The Squamish River is one of two river systems in the SLRD that are subject to frequent flooding, and that hold the highest consequences in terms of potential impacts.
In 2017, the SLRD was awarded a grant from the Emergency Management B.C. Disaster Mitigation Program for the development of flood plain mapping, risk assessment and flood mitigation planning for the Upper Squamish Valley area, located in SLRD Electoral Area D.
The Upper Squamish River Flood Hazard Mapping and Risk Assessment was completed in 2018 and shows that:
- Almost all of the valley is subject to geomorphic hazards.
- A potential outbreak flood from an upstream landslide blocked river could reach populated areas within a few hours and raise the water surface by several meters.
- At the 50-year flood event and above, most of the valley floor is flooded, with typical depths of 1 to 2 m within the inundated area.
- When areas are inundated, much of it has a high hazard rating and classified as dangerous for most to all people.
- Flood inundation affects all four receptors evaluated; people, the economy, the environment, and culture within the Upper Squamish River Valley.
- Natural geomorphic changes at the Squamish-Cheakamus confluence could potentially cause an increased water surface extending upstream nearly to populated areas at river kilometer 30.
The study recommends:
- Sharing the results with key authorities, stakeholders and the public in order to reduce potential loss-of-life and flood damages during future extreme flood events through education and awareness.
- Planning new development away from high hazard areas and implementation of the Squamish River FCLs in order to create more flood resilient development.
- Access and egress routes requiring improvement be identified and the location of temporary evacuation areas be determined.
- Consideration also be given to relocating or flood-proofing existing housing and other development in extreme flood hazard areas.
- Considering that the Squamish River channel is highly dynamic and considering the ongoing aggradation, the river channel should be monitored and re-surveyed every 5 to 10 years and the hydraulic model updated as required.
- During future flood events, high water marks should be obtained to allow for future model calibration.
The project results will inform both emergency management plans and development criteria, such as the Flood Control Level (FCL), in an area that is subject to recurrent flooding as well as increased development. The information derived from the SLRD study, in combination with the Integrated Flood Hazard Management Plan completed by the District of Squamish in 2017, gives a complete flood risk profile for the entire Squamish River system, which will assist both the SLRD and District of Squamish in moving forward with applications for future flood mitigation funding, where available.
For more information:
- Final report: Upper Squamish River Flood Hazard Mapping and Risk Assessment report
- Project background: Upper Squamish River Valley Flood Plain Mapping project page
- January 7, 2019 News Release
- District of Squamish report: Integrated Flood Hazard Management Plan