Appendix J – Fluvial Geomorphic Assessment McCowan Road Environmental Assessment between Steeles Avenue and Major Mackenzie Drive

TECHNICAL MEMORANDUM

DATE January 23, 2019 PROJECT No. 1662269

TO HDR Inc.

CC Steven Jagdat [email protected] FROM Andrew Forbes and Nick Peppiatt EMAIL [email protected]

FLUVIAL GEOMORPHIC ASSESSMENT IN SUPPORT OF THE MCCOWAN ROAD MUNICIPAL CLASS ENVIRONMENTAL ASSESSMENT, YORK REGION

1.0 INTRODUCTION Golder Associates Ltd. (Golder) was retained by HDR Inc. (HDR) on behalf of the Regional Municipality of York (York Region) to complete a fluvial geomorphic assessment in support of the Schedule C Municipal Class Environmental Assessment (EA) for proposed roadway improvements at McCowan Road from Steeles Avenue to Major Mackenzie Drive in the City of Markham, Ontario. This technical memorandum for the subject watercourses (the Rouge River and Robinson Creek) outlines the methods and results of the fluvial geomorphic assessment in the vicinity of the study corridor. 1.1 Background McCowan Road between Steeles Avenue and Major Mackenzie Drive is currently characterized by a four-lane arterial road that is oriented generally north-south and crosses several environmental features (including wetlands and watercourses), and a number of at-grade and grade separated railway lines and highway infrastructure (including Highway 407). Residential housing is the dominant land use in the areas adjacent to the road, noting that there are several other prominent development features and parklands in the local area, including the CF Markville shopping complex, Cresthaven Golf Club, Centennial Go Station, Milne Dam Conservation Park, Manhattan Woods Park, and a number of industrial and commercial areas (primarily located at the intersection of McCowan Road and Heritage Road, as well as in the areas to the immediate north and south of this intersection).

The study corridor has been targeted for improvements based on York Region’s Transportation Master Plan (2016) and 2017 10-Year Roads and Transit Capital Construction Program. The roadway improvements will involve measures to increase the north-south capacity of the roadway in anticipation of growth within the adjacent areas.

As shown on Figures 1 and 2, the project includes two watercourse crossings: the main stem of the Rouge River (5th order stream located 125 m north of the intersection of McCowan Road and South Unionville Avenue); and Robinson Creek (3rd order stream located 200 m north of the intersection of McCowan Road and Bur Oak Avenue). The main stem of the Rouge River is presently crossed by a bridge with a span of approximately 25 m, while Robinson Creek is currently crossed by three corrugated steel pipe (CSP) culverts, each of approximately 3 m diameter.

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Both of the subject watercourses are located in the Humber-Don tertiary watershed (OFAT, 2017) and Rouge River quaternary watershed (Toronto and Region Conservation, 2016). The headwaters of the Rouge River originate in the area of the Oak Ridges Moraine. The river system flows in a generally northwest to southeast direction and ultimately drains to Lake Ontario at a location approximately 16 km downstream of the study area. The Rouge River watershed includes a combination of mostly rural and urban land use (40% and 35%, respectively, of the total watershed area) (Toronto and Region Conservation, 2016). Flows from Robinson Creek join the main stem of the Rouge River at a location approximately 4.5 km downstream of the McCowan Road culvert crossing. 1.2 Purpose and Scope Modifications to the roadway at McCowan Road have the potential to influence channel conditions at the Rouge River and Robinson Creek. To that end, a fluvial geomorphic assessment was completed along defined ‘reach lengths’ (i.e., sections of the watercourse that include similar geomorphic characteristics and controls) to assess meander potential and channel stability. The results of the fluvial geomorphic assessments will be used to support the Class EA process, as well as to assist with the preliminary design of any modifications to the watercourse crossings (e.g., upgrades or replacement of bridges or culverts).

The specific work scope involved the following tasks:  background review and field inspections at all reach lengths to characterize channel morphology and assess bed and bank stability (assuming that well defined channel conditions are applicable);  meander belt width assessment at select reach lengths to determine the meander potential of the stream in the vicinity of the roadway improvements; and,  100-year erosion evaluation at select reach lengths to determine the long-term erosion potential of the stream in the vicinity of the roadway improvements.

Each of these tasks is described below in Section 2.0.

2.0 METHODOLOGY 2.1 Background Review and Field Inspections The following background information was reviewed to assist with the fluvial geomorphic assessment at McCowan Road:  orthoimagery from 1954, 1970, 1988, 2012 and 2016 (The Regional Municipality of York, Ontario, Canada, 2015a and 2015b) that was retrieved from the York Region spatial data service;  topographic data (contours) from 2016 (The Regional Municipality of York, Ontario, Canada, 2015c) that was retrieved from the York Region spatial data service;  Rouge River Watershed Plan (Barrett, 2007) that was obtained online; and,  evaluating the Effectiveness of ‘Natural’ Channel Design Projects (Geomorphic Solutions, Sernas Group Inc., The Toronto and Region Conservation Authority, and LGL Limited, 2009) that was obtained online.

