Chapter A - Introduction - City of Pickering

Comments in white are satisfied.
Comments in orange background are not satisfied or are new comments.
Comments in blue background can be addressed at the NFSSR stage.
Comments in yellow are deferred due to need for hydrology model.
APPENDIX A. TRCA COMMENTS ON SEATON MESPA DECEMBER 2011; MESPA TEAM RESPONSE FEBRUARY 2013
# Section #
Page # in
PDF TRCA Comment Action Required
an appropriate approach to flood plain
management.
36. 5.5.1.2 146 The study limit for the flood plain maps completed
as part of the Existing Conditions Report does not
cover the entire area slated for development. The
flood plain mapping exercise should be extended
to cover areas where there is no mapping to
confirm the limits of development and ensure the
proposed SWMFs are located outside of the flood
hazard limit and buffer. We are concerned that
the current plan calls for a number of SWMFs
located within or within close proximity to the
Regional flood plain.
37. 5.5.1.2 146 This section suggests that flood lines can be
increased as long as they are contained within the
NHS. The requirement in the Terms of Reference
is to ensure no impacts to the Seaton NHS and
downstream as it relates to flooding. The
Province as the owner of the NHS needs to be
aware of and accept any potential impacts.
38. 6.2 152 The proposed buffers from the SWMF and
associated grading to natural features are not
provided, eg.10m from woodlands, etc. per the
policies in the City’s Conformity Amendment.
39. 6.2 152 The SWMF locations and outfalls will need to be
reviewed in the field to ensure the locations are
appropriate. Some of the proposed SWMFs may
not have an appropriately safe and secure outfall
given side slopes and location of the SWMF.
40. 6.2 152 Encroachment of SWMFs into NHS corridors
should be restricted to no more than 25% of the
functional corridor width.
Complete a comprehensive flood study that
includes areas where previous flood plain mapping
was not completed. Please see Appendix B, Peer
Review Comments related to the surface hydrologic
analysis, specifically comments 6 for further details.
Revise to state that an increase in flooding within
the NHS must be assessed for impacts to natural
features and functions and appropriately mitigated.
Confirm that these buffers have been reflected in
the matrices.
This should take place as soon as possible. Site
visit days should be set up well in advance.
Revise the SWMF design and location to
accommodate this criterion.
Consulting Team’s Response
April 27, 2011
Acknowledged. A separate study is being
prepared to update the 2006 Seaton floodplain
mapping study.
Potential for increases in the NHS is being
assessed as part of the regional storm control
analysis. If increases are identified, increases to
natural features and functions will be assessed.
The buffers applied were as discussed in
Section 6.2. Floodline and meander belt buffers
to be added to the discussion.
Acknowledged. Site visits are being undertaken,
some of which will be undertaken after the
MESPA is completed.
This criterion impacts only a few SWMFs. Each
location is under review to determine whether
the 50% intrusion can be reduced.
Action Taken
MESPA December 2011
As discussed in Section B5.10.2, updates to the
floodplain mapping completed in 2006 have been
made to extend hydraulic models and floodline
mapping upstream along stream reaches in
Seaton.
See response to comment #33, above.
MESPA reflects the additional buffers and policies
of the City’s Conformity Amendment (Section B6.2
and SWMF matrices).
This is an NFSSR requirement. Where site visits
have been completed, appropriate changes to
matrices are made in the MESPA.
SWM matrices are revised to address the outcome
of assessment at each location.
TRCA Comment on MESPA
A detailed review of the geometric components
of the floodplain mapping has been provided in
our letter of October 19, 2012. There appears to
be sections missing from the study.
Not yet addressed. Comment #33 suggests no
resolution has been made with the agencies yet.
The flood impact analysis is subject to the
revisions associated with the hydrology update.
However, the current analysis involves a local
increase in both flows and water levels in
Whitevale Creek, which the TRCA cannot accept
based on the information provided. TRCA does
not agree with the arguments put forth that this is
acceptable (See New Comment, above, related
to Section 5.9.3.4). The proponent will have to
establish that no impacts to the Seaton NHS and
downstream will occur due to any changes in
hydrology.
If the proponent can show that these increases
are acceptable to all stakeholders (Province,
TRCA and City of Pickering), TRCA would
expect that a figure be created outlining any
changes in water levels and/or depths of greater
than 0.1m within the entire study area in order to
delineate all changes in the floodplain (any other
possible impacts) before agreeing that no flood
risk exists through a local increase. TRCA
needs all of the information available to
understand and accept any changes to water
levels and flood depths before assessing
impacts at the site level.
Noted.
Noted. See detailed comments on individual
SWMF locations below.
Duffin Heights was a completely different case
and was based on a very old MESP, and the
pond restricting half of the width of the corridor
was a best-efforts scenario. This was largely
Team Response
February 2013
The comments have been reviewed and
will be addressed as part of the Floodplain
Mapping Update, Seaton Lands (March
2013).
The Whitevale Assessment has been
updated based on the 2012 Duffins Creek
Hydrology Update. Refer to Section B5.3.
The hydraulic model has been included as
Appendix B5-C. This model provides the
flood elevations for all storms for all
scenarios. The Table provided in Appendix
B5-C provides the change in elevation
resulting from no controls on Whitevale
Creek. The changes in flood elevation that
are greater than 0.3m have been
highlighted in red. Please note that the
flows utilized in this analysis are from the
2012 Duffins Creek Hydrology Update. As
such the flows are higher because the
model does not include the ponds located
north of Highway 407 which will have
quantity controls. So it can be assumed
that north of Highway 407 there will not be
any changes in flood elevation.
Additionally, the model does not include
the proposed culvert improvements at
Whitevale Road that will reduce the flood
level increases. The changes in flood
elevation for the 2 through 100 year storm
events, spatially are very difficult to
distinguish on a figure or drawing. It was
felt that the analysis of the actual flood
elevations and changes in flood elevation
are more useful for this analysis. As such
the 2-100 year flood elevations were not
mapped.
The reference to Duffin Heights has been
removed. The few instances where the
25% target has not been met are further
discussed in Chapter B6.3. Recognizing
PAGE 10 February 2013