ninth line lands - peel region · tp114008 page 2 2.0 supplemental phase 1 subwatershed study...

Ninth Line Lands Scoped Subwatershed Study

Phase 2: Impact Assessment and Management Strategy Prepared for:

City of Mississauga

Prepared by: Amec Foster Wheeler 3215 North Service Road Burlington, ON L7N 3G2 (905) 335-2353

March 2017

Project No. TP114008

Ninth Line Lands Scoped Subwatershed Study

Phase 2: Impact Assessment and Management Strategy

Submitted to:

City of Mississauga

Submitted by:

Amec Foster Wheeler Environment & Infrastructure 3215 North Service Road Burlington, ON L7N 3G2

Tel: (905) 335-2353 Fax: (905) 335-1414

March 2017

TP114008

City of Mississauga Amec Foster Wheeler Ninth Line Lands Scoped Subwatershed Study Environment & Infrastructure Phase 2: Impact Assessment and Mitigation Strategy March 2017

TP114008 Table of Contents

TABLE OF CONTENTS PAGE

1.0 INTRODUCTION ............................................................................................................... 1

2.0 SUPPLEMENTAL PHASE 1 SUBWATERSHED STUDY CHARACTERIZATION ......... 2 2.1 Surface Water ....................................................................................................... 2 2.2 Groundwater .......................................................................................................... 3 2.3 Water Budget ........................................................................................................ 5 2.4 Stream Morphology ............................................................................................... 8

2.4.1 Erosion Threshold Analyses ................................................................. 8 2.4.2 Sediment Budget ................................................................................ 10 2.4.3 Headwater Drainage Function ............................................................ 11

2.5 Water Quality ....................................................................................................... 11 2.6 Natural Environment ............................................................................................ 14

2.6.1 Fisheries/Aquatics ............................................................................... 14 2.6.2 Terrestrial Ecology/Systems ............................................................... 15

2.7 Integrated Summary ............................................................................................ 17 2.7.1 Overview ............................................................................................. 17 2.7.2 Terrestrial Ecology .............................................................................. 17 2.7.3 Fluvial Geomorphology ....................................................................... 19 2.7.4 Groundwater ....................................................................................... 19

3.0 FUTURE LAND USE PLAN DEVELOPMENT ............................................................... 20 3.1 Transitway Corridor ............................................................................................. 20 3.2 Ninth Line Lands Emerging Land Use Concept .................................................. 21

4.0 IMPACT ASSESSMENT ................................................................................................. 23 4.1 Surface Water/Groundwater/Water Quality ......................................................... 23

4.1.1 Future Uncontrolled Land Use Conditions .......................................... 23 4.1.2 Stormwater Management Systems Sizing (Quantity and Quality) ...... 30 4.1.3 Water Budget and Runoff Volume Reduction ..................................... 33 4.1.4 Recommended Stormwater Management Plan .................................. 34

4.2 Stream Morphology ............................................................................................. 35 4.2.1 Meander Belt Width and Corridor Width ............................................. 35 4.2.2 Stream Length .................................................................................... 38 4.2.3 Impacts ............................................................................................... 39

4.3 Natural Environment ............................................................................................ 46 4.3.1 Direct Impacts ..................................................................................... 46 4.3.2 Indirect Impacts ................................................................................... 47 4.3.3 Mitigation ............................................................................................. 47

5.0 RECOMMENDED ENVIRONMENTAL AND STORMWATER MANAGEMENT PLAN . 49 5.1 Stormwater Management .................................................................................... 49 5.2 Watercourse Systems ......................................................................................... 49 5.3 Natural Heritage .................................................................................................. 50



5.3.1 Current Planning Context .................................................................... 50 5.3.2 Proposed Natural Heritage System .................................................... 51

6.0 REFERENCES ................................................................................................................ 55

7.0 GLOSSARY .................................................................................................................... 56

LIST OF TABLES

PAGE Table 2.1.1: Simulated Peak Flow Rates for Return Period and Regional Storm Event

Under Existing Land Use Conditions for Ninth Line Lands (m3/s) ......................... 2 Table 2.2.1 Pre-Development Water Balance Summary .......................................................... 7 Table 2.3.1 Summary of Erosion Threshold Values and Metrics ........................................... 10 Table 2.4.1. Summary of Contaminant Concentrations at Railway Under Wet Weather

Conditions ........................................................................................................... 12 Table 2.4.2. Summary of Contaminant Concentrations at Britannia Road Under Wet

Weather Conditions ............................................................................................. 12 Table 2.4.3. Comparison of Wet Weather Contaminant Concentrations at Railway

With Literature Values for Agricultural Land Use Conditions ............................... 13 Table 2.4.4. Comparison of Wet Weather Contaminant Concentrations at Britannia

Road With Literature Values for Agricultural Land Use Conditions ..................... 13 Table 4.1.1: Imperviousness / Coverage Values Based on Land Use .................................... 23 Table 4.1.2: Subcatchment Parameterization for Ninth Line Lands – Future Land Use

Conditions ........................................................................................................... 24 Table 4.1.3: Simulated Peak Flow Rates for Return Period and Regional Storm Event

Under Future Uncontrolled Land Use Conditions for Ninth Line Lands (m3/s) ................................................................................................................... 25

Table 4.1.4: Percent Change in Simulated Peak Flow Rates for Return Period and Regional Storm Event Under Future Uncontrolled Land Use Conditions for Ninth Line Lands Compared to Existing Land Use Conditions (%) ................ 26

Table 4.1.5: Erosion Assessment for Site NL-10..................................................................... 27 Table 4.1.6 Post Development Water Balance Summary ...................................................... 28 Table 4.1.7: Stormwater Management Facility Sizing Criteria for Future Land Use With

Stormwater Management Scenario ..................................................................... 31 Table 4.1.8: Simulated Peak Flow Rates for Return Period and Regional Storm Event

Under Future Land Use Conditions with Stormwater Management for Ninth Line Lands (m3/s) ....................................................................................... 31

Table 4.1.9: Percent Change in Simulated Peak Flow Rates for Return Period and Regional Storm Event Under Future Land Use Conditions with Stormwater Management for Ninth Line Lands Compared to Existing Land Use Conditions (%) .................................................................................... 32

Table 4.1.10: Erosion Assessment for Site NL-10..................................................................... 33 Table 4.2.1 Comparison of Reach Based Corridor Widths ..................................................... 37 Table 4.2.2 Summary of Watercourse Management Recommendations ............................... 42 Table 4.3.1 Direct Impacts to Natural Features ...................................................................... 46 Table 5.3.1 Summary of Existing, Retained and Created Natural Features ........................... 53



LIST OF FIGURES

PAGE Figure 2.3.2: Delineated reaches within the downstream area of the Ninth Line Lands ............. 9

LIST OF DRAWINGS

Drawing LU1: Land Use Plan (Future Conditions) Drawing WR1: VisualOTTHYMO Subcatchment Boundary Plan Drawing WR2: VisualOTTHYMO Future Uncontrolled Conditions Model Schematic Drawing WR3: VisualOTTHYMO Future Conditions with Stormwater Management Model

Schematic Drawing WR4: Stormwater Management Plan Drawing E1: Aquatic Monitoring Stations Drawing E2: Existing Conditions and Potential Impacts Drawing E4: Existing Conditions and Potential Impacts Drawing E5: Land Use Plan and Natural Heritage System Drawing E6: Land Use Plan and Natural Heritage System Drawing E7: Land Use Plan and Natural Heritage System Drawing E8: Natural Heritage System Drawing E9: Natural Heritage System Drawing E10: Natural Heritage System

LIST OF APPENDICES

Appendix A: Correspondence Appendix B: Surface Water Hydrology Appendix C: Groundwater Appendix D: Stream Morphology Appendix E: Water Quality Appendix F: Terrestrial and Aquatic Ecology

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TP114008 Page 1

1.0 INTRODUCTION

The Ninth Line Lands in the City of Mississauga are at the west limit of the City of Mississauga, and are generally bounded by Highway 407 to the west, Ninth Line to the east, Highway 401 to the north and the Highway 407/Ninth Line overpass to the south. In 2014, the City initiated the Ninth Line Lands Review to establish a planning framework for the Ninth Line Lands and guide future growth and development. As part of this process, a Scoped Subwatershed Study has been initiated in order to define and establish the constraints and opportunities within the Ninth Line Lands related to the terrestrial and aquatic ecology, stream systems, and surface water and groundwater resources (quantity/quality). The Scoped Subwatershed Study is being completed in the following three phases:

Phase 1: Study Area Characterization Phase 2: Impact Assessment/Management Strategy Phase 3: Implementation and Monitoring

The Phase 1 report has been completed in January 2015 and presented to the Technical Steering Committee for review and comments. Comments received from the representatives of the Steering Committee and associated responses and actions provided by the City’s Consulting Team are provided in Appendix A. This report summarizes the methodologies and results of the Phase 2: Impact Assessment/Management Strategy component of the overall Scoped Subwatershed Study, as well as general guidance for Phase 3 Implementation and Monitoring of the Scoped Subwatershed Study Process. Additional information is also provided regarding the supplemental investigations completed subsequent to the submission of the Phase 1 report, to inform the overall characterization of the study area.


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2.0 SUPPLEMENTAL PHASE 1 SUBWATERSHED STUDY CHARACTERIZATION

The following summarizes the additional investigations and characterization work completed, subsequent to the submission of the January 2015 Phase 1 Report.

2.1 Surface Water

Subsequent to the January 2015 Draft Phase 1 report, and in response to comments provided by Conservation Halton, additional details have been prepared and submitted to the Authority regarding the development of the VisualOTTHYMO hydrologic model, as well as refinements to the model schematic. Technical documentation has been prepared and submitted regarding these revisions (ref. Farrell/Scheckenberger-Ahmad, May 20, 2016), and a copy of this correspondence is included in Appendix B. The corresponding simulated peak flows for the existing land use conditions, based upon the revised VisualOTTHYMO hydrologic model, are presented in Table 2.1.1. Table 2.1.1 Simulated Peak Flow Rates for Return Period and Regional Storm Events

Under Existing Land Use Conditions for Ninth Line Lands (m3/s) Node/Hydrograph

Number Location

Return Period (Years) Regional Storm 2 5 10 25 50 100

79 Hwy. 407 Crossing

1.3 2.2 3.1 3.5 4.2 4.9 7.1

184 C.P.R.

Crossing 0.7 2.0 3.4 4.4 5.4 6.5 11.5

185 Derry Rd. Crossing

1.0 2.7 4.4 5.7 6.9 8.3 15.4

70 Outlet from

Osprey Marsh 10.7 17.3 24.9 34.0 43.3 54.0 109.0

104 Britannia Rd.

Crossing 6.7 16.1 26.7 35.6 44.6 54.8 158.2


7.4 17.2 28.7 38.5 48.2 59.4 177.9

145 Eighth Line Crossing

7.9 17.9 31.9 43.3 54.6 67.6 218.0

148 Trafalgar Rd.

Crossing 7.9 17.4 30.7 41.7 52.5 65.3 224.9

151 Outlet to

Sixteen Mile Creek

7.9 17.0 29.8 40.3 50.7 62.9 224.3

311 CVC - Hwy.

403 Crossing 0.5 0.9 1.3 1.7 2.0 2.3 4.2


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The refinements to the original SWMHYMO hydrologic model with the base mapping provided for the Scoped Subwatershed Study have resulted in a 50 ha +/- increase in drainage area within the hydrologic model domain. However, recognizing the size of the total model domain (i.e. 2575 ha +/-), the relative scale of this increase is noted to be marginal (i.e. 2 %) and within acceptable limits.

2.2 Groundwater

A hydrogeological characterization has been carried out based on a review of background information, a limited field program consisting of spot baseflow measurements and groundwater related findings from other disciplines. The following summarizes the findings: Physiography and Geology The Ninth Line land are situated within the Peel Plain Physiographic Region extending onto the Trafalgar Moraine in the southern part of the corridor. The Peel Plain is characterized by a gently sloping (gradient = 0.0056) glacial till plain from the north to south, with the southern 3500 m of the study area being nearly flat. Borehole logs confirm the general geologic setting indicating that the surficial overburden consists of varying thicknesses (4 m to greater than 28 m). The thicker overburden is limited to the northern and southern parts of the corridor. Discontinuous lenses of sand can be found within the Halton Till or at the bedrock interface. The underlying bedrock of the Queenston Shale was encountered between 4 and 28 metres below ground surface (mbgs) within the Ninth Line lands with an average depth to bedrock of about 14 mbgs. Bedrock elevation is highest in the central portion of the study area and lowest in the north and south portions. Hydrogeologic Setting Based on single well response tests in the Lisgar subdivision, located just east of the study area the hydraulic conductivities ranged between 3 x 10-5 m/s for silty clay fill to 8.4 x 10 9 m/s for clayey silt. The hydraulic conductivity of silty sand, sandy silt layer was calculated to be 6.5 x 10-7 m/s. The hydraulic conductivity of a coarse sand layer was calculated to be 3 x 10-6 m/s, considered low for coarse sand. A hydraulic conductivity of less than 7 x 10 8 m/s is estimated for the shale. Within the study area the 25 MOECC well records indicate that only one well was screened within the upper 5 m. As a result, the water table within the corridor is not presently quantified. Within the Lisgar subdivision shallow monitoring wells established for a study related to basement water infiltration (ref. Amec Foster Wheeler 2015) show the water table to be within 2 m of ground surface. Seasonal variations were shown to be on the order of 1 m. Water table depths within the Halton Till in other study areas are consistently within the upper 2 m with a 1 m – 2 m seasonal variation.


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Horizontal gradients in the northern half of the study area are about 0.005 as interpreted from the Lisgar Basement Water Infiltration Study data. The horizontal component of groundwater flow, particularly within the overburden, will be weak due to the low permeability of the silt/clay sediments. Given a hydraulic conductivity of approximately 10-6 m/s the groundwater velocity is on the order of metres per year. There is currently no site specific data quantifying the vertical hydraulic gradients. Based on previous literature reviews, the following are some of the hydrogeologic factors that potentially relate to fracturing in the till in the study area:

► Frequency and potential depth of fractures can depend on the clay/silt/sand content, average precipitation and temperature

► Fractures can occur up to 6 m but they are likely more prevalent within the upper 2-3 m of till

► The lateral connection within the upper fractured till can be relatively significant, compared to the massive till, but is generally localized (10’s of metres).

► Horizontal flow patterns in the upper fractured till will be controlled by local depressional topography and restricted by underlying more massive and less permeable till

► Vertical groundwater flow below the upper fractured till is generally low unless more permeable, interconnected lenses exist

► Evapotranspiration can significantly reduce water levels in the upper fractured till ► Potential lateral flow in the upper fractured till reduces more quickly as the water levels drop

due to less fracture with depth ► Gradients can be reversed within the underlying massive till (downward to upward) as

water levels in the upper fractured till lower thereby reducing recharge to depth ► Where the underlying till is massive, both vertical and horizontal groundwater flow is

restricted. The vertical hydraulic gradients are generally higher than the horizontal gradients but this depends on the larger scale groundwater flow system.