In addition to the background review, a site visit was completed on June 12, 2017. The site reconnaissance included a walk-over of the subject watercourses in the vicinity of the crossing locations to assess channel

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morphology and to identify any areas of instability. Further to these general inspections, field activities at reach lengths involved substrate sampling and Rapid Geomorphic Assessments (RGAs). The field data was used to inform the meander belt width and 100-year erosion assessments (Sections 2.2 and 2.3). 2.2 Meander Belt Assessment A belt width assessment was conducted at select reach lengths based on protocols developed by Toronto and Region Conservation Authority (TRCA, 2004). The belt width assessment included the following activities:  background preparation, comprising a detailed analysis of maps and historical aerial photographs/orthoimagery from 1954, 1970, 1988, 2012 and 2016, in order to delineate the reach lengths and examine historical land use and channel patterns;  field reconnaissance at the identified reach lengths (described in Section 2.1) to evaluate current conditions and obtain measurements of channel geometry; and,  delineation/quantification of meander belt widths at the identified reach lengths to infer the stream corridor that the channel encompassed in the past and could potentially occupy in the future.

2.3 100-Year Erosion Assessment A 100-year erosion assessment was conducted at the identified reach lengths in accordance with procedures outlined by Toronto and Region Conservation Authority (TRCA, 2007). The development of the 100-year erosion limit considered the average rate of channel migration in the vicinity of the existing bridge culvert crossings and was based on similar activities described for the meander belt width assessment (Section 2.2), namely an analysis of historical aerial photographs and a field reconnaissance.

3.0 RESULTS 3.1 Background Review and Field Inspections To account for changes in fluvial geomorphologic characteristics along a channel, watercourses are typically separated into reaches that display similar physical characteristics and controls on channel morphology. With reference to Figures 1 and 2, field observations in combination with a review of available base mapping and air photographs identified a single reach length at both the Rouge River (described herein as RR-01) and Robinson Creek (RC-01). The delineation of the reach breaks for RR-01 and RC-01 (i.e., upstream and downstream boundaries of the reach length at each of the subject watercourses) were based on observed changes in one or more of channel confinement, sinuosity or hydraulics. For RR-01, the upstream reach break is located in an area where the meander pattern of the channel transitions from fully confined to partially confined conditions, while the downstream reach break is located immediately upstream of where the watercourse enters the Milne Dam Reservoir within Milne Dam Conservation Park. For RC-01, the upstream reach break is located immediately downstream of a re-constructed portion of the watercourse (i.e., the channel has been recently re-engineered to include a prominent meander pattern and adjusted belt axis – refer to Section 3.2.1), while the downstream reach is located in an area where the sinuosity of the channel transitions from a simple to compound meander pattern.

The key characteristics of the reach lengths at the Rouge River and Robinson Creek are outlined in Tables 1 and 2. Photographs taken at the site visit of the reach lengths are presented in Attachment A.

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Table 1: Key Results from Background Review and Field Inspections at Rouge River (RR-01) General Description of Channel Additional Remarks from Reach Bankfull Channel Morphology and/or Water Feature Riparian Conditions Background Review and Field Length Width Substrate Conditions Reconnaissance - Medium to large sized permanent watercourse with well-defined channel - The existing crossing structure at (i.e., incised with visible bed and McCowan Road includes a bridge bank) that includes: with a span of approximately 25 m, - mostly alluvial controls; noting that the channel is confined by - variable sinuosity (i.e., channel the bridge abutments (90o concrete planform is relatively straight in walls) in the vicinity of the existing the vicinity of the existing bridge crossing at McCowan Road (i.e., crossing at McCowan Road, and bridge abutments represent the banks meandering at the upstream and of the channel). The configuration of downstream ends of the reach); - Riparian areas upstream the existing crossing structure likely - limited bed morphology (flat); and downstream of the limits opportunities for channel form - low to moderate side slopes (10o existing bridge crossing at and function, given that the bridge to 55o); McCowan Road include a span is less than or equal to the - slight entrenchment; and, - Silty fine dense cover of shrubs, bankfull width of the channel at the - a few examples of instream sand at grasses and small trees, crossing location. woody debris or overhanging channel bed noting that the upstream trees. (D50 = overbank zone supports an - The outlet channel from a stormwater 0.06 mm) increased number of management pond joins the main RR-01 18 to 25 m - Erosion and/or depositional features larger/mature trees. stem of the Rouge River at a location at the channel that include: - Silty fine immediately upstream of the - examples of sediment deposition sand at - Riparian area under the upstream reach break, while along the bed, with a particularly banks (D50 = bridge crossing at McCowan Robinson Creek joins the main stem prominent sediment bar at the left 0.07 mm) Road is largely absent (the of the Rouge River at a location bank side of the channel in the vicinity channel is confined by the approximately 1.5 km downstream of of the crossing; and, bridge abutments – refer to the downstream reach break. - a few instances of bank erosion, Additional Remarks for recognizing however that the riparian details). - Milne Dam Reservoir is located zones and the upper portion of the approximately 2 km downstream of banks were for the most part well the McCowan Road crossing protected against erosion with a (immediately downstream of the dense cover of vegetation. downstream reach break).

- Existing meander pattern at the study - A pedestrian bridge crossing at the reach supports partially confined Rouge River is maintained conditions (i.e., channel was shown to approximately 220 m upstream of the be in contact with the right bank valley McCowan Road crossing. wall).

