QUANTIFYING BANK EROSION AND CHANNEL SEDIMENTATION ON THE TORCH, RAPID AND GRASS RIVERS IN NORTHERN LOWER MICHIGAN

Rapid sedimentation and bank erosion have steadily reduced the navigability of the rivers in the Chain of Lakes watershed in Northern Lower Michigan during the last several decades. Historical documentation indicates that these rivers were once deep enough for steamboat travel, but now are all but impassable by even shallow draft watercraft. Beyond the navigational issues presented by sedimentation, bank erosion threatens property and water access. This study focuses on three rivers: the Torch, the Rapid, and the Grass. Each of these rivers have been affected by dramatic anthropogenic changes during the last 150 years, including extensive land cover change, channel modification, and base level changes via damming the terminal lake on the Chain.

Here we present work that quantifies bank erosion over the last eight decades via aerial and satellite imagery analysis, along with the current channel bottom depths via bathymetric measurements. This work demonstrates that significant changes have occurred, and continue to occur, to bank positions. Sections of the river with the most bank change are also the shallowest, indicating that the channel continues to evolve toward a new dynamic equilibrium. We illustrate how sections with the least change are those that have had the most active management, and suggest means by which further erosion and shallowing could be prevented, and potentially reversed.