The local hydrostratigraphy may include more permeable sand lenses and a more permeable upper fractured bedrock. These systems provide a greater potential for groundwater flow. Approximately 10 bedrock wells and 14 overburden wells have been identified between Ninth Line and Highway 407 in the MOECC database. A few of these may still be in use for domestic purposes but most are likely abandoned and no longer used. Based on the hydraulic conductivities presented in the foregoing for the overburden and shale bedrock, they are considered in general not to be viable aquifers. The Halton Till is generally considered an aquitard. It is noted however that the occurrence of discontinuous sand and gravel lenses in the sandy silt till or located at the till/bedrock interface could possibly produce limited water for domestic use, as well as the upper weathered Queenston shale. There is no Significant Groundwater Recharge Area or Highly Vulnerable Aquifer within the study area. Water well information reports water quality as “fresh”.


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Streamflow measurements presented in the Phase 1 report were carried out on September 19, 2014 at 4 locations. At the Highway 407 crossing in the north and the Derry Road crossing, no flow was observed and the flow could not be measured. The flow at the Britannia Road crossing was measured to be between 32 and 36 L/s. Where the creek crosses Eighth Line, flow was estimated to be about 55 L/s. Additional streamflow measurements were carried out on December 9, 2015. Flow at Highway 407 was 0.66 l/s, at Derry Road 1.6 l/s and at Britannia Road 24.15 l/s. Additional sites were measured; the Ninth Line culvert at Parkgate Drive 11 l/s, Longford Drive culvert 0.65 l/s and the downstream Railway culvert 32.43 l/s (replacing the Eight Line culvert). Specific locations for December 2015 can be found in Appendix C. The 2015 spot streamflow results are consistent with the 2014 results. The lack of any significant increase in flow between Highway 407 and Derry Road is consistent with the general groundwater discharge potential of the Halton Till or the glaciolacustrine sediments. The increase in flow at Britannia Road reflects, in part, the inputs from the Ninth Line culvert at Parkgate. The increase at Britannia Road, as well as the further increase at the downstream Railway culvert, likely relate to the slow release of water from the stormwater management facilities servicing the lands east of Ninth Line. The increase in water temperature between the upstream Railway water quality monitoring station and Britannia Road does not reflect a groundwater discharge source accounting for the increase in flow. Additional field observations for the creek reaches within the corridor tend to indicate a lack of groundwater discharge although some observations indicate the potential for bank seepage. The substrate is typically fine grained although there appear to some areas of coarser inclusions. Current observation of the wetland communities presented in Section 2.5 have been interpreted to be non-reliant on groundwater discharge.

2.3 Water Budget

Based on a review of the Phase 1 water balance analysis and comments provided by Conservation Halton, the pre-development analysis has been revised. The pre-development water balance analysis has been carried out using existing information regarding the area of the subject property, as well as areas of existing land use, topography and soil texture. Meteorological data in the form of monthly average temperature and precipitation are available from Environment Canada - Canadian Climate Normals 1981-2010 for the Toronto Pearson Airport Meteorological Station (43°40'38" N, 79°37'50" W), approximately 20 km east of the site, were used in preparation of the water budget for the site of the proposed land use change. Another location, Oakville South East Water Treatment Plant, where long term data were also available was considered for use in this analysis, as it is slightly closer to the site. However an examination of the precipitation and temperature data from this location indicated that it was influenced by its proximity to Lake Ontario giving it generally cooler temperatures and increased precipitation. Therefore the Toronto Pearson climate data were considered to be better suited


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to the subject development area, as it was at nearly the same latitude and away from the influence of Lake Ontario. Calculation of evapotranspiration was carried out using a computer program, EVAP (NOAA Technical Memorandum ERL GLERL-101, Cynthia E. Sellinger), which uses an accounting procedure based on the methodology originally presented by Thornthwaite (1948). Inputs to the computer model are mean monthly temperature, monthly total precipitation, latitude and hemisphere of the location of interest and soil moisture holding capacity of the soil based upon the soil properties and vegetation. The program outputs potential evapotranspiration and actual evapotranspiration. The difference between the mean annual precipitation and the mean annual evapotranspiration is the annual water surplus, which is available to either infiltrate into the soil surface or to flow over the land surface. A portion of the infiltration may flow vertically and percolate down to recharge groundwater, while a second component, termed interflow, may move laterally through shallow soils and re-emerge locally to the surface in low lying areas or stream beds. Both the interflow and direct runoff, which have not infiltrated into the ground surface together form the total surface runoff component. For each land use the percentage of pervious and impervious area was estimated based on a guidance table found on the MTO website: http://www.mto.gov.on.ca/english/publications/drainage/stormwater/section10.shtml#catchment The annual surplus determined by subtracting the actual annual evapotranspiration for the pervious areas was assigned to either runoff or precipitation by use of runoff coefficients estimated from Design Chart 1.07 of the MTO Drainage Management Manual (MTO 1997). Direct evaporation from impervious areas was assumed to be 10% of the precipitation incident upon those areas. The results of the pre-development water budget assessment are presented in Table 2.2.1


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Table 2.2.1 Pre-Development Water Budget Summary (Annual)

Land Use Area (m2)

Pervious Area (m2)

Impervious Area (m2)

Precipitation(m3)

Actual Evapotranspiration

(m3)

Runoff (m3)

Infiltration (m3)

Rural Pasture 2680000 2680000 0 2106480 1231728 349900.8 524851.2

Woodland 130000 130000 0 102180 76908 8845.2 16426.8 Light Commercial -

Lawn 11500 11500 0 9039 6205.4 425.0 2408.6

Light Commercial - Gravel

3500 3500 0 2751 1696.1 422.0 632.9

Light Commercial - Impervious

45000 0 45000 35370 3537 31833.0 0.0

Light Commercial - Total

60000 15000 45000 47160 11438.5 13580.2 22141.3

Pavement (9th Line) 90000 0 90000 70740 7074 63666 0

Water Bodies 160000 160000 0 125760 99520 1312 24928

Total 3120000 2985000 135000 2452320 1426668.5 456404.0 569247.5

% of Precipitation 100 58.18 18.61 23.21


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The water budget values presented in the foregoing are generally consistent with a water budget carried out in a similar physiographic setting to the west in the Town of Milton. A large percentage of the study area is Rural Pasture and as such the runoff to infiltration values are lower and subsequently the overall infiltration is though the study area is comprised of the lower permeability Halton Till and glaciolacustrine silt and clay.

2.4 Stream Morphology

The Phase 1 fluvial geomorphological assessment focused on the characterization of the existing watercourses within the study area. The field based fluvial geomorphological assessments indicated that the channels were relatively stable, however had poor functionality, due to the low energy gradient of the channel. Subsequent to the completion of the January 2015 Phase 1 Report, supplemental investigations were completed to characterize the watercourses within the Ninth Line Lands with respect to the following:

i. Erosion threshold analyses of key reaches of the Sixteen Mile Creek tributary, notably reaches NL-10 and NL-4.

ii. Understanding of headwater drainage function. iii. Understanding of sediment budgeting in the system.

In response to Conservation Halton comments and requests for additional characterization of the fluvial geomorphology within the study area, the results of the additional field investigations completed subsequent to the January 2015 Phase 1 Report were presented in the Ninth Line Stream Morphology Interim Report (ref. Matrix, June 2016). A copy of this correspondence is provided in Appendix D. Key findings from this additional assessment and characterization are provided in the following:

2.4.1 Erosion Threshold Analyses

The critical discharge or erosion threshold was determined through a quantitative analysis of the locations of the detailed data collection on the Sixteen Mile Creek tributary (NL-10 and NL-4; ref. Figure 2.3.2). In the Phase 1 characterization, reaches NL-10 and NL-4 were deemed the most sensitive through the rapid assessment process, with the highest RGA stability indices. Hence erosion threshold assessments were undertaken for these reaches.


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Figure 2.3.2: Delineated reaches within the downstream area of the Ninth Line Lands


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Erosion threshold values for channel boundary material (i.e., permissible velocity and critical shear stress) were evaluated for substrate distributions using various approaches derived from recognized sources examining sediment mobility of boundary material (Dunn 1959; Chow 1959; Fischenich 2001). The erosion threshold analysis results showed that the critical discharge values were equal to or higher than, the bankfull discharge in each of the sites. Based on the existing channel dimensions, the erosion threshold value was determined as 1.09 m3/s. Table 2.3.1 shows the erosion threshold values for reaches NL-10 and NL-4.

Table 2.3.1 Summary of Erosion Threshold Values and Metrics

Parameter NL-10 NL-4 Average Bankfull Discharge (m3/s) 0.93 2.33 Average Bankfull Velocity (m/s) 0.30 0.47 Average Shear Stress (N/m2) 1.44 5.59 Stream Power (W/m) 2.73 25.13 Stream Power per Unit Width (W/m2) 0.58 4.32 Critical Particle Loose sandy material Clay-silt content Critical Shear for bed material (N/m2) 2.40 -- Critical Discharge (m3/s) 1.09 1.98 Critical Discharge/Bankfull Discharge (%)

117 85

Maximum Velocity (m/s) 0.45 0.80 Maximum Depth (m) 0.90 0.80 Method Chang (1959) Dunn (1959) Flows marginally exceeding the critical discharge will generate incipient motion of sediment particles. However, higher flow values will instigate significant sediment transport, overtop the banks and dissipate energy within channel’s broad floodplain. The fragmented and low gradient nature of the watercourse inhibits the development of hydraulic conditions adequate enough to properly convey its fine sediment load. Furthermore, the tractive forces exhibited by the watercourse are considered to be insufficient to initiate and effectively sustain sediment transport within the watercourse.

2.4.2 Sediment Budget

Evidence of significant sediment production within the system was not identified within the study area. The low gradient and fragmented nature of the system attenuates the overall potential energy within the system deterring sediment production and efficient transport of fine materials. As supported by the erosion threshold assessment, the tractive forces exhibited by the watercourse are considered insufficient to initiate and effectively sustain sediment transport. As a result, the watercourse within the Ninth Line Lands essentially stores sediment, consequently resulting in insignificant production and transport of materials through the system and thus providing poor geomorphic function.


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2.4.3 Headwater Drainage Function

Headwater features were only identified within the north portion of the Ninth Line Lands, south of Highway 401 and north of Derry Road. The features are ill-defined, low gradient topographic depressions typically lined with terrestrial grasses and/or cattails. These features appeared to be ephemeral or intermittent in nature showing little evidence of active flow. Shallow, stagnant water along the base of the depression is common, hence supporting the establishment of wetland vegetation and accumulation of fine sediment and organic material. These features may provide suitable wetland habitat to support small communities of aquatic and terrestrial species. Near the south-end, the proposed development will likely affect the Sawmill Headwater Drainage system. Hence, sufficient open drainage should be incorporated to maintain proper drainage function.

2.5 Water Quality

The scoped water quality monitoring program was extended into 2015, at the request of Conservation Halton, to include one additional wet weather water quality sample. The locations for the water quality sampling are depicted on Drawing WR-5 of the Phase 1 report; a copy is included in Appendix E for reference. The wet weather sample was obtained on August 20, 2015. In accordance with the Approved Supplemental Work Plan, the grab samples were analyzed by an accredited laboratory (ALS Life Sciences Division) for the following water quality parameters:

► Anions ► BOD5 ► Metals ► Ammonia ► Total Phosphorus ► Total Suspended Solids ► E.Coli ► TKN

The lab report for the August 20, 2015 wet weather event is included in Appendix E. The statistical analyses for the wet weather monitoring have been updated to include the results of the August 20, 2015 event, to determine differences in contaminant concentrations under wet weather and dry weather conditions. The statistical analyses for wet weather monitoring at the railway and Britannia Road are summarized in Tables 2.4.1 and 2.4.2 respectively.


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Table 2.4.1 Summary of Contaminant Concentrations at Railway Under Wet Weather Conditions

Contaminant Number of Samples Range Mean/Median BOD/CBOD (mg/L) 2 2.1 - 3.1 2.6 E.coli (#/100mL) 2 1700 - 4000 2850 TKN (mg/L) 2 1.27 - 1.72 1.50 Total P (mg/L) 2 0.123 - 0.184 0.154 TSS (mg/L) 2 8.4 - 26.9 17.7 Copper (mg/L) 2 0.0029 - 0.005 0.0040 Zinc (mg/L) 2 0.0098 - 0.0136 0.0117 Lead (mg/L) 2 <0.0007 <0.0007 Nitrate+Nitrite (mg/L) 2 <0.175 <0.175

Table 2.4.2 Summary of Contaminant Concentrations at Britannia Road Under Wet Weather Conditions

Contaminant Number of Samples Range Mean/Median BOD/CBOD (mg/L) 2 <0.163 <0.163 E.coli (#/100mL) 2 1300 - 1900 1600 TKN (mg/L) 2 1.12 - 1.15 1.135 Total P (mg/L) 2 0.139 - 0.161 0.150 TSS (mg/L) 2 40.7 - 50 45.4 Copper (mg/L) 2 0.0046 - 0.0054 0.0050 Zinc (mg/L) 2 0.0144 - 0.0357 0.0251 Lead (mg/L) 2 0.00155 - 0.00158 0.00157 Nitrate+Nitrite (mg/L) 2 <0.163 <0.163

The results indicate the following:

► Surface water quality between the railway and Britannia Road under wet weather conditions exhibits a reduction in E.Coli and TKN from upstream to downstream, with increased levels of some metals (i.e. zinc and lead), possibly due to contributions from isolated urban land uses downstream of the railway.

► Surface water quality between the railway and Britannia Road exhibited an increase in TSS from upstream to downstream under wet weather conditions, suggesting possible sediment contributions along the watercourse, which may be a result of natural channel forming processes.

The results of the wet weather sampling have been compared with literature values for agricultural land use conditions as applied in the City of Toronto Wet Weather Flow Study and the Red Hill Creek Watershed in the City of Hamilton. The results of this comparison are presented in Tables 2.4.3 and 2.4.4.