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Table 2: Key Results from Background Review and Field Inspections at Robinson Creek (RC-01) General Description of Channel Additional Remarks from Reach Bankfull Channel Morphology and/or Water Riparian Conditions Background Review and Field Length Width Substrate Feature Conditions Reconnaissance - The existing crossing structure at - Small permanent watercourse McCowan Road includes three CSP with well-defined bed and banks culverts, each with a diameter of that includes: approximately 3 m. The configuration - mostly alluvial controls; of these existing crossing structures - low sinuosity; (i.e., multiple closed bottom culverts) - limited bed morphology - Silty fine limits opportunities for channel form (flat); sand with and function, recognizing the absence - variable side slopes (10o to organics and - Channel margins upstream of any defined bed or bank and 75o); and, fine gravel at and downstream of the natural substrate at the culverts, and - slight to moderate channel bed McCowan Road crossing the maintenance of multiple and include mostly low lying entrenchment. (D50 = divided flow paths (instead of a single 0.07 mm) vegetation (i.e., dense cover thread). RC-01 1-3 m of grasses with the - Erosion and/or depositional occasional shrub), while the features at the channel that - Silty clay with - A number of additional crossing include: channel bed supports fine sand and extensive aquatic vegetation structures are located at or in the - examples of sediment organics at vicinity of the Robinson Creek reach deposition along the bed (cattails and other instream the banks vegetation). length. These include: concrete box (including the formation of (D50 = culvert at Castlemore Avenue with an mid-channel bars or 0.03 mm) approximate width of 13 m (located islands). 700 m upstream of the McCowan Road crossing) and a bridge at Bur - Existing channel pattern at the Oak Avenue with an approximate study reach supports unconfined span of 18 m (located 340 m conditions. downstream of the McCowan Road crossing.

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The completed RGA forms for RR-01 and RC-01 are presented in Attachment B, while grain size results for these reaches are presented in Attachment C. The results of the RGAs suggest that RR-01 and RC-01 are in a state of transition, noting, in particular, that RR-01 included several examples of channel widening (e.g., fallen trees, exposed tree roots, basal scour on inside meander bends, etc.). 3.2 Meander Belt Assessment 3.2.1 Aerial Photography Analysis A historical air photograph analysis was completed in support of the meander belt assessment, and relied on aerial photography and orthoimagery from 1954, 1970, 1988, 2012, and 2016. These images/photos were used to evaluate changes in channel patterns and surrounding land use over time at the Rouge River (RR-01) and Robinson Creek (RC-01). The results of the historical air photograph analysis are illustrated on Figures 3 and 4, and described below.

The air photograph analysis (1954-2016) demonstrated that historical land use in the vicinity of RR-01 and RC-01, as well as in the upstream catchment areas of these watercourses, was predominated by agriculture since at least 1954, recognizing that, based on our general understanding of settlement patterns in the Greater Toronto Area, agriculture and associated land clearing has likely been the dominant land use in the Rouge River and Robinson Creek watersheds over the past approximately 100 or more years. From there, the air photos/images showed that land use transitioned to primarily urban development (residential with some commercial and light industry); this occurred between 1954 and 1970 at RR-01, and between 1988 and 2012 at RC-01. Further to this, the review of the historical air photos identified the construction of Highway 407 and several local side roads between 1970 and 1988, as well as the construction of the Milne Dam Reservoir between 1954 and 1970.

Riparian vegetation within the areas of investigation has been historically moderate in density, consisting of tree, shrub and grass cover. In some instances, this vegetation cover limited direct observation of features on the ground. Nevertheless, the channels at RR-01 and RC-01 were visible on a fairly consistent basis on all of the available aerial photography and orthoimagery.

The results of the historical air photo analysis showed that channel patterns at the Rouge River (RR-01) have remained relatively unchanged between 1954 and 2016. However, the review of the photos/images suggest that the channel has widened over time (by roughly 30% between 1954 and 2016), with the most noticeable increase occurring between 1954 and 1988. The observed widening of the channel at the study reach appears to have coincided with the development of the Milne Dam Reservoir (located immediately downstream of the downstream reach break). As such, the construction and subsequent maintenance of this reservoir likely resulted in changes to the channel/floodplain hydraulics at a local scale (i.e., reduced flow velocities and increased water levels at the channel of the study reach due to backwater effects from the reservoir), and, in turn, adjustments to cross section geometry.

The channel pattern at Robinson Creek (RC-01) appears to have been significantly altered (i.e., diverted and/or realigned) prior to 1954 and at one or more times after this, recognizing that, with few exceptions, the watercourse has historically exhibited low sinuosity and trended in a generally northwest to southeast direction. The observed changes in channel patterns at RC-01 are summarized below:

