Flooding

Risk: Moderate-High

Flood 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 to
significant 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 flooding

Work 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.