Fluvial Geomorphology

Schedule ‘C’ Environmental Assessment for 16th Avenue between Yonge Street and Woodbine Avenue

Appendix M Fluvial Geomorphology

Accessible formats are available upon request.

CLASS ENVIRONMENTAL ASSESSMENT STUDY FLUVIAL GEOMORPHIC COMPONENT 16TH AVENUE FROM YONGE STREET TO WOODBINE AVENUE

Report Prepared for: HDR CORPORATION

Prepared by: MATRIX SOLUTIONS INC.

Version 3.0 July 2018 Mississauga, Ontario

Suite 200, 2500 Meadowpine Blvd. Mississauga, ON L5N 6C4 T 905.877.9531 F 289.323.3785 www.matrix-solutions.com

CLASS ENVIRONMENTAL ASSESSMENT STUDY - FLUVIAL GEOMORPHIC COMPONENT 16TH AVENUE FROM YONGE STREET TO WOODBINE AVENUE

Report prepared for HDR Corporation, July 2018

reviewed by Tatiana Hrytsak, M.Sc. John Parish, P.Geo. Fluvial Geomorphology Specialist Principal Fluvial Geomorphologist

Ahmed Siddiqui, M.Sc., CAN-CISEC Sam Bellamy, P.Eng. Fluvial Geomorphology Specialist Principal Water Resources Engineer

DISCLAIMER

We certify that this report is accurate and complete and accords with the information available during the site investigation. Information obtained during the site investigation or provided by third parties is believed to be accurate but is not guaranteed. We have exercised reasonable skill, care, and diligence in assessing the information obtained during the preparation of this report. This report was prepared for HDR Corporation. The report may not be relied upon by any other person or entity without our written consent and that of HDR Corporation. Any uses of this report by a third party, or any reliance on decisions made based on it, are the responsibility of that party. We are not responsible for damages or injuries incurred by any third party, as a result of decisions made or actions taken based on this report.

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TABLE OF CONTENTS 1 INTRODUCTION ...... 1 2 BACKGROUND REVIEW ...... 3 2.1 Geology and Physiography ...... 3 2.2 Previous Studies ...... 5 3 REACH DELINEATION ...... 6 4 HISTORICAL ASSESSMENT ...... 6 5 FIELD ASSESSMENT ...... 8 5.1 Rapid Assessments - Methods ...... 9 5.2 Rapid Assessments - Results ...... 10 5.2.1 German Mills Creek ...... 10 5.2.2 Beaver Creek ...... 11 5.2.3 Rouge River ...... 12 6 MEANDER BELT WIDTH ...... 14 6.1 Preliminary Belt Width ...... 15 6.2 Factor of Safety ...... 15 7 CROSSING SPAN RECOMMENDATIONS ...... 16 8 CONCLUSIONS AND NEXT STEPS ...... 19 9 REFERENCES ...... 20

LIST OF FIGURES FIGURE 1 Study Area from Yonge to Woodbine Avenue ...... 2 FIGURE 2 Surficial Geology from Yonge to Woodbine Avenue ...... 4

LIST OF TABLES TABLE 1 Average Migration Rates Determined from the Aerial Imagery ...... 8 TABLE 2 Rapid Geomorphic Assessment Classification ...... 9 TABLE 3 Summary of Rapid Geomorphic Assessment Results ...... 13 TABLE 4 Summary of Rapid Stream Assessment Technique Results ...... 14 TABLE 5 Summary of Meander Belt Width Delineation ...... 15 TABLE 6 Crossing Recommendations from a Geomorphic Perspective ...... 17

APPENDICES APPENDIX A Site Photographs APPENDIX B Rapid Assessment Results APPENDIX C Belt Width Delineation Procedures (Parish 2004) APPENDIX D Individual Crossing Figures

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1 INTRODUCTION The Regional Municipality of York has retained HDR Corporation (HDR) to undertake a Class Environmental Assessment (EA) study for 16th Avenue from Yonge Street to Woodbine Avenue. The study will evaluate existing conditions and determine specific improvements. Matrix Solutions Inc. has been retained by HDR to provide fluvial geomorphological assessment of the associated watercourse crossings as part of the Class EA. To complete the assessment, the following work plan was undertaken:

• collect and review pertinent background information, such as topographic mapping, historical aerial photographs, and any previous reports that would pertain to the watercourses in the study area • use available mapping to confirm channel reach boundaries • where possible, complete channel migration analyses in order to determine 100-year erosion rates • delineate the meander belt width on a reach basis at each of the crossing structures based on mapping and aerial photographs • complete field reconnaissance to confirm existing geomorphic conditions, document any evidence of active erosion, and confirm appropriateness of the desktop results • assess appropriateness of crossing structures in relation to channel migration and adjustment

The study area includes three watercourse crossings: German Mills Creek, Beaver Creek, and the Rouge River (Figure 1). The surrounding area is fully urbanized and as a result, riparian corridors are minimal.

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Easting (m)

Study Area Watercourse Expressway / Highway W Road

Major MacKenzie Drive East

YongeStreet

R ou ge R iv

r C

UV404

Northing(m) 16th Avenue

BayviewAvenue

B ea v er C r ee k

WoodbineAvenue

1:20,000 m

200 0 200 400 Referenc e: Data obtained from GeoBase® used under license. Imagery (2015) obtained from York Region used under license. NAD 1983 UTM Zone 17N

HDR Corporation 16th Ave. Class Environmental Study UV407

Highway 7 Study Area from Yonge to Woodbine Avenue

Date: Project: Technical: Rev iewer: Drawn: 24 Mar 2017 23456 T. Hrytsak J. Parish C. Curry Disclaim er: The inform ation contained herein may be com piled from numerous third party m aterials that are subject to periodic change Figure without prior notification. While every effort has been made by Matrix Solutions Inc. to ensure the accuracy of the information presented at the time of publication, Matrix Solutions Inc. assumes no liability for any errors, om issions, or inaccuracies in the third party material.

