Annapolis Royal Tidal Surge Analysis
Annapolis Royal, Nova Scotia, has historically flooded when storm surges coincided with high tides. It is prone to flooding because the town was built upon reclaimed land using dykes constructed in the 17th century and the surrounding land is naturally subsiding. Sea level rise, coupled with more frequent and intense storm surges, increase the vulnerability of the town to flooding. To assess the future impacts of climate change, flood risk assessments were completed using LIDAR data, water modeler software, and historical tidal and flood records. Results indicate that climate change will make the town more prone to flooding. A risk and cost-benefit analysis was conducted to assess four adaptation strategies. It was concluded that the town should construct a 5.4 meter levee around the town because the insurance cost to replace the buildings damaged by future floods would exceed the cost of constructing the levee. The final report was given to the Annapolis Royal Town Council and the town is seeking funds to begin construction.
Canada’s Bay of Fundy is world renowned for its extremely large and powerful tides. It has been estimated that 100 billion tons of seawater flows in and out of the Bay twice daily with a maximum height difference of 16 meters between the low and high tides.
Annapolis Royal, Nova Scotia, is a small town (population 444 in 2006 census) located on the southern shore of the Bay of Fundy. Its location is prone to flooding because the town center was constructed upon reclaimed land in the 17th century using dykes and the land is naturally subsiding as the glacial till and sediments compress over geologic time. Available historical records evidence large storms that have caused major damage to the town, in particular, the Saxby Gale of 1869 and Groundhog Day Storm of 1976. The storm surge from these major storms (2 and 1.6 meters respectively) caused severe damage to coastal communities because they coincided with high tides. Thus, sea level rise due to climate change coupled with storm surge and coastal erosion have alarmed Annapolis Royal residents.
The Clean Annapolis River Project (CARP) initiated the Tidal Surge Project in 1998 to assess the town’s vulnerability to storm surges. It analyzed available historical records to identify the cause of past major floods and found that most major floods were due to storm surges that occurred concurrently with high tides in the Bay of Fundy. To assess the impact sea level rise will have on the town’s vulnerability, a team at the Geomatics Center at Nova Scotia Community College (NSCC) generated a flood risk assessment using LIDAR data, water modeler software, and historical tidal and flood records. They concluded that if sea level were to increase by 80 cm and a storm equivalent to the Groundhog Day Storm occurred, the town’s 5 meter high dykes are likely to be breeched. The likelihood that extreme flooding would occur in Annapolis Royal increases from an average ranging from once every 43-121 years to once every 23-55 years. In 2007, an outside consultant, Birch Hill Geosolutions, was hired to assess climate change impacts and adaptations to these impacts in Nova Scotia; Annapolis Royal was selected as a case study. Using LIDAR data and the water modeler software from NSCC, they were able to accurately recreate the flooding extent of the 1976 Groundhog Day Storm using GIS tools.
Following this, a risk and cost-benefit analysis was conducted for the construction of levees in Annapolis Royal to protect against flooding. Four alternative strategies were tested:
- Do nothing;
- Flood-proof individual buildings;
- Construct a levee around the town to protect against a 5.4 meter flood; and
- Construct a levee around the town to protect against a 6.5 meter flood.
Results indicated that option 3 was the best because the insurance cost of replacing or restoring the buildings damaged during a flood would actually exceed the cost of constructing the levee. Option 4 would offer more protection but the chance of a 6.5 meter flood occurring is negligible since a storm surge would have to coincide with the highest astronomical tide.
Finally, the LIDAR data, water modeler software, and climate projections were combined into GIS mapping to help Annapolis Royal plan for municipal land use. Composite maps were produced that highlight areas that are suitable or unsuitable for development or that should be developed with caution.
Outcomes and Conclusions
Results were presented to the Annapolis Royal Town Council in 2009 in the report Back to the Future: Town of Annapolis Royal Final Report to the Council. This report is a summary of multiple environmentally-oriented projects undertaken in Annapolis Royal to complete their sustainable community planning process. Recommendations in regards to climate change adaptation include determining the costs of a levee and associated drainage system, and seeking outside funding resources to build the levee. The town’s current financial status limits it ability to fund a levee without significant funding influx.
Feifel, K. (2010). Annapolis Royal Tidal Surge Analysis [Case study on a project of the Clean Annapolis River Project]. Product of EcoAdapt's State of Adaptation Program. Retrieved from CAKE: http://www.cakex.org/case-studies/annapolis-royal-tidal-surge-analysis (Last updated March 2010)