Hydrotechnical Analysis in Support of Environmental Assessment for Third Crossing of Cataraqui River

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1 Hydrotechnical Analysis in Support of Environmental Assessment for December 20, 2011

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3 Hydrotechnical Analysis in Support of Environmental Assessment for 1 Introduction Study Area Technical Study Objectives and Design Criteria Consideration of Hydrodynamic Impacts Hydraulic Performance Criteria Analysis of Physical and Environmental Data Bathymetry and Channel Characteristics Wind and Wind-Induced Currents Hydrologic Conditions Water Levels and Surge-induced Currents Ice Analysis Field Program Hydraulic Analyses (numerical modelling) Approach to Modelling Model Setup Existing Conditions Simulations Ice Considerations Erosion and Sedimentation Proposed Scenario Modelling Steady State Simulation of All Alternatives Dynamic Boundary Condition Simulation of V Piers Ice Considerations Scour and Erosion Summary of Impacts Construction Conditions Recommendations and Design Input Detailed Design Considerations Mitigation Opportunities Appendix A: Study Area Photos Appendix B: Existing Conditions Simulations Appendix C: Proposed Conditions (V Piers) Simulations Appendix D: Graphical Representation of Proposed Structure Impacts i

4 List of Figures Figure 2.1: Cataraqui River Study Reach 3 Figure 2.2 : Bathymetric Conditions at Proposed Crossing Location 5 Figure 2.3 : Cross Section along Proposed Alignment 6 Figure 4.1: Site Photo - Dense Emergent Vegetation 10 Figure 4.2: Site Photo - Root Mats 10 Figure 4.3: Bathymetric Characteristics of Study Reach 10 Figure 4.4: Annual Kingston Winds 12 Figure 4.5 : Historic Water Levels at Kingston (IGLD, 1985) 14 Figure 4.6: Typical Hourly Water Levels at Kingston 16 Figure 4.7: Ice Thickness Measurements at Kingston 17 Figure 5.1 Flow Monitoring at Hwy 401: Velocity (above) Direction (below) 20 Figure 5.2 Flow Monitoring at Crossing: Velocity (above) Direction (below) 22 Figure 5.3 Flow Monitoring at Belle Island: Velocity (above) Direction (below) 23 Figure 6.1 : Hydrodynamic Model Domain 26 Figure 6.2: Comparison of Existing Conditions Modelling 27 Figure 6.3: Velocity near Proposed Crossing (Boundary Cond. 1) 30 Figure 6.4: Velocity near Proposed Crossing (Boundary Cond. 3) 30 Figure 6.5: Typical Manning s Bed Shear (Pa) vs Flow Depth and Velocity 31 Figure 6.6 : Bed Shear at Proposed Crossing (Boundary Cond. 1) 32 Figure 6.7: Bed Shear at Proposed Crossing (Boundary Cond. 3) 32 Figure 6.8 :Alternative Pier Concepts 34 Figure 6.9: FESWMS Model Mesh 35 Figure 6.10: Impact of Box Girder Pier Concept 37 Figure 6.11: Impact of Tube Bridge Pier Concept 38 Figure 6.12: Impact of V Pier Concept 39 Figure 6.13: ADCIRC Mesh and Details at Proposed V Piers 41 Figure 6.14 Flow Velocities near Proposed Bridge (Boundary Cond. 1) 42 Figure 6.15 Flow Velocities near Proposed Bridge (Boundary Cond. 2) 43 Figure 6.16 Flow Velocities near Proposed Bridge (Boundary Cond. 3) 44 Figure 6.17: Impact of V Pier Concept (Boundary Cond. 1) 46 Figure 6.18: Impact of V Pier Concept (Boundary Cond. 2) 47 Figure 6.19: Impact of V Pier Concept (Boundary Cond. 3) 48 Figure 6.20: Change in Bed Shear (Boundary Cond. 1) 51 Figure 6.21: Change in Bed Shear (Boundary Cond. 3) 51 ii

