Managing Natural Assets to Increase Costal Resilience: Town of Gibsons, British Columbia

In 2020-21, the Municipal Natural Assets Initiative (MNAI) piloted the Coastal Resilience project in the Town of Gibsons, B.C. to address the impacts of climate change on aging infrastructure being facing by many coastal communities across Canada. The structures originally constructed to protect communities from storm surges are aging and unable to protect against bigger and more frequent storms caused by climate change. The Town of Gibsons is situated along the perimeter of the Salish Sea at the entrance to Howe Sound or Átl’ka7tsem. As of the 2016 federal census, the town was home to 4,605 residents. Because of its coastal vulnerability, the Town of Gibsons is actively pursuing climate adaptation planning to help mitigate future damages from forecasted sea level rise and increased storm severity and frequency. The project developed and tested a Coastal Toolbox (CT) model to determine how enhancing coastal natural assets like subtidal eelgrass, coastal vegetation or beach sediments could reduce flood and erosion impacts, especially if used alongside conventional grey infrastructure. The project team made comparisons using avoided damage costs to flooded structures and a non-monetary erosion index score. The latter compares the hypothetical beach retreat from erosion given beach elevation profiles, and a wave attenuation estimate that evaluates how much subtidal features like eelgrass will mitigate waves. Preparation of this project was carried out with financial support from Natural Resources Canada’s Climate Change Adaptation Program, the Sitka Foundation, the McLean Foundation and the Bullitt Foundation.

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Understanding and Assessing Impacts

A growing number of local governments recognize that it is as important to understand, measure, manage and account for natural assets as engineered ones. Doing so can enable local governments to provide core services such as stormwater management, water filtration and protection from flooding and erosion, as well as additional services such as those related to recreation, health and culture. The term municipal natural assets refers to the stock of natural resources or ecosystems that a municipality, regional district or other form of local government could rely on or manage for the sustainable provision of one or more local government services. A newly developed tool called the Coastal Toolbox (CT) is a first attempt to extend the natural assets methodology to coastal issues. As a leader in natural asset management, the Town of Gibsons recognizes the importance of understanding, measuring, managing and accounting for coastal natural assets. These assets have the potential to provide significant economic benefits by mitigating floods and erosion, reducing long-term maintenance costs compared to hard/grey alternatives and providing co-benefits such as habitat conservation or improvements to local recreation areas. The project team evaluated the performance of four selected natural asset options with an assumed sea level rise of 0.24 metres, based on current RCP 8.5 mid-point scenario for Gibsons (including tidal levels, and using different design storm scenarios). The analysis is based on RCP 8.5 for Gibsons Harbour from the Canadian Extreme Water Level Analysis Tool (EWLAT). The 2070 sea level rise horizon was selected because 50 years (2020-2070) is a typical lifespan for a coastal infrastructure project and it is also a strategic mid-point for the modelling, which covers a 100-year time horizon.

Identifying Actions

Local governments have numerous ways to manage natural assets. The Municipal Natural Assets Initiative (MNAI) team provides scientific, economic, and municipal expertise to support and guide local governments in identifying, valuing and accounting for natural assets in their financial planning and asset management programs, and in developing leading-edge, sustainable and climate-resilient infrastructure. MNAI uses methodologies and tools rooted in standard asset management and provides a range of advisory services to help local governments implement them. MNAI has developed the methods and tools with significant investments, piloting, refinement, peer review and documentation of lessons in multiple Canadian provinces. Many MNAI tools to-date have focused on surface water quality and quantity. For this project, MNAI collaborated with the David Suzuki Foundation (DSF) to pilot the Coastal Resilience project in the Town of Gibsons. The Coastal Resilience project’s two objectives were to:

  1. Provide the Town of Gibsons with a quantitative assessment of the benefits that coastal natural assets can offer for flood and erosion protection from coastal storms.
  2. Develop and pilot a modelling tool (the Coastal Toolbox, or CT) that coastal communities can further refine so they could understand and compare alternative natural asset management solutions to storm surge and coastal erosion.

