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Slope gradient, soil texture, and ground vegetation affecting erosion in the Lovers Creek Ravine

Slope gradient, soil texture, and ground vegetation affecting erosion in the Lovers Creek Ravine

Jack Finlayson

Lovers Creek is a notable subwatershed that is part of the Lake Simcoe watershed. It is one of several that pass through the City of Barrie’s residential areas in order to connect to Lake Simcoe. Sections of Lovers Creek are characterized by ravines that are regularly accompanied with recreational trails along the slopes or fields. The City of Barrie has demonstrated concerns regarding the erosion in the area due to the profile and soil conditions of certain slopes and the vertical profile of the creek as it meanders. This has resulted in the city developing a plan that would subdue the intensity of erosion caused by the creek or along the slopes.

There are numerous factors that contribute to erosion, however this study focused on slope gradient, ground vegetation cover, and soil texture. While these factors were selected primarily because of the equipment and time that was available for the study, they remain relevant to the on-going erosion issues at Lovers Creek. Erosion involves the natural transportation of material, altering an area over time. In the case of the Lovers Creek Ravine, the slopes and streambanks are being eroded away, causing greater amounts of sediment deposition in the creek and recreational hazards as the trails along the slopes weaken.

The study aimed to examine the potential causes for slope and streambank erosion and the impacts they may have on the slopes and creek. Given the City of Barrie’s responses and proposals to the issue of erosion in Lovers Creek, it can be assumed that erosion is currently a constant feature of the ravine, deterring the safety and environment of the area. Therefore, it would be beneficial to classify sections of the ravine that would be more susceptible to erosion, thus requiring municipal attention before the area is damaged.

Expounding on his field work experience: "I spent multiple days at the research site adapting to the landscape and difficulties of the terrain to best acquire data. It transitioned me from the strictly hypothetical aspects of geography to the reality of it, something I found myself enjoying despite the challenges" says Finlayson.

"I am particularly interested in GIS and urban studies, such as transportation systems and public space studies. Conducting field work is enjoyable to me as I like to be outside in nature, in both scenic and remote areas. Being able to study geographic processes in different parts of the world is one of my greatest interests; the farther away from places I'm familiar with, the better," he adds.

Figure 1. 500m scale of Lovers Creek Ravine study area, the surrounding residential areas, and Lake Simcoe

Study Area
The area of Lovers Creek Ravine that was studied was an approximately 50m-long strip along both sides of the creek that began by the entrance to the trails on Hurst Drive. It is less than two kilometers away from the creek’s end connection to Lake Simcoe (Figure 1). The first of the four distinct zones is characterized as a steep slope with ground vegetation. The second zone is a steep slope without any ground vegetation. The third zone is a gentle slope with ground vegetation. Finally, the fourth zone is a gentle slope without any ground vegetation (Figure 2).

Identical data collection methods were performed for each of the four zones. A profile of each slope was constructed using multiple measurements of both the length and degree of the slope. The data was collected starting at the streambank and concluded once the trail at the top of the slope was reached. Additionally, the vertical distance from the streambank to the creek was collected. These measurements for each zone also allowed for the average gradient, the percent ground vegetation cover, and the soil texture types to be plotted on top of, or alongside each profile.

For ground vegetation cover percentage, a maximum of four 2x2m quadrats were constructed along each slope, once again starting at the stream bank and concluding when the trail at the top of the slope is reached. Each 2x2m quadrat was divided into four 1x1m sections, achieving a total of 16 samples. The distance between each 2x2m quadrat plot was recorded so that it can be presented on the slope profile. A photo was taken at the zenith angle of each 1x1m section for later analysis. The analysis included overlaying a 5x5 square grid overtop of each image in order to estimate the total percent of ground vegetation cover. To determine soil texture for each zone, a maximum of five samples were collected from each zone, from the bank until the top of the slope. Afterwards, a soil texture test was conducted in order to determine the composition of sand, silt, and clay for each sample.

Discussion of Results
With the information provided about how slope gradient, ground vegetation cover, and soil texture affect erosion, the least and most susceptible zones were determined. A comparison between zones one and two were made as they both have similar steep slope gradients. Firstly however, when compared to zone three, the other vegetated study area, zone one had much less vegetation cover. Since the soil texture of zone three could be considered weaker for vegetation growth, the reason for zone one having less vegetation could be attributed to the gradient. Less vegetation along the slope could indicate weaker soil and without vegetation the slope is more prone to erosion, especially when considering the velocity that can be achieved from detached material being transported due to the steeper angle.

Figure 2. 50m scale of the Lovers Creek Ravine study area and the four distinct zones

Comparing data collected from zone one to zone two, it can be concluded that zone two is the most prone to erosion. More specifically, this is because of the low amount of ground vegetation cover and weaker soil texture. While zone two does have two silt loams and one loamy sand, which is weaker as it is considered a sand more than a loam, zone one has three instances of loams. Also, zone two’s decrease in vegetation cover to 0.00% as the slope distance increase could result in eroded materials gaining a greater velocity while travelling down the slope as there is no vegetation to stop or slow anything until the bottom by the bank. Since zones three and four do not have the negative factor of a steeper slope, the amount of ground vegetation cover and soil texture were compared to determine which is most susceptible. Zone three has considerably more ground vegetation cover than zone four. Although this may be able to prevent erosion slightly, since the factor of gravity is not as applicable as it is on a steep slope, the soil texture may be a more important factor. Zone four has much more consistent and strong soil when compared to zone three, which has more sand content overall and would therefore be more susceptible to erosion. Given the data collected however, there is no way in which a certain conclusion can be made on whether zone three or four is the least susceptible in reality. Although, if only the factors of slope gradient, ground vegetation cover, and soil texture were considered then zone three would be least prone to erosion as the slope has a gentle inclination, great ground vegetation cover, and an overall strong soil texture.

Since erosion is a continual process, it is important to study which areas may be the most vulnerable, not just the amount that is currently occurring. This is especially important within the Lovers Creek Ravine, as it allows for proactive municipal intervention before an area is too negatively affected. In this case, that would include the destruction of recreational trails, causing potential hazards and the loss of natural vegetation such as trees and also the amount of sediment deposition within the creek. Given each of the four distinct zones and the factors within this study, it can be concluded that the most susceptible area for erosion in the Lovers Creek Ravine are areas with a steeper slope gradient, little to no ground vegetation cover, and a high proportion of sandy soil or an absence of loamy soil. In the context of this study, zone two, the steep slope with no ground vegetation cover, would therefore be considered the most vulnerable. Conversely, zone three, the gentle slope with substantial ground vegetation cover, would be considered the least vulnerable.

Despite these results, the many factors that were excluded from this study may have an even larger impact on the causes of erosion than the factors that were studied. For example, fluvial geomorphology involves the interaction of running water and the landscape, which in this case would be Lovers Creek and the ravine. As the creek traverses through the ravine, it is eroding part of the streambank of zone four which is why there is a significant drop-off from the streambank to the creek. While in the context of this study, it was debatable over zone three or zone four being the most resilient with regards to erosion, this example showcases how other factors may have a larger impact than those studied and should be taken into consideration. Future studies on erosion within the Lovers Creek Ravine should expand the number of factors taken into account to better understand the relationship of the ravine slopes with the creek and what makes an area most vulnerable. This will also improve the accuracy and design from the municipality to ensure that the environment of the area is protected.

Jack Finlayson is a fourth year geography student at York University and will be graduating in April 2022. The study was the basis of a field studies course in Physical Geography under Prof. Kathy Young.