Useful for Mitigation, Preparedness, Response and Recovery Planning
To set the overall context of emergency management planning, we briefly review the major natural and anthropogenic (caused by humans) hazards that may impact Hillsboro. Some of the hazards, such as earthquakes, may affect all of Hillsboro more or less uniformly. Other hazards, such as floods, may affect only limited portions of Hillsboro.
Note: This community hazard analysis is excerpted from our City of Hillsboro Multi-Hazard Mitigation Plan, To see more specific information on any of these hazards, please consult the cited chapter of the mitigation plan.
Floods. Portions of Hillsboro are at risk from flooding along the Tualatin River, Rock Creek, Dairy Creek and smaller tributaries. In addition, other portions of Hillsboro, outside of the mapped floodplains, may also be subject to flooding from local storm water drainage or from creeks too small to be mapped by FEMA. Flood hazards are addressed in Chapter 6.
Winter Storms. All of Hillsboro is subject to the effects of winter storms, including wind, rain, snow and ice, as well as secondary effects such as power outages. However, the severity of impacts and types of impacts will vary with location within Hillsboro. Winter storm hazards are addressed in Chapter 7.
Earthquakes. All of Hillsboro is subject to the impacts of earthquakes, including not only major earthquakes on the Cascadia Subduction Zone off the Oregon coast, but also smaller crustal earthquakes within western Oregon. Even though the frequency of earthquakes is low, the potential impacts are large. Overall, of all the natural hazards, earthquakes probably pose the greatest threat to Hillsboro. Earthquake hazards are addressed in Chapter 8.
Volcanic Hazards. For Hillsboro, the likely impacts of volcanic events are ash falls, with potential impacts on the electric, water and storm water systems and potentially significant health effects for at-risk residents (e.g., those with respiratory ailments). Volcanic hazards are addressed in Chapter 9.
Landslides. The level of landslide risk in Hillsboro is appears very low because there are neither hills nor other areas with steep slopes in Hillsboro. A few bank areas along stream channels might be subject to very localized landslides; however, there appears to be little or no inventory of either buildings or infrastructure in these areas. Thus, the risk posed by landslides in Hillsboro appears negligible and landslides are not considered further in the hazard mitigation plan.
Wildland/Urban Interface Fires. The level wildland/urban interface fire risk in Hillsboro is very low because there are no large forested areas or other high vegetative fuel load areas within or immediately adjacent to Hillsboro. Wildland/urban interface fires are not considered further in the hazard mitigation plan.
Dam Failures. Portions of Hillsboro are in the inundation areas from failure of the Scoggins Dam. For Hillsboro, the potential inundation area is very similar to the FEMA-mapped 500-year floodplain. Dam failures are addressed in Chapter 10.
Disruption of Utility and Transportation Systems. All of Hillsboro is also subject to disruption of utility and transportation systems from winter storms and other natural hazards, as well as from anthropogenic causes. Such disruptions are addressed in Chapter 11.
Hazmat Incidents. Human-caused hazards, such as hazardous material releases, are possible nearby or downwind from fixed site concentrations (e.g., industrial sites) as well as along transportation corridors from truck or railroad accidents. All of Hillsboro is potentially subject to hazmat incidents. Hazmat incidents are addressed in Chapter 12.
Terrorism. The term “terrorism” is broadly inclusive of all deliberate malevolent actions intended to damage property or inflict casualties or to coerce or intimidate into behavioral or political change. Hillsboro does not have potential sites of national significance, although any major public or private facility is a potential target, albeit with a very low probability of occurrence. Terrorism is addressed in Chapter 13.
In evaluating these natural or human-caused hazards, it is important to recognize that the risk to Hillsboro (i.e., the potential for damages, economic losses, and casualties) varies markedly from one hazard to another. Risk depends on the combination of the frequency and severity of hazard events and on the value and vulnerability of infrastructure, buildings, and people to each potential hazard. Risk is thus always probabilistic in nature. Some hazard events, such as winter storms, happen every year to at least some extent. Other hazard events, such as major earthquakes may happen only once every few hundred years. However, risk from earthquakes is high, even though the frequency of occurrence is low, because the consequences (damage, economic losses, and casualties) may be very high.
Relative Risk. The approximate level of relative risk posed to Hillsboro by each of the hazards covered in this mitigation plan is summarized below in table below. This ranking is based on quantitative/qualitative judgment about the likely long-term average annual damages and losses in Hillsboro from each hazard, taking into account the probability of major hazard events and the severity of damages and losses if (when) such events occur.
Hazard |
Relative Risk to Hillsboro |
Earthquakes |
High |
Floods |
Moderate |
Winter Storms |
Moderate |
Disruption of Utility and Transportation Systems
|
Moderate |
Hazmat incident – Transportation |
Moderate |
Hazmat incident – Fixes Sites |
Low |
Dam Failures |
Low |
Volcanic Eruptions |
Low |
Terrorism |
Low |
Wildland/Urban Interface Fires |
Very Low |
Landslides |
Very Low |