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2 BACKGROUND REVIEW

2.1 Geology and Physiography The study area is situated within the Peel Plain physiographic region (Chapman and Putnam 1984). Within the confines of the study area, the Peel Plain physiographic region is characterized as a gently sloping till plain formed of dense, glacially derived, clay deposits containing both bevelled till and drumlinized landform features. Surficial geology within the study area consists of alternating arrangements of fine-textured glaciolacustrine deposits and stone-poor carbonate-derived silty to sandy till (Figure 2). The fine-textured glaciolacustrine deposits are generally defined by massive well-laminated silt and clay with minor sand and gravel inclusions. German Mills Creek and the Rouge River are all characterized by these fine-textured deposits. The north section of Beaver Creek consists of the stone-poor silty to sandy till deposits, while the south section is characterized by the same fine-textured deposits.

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StudyArea Wa terco urse ExpresswaHighwa y/ y W Roa d Surficial Geology 5b : Stone-po5b: ca o rbo r, na te-derivedsandsiltyto ytill 5d : Glac5d: iolac ustrine-derivedclayeysiltyto till 8a : Ma8a: ssive-welllam ina ted Ma jor Ma c Kenzie Drive East 9c: Foresho9c: re-ba sinadep l o sits 19: Mo 19: d ernalluvial dep o sits 20: Orga 20: nicdep o sits

Yonge Street Yonge

R ou ge R iv

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Bayview Avenue Bayview

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WoAvenue o d b ine

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HDRCorpo ration 16th Ave.16thClass Environm entalStudy UV407

Highw a y 7 Surficial Geology from Yonge to Woodbine Avenue

Date: Projec t: Tec hnica l: Review er: Draw n: 24 Ma24 2017 r 23456 Hrytsak T. Parish J. CurryC. Disclaimer:The informa tionco ntainedherein ma ybe co m p iledfrom numerous thirdpa ma rty terialsthaare subjec t periodto t iccha nge Figure withopriorno ut tifica tion.While every effoha been srt ma d eby Ma Solutions trix ensureto Inc the. ac c uracof ythe informa tionpresented at thetime of publica tion,Ma Solutions trix assumesInc . no liab ilityforany om errors, issions,inaor c c urac iesinthe thirdpa ma rty terial.

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2.2 Previous Studies

Hwy 404 Road Crossing - 16th Avenue and Major Mackenzie Drive - Rouge River, Markham, ON: Fluvial Geomorphological and Meander Beltwidth Assessment (Water’s Edge 2014) A meander belt width assessment was completed for the Rouge River north of 16th Avenue in 2014 in support of a proposed Highway 404 mid-block road crossing between 16th Avenue and Major Mackenzie Drive. The study determined the reach to be ‘transitional’ based on a Rapid Geomorphic Assessment (RGA) assessment score of 0.36. The primary mode of adjustment was widening followed by aggradation, degradation, and planform adjustment. Bankfull widths ranged from 5.8 to 9.0 m and the average bankfull width was 7.5 m. Average bankfull depth was 0.8 m.

The historical assessment revealed that the planform had significantly changed between 1970 and 1995. There were meander cut-offs and also downstream migration. It was suggested that some of this adjustment, mainly the cut-offs, may be related to the development of the golf course during this time period. Based on this the historical 1970 planform was not used in determining the meander belt width. The preliminary belt width was delineated as 69.0 m based on the governing meander amplitudes. Historical planforms were compared to determine migration rates. An average 100-year migration rate of 33.2 m was calculated and applied to the preliminary belt width to determine a final belt width of 102.2 m.

Rouge River - Buttonville Airport Redevelopment: Meander Belt Width and Redside Dace Habitat Setback Assessment (Geomorphic Solutions 2012) A meander belt width assessment was completed for the Rouge River south of 16th Avenue in 2012 in support of a redevelopment application for the Buttonville Airport lands. The study determined the reach to be ‘in adjustment’ based on a RGA assessment score of 0.57. The dominant mode of adjustment was observed to be widening; however, there was also evidence of aggradation, planform adjustment, and degradation. Indicators included basal scour, fallen and leaning trees, outflanked gabion baskets, and fracture lines along the top of bank. At the time of the assessment, the surrounding vegetation remained dominated by manicured grass from the former Markham Golf and Country Club. Undercuts were common and ranged from 0.10 to 0.30 m. Bankfull widths ranged from 6.0 to 6.6 m, average bankfull depth was 1.1 m. Substrates consisted of gravel and small boulders at riffles. In the pools, substrates were till, fine silt, and sand.

The meander belt width assessment employed a desktop approach which was verified based on empirical equations. The desktop approach yielded a belt width of 66 m, while empirical approaches yielded results of 48 m, 73 m, and 79 m. It was determined that the empirical results sufficiently supported the desktop delineated belt width. No factor of safety was applied to the belt width. A Redside Dace habitat setback of 30 m was applied to the west side of the channel. It was only applied to this side as this was the area of interest for the proposed development.

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3 REACH DELINEATION The amount and size of sediment inputs, valley shape, land use, or vegetative cover vary over the length of a stream. Lengths of channel that exhibit similar characteristics with respect to these parameters are known as reaches. Reach lengths vary with the scale of the channel, often longer for a larger watercourse, while smaller watercourses exhibit more variability resulting in shorter reaches. Delineation of reaches is beneficial as it enables grouping and identification of general channel characteristics.

The process of delineating reaches considers external parameters such as local geology, topography, and valley setting, hydrology, riparian vegetation, and land use. Consideration is also given to characteristics that reflect these external influences such as sinuosity, gradient, and dimensions (Parish 2001).