5 List of Tables Table 4.1 : Maximum Windspeeds at Kingston (Canadian Climate Normals) 11 Table 4.2: Kingston Airport Extreme Winds by Direction (m/s) 11 Table 4.3 : Average Runoff Depths over the Watershed (in mm) 13 Table 4.4 Design Water Levels at Kingston (MNR, 2001) 15 Table 4.5 : Relevant Site Water Levels 15 Table 4.6 Preliminary Analysis of Ice Thickness 17 Table 4.7 Design Water Levels With Ice Cover at Kingston 18 Table 4.8: Ice Cover Water Levels (December through April) 18 Table 6.1: Hydraulic Modelling Boundary Conditions 24 Table 6.2 Recommended Design Water Levels at Site 28 iii

6 Limitations The analyses presented in this report have been prepared in support of the Environmental Assessment for the Third Crossing of the Cataraqui River in Kingston. The data used in this report and the level of analyses developed herein is considered appropriate for the purposes of the Environmental Assessment. Existing (pre-bridge) and proposed (postbridge) hydrodynamic conditions have been simulated numerically in order to assess potential impacts of the proposed works. Preliminary guidance is provided for design considerations based on expected hydraulic and ice conditions at the site. This guidance is not intended to support detailed design of the structure. Localized forces due to ice and flow, as well as local scour conditions are very sensitive to the geometry of the in-water structures and the local bed characteristics. It is important that these conditions are assessed on the local level once pier geometry and locations are confirmed in order to support the detailed design process. iv

7 1 Introduction The City of Kingston is undertaking an Environmental Assessment to determine the need for and feasibility of implementing additional transportation capacity across the Cataraqui River. The EA is proceeding in two stages. Stage 1 work provided for the evaluation of alternative crossing options and locations, based on a wide range of considerations within an EA Study area extending from the La Salle Causeway in the south, up to the Highway 401 crossing in the north. The Stage 1 work recommended a bridge crossing at John Counter Boulevard and Gore Road. The results of this Stage 1 work are summarized in the Stage 1 Summary Report (JLR, 2010). In May, 2010, the City authorized that the EA proceed to Stage 2. This stage has included fieldwork investigations and technical studies to evaluate options for achieving the third crossing at the preferred location, and to identify the impacts and mitigation measures associated with the various bridge design and construction options. This report presents the methodology and results of the hydrotechnical analyses, supporting fieldwork and preliminary design guidance in support of the evaluation of bridge crossing alternatives at the preferred location and the identification of potential impacts associated with hydrodynamic processes within the region. The hydrodynamic conditions at the site are relevant to considerations of pier structure requirements, fisheries habitat and typical hydrotechnical parameters such as currents, water levels and erosion and sedimentation processes. The primary objective of this report is to provide documentation in support of the Class EA process, specifically relating to hydrotechnical conditions, impacts of proposed works and design implications. To that end, this report presents information regarding: Collection and analysis of relevant physical and environmental data Field investigations Hydrotechnical modelling of existing conditions Hydrotechnical modelling of alternatives Interpretation of results with regard to design criteria Opportunities for mitigation of impacts In this report, analysis is focused on identifying hydrotechnical impacts associated with in-water structures to be constructed along the alignment of the proposed bridge. In general, reference to the proposed bridge crossing relates to the immediate vicinity of the bridge corridor in the Cataraqui River. While the majority of impacts are expected to be very localized near the proposed bridge piers, minor influences and impacts may be simulated some distance from the proposed bridge location. Therefore, reference is also made to the Study area (or Study reach ), which includes the modelled region between the LaSalle Causeway and the Highway 401 bridge crossing. Where most relevant, site specific information as well as the generalized or overall findings of the analyses and interpretation of the analysis results are summarized within 1

