Coastal Sensitivity to Sea-Level Rise

The Theme

Climate warming is expected to cause warming of the oceans and the partial melting of glaciers and ice-caps, resulting in a global rise in sea level. By the end of this century, the global mean sea-level rise could amount to 0.09 to 0.88 metres (Intergovernmental Panel on Climate Change 2001). In Canada, where the total coastline exceeds 203 000 kilometres, sea level rise is a significant issue.

This map shows the sensitivity of the coastlines of Canada to the expected rise in sea level, due to climate warming. Sensitivity here means the degree to which a coastline may experience physical changes such as flooding, erosion, beach migration, and coastal dune destabilization. It is measured by a sensitivity index, which is a modified version of the coastal vulnerability index of Gornitz (1990). This sensitivity index is obtained by manipulating scores of 1 to 5 attributed to each of seven variables: relief, geology, coastal landform, sea-level tendency, shoreline displacement, tidal range, and wave height.

Also shown on this map (blue shading) are the expansions of the submerging areas in Canada's coasts, due to climate warming.

Sensitivity Projection

As shown in the map, sensitivity index scores range from 0.8 to 56.7. Two major regions of high sensitivity are identified: 1) Atlantic Canada (much of the coasts of Nova Scotia, Prince Edward Island, and New Brunswick); and 2) parts of the Beaufort Sea coast. Small areas of high sensitivity occur in Quebec, Newfoundland and Labrador, and British Columbia.

As sea level rises, storm surges will inflict greater damage on communities located close to the level of the ocean. A reminder of this was the flooding of Charlottetown, Prince Edward Island by a storm surge in January 2000. Other communities at risk include Placentia in Newfoundland and Labrador, and even downtown Halifax. The lowlands at the head of the Bay of Fundy are also at risk from storm surges. This area was devastated in the great storm surge of 1869, the so-called 'Saxby Tide'. With accelerated sea-level rise, the dykes will be breached by some of the high tides by the middle of the century.

The other large area of high sensitivity is the Beaufort Sea, where some of the most rapid coastal erosion rates in Canada are found. The problem is exacerbated by the thawing of permafrost in beach sediments. Storm surges commonly cause flooding in this region. Settlements such as Tuktoyaktuk will undoubtedly experience further difficulties in the coming years. An additional concern in this region is that the extent and duration of sea ice will be reduced as the climate warms, thus allowing storms to flood and erode the coast more frequently. Note that coastal erosion is restricted to summer months, and cannot occur in winter when the ocean is frozen.

A rising sea level will result in more coastal erosion in this century. However, when compared with Europe and Japan, where expenditures on coastal protection are in the many billions of dollars, Canada is fortunate in having low population densities and small amounts of infrastructure at risk. Awareness of the expected sea-level rise and coastal erosion, which have been occurring for many thousands of years, should ensure that future developments are set back from threatened areas.

Photos of Canadian Coasts

Photographs A to L illustrate the diversity of Canadian coasts and the wide range of impacts that might be expected.

Photograph A: Prince Patrick Island, Northwest Territories. This low, ice-congested, sandy coastline is moderately sensitive to sea-level rise (score 9.6), particularly to inundation and coastal retreat. If the extent and duration of open water increases (due to global warming), additional effects could include overwashing and development of barrier beaches. Photo by R.B. Taylor. GSC 1998-038-A

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Photograph A. Prince Patrick Island, Northwest Territories

Photograph B: Bylot Island, Nunavut. This part of Bylot Island has a low sensitivity overall (score 3.6). However, unlike the high, rocky coast in the background, the low barrier beach could migrate landward due to more frequent overwashing, particularly if the duration and extent of ice cover decreased. The backbarrier lowland (right) is vulnerable to inundation. Photo by R.B. Taylor. GSC 1998-038-B

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Photograph B. Bylot Island, Nunavut

Photograph C: Devon Island, Nunavut. A small percentage of eastern Arctic coasts consist of tidewater glaciers. These are sensitive not only to sea-level rise, but also to increases in open water extent and duration which could increase calving rates and change coastal configuration. This region has a moderate sensitivity (score 8.0). Photo by R.B. Taylor. GSC 1998-038-C

