential WUI Treatments The definition and mapping of the WUI is the creation of a planning tool to identify where structures, people, and infrastructure are located in reference to each other. This analysis tool does not include a component of fuels risk. There are a number of reasons to map and analyze these two components separately (population density vs. fire risk analysis). Primary among these reasons, is the fact that population growth often occurs independent from changes in fire risk, fuel loading, and infrastructure development. Thus, making the definition of the WUI dependent on all of them would eliminate populated places with a perceived low level of fire risk today, which may in a year become an area at high risk due to forest health issues or other concerns. By examining these two tools separately, the planner is able to evaluate these layers of information to see where the combination of population density overlays on top of areas of high current fire risk and then take mitigative actions to reduce the fuels, improve readiness, directly Washington County, Oregon Community Wildfire Protection Plan pg 70 earthquake occurrences in Washington County. Earthquake Hazard Maps 3.8 and 3.9 from the United States Geological Survey illustrate earthquake probability and past Ground shaking, landslides, liquefaction, and seismicity – earthquake activity – in Oregon. These amplification are the specific hazards associated maps identify the location and extent of the with earthquakes. The severity of these hazards earthquake hazard. depends on several factors, including soil and slope conditions, proximity to the fault, earthquake Vulnerability Assessment magnitude, and the type of earthquake. The local faults, the County’s proximity to the Earthquake damage occurs because humans Cascadia Subduction Zone, potential slope have built structures that cannot withstand severe instability, and the prevalence of certain soils subject shaking. Buildings, airports, schools, and lifelines to liquefaction and amplification combine to give (highways and phone, gas, and water lines) suffer the County a high-risk profile. damage in earthquakes and can cause death or injury to humans. The welfare of homes, major Earthquake-induced landslides are possible in businesses, and public infrastructure is very areas with steep slopes, especially in old landslide important. Addressing the reliability of buildings, areas such as the West Hills of Portland and the critical facilities, and infrastructure, and Coast Range at the western edge of Washington understanding the potential costs to government, County. They are also possible in the Tualatin and businesses, and individuals as a result of an Chehalem Mountains which border the county on earthquake, are challenges faced by the County. the north and south respectively. Soil liquefaction and ground-shaking along the floor of the Tualatin There are five faults within Washington County: Valley are potential risks faced by the County. Tualatin-Sherwood; Oatfield; Costco; Gales Creek; Washington County’s location also puts it at risk and the 30-Mile Portland Hills Fault which is from a Cascadia Subduction Zone earthquake. confirmed to be active. These faults have been identified as having a potential to cause crustal fault Oregon Senate Bill 2 (2005) directed DOGAMI earthquakes. and community partners to develop a statewide seismic needs assessment. The survey included K-12 Hazard History public school buildings and community college buildings that have a capacity of 250 or more Washington County was affected by the persons, hospital buildings with acute inpatient care February 28, 2001, 6.8-magnitude earthquake facilities, fire stations, police stations, sheriffs' offices centered in Pierce County, Washington. The and other law enforcement agency buildings. earthquake was felt throughout western Washington DOGAMI scored each building and then used the and alarmed many Oregonians. While the effects in score to rank buildings in one of 4 collapse potential Washington County were not great, the earthquake categories – Low, Moderate, High, and Very High. affected some schools and local businesses. These categories describe how the building will Portland and the surrounding areas have records behave in an earthquake scenario. Final assessment of earthquake events, including a 5.3 magnitude of the 165 buildings evaluated in Washington earthquake in 1877, a 5.5 magnitude earthquake in County were released in 2007. Appendix F includes 1962, and a 5.5 magnitude earthquake in 1993. a map that shows the Washington County sites.10 Oregon ranks third in the nation for potential International