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Table 2.4.3 Comparison of Wet Weather Contaminant Concentrations at Railway With Literature Values for Agricultural Land Use Conditions

Contaminant Measured

Concentration Literature Values

TWWF RHCWP BOD/CBOD (mg/L) 2.6 2 E.coli (#/100mL) 2850 100,000 TKN (mg/L) 1.50 1.0 2.8 Total P (mg/L) 0.154 0.2 0.5 TSS (mg/L) 17.7 100 400 Copper (mg/L) 0.0040 0.008 0.005 Zinc (mg/L) 0.0117 0.018 0.010 Lead (mg/L) <0.0007 0.004 Nitrate+Nitrite (mg/L) <0.175 2.5

Table 2.4.4 Comparison of Wet Weather Contaminant Concentrations at Britannia Road With Literature Values for Agricultural Land Use Conditions

Contaminant Measured

Concentration Literature Values

TWWF RHCWP BOD/CBOD (mg/L) <0.163 2 E.coli (#/100mL) 1600 100,000 TKN (mg/L) 1.135 1.0 2.8 Total P (mg/L) 0.150 0.2 0.5 TSS (mg/L) 45.4 100 400 Copper (mg/L) 0.0050 0.008 0.005 Zinc (mg/L) 0.0251 0.018 0.010 Lead (mg/L) 0.00157 0.004 Nitrate+Nitrite (mg/L) <0.163 2.5

The results in Tables 2.4.3 and 2.4.4 indicate that the contaminant concentrations of TKN and metals as determined from the wet weather sampling in the Ninth Line Lands are generally comparable to literature values for agricultural land use conditions. The results further indicate that the concentrations of E.Coli, Total P, TSS and Nitrate + Nitrite are below literature values for agricultural land use conditions. The results further indicate elevated concentrations of BOD5 at the railway compared to literature values, with lower values at Britannia Road. The median EMC’s for each wet weather event and location have been compared with current Provincial Water Quality Objectives (PWQO’s) for various contaminants, in order to determine the number of exceedances under existing land use conditions. Contaminants have been listed when available guidelines have been provided within the PWQO’s or within The Canadian Council of the Ministers of the Environment (CCME) Water Quality Index. The results indicate that concentrations of all contaminants except E.Coli and chloride are below PWQO levels, indicating an overall high quality of surface water within the open watercourse through the Ninth Line Lands, as compared to other comparable systems.


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2.6 Natural Environment

The Phase 1 Characterization Report includes a characterization of natural environment features and wildlife within the subject lands. The work program was focused on confirming the information and data collected as part of the Ninth Line Corridor Study (NSEI 2012) as well as addressing the recommendations and specific concerns regarding Species at Risk (SAR) outlined in NSEI report. The background review included compiling species lists based on wildlife atlases, information from the Natural Heritage Information Centre (NHIC) database, and reviewing background reports and other studies. Detailed data were collected on the aquatic environment within the subject lands to fill a data gap. A total of 15 field visits were completed between April 2014 and June 2015 by NRSI biologists.

2.6.1 Fisheries/Aquatics

Aquatic assessments conducted for Phase 1 Characterization consisted of a detailed characterization of aquatic habitats including barriers to fish migration, sources of baseflow, seeps, springs, and unmapped tributaries. The fish community was assessed for the watercourses (June 2014), and the online ponds south of Britannia Road (June 2015). This information was added to background information on fish species reported from the area between 1957 and 2013. Aquatic features within the subject lands are characterized by highly impacted watercourses and on-line stormwater management facilities created, in part, for drainage from Highway 407. The June 2015 fish community assessment was completed following the submission of the Phase 1 Characterization Report and at the request of Conservation Halton (CH). Field forms have been appended to this report as Appendix F. The on-line stormwater management facilities provide habitat for warmwater fish species. During the June 2015 fish community assessment, 3 additional aquatic habitat areas were found within the online pond downstream of Britannia Road. The survey locations are illustrated on Drawing E1. The character of the 3 new stations is described below (the reader is referred to the Phase 1 report for descriptions of the other stations). AHP-008 is located at the upstream extent of the area surveyed in 2015. At the time that field surveys were conducted, this portion of the online pond consisted of a meandering low flow channel within an inundated floodplain. The low flow channel banks were densely vegetated with terrestrial grasses and cattails, while the floodplain consisted of dense cattails and phragmites. The channel substrate was dominated by silt with some clay and muck noted. AHP-009 is located downstream and to the east of AHP-008. This section was described as an online pond with a meandering low flow channel and an island. The pond ranged in width from 200-300m. Substrate consisted of silt and muck with some clay. Dense terrestrial grasses and cattails were present throughout the floodplain, riparian area, and within the pond. AHP-010 is located downstream and to the west of AHP-009. Conditions within AHP-010 were the same as AHP-009, including the presence of a low flow channel, soft unconsolidated silt and muck substrate, and dense terrestrial grasses and cattails. Aquatic habitat data forms for AHP-009 through AHP-010 are provided in Appendix F.


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During the June 2015 fish community assessment the following species were observed by NRSI biologists at AHP-008 to 010:

► Common Carp (Cyprinus carpio), ► Pumpkinseed (Lepomis gibbosus), ► Bluegill (Lepomis macrochirus), ► Golden Shiner (Notemigonus crysoleucas), ► Bluntnose Minnow (Pimephales notatus), ► Fathead minnow (Pimephales promelas), ► Black crappie (Pomoxis nigromaculatus), and ► Creek Chub (Semotilus atromaculatus)

2.6.2 Terrestrial Ecology/Systems

The Phase 1 Characterization Report includes detailed descriptions of all terrestrial field surveys. No additional field surveys were completed following the submission of the Phase 1 report. Flora

The Phase 1 Background Report included a review and update to the Ecological Land Classification mapping from the NSEI study. Based on this review and update, the majority of the subject lands consist of cultural meadow (i.e. idle farm fields), woodlots, anthropogenic uses, and stormwater management facilities. No rare or specialized ELC communities were identified within the subject lands (Drawing E2 through E4). NRSI observed 2 additional communities not previously identified in the NSEI study (2012): Graminoid Mineral Meadow Marsh (MAM2), and Thicket Swamp (SWT). Background information (MNR 2013a) identified that 8 significant plant species are reported from within 1km of the subject lands. None of these species were observed by NRSI; however a small cluster of (10) Kentucky Coffee-trees (Gymnocladus dioicus) was observed within a Cultural Meadow (CUM1) south of Britannia Road. In total, 17 species designated as regionally rare within Peel and Halton Regions (Varga et al. 2000) were identified during vegetation surveys by NRSI. ELC mapping identified 26.14ha of wetland within the subject lands, including Graminoid Mineral Meadow Marsh (MAM2), Reed-canary Grass Graminoid Mineral Meadow Marsh (MAM2-2), Cattail Mineral Shallow Marsh (MAS2-1), Green Ash Mineral Deciduous Swamp (SWD2-2), and Thicket Swamp (SWT). Following a review of the Phase 1 Characterization Report, CH requested that all wetlands within the subject lands be evaluated for significance. NRSI held a conference call with CH and MNRF staff to discuss the feasibility and necessity of evaluating the wetlands. Based on the proposed land use concept, and other constraints including the proposed Transitway alignment, agency staff agreed to postpone evaluating the wetlands (pers. comm. Eplett, M., Maitch, L., and Howatt, M., 2016). During the conference call, NRSI staff spoke with Megan Eplett (MNRF) regarding the Kentucky Coffee-trees found within the subject lands. Based on this conversation, as well as professional


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experience, it was determined that these trees are planted and are located far outside of their natural range. As such, MNRF indicated it is not necessary to protect or transplant these trees or to plant new specimens in the Natural Heritage System (NHS). Rather MNRF prefers that plantings include only locally native species (pers. comm. Eplett, M. 2016). The minutes from this conference call are provided in Appendix F. Fauna

Breeding Bird Surveys

Breeding bird surveys were conducted throughout the subject lands in 2014. Specific Species at Risk (SAR) breeding bird surveys were also conducted to identify the presence of Barn Swallow (Hirundo rustica), Bobolink (Dolichonyx oryzivorus), Common Nighthawk (Chordeiles minor), and Eastern Meadowlark (Sturnella magna). NRSI observed predominantly common species including 45 species that exhibited signs of breeding. In total, 3 SAR were observed within the subject lands: Barn Swallow, Bobolink and Eastern Meadowlark. Suitable habitat for Barn Swallow was noted in 2 locations where 2 inactive nests were observed, and the species was observed foraging throughout the subject lands. The northern location is no longer present due to a fire that occurred on this property in 2014, shortly after field surveys were conducted by NRSI. Bobolink was observed flying overhead, and a single Eastern Meadowlark was observed during breeding bird surveys. The available meadow habitat for these species is currently a narrow strip wedged between Highway 407 and the Lisgar residential area to the east that consists of idle agricultural lands, and does not appear to provide habitat for these two bird species due to the narrow configuration and small area. A total of 4 bird species of Conservation Concern including Canada Warbler (Cardellina canadensis), Caspian Tern (Hydroprogne caspia), Eastern Wood-pewee (Contopus virens), and Wood Thrush (Hylocichla mustelina) were observed within the subject lands. Suitable habitat for Canada Warbler and Caspian Tern is not present within the subject lands. Eastern Wood-pewee and Wood Thrush were both observed exhibiting breeding evidence within suitable habitat. A single Trumpeter Swan (Cygnus buccinator) was observed incidentally in the month of May. Herpetofauna

Background information identified 22 species of herpetofauna reported from within 10km of the subject lands. NRSI field investigations confirmed the presence of 7 species through visual encounter surveys for snakes and turtles, and anural call surveys conducted at 8 stations throughout the subject lands. A single snake species, Eastern Gartersnake, and a single turtle species, Midland Painted Turtle, were observed during field surveys in 2014. Northern Green Frog (Lithobates clamitans), Spring Peeper (Pseudacris crucifer) and Tetraploid Gray Treefrog (Hyla versicolor) were recorded during anuran call surveys, and American Bullfrog (Lithobates catesbeiana) and Northern Leopard Frog (Lithobates pipiens) were observed incidentally by NRSI biologists during other field surveys. No herpetofauna SAR or SCC were observed by NRSI biologists during 2014 or during the Ninth Line Corridor Study field surveys completed in 2011 (NSEI 2012).


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Butterflies and Odonates

During visual encounter surveys conducted in May and August 2014, NRSI biologists observed 10 species of butterfly and 9 species of odonata. The majority of these species were observed within the cultural meadows in the subject lands, which provide ample nectaring plants for these species. A single butterfly SCC, Monarch (Danaus plexippus), was observed by both NRSI biologists and NSEI (2012) through the Ninth Line Corridor Study. No odonate SAR or SCC were observed within the subject lands. Mammals and Incidental Wildlife

Of the 22 mammal species identified during the background review, 6 were observed within the study area by NRSI biologists including Eastern Chipmunk (Tamias striatus), Eastern Gray Squirrel (Sciurus carolinensis), Northern Raccoon (Procyon lotor), Striped Skunk (Mephitis mephitis), White-tailed Deer (Odocoileus virginianus), and a mouse species (Peromyscus spp.). No mammal SAR, SCC or regionally rare species were observed within the study area. Bat cavity assessments were conducted within suitable woodlands and forested areas as part of the significant wildlife habitat assessment. Several large snags were observed by NRSI biologists during these surveys and the potential exists for Little Brown Myotis (Myotis lucifuga) to be present within the subject lands.

2.7 Integrated Summary

2.7.1 Overview

The following key findings have been determined based upon an integrated, inter-disciplinary assessment of the study area characterization as presented in the foregoing:

► No provincially significant wetlands are located within the Ninth Line Lands. ► Woodlands within the subject area are significant based upon the criteria outlined in the

City of Mississauga’s Natural Heritage and Urban Forest Strategy Report (NSEI et al., 2014).

► Habitat of three (3) species of Conservation Concern have been confirmed. ► Field reconnaissance has confirmed the presence of four (4) SAR (Barn Swallow,

Bobolink, Eastern Meadowlark, and Kentucky Coffee-tree) although the number of these species was noted to be low.

► The groundwater connection to stream reaches and terrestrial communities, within the study area, does not appear to be significant.

Further details regarding the integrated assessment are provided below.

2.7.2 Terrestrial Ecology

An analysis of the significance and sensitivity of existing natural features and species was carried out as part of the Phase 1 Characterization Report. This analysis included features and habitats that were identified during the background review and field surveys conducted by NRSI biologists. The significance and sensitivity of these features and habitats was based on


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information provided in policies, legislation, and planning studies effective within the areas. The land use plan, the currently proposed Transitway are within the adjacent lands (120m) of natural features and areas within the subject lands. No provincially significant wetlands are located within the study area, based on a review of background information. The Ninth Line Corridor Study (NSEI 2012) indicated that all the wetlands within the study area should be considered significant based on the fact that wetlands are uncommon in the City. The woodlands within the subject lands are significant based on the criteria outlined in the City of Mississauga’s Natural Heritage and Urban Forest Strategy Report (NSEI et al. 2014). As per the City of Mississauga’s Official Plan Amendment 27, significant natural features will be considered for integration into the Natural Heritage System, and will generally be included within the Green System (City of Mississauga 2014). The Dry-Fresh Sugar Maple Deciduous Forest (FOD5) at the south end of the subject lands (Drawing E2 through E4) contains confirmed Bat Maternity Colony SWH and Candidate Raptor Wintering Habitat SWH. Numerous candidate Snake Hibernacula were identified in the form of old stone foundations from barns, and other structures. The majority were found in the Dry-Moist Old Field (CUM1 and CUM1-1) communities. Candidate Turtle Wintering habitat is present within the large stormwater management facilities (OAO) within the subject lands. Based on background review, the results of field surveys conducted by NSEI (2012) and NRSI, and a comparison of habitat requirements with existing conditions, habitat for 3 species of Conservation Concern was confirmed to be present within the subject lands as detailed in the Phase 1 Characterization Report. The FOD5 community at the south end of the subject lands provides habitat for Eastern Wood Pewee and Wood Thrush, both of which are likely breeding in this area based on the results of breeding bird surveys in the woodland. Monarch butterflies were observed widely throughout the meadow habitat within the study area (CUM1 and CUM1-1) and are likely breeding on the milkweed plants present (MNRF 2014b, COSEWIC 2013). Surveys completed by NRSI biologists in 2014 identified the presence of 4 SAR, including Barn Swallow, Bobolink, Eastern Meadowlark, and Kentucky Coffee-tree. Suitable nesting habitat for barn swallow is present within the study area in the form of barns and sheds adjacent to meadow habitat (CUM1 and CUM1-1) and foraging habitat associated with the large stormwater management facilities. Both of these species were observed at numerous locations within meadow habitats. The results of field surveys carried out by NSEI (2012) and NRSI found low numbers of these species, with no breeding pairs being observed in either study. High quality breeding habitat for Bobolink and Eastern Meadowlark is not found in the subject lands. A small cluster of Kentucky Coffee-trees, designated as Threatened both provincially and nationally (MNRF 2014b, COSEWIC 2013), were observed within the subject lands. The location of these trees is outside the mapped range of this species in Ontario. As noted earlier, and in the Phase 1 Characterization Report, the FOD5 community may provide suitable habitat for the provincially Endangered bat species Little Brown Myotis. Candidate Bat Maternity Colonies were confirmed within this woodland through cavity assessments


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2.7.3 Fluvial Geomorphology

The low permeability of subsurface materials resulting from the local geology provides little groundwater discharge into streams and also prevents effective infiltration of surface runoff. From an instream perspective, the low gradient and fragmented nature of the watercourse attenuates the overall potential energy within the system deterring sediment production through erosive processes and diminishing efficient transport of fine textured materials characteristic of the area. As a result, the watercourse lacks significant hydraulic variability and exhibits poor geomorphic function generating low quality aquatic habitats. The low gradient and poor drainage capabilities of the area increase the channels’ susceptibility to bank topping flows and floodplain inundation. Oversaturation of fine textured surface material can lead to bank seepage and a reduction of bank shear strength in areas where vegetation is sparse. These areas tend to be prone to bank slumping providing small quantities of fine sediment into the stream which the system is incapable to effectively transport based on determined erosion threshold values and field observations. The systems lack of efficient flow and sediment conveyance capabilities impairs its ability to provide good quality aquatic habitat for fish species but provides suitable conditions for wetland vegetation colonization.

