Royal Rouge Trail Erosion Control Project - Toronto and Region ...

2. Concept 2 – Extended Retaining Wall and Trimming
These options were formally reviewed and discussed by the Community Liaison Committee
(CLC) at Meeting #1, held on the evening of June 18 th , 2009 at the Tall Pines Community
Centre located at 64 Rylander Boulevard in Toronto, Ontario. A description and evaluation of
the preliminary alternatives follows. The evaluation includes an examination of the types and
extents of impacts, both positive and negative, of each alternative.
4.1.1 “Do Nothing” Alternative
The “do nothing” option is a mandatory alternative that must be considered in the Class EA
process, as it is used to justify the need to undertake a remedial flood or erosion control
project. Should the “do nothing” option, or other Conservation Authority programs such as
land acquisition be deemed to be a more acceptable solution, then there is no further
consideration for remedial action and the Class EA process terminates.
Under the “do-nothing” alternative recession is expected to continue until the slope reaches a
stable inclination, referred to as the long-term stable slope crest (LTSSC), which would result
in loss of a significant portion of the existing tableland, and an additional amount, including
two existing swimming pools, being placed within the erosion hazard limit. In general, the
recession rate was calculated to be approximately 0.18 metres per year. The following table
provides an estimate of the projected length and time it will take for each of the properties to
recede to the LTSSC:
Table 12. Estimate of Time to Long-Term Stable Slope Crest.
Lot No.
Total Projected Crest Loss (m)
Time Estimated to
LTSSC
LTSSC
LTSSC (years)
(Vegetated Slope) (Bare Slope)
30 4 7 20 to 40
32 4 7 20 to 40
34 4 7 20 to 40
36 5 8 15 to 20
38 2 5 10 to 25
40 5 8 30 to 45
42 3 5 15 to 25
44 6 9 30 to 50
46 9 11 5 to 15
48 9 11 5 to 15
Source: Terraprobe, 2008.
Figure 18 shows the anticipated position of the slope crest in 100 years, based on an
average annual recession rate of 0.18 m / yr away from the instability of the valley wall. It
should be noted that the planning horizon for the do-nothing scenario is 100 years.
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Project Plan
Toronto and Region Conservation Authority
Royal Rouge Trail Erosion Control Project January 2010