Implementation

Natural asset management strategies require a multidisciplinary, team-based approach. The MNAI process therefore begins with an initial engagement session with community representatives from a range of disciplines. In 2020, the project team held a series of multi- stakeholder workshops to discuss, identify and prioritize existing coastal natural assets, and to isolate the most promising candidate management options that would both reduce damages from storms and provide co-benefits such as habitat conservation or improvements to local recreation areas. Workshops included employees from the Town of Gibsons municipal office and the District of Sechelt, as well as residents and experts from the Nicholas Sonntag Marine Education Centre and University of British Columbia. This larger group is referred to hereafter as the stakeholder group. Workshop outputs included:

  • Identification of the geographic region of interest and important areas of focus.
  • A detailed understanding of the flood and erosion problems faced by the Town of Gibsons and important coastal processes.
  • Itemization of existing coastal natural assets in the Town of Gibsons and identification of asset management alternatives for modelling.
  • Itemization of available data and identification of outstanding data needs and knowledge gaps. Methods focused on comparing modelled storm and erosion protection benefits of natural asset management options with and without those management options applied.

In order to achieve the Coastal Resilience project’s objectives, the project team took the following five steps:

  1. Identified and selected coastal protection options for modelling.
  2. Incorporated coastal protection options in the Coastal Toolbox.
  3. Specified sea level rise assumptions and constructed design storms.
  4. Developed simulation modelling using the Coastal Toolbox.
  5. Evaluated results and estimated benefits.

Outcomes and Monitoring Progress

Results of the analysis suggest natural asset options like beach nourishment, shoreline planting and eelgrass planting have the potential to reduce erosion vulnerability on the South Side beaches. On the Marina Side, eelgrass planting and sediment improvement hold the greatest promise of erosion reduction benefits. With regards to flood protection, estimates from the CT indicate that buildings along the South Side are not at risk of flooding due to their higher elevations, even under extreme storms, high tides and surge scenarios. On the Marina Side, flood risk is potentially much costlier with 14 to 52 buildings at risk of flooding (depending on the storm size). Storms affecting the Marina Side could result in flood damages estimated at up to $3.4 million for a single storm, or $16.2 million cumulatively for multiple storms over a 100-year time horizon. However, since the major contributing factor for flooding in the Town of Gibsons is tide levels, not wave run-up, the CT results suggest minimal impact. A combined option (beach nourishment + shoreline planting/sediment improvement) provided only minimal protection against flooding, with avoided costs of no more than one per cent. Overall, this pilot project demonstrated that:

  1. Natural assets would provide protection against wave energy and water run-up, but not against storm surges and high tides.
  2. The CT is a rapid and easy-to-use tool that is sufficient for high-level initial screening and for quantifying the benefits associated with coastal natural assets.
  3. There are challenges associated with applying a generic tool to different types of coastlines; at its current stage of development, the CT will be most applicable to areas with sandy shores.
  4. There’s a need for a whole systems approach including exploring the role of watersheds in flood management.

Next Steps

Local governments wishing to consider using the CT should review the full technical guidance document as well as the results from the New Brunswick pilot. Current applications of the CT will likely still require combining local knowledge with professional expertise for some key modelling steps. A useful next step would be to further develop the CT to accommodate a wider range of beach types in the erosion model and further refine the Coastal Resilience framework and model. The Town of Gibsons and/or MNAI and DSF may refine project results through sensitivity analysis, model adjustments to recognize a wider range of beach types and expanded economic analysis. Several assumptions are associated with the baseline parameter estimates, and a useful next step would be to examine the impact of these assumptions on results by performing various sensitivity analyses. For example, the CT sub-models are based on several assumptions about physical processes related to storms, waves and erosion. As such, it would be useful to tune a few key variables by ±20% (e.g., wave run-up, beach retreat distance, total flood levels) before performing the final indicator calculations to test the impact of these adjustments on final results.

Resources

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