2.7.4 Groundwater

As discussed in Section 2.2 the groundwater connection to stream reaches and terrestrial communities, within the study area, does not appear to be significant. The lack of groundwater discharge and recharge function for the site specific aquatic and terrestrial communities is consistent with the area’s hydrogeological setting and ecological observations.


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3.0 FUTURE LAND USE PLAN DEVELOPMENT

3.1 Transitway Corridor

During the course of the Shaping Ninth Line Study, including the related Scoped Subwatershed Study, the need for a better understanding of a major land use influence was identified related to the Ministry of Transportation (MTO) planning for a Transitway, to be located through the Ninth Line Lands, in order to service GO and regional/ local commuter transit. MTO had completed a preliminary Transitway corridor protection study in 1998 for the full limit of the Transitway from Highway 403 in Burlington to Markham Road in Markham. The focus of that study was to establish the mainline Transitway alignment and assess station locations, parking facilities, access connections and associated facilities, with the objective of determining the general property requirements necessary to implement the Transitway. Due to the high level nature of the 1998 MTO Study, impacts to the flood plain (stormwater conveyance and riparian storage) within the Ninth Line lands was not specifically analyzed or assessed. As such, an assessment of Transitway alignment alternatives has been undertaken as a companion initiative to the planning of the Ninth Line Lands, to complement the 1998 MTO Study, and concurrently consider the overall stormwater management requirements within the Ninth Line Lands. The findings and recommendations for that study have been documented in the Highway 407 Transitway Corridor Assessment within the Ninth Line Lands (Amec Foster Wheeler, October 2016). Agency and stakeholder consultation has been undertaken as part of the functional assessment for the Transitway, specifically with Ministry of Transportation (MTO), Ministry of Natural Resources and Forestry (MNRF), and Conservation Halton to secure concurrence with respect to the preliminary alignment and stormwater management plan for the transitway. A record of the agency consultation is included in Appendix A. Through this process, it was identified that the Regional Storm (Regulatory) Floodplain through the Ninth Line Lands encompasses some existing residential development east of Ninth Line and north of Britannia Road. As such, it was recognized that an opportunity existed to provide flood protection for the existing development east of Ninth Line, and to also optimize the development potential within the Ninth Line Lands, through the application of equivalent cut/fill balancing along the Transitway between Britannia Road and Derry Road, within the future development east of the Transitway. This concept was presented to the respective stakeholders noted above, and has received general support. Conservation Halton subsequently provided conceptual approval of the flood protection landform approach, however noted that additional detailed design information was required to provide full approval of the concept (ref. Howatt-Ahmad, October 28, 2016). The functional assessment for the Transitway also noted requirements to provide parking facilities adjacent to the Transitway. The planning for the parking facilities was integrated with the overall planning for the Ninth Line Lands, recognizing the need to accommodate these facilities beyond the designated right-of-way for the Transitway. Although the siting and size of


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these facilities has not been conclusively determined, general guidance has been provided by MTO to account for the inclusion of these facilities within the Ninth Line Lands. The planning and functional design of the Transitway segment through the Ninth Line Lands is currently proceeding through a separate Class Environmental Assessment process being initiated by MTO. It is anticipated that this process will build upon the consultation and guidance provided by the October 2016 Functional Assessment by Amec Foster Wheeler.

3.2 Ninth Line Lands Emerging Land Use Concept

The Shaping Ninth Line Study is intended to establish a planning framework for the Ninth Line Lands, to guide their future growth and development. It is being carried out in accordance with the Planning Act and the Environmental Assessment Act through the Municipal Class Environmental Assessment process for any future required municipal infrastructure. The Study will form the basis for amendments to the Region of Peel and City of Mississauga Official Plans. The Study involves a two phase process with Phase One complete and work continuing on Phase Two:

► Phase One: Background Review & Emerging Land Use Concept

The focus of Phase One was the development of a Vision and Guiding Principles for the Ninth Line Lands, as well as a draft Emerging Land Use Concept. The Concept was based on the identification of opportunities and constraints to development which arose from a detailed review and analysis of background information and the existing policy framework. The assessment included a technical evaluation of transportation, servicing and stormwater management, as well as the review of considerations such as cultural heritage, natural heritage and agriculture.

► Phase Two: Study Implementation Strategy

The Emerging Land Use Scenario is being used as a basis for the preparation of a Growth Management Analysis to determine if the Lands are necessary to accommodate population and employment growth in the Region, and the degree to which the land use scenario is appropriate and supportive of intensification and density targets within the context of a Municipal Comprehensive Review (MCR), as required by Provincial policy. Arising from the MCR, a draft Regional Official Plan amendment will be developed. In addition, Phase Two will involve the preparation of a Fiscal Impact Analysis and the completion of the transportation, servicing and scoped subwatershed studies, as well as the preparation of urban design guidelines. The results of this work will be reflected in a Final Ninth Line Lands Plan. In addition to the Vision and Guiding Principles, the Plan will establish specific policies on key issues such as transportation, urban design and cultural heritage. It will also include proposed amendments to the policies of the Regional Official Plan and the City’s Official Plan, and to the City’s zoning regulations.


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The Study process includes an extensive community engagement program which is designed to ensure meaningful consultation with all participants. The draft Emerging Land Use Concept was presented for review at two Public Workshops in June 2016, as well as a Landowners Meeting. The key directions included:

► Protection of a realigned route for the 407 Transitway and which achieves flood protection and drainage objectives based on the recommendations of the Functional Assessment of Transitway Alternatives through Ninth Line Lands (Amec Foster Wheeler, October 2016), including the application of cut-fill balancing to provide flood protection north of Britannia Road;

► Recognition of two Transitway stations one north of Derry Road and the other south of Britannia Road, and related higher density mixed use and residential development (3-13 storeys) and other facilities including parking;

► Protection of a linked natural heritage system including lands subject to flooding and key natural heritage and hydrological features;

► Recognition of key existing and planned features and facilities including the Bussell House property which is historically and architecturally significant; a westerly extension of Argentia Road; Hydro Corridor; rail line; Union Gas Pipeline and related facilities; and a proposed community centre and park between Britannia Road and Eglinton Avenue;

► Identification of two Business Employment areas one north of the Hydro Corridor and the other south of Eglinton Avenue; and,

► Recognition of the remaining developable lands as areas which would be developed primarily for a range of residential uses including townhouses ( 3-4 storeys) and mid-rise apartments (3-6 storeys).

Subsequent to the public review, further analysis by Amec Foster Wheeler with respect to the FPL resulted in a revised approach to flood protection in that area which involves a cut and fill alteration approach for floodplain management. The Emerging Land Use Concept has been revised to reflect this approach which also provides the potential for some additional lands for development (+/- 12 hectares) north of Britannia Road. In addition, maximum building height was reduced to 10 storeys at major intersections and adjacent to the Derry transit station, while the minimum height of development was increased from three to four storeys in those locations. Drawing LU1 reflects the revised Emerging Land Use Concept. The Concept would result in an ultimate population of 8,500 -12,225 as well as between 510 and 682 jobs for a density of 82-117 people and jobs combined per hectare. The revised Emerging Land Use Concept has been evaluated with respect to transportation and servicing (water / wastewater). No significant changes have been identified arising from those technical evaluations. The Concept forms the basis for the Growth Management Analysis as well as the Final Study Report and Regional and City Official Plan Amendments.


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4.0 IMPACT ASSESSMENT

Analyses and assessments have been completed to determine the potential impacts of the proposed land use change within the Ninth Line Lands on the area’s resources, in the absence of contemporary management practices in-place. The purpose of the testing has been to specifically determine how the land use impact and management concept satisfies various objectives regarding the preservation and/or enhancement of natural features and system functionality. The following section presents the findings of the impact assessment related to the specific study disciplines.

4.1 Surface Water/Groundwater/Water Quality

4.1.1 Future Uncontrolled Land Use Conditions

Surface Water

Hydrologic analyses have been completed in order to assess the impacts of the proposed land use concept for the Ninth Line Lands, in the absence of stormwater management controls for flood and erosion control. The VisualOTTHYMO hydrologic model for the existing land use conditions has been used for this assessment. The hydrologic model has been further revised to represent the future land use condition as per land use plan provided. The model has been rediscretized within the limits of the Ninth Line Lands in order to represent the future drainage areas and outlets, premised upon retaining pre-development drainage patterns, and generally separating the drainage for the Transitway from the drainage within the future urban development. The impervious coverage for each land use is summarized in Table 4.1.1. The subcatchment parameters for key parameters of interest are summarized in Table 4.1.2, and the corresponding subcatchment boundary plan and model schematic are presented in Drawings WR-1 and WR-2 respectively.

Table 4.1.1: Imperviousness / Coverage Values Based on Land Use

Land Use Imperviousness (%)Greenlands 5 Business Employment/Convenience/Commercial/Motor Vehicle Commercial/Utility

90

Residential Low Density I 65 Residential Low Density II 70 Medium Density 75 Mixed use 68 Public Open Space 351.

Hydro Corridor 2 Online SWM Ponds 50 Hwy 407 Embankment 5 Proposed Transitway N/A2.

NOTE: 1. Impervious coverage for Park 459 has been simulated as per the approved hydrologic modelling (ref. Farrell/Bishop-Ahmad, July 30, 2014).

2. Impervious coverage for the Transitway determined based on MTO’s typical Transitway cross-section, & total drainage area for the corresponding subcatchment.


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Table 4.1.2: Subcatchment Parameterization for Ninth Line Lands – Future Land Use Conditions

Catchment ID

Area (ha)

Imperviousness(%)

CN AMC

II

CN AMC III

Slope (Pervious / Impervious %)

Tp (hrs)

200 22.6 62.68 79 90 2/0.9 N/A 201 11.7 14.42 82 91 0.6/0.6 0.87 202 2.1 5.00 80 90 1.6/1.6 0.28 203 4.2 90.00 79 90 2/1.4 N/A 204 12.7 5.00 80 90 0.3/0.3 1.30 205 11.2 5.00 80 90 0.7/0.7 1.00 206 9.4 18.76 83 92 0.6/0.6 0.92 207 27.5 71.70 79 90 2/0.5 N/A 208 10.2 15.78 82 91 0.4/0.4 1.00 209 15.7 49.58 73 86 0.6/0.6 N/A 210 8.5 26.99 73 86 0.9/0.9 N/A 211 37.1 75.00 79 90 2/0.5 N/A 212 13.6 20.80 79 90 0.3/0.5 N/A 213 27.1 5.00 80 90 0.4/0.4 1.39 214 3.1 5.00 80 90 0.4/0.4 0.52 215 1.8 67.25 79 90 2/0.5 N/A 216 10.8 17.46 82 91 0.2/0.2 1.43 217 36.6 5.00 80 90 0.6/0.6 1.11 218 2.5 5.00 80 90 0.2/0.2 0.81 219 1.4 5.00 80 90 1.34/1.34 0.23 220 3.2 75.00 79 90 2/0.5 N/A 221 2.5 5.00 80 90 0.2/0.2 0.65 222 17.8 25.49 86 93 0.6/0.6 N/A 223 2.1 75.00 79 90 2/0.5 N/A 224 5.9 22.69 79 90 0.6/0.6 N/A 300 5.9 5.00 74 87 1.16/1.16 0.37 301 5.8 19.86 83 92 0.82/0.82 0.66 302 11.3 75.00 79 90 2/0.7 N/A 303 5.5 5.00 80 90 1.61/1.61 0.38 304 6.3 14.00 82 91 2.2/2.2 0.28 305 2.2 90.00 79 90 2/1 N/A

The VisualOTTHYMO hydrologic model for the future land use conditions has been used to determine the peak flow rates for the 2 year through 100 year return period storm events, as well as for the Regional Storm event at key locations within, and downstream of, the Ninth Line Lands, in the absence of stormwater management controls. As per the existing conditions


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assessment, the 12 hour SCS distribution has been used for design storms for the return period storm events. Soil conditions corresponding to AMC II conditions have been used for the 2 year through 100 year storm events, and all existing and approved stormwater management facilities have been represented within the model. For the Regional Storm event, soil conditions corresponding to AMC III conditions have been simulated, and all existing stormwater management facilities have been removed from the hydrologic model. The simulated peak flow rates for future uncontrolled land use conditions are summarized in Table 4.1.3, and the percent difference compared to existing land use conditions are presented in Table 4.1.4. Table 4.1.3: Simulated Peak Flow Rates for Return Period and Regional Storm Event

Under Future Uncontrolled Land Use Conditions for Ninth Line Lands (m3/s)

Node/Hydrograph Number

Location Return Period (Years) Regional

Storm 2 5 10 25 50 100


1.3 2.2 3.1 3.5 4.2 4.9 7.1

184 C.P.R.

Crossing 2.9 4.1 5.4 6.4 7.4 8.5 12.4


3.6 5.4 7.4 8.9 10.4 12.1 17.3

70 Outlet from

Osprey Marsh 10.6 17.1 24.6 33.5 42.7 53.3 107.8

104 Britannia Rd.

Crossing 7.7 16.1 26.4 35.0 43.7 53.5 158.2


7.8 17.5 28.9 38.6 48.4 59.5 183.2


8.4 18.2 32.2 43.5 54.8 67.7 219.8

148 Trafalgar Rd.

Crossing 8.7 18.1 31.6 42.7 53.7 66.5 226.7

151 Outlet to

Sixteen Mile Creek

8.7 17.9 31.0 41.6 52.1 64.4 226.3

311 CVC - Hwy.

403 Crossing 1.8 2.7 3.6 4.5 5.2 6.0 4.9


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Table 4.1.4: Percent Change in Simulated Peak Flow Rates for Return Period and Regional Storm Event Under Future Uncontrolled Land Use Conditions for Ninth Line Lands Compared to Existing Land Use Conditions (%)

Node/ Hydrograph

Number Location


79 Hwy. 407 Crossing 0 0 0 0 0 0 0

184 C.P.R. Crossing 311.4 107.0 60.0 46.1 36.3 30.5 7.4

185 Derry Rd. Crossing 260.0 101.1 69.1 56.1 51.2 45.4 12.4

70 Outlet from Osprey

Marsh -0.7 -0.9 -1.2 -1.5 -1.3 -1.2 -1.1

104 Britannia Rd.

Crossing 15.5 0.2 -1.2 -1.6 -2.1 -2.4 0.0

120 Hwy. 407 Crossing 5.5 1.7 0.7 0.4 0.4 0.3 3.0

145 Eighth Line Crossing 6.7 1.7 1.0 0.4 0.3 0.1 0.8

148 Trafalgar Rd.

Crossing 10.3 4.0 3.0 2.4 2.3 1.9 0.8

151 Outlet to Sixteen

Mile Creek 10.4 5.0 3.9 3.2 2.8 2.4 0.9

311 Sawmill Creek

Subwatershed - Hwy. 403 Crossing

237.0 197.8 173.5 171.5 162.1 155.1 17.2

The results in Tables 4.1.3 and 4.1.4 indicate that the proposed development of the Ninth Line Lands, in the absence of stormwater quantity (flood) controls, would generally be anticipated to result in increased return period peak flows for all events up to and including the Regional Storm event. The reduced flows at the outlet of the Osprey Marsh are considered attributable to the reduction in drainage area toward the north limit, as a result of the grading within the Ninth Line Lands. Of particular note, the results indicate that the proposed development of the Ninth Line Lands in the absence of stormwater quantity controls would be anticipated to result in significant increases for the portion of the development area within the local headwaters (i.e. drainage upstream CPR crossing) and the headwaters of the Sawmill Creek Subwatershed. Further it is noted that the simulated 100 year peak flow within the Sawmill Creek Subwatershed exceeds the simulated Regional Storm peak flow, hence the 100 year event is recognized as the Regulatory Event for the portion of the Ninth Line Lands within the Sawmill Creek Subwatershed. Additional analyses have been completed to determine the increased erosion potential which would result from the proposed development of the Ninth Line Lands. For the purpose of this


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assessment, the change in runoff volume above the critical erosion threshold has been determined under existing and future uncontrolled land use conditions, for the 4 hour 25 mm Chicago Storm. This assessment has been completed for erosion site NL-10, applying the critical flow rate established by the fluvial geomorphologic assessment. The results of this assessment are presented in Table 4.1.5.

