Peering over the Precipice: Using Archival Records to Extend our Knowledge of Historical Bluff Retreat on Lake Huron

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Coastal bluffs composed of till or other Quaternary sediments can be found in abundance in the Laurentian Great Lakes, including the southeastern shoreline of Lake Huron. From just north of Grand Bend all the way up to Goderich and beyond, Lake Huron’s bluffs are composed of a remarkably dense clay-silt till unit called the St. Joseph till (figure 1). As water levels in the Great Lakes rise and fall, these bluff shorelines experience occasional to frequent retreat initiated by wave-driven erosion of their toes, which steepens the rest of the slope, making it unstable (figure 2). Toe erosion occurs at times of rapidly rising lake levels, when the water is rising too quickly for the beach to adapt to the new water level.

Figure 1 (left): Example of the St. Joseph till unit from a bluff near Bayfield. Note the clasts of various lithologies “floating” in the clay-silt matrix. (Photo Ben Woodward); Figure 2 (right): Example of a vertical section of the bluff face after significant toe erosion in 2019/20. Taken at Howard Street Beach in  Bayfield. (Photo Ben Woodward)

Along the Lake Huron shoreline, there is a net movement of sand from north to south due to longshore drift. When structures like piers and groynes are built perpendicular to the shoreline, they block the movement of sand, creating sediment-starved pockets to their south (figure 3). As a result, beaches are thinner, and toe erosion is most severe. Drainage also plays an important role. Rates of bluff retreat are highest where residential or agricultural (tile) drains empty directly onto the bluff face (figure 4).

In 2019 and 2020, water levels on Lake Huron were the highest since 1986 (figure 5). With this high water came renewed concerns surrounding bluff erosion. Bluff retreat is a significant liability for property owners and municipalities, and recent research suggests that it may be contributing to harmful algal blooms (HABs) in the Great Lakes.1

Figure 3: Longshore drift (left) causes the net movement of sand from north to south in the section of shoreline between Goderich and Grand Bend. Where groynes (middle), piers (right), or other perpendicular shoreline structures are built, sand is trapped to their north, and the area to their south is starved of sand. Air photos courtesy of the University of Waterloo Geospatial Centre.
Figure 4: Drainage onto the bluff face can accelerate bluff erosion. In this example, tile drains are emptying directly onto the bluff face. (Photo Ben Woodward)
Figure 5: Water Level Data for Lake Michigan-Huron – 1918 to 2022. Lake level data from the United States Army Corps of Engineers.

Traditionally, historical research has not been emphasized in disciplines like geomorphology and Earth science, where principles like uniformitarianism have implied that information about a landscape’s past can be gleaned simply by observing processes occurring during the present. However, historical research can provide significant insights into geomorphological processes such as bluff retreat. Since bluff retreat is episodic and occurs over long timescales, many shorelines of the Great Lakes have not yet experienced a full cycle of erosion since the proliferation of technologies like remotely piloted aircraft systems (drones), LiDAR, or even colour air photos. Therefore, the historical record is often our best means of answering important questions about these systems, especially those surrounding retreat rates and slope change over time.

In 2023, I completed an undergraduate thesis in Geography investigating bluff retreat along the Lake Huron shoreline between Grand Bend and Goderich. This project relied heavily on historical documents, including air photographs, historical maps, newspapers, postcards, and artwork. While air photos are useful for assessing changes to the form of a bluff, they are limited in their ability to describe the exact processes that acted on the bluff to produce that form. This is where other types of historical imagery are useful. Rather than attempting to extract quantitative measurements of bluff position and slope from these documents, I interpreted them qualitatively to better understand the processes of change, and the timing of significant events. This post will describe how interpreting each of these types of historical records contributed important insights into the characteristics of the Lake Huron bluff shoreline and its long-term rates of retreat.

Historical Air Photographs

Digitizing bluff crests and toes from historical air photos of the Lake Huron shoreline was a fruitful exercise, as it provided an excellent baseline for which areas were experiencing bluff retreat and how rapidly this retreat was occurring. Air photo datasets depicting the Lake Huron shoreline are typically available approximately once per decade from 1955 to 2020. While three lake level oscillations are fully or partially covered in the 65-year period of the available dataset, the period before 1955 remains missing. Further, the once-per-decade temporal resolution leaves the timing of certain events vague, making it difficult to answer questions about how the bluff face changes in response to erosion of the bluff toe.

Nevertheless, this indispensable dataset, in tandem with more recent digital elevation models, showed that for the last ~70 years, most of the shoreline has experienced minimal retreat. However, some areas, such as Poplar Beach Road, just north of Grand Bend, have seen retreat at rates of as much as 1.2 meters per year (figure 6). The air photo dataset also showed that while some areas saw consistent bluff retreat over the past 70 years, bluff retreat has slowed in some areas (e.g. Bayfield) since the 1950s and hastened in others.

Figure 6: Historical Top-of-Bank Positions at Poplar Beach: 1955 – 2022.