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Photograph C. Devon Island, Nunavut

Photograph D: Placentia, Newfoundland and Labrador. This is an example of a high sensitivity location within a region assessed to be at low risk overall (score 3.2). The low, gravel beach-ridge plain has been inundated several times in recent years during storms. This could occur more frequently in the future. Photo by D.L. Forbes. GSC 1998-038-D

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Photograph D. Placentia, Newfoundland and Labrador

Photograph E: Îles-de-la-Madeleine, Quebec. At least three nearshore bars dissipate wave energy on this dune coast (score 33.8). Similar coasts exist throughout the southern Gulf of St. Lawrence. Impacts could include dune instability, changes in configuration of nearshore bars, and erosion of beaches. Photo by E.H. Owens. GSC 1998-038-E

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Photograph E. Îles-de-la-Madeleine, Quebec

Photograph F: Story Head, Nova Scotia. This region is highly sensitive (42.8). The low, curving barrier beach in the photo retreats 8 metres annually, and will soon become detached from the eroding drumlin remnant in the foreground, exposing a sheltered inlet to Atlantic storm waves. Accelerated sea-level rise will result in more frequent changes at the outer coast, accompanied by the formation of new barriers, and inundation of coastal marshes. Photo by J. Shaw. GSC 1998-038-F

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Photograph F. Story Head, Nova Scotia

Photograph G: Pointe aux Outardes, Quebec. Holocene deltas along Quebec's North Shore are pockets of moderate sensitivity in an otherwise low sensitivity region. Future sea-level rise would result in increased coastal erosion and coastal mobility in these areas. Photo courtesy of J.-C. Dionne.

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Photograph G. Pointe aux Outardes, Quebec

Photograph H: North Richibucto Beach, New Brunswick. The gulf coast of New Brunswick has moderate to high sensitivity levels - this area has a score of 16.0. This low, sandy barrier beach could experience increased rates of overwashing, retreat, and inlet migration. Erosion of peat cliffs and inundation of backbarrier marshes could also be expected. Photo courtesy of E.A. Bryant.

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Photograph H. North Richibucto Beach, New Brunswick

Photograph I: Northeast Graham Island, British Columbia. This is one of two regions of high sensitivity in British Columbia - the score is 24.8. The sandy bluffs in this photo are retreating up to 12 metres annually, supplying sediment to prograding beaches elsewhere in the region. Photo by C.L. Amos. GSC 1998-038-G

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Photograph I. Northeast Graham Island, British Columbia

Photograph J: Beaufort Sea coast, Yukon Territory. These 5 metre-high bluffs at Kay Point are retreating due to thawing of ice wedges, undercutting of polygons, and block slumping. The sensitivity score of this region is 11.7. If open water duration increased, the coast would be exposed to waves much higher than those that exist today. Photo by D.L. Forbes. GSC 1998-038-H

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Photograph J. Beaufort Sea Coast, Yukon Territory

Photograph K: Toba Inlet, British Columbia. Like much of British Columbia's coast, this fiord, surrounded by mountains rising above 1800 metres, is at low risk of modification by a sea-level rise. The sensitivity index here is 1.9. Nevertheless, there could be impacts, including inundation of the numerous bayhead deltas in the region. Photo courtesy of J.P.M. Syvitski.

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Photograph K. Toba Inlet, British Columbia

Photograph L: West coast of Hudson Bay, Manitoba. This low coast with sandy beaches, raised beaches, and coastal marshes is moderately sensitive. The effects of global sea-level rise would be mitigated by ongoing crustal rise here and elsewhere in Hudson Bay. Photo courtesy of I.P. Martini.

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Photograph L. West Coast of Hudson Bay, Manitoba

Data Source

J. Shaw, R.B. Taylor, D.L. Forbes, M.-H. Ruz, and S. Solomon. 1998. Sensitivity of the Coasts of Canada to Sea-level Rise. Geological Survey of Canada Bulletin 505. Ottawa.

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