On very early Sunday morning, my partner Nick and I ventured to Glendon once more to observe the Don River that follows through the campus. We were assigned segment 8 of the river which was near enough to the school so there was not too much trekking through the woods and had a very active walking path running alongside the river.
In our section it became immediately evident that there was previous bank stabilization effort as evidence of the rocks materials (ripraps, loose rocks staked or laid down along a riverbed) used to for structuring against erosion. But it has unmistakably failed or done little work to stop soil erosion in the area. The main issue that the rocks have no clear structure or working to their highest potential. The main problem is that the rocks have moved from their primary set location which defeats the purpose of them being put there in the first place. Some sort of system like a caged riprap or gabion is needed to actually retain the soil and plants that are slumping into the riverbed (Arquitt, Johnstone, 2008).
Previous Rock retaining wall
Soil erosion was a major issue in our area as we found multiple regions that plant roots were not anchored to anything and exposed to air. Vegetation roots can provide stability to stream banks but this stabilization disappears once there is not soil which leads to over-widening of the stream and increased bank sedimentation (Donat, 1995). Unstable banks lead to lateral erosion which increases stream width while decrease stream velocity leading to sediment deposition (Valko et al, 2011). At Glendon, we were not able to claim if the vegetation with the roots exposed was deceased or not. We visited the campus at the end of November, by then all the leaves had fallen from the trees which would have been a clear indicator if they were alive or not. One could hypothesis that they are still alive as only a section of their roots (ones facing the riverbed) were exposed.
Evidence of root exposure
How to restore the area?
The retaining wall in our region failed its job as a retaining wall. To stop the slope slumping is adding either a caged riprap or gabion, both would serve a similar function of holding the rock or other material in place. At the moment, the rocks in the area are hardly doing anything to stop soil erosion or caving in of the bank therefore new structure needs to be put in to hold the bank in place.
Stock photo: http://www.alamy.com/stock-photo/sandbank-dorset.html
Other remediation effort should be adding in further vegetation to retain the soil as the vegetation at the moment is failing. It was found that willow trees as they have a large root system function well for the purpose but other tree or shrub species can function the same way (Donat, 1995).
Arquitt, S., Johnstone, R. (2008). Use of system dynamics modelling in design of an environmental restoration banking institution. Ecological Economics. 65(1) :63-75
Donat, M. (1995). Bioengineering Techniques for Stream bank Restoration A Review of Central European Practices. Ministry of Environment, Lands and Parks. 32: 1-86
Valko, O., Torok, P., Tothmeresz, B., Matus, G. (2011). Restoration Potential in Seed Banks of Acidic Fen and Dry‐Mesophilous Meadows: Can Restoration Be Based on Local Seed Banks? Restoration Ecology. 19(101): 9-15