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 In 1954, the section of Robinson Creek at the upstream end of the study reach (i.e., uppermost 225 m of the study reach that is centered over McCowan Road), as well as at the approximate mid-point of the study reach (i.e., from approximately 750 to 950 m downstream of McCowan Road, where the watercourse is oriented north to south), was historically marked by a strong meandering pattern, noting two particularly prominent meander bends that were located in the in the vicinity of the McCowan Road crossing. In contrast, the channel for the remaining portion of the study reach included a relatively straight alignment. The results suggest that lengthy sections of the channel were straightened before 1954 to accommodate agricultural practices, while the identified sub-sections of the channel at the upstream and mid-point of the study reach were left to adjust naturally.  From 1970 to 2016, the air photograph analysis showed that, with few exceptions, the channel followed a mostly straight alignment for the full extent of the reach, and remained relatively unchanged (only minor adjustments – limited evidence of channel movement). The watercourse at the upstream end of the study reach (i.e., section of channel that was formerly characterized by a strong meandering pattern) appears to have been straightened between 1954 and 1970 to accommodate agriculture and/or urban development, while a 250 m section of the watercourse at the downstream end of the study reach was shown to be re-engineered between 2012 and 2016 (i.e., formerly straightened section of channel was replaced by a channel with four interconnected meander bends). Despite the identified changes to the channel patterns (from 1954 through 2016), the meander belt axis at the study reach demonstrated no discernible shift. For that matter, any meander bends at the watercourse have demonstrated limited evidence of lateral or downstream movement, particularly over the most recent period of the historical air photo record. Of note, the channel upstream of the study reach was shown to be significantly altered between 2012 and 2016. This section of Robinson Creek was characterized by a mostly straight channel planform between 1954 and 2012, and has since been re-engineered to include a prominent meandering pattern, noting that, as part of these engineering works, the channel (and associated meander belt axis) has been shifted toward the left bank side of the floodplain. 3.2.2 Belt Width Calculations The meander belt width estimates at Rouge River (RR-01) and Robinson Creek (RC-01) are illustrated on Figures 5 and 6, respectively. A summary of the meander belt width estimates is provided below.

The meander belt width estimate for the study reach at RR-01 is outlined as follows, and corresponds to the TRCA guidelines for a partially confined channel:  A preliminary meander belt width was measured to be on average approximately 74 m (i.e., average of the estimated preliminary belt widths at the narrowest and widest sections of the valley – see below). This estimate of the preliminary belt width considered the following:

▪ The channel at the study reach was observed to be partially confined along the right bank (south) side of the valley for the duration of the historical air photo analysis. As such and in accordance with TRCA guidelines, the meander belt width for the right bank side of the channel was aligned with the top of the right bank valley wall for the full extent of the study reach. The available topographic data from York Region was used to infer the top of valley wall along the right bank of the channel planform (estimated to be at an average elevation of roughly 170 m asl), recognizing that a detailed topographic survey should be completed to refine this estimate. The meander belt width for the left bank (north) side of the channel was delineated based on the outer-most meander bends at the study reach.

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▪ The estimates of the preliminary belt width were shown to vary due to the irregular pattern/form of the right bank valley wall (refer to Figure 5).  The existing meander belt width was estimated to be approximately 96 m. The calculation of the existing belt width combines the preliminary meander belt width with the average bankfull width of the channel (22 m), as estimated in the field (e.g., 74 m + 22 m = 96 m).  A final meander belt width was estimated to be approximately 106 m (with consideration of the average preliminary belt width). This final belt width combines the estimated existing belt width with a safety factor of 1.1 in order to account for potential changes in upstream hydrology and channel movement.

The meander belt width estimate for the study reach at RC-01 is summarized as follows, and corresponds to the TRCA guidelines for an unconfined channel:  A preliminary belt width was measured to be approximately 36 m. The preliminary meander belt width represents the measured width between the outer-most meander bends based on historical imagery from 1954 through 2016, with consideration of the following: ▪ Based on TRCA protocols, it is understood that portions of the channel planform that have been modified no longer represent the natural meander potential of a watercourse, meaning that these altered sections of the channel prevent reliable measurements of a meander belt width. To that end and in accordance with TRCA guidelines, the meander belt width for the study reach at Robinson Creek was determined based on the historic air photographs that recorded the position of the unaltered channel configuration. This meant that the belt width measurements were estimated using the section of the watercourse that is located at the upstream end and middle portion of the study reach and that were observed to support a strong meandering pattern in 1954.  The existing meander belt width was estimated to be approximately 39 m. The calculation of the existing belt width combines the preliminary meander belt width with the average bankfull width of the channel (approximately 2 m), as estimated in the field (36 m + 2 m = 38 m).  The final meander belt was estimated to be approximately 46 m. This final belt width combines the estimated existing meander belt width (38 m) with the estimated 100-year migration distance (7.5 m) (i.e., average rate of channel migration over the past 30 years of the historical air photo record). 3.3 100-Year Erosion Limit In accordance with TRCA protocols, the 100-year erosion limit for the Rouge River (RR-01) and Robinson Creek (RC-01) were assessed based on the average rate of channel migration at the relevant study reach. In general, the estimates considered all of the available photos/images (i.e. 1954, 1970, 1988, 2012, and 2016).

The 100-year erosion limit at the reach length of the Rouge River (RR-01) was assessed based on the average rate of channel migration at the following meander bends as shown on Figure 5:  Meander Bend #1 (located 120 m upstream from McCowan Road) – average migration rate of 13 cm/yr.  Meander Bend #2 (located 400 m downstream from McCowan Road) – average mitigation rate of 10 cm/yr.  Meander Bend #3 (located approximately 1 km downstream of McCowan Road) – average migration rate of 21 cm/yr.

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Based on the historical analysis, the 100-year erosion limit at RR-01 was estimated to be approximately 64 m. This 100-year erosion limit was determined by extending the average rate of migration at the most active meander bend over a 100-year time span (0.21 m/yr * 100 = 21 m), and then applying this distance to either side of the average width of the bankfull channel (21 m * 2 + 22 m = 64 m).

