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Evidence suggests St. Clair erosion is not ongoing, but causes remain unknown

There is no evidence of ongoing erosion in the St. Clair River, according to the comprehensive bathymetric surveys undertaken since 2000. Furthermore, bottom shear stresses, were determined to be insufficient to erode the bed material along the thalweg and most other areas of the river bed. Given that there are no bathymetric surveys between the two measurements from 1971 to 2000, it is difficult to determine when the conveyance in the St. Clair River may have changed and whether this change was progressive or episodic in nature. There are three indirect lines of analysis to suggest that the conveyance change was episodic and occurred in the mid-1980s, followed by a gradual transition to the current regime. It is difficult to state when the period of a stable morphologic regime began, but it may have coincided with the relatively low lake levels of the past decade. It is also unknown what caused the morphological changes observed in the St. Clair River. Overall, the change in conveyance in the St. Clair River likely has been the result of a combination of several factors. The Study determined that while the record ice jam of 1984 was not the key contributing factor, seasonal ice jams do appear to play a role. Fluctuations between extreme highs and lows of upper Great Lakes water levels, such as those experienced in the mid-1980s, also could have contributed to the increase in the river’s conveyance. Ship navigation effects, such as propeller wash, are the most plausible explanation of some of the active bedforms and low level bed material flux in the river, and require further investigation. Other possible minor contributing factors to the change in conveyance could include maintenance dredging in the river, shipwrecks and the construction of shoreline protection works.
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St. Clair 2D RMA2 Modelling
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St. Clair Ice Jam Modelling
St. Clair Quaternary Geology Synthesis
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