Effects of simulated water level management on shore erosion rates. Case study: Baskatong Reservoir, Quebec, Canada

This study was carried out as part of a feasibility study on the constructi on of a hydroelectric generating station at Mercier dam at the outlet of th e Baskatong reservoir in Quebec. The study dealt mainly with a comparison o f the current and future bank erosion rates of the reservoir. Given the yea r of impounding of the Baskatong reservoir, i.e., 1927, it was possible to track bank erosion rates using field surveys and photogrammetric and numeri cal analyses. It was noted that in certain areas, such as Du Diable Bay and Windigo Bay, the Baskatong reservoir banks were substantially affected by erosion. Estimates indicate that the banks have receded by about 10 to 15 m over a 20-year period. The banks most affected by erosion are those contai ning sandy material of fluvioglacial or glaciolacustrine origin with bluffs greater than 2 m in height and characterized by the longest fetches. In on e section of Windigo Bay, banks had receded by about 30 m in 20 years. Wave action is the main factor responsible for bank erosion, especially in area s highly exposed to long fetches. In fact, there is a correlation between b ank erosion rates, fetch distribution, and the erosive energy of waves. It has been noted that receding banks with the highest erosion rates are linke d to the greatest wave erosion energy. Based on the values obtained using s imulated reservoir water levels, while taking into account the future const ruction of a new generating station, bank erosion rates appear to be compar able to those measured under actual conditions, though erosion rates could increase by about 28-30% in the areas most affected by erosion at the prese nt time.