History of Lake Huron Bluff Erosion

Since Lake Huron water levels and thus bluff erosion ebb and flow according to multi-decadal cycles, it is beneficial to research bluff erosion through a historical lens. Since 1955, air photos depicting this area of the shoreline have been taken approximately once per decade. Interpretation of these air photos allows for bluff crests and toes to be plotted, and retreat and slope to be calculated to a reasonable degree of accuracy. While such air photos are not available before 1955, other historical resources, such as town plans, postcards, and newspaper articles tell the story of how southeastern Lake Huron's bluffs have changed since European settlement. While such records must be interpreted qualitatively, they provide valuable insights into when and how the bluffs have changed over the past 170 years.

One of the earliest available maps of this stretch of the shoreline is a town plan for Bayfield created in 1856. The town plan shows that immediately south of the Bayfield River, the bluff extended three lots (~100 meters) further into Lake Huron than it does now. While it is unknown how accurately the bluff crest was surveyed in this map, the fact that lot lines and roads were plotted on this section of the shoreline shows that the bluff did in fact extend into this area.

This Bayfield town plan is part of the collection of the  Bayfield Historical Society . This and other items can be viewed using the  Bayfield Historical Web Map .

Interpretation of historical postcards provides valuable insights into how the bluff has changed between the 1900s and the 1960s. Postcards not only show when and where the bluff was eroding, but also depict how the bluff slope evolved in the years following toe erosion events, allowing us to position current bluff changes in the context of historical ones.

Air photos taken in the years 1955, 1963, 1978, 1985, 2006, 2010, 2015, and 2020 have allowed for rates of bluff erosion over the last 70 years to be quantified. Rates of bluff erosion are typically calculated in terms of bluff crest retreat, as this a more consistently interpreted geomorphic feature than the bluff toe. Quantifying bluff retreat over long periods of time is useful for delineating property setbacks so that people do not build too close to the bluff. That said, this should be done with many sets of air photos as bluff erosion occurs cyclically rather than at a constant rate per year.

Air photos can also be used to calculate an approximate slope of the bluff at the time it was taken if both the bluff crest and toe are digitized. Calculating the slope at different times for the same site is useful for understanding how different sites respond to changes in lake level.

The interactive map below shows rates of bluff crest retreat and changes in slope over the past 70 years.

Advances in GIS and Remote Sensing since the last period of high lake levels in 1986 will allow us to better understand how Lake Huron's bluffs change in response to lake level fluctuations. Airborne LiDAR captured over this stretch of shoreline in 2022 captured the bluff crest at centimeter-scale resolution. Comparison of the 2022 LiDAR DEM with the 2020 SWOOP orthoimagery dataset shed light on how toe erosion propagates up the bluff in the years following a rapid rise in lake levels.

Drones have the ability to create high resolution digital elevation models of the bluff using structure from motion analysis, allowing for monitoring of micro-scale changes in the bluff at much more frequent intervals. Further, by capturing high resolution images of the bluff, a better understanding of how on-bluff vegetation communities change in response to erosion could be established.

Finally, nearshore mapping of both bathymetry and substrate could help us improve our understanding of how the lakebed in this area influences how much wave energy reaches the shore, and thus the toe of the bluff.

This StoryMaps collection was created as part of the Esri Canada GIS Scholarship Program.

This research was undertaken as part of an undergraduate thesis supervised by Dr. Quinn Lewis, Department of Geography and Environmental Management, University of Waterloo. Significant mentorship was also provided by Dr. John Johnston, Department of Earth and Environmental Sciences, University of Waterloo.

Funding for this project was graciously provided through the  Lake Huron Coastal Centre 's Geoff Peach scholarship.

Historical/archival resources for this project were graciously provided by the Bayfield Historical Society and the University of Waterloo Geospatial Centre.

This project would not have been possible without the assistance of several local landowners, experts, and organizations who shared their decades of shoreline knowledge with me.