6.1. OVERVIEW: There are many and diverse threats to public health and safety in Boundary County, both natural and man made, the most critical of which are wild land fire and flooding. The Boundary County All-Hazard Mitigation Plan, first developed in 2005 and to be updated regularly, offers the clearest assessment of naturally-occurring hazards in Boundary County, and forms the primary plan for responding to most natural disasters within Boundary County. The Boundary County All-Hazard Plan is maintained in the Planning and Zoning Office and is used as the prime reference for the development of this component.
6.2. FAULTING/EARTHQUAKES:
6.2.1. Earthquake History: Three significant earthquakes have been documented in Boundary County by the Department of Homeland Security since 1952, and no damage was recorded in any of these events. On September 9, 1952, a 4.0-magnitude earthquake occurred near the City of Bonners Ferry. In 1984, two earthquakes were reported, the first occurring north of Moyie Springs July 30 and measuring 4.1 on the Richter Scale, the next occurring November 27 about 10 miles north of Bonners Ferry and measuring 3.2.
6.2.2. Fault Lines: The U.S. Geological Survey has designated a group of several faults as the North Idaho Fault System. There are no documented active faults in Boundary County, however, the “Purcell Trench” runs down the center of the Kootenai Valley floor and there a several other faults outside Boundary County, some of which could impact the county in the event of a large earthquake.
6.3. GROUND FAILURE:
6.3.1. Landslides and mudslides: A landslide is defined as a mass movement of rock, earth or debris down a slope, and several types of landslides have occurred in Boundary County in the 20th Century. Typically, the steeper the slope, the more likely it is that a slide will occur, though this is also dependent on the geology and soils particular to each site. Loose soils on steep slopes with little or no vegetative cover are highly susceptible to slide, and human activity can add to this problem through increased development near such slopes and construction, including road work and site preparation, that decreases slope stability. The most common “triggers,” events that cause a landslide, are a combination of precipitation and human activities, especially road building on sloped areas. Late spring to early summer is the peak season for slides. Slide danger is often exacerbated as a result of some other natural disaster, such as wild fire.
6.3.2. Significant Landslide Events in Boundary County: March, 1954, a mudslide killed two people in Bonners Ferry. March, 1959, a mudslide caused a train derailment; February, 1961, mudslide with no reported damage. May, 1961, mudslides caused road closures. May, 1965, mudslides blocked and washed out roads. March, 1972, a mudslide covered a house. June, 1974, a mudslide dislodged an estimated 45,000 cubic yards of earth, no damage listed. January, 1981, mud slide causes minor damage. March, 1997, a mudslide near Mirror Lake Golf Course swept a car off U.S. 95 and damaged the roadway. October, 1998, a major slide above the District 2 Road north of Bonners Ferry destroyed the roadway, seriously damaged the railroad, swept heavy equipment into a field below the slide and forced school and highway closures for an extended period.
6.3.3. Exposure Assessment: Most of the property exposed to danger from landslides lies along the major roadways in Boundary County. The FEMA Landslide Risk Map identifies the majority of Boundary County as being at low risk from landslide, though an area of moderate susceptibility but low incidence exists in the northeast portion of Boundary County extending from Eastport in an area bounded by the Moyie River and the Montana state line and extending south nearly to Highway 2.
6.4. AVALANCHES: Avalanche danger is a threat in Boundary County, mainly at higher elevations where action by wind on the snow pack carves cornices that can give way with catastrophic results. The greatest threat is to those who travel to these remote areas for winter and spring recreation, and no damage by avalanche to date has resulted in damage to improvements to property. With the increasing demand for land for residential use, however, the possibility of development in areas prone to avalanche is growing.
6.5. WILD FIRE: Of all the natural disasters that occur in Boundary County, forest and wildfires are the most frequently occurring events, and a high proportion of these events occur in or near human habitation. Forest Fires in Boundary County have covered large areas of land, and with prevailing dry conditions, the build up of combustible fuels, and forest stressed by disease and overcrowding, it is reasonable to assess the risk of danger from forest and wildfire as high. With increased development, it is reasonable to predict that potential loss of structures and possibly human life in the event of a fire event are extremely high. In 2003, Boundary County contracted with Inland Forest Management (IFM) to develop and complete the Wildland/Urban Interface Fire Mitigation Plan, which included numerous considerations to reduce the risk of catastrophic loss, including risk assessment, public involvement, and setting strategies and priorities.
6.5.1. History: Several large fires have been documented in Boundary County since 1900, some of them in what is now the wildland/urban interface. In 1910, a fire burned along Katka face and into Montana. In 1926, the Hellroaring fire burned from Round Prairie to the top of Queen Mountain. In 1931, the Deer Creek fire started in Lower Deer Creek and burned north and east into the Yaak River drainage in Canada. In 1967, both the Sundance and Trapper Peak fires burned in the Selkirk Mountains, showering the Kootenai River valley with firebrands and ash. In the past 18 years, an average of 23.4 wildfires per year have been fought on USFS protection lands and 26 per year on IDL protection lands. In 2002, the Myrtle Creek fire seriously damaged the water supply of the City of Bonners Ferry.
6.5.2. Protection: Following the development of the Wildland/Urban Interface Fire Mitigation Plan in 2003, Boundary County established the “Fire Safe” program, which provided expert assistance in protecting structures against the dangers of wildfire by establishing “defensible space,” an area around structures treated by reducing fuels to provide a safe area for firefighters, and a “survivable space,” an area designed to sufficiently reduce fire intensity to help the building survive.