8 the report. However, due to the nature of the analyses performed, and the spatial extent of the information generated by the modelling, much of the information is presented in a graphical format in the appendices of this report. 2 Study Area The Cataraqui River drains a watershed of approximately 910 km 2 (Acres, 1977), and forms the southern basin area of the Rideau Canal System. As such, it is both an important navigable waterway, joining the Great Lakes region and the Ottawa River, as well as a UNESCO World Heritage Site, National Historic Site and Canadian Historic River. The river is controlled through the various locks and dams on the waterway, with significant storage within the numerous lakes along the system. The characteristics of the Cataraqui River are quite varied throughout the Kingston region, with sections of rapids, riffles and low lying broad backwater areas and lakes. However, within the City of Kingston, it is a wide and relatively shallow river as it approaches its outlet to Lake Ontario, with a distinct navigation channel which is maintained through dredging activities. Outside this channel, the riverbed is generally flat with typical depths on the order of 1.5 m, deepening to approximately 4.5 m within the navigation channel. A discussion of water levels and relative datum references is provided in Section 4. The reach of interest is shown in Figure 2.1. The proposed crossing is to extend from John Counter Boulevard on the west side of the river, to Gore Road on the east side of the river, which situates the bridge alignment just upstream of Belle Island, at a section of the watercourse which is approximately 1 km wide. This crossing location is within a reach of the river that is constrained upstream at the Highway 401 bridge crossing, and downstream at the LaSalle Causeway (Highway 2) crossing. These structures provide convenient and practical boundaries to the reach of interest for this analysis. The watercourse at the Highway 401 crossing is approximately 30 m wide and well defined within the 401 bridge section, and immediately upstream. Downstream of Highway 401, the floodplain begins to widen significantly and is dominated by dense wetland vegetation with heavy root mats that define the normal water`s edge. The watercourse continues to widen in the downstream direction approaching Belle Island, as the wetland fringe narrows and the water`s edge expands towards the natural toe of slope of the floodplain area. At the proposed crossing location there is limited fringe vegetation, although aquatic vegetation is heavy throughout this area in the summer months. Moving downstream from the proposed crossing location, the river begins to narrow again due to the encroachment of Belle Island and Belle Park. Belle Park is an old fill area with a history of contamination concerns, and is the site of the Belle Park Municipal Golf course. There is a relatively significant vegetative buffer separating the golf course from the river, and emergent wetland vegetation is common along the shoreline of Belle Island. 2

9 Figure 2.1: Cataraqui River Study Reach 3

10 The river widens again immediately downstream of Belle Island before a gradual narrowing as it approaches the LaSalle Causeway. The river outlets to Lake Ontario (upper St. Lawrence River) via three gaps in the Causeway, spanned by two fixed bridge structures and the bascule lift bridge. These gaps are typically on the order of 40 m in width. The local bathymetry and typical cross section at the proposed crossing structure are presented in Figures 2.2 and 2.3 respectively. Key representative water levels (discussed further in Section 4) are included in Figure 2.2. The hydrodynamic conditions in the reach are influenced by the hydrologic conditions and runoff contributions from upstream areas, wind generated stresses on the wide and open watercourse surface and water level fluctuations in Lake Ontario. The relevance of these various forces is discussed in greater detail in Section 6. In general, velocities within the watercourse near the proposed crossing are relatively small under all conditions considered, and negligible under typical river conditions. The hydrodynamics of the reach are in many cases more like a shallow lake than a river. Ice typically forms in the winter months over the entire reach and melts in place in the spring. The alluvial sediments (river bed materials) within the lower reaches of the Study area are described in Golder, A brief summary of the conditions described within the lower reach of the Study area is presented here (the reader is directed to the referenced Geotechnical reports and technical memoranda for official interpretation of geotechnical conditions). In general, the limestone bedrock is found near surface along the banks of the Cataraqui River, at about 72 metres elevation, but dips to elevations of approximately 36 to 55 metres within the Cataraqui River, creating a bedrock valley within the river. This valley is filled with younger alluvial deposits up to an elevation of approximately 70 to 73 metres except for the dredged channel which is slightly deeper. These alluvial deposits within the Cataraqui River generally consist of a surficial layer of soft organic matter underlain by soft to very stiff clay or silty clay over a thin layer of glacial till or very dense silty sand with some gravel. Below this, bedrock has been inferred by sampler refusal. The soft greyish brown organic matter, sometimes referred to as muck, has a thickness of about one to two metres in the southern portion of the reach, and thicknesses of 0.8 to 6.4 m for samples near the proposed alignment. The underlying firm to stiff clay to silty clay is quite thick within the channel (up to 31 m for samples near the proposed alignment), tapering down to nothing near the banks of the Cataraqui River. The glacial till and silty sands generally show thicknesses of less than one to two metres. Vegetation within the watercourse varies throughout the season, and can be particularly thick during the summer months. Bowfin s fisheries report (2011) notes primary slow moving, soft substrate habitat with abundant submergent and floating vegetation and species noted include northern water-milfoil, curly-leaved pondweed, water lily, flatstemmed pondweed, Canada waterweed, coontail and tapegrass). While this condition is not a critical consideration in the hydraulic analysis process, it does tend to increase flow resistance in summer months and affects the choice of hydraulic modelling parameters. It may also help to stabilize bed sediments (USEPA, 2006). 4

