Two weeks ago on Thursday, November 24, 2016, Bonnie and I had quite the adventure visiting YorkU Keele Campus’ beautiful sister campus, Glendon. Fun fact: there are ghost stories about the campus. We were assigned to survey and take pictures of segment seven of the Don River, located behind the Proctor Field House and right by the bridge to the large parking lot nearby. The coordinates of the checkpoint were 43˚43’46″N, and 79˚22’36″W.
We arrived around 4:15-4:20 pm, it was a very windy and chilly day as the average temperature was 3˚C and began to make way for segment Our after locating and cross-referencing Google Maps with the Glendon Campus Map. While on the way to the checkpoint, we noticed that the this was part of the main hiking route with Dawn, as it was right beside the main staircase that was taken down the field house and by the red bridge and car entry/exit. Our checkpoint began southwest of the red bridge and ran up towards the northeast of the Don River.
We started taking photos as we trekked northeast from the red bridge. The riverbank was definitely slumping, as we took pictures I noticed that there were previous attempts to restore the bank. Ripraps (stacked rocks along a riverbank) were sparsely spread across the riverbank and seemed to hold back some of the parts, but they were not enough as the soil slumped over more of the stone and pushed elsewhere (Lee et al., 1997). Retaining walls were also used, but they too failed to hold back the eroding bank (Hassiotis et al., 1997). This has been particularly true for some of the northern parts of the riverbank as well as for the majority of the southern section as well. Additionally, gabions were used, however, proved to be much more effective as shown below and because they are a more intricate system of rock and wire (Norman et al., 2014).
Unfortunately, these attempts proved to be futile, as there was a multitude of riverbank areas that slumped. Some living vegetation began to sink into the river; however, there were also many fallen/dead trees and vegetation in the river that accumulated along the edges of the bank. There were also roots of trees exposed to the air, thus explaining why some of the trees looked dead (regardless of winter) including into the river. There were also some signs of human interaction/littering, meaning that humans hanging out and drinking by the bank may have also led to more slumping due to the traffic.
Disclaimer: Please excuse some of the pictures (it got dark very quick).
What can we do to remediate the land?
An excellent solution to the slumping river is to add in more metal wire gabions to further hold the slumping bank for critical areas that are prone to falling to make a greater difference in riverbank stabilization (Norman et al., 2014).
The use of coir (coconut fiber) sheets is also an excellent stabilization technique. These sheets are made out of the husks of coconuts, which are processed and interweaved into large sheets. These sheets protect the soil from excessive moisture and consequently, from the erosion of the upper layers of the soil. This will allow the natural vegetation or other plants used in the stabilization process to grow and set more of their roots, as the soil will have an increased bearing capacity proven by Chaple and Dhatrak in 2013 on clayey soil.
An additional preventative measure can include the planting of willow or poplar trees, whose extensive root systems can be used to lock in soil and further prevent the slumping and slow land-sliding of the Don Riverbank though Glendon. Planting these trees and/or shrubs should not impede on the biodiversity of the land as there are native willow and poplar species found in the GTA. These plants are very effective when used with ripraps as Wilkinson discussed in 1999.
By using a combination of the methods listed above and using these methods on critical areas of slumping, the stabilization of the riverbank may be expedited, and recovery may begin.
Until next time, Barry out!
Chaple, P. M., & Dhatrak, A. I. (2013). Performance of Coir Fiber Reinforced Clayey Soil. The International Journal Of Engineering And Science, 2(4), 54–64.
Hassiotis, S., Chamean, J. L., & Gunaratne, M. (1997). Design method for stabilization of slope with piles. Geotechnical and Geoenvironmental Engineering, 123(April), 314–323.
Lee, J. M., Nahajski, A., & Miller, S. (1997). RIVERBANK STABILIZATION PROGRAM By Joan M. Lee/ P.E., Anthony Nahajski/ and Sky MiIler,3 P.E., Members, ASCE. Journal of Water Resources Planning and Management, 123(October), 292–294.
Norman, L., Villarreal, M., Pulliam, H. R., Minckley, R., Gass, L., Tolle, C., & Coe, M. (2014). Remote sensing analysis of riparian vegetation response to desert marsh restoration in the Mexican Highlands. Ecological Engineering, 70, 241–254. https://doi.org/10.1016/j.ecoleng.2014.05.012
Wilkinson, A. G. (1999). Poplars and willows for soil erosion control in New Zealand. Biomass and Bioenergy, 16(4), 263–274. https://doi.org/10.1016/S0961-9534(99)00007-0