The 100-year erosion limit at Robinson Creek reach (RC-01) was assessed based on the average rate of channel migration at the following meander bends as shown on Figure 6:  Meander Bend #1 (located approximately 230 m upstream of the McCowan Road crossing) – average migration of 4 cm/yr.  Meander Bend #2 (located approximately 570 m downstream of the McCowan Road crossing) – average migration of 9 cm/yr.  Meander Bend #3 (located approximately 850 m downstream of the McCowan Road crossing) – average migration of 7 cm/yr.  Meander Bend #4 (located approximately 200 m upstream from the downstream reach break at Roy Rainey Avenue) – average migration of 10 cm/yr. Based on the historical analysis, the 100-year erosion limit at RC-01 was estimated to be approximately 22 m. This 100-year erosion limit was determined by extending the average rate of migration at the most active meander bend over a 100-year time span (0.10 m/yr *100 = 10 m), and then applying this distance to either side of the average width of the bankfull channel (10 m * 2 + 2 m = 22 m).

4.0 SUMMARY AND CONCLUSIONS A fluvial geomorphic assessment was completed at study reaches of the Rouge River (RR-01) and Robinson Creek (RC-01) to support a Schedule C Municipal Class EA for the proposed roadway improvements at McCowan Road from approximately Steeles Avenue to Major Mackenzie Drive. The key findings of the assessment are summarized below:  The results of the field studies and historical air photo analysis at the reach length of the Rouge River (RR-01) and Robinson Creek (RC-01) suggest that the channels are generally stable, noting the following observations:

▪ The planform of the channels is relatively straight in the vicinity of the crossing locations at McCowan Road, and, in the case of the Rouge River, meandering in the areas upstream and downstream of the crossing (the meander bends that formerly characterized channel conditions at the Robinson Creek crossing were re-aligned/straightened between 1954 and 1970). ▪ The geometry of the channels is slightly entrenched (i.e., well-incised between moderately sloped banks), while the profile of the channels is relatively flat. ▪ The channels include instances of bank erosion and bed deposition in a few locations, recognizing however that the banks and riparian zones are for the most part well protected against erosion with a dense cover of vegetation.

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▪ The channel at the Rouge River has shown some widening over time (by roughly 30% between 1954 and 2016), with the most noticeable increase occurring between 1954 and 1988 (likely as a result of the development and maintenance of the Milne Dam Reservoir and the associated changes to upstream channel/floodplain hydraulics at a local scale); however, any meander bends at this watercourse, as well as at Robinson Creek, have demonstrated limited evidence of lateral or downstream movement over the most recent period of the historical air photo record. ▪ the configuration of the existing crossing structures likely limits opportunities for channel form and function (e.g., the existing bridge span at the Rouge River crossing is less than or equal to the bankfull width of the channel, and the use of multiple closed bottom culverts at the Robinson Creek crossing prevent the development/maintenance of any defined bed or bank, natural substrate, and single thread flow path).  Based on the results of the desktop analysis, the meander belt width of the reach length of the Rouge River (RR-01) is approximately 106 m (with consideration of the average preliminary belt width), while the meander belt width at the reach length of Robinson Creek (RC-01) is 46 m. In accordance with TRCA guidelines, the meander belt width for RR-01 was aligned with the top of the right bank valley wall to account for the partial confinement of the channel.  Based on the results of the desktop analysis, the 100-year erosion limit at the reach lengths of the Rouge River (RR-01) and Robinson Creek (RC-01) is 64 m and 22 m, respectively.

It is understood that roadway improvements at McCowan Road may involve upgrades or replacement of the existing crossing structures at the Rouge River (bridge with an approximate span of 25 m) and Robinson Creek (three culverts, each of approximately 3 m diameter). According to TRCA protocols, crossing structures should be constructed outside of the meander belt width of a watercourse to the extent possible, or, alternatively, the features should be designed to match or exceed the 100-year erosion limit of the channel. However, for the study reach at the Rouge River, it is recognized that spanning a crossing structure the length of the estimated belt width or 100- year erosion limit of the channel would be impractical and cost prohibitive. Furthermore, Golder is of the opinion that a crossing span less than the estimated dimensions of the meander belt width and 100-year erosion limit at RR-01 would be appropriate for this particular study, with consideration of the following:  The channel of the Rouge River in the vicinity of the McCowan Road crossing is relatively straight, stable, and partially confined to the right bank valley wall, noting that:

▪ The channel at the crossing location, and, for that matter, at locations upstream and downstream of the crossing, has shown limited evidence of movement over the most recent period of the historical air photo record (between 1988 and 2016). ▪ There is no evidence to suggest that meander bends located upstream of the crossing are at risk of encroaching on existing or future infrastructure at McCowan Road (via lateral and/or downstream migration).  The valley of the Rouge River at the McCowan Road crossing has been re-configured to accommodate the existing crossing structure, recognizing that the existing bridge span and adjoining abutments are located well within the boundaries of the estimated belt width and 100-year erosion limit of the study reach.  Any upgrade or replacement of the existing crossing structure at the Rouge River will be designed to convey up to and including the 100-year flow or Regional event; hence, major flows will be directed to the channel