6.6. FLOODS:
6.6.1. History: Floods have long played a role in shaping Boundary County, and the silt deposits laid down over the millennia in the Kootenai River valley have helped create some of the most productive agricultural lands in the world. In the 1900s, these regular floods often caused significant damage, mostly within the City of Bonners Ferry and to farms along the riverbanks, with major floods recorded in 1933, 1934, 1948, 1957, 1964 and 1972. The completion of the Libby Dam in the early 1970s and the establishment of a major system of dikes in the county have largely controlled flooding along the Kootenai River, but high-water years and recent increased seasonal river flows designed for sturgeon recovery have resulted in limited flooding and contributed to the erosion and deterioration of some of the county dikes. In 1996, county commissioners declared an emergency for a spring run-off flood event. A flood event in 2002 caused crop damage estimated at $700,000, and another in 2006 caused several million dollars in damages and damaged the majority of dikes throughout the county.
6.6.2. Types of Flooding:
6.6.2.1. Ravine Flooding: Ravine flooding occurs when water leaves channels, lakes, ponds and other confinements due to precipitation, runoff and ravine ice formation. The two key periods of ravine flooding are during spring runoff and from winter rains and snowmelt. Ravine floods typically are low-velocity events affecting large areas of land for a prolonged period of time, most often affecting agricultural production. Structural damage can typically be mitigated by sandbagging or diversion.
6.6.2.2. Flash Flooding: Flash floods have higher velocity but affect smaller geographic areas than ravine floods, but have the potential to cause significantly more damage when they occur in developed areas. Such floods crest quickly, and most often occur in hilly or otherwise confined terrain, principally along smaller rivers, creeks and drainages. Flash floods on alluvial fans pose a growing hazard as development in these areas grows. Alluvial fans are gently sloping, fan-shaped landforms created over time by water-borne deposit of eroded sediment, typically at the base of mountain ranges. Given that alluvial fans tend to occur in apparently dry conditions, homeowners who build on them are often shocked to find that they can be the site of destructive floods, usually characterized by relatively shallow depths but high velocity and debris content, often striking with little or no warning. Development in urban/wildland interface areas pose unique risks, as flash floods may originate in mountainous terrain and grow in intensity and severity before entering the urban environment where vegetation has been removed, where bridges and culverts restrict flow and where buildings and paving have greatly expanded impermeable surface which exacerbate the severity of damage. The most catastrophic flash floods are those that result from dam failure. The Libby Dam, Moyie Dam and Smith Creek Hydro pose the only known dam failure risks in Boundary County. Pre-disaster mitigation plans are in place for the Moyie Dam and the Libby Dam.
6.6.2.3. Ice/Debris Jam Flooding: Floods resulting from ice formation are a relatively common spring occurrence, particularly on the Moyie River in the Eastport area. Ice jam formation depends on air temperature and physical conditions in the river channel. Ice cover on a river is formed when water temperature reaches its freezing point, and large quantities of ice are produced, flow downstream and consolidate. With warming temperatures and warming stream flows, this ice eventually breaks up and flows downstream. This ice can form jams at various points in the river; on islands, sharp bends, on other ice sheets or at man-made structures such as bridge abutments. Debris jams usually occur as a result of land or mudslide along the banks of a stream or river. Flooding occurs as water is diverted beyond normal banks and may extend well beyond normal floodplain boundaries. Additional high-velocity flooding may occur when a jam suddenly breaks, sending backed-up water rushing downstream.
6.6.3. Floodplain: Boundary County’s recognized floodplains were mapped by the Federal Emergency Management Agency and incorporated into Flood Insurance Rate Maps created in August, 1982. Many of the areas along streams and creeks were mapped to determine base flood elevation, but much of the area, especially along the Kootenai River, are in unnumbered A Zones, which are areas within the floodplain for which no base flood elevation has been determined. Development in A Zone floodplain is permitted, but requires additional steps to ensure compliance with FEMA flood damage prevention measures required for participation in the FEMA flood insurance program. Adherence to program standards is monitored by FEMA, and compliance failure can result in the entire county being disqualified from flood insurance participation, adversely affecting the ability to finance real estate. In the history of the FEMA Flood Insurance Program in Boundary County, four claims have been filed. It is reasonable to predict that increasing demands for development under current county management provisions make both the potential for violations of FEMA standards more likely as well increase the risk for property damage resulting from flood events.
6.7. WINTER STORMS: As frequently experienced in Boundary County, especially at higher elevations, severe winter weather and heavy snow and ice can block roads, break power lines, cause extended power outages, topple trees and cause flooding, landslides and avalanches. Blocked roads and limitations on access to emergency services is a significant concern in Boundary County. In recent years, homes and property have been destroyed by fire due to lack of sufficient access. Winter storms exacerbate the distances emergency responders must travel.
6.7.1. Frequency: Boundary County experiences a “severe winter storm” at least once every year, with the communities of Trout Creek, Porthill, Eastport and along the Moyie River Road most adversely affected. Federal disaster events were declared as a result of winter weather in February, 1996, November, 1996, and January, 1997. The winter of 1996-1997 was considered a record year for snowfall and heavy spring rain in Boundary County, with snow collapsing buildings around the county and damaging spring mudslides and floods. There have been no recorded serious winter storm events since 1997, but heavy snow years typically occur every 10 to 15 years.