For the 16th Avenue study area, reaches were delineated in the vicinity of the crossing. Road crossings often serve as reach breaks due to impacts from the crossing structure or changes in land use on either side of the road that impact morphology. Separate reaches were used for both German Mills Creek and Beaver Creek because the crossing structures were so substantial. Beaver Creek was piped under the Leslie Street/16th Avenue intersection resulting in vastly different conditions on either side. The Rouge River was also separated into two reaches upstream and downstream of 16th Avenue.

4 HISTORICAL ASSESSMENT Streams are dynamic landscape features. Over time their configuration and position within the floodplain changes as a result of meander evolution and development, and channel migration processes. These lateral and down-valley planform adjustments can be observed and often quantified by reviewing historical aerial photographs. Depending on photograph quality and scale of the channel of interest, 100-year erosion rates may be determined by measuring the distance from known control points to a governing meander bend over the available historical record. Historical aerial photographs are also analyzed to determine changes in surrounding land use which may have impacted channel migration. For the 16th Avenue study area, historical aerial photographs from 1970, 1978, and 1999 were reviewed. The historical orthoimagery was obtained from York Region.

In 1970 imagery, the dominant land use for the 16th Avenue corridor was agricultural and rural. The most notable features were Buttonville Airport and a small area of residential development south of 16th Avenue west of Bayview Avenue. German Mills Creek flowed at the base of the railway track embankment north of 16th Avenue. South of 16th Avenue the creek flowed in a generally southeast direction between residential development to the east and industrial land use to the west. German Mills Creek was constrained by the surrounding land use and was presumably altered to accommodate the land use. Beaver Creek was an open watercourse that flowed through two separate crossings: one at Leslie Street and another at 16th Avenue. Upstream of Leslie, the creek was general sinuous,

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however there were some sections that appeared to have been straightened. This included a section along the edge of an agricultural field and approaching the Leslie Street crossing. South of 16th Avenue, Beaver Creek flowed adjacent to an agricultural property. The channel does not appear to have been modified beyond the 16th Avenue crossing. At the Rouge River crossing, development of the Markham Golf and Country Club appears to be ongoing on the south side, while the north side is undeveloped. As noted in the Water’s Edge (2014) report there are a number of meanders on the north side in 1970 that were subsequently cut off, potentially as part of the golf course development.

In the 1978 imagery, land use remains relatively unchanged through the study area. Industrial land use has expanded on the north side of 16th Avenue adjacent to German Mills Creek, further encroaching on the channel. On the south side of 16th Avenue there is minimal change; German Mills Creek continues to flow in a south east direction through residential and industrial land use. No notable changes occurred at the Beaver Creek crossing. For the Rouge River, golf course development continued on the south side of 16th Avenue. No major changes to the channel were noted. The north side of 16th Avenue remained undeveloped.

In the 1988 imagery, land use is beginning to transition from predominantly rural to more intense residential and industrial development. Additional alterations were made to German Mills Creek on both the north and south side of 16th Avenue. North of 16th Avenue, the creek was channelized upstream of the railway tracks. Downstream of the railway tracks, the industrial land use to the east is no longer ongoing. South of 16th Avenue, the creek continues to flow through a narrow area abutting industrial and residential land use. A bend has been removed south of Duncan Road straightening the channel. The land surrounding Beaver Creek at Leslie Street and 16th Avenue is transitioning to commercial and industrial development. West of Leslie Street, an agricultural property is no longer in use and has allowed a previously straightened section of Beaver Creek to redevelop sinuosity. South of 16th Avenue, commercial development is ongoing and includes a new crossing of Beaver Creek (Mural Street). There has been some straightening of the creek at the downstream end to facilitate this crossing. At the Rouge River crossing, golf course development has expanded north of 16th Avenue. The highly sinuous planform of the Rouge River continues to adjust and develop, with a few bends approaching cut off. A number of crossings were in the process of being built for golf cart use.

Extensive residential and commercial development occurred between 1988 and 1999, particularly between Bayview Avenue and Leslie Street. The study area in the 1999 imagery is nearly fully developed. The widening of 16th Avenue from two to four lanes also occurred between 1988 and 1999 resulting in new crossing structures for the creeks in the study area. German Mills Creek underwent substantial realignment to facilitate development south of 16th Avenue. A section of approximately 300 m which previously flowed in a general southeast direction was realigned to flow south through a narrow riparian corridor. This allowed for additional residential development to the east. In addition to the 16th Avenue widening, Red Maple Road was constructed parallel to 16th Avenue on the south side. This resulted in substantial changes to the crossing structure for German Mills Creek. In the 1988 photo the crossing structure was approximately 15 m in length; in the 1999 imagery the crossing structure

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extends approximately 100 m in length. North of 16th Avenue, German Mills Creek has undergone rehabilitation to realign it away from the railway tracks and re-establish a narrow corridor. The corridor is constrained by new residential development to the east. At Leslie Street and 16th Avenue, Beaver Creek was also modified to accommodate residential development. West of Leslie Street, the creek was fully straightened to its current planform and bound by residential development on either side. The crossing at Leslie Street was removed and replaced by the existing infrastructure that pipes the channel southeast beneath the intersection, outletting south of 16th Avenue. South of 16th Avenue a minor realignment appears to have been completed removing a small bend to protect commercial development along the western side of the creek. At the Rouge River crossing, the golf course was completed between 1988 and 1999. A number of meanders were cut off, presumably as part of the golf course development. Several cart path crossings were also installed. The 16th Avenue crossing structure was upgraded from an undersized crossing to a larger bridge structure. The new bridge structure also included a cart path adjacent to the Rouge River. A bend was removed upstream of the structure to establish a straight planform through the bridge.

