Mapping Elevation Changes in Coastal Sand Dunes

Coastal sand dunes provide important ecosystem services that are often overlooked, with their value becoming especially apparent in their absence. These services include protection of the coast, plant and animal species such as the endangered piping plover, as well as prevention of erosion from rising sea levels or high winds. Figure 1 shows a coastal sand dune at Wasaga Beach. To learn more the importance of sand dunes, click  here , and to learn more about the piping plover, click  here. 

To ensure that the ecosystem services of dunes are preserved, multiple methods of mitigation can be put in place to help them recover sand over time and hopefully stabilize. One of these methods is sand fencing. Sand fencing allows sand being moved by the wind to be deposited after hitting the fence, building up gradually until the fence can be scaled down or removed altogether (Lake Huron Coastal Centre, 2023). Figure 2 shows an example of sand fencing at Wasaga Beach.

Vegetation is another method, with the roots of plants, often beachgrass, securing sand in its place and making it less likely to be blown away (Lake Huron Coastal Centre, 2023). By fencing off these areas of beachgrass, trampling is reduced and the plants can grow without potential damage from humans. Figure 3 shows a fenced-off area of beachgrass at Wasaga Beach. Similar perimeters have also been set up around piping plover nests to ensure beachgoers do not get too close. To learn more about sand dune stabilization techniques, click  here. 

This project centres on the comparison of elevation data at two beach sites over two years. The two sites focused on are home to essential sand dunes that have been threatened, but are now the centre of mitigation and restoration efforts. These two sites are Burlington Beach and Wasaga Beach, with Figure 4 showing their locations. Combined, the two sites attract millions of visitors every year (Ontario Parks, 2023), putting them at greater risk of damage and misuse.

By assessing the growth or reduction of the dunes, we can better understand whether current stabilization efforts are having a positive impact or not.

The objective of this project is to utilize ArcGIS Pro to showcase the transects at each data collection site, allowing us to then compare profile graphs of the most closely recreated transects over the two years of field data collection.

The data used in this project consists of GNSS points with easting, northing, and orthographic height information, as well as the average height of the lake and the quality of the collected points. The points were collected by myself and other student research assistants in 2022, where we learned to use a Leica GS16 rover, shown in Figure 5. The goal was to recreate the data collected by other students in 2021 and allow for annual comparison.

Figure 6 shows both the 2021 and 2022 transects at Burlington Beach, while Figure 7 displays them at Wasaga Beach. The transects are directly overlayed on top of each other to show the variation in their locations. Some were only completed in either 2021 or 2022, meaning they cannot be the subjects of comparison.

While a GPS was used to locate the more or less exact starting and ending points of each 2021 transect in 2022, we can see that it was easy to veer off course, resulting in a curved transect. This was corrected as more transects were completed, as students became more familiar with the rover and made sure to be aware of the direction of their walking path.

GNSS utilizes the interconnected web of satellites currently orbiting Earth, with the rover receiving signals and determining its own location based on how long these signals take to travel (Global GPS Systems, 2023). Though, when trees, hydro lines, or other obstructions are present in the study area, the quality of data can be reduced, or the rover could fail to receive the signals altogether. Figure 8 illustrates the difference in quality across one of the 2022 Burlington Beach transects, with darker points corresponding to lower quality and lighter points corresponding to higher quality. Fortunately, all of the points were of high enough quality (> 0.05m) so that none needed to be omitted. We can see a clear correlation between quality and tree cover, with quality greatly lessening when satellite signals cannot reach the rover as easily.

Figures 9 and 10 use a method of interpolation, inverse distance weighted (IDW), which uses known elevation values to infer what the surrounding values will be. Figure 9 shows this method at Burlington Beach, while Figure 10 shows it at Wasaga Beach, both for transects that were closest in location and most accurate to each other. To learn more about how IDW works,  click here .

Figure 11 is a direct overlay comparison between the 2021 and 2022 profile graphs at Wasaga Beach. While a profile graph with both years overlayed could have been made for Burlington Beach, the fact that the transects were not recreated closely enough made a potential graph misleading, as it appeared that the beach had greatly changed in just one year when that was not the case.

By looking at the interpolation for Burlington Beach, we can see that there were positive and negative developments. Areas of higher elevation increased closer to the water which is positive, but the maximum elevation dropped overall. The shape of the dunes have remained largely the same, which signals that no big weather events occurred that set back the growth of the dune.

At Wasaga Beach, the interpolation shows that the maximum elevation stayed mostly constant, not dropping more than 1masl, and the minimum elevation decreased overall. In the profile graph, approximately 45m from the profile start is an area of interest, as the elevation noticeably increased from 2021. This transect saw overall positive development, which signals that mitigation efforts are helping the dune to retain sand.

While the Burlington Beach and Wasaga Beach transects did vary in location and detail, by using interpolation and profile graphing, clear comparisons could be made to get a better of idea of their progress.

So the question is, why should you care? Well, ultimately, sand dunes play an important role in protecting human and natural landscapes from erosion and help us to recover from intense storms that are only getting more frequent with the worsening of climate change. By being aware of the impacts of losing valuable sand dunes and of the kinds of mitigation efforts that are in place, we can be more conscious visitors to beaches that make sure not to interrupt dune growth.

Global GPS Systems. (2023, May 12). GNSS constellations: How They Work and How They Improve GPS. Global GPS Systems. https://globalgpssystems.com/gnss/gnss-constellations-how-they-work-and-how-they-improve-gps/#:~:text=How%20Does%20GNSS%20Work%3F,its%20distance%20from%20the%20satellite.

Lake Huron Coastal Centre. (2023). Beach and Dune Stabilization. Lake Huron Coastal Centre. https://www.lakehuron.ca/beach-and-dune-stabilization

Ontario Parks. (2023, May 19). How to plan your visit to Wasaga Beach Provincial Park. Parks Blog. https://www.ontarioparks.com/parksblog/wasaga-beach/#:~:text=Wasaga%20Beach%20Provincial%20Park%20is,2%20million%20visitors%20every%20year!