11 Figure 2.2 : Bathymetric Conditions at Proposed Crossing Location 5

12 Section Across Proposed 3rd Crossing Alignment (looking North) Year Lake Ontario Level = 76.0 m - does not include surge allowance Elevation (m) Lake Ontario Summer Levels 95%, 50% and 5% Lake Ontario Ice Season Levels 95%, 50% and 5% Lake Ontario datum = 74.2 m Distance (m) Figure 2.3 : Cross Section along Proposed Alignment (IGLD 1985 Water Level Reference) 6

13 3 Technical Study Objectives and Design Criteria The broader objectives of this study are to provide input to the EA process through technical documentation of existing conditions, impacts and opportunities associated with various alternatives, and technical guidance in support of preliminary design tasks. More specifically, the analysis results and recommendations presented in this document are intended to provide relevant information in support of approval submissions, and to ensure that the various objectives and design criteria of all relevant approval agencies are adequately addressed to the level expected of the EA study. Agencies with mandates related to the hydrotechnical performance and impacts of the third crossing may include (but are not necessarily limited to): Ontario Ministry of Transportation (MTO) Parks Canada (PC) (covering concerns of Transport Canada as well) Department of Fisheries and Oceans (DFO) Cataraqui Region Conservation Authority (CRCA) The City of Kingston Ontario Ministry of Natural Resources (MNR) 3.1 Consideration of Hydrodynamic Impacts In general, concerns with regard to potential impacts of the proposed crossing structure include: changes in local and regional water levels, changes in currents and local velocities which may affect water quality and habitat, changes in erosion and deposition patterns, changes in ice movements, and changes in flood storage availability The analyses presented in this report are directed at addressing these issues based on the available information on the physical characteristics of the system, the environmental conditions which drive the hydrodynamic processes, and the proposed physical characteristics of the alternatives under consideration. 3.2 Hydraulic Performance Criteria In addition to establishing the impacts of the proposed works, and viable methods of managing those impacts where necessary, there are numerous hydraulic performance criteria that are required for bridges in order to ensure that the structure provides for safety of vehicles and pedestrians under pre-defined hydrologic and hydraulic conditions, 7

