Shoreline erosion at Crean Lake, Prince Albert National Park, Saskatchewan
Jersak, Todd Raymond
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During the winter of 1958 - 1959 a dam was constructed at the outlet of Crean Lake. The water level of the lake was increased at that time to increase public access to the lake and to increase water depths over lake trout shoals. Accelerated erosion of the Crean Lake shoreline commenced with this impoundment. This study has found that the rate of recession of the Crean Lake shoreline was greatest shortly after impoundment and has been declining ever since. The fact that recession rates have been declining, even though limited water level data indicate that water levels have remained considerably and consistently higher than pre-impoundment levels, suggests that a new shoreline equilibrium is being approached. Existing literature indicates that shoreline erosion provides sediment to the nearshore environment and in the process contributes to the establishment of a new equilibrium. As a new equilibrium is approached the amount of erosion necessary to deliver sediments to the nearshore becomes less. Recession rates may also be declining due to the increased level of beach armouring which has resulted from the erosion and mass wasting of shoreline bluffs. These facts may explain the declining rate of erosion of the Crean Lake shoreline. For the time period directly after impoundment the percentage of bluff gravel and bluff fines were found to be strongly related to the rate of recession. Since the mid-1960's, bluff heights have been found to be the most strongly related to the recession and erosion of the Crean Lake shoreline. This study also investigated sedimentation over lake trout spawning shoals and the effect that ice-push had on shoreline erosion. Sedimentation over shoals varied considerably within the lake. In general, the greatest quantities of sediment and the coarsest clasts were deposited closer to shore while the material deposited farther offshore, in deeper water, was less plentiful and finer-grained. Ice-push along the shoreline was subjectively observed to occur during both winters monitored but not at levels intense enough to contribute significantly to the erosion of the shoreline.