After the modifications between 1988 and 1999, the watercourses in the study area have remained relatively unchanged. Commercial and residential development has continued between 1999 and 2015. The Markham Golf and Country Club appears to have closed between 2007 and 2011. The property has remained vacant, allowing vegetation to recolonize the previously manicured greens and fairways.

Average rates of channel migration were measured using the historical imagery where possible, and are presented in Table 1. When sections of the watercourse are obscured by vegetation cover, or when sections are modified and realigned to accommodate development, migration rates cannot be determined.

TABLE 1 Average Migration Rates Determined from the Aerial Imagery

Reach Average Migration Rates (m/yr) GM-1 N/A* GM-2 N/A* BC-1 N/A* BC-2 N/A* RR-1 0.27 RR-2 0.34 *Migration rates could not be accurately determined due to historical channel realignment

5 FIELD ASSESSMENT Field assessments were completed over two days: October 28 and November 4, 2016, following legislated and Matrix Health and Safety Standards. The date of assessment for each crossing is noted in the results section (Section 5.2). The field assessment employed two established reconnaissance techniques to gather data on channel health and stability: the RGA and the Rapid Stream Assessment

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Technique (RSAT). Photographs of channel conditions at each crossing can be found in Appendix A, and rapid assessment checklists (both RGA and RSAT) are provided in Appendix B.

5.1 Rapid Assessments - Methods The RGA was designed by the Ontario Ministry of Environment (MOE 2003) to assess reaches in rural and urban channels. This qualitative technique documents indicators of channel instability. Observations are quantified using an index that identifies channel sensitivity based on the presence or absence of evidence of aggradation, degradation, channel widening, and planform adjustment. Overall the index produces values that indicate whether the channel is Stable/In Regime (score ≤0.20), Stressed/Transitional (score 0.21 to 0.40), or Adjusting (score ≥0.40; Table 2).

TABLE 2 Rapid Geomorphic Assessment Classification

Factor Classification Interpretation Value The channel morphology is within a range of variance for streams of similar In Regime or Stable <0.20 hydrographic characteristics; evidence of instability is isolated or (Least Sensitive) associated with normal river meander propagation processes 0.21 Transitional or Stressed Channel morphology is within the range of variance for streams of similar to0.40 (Moderately Sensitive) hydrographic characteristics but the evidence of instability is frequent In Adjustment Channel morphology is not within the range of variance and evidence of >0.41 (Most Sensitive) instability is widespread

The RSAT was developed by John Galli at the Metropolitan Washington Council of Governments (Galli 1996). The RSAT provides a more qualitative and broader assessment of the overall health and functions of a reach. This system integrates visual estimates of channel conditions and numerical scoring of stream parameters using six categories:

• Channel Stability • Erosion and Deposition • Physical In-stream Habitat • Water Quality • Riparian Conditions • Biological Indicators

Once a condition has been assigned a score, the total of these scores produces an overall rating which is based on a 50 point scoring system. The result of the assessment then categorizes the stream as ‘Low’ (<20), ‘Moderate’ (20 to 35), or ‘High’ (>35) stream quality.

While the RSAT scores streams from a more biological and water quality perspective than the RGA, this information is also of relevance within a geomorphic context. This is based on the fundamental notion that, in general, the types of physical features that generate good fish habitat tend to represent

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good geomorphology as well (i.e., fish prefer a variety of physical conditions - pools provide resting areas while riffle provide feeding areas and contribute oxygen to the water - good riparian conditions provide shade and food - woody debris and overhanging banks provide shade). Additionally, the RSAT approach includes semi-quantitative measures of bankfull dimensions, type of substrate, vegetative cover, and channel disturbance.

5.2 Rapid Assessments - Results The following sections provide a summary of reach observations for each of the assessed watercourses. The rapid assessment techniques score the watercourses on a reach basis, to identify the dominant geomorphic processes of adjustment and channel health. It should be noted that while this is a reach based assessment, there may be localized areas each reach that experience differing conditions than the overall reach assessment. The results of the RGA and RSAT techniques are provided in Tables 3 and 4, respectively.

5.2.1 German Mills Creek The German Mills Creek crossing was assessed on October 28, 2016. On the upstream side the channel was assessed from the rail crossing to the 16th Avenue crossing, approximately 140 m. On the downstream side approximately 200 m of channel length was assessed.

North of 16th Avenue (GM-1), the channel is severely confined by the railway tracks to the west and residential development to the east. The channel flows through a narrow 30 m corridor between embankments for the surrounding land use. There is one near-90 degree bend where the outer bank is armoured by gabion baskets to protect a parking area located at the top of the valley. The remainder of the reach is straight. It appears that the channel has been modified as part of a channel restoration. The bankfull dimensions were consistent throughout the reach, as was the spacing of the riffle features. Bed material consisted of coarse angular gravels. Bankfull width was 4.60 m and bankfull depth was 0.50 m. No indicators of adjustment were noted through the reach, the RGA score classified the reach as ‘In Regime.’ The RSAT score classified the reach as ‘Moderate’ with biological indicators and riparian conditions as limiting factors. There was a long, wide riffle area approaching the 16th Avenue crossing. The bankfull width was approximately 8.90 m through the riffle. The crossing structure consisted of four large concrete box culverts, which had a combined width of 16.8 m. Large woody debris had accumulated in front of the structure. No scouring or erosion was noted near the structure.