Table 4.1.5: Erosion Assessment for Site NL-10

Volume of Erosive Flow (m3) % Difference

Existing Land Use Future Uncontrolled Land Use 10178 11705 15

The results in Table 4.1.5 indicate that the proposed development of the Ninth Line Lands, in the absence of stormwater controls, would be anticipated to increase the volume of erosive flows by 15% compared to existing conditions. Groundwater

Land use change through urban development can affect the pre-development groundwater system through the following:

► A reduction in infiltration and related recharge due to increased area of impervious surfaces and a subsequent lowering of the water table;

► The construction and existence of subsurface infrastructure (i.e. servicing and utility trenches, building foundation drains). Temporary lowering may result from dewatering activities during construction. Ongoing water table lowering may result from gravity drained foundation collection systems or the use of sump pumps connected to foundation drains. In addition the permeable backfill in utility trenches can act to intercept groundwater, provide preferential flow and lower the water table.

The infiltration potential, and subsequent recharge, is considered relatively low given the fine grained nature of the surficial soils and the expected seasonally high water table normally found within the Halton Till. The potential fractured nature of the Halton Till could increase infiltration in the shallow sediments during seasonal water table lows. A water budget assessment has been completed for the proposed development of the Ninth Line Area. The water budget assessment has applied the same methodology as was used for the pre-development water budget assessment, and the land use conditions have been revised as appropriate to reflect the proposed development within the Ninth Line Lands. The results of the post-development water budget are presented in Table 4.1.6


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Table 4.1.6 Post Development Water Budget Summary (Annual)

Land Use Area m2

Pervious Area m2

Impervious Area m2

Precipitationm3

Actual Evapotranspiration

m3

Runoff m3

Infiltration m3

Public Open Space 367567 367567 0 288908 198339 13585 76983

Greenland 1541679 1541679 0 1211760 708556 201282 301922

Business Employment 105957 37085 68872 83282 25424 50091 7767 Residential Medium Density

706185 423711 282474 555061 250837 215482 88742

Mixed Use 112905 56452 56452 88743 34899 42021 11823

Utility 132108 46238 85870 103837 31699 62454 9684

Road Pavement 153600 0 153600 120730 12073 108657 0

Water Bodies 160000 160000 0 125760 99520 1312 24928

Totals 3120000 2472732 647268 2452320 1287811 673993 490516

% of Precipitation 100 52.5 27.5 20.0


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Compared to the results presented for the pre-development water budget assessment, the results of the post-development water budget assessment indicate that the proposed development of the Ninth Line Lands would result in a decreased percentage of evapotranspiration, increased runoff and reduced infiltration. These trends are a reflection of the increase in impermeable areas reducing the area available for infiltration and a decrease evapotranspiration from areas of vegetation. The potential 3.2 % reduction in infiltration is considered relatively insignificant given that the local groundwater function to the aquatic and terrestrial communities within the study area is not significant and the reduction in infiltration within the study would be extremely small in the overall subwatershed setting. Furthermore, importation of lake based water is also expected to offset a portion of the reduction in infiltration. Groundwater flow within the Halton Till is considered low and large volumes are not expected to be occur but relatively higher groundwater flows may be potentially encountered where subsurface infrastructure encounters extensive sand lenses or a highly fracture portion of the upper Queenston shale. Dewatering within these deeper hydrostratigraphic units may lower the water table. A more significant issue may be the volume of dewatering necessary or whether the dewatering is short term or long term depending on the hydraulic connection and the type of subsurface structure. Current observations indicate that the aquatic and terrestrial features do not appear to be groundwater functionally supported systems. Given the nature of the surficial Halton Till and the apparent lack of groundwater discharge functionality, it is currently considered that the hydrogeological sensitivity is low with respect to ecological function and there are no significant recharge/discharge areas in the proposed development area. The importation of lake based water and subsequent infrastructure leakage and irrigation can potentially add water to the groundwater flow system and offset the reduction in natural infiltration. The potential for groundwater contamination is low given the fine grained nature of the Halton Till. Based on the above discussion, the overall site specific hydrogeologic sensitivity is considered low. The aquifer setting within the study area is considered marginal but regardless, the potential quantity and quality impacts on the on the discrete sand lenses and shallow bedrock are considered minimal. Surface Water Quality

Urban development is recognized to increase the concentration and total mass loadings of various water quality indices, specifically metals and oils/grease, compared to pre-developed land use conditions. If unmitigated, these changes in surface water chemistry could result in adverse impacts to downstream aquatic and terrestrial systems which rely on surface water for sustenance. For this reason, current Provincial Guidelines require stormwater quality controls be implemented for all new development. Within the Sixteen Mile Creek Watershed and the


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Sawmill Creek Subwatershed, stormwater quality control to an Enhanced standard of treatment is required for all new development.

4.1.2 Stormwater Management Systems Sizing (Quantity and Quality)

Hydrologic analyses have been completed in order to determine the sizing criteria for stormwater management facilities which would be required to mitigate the hydrologic impacts of the future development, specifically related to increased peak flows and erosion potential along the receiving watercourses. The VisualOTTHYMO hydrologic model has been modified in order to incorporate reservoir routing elements, representing stormwater quantity and erosion control practices within the future land use. The hydrologic model schematic corresponding to the future controlled land use conditions modelling is presented in Drawing WR-3. For the purpose of this assessment, the following approach has been applied to establish the preliminary locations for incorporating routing elements into the VisualOTTHYMO hydrologic model to represent representing the future land use condition with stormwater management:

► Routing elements representing stormwater management facilities for the Ninth Line Lands to be located east of proposed Transitway, and upstream of existing major crossings (i.e. Derry Road, Britannia Road, and CPR).

► Number of routing elements representing stormwater management facilities has been minimized to the extent possible.

► Separate stormwater management to be provided for Transitway; for the purpose of this assessment, it has conservatively been assumed that no stormwater management would be provided for the segments of the Transitway discharging to the Sixteen Mile Creek Watershed.

► A single routing element has been incorporated into the VisualOTTHYMO model to represent the combined hydrologic function of the stormwater management facilities within the portion of the Ninth Line Lands and the segment of the Transitway within the Sawmill Creek Subwatershed.

The unitary storage and discharge criteria for erosion and flood control have been iteratively adjusted until the requisite erosion and flood control has been achieved, premised upon providing peak flow reduction for all operating conditions [i.e. extended detention for erosion control and peak flow reduction for flood (to existing rates or lower) control up to the 100 year return period flow condition], consistent with conventional practice. The unitary volumes have been adjusted by incremental multiples of 25 m3/imp. ha for this assessment, and the unitary discharge rates have been determined based upon the unitary critical erosion flow and 100 year return period flow within the respective subwatersheds. The analyses have also evaluated requirements to provide post-to-pre control for the Regional Storm event along the regulated watercourses, consistent with current practice in Conservation Halton jurisdiction. The resulting unitary storage and discharge criteria under this stormwater management scenario (end-of-pipe only) are summarized in Table 4.1.7.


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Table 4.1.7: Stormwater Management Facility Sizing Criteria for Future Land Use With

Stormwater Management Scenario

Quantity Component Cumulative Unitary

Volume (m3/impervious ha)

Unitary Discharge (m3/s/ha)

Sixteen Mile Creek Erosion 275 0.002 2 Year 450 0.090 5 Year 600 0.380 100 Year 875 1.020 Regional Storm 1775 1.53 Sawmill Creek Subwatershed Erosion 275 0.002 5 Year 500 0.383 100 Year 800 1.28

The VisualOTTHYMO model for the future land use conditions scenario has been revised to incorporate the storage-discharge relationships for the routing elements representing the various proposed stormwater management facilities within the study area, and the model executed to determine the 2 year through 100 year return period peak flows, as well as the simulated peak flow rate for the Regional Storm under future land use conditions with stormwater management. The simulated return period and Regional Storm peak flows are presented in Table 4.1.8, and the percent difference compared to existing land use conditions is presented in Table 4.1.9. Table 4.1.8: Simulated Peak Flow Rates for Return Period and Regional Storm Event

Under Future Land Use Conditions with Stormwater Management for Ninth Line Lands (m3/s)

Node/ Hydrograph

Number Location


79 Hwy. 407 Crossing 1.3 2.2 3.1 3.5 4.2 4.9 7.1

184 C.P.R. Crossing 0.7 1.5 2.6 3.6 4.5 5.6 11.3

185 Derry Rd. Crossing 0.7 1.9 3.3 4.6 5.8 7.1 14.8

70 Outlet from Osprey

Marsh 10.6 17.1 24.6 33.5 42.7 53.3 107.8

104 Britannia Rd. Crossing 6.5 15.5 26.0 34.6 43.3 53.1 152.9

120 Hwy. 407 Crossing 7.2 16.8 28.3 38.0 47.8 58.9 177.8

145 Eighth Line Crossing 7.6 17.3 31.2 42.4 53.6 66.4 214.9


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Table 4.1.8: Simulated Peak Flow Rates for Return Period and Regional Storm Event Under Future Land Use Conditions with Stormwater Management for Ninth Line Lands (m3/s)

Node/ Hydrograph

Number Location


148 Trafalgar Rd. Crossing 7.7 17.0 30.3 41.2 52.1 64.8 222.2

151 Outlet to Sixteen Mile

Creek 7.8 16.7 29.6 40.1 50.5 62.6 221.9

311 CVC - Hwy. 403

Crossing 0.5 0.8 1.0 1.5 1.9 2.3 n/a

Table 4.1.9: Percent Change in Simulated Peak Flow Rates for Return Period and

Regional Storm Event Under Future Land Use Conditions with Stormwater Management for Ninth Line Lands Compared to Existing Land Use Conditions (%)

Node/ Hydrograph

Number Location



0 0 0 0 0 0 0

184 C.P.R. Crossing 0.0 -26.0 -23.8 -18.0 -16.3 -14.0 -2.2


-26.0 -31.1 -25.9 -20.0 -16.7 -14.0 -4.2

70 Outlet from

Osprey Marsh -0.7 -0.9 -1.2 -1.5 -1.3 -1.2 -1.1

104 Britannia Rd.

Crossing -3.1 -3.8 -2.6 -2.9 -3.0 -3.1 -3.4


-3.2 -2.7 -1.5 -1.1 -0.9 -0.8 -0.1


-4.3 -3.1 -2.3 -2.2 -1.9 -1.8 -1.4

148 Trafalgar Rd.

Crossing -2.2 -2.1 -1.4 -1.1 -0.9 -0.8 -1.2

151 Outlet to Sixteen

Mile Creek -1.9 -1.5 -0.7 -0.5 -0.4 -0.5 -1.1

311

Sawmill Creek Subwatershed -

Hwy. 403 Crossing

-14.8 -18.5 -21.2 -10.3 -5.6 -2.1 n/a


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The results in Tables 4.1.8 and 4.1.9 indicate that the application of the proposed unitary storage and discharge criteria would provide full post-to-pre control for all events up to and including the Regional Storm event, hence providing full flood mitigation for the proposed development within the Ninth Line Lands. The results further indicate that the stormwater management criteria would result in an over-control condition upstream of Derry Road. During the course of establishing the unitary sizing criteria, it was noted that the crossing at Britannia Road represented the governing site for providing post-to-pre control, hence, the over-control condition upstream of Derry Road is required in order to achieve post-to-pre control at Britannia Road. Additional analyses have been completed to determine the volume of runoff above the critical flow rate for erosion, under future land use conditions with proposed stormwater management. The analyses have further determined the percent mitigation which would be achieved with the proposed stormwater management sizing for erosion control. The results of this assessment are presented in Table 4.1.10.

Table 4.1.10: Erosion Assessment for Site NL-10

Volume of Erosive Flow (m3) % Mitigation

Existing Land Use Future Uncontrolled

Land Use Future Land Use

with SWM 10178 11705 10245 95.6

The results in Table 4.1.10 indicate that the proposed unitary storage and discharge requirements would provide 95.6 % mitigation of the increased erosion potential. Furthermore, the resulting extended detention storage and discharge for the stormwater management would result in a the corresponding drawdown time from the facilities at, or below, 48 hours (i.e. less than 2 days), hence the recommended unitary storage and discharge criteria would not result in onerous operations and maintenance requirements compared to current generic standards and requirements for providing erosion control as per current Provincial guidelines.

4.1.3 Water Budget and Runoff Volume Reduction

In addition to the requirements for erosion and flood control, stormwater management for future development is also required to provide water budget and runoff volume reduction, in accordance with current City standards. The reduction in infiltration noted in the Impact Assessment can be mitigated through Low Impact Development Best Management Practices (LID BMPs). Areas to promote infiltration are limited given the predominance of fine grained soils. During site specific investigation, areas of highly fractured till, near surface sand lenses or bedrock may be considered to promote infiltration. Current stormwater management requirements in the City of Mississauga require that all future development capture and retain the first 5 mm of runoff from future development. While this


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requirement has not been specifically or explicitly incorporated into the hydrologic analyses for erosion and flood control, it has nevertheless been recognized in developing the stormwater management plan for the Ninth Line Lands. Due to the limited infiltration capacity of the soils within the study area, and based upon findings in settings with similar soil conditions, it is anticipated that the capture required to maintain pre-development infiltration would be less than the 5 mm amount required in accordance with City standards. Consequently, it is anticipated that other practices to reduce runoff volume (i.e. green roofs, rain barrels, cisterns, etc.) would be required in order to satisfy the City’s standard to capture the first 5 mm of runoff. Based upon the findings of the water budget assessment, a residual increase in runoff volume would be anticipated, due to the reduction in evapotranspiration under the urbanized condition and the associated increase in runoff volume. It is further noted that pending Provincial Criteria for stormwater management is currently understood to require management of the 90 percentile event (greater than 25 mm) from future land use conditions; additional guidance regarding the methods for managing runoff from the 90 percentile event (i.e. rainwater harvesting, infiltration, filtration/conveyance, etc.) is anticipated to be provided by the Province and is to be addressed in the stormwater management plan for the Ninth Line Lands accordingly.

