Landslides
Risk: ModerateLandslides include a range of downhill earth movements, including slope failures, and rock falls. Landslides can be extremely destructive and are caused by a number of pre-existing and contributing factors including heavy rainfall or rapid snowmelt, erosion, poor construction practices, freezing and thawing, earthquakes and volcanic eruptions (SLRD, 2015).Due to the mountainous topography and high levels of annual rainfall, Squamish and the surrounding area are highly susceptible to landslide events. Landslide events are common along the steep valley walls and have resulted in significant alterations to river grades over the past several hundred years. Climate change is projected to increase landslides as an indirect impact of more and heavier rain.There have been a number of significant landslides in the area around Squamish, including the 2008 Porteau Cove rockfall which closed Highway 99 for 5 days. More recently in 2015, a large rockfall occurred on the Chief. The slide happened just before 12 p.m. PT when what police describe as a 1,000 cubic metre granite slab fell away from the mountain in the North Walls area of the north peak, near a climbing route called Northern Lights.Video Link
Earthquake
Risk: Low-ModerateEarthquakes may be described as “sudden movements of earth, caused by an abrupt release of strains that have accumulated over time along fault lines” (Coppola, 2011). Notably, many secondary hazards are triggered by earthquakes including landslides, rockslides, avalanches, and multiple utility failures from downed lines and collapsed pipes. Damage to buildings generally begins to occur at magnitude six while an earthquake above magnitude seven may be a major disaster if it occurred near a populated area. Although a low probability, if an earthquake were to occur, much of Squamish’s infrastructure would be at risk for structural damage. Ground shaking, liquefaction, and earthquake-triggered landslides represent the most significant earthquake related threats to Squamish (Journeay, 2011).Mega-thrust earthquake:“This type of quake occurs, on average, every 500 to 600 years, but the intervals between events have been as short as100 to 300 years. Scientists have estimated that there is about a 12% chance of a similar magnitude quake in the next 50 years” (Auditor General of British Columbia, May 2014).Shallow-focus earthquake: Shallow-focus earthquakes occur within the earth’s crust along fractures, generally at depths less than 35 kilometres. This class affects a smaller area than a deep earthquake of the same magnitude, but the shaking is usually more intense and aftershocks more numerous. The probability of a shallow crustal earthquake causing considerable damage in British Columbia has been estimated at approximately 12% in the next 50 years. To better understand these quakes, more information is needed about where the active faults are. (Auditor General of British Columbia, May 2014).Deep sub-crustal earthquake: can occur as deep as 80km within the North American Plate, on which Squamish rests. Scientists estimate the frequency of deep sub-crustal earthquakes at about 60% in the next 50 years.All development on flood plain land is vulnerable to liquefaction in the event of a shallow-focus seismic event. Our substantial commuter population risks being isolated from home and family if an earthquake closes Highway 99 on either side of DOS. Older building stock, including the Fire Hall and other critical public service infrastructure, are not earthquake resistant without strengthening work. There are limited reception centre options for evacuated people, including potentially high numbers of tourists/visitors.
Hazardous Materials Release
Hazardous materials processing and storage accidents are common. Most HAZMAT events occur during road or rail transportation. Accidents at industrial sites occur from natural disasters, fire, human error, infrastructure deterioration and failure, accidents and intentional damage. The success of safety standards and procedures for containment rely on the degree of enforcement and a level of environmental control.There have been a number of hazardous materials release incidents in Squamish, including:2015 Wharf fire at Squamish Terminals: ignited creosote pilings and generated clouds of noxious smoke that blanketed Squamish. A Shelter-In-Place order was declared overnight and lifted the following morning. Creosote is a probable human carcinogen with a range of other health effects. Creosote can move through the soil to groundwater and once there, can take many years to break down. 2006 Squamish Harbour Marine Oil Spill: A ship, the Westwood Anette became damaged while leaving port, resulting in 29,000 litres of bunker oil spilled in Squamish Harbour, causing substantial environmental damage within the Squamish Estuary and land areas within the Squamish Harbour. 2005 CN Rail derailment in Squamish: Nine cars derailed, spilling 40,000 litres of Sodium Hydroxide (caustic soda) in the Cheakamus River and Squamish River systems, “more than 500,000 adult and young salmon, steelhead, trout, lamprey and other species died of suffocation from skin burns and gill haemorrhaging. Birds and animals that rely on the Cheakamus salmon for food were also affected by the spill.” (Ministry of Environment).