The crossing structure extends south of 16th Avenue and also conveys the channel beneath Red Maple Road, which runs parallel to 16th Avenue. The channel width exiting the structure is the same as the structure width. There is a large woody debris jam downstream of the crossing which extends across the full width of the channel. There is also evidence of high flows inundating the full width of the corridor. Continuing downstream the channel narrows to approximately 5.5 m bankfull width. The channel cross-section is a deep, slow pool, resulting in substantial accumulation of unconsolidated silt and

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organics. There is also evidence of overbank flows in this section. Debris jams were common throughout the reach leading to frequent areas of unconsolidated silt and organic deposition. Chutes have also formed as a result of the frequent debris jams forcing flow onto the floodplain area. Riparian vegetation consisted of dense overhanging woody debris. Bankfull width was relatively consistent ranging from 4.80 to 5.50 m and bankfull depth ranged from 0.45 to 0.68 m. Bank heights ranged from 0.50 to 0.75 m. Substrates were variable frequently consisting of fine deposition while other sections had coarse angular rip-rap material. The RGA score classified the reach as ‘Transitional’ with aggradation as the primary mode of adjustment and widening as a secondary mode. The RSAT score classified the reach as ‘Moderate’ with instream habitat and water quality as limiting factors.

5.2.2 Beaver Creek The Beaver Creek crossing was assessed on October 28, 2016. Beaver Creek is piped beneath the intersection of Leslie Street and 16th Avenue. The creek drains into the pipe west of Leslie Street, 200 m north of the intersection. The creek exits the pipe on the southeast side of the intersection. West of Leslie, 130 m of channel length was assessed. South of 16th Avenue, 120 m of channel length was assessed.

West of Leslie Street (BC-1), Beaver Creek has been historically straightened and flows through a wetland area with minimal fluvial form. The channel was low gradient with very minimal flow. Surrounding vegetation was dense wetland species such as cattails and tall grasses. The channel bed was unconsolidated clay. Bankfull dimensions were consistent with a width of 4.75 to 4.85 m and depth of 0.45 to 0.55 m. Banks were low and relatively flat. The channel drains into a large concrete catch basin structure. The structure had large metal grates to keep debris from entering the pipe. The grates were covered by woody debris. The RGA score classified the reach as ‘In Regime’ due to the lack of indicators of geomorphic processes. The RSAT score classified the reach as ‘Moderate’ with water quality and instream habitat as limiting factors.

Downstream of 16th Avenue (BC-2), Beaver Creek exits the pipe through an arched culvert. An outfall also joins the channel from beneath 16th Avenue. The two channels are separated by a narrow vegetated island which is likely inundated during high flows. There is a three layer gabion basket wall armouring the bend along the west bank. The channel bed is also armoured by gabion baskets. The channel is approximately 6.2 m wide downstream of the crossing. This area extends approximately 20 m downstream, ending at a riffle which backwaters upstream to the culvert. At the riffle the channel begins to narrow and regain a more natural form. The channel bed transitions from gabion lined to coarse gravels. Bankfull width ranged from 4.5 to 5.0 m and bankfull depth ranged from 0.40 to 0.65 m. Approximately 60 m downstream of 16th Avenue, the channel regains sinuosity. Bar deposits and toe erosion was noted through the bends. Woody debris has been used to create cabled log jams along a series of bends that are severely eroding. Surrounding vegetation was dominated by a coniferous woodlot and tall grasses. Bed morphology is well-developed displaying alternating pools and riffles. The RGA score classified the reach as ‘In Regime’ with degradation and widening as the dominant modes

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of adjustment. The RSAT score classified the reach as ‘Moderate’ with riparian conditions as the limiting factor.

5.2.3 Rouge River On either side of the 16th Avenue crossing, the Rouge River flows through the former Markham Golf and Country Club property. The course has been closed for several years and has since been divided into two properties, separated by 16th Avenue. The Rouge River crossing was assessed on two separate dates due to property access limitations. The property south of the crossing was visited on November 4, 2016 and the property north of the crossing was visited on May 16, 2017.

North of 16th Avenue, approximately 350 m of channel length was assessed. The channel is surrounded by a narrow riparian buffer approximately 5.0 to 10.0 m in most areas. Riparian vegetation consists of mixed deciduous and coniferous trees, tall grasses, and herbaceous vegetation. While the golf course is no longer in operation, the fairways and greens have been generally maintained as manicured lawn, restricting regrowth of the riparian area. The channel was very sinuous through the property with over-widened bends and deep pools. Channel banks were approximately 0.75 to 1.50 m in height and primarily vertical. Slumping and undercutting banks were common through the reach. Substrates consisted of fine sand and silt in pools with some medium gravels. Riffles consisted of a wide distribution of gravels from pebbles to small boulders. Several large sand deposits were noted, frequently in bends and other slow, deep areas. Bank erosion on the inside of meander bends was also seen. Bankfull width ranged from 6.4 to 7.0 m, while bankfull depth ranged from 0.85 to 1.15 m. Wetted depth varied from 0.16 to 0.25 m in riffles, to 0.30 to 0.65 m in pools during the assessment. A number of former cart bridges were noted through the reach which had been overtopped by a recent high flow event and were in poor condition. The RGA classified the channel north of 16th Avenue as ‘Transitional’ with aggradation and widening as the dominant forms of adjustment. Aggradation was indicated by lateral bars, mid-channel bars, deposition on point bars, and deposition in the overbank zone. Widening was indicated by fallen trees, scour on inside meander bends, steep bank angles, and scour through more than 50% of the reach. The RSAT score classified the channel as ‘Moderate’ with riparian conditions as the limiting factor.

Approaching the existing crossing structure at 16th Avenue, the channel consists of a riffle and long gravel run. There is a more permanent cart path bridge with abutments approximately 20 m from the 16th Avenue crossing. Downstream of the cart path bridge, there is erosion on both banks, severe undercutting on the west bank, and placed angular stone. The planform alignment is angled towards the eastern side abutment as it approaches. At the upstream opening of the structure, the channel bankfull width is approximately 11.5 m. The existing crossing structure is a flat, clear span bridge. The channel is conveyed alongside a paved golf cart path, which is located along the west side of the crossing. The wetted width extends from below the golf cart path to the eastern abutment. There is no visible bank structure along the eastern side. On the western side, rip-rap and small boulders protect the cart path. The cart path is sufficiently low that it would be inundated during high flow events. Near

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the downstream end of the crossing, a mid-channel bar extends from beneath the crossing structure. A portion of the bar is vegetated where it extends beyond the structure and receives more sunlight. Downstream of the structure the channel is approximately 10 m wide as a result of the lack of bank material and vegetation beneath the structure to define the cross-section. The channel then gradually narrows over approximately a 10 m distance back to a 6 m bankfull width.