4.1.4 Recommended Stormwater Management Plan

The following technologies and practices are available to address the stormwater management criteria noted in the foregoing: TSS removal as per MOECC criteria:

► Wet end-of-pipe facilities (i.e. wetlands, wet ponds, hybrid facilities). ► Vegetated technologies (i.e. grassed swales, buffer strips, etc.). ► Oil/grit separators. ► Bioswales/biofilters. ► Infiltration trenches.

Thermal control as per MNRF Guidelines:

► LID infiltration BMPs ► Urban terrestrial canopy (also NHS) ► Facility shading (includes orientation and length/width ratio) ► Facility cooling trenches ► Facility bottom draws ► Stormwater management facility orientation ► Concrete Sewer System ► Underground Storage Facilities ► Green & White roofs ► Floating Islands ► Other measures


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Erosion Control:

► End-of-pipe facilities (i.e. wetlands, wet ponds, hybrid facilities, dry ponds). ► LID infiltration-based BMPs (i.e. bioswales/biofilters with underdrains, infiltration

trenches, rain gardens, perforated pipes, etc.) Flood/Quantity Control:

► End-of-pipe facilities (i.e. wetlands, wet ponds, hybrid facilities, dry ponds). ► Underground Storage Facilities ► Surface storage (i.e. rooftop/parking lot storage)

The selection of the appropriate stormwater management practice is dependent upon the size and land use conditions within the development area. The following general principles have been applied in developing the recommended stormwater management plan:

i. Wet end-of-pipe facilities are preferred, particularly for residential developments, due to their ability to address multiple stormwater management requirements (i.e. quantity, quality, thermal mitigation, and erosion control).

ii. The stormwater management system for the transitway is not to be integrated with the stormwater management for the balance of the development, in accordance with the requirements of MTO.

iii. Where drainage areas are insufficient to support an end-of-pipe facility (i.e. drainage areas less than 5 ha), source controls (i.e. underground storage, surface storage, LID BMP’s, oil/grit separators, vegetated technologies, etc.) are to be applied.

iv. LID BMP’s are to be applied throughout the development area, and sized for capturing the first 5 mm of runoff.

v. Regional Storm controls are to be incorporated into the design of wet end-of-pipe facilities.

4.2 Stream Morphology

An assessment of the proposed development plan in terms of its potential impacts to on the existing watercourse and fluvial geomorphology within the study area (Ninth Line Corridor) has been undertaken focusing on two key components:

► Meander belt width and corridor width ► Stream length

4.2.1 Meander Belt Width and Corridor Width

For the purpose of this study, reach specific meander belt widths have been determined from a geomorphic perspective through the application of various empirical approaches. The average meander belt width for each reach assessed within the study area has been reported in Table 4.2.1. A meander belt width defines the area that a watercourse currently occupies or can


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be expected to occupy in the future. The meander belt widths have been determined on a broad scale and, as such, should be subject to refinement during subsequent, more detailed phases of planning. The proposed development plan includes a corridor width that has been assigned for the Sixteen Mile Creek. Table 4.2.1 also shows the reach specific corridor widths obtained from the proposed land development plan. Specific areas where the existing meander belt width is in conflict with the proposed corridor have been identified. A properly designed corridor width ensures that the channel can safely migrate, and occupy the required space for dynamic equilibrium; simultaneously the proposed corridor width should be greater or equal to the meander belt width of the channel.


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Table 4.2.1 Meander Belt Width and Watercourse Corridor Requirements

Reach

Meander Belt Widtha

Proposed Corridor Widthd

(m)

Variance of

Proposed Corridor

Width (m)

Preliminary MBW (m)

10% factor of Safety

on either side of

Channel

CH Setbackb

(m)

Side Slopesc

(m)

Minimum Corridor

Width (m)

NL-7 28 3 30 15h 76 230 +154

NL-8 42 4 30 15h 91 170 +79

NL-9 31 3 30 15h 79 89 +10

NL-10 28 3 30 15h 76 27e -49

NL-11 31 3 15b 15h 64 145 +81

NL-12 31 3 15b 5 54 150

(31-194)f +96

(min: -23)

NL-13 25 2 15b 15h 57 27e -30

NL-14a 18 2 30 10 60 50

(40-100)f -10

NL-14b 25 2 30 10 67 50

(50-100)f -17

NL-15 15 2 30 Outside Study Limits

47 Outside Study Limits

Outside Study Limits

NLT-1 28 3 Discussed

Below Discussed

Below 31

Discussed Below

Discussed Below

HDFg 25 2 30 10 67 50 -17 a Preliminary Meander Belt Width (MBW) determined by averaging results of various empirical approaches based on existing channel width. A 10% factor of safety was added to either side of the channel. Conservation Halton requires an additional 15m setback from greatest hazard for major valley systems or 7.5m for minor valley systems, respectively. The Final MBW combines the Preliminary MBW, including the 10% factor of safety on either side of the channel, with the appropriate setback as outlined in Conservation Halton’s policy documentation, and corresponding side slopes provided by Amec Foster Wheeler. b Sixteen Mile Creek, along with its associated tributaries, is considered a major valley system within Conservation Halton’s regulatory policy documentation. As a result, the 15m setback was applied to each reach. This setback includes a 6m erosion access allowance. The setback is typically applied to both sides of the channel but for some reaches the setback was only applied to the east side of the channel as HWY 407 is situated along the west. Application of setback to existing constructed watercourses to be discussed with Conservation Halton c Side slope values determined based upon preliminary hydraulic analyses; side slopes to be verified at detailed design.. d Proposed corridor width estimated from width of areas delineated as Natural Hazards in the Proposed Land use Plan. e Proposed corridor width constrained by existing infrastructure and significant ecological communities.


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f Proposed corridor varies throughout the extent of the reach therefore average corridor width presented along with minimum and maximum values in brackets. g Channel form within headwater drainage area resembled that of the watercourse south of the C.P.R. rail line and thus MBW values similar to NL-14b were applied. h Side slopes to remain as per currently confined watercourse corridors.

As indicated in Table 4.2.1, there are several locations where the proposed corridor does not meet the desired target value. Ideally, these areas should be reviewed in order to assess opportunities to maximize the corridor. It is acknowledged that the infringement is partially due to the transitway, resulting in little potential area for the channel corridor; furthermore, several reaches represent the constructed watercourses implemented in support of Highway 407 which pre-dated current Regulatory standards for watercourse planning and hence did not include buffers or setbacks at the top of the valley slopes. Also, when reviewing these infringements in a plan view, they are more local, representing ‘pinch points’ where the transitway bends to the east, resulting in narrowing of the channel corridor. The corridor values in Table 4.2.1, provide the meander belt width, valley side slopes and CH buffer. From the geomorphic perspective the most critical aspect of these values is the meander belt width, which more closely depicts the potential hazard area. If there are potential constrictions in the corridor, at a minimum the meander belt width value should be respected.

4.2.2 Stream Length

The second key component investigated as part of the Phase 2 Impact Assessment focuses on identifying areas where loss of stream length is anticipated. Stream length contributes to the drainage density of the study area which in turn supports natural channel functions within the system. The maintenance of the overall channel length within a system also ensures that the habitable area and the ecological benefits can be preserved. Efforts should be made to maintain the length of open channels in the post-development landscape to mitigate potential adverse impacts to drainage density and existing habitat availability. Open channel may include defined stream corridors, swales in public spaces, as well as connecting channels within larger corridors (i.e. channel from outlet before connecting to a larger channel). The proposed development plan does not include existing watercourses therefore a detailed comparison of changes in overall stream length between pre- and post- development scenarios was not feasible. However, a high level assessment identifying areas where the proposed development will undergo channel realignment, redesign, and/or watercourse removal as a result of the proposed development has been undertaken. Due to the proposed land development features, particularly, the proposed Transitway and residential developments, specific portions of Sixteen Mile Creek would be directly and indirectly affected, necessitating realignment and redesign of certain channel reaches. The proposed development plan and transitway will require an estimated 2.4 km of watercourse (permanent and intermittent) to be realigned within the area north of Derry Rd., inclusive of the headwater area north of the C.P.R. rail line. The proposed natural hazard corridor within this section of the Ninth Line corridor can accommodate a straight channel length of approximately 1.9 km resulting in a net loss of 0.5 km under the proposed development plan. Given the very low gradient in the area, a designed channel may only be able to achieve a sinuosity of 1.1, which


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effectively adds 10% to the channel length. Essentially this would account for an additional 190 m reducing the potential net loss of channel length to approximately 310 m. Required channel re-alignments may alter the existing drainage density of the system which is dependent on the channel length and the contributing drainage area at the point of interest. The 2.2 km of watercourse between the online stormwater management pond south of Derry Rd and the Britannia Rd. crossing will be affected by proposed floodplain regrading and lowering. Although a significant portion of the channel is affected, essentially the channel length within this area is to be maintained.

4.2.3 Impacts

According to the proposed land development plan within the Ninth Line Lands, the subject site and in particular the Sixteen Mile Creek will likely be impacted directly and indirectly by the various development features outlined in the proposed land use plan. The following section outlines the potential impacts on stream morphology related to the proposed development plan. The proposed development plan intends on developing over most of the minor headwater areas located within the north portion of the Ninth Line Lands, south of Highway 401 and north of the rail line. The current land use plan proposes utilizing this area for business employment and public lands. These headwater features, although ill-defined and intermittent in nature, currently serve a function to maintain natural watercourse function by conveying flows to the main channel, contributing to the existing drainage density of the system. Although overall the channel lacks the ability to efficiently convey flows, these features still contribute to the functionality of the overall system. Care should be taken when developing this area to ensure some component of open drainage is included and/or combined with implementation of stormwater management techniques to maintain proper drainage to the main channel. With regards to the main channel, reaches NL-14a, NL-14b, NL-13, and NL-12 are subject to a reduction in available meander belt floodplain width area under the proposed development plan. These reaches currently encompass the watercourse segments extending north from Britannia Rd. to the C.P.R. rail line. Under the proposed development plan, the watercourse has been confined to the west side of the study area minimizing the area available for natural channel processes to operate. Reach NL-14a and NL-14b would need to be realigned to accommodate the proposed medium density residential development, Transitway station and Transitway at the north end of study area. The information in Table 4.2.1 indicates that the proposed corridor dimensions for reaches NL-14a and NL-14b which lie upstream of Derry Road, would generally meet the requirements for the watercourses. This conclusion is premised upon providing a 15 m buffer and stable side slope along the east side of the corridor only, and the meander belt width between the toe-of-slope for the Transitway and the existing toe-of-slope for Highway 407; no additional side slopes and/or buffers are proposed to be included along the Highway 407 corridor. This conclusion is also premised upon providing the meander belt width to the toe-of-slope along Highway 407 (i.e. partially within the Highway 407 right-of-way), and does not allow for expansion of Highway 407 beyond the existing right-of-way. Although the watercourse


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corridor concept has been presented to MTO as part of the Transitway Alternative Assessment, acceptance of this condition should be confirmed. The most heavily constrained section of the Ninth Line Lands is the area located immediately south of Derry Rd. This area is confined due to existing features which include the Union Gas utility corridor, a Significant Woodland feature, an existing on-line stormwater management facility and Highway 407. These pre-existing constraints significantly limit the area available to accommodate the Transitway alignment within this section of the study area. Given these limitations, the conceptual design proposes constructing the Transitway on piers and traversing the existing watercourse through the entirety of reach NL-13 and extending into the upstream portion of reach NL-12. The proposed alignment would warrant considerable channel realignment to appropriately accommodate abutments within the stream corridor, but overall channel length would presumably be maintained. Further consideration would be required to ensure geomorphic functions are maintained and that the new channel alignment does not pose a risk to existing infrastructure or newly constructed abutments. The corridor floodplain area located immediately downstream of the on-line stormwater management facility, encompassing the watercourse of reaches NL-12 and NL-11, is expected to undergo significant floodplain modification under the proposed development plan proposed medium density residential development constrains the creek corridor within this section of the study area, as such the remaining floodplain is to be regraded and lowered to accommodate Regional Storm flood volumes. Excavating the floodplain area would reduce the bankfull elevation of the watercourse increasing the frequency of bankfull exceedance and flooding. It is acknowledged that this proposed work would address the Regional Storm flows and thus an assessment is required to determine the extent of lowering that can be achieved without compromising channel functions. The channel in this area has a very low gradient and is relatively ineffective in moving sediment. Reducing the instream energy by placing frequent flows (bankfull ~ 1.5 to 2-year return flow) on the floodplain, has the potential to further impede the ability of the channel to convey its sediment load. It is anticipated as the design process progresses, there would be an optimization exercise which balances the extent of lowering with channel functions. With regards to the tributaries, NLT-1 is the only tributary affected by the proposed land use plan. This channel acts as a connection between the Osprey Marsh and the main channel with its confluence located in reach NL-11 just north of Britannia Rd. With the exception of the last 80 m of channel prior to its confluence, the small connection channel is predominantly concrete lined with a grassy meadow floodplain. The proposed residential development, trail and Transitway, are currently planned to be constructed over NLT-1. Additional analyses have been completed to evaluate the management alternatives for watercourse NLT-1. The following management alternatives have been considered, and are depicted conceptually on Drawing WR-9:


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i. Construct new watercourse north of Britannia Road along alignment of existing watercourse;

ii. Construct new watercourse extending south from the existing Ninth Line crossing at the outlet of the Osprey Marsh toward Britannia Road, and west along the south side of Britannia Road toward the existing watercourse (i.e. Reach NL-10).

Preliminary hydraulic analyses have been completed to determine the required dimensions of the watercourse and hydraulic structures for each alternative evaluated for watercourse NLT-1. The corridors have been sized based upon the following criteria:

► Corridor and hydraulic structures to be sized to maintain existing water surface elevations at existing Ninth Line crossing at outlet of Osprey Marsh (i.e. no increase in flood risk upstream of existing Ninth Line crossing).

► Bottom width to be 30 m minimum to address meander belt width requirements; bottom width increased as required to address hydraulic constraint at Osprey Marsh.

► Watercourse corridor side slopes of 3:1. ► Manning roughness coefficients of 0.1 for corridor side slopes and 0.06 for floodplain to

represent denser vegetation alongside slopes and brush along floodplain. ► Proposed crossings not to be overtopped during Regional Storm event.