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1662269 HDR Inc. January 23, 2019 and crossing structure openings, with limited opportunities to outflank the crossing feature and erode a separate flow path. ■ The historical air photograph analysis demonstrated that channel migration in the recent period of record (i.e., 1988 onward) has occurred at a relatively low rate, meaning that, if needed, any repairs or maintenance at the study reach could be readily accommodated within a reasonable timeframe. For the reasons identified above and from the perspective of fluvial geomorphology, it is suggested, from a preliminary recommendations standpoint, that any upgrade or replacement of the existing crossing structures at the study reaches of the Rouge River and Robinson Creek include a width of approximately 45 m and 22 m, respectively, if feasible. The suggested crossing dimension for the Rouge River roughly corresponds to both two (2) times the average bankfull width of the channel and two (2) times the average migration rate of the channel (based on the most active meander bend at this study reach), while the suggested crossing dimension for Robinson Creek matches the estimated 100-year erosion limit of the channel. The opening of any new bridge structure at the Rouge River should be centered/positioned toward the left bank side of the channel, given that the right bank is confined by the valley wall. The proposed span for the crossing structures at Mccowan Road are expected to result in improved opportunities for channel form and function at each of the study reaches, recognizing the inherent constraints on these considerations under current conditions (due to the configuration of the existing crossing structures - refer to Section 3.1 for details). As part of this, the proposed span of the Mccowan Road crossing at Robinson Creek will be in line with the associated dimensions of the crossing structures that are located immediately upstream and downstream (at Castlemore Avenue and Bur Oak Avenue, respectively), as well as with the characteristic meander amplitude of the section of channel that has been re­ engineered in recent years at the upstream reach.

The recommendations described above are based on the results of the fluvial geomorphology assessment alone. Any modification to the crossing spans will also need to consider input from other technical considerations, including the required hydraulic conditions ( e.g., flood conveyance for the design event) and the relevant ecological functions (e.g., wildlife passage in the riparian zone). 5.0 CLOSURE We trust that this technical memorandum meets your needs at this time. If you have any questions, please do not hesitate to contact the undersigned.

This Report was authored under a Subconsultant Agreement between HDR and Golder for the Regional Municipality of York’s (“Owner”) projects. The Report is provided to HDR and Regional Municipality of York for their use, utilizing their judgment, in fulfilling a portion of HDR’s particular scope of work. No other party may rely upon this report, or any portion thereof, without Golder’s express written consent and any reliance of the reports by others will be at that user’s sole risk and liability, notwithstanding that they may have received this Report through an appropriate user. In addition, Golder shall not be liable for any use of the Report for any purpose other than that for which the same was originally prepared or provided by Golder, or any improper use of this Report, or to any party other than HDR.

Yours truly, GOLDER ASSOCIATES LTD.

Nick Peppiatt, BEng Andrew Forbes, MSc, PGeo Water Resources Specialist Associate, Senior Geoscientist JL/NP/AF/ng/mp \\golder.gdslgallwhitby\active\201613 proj\1662269 hdr_classea_mccowanrd\fluvial geomorphology\04. reporting\04. finalrevision_23jan2019\01. tech memo\1662269-tm-rev0-hdr fluvial geomorphic-mccowan-23jan2019.docx

.Golder 11/13 \2PAssociates 1662269 HDR Inc. January 23, 2019

Attachments: Figures: Figure 1: Reach Length for Rouge River Crossing at McCowan Road (RR-01) Figure 2: Reach Length for Robinson Creek Crossing at McCowan Road (RC-01) Figure 3: Historical Channel Patterns for Rouge River Crossing at McCowan Road (RR-01) Figure 4: Historical Channel Patterns for Robinson Creek at McCowan Road (RC-01) Figure 5: Estimated Meander Belt Width for Rouge River Crossing at McCowan Road (RR-01) Figure 6: Estimated Meander Belt Width for Robinson Creek Crossing at McCowan Road (RC-01)

Attachment A – Photographs Attachment B – Results of Rapid Geomorphic Assessments Attachment C – Grain Size Distribution Curves

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REFERENCES

Barrett, S. (2007). Rouge River Watershed Plan - Towards a Healthy and Sustainable Future. Toronto: Toronto and Region Conservation.

Geomorphic Solutions, Sernas Group Inc., The Toronto and Region Conservation Authority, and LGL Limited. (2009, February). Evaluating the Effectiveness of 'Natural' Channel Design Projects: An Introduction and Preliminary Assessment of Sites in TRCA's Jurisdiction. Toronto and Region Conservation Authority.

Infrastructure Management and Project Management Office Transportation Services. (2017, January). 2017 10- Year Roads and Transit Capital Construction Program. York Region. Retrieved from http://www.york.ca/wps/wcm/connect/yorkpublic/0d954ef4-12b6-4ac7-931d- 39a3d1269dff/2015+Approved+Roads_8_11_year_Ver2.pdf?MOD=AJPERES

The Regional Municipality of York, Ontario, Canada. (2015a and 2015b). Historical Imagery Web Mapping Services Application Programming Interface.

The Regional Municipality of York, Ontario, Canada. (2015c). Contours 1m, 2016.

The Regional Municipality of York, Ontario, Canada. (2015b). Current Year Orthophotography Web Mapping Services Application Programming Interface.

Toronto and Region Conservation. (2016, July 27). Watershed Features. Retrieved from Toronto and Region Conservation: https://trca.ca/conservation/watershed-management/rouge-river/watershed-features/

TRCA [Toronto and Region Conservation Authority]. (2004, January). Belt Width Delineation Procedures.

TRCA [Toronto and Region Conservation Authority]. (2007, September). Watercourse Crossing Design and Submission Requirements.

York Region. (2016, November). 2016 Transportation Master Plan.