seismic events in early 2010 earthquake losses, which are projected to exceed $12 increased national and local awareness of the billion in case of a major event in the Cascadia realities of earthquake hazards. The Oregon Region Subduction Zone. Department of Consumer and Business Services’ Data Sources 2009 survey of homeowners revealed that only about 20% of Oregonians have earthquake insurance DOGAMI and the United States Geological despite the fact that “Oregon is among the states at Survey (USGS) collect and maintain databases for highest risk for a major earthquake.”11 Washington County Natural Hazard Mitigation Action Plan! 3-15! Section 3: Hazard Identification and Risk Assessment Exhibit 3.8: Estimated Earthquake Damage Summary Risk Assessment for Washington County, 1999 and 2010* Factors included in an assessment of earthquake Washington 8.5 Cascadia 500-year model risk include population and property distribution in County Subduction Zone the hazard area, the frequency of earthquake events, Event landslide susceptibility, buildings, infrastructure, Injuries 555 2,910 and disaster preparedness of the region. This type of analysis can generate estimates of the damages to Death 10 62 the County due to an earthquake event in a specific Displaced 2,062 7,666 location. households DOGAMI estimates that, when a Cascadia Short term shelter 1,284 4,660 Subduction Zone earthquake does shake the area needs along the Juan de Fuca Plate, “Oregon can expect an estimated 5,000 fatalities and over $30 billion in Economic losses $931 million/ $3.8 billion / damages.”12 At the subduction zone the Juan de for buildings $1.16 billion* $4.74 billion* Fuca Plate is sliding underneath the North Operational the day American Plant at a rate of about 1-2 inches per year. after the quake As the pressure builds, it must sometimes be Fire stations 66% NA released in violent megathrusts. The most recent earthquake of significant size along the subduction Police stations 64% NA zone was offshore, near Eureka California in early January 2010. Schools 64% NA In 1999, DOGAMI produced a special report on Bridges 79% NA potential earthquake damage in Oregon under two Economic losses to different scenarios: a magnitude 8.5 Cascadia Subduction Zone earthquake and a 500-year return Highways $15 million / $61 million / interval (based on an average earthquake on each $18.7 million* $76.1 million* fault across Oregon). DOGAMI determined that Airports $5 million / $23 million / Washington County faces a high risk of damage and $6.2 million* $28.6 million* loss from this second type of event. Exhibit 3.8 on Communications the next page adjusts the economic loss estimates Systems from DOGAMI’s 1999 report to account for inflation and reflect potential economic loss in 2010 dollars.13 Economic losses $752,000 / $4 million / $938,000* $4.98 million Operating the 60% NA day of the quake Debris 763 2,817 generated (thousands of tons) Source: Wang, Yumei and J.L. Clark, “Earthquake damage in Oregon: Preliminary estimates of future earthquake losses”, Special Paper 29, DOGAMI, 1999. *Note: 1999 dollars were adjusted for inflation to represent estimated economic loss in 2010 dollars. (Source: Bureau of Economic Analysis - Price Indexes for Personal Consumption Expenditures by Major Type of Product. Washington County Natural Hazard Mitigation Action Plan! 3-16! Section 3: Hazard Identification and Risk Assessment Map 3.8 Map 3.9 Oregon Seismic Hazard Map Seismicity of Oregon 1990 - 2006 Source: United States Geological Survey, National Seismic Hazard Maps, 2008 Source: United States Geological Survey, National Seismic Hazard Maps, 2006. Note: Depth is in kilometers. Earthquakes represented by circles with the color representing the depth range. Volcanic Eruption Hazard Vulnerability Assessment The CVO Volcanic tephra fall map is based on Volcanic eruption is not an immediate threat to the combined likelihood of tephra-producing the residents of Washington County, as there are no eruptions occurring at Cascade volcanoes. active volcanoes within the County. Nevertheless, Probability zones extend farther east of the range the presence of a few geologically young volcanic because winds blow from westerly directions most structures in the County and the secondary threats of the time. The map shows annual probabilities for caused by volcanoes in the Cascade region must be a fall of one centimeter (about 0.4 inch). The patterns considered. Volcanic ash can contaminate water on the map show the dominating influence of supplies, cause electrical storms, create health Mount St. Helens as a tephra producer. Because problems, and collapse