Community Hazard Analysis

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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 risk analysis is excerpted from our City of Hillsboro Community Risk Analysis,

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.

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.

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 pose the greatest threat to Hillsboro.

Volcanic Hazards

The likely impacts of volcanic events are ash falls, with potential impacts on the electric, water and storm water systems. There are potentially significant health effects for at-risk residents (e.g., those with respiratory ailments).

Landslides

The level of landslide risk in Hillsboro appears very low because there are neither hills nor other areas with steep slopes in Hillsboro. A few bank areas along stream channels may be subject to very localized landslides. 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.

Wildland/Urban Interface Fires

The level wildland/urban interface fire risk in Hillsboro is low because there are no large forested areas or other high vegetative fuel load areas within or immediately adjacent to Hillsboro.

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.

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 man made causes.

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.

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 but a very low probability of occurrence.

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 - Fixed Facility  Low
 Dam Failures  Low
 Volcanic Eruptions  Low
 Terrorism  Low
 Wildland/Urban Interface Fires  Very Low
 Landslides  Very Low