Don river bank stabilization: current progress at Glendon College

Although the process of bank erosion in rivers can be found to integral of the overall functioning of rivers (promotes vegetation succession, creates dynamic habitats for species etc); generally people managing these areas try their best to prevent this (Florsheim et al., 2008). Various techniques can be used to do the latter. Today I’ll be sharing my views on a particular 100m of the Glendon River Bank; what has been done, and what can be done.

My partner, Raquel and I arrived at Glendon College around 2:30pm on Wednesday November 16th. The weather was rather cloudy and glum, and it was slightly chilly and windy although the temperature was still above 0ºc. On neither side were not any direct trails to approaching the bank sides. Our section was indicated as Section 6. It was slightly North-West of the Glendon Gallery, and West of the bridge that leads into the parking lot F. Essentially we observed from the bridge, to the first bend on the stream, in the Western direction. Our segment is circled below:

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(2:37pm) From standing on the bridge, we noticed the left side of the stream had some previous restoration efforts done to keep the bank from slumping. There was a mass of piled, slated type stones that only went for a small portion of the bank (~10-15m). In this section of the steam there was also a completely fallen over dead tree. The rock wall is similar to gabion type structure, although without the caging aspect (usually has a wire cage full of stones of some sort). Although, a portion of this stone structure (directly under the clump of trees) has completely fallen a part, most likely into the water. This area just be restored to meet the standards of the rock wall in the other parts of this small segment.

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(2:37pm) Still standing on the bridge, now looking at the right side of the river bank, we see no similar gabion type structure in this area. The bank is very low and and seems very level (slumping into) with the water. Although, a lot of woody tree species are planted on this side of the bank, which can be considered as another erosion preventative method. The planting of trees and shrubs along bank sides has been used as an “afforestation” technique in order to secure banks and slopes (Evette et al., 2009). Perhaps this method was successful earlier in time, but it doesn’t necessarily appear to be currently. However, having the land relatively level in terms of height, of the river, could be beneficial for many species to access.

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(2:37, 2:38pm , 2:39pm) More towards just before the first curve, and throughout the curve of the steam on the left side, we see a complete gambion structure (caged rocks) along the bank-side. This structure continues for the remainder of our portion of our segment, on the left-hand side of the bank. Gabions are often used when there isn’t already enough available (or large enough) rock to withstand erosive pressures and forces (Freeman & Fischenich, 2000).  In this particular portion of the segment, there is some abnormal tree growth just outside the gambion structure (as you can see in both of the following photos). The conditions might not be good for the tree, but it could provide some sort of habitat for other species.

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(2:42) The area of the bank just before the curve, on the right side,  is not as level as it was towards the bridge, although continues to have no stabilization like the left side, and continues to slope into the river. Less tree species seem to be planted in this portion of the segment, in comparison to near the bridge. This area definitely seems more tiered, is much taller, and is more like a coastal shelf, in comparison to the portion near the bridge (same side).

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(2:42pm, 2:42pm) When we get to the curve of the stream, the right side of the bank seems to be more stabilized then the previous portion of the segment. It’s not level with the water, it’s tall, and although tiered like the previous photo, it’s not as layered, and doesn’t slope like it does before the curve of the stream. There still appears to be previous stabilization efforts (i.e such as a gambion) on this side of the bank. Although, in the curve, unlike just before the curve, there is an abundance of planted trees again along the  bank side (this could have been an intentional restoration effort strategy as previously mentioned).

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It is evident that previous efforts have been done in portions of this river, more concentrated however to the left side. As the restoration efforts appear to have worked, the right side seems to require an equal amount of consideration at this point.

References: 

Evette, A., Labonne, S., Rey, F., Liebault, F., Jancke, O., & Girel, J. (2009). History of bioengineering techniques for erosion control in rivers in Western Europe. Environmental Management, 43(6), 972-984.

Florsheim, J. L., Mount, J. F., & Chin, A. (2008). Bank erosion as a desirable attribute of rivers. BioScience, 58(6), 519-529.

Freeman, G. E., & Fischenich, J. C. (2000). Gabions for streambank erosion control (No. ERDC-EMRRP-SR-22). ARMY ENGINEER WATERWAYS EXPERIMENT STATION VICKSBURG MS ENGINEER RESEARCH AND DEVELOPMENT CENTER.

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