South of 16th Avenue, the channel was assessed on November 6, 2016. High flow conditions limited in-channel access during the assessment. Therefore the field assessment focused on high level confirmation of existing conditions previously reported by Geomorphic Solutions (2012). The assessment also focused on identifying any potential downstream impacts from the existing crossing structure.

Compared to the northern property, the property south of 16th Avenue has not been maintained. Fairways and greens have not been mowed allowing tall grass and herbaceous vegetation to re-establish. Manicured lawn is no longer dominant on the property, as was noted in 2012 by Geomorphic Solutions. This transition in vegetation appears to have improved bank stability as compared to the photos from the Geomorphic Solutions report. The channel is very sinuous with over-widened bends and deep pools. A number of crossing structures remain from the golf course, most in poor condition due to outflanking and erosion at the abutments. Bankfull width and bankfull depth were on average 6.7 m and 0.85 m. Substrate at the riffles was well packed coarse gravel, silt, and fine sand was deposited in pools. The RGA assessment score classified the channel as ‘In Regime’ with widening and aggradation as the dominant forms of adjustment. This differed from the Geomorphic Solutions classification of ‘In Adjustment.’ Some of the difference may be attributed to reduced bank erosion as a result of the difference in vegetation. It could also be because high water levels during the 2016 assessment obscured indicators of adjustment. The RSAT score classified the channel as ‘Moderate’ with no significant limiting factor.

TABLE 3 Summary of Rapid Geomorphic Assessment Results

Factor Value Reach Stability Index Condition Aggradation Degradation Widening Planimetric Adjustment

GM-1 0.00 0.00 0.00 0.00 0.00 In Regime GM-2 0.55 0.14 0.37 0.00 0.26 Transitional BC-1 0.11 0.00 0.00 0.00 0.02 In Regime BC-2 0.22 0.14 0.12 0.00 0.12 In Regime RR-1 0.66 0.14 0.50 0.00 0.32 Transitional RR-2 0.33 0.00 0.37 0.00 0.17 In Regime

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TABLE 4 Summary of Rapid Stream Assessment Technique Results Factor Value

Reach Overall Score

Water Water Condition Scour / / Scour Quality Habitat Channel Channel Stability Riparian Riparian Instream Instream Biological Condition Indicators Deposition

Max. Score 11 8 8 8 7 8 50

GM-1 7 5 5 4 3 2 26 Moderate GM-2 6 3 2 3 3 3 20 Moderate BC-1 6 4 2 2 4 3 21 Moderate BC-2 6 4 5 4 3 4 26 Moderate RR-1 5 4 6 6 2 5 28 Moderate RR-2 6 5 5 5 5 5 31 Moderate

6 MEANDER BELT WIDTH Streams and rivers are dynamic features that change their configuration and position within a floodplain by means of meander evolution, development, and migration processes. When meanders change shape and position, the associated erosion and depositional processes can cause loss or damage to private property and infrastructure. For this reason, when development or other activities are contemplated near a watercourse, it is desirable to designate a corridor that is projected to contain all of the natural meander and migration tendencies of the channel. Outside of this corridor, it is assumed that private property and structures will be safe from the erosion potential of the watercourse. The meander belt width therefore, defines the area that a meandering watercourse currently occupies and is expected to occupy in the future. All associated natural channel processes occur within this space.

The Belt Width Delineation Procedure is applicable to a range of systems and follows a process-based methodology for determining the meander belt width based on background information, historical data (including aerial photography), degree of valley confinement and channel planform (Parish 2004). Due to the spatial variability of modifying and controlling influences on channel form, two reaches situated immediately up/downstream of each other could show marked differences in planform configuration. It is for this reason that meander belt width delineation occurs on a reach-by-reach basis. Empirical methods may be used in place of the procedure outlined above when the channel planform cannot be accurately delineated due to the small scale of the channel, or when the channel has been heavily altered through channelization.

A summary of the procedure used to delineate the meander belt width is provided below, and the guidance document (i.e., the Belt Width Delineation Procedure) is provided in Appendix C.

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6.1 Preliminary Belt Width In the case of unconfined watercourses, the meander belt width is delineated based on existing and historical planform alignment. This is done by first identifying the meander belt axis which is a conceptual line that shows the general down-valley orientation of the meander pattern. The meander belt width is centered on this axis. To establish the meander belt, lines are drawn parallel to the governing outermost meanders of the channel planform, following the meander axis. Surrounding topography is also considered in this step. The distance between the two lines is measured and used to represent the width of the preliminary meander belt. Preliminary meander belt width values for the study area are summarized in Table 5. Preliminary meander belt widths are shown on the individual crossing figures located in Appendix D.

6.2 Factor of Safety From a geomorphic perspective, the 100-year migration rate typically represents the erosion setback to be applied to either side of the meander belt width in order to account for long-term adjustments in channel form (i.e., bank erosion and channel migration over time). Multiple years of historical imagery are used to measure channel migration rates and establish an erosion setback. This erosion setback is subsequently added to each side of the preliminary belt width to arrive at the final belt width. In cases where a lateral migration rate cannot be accurately quantified, a factor of safety equivalent to 10% of the preliminary belt width is applied to either side of the channel (for a total of 20%). In some cases within the study area under consideration, the level of accuracy in quantifying migration rates was determined to be insufficient for application in the meander belt width delineation. The inaccuracy is primarily due to sections of the watercourse planforms being obscured by vegetation cover, but also modifications to channel planform and corridors in some cases to accommodate the surrounding development. Therefore, in those cases, a factor of safety was incorporated within the meander belt widths, in accordance with these standard delineation procedures. Final meander belt widths are provided in Table 5 and shown on the individual crossing figures located in Appendix D.