14 and to ensure that the necessary functions of the structure from hydraulic and recreational perspectives are accommodated. The majority of the design criteria of interest are stipulated by the Canadian Highway Bridge Design Code (CSA, 2006), with reference to Ontario Ministry of Transportation Drainage Management Manuals. Generalized design criteria and considerations relevant to the hydraulic analyses include hydraulic performance requirements, and considerations of design (hydraulic) loads. The relevant criteria for a bridge structure such as that proposed for the third crossing of the Cataraqui River are discussed below. The design flood criteria for this structure (assuming a Rural Arterial / Collector Road designation) would be a 50 year flood condition (MTO, 1980). It is noted that the check flood for bridges in Ontario is the 100 year design flood (MTO, 2002). Given the hydraulic considerations of the site, and the significance of the proposed structure with respect to emergency access and egress, the analysis performed herein has been based on a 100 year design criteria, where sufficient data exists to establish probabilistic parameters. Due to the regulated nature of the watercourse, and the complex statistical characteristics of wind conditions and water levels within the reach, rigorous statistical evaluation of the largely independent multiple environmental variables is not feasible, and the approach has been to assume a combination of events that would provide hydraulic conditions equivalent to a 100 year event or greater. This is discussed further in Section 4. In general, the design criteria from a hydraulic perspective are as follows: The deck of the proposed structure shall be established to achieve vertical clearance requirements from the soffit of the structure to the design high water level, defined as follows: o Not less than 1.0 m for freeways and arterial or collector roads, o Measured from the highest water level at which navigation is likely to occur, for structures on a navigable waterway. The approach grade of the proposed structure shall also achieve a freeboard from the edge of through-traffic lanes to the design high water level, not less than 1.0 m for freeways and arterial or collector roads. Furthermore the approach grade and structure soffit elevations shall be established to ensure that upstream flooding potential is not exacerbated. Scour protection requirements for structure foundations are to be provided such that failure will not occur as a result of the check flood, as previously defined. In addition to ensuring these criteria are achieved under the design hydraulic conditions, the analyses presented in this report are intended to provide preliminary guidance on the hydraulic and related loads that would be experienced by the structure. These loads include where relevant: Static Pressure Buoyancy Stream Pressure Wave Action Scour and Debris Considerations 8

15 Loading on the proposed structure due to ice on the river is also of relevance and discussed in this report. In general, ice loading considerations shall include where relevant: Dynamic ice forces due to collision of moving ice sheets or floes carried by stream currents or driven by wind action Static forces due to thermal movements of continuous stationary ice sheets Lateral thrust due to arching caused by ice dams or jams Static or dynamic vertical forces acting on the substructure due to effects of fluctuating water levels or dynamic effects of colliding ice. 4 Analysis of Physical and Environmental Data The hydraulic conditions (water levels and velocities) within a typical watercourse result from the passage of a flow through a defined channel, and the resistance of the channel and in-water structures to the passage of that flow. In the case of the site of the proposed Third Crossing, the cross section of the river is much larger than that which would typically be required to pass the largest flows experienced locally and as a result, the flowrate is not significantly important in defining the hydraulic conditions within the channel. While the controlled flowrates are relevant to this study, the broad and shallow cross section at the proposed crossing will be influenced significantly by local wind conditions, and water levels within the channel are primarily defined by the water levels in Lake Ontario. As a result, there are a number of environmental variables that are important to define the design hydraulic conditions within the river at this location. In addition to the environmental conditions which drive the flows within the watercourse, the physical characteristics of the channel, including depths, bed characteristics, vegetation characteristics and channel obstructions are important in the hydrodynamic analysis. A summary of the data collected and analyzed in support of the assessment of hydraulic conditions and the evaluation of bridge and pier alternatives is provided in the following sections. 4.1 Bathymetry and Channel Characteristics The bathymetry of the watercourse between the LaSalle Causeway and the Highway 401 bridge was surveyed by Monteith Ingram in 2009, and provided the basis for the development of the numerical model for the reach. Topographic information relevant to the numerical modelling was derived from Ontario Ministry of Natural Resources Digital Elevation Modelling. All elevations used in the modelling were input with reference to as geodetic elevations, in UTM (Zone 18) coordinates. The characteristics of the emergent wetland vegetation along the watercourse in the upper reaches are such that it is an ineffective flow area. The root mass is very dense, and is typically elevated well above the normal water level of the channel (see Figures 4.1 and 9

16 4.2). The edge of this emergent vegetation was therefore assumed to be the edge of the active channel for modelling purposes. Characteristics of the bridge structures at Highway 401 and the LaSalle Causeway were obtained from existing design drawings where available. Photos of these structures and general photos of the Study reach are included in Appendix A. An overview of the reach bathymetry is presented in Figure 4.3. Figure 4.1: Dense Emergent Vegetation Figure 4.2: Root Mats Figure 4.3: Bathymetric Characteristics of Study Reach 10

