Chapter A - Introduction - City of Pickering

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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
Area Parks over 4 hectares Parks 4 hectares and under Stormwater Management Facilities Single Family Residential Single Family Residential (Frontage less than 12.2m) Semi-detached Residential Townhouses, Maisonettes, Row Houses, etc. Apartments Schools and Churches Industrial Commercial Heavily Developed Areas Paved Areas COMMENT MESPA RESPONSE (December 2011) CITY RESPONSE (October 2012) RESPONSE Runoff Coefficient 0.20 0.25 0.55 0.60 0.65 0.65 0.75 0.75 0.75 0.90 0.90 0.90 0.95 Another issue arising from the hydrological modelling is the percent changes in flow even with stormwater management controls. Table B5.12 notes some very significant changes at some nodes (i.e. 71% at a 2 year, -18% for others, etc.). This may result in a number of intermittent streams becoming permanently flowing and causing significant alteration to the channel form and function in the future. 100%, a more appropriate value has been assigned. See Chapter B5.3.2. For clarification: • % Imp values for hydrologic modeling completed as part of the NFSSR’s shall be based on Table 18 “Typical Impervious Values by Land Use”, page 67, of the “City of Pickering Stormwater Management Guidelines”. • %IMP values for hydrologic modeling completed as part of detailed design phase shall be based on actual measurements. REPORT CHAPTER AND SECTION Erosion Analysis The ToR specifies that the most critical values for the erosion thresholds were to be utilized in the erosion analysis. However, Table 5.2 indicates that an average value was used for the thresholds. This is of particular concern when the two values are significantly different (i.e. D5 0.909 m 3 /s vs. 0.546 m 3 /s). Moreover, there are two reaches labelled U10, with two different threshold discharges, one from Duffin Heights with a threshold value of 0.68 m 3 /s and another with a value of 0.203 m 3 /s. As this was determined to be the most critical reach for Urfe Creek, it is unclear which value was used. Furthermore, please clarify how this was determined to be the most critical reach when Reach U16 was the most critical reach used in the Duffin Heights analysis. The CPDP stated that the MESP should conduct an erosion sensitivity analysis for all receiving watercourses on a subwatershed basis. Given that, it is unclear why the recommendations are stating that the erosion criteria be applied to different watercourses (i.e., Ganatsekiagon Creek should use Urfe Creek and Whitevale Creek should use West Duffins Creek). It is not appropriate to transpose criteria from different subwatersheds as the erosion processes may be quite different. Moreover, applying stringent criteria across the board like this may result in too much storage being provided for a given subwatershed, which may actually disrupt the stream processes more. It should be noted that unnecessarily holding back flow and discharging it over long periods of time (i.e. 120 hours) may have negative impacts on stream form and function. Current research (MacRae, 2006) has suggested that conventional practices of utilizing end-of-pipe facilities to offset the hydrologic effects of urbanization are insufficient to prevent increased channel erosion and deterioration of aquatic habitats. The erosion analysis have been completed based upon the critical thresholds provided by the fluvial geomorphologist, and have applied the critical threshold within each Subwatershed. Further discussion on this approach is provided within Chapter B5.9. The use of LID techniques at the source level, has been proposed throughout the study area to mitigate the issue of increased runoff volumes. The erosion analyses have been updated to include an assessment of the reduced erosion potential which would be anticipated to result from the implementation of LID practices. The QUALHYMO hydrologic model has been calibrated using the approach discussed with the TRCA and the City of Pickering. Details regarding the calibration methodology are provided in Chapter B5.9 As previously discussed with the SLG previously, the erosion assessment will need to be re-assessed based on the updated hydrology model for the Duffins Creek. City staff will provide detailed comments once the reassessment has been completed, and submitted for review. Following additional discussions with the TRCA at several meetings, it has been decided that the Qualhymo model does not require updating based on the new hydrology. As outlined in Chapter B Section 5.2 the Qualhymo model has served the purposes of identifying the need for LID measures in combination with endof-pipe facilities and also providing direction towards the extended detention criteria for SWM facilities (i.e. 25mm extended detention for 120 hours). The 2011 Erosion Assessment is therefore presented again in the 2013 MESPA. Chapter B5.2 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 10 Amos Environment + Planning
Page 1 and 2: CHAPTER A - INTRODUCTION 1.0 STUDY
Page 3 and 4: of alternatives for the arterial an
Page 5 and 6: These MESP study requirements were
Page 7 and 8: ownership of the Province. Lands ou
Page 9 and 10: Within the MESP Study Area, Ganatse
Page 11 and 12: hydrology for erosion and flood con
Page 13 and 14: It is important to note that the ME
Page 15 and 16: projects are considered pre-approve
Page 17 and 18: Table A9.2 provides a summary of th
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Chapter A - Introduction - City of Pickering

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