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1662269 HDR Inc. January 23, 2019

FIGURES

S:\Clients\Region_of_York\McCowan_Road\99_PROJ\1662269\40_PROD\0007_Fluvial_Geomorphology\1662269-0007-CS-0001.mxd

E

C

K

A

R

D T

C

R

E E K K  Stormwater Management Pond Pond Management Stormwater

MCCOWAN ROAD ROAD MCCOWAN

Existing Bridge Bridge Existing span of 25 m) of 25 span (with approx. (with



RR-01 RR-01 M

I

L

N

E

C

R

E

E K K Milne Dam Reservoir Dam Milne

H

I G

H

W

A 4 Y

0 7 

HIGHWAY 7

R O

B

I N

S

O

N

C

R

E

E K K 1662269 1662269 NO. PROJECT CONSULTANT (RR-01) ROAD AT CROSSING MCCOWAN RIVER ROUGE FOR LENGTH REACH TITLE YORK OF REGION MARKHAM, OF CITY DRIVE MACKENZIE MAJOR TO AVENUE STEELES ROAD, MCCOWAN PROJECT HDR INC. CLIENT 3. 2. 1. REFERENCE(S) LEGEND UTM ZONE 17N 17N ZONE UTM

PROJECTION: TRANSVERSE MERCATOR DATUM: NAD 83 COORDINATE SYSTEM: COORDINATE 83 NAD DATUM: MERCATOR TRANSVERSE PROJECTION: 2016 WMS, YORK OF REGION IMAGERY: 2016 OBTAINED YORK OF REGION LIO, DATA: MNRF BASE

Watercourse Flow Direction Reach Study the Beyond Channel of Centreline Estimated (2016) Study Reach atChannel Observed Alignment Break Reach

1:12,500 1:12,500 0

CONTROL CONTROL

250 250

APPROVED APPROVED PREPARED DESIGNED YYYY-MM-DD REVIEWED REVIEWED ^ _ LOCATION LOCATION SITE

500 500 REV. 0

AF AF NP/JT NP/JT NP 2017-08-25

METRES METRES 750 750

FIGURE FIGURE 1

IF THIS MEASUREMENT DOES NOT MATCH WHAT IS SHOWN, THE SHEET SIZE HAS BEEN MODIFIED FROM: 0 25mm S:\Clients\Region_of_York\McCowan_Road\99_PROJ\1662269\40_PROD\0007_Fluvial_Geomorphology\1662269-0007-CS-0002.mxd with approx. span of 13 m 13 of span approx. with Concrete Box Culvert Culvert Box Concrete

Management

Stormwat Stormwat  er er

Pond Pond 

B

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A

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Stormwater Management Pond Pond Management Stormwater  Three CPS Culverts each of 3 m diameter diameter m 3 of each Culverts CPS Three 

with approx. span of 18 m 18 of span approx. with

Concrete Box Culvert Culvert Box Concrete

MCCOWAN ROAD ROAD MCCOWAN

RC-01 RC-01

CASTLEMORE AVENUE 

(with approx. span of 32 m) m) 32of span approx. (with

AVENUE RAINEY ROY Existing Bridge Bridge Existing 

Stormwater Management Pond Pond Management Stormwater 

UTM ZONE 17N 17N ZONE UTM 1662269 1662269 NO. PROJECT CONSULTANT (RC-01) ROAD MCCOWAN AT CROSSING CREEK ROBINSON FOR LENGTH REACH TITLE OF YORK REGION MARKHAM, CITY OF DRIVE STEELES MACKENZIE AVENUEROAD, MCCOWAN TOMAJOR PROJECT INC. HDR CLIENT 3. 2. 1. REFERENCE(S) LEGEND

PROJECTION: TRANSVERSE MERCATOR DATUM: NAD 83 COORDINATE SYSTEM: COORDINATE 83 DATUM:MERCATOR NAD TRANSVERSE PROJECTION: 2016 WMS, YORK OF REGION IMAGERY: 2016 OBTAINED YORK OF REGION DATA: LIO, BASE MNRF

Watercourse Watercourse Direction Flow Reach Study the Beyond Channel of Centreline Estimated (2016) Reach Study at Channel Alignment Observed Break Reach

1:6,230

0

CONTROL CONTROL

100

APPROVED APPROVED PREPARED DESIGNED YYYY-MM-DD REVIEWED REVIEWED ^_

LOCATION SITE 200

REV. 0 METRES 300 AF AF NP/JT NP/JT NP 2017-08-25

FIGURE FIGURE 2

IF THIS MEASUREMENT DOES NOT MATCH WHAT IS SHOWN, THE SHEET SIZE HAS BEEN MODIFIED FROM: 0 25mm 185 184 LEGEND 173 184 175 174 175 Reach Break Observed Channel Alignment in 1954 Observed Channel Alignment in 1970 Observed Channel Alignment in 1988

180 174 Observed Channel Alignment in 2016 1m Contour Elevation

167 Flow Direction

167

171

168 179 178

177

176 169

173

168 168 172 Milne Dam 167 Reservoir 

171

169 168 168 170 167 168 167 169 Existing Bridge 167 (with approx. span of 25 m) 167 ^_ SITE 167  169 LOCATION 170 167 167 167 167 167