17 4.2 Wind and Wind-Induced Currents Wind data from the Kingston Airport has been collected and analyzed to assess typical wind persistence and probabilistic conditions. Kingston winds for the period of 1987 to 2007 were analyzed with respect to direction, magnitude and persistence. The annual wind characteristics are presented in Figure 4.4. The figure shows the predominance of the winds from the south and west. Canadian Climate Normals for Kingston for 1970 to 2000 provide information with respect to maximum hourly and gusting wind speeds. This information is presented in Table 4.1. Table 4.1 : Maximum Windspeeds at Kingston (Canadian Climate Normals) Parameter Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Max Hrly. (m/s) Max Gust (m/s) Gust Dir (deg) SW N SW SW SW SW SW SW SW SW S SW Statistical analysis of the local wind data provides probabilistic hourly windspeeds as presented in Table 4.2. Table 4.2: Kingston Airport Extreme Winds by Direction (m/s) T (yrs) N NE E SE S SW W NW The annual data indicates that the predominant winds are from the southwesterly quadrant, with largest contributions from due south and due west. High winds can obviously be experienced from any direction however (Table 4.2). The orientation of the watercourse within the reach of interest is such that the hydrodynamics will be sensitive to south/southwest and north/northeast winds. Furthermore, the situation of the site at the easterly end of Lake Ontario will result in an increased sensitivity to lake oscillations and setup generated by the predominant southwesterly wind conditions. 11

18 Figure 4.4: Annual Kingston Winds 4.3 Hydrologic Conditions There is limited flow data available for the Cataraqui River in the vicinity of the Study Area. The Cataraqui Region Conservation Authority (CRCA) has had some preliminary analysis performed in support of their water budget studies for management of local water resources, but actual flow data for the lower reach was not available. The flow in the Cataraqui River at Kingston Mills is partly dedicated to power generation at the small hydro station, but large flows are reportedly passed without any detailed record of such conditions. The CRCA water budget estimates provide average runoff depths over the km 2 watershed area. Those values are presented in Table 4.3. Considering the highest runoff months of February and March, this equates to an average spring flow of approximately 17 m 3 /s. Under low flow conditions of July, the average flow would equate to approximately 4 m 3 /s. While these flow estimates are based on coarse data, and do not account for daily fluctuations in the instantaneous flow rates, they do provide an estimate of the typical higher and lower average flow conditions. 12

19 Table 4.3 : Average Runoff Depths over the Watershed (in mm) Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Ann Depth Parks Canada (Rideau Canal Office) does operate a spillway at the hydro facility to pass heavy freshet flows, but does not have a rating curve for the structure, and therefore can not provide firm numbers for flood flows. They estimate that flow rates during heavy freshet events are in the order of 50 m 3 /s. This is consistent with an analysis of the Rideau Canal hydrologic management approach (Acres, 1994) which indicates that the flowrate at Kingston Mills with a probability of exceedance of 1% would be approximately 50 m 3 /s given the operating policies at that time. An optional Early Filling operating strategy investigated in that study would generate a 1% flowrate of approximately 75 m 3 /s. Given the significant storage in the upstream system, and the significant cross sectional conveyance capacity within the reach of interest, modelling (Section 6) suggests that it would require flows of an order of magnitude higher than 50 m 3 /s to generate any significant flow velocities and water level increases within the Study area. It is important to note that the regulatory floodlines for the lower Cataraqui River are developed based on Lake Ontario water levels with an allowance for wave uprush. This would further suggest that the flow conditions within the lower reaches of the river are not the primary consideration in the development of high water levels within this reach. Based on the review of background information, the design flow assumed in this analysis would be approximately 50 m 3 /s, but it is stressed that this condition is not the overall hydraulic design condition recommended for the structure. The physical characteristics of the reach are such that it is in effect a lake-like setting, and the flows are not the critical consideration with respect to establishing design water levels or velocities at the structure. The effective flow area of the cross section at datum water level (74.2 m) is estimated to be about 775 m 2. Higher water levels would of course result in larger flow areas, and it is evident that even local flows on the order of 500 m 3 /s (which are not relevant to this site) would result in average velocities of less than 1 m/s if evenly distributed across the section. This is of course not the case, but it is shown through the modelling of existing conditions (Section 6) that wind or surge conditions are more effective than flows in generating high velocities at the proposed crossing location, and conditions more significant with respect to design considerations. 4.4 Water Levels and Surge-induced Currents Water levels in the Great Lakes and St. Lawrence River system are usually defined with respect to the 1985 International Great Lakes Datum (IGLD 1985); the bench mark for this datum is located in Rimouski Quebec. Low water datum for Lake Ontario, defined with reference to this benchmark is 74.2 m elevation. It is more convenient for landbased transportation projects to work from the Geodetic Survey of Canada (GSC) datum 13