TABLE 5 Summary of Meander Belt Width Delineation Preliminary 100-year 20% Setback* Final Meander Reach Crossing Meander Belt Migration Rate* (m) Belt Width (m) Width (m) (m) GM-1 German Mills Creek 40 N/A 8 48 GM-2 German Mills Creek 40 N/A 8 48 BC-1 Beaver Creek 30 N/A 6 36 BC-2 Beaver Creek 30 N/A 6 36 RR-1 Rouge River 65 27 NA 92 RR-2 Rouge River 65 34 NA 99 *Where migration rates could not be determined (see Table 1), a 20% factor of safety was applied

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7 CROSSING SPAN RECOMMENDATIONS Existing crossings are used as a starting point against which to evaluate geomorphic risk of the watercourse and make recommendations to inform the preferred design option for a crossing. The following conditions are evaluated for crossing recommendations:

• Channel size: the potential for lateral channel movement and erosion generally increases with channel size. Erosive forces in larger watercourses often exceed the resistive forces of vegetation, resulting in channel erosion and migration. On the other hand, headwater streams typically exhibit low rates of erosion and migration due to the presence of vegetation.

• Valley setting: watercourses with wide, flat floodplains and low valley settings tend to migrate laterally across the floodplain over time. Watercourses that are confined in narrow, well-drained valleys are less likely to erode, but are susceptible to downcutting and channel widening.

• Meander belt width: a meander belt width defines the area that a meandering watercourse currently occupies and is expected to occupy in the future. This value has been used by regulatory agencies for corridor delineation of natural hazards. The use of the meander belt width for structure sizing has been established as a criterion for some regulatory agencies. This criterion represents a very conservative approach for crossing design.

• Meander Amplitude: The meander amplitude and wavelength are important parameters to ensure that channel processes and functions can be maintained within the crossing. For the purposes of this protocol, the meander amplitude of the watercourse would be measured in vicinity of the crossing and used as a guide to determine the relative risk to the structure.

• Rapid Geomorphic Assessment: the RGA provides a measure of channel stability. Channels that are unstable tend to be actively adjusting. Conservative crossing design approaches are required to accommodate unstable, actively adjusting channels.

• 100-year migration rates: migration rates are estimated using historical aerial photography. Higher migration rates indicate a more unstable system and higher geomorphic risk.

Table 6 summarizes the recommendations for the proposed crossings from a geomorphic perspective, based on the considerations outlined above.

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TABLE 6 Crossing Recommendations from a Geomorphic Perspective Existing Structure Average Upstream Preliminary 100-year (m) Recommended Bankfull RGA Meander Crossing Reach Meander Belt Migration Opening Structure Span Comment Width Results Amplitude Width (m) Rate (m) Type Width (m) (m) (m) (m) The recommended GM-1 4.60 40 In Regime 4 cell structure span German closed corresponds to a Mills N/A* N/A 16.8 15 bottom dimension that is Creek In GM-2 5.50 40 box three times the Transition bankfull width Pipe The recommended Beaver BC-1 4.80 30 In Regime arch and 3.78 and crossing spans the N/A* 14.5 14.5 Creek circular 2.7 amplitude of the BC-2 4.75 30 In Regime pipe upstream meander In The recommended RR-1 6.70 65 Rouge Transition crossing spans the 31 30 Bridge 20 30 River amplitude of the RR-2 6.00 65 In Regime upstream meander * Migration rates could not be determined due to past modification or substantial tree cover

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The average bankfull width for German Mills Creek is 5.05 m, upstream and downstream of the crossing. Additionally, the channel has been previously realigned. The preliminary meander belt width for this channel was determined to be 40 m. Due to the previous realignment and straightening of the watercourse, the meander amplitude upstream of the crossing and the 100-year migration rate could not be determined. Through the RGA, the reach upstream of 16th Avenue was identified as ‘In Regime,’ and the reach downstream was identified as ‘In Transition,’ with aggradation and widening being the dominant modes of adjustment. No evidence of planform adjustment was noted in either reach. At present, a four-cell closed bottom box culvert is present at the crossing, with a total span of approximately 17 m. While the culverts are in relatively good condition, the structure extends a length of approximately 100 m. Such a substantial structure likely impedes channel function and connectivity. It is understood that given that the culverts are in relatively good condition, it is unlikely that the culverts will be replaced at present. However, should this crossing be replaced in the future, an open-span structure of 15 m is suggested from a geomorphic perspective. This span will improve channel function and connectivity. Given the relatively low risk due to migration, as determined through the rapid assessment, a crossing spanning the meander belt width is not required. The recommended span corresponds to approximately three times the bankfull width, to account for potential migration of the watercourse through the culvert.

In the case of Beaver Creek, the average bankfull width of both the upstream reach and downstream reach is 4.78 m. The preliminary meander belt width of this watercourse was measured to be 30 m. Due to historical modification of the channel, the 100-year migration rate could not be determined. The rapid assessment indicated that both the upstream and downstream reaches of this creek were ‘In Regime,’ no evidence of planform adjustment noted. The meander amplitude of the upstream meander bend was measured to be 14.5 m. Currently Beaver Creek crosses 16th Avenue through two structures, a pipe arch and circular pipe, side by side. The structures appeared to be in relatively good condition, albeit with a significant accumulation of debris and sediment at the inlet. Additionally, given that there is a grade control within the structure, it is likely that this structure presents a barrier to terrestrial and aquatic wildlife passage. It is understood that this crossing is unlikely to be replaced, as the structures are in relatively good condition. However, should this crossing be replaced in the future, a clear span structure with an opening width of 14.5 m is recommended, which corresponds to the meander amplitude of the channel upstream of the crossing. This span will improve channel function and connectivity beyond existing conditions. This is also approximately equivalent to three times the average bankfull width. This span ensures that the amplitude is accommodated within the crossing, accounting for potential migration through the culvert, while also allowing for wildlife passage.