The results of this assessment have indicated that the 30 m meander belt width and corridor dimensions noted above would adequately address the hydraulic criteria at the existing Ninth Line crossing for the realignment alternative 2, however a significantly larger corridor (i.e. bottom with in excess of 60 m) would be required under realignment alternative 1 in order to address the hydraulic criteria at the existing Ninth Line crossing. This is considered attributable to the 1 m increase in tailwater elevation for the Regional Storm under alternative 2, due to the existing crossing of Britannia Road. Although a narrower watercourse corridor would be required under alternative #2, the portion of the Secondary Plan Area in the vicinity of Britannia Road is currently spatially constrained due to the requirement to maintain the existing watercourse alignment for reaches NL-10 and NL-11, as well as the requirement to accommodate the future Transitway through this area. While the configuration of the realigned watercourse NLT-1 as per alternative 2 may be accommodated through this area, further discussion is required with Conservation Halton regarding the required buffers through this area and associated opportunities for an alternative buffer dimensions given the competing objectives. These alternatives will require further review, with consideration for other factors and considerations (i.e. economics, land use, flood protection, natural system connection). Watercourse Management As discussed in the previous sections, the proposed development plan will have direct impacts on Sixteen Mile Creek warranting further geomorphic consideration. Areas which may be potentially impacted as a result of the proposed development plan are outlined below:

► Headwater Area (south of Highway 401 and north of the rail line);


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► Realignment and/or redesign of reaches NL-13, NL-14a, NL-14b (north and south of Derry Rd);

► Channel enhancement due to floodplain modification within NL-11 and NL-12 (north of Britannia Rd and south of on-line SWM facility);

► Watercourse crossings at Derry Rd (NL-13 and NL-14a) and Britannia Rd (NL-11 and NL-10);

► Tributary connecting Osprey Marsh to the main channel north of Britannia Rd (NLT-1)

Generalized watercourse management recommendations have been provided which should be refined in subsequent phases of the development process. A summary of impacted watercourse areas and management recommendations based on the current land use plan is provided in Table 4.2.2.

Table 4.2.2 Summary of Watercourse Management Recommendations

Impacted Reach

Impact Management Recommendations

HDF Area

► Proposed development not supportive of HDF area located north of C.P.R. rail line. Area to be developed eliminating existing HDFs.

► 1.5 km of stream length to be realigned

► Incorporate HDFs into watercourse corridor

► Proposed corridor width should be greater or equal to the meander belt width specified in Table 4.2.2.

NL-14b

► Transitway design conflicts with existing watercourse

► Proposed development plan encroaches on existing meander belt width

► Realignment of 700 m of existing watercourse is required to accommodate proposed transitway design.

► Channel design work should aim to enhance hydraulic and geomorphic functionality of the system.


NL-14 a

► Transitway design conflicts with existing watercourse and Derry Rd. crossing

► Proposed development plan encroaches on existing meander belt width

► Proposed transitway may conflict with watercourse at Derry Rd. crossing.

► Realignment of 200 m of existing watercourse is required to accommodate proposed transitway design.

► Channel design work should aim to enhance hydraulic and geomorphic functionality.


► Existing watercourse crossing at Derry Rd. should be maintained if possible


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Impacted Reach


► Modification/redesign of crossing at Derry Rd. should consider natural geomorphic processes.

NL-13

► Transitway design conflicts with 600 m of existing watercourse

► Proposed corridor constrained by existing on-line pond, significant ecological habitat, Highway 407 and Union Gas Utility Corridor.

► Proposed Transitway may conflict with watercourse at Derry Rd. crossing.

► Elevated design of Transitway above existing watercourse is recommended in areas where Transitway alignment overlaps with existing watercourse alignment.


► Vegetative bank treatment techniques may not be suitable to provide channel stability under shaded environments.

► Bank armouring may be warranted should vegetative treatments be deemed inadequate.

► Existing watercourse crossing at Derry Rd. should be maintained if possible.

► Any modification/redesign of crossing at Derry Rd. should consider natural geomorphic processes.

NL-12

► Transitway design conflicts with upstream 150m of existing reach.

► Proposed transitway crosses watercourse at outlet of on-line SWM pond

► Proposed development plan constrains upstream end of reach immediately downstream of on-line SWM pond outlet

► Narrowing and regrading of floodplain to accommodate proposed residential development will impact 1.4 km of existing watercourse

► Realignment of existing watercourse may be required to accommodate proposed transitway design immediately downstream of on-line SWM pond outlet.

► Geomorphic processes should be considered during the detailed design phase of the transitway.

► Stream length should be maintained.


► More comprehensive geomorphic assessment required during later phases of development process (specifically detailed design of Transitway) to accurately assess


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Impacted Reach


potential impacts and develop suitable solutions.

NL-11

► Narrowing and regrading of floodplain to accommodate proposed residential development will impact 850 m of existing watercourse

► Proposed Transitway may conflict with watercourse at Britannia Rd. crossing.

► Stream length should be maintained.

► More comprehensive geomorphic assessment required during later phases of development process (specifically detailed design of transitway) to accurately assess potential impacts and develop suitable solutions.

► Watercourse crossing at Britannia Rd. should be maintained.

NL-10

► Proposed Transitway encroaches on existing meander belt width

► Proposed Transitway may conflict with watercourse at Britannia Rd. crossing.

► Proposed corridor width should retain existing corridor to existing top-of-slope.

► Watercourse crossing at Britannia Rd. should be maintained.

NLT-1

► Proposed development plan to be updated to include watercourse corridor to accommodate realignment of reach NLT-1; preliminary preferred alternative would construct realigned watercourse extending from existing Ninth Line crossing at outlet of Osprey Marsh south toward Britannia Road, and west along south side of Britannia Road toward existing watercourse NL-10.

► Additional discussion required to establish full corridor dimensions, including buffer requirements, for preliminary preferred alternative realignment for watercourse.

► Design alternatives aimed at relocating the connection channel will need to be investigated further in later phases of the development process;

The incorporation of the meander belt width into stream corridor dimensions, allows watercourses sufficient lateral width to permit channel migration without risking damage to surrounding infrastructure and property. For this reason, the recommended corridor widths should be maintained regardless of whether a watercourse remains in place or is relocated on the landscape. Respecting the meander belt width for reaches located within the study area is warranted to accommodate natural channel function and minimize risk to surrounding areas and infrastructure. As the proposed Transitway alignment and urban development significantly affect the existing floodplain and watercourse corridor, channel re-alignment and/or redesign alternatives are anticipated. Stream re-alignment and enhancement may provide a significant environmental


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benefit to important habitat provided it occurs in a carefully studied, controlled and staged manner. Hydraulic and geomorphic functionality may be enhanced through channel design work if the following objectives are addressed as part of detailed studies:

i. Improved conveyance capacity ii. Improved channel gradient, supportive of higher flow and sediment transport iii. Maintaining stream length

Re-alignment of channel segments can lead to a reduction in overall stream length affecting the drainage density and the overall natural function of the system. Typically, the loss of stream length can be partially compensated by introducing a definite level of sinuosity or meandering pattern in the overall design. This can be a challenge in the channels in the study area, due to the low energy gradients. Adding channel length results in an even lower gradient, which potentially compromises channel function. Thus, the realigned channel designs will be challenged to add much sinuosity while still maintaining functions, such as sediment conveyance. As such, efforts are encouraged to maintain stream length where ever possible to minimize negative impacts to natural channel function. Application of natural channel design techniques for stabilization may be inadequate in areas where excessive shading is expected. As a result, bank armouring may be required in areas beneath the proposed elevated Transitway south of Derry Rd. to provide effective long-term protection for proposed piers/abutments. The proposed lowering of floodplain elevations to facilitate regional flood control needs to be assessed and designed carefully. The extent of floodplain lowering needs to be balanced against the natural channel functions and sediment conveyance in this area. Given the low channel gradients, the channel struggles to convey the sediment in the system. Lowering the bankfull elevation to permit more frequent floodplain inundation would result in reducing instream energy. As both channel function and regional flood controls are important, the balancing of the functions and objectives needs to be completed during the design phase. The loss of stream length related to development of headwater areas should be compensated through an integrated design approach. The function of headwater streams can be mimicked through the combined implementation of stormwater management techniques with sufficient maintenance of open conveyance systems, to maintain drainage density and natural stream function. The creation of new open swales, for example within public open spaces, could be employed as part of the management strategy to address areas where stream length may be lost. Ideally, existing watercourse crossings would be maintained. Should road widening be warranted, it is recommended that the crossing structure be assessed to ensure channel functions are not affected. New crossings are proposed to be placed close to existing structures (based on transitway and 407 ramps). As per Conservation Halton guidelines and standard


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industry practice, the opening size of the structures should be at least 3x the bankfull width of the channel. Natural Environment

4.3 Natural Environment

The following discussion of impacts is based on the Phase 1 Characterization with the additional information and updates as described in Section 2.5 of this report. The impact analysis has been completed using the most recent information and proposed land use plan.

4.3.1 Direct Impacts

Several proposed land use changes will directly impact existing natural environment features within the subject lands. The most notable change is the currently proposed alignment of the Transitway that will extend through the subject lands running parallel to Highway 407. The alignment used for assessing impacts to the natural environment was identified as part of a feasibility study. As noted, a Class Environmental Assessment (EA) has been initiated and will further evaluate various alternatives. At this time, the proposed alignment of the Transitway results in the majority of impacts to natural environment features within the subject lands. Drawing E2 through E4 illustrate the proposed Transitway alignment with the existing vegetation communities and aquatic features. As a result of the proposed Transitway alignment, floodplain modifications are also required to maintain riparian storage and prevent flooding onto, and across, the Highway 407 and Transitway. At this time, in one part of the plan (upstream of Britannia Road) the proposed solution is to conduct a strategic cut/fill operation between Derry Road East and Britannia Road, south of the on-line stormwater management facilities. This approach has direct impacts to natural environment features within the subject lands. Table 4.3.1 summarizes the anticipated direct impacts based on the currently proposed Transitway alignment, the flood management proposed, and the land use plan.

Table 4.3.1 Direct Impacts to Natural Features

Natural Feature

Type

Existing Area (ha)

Transitway Direct Impacts

(ha)

Cut/Fill Impacts

(ha)

Development Direct

Impacts (ha)

Total Area Directly

Impacted (ha) Meadow 182 43 16 88 146 Wetland 24 6 3 10 19

Woodland 19 1 1 6.83 9 Based on the proposed Transitway alignment and the cut/fill flood management, the existing watercourse will need to be relocated within a corridor adjacent to Highway 407. In addition, the existing outlet from the Osprey Marsh (reach NLT-1) will be re-aligned to accommodate the Transitway and address floodplain hydraulics north of Derry. These proposed changes result in the following direct impacts:

► Removal of 71 ha of natural area ► Potential bird nest destruction due to tree and vegetation removal


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► Adjustment to 1 ha of fish habitat in the on-line stormwater management facilities ► Re-alignment of 2.3 km of watercourse

The proposed development concept has been established based on maximizing the amount of developable area, while minimizing impacts to the natural environment features. The land use concept is illustrated on Drawing E5 through E7, and results in additional direct impacts to natural environment features including:

► Removal of 104 ha of natural area ► Removal of Barn Swallow nesting habitat ► Potential bird nest destruction

4.3.2 Indirect Impacts

The majority of indirect impacts are a result of the proposed Transitway alignment, which has the largest effect on natural environment features within the subject lands. The proposed alignment, illustrated on Drawing E5 through E7 will remove portions of existing wetland, woodland, and requires the re-alignment of the watercourse. Based on these direct impacts the following indirect impacts are anticipated

► 8.63 ha of wetland will be hydrologically isolated ► 161 m of new woodland edge will be created ► Reduction in foraging areas over meadows for insectivores ► Alteration to surface water flow patterns due to grading and re-alignment of the

watercourse ► Sedimentation and erosion during construction ► Disruptions to wildlife from noise and dust during construction

4.3.3 Mitigation

The subject lands currently consist of disconnected woodlands, isolated pockets wetlands, highly disturbed meadow areas, and a watercourse with poor quality aquatic habitat and water quality. Based on the foregoing direct and indirect impacts, a Natural Heritage System (NHS) has been proposed that serves to create a connected natural system that will enhance the retained features, mitigate the removal and alteration of natural features, and provide resilience to the natural areas. The NHS is not considered mitigation for the removal of natural areas and features in the traditional sense. Rather the goal is to provide a new more functional and connected system where existing and retained features are enhanced with other features. Compensation for removed natural features (e.g. trees, portions of woodlands, meadow habitat) can occur within the NHS. The proposed NHS will provide the following:

► Connected system of woodlands, wetlands, meadows, and riparian areas ► Re-aligned watercourse with enhanced habitat and an overall wider watercourse corridor ► Diversity of wetland types within the watercourse corridor and the floodplain ► Higher quality habitat for wildlife than the existing condition


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► Opportunities for specialized habitat (e.g. turtle nesting areas, barn swallow structures, snake hibernacula)

► Connected natural system that enhances wildlife movement corridors and linkages. Overall, the created and enhanced natural features will provide a higher quality habitat for wildlife. The emphasis has been placed on the creation, and enhancement of woodlands and wetlands within the NHS. The NHS is further discussed in Section 5.3 of this report.


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5.0 RECOMMENDED ENVIRONMENTAL AND STORMWATER MANAGEMENT PLAN

5.1 Stormwater Management

The recommended stormwater management plan has been developed based upon the principles provided in Section 4.1.4, and the sizing criteria presented in Section 4.1.2. The recommended stormwater management plan is presented in Drawing WR-4. Key components of the recommended stormwater management plan are as follows:

► Wet ponds are recommended for the future urban development north of Britannia Road and north of Derry Road as well as in the Sawmill Creek Subwatershed, as noted on the attached plan.

► Source controls are recommended for the future development lands south of Britannia Road within the Sixteen Mile Creek Watershed as noted on the attached plan. The specific type of source controls are to be selected based upon the contributing land use and in consultation with the City of Mississauga.

► Source controls are recommended for the future development lands immediately south of Eglinton Avenue West within the Sawmill Creek Watershed, due to anticipated phasing of development for the portion of the Ninth Line Lands in the vicinity of Eglington Avenue. The specific type of source controls are to be selected based upon the contributing land use and in consultation with the City of Mississauga.

► LID BMP’s shall be applied throughout the future development lands, and shall be sized to capture the first 5 mm of runoff. The specific type of LID BMP shall be determined based upon the contributing land use and in consultation with the City of Mississauga.

► The stormwater management plan for the Transitway is to be determined through a separate Class Environmental Assessment process for the transitway, and shall be established with regard for the stormwater management criteria presented herein.

Clay plugs and anti-seepage collars could be utilized to prevent preferential flow along infrastructure backfilled material. Dewatering to implement servicing may be necessary and the volume and length of time of the dewatering may vary. A dewatering water management plan may be necessary to address local lowering of the water table and appropriate discharge of water. For dewatering volumes greater than 50,000 l/day at Permit to Take Water will be required from MOECC.