20 as this is the reference typically used by municipalities in local benchmark networks. While the difference between these systems is not large (0.04 m at Kingston), it is important to ensure that documented elevations are understood. The elevations provided in this document are defined with respect to GSC datum in most cases. Where IGLD 1985 reference is used, this is specifically noted. An evaluation of water levels has been completed based on average monthly Lake Ontario water levels and the hourly (or more frequent) monitoring data for Kingston at Portsmouth Olympic Harbour (approximately 4 km west of LaSalle Causeway). While design water levels at the proposed bridge crossing are expected to be slightly different than those at the gauging location due to the effects of wind setup, hydrologic influence, and possibly routing lag effects of the LaSalle Causeway, the Kingston water levels are the best local record, and are expected to provide an appropriate baseline reference. Hourly water levels at Kingston (elevations referenced to IGLD, 1985) were considered on a monthly basis in order to evaluate the percentage of time (based on historic record from 1962 to 2010) that the water level would be expected to be above or below a given value. The results of the analysis are presented in Figure 4.5, and show the seasonal trends in water levels with October through January typically representing the lowest water levels, and May through July typically representing the highest water levels. Probabilistic design water surface elevations (WSEL) for Lake Ontario at Kingston have been assessed by the Ontario Ministry of Natural Resources, based on maximum long term water levels and regional wind setup conditions. Design water levels at the site are presented in Table 4.4, with relevant reference water levels summarized in Table 4.5. Kingston Water Levels (m) WSEL (m) % Of Time Less Than Figure 4.5 : Historic Water Levels at Kingston (IGLD, 1985) Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 14

21 Table 4.4 Design Water Levels at Kingston (MNR, 2001) Return Period (Yrs) Highest L. Ontario Monthly Mean (m) Instantaneous Kingston Level (m) Note 1: 100 Year design water level in Kingston typically represented as 76.0 m. Table 4.5 : Relevant Site Water Levels Condition WSEL Reference Low Water Datum (LWD) m Canadian Hydrographic Service (L.Ontario) Average High Water (AHW) m Ministry of Natural Resources (L.Ontario) C.R.C.A Regulatory W.L m Cataraqui Region Conservation Authority Note 1: This water level is applied as the Regulatory Limit within the Study area (based on Lake Ontario water level and allowance for wave action). It is noted that the data presented in Figure 4.5 above is based on hourly water level records at Kingston, and therefore may be further subject to shorter-term surge or seiche oscillations generated locally. A preliminary review of surge potential based on the hourly water level records indicates historic surges in the order of m to 0.44 m often over the course of a few hours. Review of more frequent observations indicates that historic surges have been as high as 0.7 m ±. Typical water level records and examples of large positive and negative surges are presented in Figure 4.6. A general review of hourly water level data correlation with hourly wind conditions and regional daily flow data indicates that there are no obvious correlations. While sustained southwest windspeeds can cause setup in the eastern end of Lake Ontario, the shorter term data is generally uncorrelated. Water levels relevant to ice cover conditions are based on the expected Lake Ontario water levels during winter (ice period) months, and are provided in Section