Historical Postcards, Photographs, and other Artwork

In villages and towns along the shoreline, postcards and photographs depicting the bluff face are abundant in archival collections, dating back to the late 1800s. This allows for the timing of significant events that do not appear in the air photo record, such as the installation of the piers at Bayfield’s harbour in the early 1890s (figure 7). Further, photographs and postcards are often available in years when air photos were not captured. By observing the slope, shape, and vegetation cover of the bluffs depicted in historical photographs and postcards, erosion events can be more accurately timed than they can by using the air photo for the corresponding decade.

Figures 7a and 7b: Postcards showing the mouth of the Bayfield River in the 1890s and 1900s,

A notable finding made possible by consulting historical photographs was that bluff erosion along Lake Huron was occurring in years where lake level was not at its highest. For example, a photograph in a news clipping from August 12, 1969, reveals that notable bluff erosion occurred that summer (figure 8), a year when Lake Huron’s water levels were at their historical average. However, closer examination of the hydrograph reveals that while lake levels were average that year, they were quickly rebounding from historic lows in the mid-1960s. This suggests that bluff erosion is a consequence of rapidly rising, rather than high, lake levels, something that has been noted by other scholars.2

Figure 8: A news clipping showing bluff erosion near Bayfield in August 1969.

Artworks depicting the shoreline can also provide valuable information. Figure 9 shows a painting by Joan Truitt, which depicts part of the shoreline in Bayfield as it was in the 1930s. The point of land shown in the painting (Poplar Point) no longer exists today but is remembered by many longtime Bayfield residents.

Figure 9: Painting of Poplar Point from the south by Joan Campbell Truitt. Bayfield’s south pier can be seen to the north in the background.

Historical Newspapers

In addition to images, local newspapers also provide valuable written descriptions of the bluffs. Recently digitized by the Huron County Museum, the archives of the Exeter Times-Advocate, Goderich Signal-Star, and Clinton News-Record include several articles discussing bluff erosion between Grand Bend and Goderich. Most of these date to the lake level rises of the early 1970s and mid 1980s (periods also covered by the air photo record). The September 19, 1974, issue of the Goderich Signal-Star noted that “high water levels in the ground” (interpreted as a lack of infiltration and high surface drainage) were contributing to shoreline erosion near Bluewater beach. The December 3, 1986, issue of the Exeter Times-Advocate shared an eyewitness account where a resident noted that erosion was always worse when winds came from the north or the northwest.

Historical Maps

The southeastern shoreline of Lake Huron was documented, for example, in Belden’s Atlas of Huron County, published in 1879, and Bayfield’s town plans of 1856 and 1835. In the case of Bayfield, all three maps depict a shoreline quite different from the one that exists today, with the bluff jutting out into the lake immediately to the south of the Bayfield River (figure 10). Bayfield’s 1856 town plan shows the bluff crest extending significantly further westward into Lake Huron than it does today. This region includes several lots where land does not exist today, along with an entire street (Bruce Crescent), now gone.

Figure 10: Bayfield’s 1856 town plan shows the bluff crest extending significantly further westward into Lake Huron than it does today. This region includes several lots where land does not exist today, along with a street (Bruce Crescent).

Oral History

The people who know the shoreline best are often those who have lived along it their entire lives. I had the privilege of meeting some of these individuals, visiting their sections of the shoreline, and hearing their accounts of how the bluff changed during the lake level rises of the early 1970s, mid 1980s, and over the past few years. Their accounts included accurate and verifiable distances of bluff toe retreat, the timing of erosion events, descriptions of processes (e.g. drainage, vegetation change, freeze-thaw, beach sand movement etc.) that acted on the bluff, and the impact of shore defenses and even offshore factors (e.g. rocky lake bottoms) on bluff retreat. One resident noted how they had seen a section of their cedar-covered bluff deforested on two occasions due to bluff erosion, only to be recolonized again by cedars during less erosive periods. My conversations with these individuals provided crucial insights not available in the written record or any other dataset.

Combining historical research with meticulous field observation and GIS analysis can expand and reaffirm our understanding of landscapes, creating a more holistic picture. While we will sadly never know how the bluff system worked in its natural form, when there were no shoreline structures and Ontario was much more forested, the historical record can provide valuable insights into how this disturbed system has evolved over the past 190 years, and how it may continue to evolve into the future.

Resources

Notes

[1] Bocaniov, S. A., D. Scavia, and P. Van Cappellen. “Long-term phosphorus mass-balance of Lake Erie (Canada-USA) reveals a major contribution of in-lake phosphorus loading.” Ecological Informatics 77 (2023): 102131. https://doi.org/10.1016/j.ecoinf.2023.102131
[2] Braun, K. N., C. R. Mattheus, and E. J. Theuerkauf. “The geomorphic role of large wood in the coastal zone: Mobilization threshold and beach morphology impacts in the North American Great Lakes.” Geomorphology 411 (2022): 108292. https://doi.org/10.1016/j.geomorph.2022.108292
Featured Image: Lake Huron Coastline, Looking North from Poplar Beach Road (Photo Ben Woodward)

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Ben Woodward

Ben is pursuing an MSc in Earth Science at the University of Waterloo investigating coastal erosion in southern Lake Huron. Ben is the creator of the Local History Atlas of Canada, a dynamic web map showcasing the history of Canadian communities. Ben also contributes to the Canadian Geography Workshop Series, and is a fellow of the Royal Canadian Geographical Society.

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