4.8 The Bay of Fundy and the tides of climate change

3.2 Context and climate vulnerability

The region has experienced flooding events in the past. During the notorious "Saxby Gale" of 1869, the combination of high tides, a tropical and an extratropical system generating gale force winds and low atmospheric pressure, the sea level reached 10.1 m and the maximum storm surge 21.6 m, causing massive flooding, casualties and severe damage, and all but separating Nova Scotia from New Brunswick. In recent years, the frequency of dyke overtopping has increased, but without coming close to water levels such as during the Saxby gale and affecting mostly agricultural land. Most damage has come from freshwater flooding, for which the dykes actually present a problem, since they prevent rapid draining of storm water. In 1961, a freshwater flood reached a level of 8.7 m. Increases in both storm surge frequency and sea level rise have been measured in the region. Records of hurricane and tropical storms that have passed through the study area show that the frequency of storms has more than tripled in the past 25 years compared to records over the past century (figure 27).

Maximum storm strength (but not necessarily at the impact site) of hurricanes and tropical storms that have passed through the Tantramar region.

Figure 27. Maximum storm strength (but not necessarily at the impact site) of hurricanes and tropical storms that have passed through the Tantramar region.

Source: Lieske and Bornemann (2011)

Although recent events have been less severe, the vulnerability remains. Lieske and Bornemann (2011) found that the average height of the 27.6 km of dykes in the Tantramar region is 8.6 m, which is lower than even the least severe prediction based on the current 1:10‐year sea level estimate of 8.9 ± 0.1 m (Figure 28). Even without considering future sea-level rise, 89% of the dykes would be overtopped in a 1:10 years event. Clearly, the Tantramar region is at immediate risk of a major flood event. Some dykes also exhibit high levels of erosion (Lieske and Bornemann, 2011). Sea level rise will potentially exacerbate those risks further. Erosion however is rather caused by the strong tidal currents than by storm surges (Lieske and Bornemann, 2011).

Dyke centreline elevation.

Figure 28. Dyke centreline elevation.

Source: Lieske and Bornemann (2011)

The analysis (using ESRI ArcGIS 10.1) of the state of the dykes protecting the low‐lying lands from coastal flooding and of the terrestrial assets at risk under different flood scenarios, using digital elevation models (DEM) based on LiDAR data, combined with other sources including ground surveys, reveals that the area behind the dykes is at risk of flooding and several types of assets are vulnerable to those inundations. Apart from their height, two additional factors potentially increase the vulnerability of the dyke system to coastal flooding: lack of vegetation cover and distance to open water. Vegetation stabilises dykes and its absence leads to higher erosion rates. The distance to the open water, and therefore the presence of buffer zones reduces the kinetic energy of arriving waves. Exposed dunes experience the highest wave energy. Only 63% of the dykes are vegetated, leaving a third without protective cover (figure 29). In many areas, dykes are close to the coast; 22% are less than 25 m to the shore (coastal or riverine) (figure 30).

Euclidean distance to coast.

Figure 29. Euclidean distance to coast.

Source: Lieske and Bornemann (2011)

Normalized Differentiation Vegetation Index. Values greater than 36 are areas with a majority of vegetation.

Figure 30. Normalized Differentiation Vegetation Index. Values greater than 36 are areas with a majority of vegetation.

Source: Lieske and Bornemann (2011)

Interestingly, the potentially flooded area does not increase much under the different climate scenarios, from 20.6% to 21.9% of Sackville and from 9.2% to 9.9% of the Tantramar Planning District. This is due to the topology of the area. However, the depth of flooding would be greater, leading to more important damages in the flooded areas (Lieske and Bornemann, 2011). The number of parcels affected by a 1:10 years flood rises from 1049 to 1169 under progressive sea level rise scenarios and that of building and structures from 156 to 266. Amongst those, key transportation corridors are impacted under all scenarios. Within Sackville, some non‐flooded areas could nevertheless be isolated as “islands” during a flood event. With the exception of the westward portion of the TransCanada highway, all major roadways exiting Sackville are cut off.

The town of Sackville is starting to take into account the risk of flooding. It recently updated its building code, raising the allowable flood level by one meter. This means that buildings are not allowed to have any openings, such as doors or windows, above that height (Schauffler, 2014). In recent years, the Tantramar region has participated in the Federation of Canadian Municipalities’ Partners for Climate Protection Program.

The public’s perception of climate change depends on which aspect of the phenomenon is considered. In a study involving 14 focus groups and 172 participants, 81% judged that the problem of climate change was either “severe” of “considerable” (Lieske et al., 2013). 70% of the respondents believed there was a “severe” or considerable” risk of dyke failure as a result of climate change. However, only 35.6% of respondents viewed themselves at personal risk in the event of a dyke failure. Exposure to various information on those topics increased the awareness and severity of perceived risk in the focus groups (Lieske et al., 2013).