5.2 Watercourse Systems

The preceding assessments are summarized as follows:

i. The critical erosion threshold value for the Sixteen Mile Creek is almost equal to the bankfull discharge, indicating that the channel hydraulic and morphometric characteristics are not supportive of sediment transport processes.

ii. The proposed land development plan necessitates stream realignment to facilitate proposed Transitway corridor, trails and other features. Through application of natural channel design principles in the detailed design process can provide opportunities to


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improve fluvial function and dynamic equilibrium through enhanced sediment transport capabilities.

iii. Under the proposed development plan an estimated net loss of 0.5km of stream length is anticipated reducing the overall drainage density of the study area. The loss of stream length may be mitigated by incorporating open swales in development designs, and strategically adding channel length to the watercourse where possible.

iv. The proposed development plan is not supportive of the Tributary NLT-1, connecting Osprey Marsh to the main channel north of Britannia Rd. Design alternatives aimed at relocating this connection channel have been proposed but will required a more comprehensive investigation to determine the most appropriate solution.

v. The proposed corridor widths depicted in the proposed land development plan are less than existing meander belt widths of the Sixteen Mile Creek. In certain areas of the Sixteen Mile Creek, the proposed corridor width is in conflict with the Transitway ROW limits (e.g. reaches NL-14b, NL-14a, NL-13, NL-12 NL-10) reducing the area available for fluvial processes to operate and increasing potential risk to proposed developments and infrastructure. The proposed corridor width should respect the delineated meander belt width of the channel to minimize potential risks.

vi. Narrowing and regrading of floodplain to accommodate proposed residential development within reach NL-11 and NL-12 is intended to reduce floodplain elevations altering flood frequency and sediment conveyance capabilities of the watercourse. A more comprehensive geomorphic assessment required during later phases of development process (specifically detailed design of Transitway) to accurately assess potential impacts and develop suitable solutions.

5.3 Natural Heritage

5.3.1 Current Planning Context

The Region of Peel Official Plan identifies a ‘Greenlands System’ that consists of Core Areas, Natural Areas and Corridors, and Potential Natural Areas and Corridors that span the City of Mississauga, City of Brampton and Town of Caledon (Schedule A) (Region of Peel 2014). Based on Schedule A, the subject lands contain no Core Areas of the Greenlands System at this time. Lands to the east of the subject lands include limited and isolated Core Areas. The Region of Peel is preparing an Official Plan Amendment that will bring the Ninth Line Lands into the Official Plan boundary and will identify Core Ares within these lands. The City of Mississauga Official Plan (2010) identifies a ‘Green System’ that includes the City wide Natural Heritage System, Urban Forest, Natural Hazard Lands, and Parks and Open Space. Schedule 3 in that document illustrates the Natural Areas and Hazard Lands that are included in the Green System. Based on Schedule 3, the subject lands are considered a ‘Special Study Area’ and are subject to the Town of Milton (1997) and Region of Halton (2009) Official Plans until such time as the lands are incorporated into the City of Mississauga Official Plan. Lands to the east of the subject lands include a narrow corridor of Significant Natural Areas and Natural Green Space surrounding a watercourse and Other Wetland (City of Mississauga 2010). As part of the Regional Official Plan Amendment Number 38, the Region of Halton removed the Ninth Line Corridor Policy Area from its Official Plan (Halton Region 2009). According to the


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Region of Halton’s NHS, Key Features are located west of Highway 407 and are associated with watercourses and floodplain areas. The Town of Milton’s Official Plan underwent an Official Plan Amendment (OPA no. 31) (2010) to bring the document into conformity with the Growth Plan for the Greater Golden Horseshoe and the Sustainable Halton Plan. OPA 31 also revised the Town of Milton boundary to conform with the annexation of the Ninth Line Lands to the City of Mississauga. The Official Plan figures and schedules were also updated to reflect the change in boundary. In 2012, NSEI prepared the Ninth Line Corridor Study for the City of Mississauga with the goal of identifying Candidate Natural Areas with potential to be included in the City’s NHS. The current proposed NHS considered these areas and attempted to incorporate as many features as possible while balancing other land use needs in the subject lands. The proposed NHS, as described in the following, includes the Candidate Natural Areas NL4 (the Significant Woodland within the Union Gas property), the majority of NL6 (the pond and watercourse corridor located south of Britannia Road West), and NL8 (the Significant Woodland at the south end of the Ninth Line Lands). The NHS identified within the current report incorporates the existing information for the Regional Greenlands System and the Municipal Green System, as well as the Region of Halton NHS. Where possible, connections to the NHS and Greenlands System outside of the Ninth Line Lands have been maintained or created to enhance connectivity. These connections include a watercourse corridor northwest of Britannia Road (reach NLT-1) that connects the Osprey Marsh on the northeast side of Ninth Line to the NHS within the subject lands, and the East Branch of Sixteen Mile Creek corridor (between reach NL-6 and NL-7), under Highway 407 that connects the NHS to the Region of Halton and Town of Milton NHS. The Ninth Line Lands NHS was created based on the goals and objectives of the Region of Peel, City of Mississauga, and Region of Halton as stated in their Official Plans and natural heritage policies.

5.3.2 Proposed Natural Heritage System

Due to the currently proposed alignment of the Transitway, many natural heritage features identified during Phase 1 of this study cannot be protected in situ. As such, a NHS has been proposed and identified within the corridor created by Highway 407 and the proposed Transitway. The goals and objectives of the Region of Peel Greenlands System, the City of Mississauga Green System and NHS, the Halton Region Sustainable Halton NHS, and the Town of Milton’s NHS were reviewed and have been considered in the development of the proposed NHS. In addition to the NHS corridor, two (2) Significant Woodlands identified during Phase 1 and the NSEI report (2012) will be protected and incorporated into the NHS. The re-aligned Osprey Marsh outlet (reach NLT-1) and its corridor will also be protected and incorporated into the NHS. These features are located east of the Transitway and outside of the main NHS corridor. Natural heritage features to be removed from the subject lands will be compensated for within the NHS corridor and a plan for enhancement of this corridor is recommended, which provides an overall benefit for the quality of natural area.


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The proposed NHS is based on a re-aligned East Branch of Sixteen Mile Creek situated between the Transitway and Highway 407. Substantial area is available within this corridor to create and enhance natural features. Drawing E8 through E10 provide a conceptual illustration of the NHS. Included in the corridor are wetland, woodland and meadow habitats. Where possible, existing features within this corridor have been retained (e.g. watercourse, wetlands), and buffers have been included within the overall NHS, with the exception of the southern Significant Woodland. The proposed NHS within the subject lands provides a linear and connected corridor for wildlife movement between Highway 407 and the proposed Transitway. The City of Mississauga Green System and Region of Peel Greenlands is limited east of Ninth Line with natural areas generally restricted to watercourse corridors and stormwater management facilities. West of Highway 407, key features in the Region of Halton’s NHS include watercourses and narrow riparian areas. The proposed NHS, therefore, provides limited connection to features beyond the subject lands. Culverts under Highway 407 will provide some connectivity to key features in the Region of Halton’s NHS, although limited due to the size and the volume of traffic on Highway 407. A hydro corridor at the north end of the subject lands does provide a connection to features east of Ninth Line; however existing urban development restricts the quality of this connection. The outlet of Osprey Marsh (reach NLT-1), located north of Britannia Road West, currently provides a very limited connection to the wetland upstream and east of Ninth Line at Osprey Boulevard. The proposed re-alignment of this watercourse reach provides an opportunity to enhance both the aquatic habitat, and the NHS connection to the east. The watercourse and its corridor would be situated under the Transitway in an open system. The corridor can accommodate vegetation that will enhance the aquatic habitat and provide a connection for small wildlife to move further upstream. The north-south orientation of the Transitway also provide for optimum light levels during daylight hours to allow for vegetation establishment. The re-aligned Osprey Marsh outlet will provide a highly desirable east-west connection. Other opportunities for east-west wildlife movement across the Transitway are limited due to the nature of the natural heritage features in adjacent areas; however anticipated frequency of buses travelling along the Transitway is much less than a typical road, thereby providing some opportunity for wildlife movement. Despite the opportunity provided for north-south wildlife movement and limited east-west movement, the NHS is entirely surrounded by urban development so realistically will not provide high quality habitat for many species. Wildlife adapted to urban conditions will use the habitat provided, as well as the minimal connections to natural features outside the subject lands. The proposed NHS will provide a more connected and resilient system of natural heritage features within the subject lands over current conditions. The protected and recreated features will provide habitat for the species reported from the area during Phase 1, and will provide a ‘stop-over’ site for species migrating through the area. An estimate for the area of wetlands, woodlands, and meadows within the proposed NHS has been calculated. Table 5.3.1 provides details on the amount of natural area created based on the concept provided in Drawing E8 through E10.


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Table 5.3.1 Summary of Existing, Retained and Created Natural Features

Natural Feature Type

Existing Area (ha)

Retained Area in the NHS (ha)

Area of Created Feature in the NHS

Total Area in the NHS

Meadow 182 0 30 30 Wetland 24 9 40 40*

Woodland 19 11 31 42 *Created wetland within the NHS includes areas of existing wetland The proposed area of wetland within the NHS is double the existing area. Substantial floodplain area is available for wetland creation along the watercourse corridor and surrounding the online stormwater management facilities. The area of woodland that is retained within the NHS includes the Significant Woodlands identified as part of Phase 1 and in the Ninth Line Corridor Study (NSEI 2012). An additional 30.51 ha of treed area is proposed as part of the NHS, which more than doubles the existing area of woodland within the subject lands. The protection and creation of wetland and woodland will provide quality habitat for wildlife within the NHS. The existing meadow areas within the subject property includes 182ha of herbaceously dominated idle agricultural field. These features are located within lands that are designated for agriculture and have been left idle. The area of meadow within the NHS will consist of quality species aimed at attracting wildlife, insects, and other species that use meadow habitat. The meadow areas within the proposed NHS will provide foraging and some nesting habitat. Based on the low numbers of bird species that use the existing cultural meadow areas, and the limited breeding evidence observed, the removal of the idle agricultural land as part of the proposed transitway and land development is expected to have minimal impact to the existing populations, particularly with the creation of quality meadow habitat in the NHS. Overall, the existing condition includes 224.19 ha of natural area (including the existing idle agricultural fields), while the proposed NHS includes 120.37 ha of natural area. The idle agricultural fields and herbaceously dominated cultural meadow composes over 80% of the existing natural area. The creation and enhancement of natural features within the proposed NHS provides a connected and varied system of habitat features that is considered functionally superior to the existing system. Buffers protect features and ecological functions by mitigating impacts of development and site alteration (Halton Region 2015). Buffers provide slope stability, attenuate stormwater runoff, reduce human intrusion into sensitive environmental features, protect tree roots, provide safety zones for tree fall, enhance woodland interior and edges through native species and plantings, enhance wildlife habitat and provide corridors for wildlife movement, and allow opportunities for passive recreational activities (City of Mississauga 2015). Conservation Halton policies and guidelines (CH 2006) recommend a 30 m buffer for Significant Woodlands, measured from the tree dripline. The northern woodland is entirely surrounded by existing development, which is not proposed to change, and as such, there is no opportunity to


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provide an additional buffer to this feature. Based on the existing land use surrounding the southern woodland, and the future land use details, a reduced buffer may be an effective solution. This buffer should be evaluated through a future Environmental Impact Study. Within the NHS corridor created wetlands will be provided a 15 m buffer, and retained wetlands will be provided a 15 m buffer, where possible. Re-created features within the NHS corridor will be given a 15 m buffer. Based on Conservation Halton policies (CH 2006) warmwater fisheries, intermittent, and permanent watercourses require a 30 m setback from the bankfull channel. This setback is included within the NHS, where possible. The entire corridor located between Highway 407 and the proposed Transitway Is proposed to be naturalized in a complex of wetlands, woodlands, meadow habitats, and watercourses.


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6.0 REFERENCES

City of Mississauga. 2010. Mississauga Official Plan. Consolidation Version 9 – March 11, 2016.

City of Mississauga. 2014. Official Plan Amendment 27. June 23, 2014.

Conservation Halton (CH). 2006. Policies and Guidelines for the Administration of Ontario regulation 162/06 and Land Use Planning Policy Document. Approved April 27, 2006. Amended November 26, 2015

Halton Region. 2009. Official Plan. Halton Region Official Plan Package – January 13, 2016 – September 28, 2015 Interim Office Consolidation – OMB Hearing Case Nos PL091166, PL111358, and PL110857.

North-South Environmental Inc. (NSEI). 2012. 2012. Ninth Line Corridor Study. March 2012.

Region of Peel. 2014. Official Plan. Office Consolidation October 2014

Town of Milton. 1997. Town of Milton official Plan – Consolidated August 2008.

Town of Milton. 2010. Amendment No. 31 to the Official Plan of the Corporation of the Town of Milton. June 14, 2010


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7.0 GLOSSARY

Abbreviation Acronym / Definition

AHP Aquatic Habitat section AMCII Antecedent Moisture Condition II AMCIII Antecedent Moisture Condition III ANSI Areas of Natural and Scientific Interest BCR Bird Conservation Region BMP Best Management Practice BOD Biochemical Oxygen Demand CCME The Canadian Council of the Ministers of the Environment CH Conservation Halton CNR Canadian National Railway COSEWIC

Committee on the Status of Endangered Wildlife in Canada

COSSARO Committee on the Status of Species at Risk in Ontario CUM1 Cultural Meadow

CUM1-1 Dry-moist Old Field Meadow Type

EA Environmental Assessment ELC Ecological Land Classification EMC Event Mean Concentration ESA Endangered Species Act FOD Deciduous Forest FOD5 Dry-Fresh Sugar maple Deciduous Forest GW Groundwater HDF Headwater Drainage Feature HEC-RAS Hydraulic Engineering Centre – River Analysis System LGMP Living Green Master Plan LID Low Impact Development LiDAR Light Detection and Ranging OTTHYMO model University of Ottawa Hydrologic Model MAM Meadow Marsh MAM2 Graminoid Mineral Meadow Marsh MAM2-2 Reed Canary Grass Graminoid Mineral Meadow Marsh MAS2-1 Cattail Mineral Meadow Marsh MBW Meander Belt Width MEA Municipal Engineers Association MNRF Ministry of Natural Resources and Forestry MOECC Ministry of the Environment and Climate Change MTO Ministry of Transportation Ontario NAR Not at Risk NAS Natural Areas System


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Abbreviation Acronym / Definition

NHIC Natural Heritage Information Centre NHS Natural Heritage System NSEI 2012 The Ninth Line Corridor Study OAO Open Aquatic OMB The Ontario Municipal Board OPA Official Plan Amendment PIF Partners in Flight PPS Provincial Policy Statement PWQO Provincial Water Quality Objectives RGA Rapid Geomorphic Assessment ROPA Regional Official Plan Amendment ROPA 21 Regional Official Plan Amendment Number 21 RSAT Rapid Stream Assessment Technique SAR Species at Risk SARO Species at Risk in Ontario SCS Soil Conservation Service SWD2-2 Green Ash Mineral Deciduous Forest SWH Significant Wildlife Habitat SWT Thicket Swamp TKN Total Kjeldahl Nitrogen Total P Total Phosphorus UAV Unmanned Aerial Vehicle

ninth line lands - peel region · tp114008 page 2 2.0 supplemental phase 1 subwatershed study...

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