Flooding
Risk: Moderate-HighFlood events can range in scale from minor to major. Minor events often present little threat to the public with minimal or no property damage. Major events can cause extensive damage or destruction to critical infrastructure, while presenting a high degree of danger to the public.Floods can be either slow or fast rising, generally developing over days or weeks. The geography of Squamish combines four of the five most commonly flooded land types, i.e., river floodplains, basins and valleys affected by flash flooding, land below water-retention structures (dams), and low lying coastal and inland shorelines.Several conclusions can be drawn from the flood history of Squamish:1. All the rivers in Squamish pose a risk of flooding. All have caused multiple and damaging floods in the past. Damaging floods have also occurred as a result of coastal inundation from Howe Sound.2. The flood risk in Squamish has strong seasonal variations. Most flooding has taken place between October and December. Major floods have also taken place in August.3. Unlike many other B.C. communities, the spring freshet (typically in late May, June, and early July) has not been a major cause of flooding on local rivers.4. The frequency of floods causing significant damage has decreased over the past 30 years compared to earlier time periods. This is attributed tosignificant improvements made to the dike system.5. Extreme precipitation (rain and snow) has occurred on at least 5 occasions since 1980. These continue to test the limits of flood protection structures. The October 2003 flood was the most recent and most severe condition recorded in recent decades, and involved the Squamish and Cheakamus Rivers. The 2003 flood saw 369 mm of rain in 4 days, and caused 360 people to be evacuated and $30 million damage. Dikes were almost overtopped.Squamish is particularly susceptible to heavy rain and high wind events and extreme temperature events may become more common as the climate changes. With climate change, Atmospheric Rivers (Pineapple Express) are predicted to double in duration and frequency, causing increases in overland flooding such as sewer back-ups and nuisance floodingWork is underway on Squamish River Dike upgrades in Brackendale between the Aikwucks and Waiwakum Squamish Nation Reserves. The scope of the project will enhance the community’s flood protection and includes raising, widening and strengthening the dike for approximately one kilometre.Identified in the District of Squamish Integrated Flood Hazard Management Plan (IFHMP) as the highest priority project to bring Squamish’s dikes up to increasing provincial standards, the District’s dike raising project is expected to significantly reduce the risk of flooding and protect residential, commercial and environmentally sensitive areas within the community including Brackendale, Garibaldi Estates and Squamish Nation reserve lands. The project will also protect critical transportation infrastructure including Highway 99 and CN Rail.This work is being done thanks to a $3.9 million grant through the Federal Gas Tax Fund. The grant will fund the full estimated cost of the project.
Debris Flow
Risk: HighDebris flows are very fast-moving, liquefied landslides that carry soil and other debris including boulders, and vegetation. Debris flows are most often triggered during periods of intensive rainfall resulting in high soil saturation levels but can also be triggered by rockfall or avalanche on unstable slopes. Known debris flow hazards within Squamish include the Cheekye Fan and Stawamus River.Concave slopes like gullies and ravines are particularly susceptible to debris flows because they tend to concentrate surface water runoff and accumulate surface water and loose soil. Debris flows can be the result of natural factors and man-made interventions (SLRD, 2015). BCG Engineering reports that due to the impacts of climate change, both the frequency and magnitude of debris flow events on the Cheekye Fan are expected to increase.If you live near or visit areas prone to debris flows, you should become familiar with the terrain between your property and the creek channel and fan apex. During a major flood event, creeks may suddenly change course and flow along a new or abandoned flood channel, and debris flow material may run out onto the fan area. Terrain features to be aware of include: abandoned creek channels; levees; scarred trees; and local deposit features.There are a number of vulnerabilities associated with the Cheekye Fan debris flow hazard in particular. This inlcudes the new residential development at the base of the Cheekye Fan, although this will be mitigated by the construction of a massive debris barrier. Within the current debris flow zone, there are several First Nations reserves, the neighborhood of Brackendale, a BC Hydro substation, Highway 99, and two schools. Most scenarios also show the debris flow running down the highway as the path of least resistance. This means the highway will be closed for many days impacting transportation to/from north of Squamish. The debris flow could also cause a dam outburst flood on the Cheakamus River, causing flooding as a secondary hazard.
