Xwu'nekw Park Sea Dike

In 2017, the District of Squamish, British Columbia, recommended a sea dike for the Xwu’nekw Park (pronounced Whoo-Nay-Oak) as part of their Integrated Flood Hazard Management Plan to protect the community and downtown core from coastal flooding and other impacts resulting from ongoing climate change. Xwu’nekw in the Squamish language means ‘where large canoes are beached,’ and today, the park is home to a Squamish Nation canoe restoration shelter and a paddling club storage facility. To determine the impact of current and future climate change on the proposed Xwu’nekw Park Sea Dike, a climate resilience assessment was conducted. Of the ten climate change risk scenarios assessed, only three were deemed as moderate risk. These scenarios were related to ocean acidification, coastal flood level increase and a wave overtopping event. After conducting the assessment and receiving recommendations to improve the resilience of the sea dike, Squamish entered the design phase and solicited feedback from the public on two dike design options. The agreed upon dike design will be an inset sea wall made of steel sheet pile that will incorporate habitat enhancements and restoration features and maintain public park use and water accessibility. Squamish has submitted several permit applications and is currently awaiting approval for the permits. Sea dike construction is anticipated to begin in August 2023.

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Understanding and Assessing Impacts

Located at the head of Howe Sound, Squamish is frequently exposed to floods and flood-related hazards such as erosion and storm surge. In 2017, Squamish developed an Integrated Flood Hazard Management Plan (IFHMP) to map flood risk areas. Based on guidance from the provincial government, the plan assumes that by 2100, climate change will raise sea levels by 1 metre and peak river flows will increase by 10%. The results from the IFHMP reaffirmed that Squamish is at risk from coastal flooding and determined that the existing dikes will not provide protection during a 200-year return period flood.

In 2019, a Climate Lens Resilience Report was conducted as part of Infrastructure Canada’s funding requirements to determine how climate change would affect the sea dike design proposed by the IFHMP. A PIEVC Practitioner Risk Assessment approach was used to determine the impact of climate change during dike construction (2020) and throughout the dike’s service life (2100). Six climate change parameters and two cumulative events were used; wildfire air quality, extreme heat events, sea level rise, storm surge, wind wave effects, ocean acidification, an increased coastal flood level event and a wave overtopping event. Climate data and trends were obtained from the literature and provincial documents, and current temperature data was sourced from Pacific Climate Impacts Consortium and Government of Canada Historical Weather Data. Ten climate change risk scenarios were assessed based on the likelihood and consequence of a climate hazard exceeding a predetermined threshold value and adversely affecting the sea dike. Of the ten scenarios assessed, three were found to be moderate risks related to ocean acidification, coastal flood level increase, and wave overtopping.

Identifying Actions

The risk assessment generally determined the sea dike to be resilient over the next 100 years. The following recommendations were provided to inform decision-making for the proposed design and construction of the sea dike:

  • Building adaptive capacity into the dike design to allow for a future additional 1-metre increase in dike crest height to accommodate continued sea level rise;
  • Designing the dike to incorporate erosion resilience measures;
  • Analysis to determine whether habitat enhancement features at the dike toe could also support wave attenuation and reduce the risk of wave overtopping; and
  • Consider ocean acidification in the design of exposed elements to accommodate expected corrosion performance.

After conducting the risk assessment and other geotechnical surveys, the design phase was initiated. Squamish solicited feedback from marine and park recreation interests, environment stakeholders, the general public, local tourism and business sectors and governments including the Squamish Nation, the Province of BC and Federal agencies. In June 2020, two initial dike design concepts were presented for community input, and in the following month, a final design concept was confirmed.

Implementation

After the dike design concept was finalized, Squamish submitted permit applications to Canadian Navigable Waters Act, Dike Maintenance Act, and the Fisheries Act and Heritage Conservation Act. Squamish also completed an Archeological Impact Assessment in advance of site work to evaluate and manage any potential archeological resources on the proposed site.

Outcomes and Monitoring Progress

The proposed Xwu’nekw Park Sea Dike, when complete, will protect 3.5 km2 of coastal flood hazard area. The dike will have a “notched” or inset sea wall made of steel sheet pile with a vertical face on the water side of the dike to avoid encroaching on the existing canoe shelter and paddling storage. The dike will maintain approximately 4,500 square metres of usable facility space in the park with an approximate width of 24 metres. The concept design will facilitate future water uses such as docks, and potential boat storage and public amenity uses. The final design will also integrate habitat enhancement and restoration features to increase ecological complexity and habitat value in the marine environment.

Next Steps

The proposed sea dike design is currently awaiting approval and construction is anticipated to begin in August 2023.

Resources

Link to Full Case Study

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