The climate affects shoreline processes in a number of ways. This case study uses the climate change data from the projections published by Ville de Montreal in its Climate Change Adaptation Plan, which shows predicted higher average temperatures, heavy rainfalls, droughts, and more destructive storms. More frequent and more severe storms will cause the greatest increase in erosion to unprotected shoreline along the Kahnawà:ke shoreline. The potential impacts of higher average temperatures include milder winters with shorter periods of ice cover, more frequent freeze-thaw cycles, and potential changes to the plant species found along the shoreline. Shorter ice periods increase the risk of erosion by shorting the period that shore-fast ice protects the bank and potentially extending the shipping season. Freeze-thaw cycles weaken exposed clay soils, which in turn makes them more easily eroded. Shoreline plants strengthen the soil with their roots so changes to those species could impact erosion rates. Heavy rainfall produces surface runoff when there is insufficient time for the water to be absorbed by the land. Surface runoff frequently contributes to erosion at the crest of shoreline banks, and saturated banks are more prone to slope failure. During our field review we did not observe any erosion scarps that we thought were caused by surface runoff, so it is not confirmed as an issue along the Kahnawà:ke shoreline but has the potential to be. Changes to both water levels and storm frequency/duration are potentially the most important climate change parameters for the Kahnawà:ke shoreline. This case study undertakes an erosion hazard assessment. A relative erosion risk rating was developed for each of the 44 shoreline reaches. The rating is intended to convey the risk or likelihood of erosion occurring over the coming years. It is based on a qualitative assessment of erosion indicators.
This report presents a shoreline vulnerability assessment study completed for a portion of the Kahnawà:ke shoreline on the St. Lawrence River in Quebec by Shoreplan Engineering Limited for use by the Kahnawà:ke Environment Protection Office (KEPO). The study examines climate change, erosion and flooding processes and risks, shoreline protection structures, and shoreline management planning. A two-day field review was conducted to assess and document conditions within the study area. Aerial surveying and aerial photography work were completed by a sub-contractor. A relative erosion risk rating was developed for each of the 44 shoreline reaches included in this study. The risk rating is intended to convey the relative level or extent of erosion that is expected over the coming years; it does not consider the consequences of that erosion. The rating for each reach should be viewed as relative to other reaches within the study area, but not to other shoreline on the St. Lawrence River. The most significant cause of erosion of the above water bank within the study area is due to wind wave action, particularly at high water levels. Ship waves contribute to that erosion, but to a lesser degree. River currents will also contribute to erosion, but to an even lesser degree, due to their relatively low speed at this wide section of the river. A review of published climate change projections showed predicted higher average temperatures, heavy rainfalls, droughts, and more destructive storms. Each of these has the potential to affect erosion processes along the Kahnawà:ke shoreline, but more frequent and more severe storms will cause the greatest increase in erosion to unprotected shoreline. Possible prevention and protection solutions were described for a number of reaches. The study concluded by noting that KEPO’s shoreline management plan should include adaptive measures to accommodate the impact of climate change.