Daisy Lake Dam
Risk: ModerateLocated just south of Whistler, the Daisy Lake Dam, on the Cheakamus River, presents a catastrophic dam failure hazard to Squamish. Before flowing into Howe Sound, The Cheakamus River connects with the Squamish River which passes directly through the community of Squamish. BC Hydro monitors and controls flow levels from the Daisy Lake Dam. The lowest lying areas are more vulnerable to any emergency release or dam failure scenario, but inundation areas and depth of inundation are dependent on the nature of the hazard event – e.g. an emergency release due to storm/flood scenario compared to a release due to a severe earthquake event. BC Hydro has mapped eight inundation scenarios to assist emergency planning.Catastrophic dam failures are rare, but can cause immense damage and loss of life when they occur. Failures are often attributed to poor design and severe weather events which cause water levels to exceed the maximum capacity of the dam.
The Barrier
Risk: LowThe high vertical cliff at the Barrier has long been debated regarding its potential for catastrophic collapse. Large-scale collapse of The Barrier is also extremely unlikely, but could potentially block the Cheakamus River. A blockage of this nature increases the possibility of a debris flow that could affect all of Paradise Valley, with the most intense impacts occurring near the District’s northern boundary. Despite public misconceptions, there is no scientific evidence that collapse of the Barrier could drain Garibaldi Lake or cause extreme flooding in downstream neighbourhoods along the Squamish River.This hazard has been sensationalized in various media sources (Wikipedia, newspaper articles, youtube videos) which has compounded the common misconception. The more realistic hazard is that rockfall from the barrier could block the Cheakamus River which could then cause an outburst flood. Even this is a very low probability event and has been concluded to pose limited flood risk within District boundaries due to significant upstream attenuation (storage, smoothing out of peak flows). The consequences are much higher for areas immediately downstream of Rubble Creek.
Volcanic Eruption
Volcanic eruptions in Canada are a rare event. Though infrequent, volcanoes can be catastrophic enough to warrant serious attention (Institute for Catastrophic Loss Reduction, 2010)”. A volcano is a vent in the crust of the Earth’s surface through which molten rock (magma) is extruded onto the surface of the earth as lava and volcanic debris flows, and also into the Earth’s atmosphere as volcanic gases and rock fragments. The District of Squamish sits within the Garibaldi Volcanic belt, part of the Pacific Ring of Fire. (Hickson, Mulder & Stasiuk, 2004). The Garibaldi Volcanic belt includes Mt. Garibaldi, Mt. Price, Black Tusk, Mt. Meager, Mt. Cayley, Mt. Fee and Mt. Silverthrone.Volcanoes are one of the few hazards that typically exhibit clear precursor activity. (Hickson, Mulder & Stasiuk, 2004). Should a volcano erupt in the Squamish area, this precursor activity would give the District time to plan an emergency response, limiting the amount of injury and loss of life. However, an erupting volcano threatens infrastructure such as highways, roads, and railways. Ash can pollute water supplies and collapse buildings, especially when it falls wet. Airborne ash clouds can adversely affect aircraft corridors and the routing of flights. Heavy ash fall may reduce sunlight, causing a sudden demand and possibly brownouts of electrical power. Ash can clog water systems, sewage plants, and all kinds of machinery, cause roofs to collapse and electrical short circuits. Fine ash is extremely slippery, hampering driving and walking. Ash can also damage the lungs of small infants, elderly, and those having respiratory problems (Institute for Catastrophic Loss Reduction, 2010)Video Link
