Chapter A - Introduction - City of Pickering

COMMENT MESPA RESPONSE (December 2011) CITY RESPONSE (October 2012) RESPONSE
This was verified by running both models, which resulted in the following
time to peak for flows for Whitevale, Ganatsekiagon and Urfe Creeks of 5,
6 and 6.5 hours, from the AMEC Model, whereas the time to peak for
those creeks in Aquafor’s 2002 Model were 9, 9.25 and 8 hours,
respectively. It is important that Aquafor’s 2002 Model was calibrated to 6
different streamflow gauges throughout the Duffins Creek watershed,
including one gauge on Urfe Creek, while AMEC’s Model was not
calibrated at all.
REPORT CHAPTER
AND SECTION
From a Regional flow perspective, the MESP states that the model
indicates an increase in Regional flows of 3% at the downstream node
through the Pickering/Ajax Special Policy Area (SPA) and the location of
the Duffins Dyke. The MESP recommends that Regional control not be
provided in the stormwater facilities as widespread distributed regional
control is expected to increase downstream flow levels more. However,
the actual analysis was not completed. Alternatively, the MESP
recommends the formalization of natural valley storage that exists within
Ganatsekiagon Creek and Urfe Creek. It is unlikely this recommendation
will be approved by TRCA, therefore, regional control may be required
within the neighbourhood plans. This means that efficiencies may need to
be found such as co-location of stormwater facilities and parks, otherwise
large tracts of land may be required for regional storage.
The recommendation that 2 to 100 year and Regional stormwater
quantity controls are not required for Whitevale Creek has not been
appropriate justified. It is understood that the reason that no water
quantity controls are proposed within Whitevale Creek was to ensure that
the flows from this subcatchment are conveyed through the system prior
to the peak flows from the upstream West Duffins catchments arriving
which thereby lessens the downstream flooding impacts. However, this
does not take into account the impact that uncontrolled flows would have
on the instream channel itself – namely, from the lower return period
flows, which could significantly change the existing channel form,
especially if the re-calibration shows that the existing flows for Whitevale
Creek are reduced and closer to the Aquafor 2002 Model.
Given the deficiencies outlined above, the reliability of AMEC’s
uncalibrated model and the validity of the report’s recommendations
cannot be accepted at this time. Staff recommends that the Aquafor 2002
Model be updated to include the more specific information from the
Seaton area utilizing the same methodology for determining the
parameters (CN*, time to peak, area, subcatchments etc.) and calibration
procedure in order to recalibrate the model using eight more years of
streamflow and rainfall data (from 2002 to 2010). Accurate modelling is
required in order to move forward and make reasonably accurate
recommendations for such a large-scale development as Seaton,
specifically due to the known presence of the flood prone communities
downstream.
The Future Conditions model will be updated using the City’s
Neighbourhood Plans. The following runoff coefficients should be used
for the different land uses as they reflect the actual built form that is to be
expected in Seaton as stated in Section 8.1.
As discussed at the technical meeting, the City’s runoff
coefficients have been utilized. The RC values have
been converted to percent impervious. Where this
results in percent impervious greater than or equal to
No action required for MESPA as hydrology
component is being addressed through the
2012 Duffins Creek Hydrology Update.
No response required.
The Sernas Group Inc., Stonybrook Consulting Inc. December 2011, Revised February 2013 Master Environmental Servicing Plan - Amendment
SPL Beatty, Bird and Hale Limited, Earthfx Inc. 07161 Seaton Community, City of Pickering
AMEC Earth & Environmental, R.J. Burnside Appendix A7 – Page 9
Amos Environment + Planning