River bank stabilization policies are currently being reconsidered in many areas, because of the increased awareness of the unsustainable nature of many historic techniques (steel barriers etc.) and also the somewhat recent acknowledgement of the role bank erosion plays in providing important ecosystem services to an area (Piegay et al. 2005). This has left river managers seeking to preserve bank erosion inside what is known as the “defined erodible corridor.” Which is basically a set of guidelines which allows rivers to migrate freely within a defined corridor, limiting any potential serious hazards. This erodible corridor concept uses more of a biotechnical engineering approach, instead of traditional engineering and hard-armored methods, and may be a good solution for the Don River at Glendon Campus (Li and Eddleman 2002).
For this Project, my partner Arnab and I arrived to Glendon Campus around 11:00am in November 22, 2016 one of the coldest days of the year so far. Our 100m section, segment 12 was the most southern and eastern segment of the Don River assigned (Figure 1)
We started our documentation of the river banks at the most north-west point, and proceeded south-east, downstream. Right from the start of our segment, we found clear signs of erosion. Although this sand/silt section may provide perfect turtle nesting area, it is a clear sign of heavy erosion, and plants cannot survive. Following this section, erosion became more and more evident through various severe bank slumping signs, and severe undercutting of river bank trees. The undercutting will eventually lead to tree and plant mortality, which will remove their root systems that are important for stabilizing the banks, and in turn lead to more bank slumping. There were 2 different techniques of previous bank stabilization: gabions and large rock boulders (Li and Eddleman 2002). However, no signs of vegetation stabilization techniques were observed, such as: live stakes, fascines or crib walls, joint planting or geogrids (Li and Eddleman 2002).
There is no doubt that some action needs to be taken place, as the banks of the Don River at Glendon College are severely slumping, leading to the degradation of the river. There have been past stabilization methods observed in this section which have proven very effective for simply stabilizing the banks. However, they do not provide important habitats for various aquatic and terrestrial organisms and plants. However, the large boulder technique is definitely a step in the right direction, in relation to the gabions. In the future, it is my recommendation that a much more biotechnical engineering approach be taken at stabilizing the Don River banks. This type of approach would incorporate specific planting zones, with specific materials and plants in each zone which would provide the best of both worlds, bank stabilization to prevent slumping, and important habitat to preserve biodiversity.
Toe zone- bank portion between bed and average water height
Splash zone- bank portion between normal high-water and normal low-water levels
Bank zone- bank portion above normal high-water levels
Terrace zone- bank inland from the bank zone
By incorporating these zones, river bank stabilization can be much more effective and ecologically efficient.
Piegay, H., Darby, S.E., Mosselman, E. and Surian, N. (2005). Review of techniques available for delimiting the erodible river corridor: a sustainable approach to managing bank erosion. River Research Applications. 21: 773-789.
Li, M.H, Eddleman K.E. (2002). Biotechnical engineering as an alternative to traditional engineering methods: a biotechnical stream bank stabilization design approach. Landscape and Urban Planning. 60: 225-242.