roofs. Additionally, lahars small eruptions are more numerous than large (mudflows) from Mount Hood can cause the loss of eruptions, the probability of a thick tephra fall at a a major potable water supply for the county. given locality is lower than that of a thin tephra fall. Hazard History The annual probability of a fall of one centimeter or more of tephra is about 1 in 10,000 for Washington Mount Hood and Mount St. Helens are two County. This is small when compared to other risks active volcanoes in the vicinity of Washington faced by the county. The USGS map on the County. Mount Hood is east of Washington County following page illustrates potential tephra fall in the and is more than 500,000 years old. It has had two region. At the time of this update, sufficient data significant eruptive periods, one about 1,500 years was not available to determine volcanic eruption ago and another about 200 years ago. Mount St. vulnerability in terms of explicit types and numbers Helens is located in southern Washington State and of existing and future buildings, infrastructure, or has been active throughout its 50,000-year lifetime. critical infrastructure. The most recent eruption of Mount St. Helens Though unlikely, the impacts of a significant ash occurred on May 18, 1980, with five smaller fall are substantial. Persons with respiratory explosive eruptions in a period of five months. problems are endangered, transportation, There has been no recent volcanic activity in communications, and other lifeline services are close proximity to the County. The 1980 explosion of interrupted, drainage systems become overloaded/ Mount St Helens in southern Washington State is the clogged, buildings can become structurally latest on record though both Mount St. Helens and threatened, and the economy takes a major hit. Any Mount Hood remain listed as active volcanoes. future eruption of a nearby volcano (e.g., Hood, St. Risks for Washington County associated with Helens, or Adams) occurring during a period of regional volcanic activity would be ash fall, air easterly winds would likely have adverse quality, and possible economic or social disruption consequences for the County. due to air traffic issues due to the ash cloud. Risk Assessment Data Sources Washington County faces no direct threat from a The United States Geological Survey-Cascades volcanic eruption. However, its proximity to a Volcano Observatory (CVO) produced volcanic number of Cascade Range volcanoes places the hazard zonation reports for Mount St. Helens and County at risk from ash fallout originating from Mount Hood in 1995 and 1997. The reports includes such an event. The County also faces an indirect a description of potential hazards that may occur to threat to its water supply based on a volcanic immediate communities. The CVO created an scenario impacting the Bull Run Water System. Due updated annual probability of tephra (ash) fall map to the extreme variability of the impact of a volcanic for the Cascade region in 2001, which could be a eruption on Washington County, there is insufficient rough guide for Washington County in forecasting data at the time of this update to determine the potential tephra hazard problems. The map potential losses associated with this hazard. identifies the location and extent of the hazard. Washington County Natural Hazard Mitigation Action Plan! 3-17! Section 3: Hazard Identification and Risk Assessment Section 3 Endnotes 1 FEMA, Disaster Search. Accessed April April 20, 2010. << http://www.fema.gov/femaNews/disasterSearch.do>> 2 Ibid 3 Washington County Community Development Code, Section 421 4 DOGAMI, << www.oregongeology.org>> 5 Washington County New, Press Release. “Routine Operations Resume in County after Record-Breaking Winter Storm.” 12/31/2008. 6 FEMA, Disaster Search. Accessed April 20, 2010. << http://www.fema.gov/femaNews/disasterSearch.do>> 7 Oregon State Police, Office of State Fire Marshal, Annual Report, 2009. 8 Washington County Community Wildfire Protection Plan, 2007 9 Ibid 10 Statewide Seismic Needs Assessment using Rapid Visual Screening. DOGAMI, 2007. 11 Oregon Department of Consumer and Business Services, News Release. “Twenty percent of Oregonians insured for earthquakes.” 1/15/2010. 12 DOGAMI Winter Cascadia Newsletter, 2010. 13 Wang, Yumei and J.L. Clark, “Earthquake damage in Oregon: Preliminary estimates of future earthquake losses”, Special Paper 29, DOGAMI, 1999. Washington County Natural Hazard Mitigation Action Plan! 3-18! Section 3: Hazard Identification and Risk Assessment Map 3.10 Map 3.11 Potentially Active Volcanoes Mount Saint Helens Ash Fall Model in the Western United States