|Citation||Kerr Wood Leidal. 2015. District of Squamish Integrated Flood Hazard Management Plan, Final DRAFT Background Report. Prepared for District of Squamish.|
|Organization||District of Squamish|
|Abstract/Description or Keywords||The District of Squamish (District) is set in a beautiful but hazardous natural environment that includes:
• flood hazards from the Squamish, Mamquam, Cheakamus, Cheekeye, and Stawamus Rivers;
• debris flow hazards from the Cheekeye River and smaller local creeks; and
• coastal flood and tsunami hazards from Howe Sound.
The District lies within traditional territories claimed by the Squamish Nation. Ten Squamish Nation reserves
located throughout the shared floodplain create an inseparable common interest in flood protection. The District
also lies within traditional territories claimed by the Tsleil-Waututh Nation.
In 1994, the District of Squamish completed a Flood Hazard Management Plan (FHMP) to help achieve an
appropriate balance between flood protection and community development. Twenty years after its release, key
parts of the 1994 FHMP have become obsolete as a result of community growth, improved understanding of
flood hazards, and the emergence of new tools for flood hazard management.
Integrated Flood Hazard Management Plan
In February 2014, the District retained a multi-disciplinary consulting team led by Kerr Wood Leidal Associates
Ltd. (KWL) to prepare a new Integrated Flood Hazard Management Plan (IFHMP). The IFHMP project will be
supported by a multi-stage public consultation process and a technical working group that includes regulators,
key major industry representatives, and the Squamish Nation.
This Background Report is the first major deliverable of the IFHMP, which is scheduled for completion in 2016.
The Background Report provides an overview of:
• specific hazards that will be addressed in the IFHMP and the areas at risk from each;
• the current state and context of the District’s flood protection program, including policy instruments as well
as the local portfolio of structural flood protection works;
• regional, provincial, national and international guiding principles for the IFHMP process;
• pre-requisite technical updates including river modelling, coastal flood analysis, and a high-level geohazards
• preliminary conclusions and recommendations that arose during the compilation of background materials.
Most river floods occur in the fall and early winter when large and intense multi-day storms create high flows on
the local rivers, and when precipitation falling as rain throughout the watershed can bring additional runoff
contribution from alpine snowmelt. Sediment aggradation gradually or periodically increases the flood risk in
some areas by filling in the river channels. Erosion is a separate but related hazard where riparian development
has encroached into the flood corridor.
Areas at risk of river flooding include Paradise Valley (Cheakamus River), the low-lying corridor that follows
Highway 99 from Brackendale to Downtown Squamish (Squamish and Mamquam River), and from Valleycliffe
to Stawamus I.R. No. 24 (Stawamus River). The value of infrastructure vulnerable to the Squamish River alone
exceeds $2.4 billion. The majority of community services and commercial areas are at risk of flooding, as are
most of the local Squamish Nation reserves. Coastal Hazards
Coastal water levels at Squamish are a function of tide, storm surge, local effects, and wind waves. Coastal
floods typically occur when external storm surges combine with the highest tides of the year during the winter
storm season. The IFHMP has adopted the Province’s climate change guidelines, which recommend an
allowance of 1 m of Sea Level Rise (SLR) by year 2100. The coastal flood assessment has identified other key
gaps in the current understanding of local tsunami hazards, subsidence, datum adjustments, wind set-up, and
Debris Flow Hazards
Debris flows involve very large peak discharges of substantially-sized material moving at relatively high
velocities. The Cheekeye River is one of the most studied debris flow hazards in BC; the corresponding hazard
area includes the entire Cheekeye Fan from Cheakamus I.R. No. 11 to Brackendale. Other small creeks around
the District are potentially subject to debris flows, and previous studies have found the Stawamus River may be
subject to a transitional process referred to as a debris flood.
In 2004, responsibility for development in flood hazard areas was shifted from the provincial government to local
municipalities. The District’s 2009 Official Community Plan (OCP) provides strategic policies for flood hazard
management planning and protection but does not specify Development Permit Areas for flood and erosion
hazards. The District does not have a floodplain bylaw. Hazard assessments are currently mandated under
rezoning, subdivision and building permit processes through provincial statutes such as the Land Title Act and
the Community Charter. The District’s complex hazards are frequently beyond the scope of these site-specific
This Background Report includes a review of flood hazard management policy measures adopted by Canadian
jurisdictions ranging from nearby local municipalities to the federal government. Many international jurisdictions
face even higher levels of flood risk and have naturally developed more sophisticated flood hazard management
policies. International examples reviewed for this report include case studies from Europe and the United
In addition to implementing policy and planning measures, the District maintains a portfolio of structural flood
protection works to protect the Squamish community. The District portfolio primarily consists of dikes, riprap
erosion protection revetments, and ancillary structures regulated under the Dike Maintenance Act. The District’s
structural flood protection works are complemented by a number of unregulated First Nation, privately-owned,
“orphaned”, and de facto dikes and training berms on many of the local creeks and rivers.
The most significant element of the District portfolio is the integrated ±20 km long Squamish River and
Mamquam River dike system constructed by the province in the early 1980s. Other structural flood protection
works are located throughout the Paradise Valley (Cheakamus River), along the Cheekeye River upstream of
Highway 99, and adjacent to the Valleycliffe neighbourhood (Stawamus River). Updated hydraulic modelling,
including an allowance for flow increases as a result of climate change, confirms that some structures currently
do not provide the intended level of flood protection.
Coastal flood protection is currently provided by a variety of low, non-standard works around downtown. The
District’s only regulated sea dike extends from the foot of Cleveland Avenue around to the west end of Winnipeg
Street. Conflicts with development have created challenges for future dike raising. Flood Protection Gap Analysis
The Background Report closes by contrasting current and future flood hazards against the District’s flood
hazard management program, drawing conclusions about where the existing program may be unable to deliver
the desired level(s) of protection. These conclusions take the shape of a gap analysis focussed on both policy
and structural program elements.
Key policy gaps are identified in the categories of risk management and analysis, regulation, and public
education. The most notable gaps include planning for climate change, particularly SLR, and the need for a
floodplain bylaw and/or flood hazard development permit areas. Key structural flood protection gaps are
identified in the categories of design standards, jurisdiction and access, inspection, reporting and compliance,
and environment and community. The most notable gaps include coastal defences, access challenges,
particularly the lack of a continuous Statutory Right-of-Way, and outstanding maintenance issues.
The subject matter for this report was discussed by the IFHMP Technical Working Group at a meeting on
June 16, 2014. The draft report was presented to District Mayor and Council on August 19, 2014.
|Regional Watershed||Howe Sound & Sunshine Coast|
|Sub-watershed if known|