167 M

C

C

O 173 W

A 167 174 N

R 169 O 170 171 170 174 A 167 D 167 168 0 100 200 300 172 RR-01 167 171

167 169 171 167 1:4,000 METRES 167

170 174

171 REFERENCE(S) 172 1. BASE DATA: MNRF LIO, REGION OF YORK OBTAINED 2016 2. IMAGERY: REGION OF YORK WMS, 2016 173 3. PROJECTION: TRANSVERSE MERCATOR DATUM: NAD 83 COORDINATE SYSTEM: UTM ZONE 17N 173

175 174

175 174 CLIENT

176 174 HDR INC. 175 174

177 PROJECT

175 MCCOWAN ROAD, STEELES AVENUE TO MAJOR MACKENZIE DRIVE 176 177 CITY OF MARKHAM, REGION OF YORK 178 173 172 175 174 177 TITLE 179 175 HISTORICAL CHANNEL PATTERNS FOR ROUGE RIVER 172 174 176 177

CROSSING AT MCCOWAN ROAD (RR-01) SHOWN, THIS IS SHEET THEBEEN WHAT SIZE MATCH IF MEASUREMENTNOT HAS DOES MODIFIED FROM: CONSULTANT YYYY-MM-DD 2017-08-25 25mm 25mm 176 DESIGNED NP 176 178 HIGHWAY 407 177 179 PREPARED NP/JT 179 176 177 178 180 REVIEWED AF 176 175 177 175 APPROVED AF 175 179 177 178 176 175 PROJECT NO. CONTROL REV. FIGURE 1662269 0

S:\Clients\Region_of_York\McCowan_Road\99_PROJ\1662269\40_PROD\0007_Fluvial_Geomorphology\1662269-0007-CS-0003.mxd 3 0 S:\Clients\Region_of_York\McCowan_Road\99_PROJ\1662269\40_PROD\0007_Fluvial_Geomorphology\1662269-0007-CS-0004.mxd 208 208 203 203 with approx. span of 13 m 13 of span approx. with 200 200 211 209 209 201 201 197 197 211 Concrete Box Culvert Culvert Box Concrete

202 202 199 199 198 198 201 201 197 197 200 200 210 210

206 206 200 200 199 199 206 206 202 202 206 206  201 201 202 202 205 205 202 202 205 205 205 202 202 210 210 203 203 204 204 205 205 203 203 203 203 206 206 203 203 207 207 211 208 208 209 209 209 209 209 209 210 210 205 205 209 209 209 209 208 208  Three CSP Culverts each of 3 m diameter diameter m 3 of each CSP Culverts Three 211 204 204

with approx. span of 18 m 18 of span approx. with Concrete Box Culvert Culvert Box Concrete

204 204 205 205 208 208 RC-01 RC-01 207 207 210 210

210 210

206 206 214 214 208 208 209 209 210 210 209 209 208 208 212 212  205 205 213 213 212 212 211 213 213 203 203 211 207 207 209 209 203 203 208 208 209 209 204 204 202 202 208 208 210 210 212 212 210 210 213 213 209 209 209 209 209 209 205 205 208 208 209 209 207 207 201 201 209 209 209 209 200 200 212 212 208 208 207 207 213 213 205 205 200 200 205 205 207 207 201 201 208 208 204 204 (with approx. span of 32 m) m) 32of span approx. (with

Existing Bridge Bridge Existing 212 212 

199 199 198 198 200 200 199 199 200 200 211 199 199 197 197 198 198 210 210 209 209 196 196 200 200 209 209 199 199 201 201 200 200 199 199 204 204 210 210 197 197 205 205 195 195 211 206 206 202 202 194 194 199 199 198 198 194 194 212 203 203 201 201 UTM ZONE 17N 17N ZONE UTM REACH. STUDY OF LIMITS 1662269 1662269 NO. PROJECT CONSULTANT H TI OF YORK REGION MARKHAM, CITY OF DRIVE STEELES MACKENZIE AVENUEROAD, MCCOWAN TOMAJOR PROJECT INC. HDR CLIENT 3. 2. 1. REFERENCE(S) 1. NOTE(S) LEGEND CROSSING AT MCCOWAN ROAD (RC-01) ROAD AT MCCOWAN CROSSING

TLE TLE ISTORICAL CHANNEL PATTERNS FOR ROBINSON CREEK CREEK ROBINSON FOR PATTERNS CHANNEL ISTORICAL PROJECTION: TRANSVERSE MERCATOR DATUM: NAD 83 COORDINATE SYSTEM: COORDINATE 83 DATUM:MERCATOR NAD TRANSVERSE PROJECTION: 2016 WMS, YORK OF REGION IMAGERY: 2016 OBTAINED YORK OF REGION DATA: LIO, BASE MNRF THE BEYOND YEAR GIVEN OF CHANNEL ALIGNMENT OBSERVED DENOTE LINES BROKEN

Flow Direction Direction Flow Watercourse Elevation 1mContour 2016 in Channel Alignment Observed 2012 in Channel Alignment Observed 1988 in Channel Alignment Observed 1970 in Channel Alignment Observed 1954 in Channel Alignment Observed Break Reach

1:6,000

0

CONTROL CONTROL

100

APPROVED APPROVED PREPARED DESIGNED YYYY-MM-DD REVIEWED REVIEWED ^_

LOCATION SITE 200

REV. 0 METRES AF AF NP/JT NP/JT NP 2017-08-25 300

FIGURE FIGURE 4

IF THIS MEASUREMENT DOES NOT MATCH WHAT IS SHOWN, THE SHEET SIZE HAS BEEN MODIFIED FROM: 0 25mm