Don Riverbank Assessment – Segment 7

On Thursday November 24th, Barry and I decided to take a trip to the Glendon campus to assess the segment of the Don Riverbank assigned to us. We were assigned segment 7 of the river, which was conveniently located North of the Glendon Athletic Club, as shown in the map below.

segment-7

We arrived at Glendon at approximately 4:12 PM, and we located the segment of the river at approximately 4:25 PM. It was a rather cold day, as temperatures were around 7°C. Segment 7 of the river is located between a winding road that curved downhill to lead to the F parking lot, and the F parking lot itself. This segment begins where the red bridge is located, and ends at the part of the river that corresponds to the curve of the winding road. For better clarification, the beginning and end are indicated in the figure below:

beginning-and-end

The following image indicates the approximate coordinates of where our photos were taken.

Coordinates.PNG

We began by taking photos from the south side of the river, facing the athletic centre. Please excuse the fact that as each photo was taken, the series of photos progressively got darker due to the sun setting.

Upon analysis of these photos, we noticed that the riverbank was slumping. There is evidence of previous bank stabilization in this segment of the river. One previous stabilization effort can be seen under the red bridge at the bridge abutments, where riprap is present. Riprap involves the piling of stone fragments to form a foundation to protect the riverbank from scour. The BC Ministry of Environment states that riprap is a  widely used stabilization technique that is durable and often readily available. However, some drawbacks of riprap is that they are not suitable for steep slopes, and they may also damage aquatic and riparian habitats. Also, some people generally find ripraps to be unappealing to the eye.

Further evidence of previous stabilization efforts can be seen in the photos since gabion baskets are present. Gabion baskets are the wire baskets filled with rock. They are typically used to protect banks and stabilize slopes (Freeman and Fischenich 2000). As we can see in the series of photos, the gabion baskets at this section of the riverbank were located directly on a slope itself. The wire is often galvanized (coated with zinc) to prevent rusting. An advantage of gabion baskets is that they require about one third of the thickness of materials compared to ripraps. However, riprap is often preferred as it is less labour intensive to place.

The following series of photos were taken from the north side of the Don River, facing the F lot parking lot.

We took close-up photos of the gabion baskets when we reached this side of the river. The last three photos of the series provide an overview of the segment we were analyzing – these photos were taken uphill of the path leading to the parking lot. Upon arriving on the south side of the river, we noticed that there were lots of debris present. The debris shows the impacts that humans can have on these riverbanks, which is very difficult to look at. Seeing all the debris that may have been carried down here by wind or by reckless individuals, it got us thinking that a lot more debris must be present at the other segments, since it is often a difficult and out-of-the-way task to climb down the slumping riverbank carefully in order to pick up the garbage.

We noticed that both sides of the riverbank had retaining walls. Retaining walls serve to hold back a slope in attempt to prevent further erosion (Kosiw et al. 2008). Typically, concrete is used, as in the case of this segment of the riverbank. Barry and I have also noticed that these retaining walls appear to be damaged, thus making us question if they will be restored. The retaining walls at the north side of the river appear to be fine, however; they appear to be defective on the south side, as the concrete pieces are no longer level with one another. We hope to see that these retaining walls will be repaired.

Overall, this trip to Glendon has provided Barry and I some insight to the condition of this particular segment of the Don River. We would like to see more gabion baskets being incorporated, as there was only a small section of the riverbank that was stabilized by a gabion basket. It was great to see that bank stabilization has already been implemented, however; we hope that the retaining walls will be repaired on the south side of the river!

References

The BC Ministry of Environment, Lands and Parks. 2000. Riprap design and construction guide. [Online]. Available http://www.env.gov.bc.ca/wsd/public_safety/flood/pdfs_word/riprap_guide.pdf

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.

Kosiw M., Parks K., Besley S. Solutions to riverbank erosion: A summary of current shoreline stabilization techniques for the Gull River in Minden, Ontario. [Online]. Available http://www.haliburtoncooperative.on.ca/literature/sites/default/files/TP-584_Solutions_to_Riverbank_Erosion.pdf

 

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