For the Rouge River, the average bankfull width of both the upstream and downstream reaches was measured to be 6.35 m. The watercourse is partially confined, with close proximity to adjacent valley walls. The preliminary meander belt width, drawn tangentially to the outside meander bends, and coinciding with the tops of the valley walls, was determined to be 65 m. The 100-year migration rate for this watercourse averaged 31 m for both upstream and downstream reaches. Similarly, the amplitude of

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the meander upstream of the crossing was measured to be 30 m. Through the RGA, the upstream reach was identified as being ‘In Transition,’ while the downstream reach was identified as being ‘In Regime.’ 16th Avenue currently crosses the watercourse via a 20 m span bridge. While the bridge is in relatively good condition, the outside meander bend of the river is in contact with the eastern abutment of the bridge. However, minimal downstream impacts were noted downstream of the crossing. This implies that the existing structure is not significantly affecting the downstream form and function of the channel. Therefore it is understood that the culvert is unlikely to be replaced at present. Should the crossing be replaced in the future, a 30 m span is recommended. This span is slightly larger than three times the bankfull width, but ensures that the meander amplitude and 100-year migration rate is accommodated within the crossing.

8 CONCLUSIONS AND NEXT STEPS A fluvial geomorphic assessment was completed for three watercourse crossings of 16th Avenue in Markham, Ontario. Two of the crossings were for watercourses that have been heavily modified historically: German Mills Creek and Beaver Creek. German Mills Creek crosses 16th Avenue and Red Maple Road through four box culverts extending approximately 100 m in length. Such a substantial structure impedes channel function and connectivity. Beaver Creek is piped beneath the intersection of Leslie Street and 16th Avenue. The creek is piped for a distance of approximately 260 m. The area where the channel currently outlets south of 16th Avenue has been modified with a gabion wall and in-channel structures. It is likely that in-channel work would be needed to support any potential extension of the existing structure. The Rouge River crossing consists of a clear span bridge. The bridge currently encompasses the channel and an unused golf cart path. While the outside meander bend is in contact with the eastern abutment of the bridge, minimal downstream impacts as a result of the crossing were noted. This implies that the existing structure is not significantly affecting the downstream form and function of the channel.

In providing recommendations for a crossing, existing crossings are used as a starting point against which to evaluate geomorphic risk of the watercourse and make recommendations to inform the preferred design option for a crossing. The conditions used to evaluate a crossing from a fluvial geomorphic perspective include the channel size, valley setting, meander belt width, amplitude, results of the RGA, and the migration tendencies of the channel.

While it is understood that these crossings are unlikely to be replaced at present, recommendations were made for the potential future replacement or modification of the crossing structures, which integrated the existing conditions data to determine an appropriate span, from a geomorphic perspective. Given the low risk for migration for the three watercourses, crossings spanning the meander belt width are not required from a geomorphic hazard perspective. In the case of German Mills Creek, a span of 15 m, representing a width equivalent to three times the bankfull width is recommended, should the culvert be replaced. For Beaver Creek, should the culvert be replaced, a span

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of 14.5 m is recommended, which is approximately equivalent to three times the bankfull width, but also the amplitude of the upstream meander. Should the Rouge River crossing be replaced, a span of 30 m is recommended from a geomorphic perspective, which is slightly greater than three times the bankfull width, but ensures that the amplitude of upstream meander is contained within the crossing, in the event that it migrates downstream.

9 REFERENCES Chapman L.J. and D.F. Putnam. 1984. The Physiography of Southern Ontario. Third Edition. Ontario Geological Survey, Special Volume 2. Ontario Ministry of Natural Resources. Toronto, Ontario. July 9, 1984.

Galli J. 1996. “Rapid Stream Assessment Technique (RSAT) Field Methods.” Draft memorandum. Metropolitan Washington Council of Governments. Washington, D.C. 36 pp.

Geomorphic Solutions. 2012. Rouge River - Buttonville Airport Redevelopment Meander Belt Width and Redside Dace Habitat Setback Assessment. Report prepared for Cadillac Fairview Corporation Ltd. March 2012.

Ontario Ministry of the Environment (MOE). 2003. Stormwater Management Planning and Design Manual. Queen’s Printer. Ottawa, Ontario. March 2003. http://www.ontario.ca/document/stormwater-management-planning-and-design-manual

PARISH Geomorphic Ltd. (PARISH). 2004. Belt Width Delineation Procedures - REVISED. Report prepared for the Toronto and Region Conservation Authority. September 2001. Revised January 2004.

PARISH Geomorphic Ltd. (PARISH). 2001. Geomorphological Protocols for Subwatershed Studies. Report prepared for the Regional Municipality of Ottawa-Carleton. April 2001.

Redside Dace Recovery Team. 2010. Recovery Strategy for Redside Dace (Clinostomus elongatus) in Ontario. Ontario Recovery Strategy Series. Prepared for the Ontario Ministry of Natural Resources. Peterborough, Ontario.

Water’s Edge. 2014. Highway 404 Road Crossing between 16th Avenue and Major Mackenzie Drive. Rouge River - Markham, ON. Meander Beltwidth and Fluvial Geomorphic Assessment. Report prepared for URS Canada Inc. October 30, 2014.

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APPENDIX A Site Photographs