22 Typical Annual Hourly Water Levels at Kingston WSEL (m) above Datum Elevation of 74.2 m Day of Year Kingston Water Levels Nov 12 and 13, 1992 WSEL (m) Nov-92 Kingston Water Levels April 18, /04/2004 0:00 18/04/2004 3:00 18/04/2004 6:00 18/04/2004 9:00 18/04/ :00 18/04/ :00 18/04/ :00 18/04/ :00 19/04/2004 0:00 12/11/ :00 12/11/ :00 12/11/ :00 12/11/ :00 13/11/1992 0:00 13/11/1992 3:00 13/11/1992 6:00 13/11/1992 9:00 13/11/ :00 Date/Time WSEL (m) Apr-04 Date/Time Figure 4.6: Typical Hourly Water Levels at Kingston (Top) Compared with: November 1992 Surge 15 Min. Record (Middle); and April 2004 Surge 3 min. Record (Bottom) 16

23 4.5 Ice Analysis Ice cover is relevant to the design of the proposed crossing structures due to the ice forces generated. There is some limited historic information available for ice conditions in the Kingston Region, including historic ice thickness and historic semi-quantitative ice cover charts for the Great Lakes region. This information has been analyzed in an effort to establish relevant ice characteristics for design considerations. Ice thickness records are available for a number of dates between 1980 and 1995 (CIS, 2011). The ice thickness measurements are on an occasional basis during the winter months, and therefore, it is not guaranteed that the maximum ice thickness was observed in the measurements. The measured data is presented in Figure 4.7. Kingston Ice Thickness Ice Thickness (cm) /02/ /02/ /02/ /02/ /02/ /02/ /02/ /02/ /02/ /02/ /02/ /02/ /02/ /02/ /02/ /02/1995 Date Figure 4.7: Ice Thickness Measurements at Kingston An analysis of the annual measured extremes suggests a 100 year ice thickness in the order of 0.84 m based on this data. It is noted that this thickness is typical of maximum ice thicknesses experienced in Great Lakes harbours (Wortley, 1985). Table 4.6 Preliminary Analysis of Ice Thickness Return Period (Yrs) Ice Thickness (cm)

24 A review of the regional ice charts of Lake Ontario, focusing on the Kingston region indicates that the ice cover on the river is quite variable from year to year, depending largely on climate conditions. Some years are largely ice-free, potentially coinciding with mild wet winters. A review of the historic ice cover charts from the Canadian Ice service for through suggests that ice cover is not typically established until mid to late December, with ice-free conditions arriving again as late as April 25 th. This data indicates that thick lake ice is not generally established until early February, but it can linger until April. Given these observations, ice-cover design water levels should include December through April water levels, and have been estimated on this basis for the purposes of preliminary design. A probabilistic analysis of extreme (hourly) water levels for December through April, based on data results in the instantaneous water levels presented in Table 4.7 below. Table 4.7 Design Water Levels With Ice Cover at Kingston Return Period (Yrs) Water Level (m) A review of long term monthly water levels for Lake Ontario shows that historic maximum and minimum monthly mean water level ranges for December through April are approximately 75.15m m and m m respectively (CHS, 2011). Recommended ranges of water levels for ice conditions at the proposed bridge crossing are presented in Table 4.8 Table 4.8: Ice Cover Water Levels (December through April) Condition WSEL Source Long Term Average (Static Ice) 74.49m to 74.84m USACE Lake Ontario Mean Monthly WSEL ( ) Historic Extremes (Static Ice) 73.70m to 75.61m USACE Lake Ontario Mean Monthly WSEL ( ) 100 Year Extremes (Dynamic Ice) 73.65m to m Statistical analysis of CHS Hourly WSEL ( ) Winter Surge Conditions -0.25m to +0.47m Extracted surge values from CHS Hourly WSEL ( ) 5 Field Program The relatively slow moving currents and large Study area are challenges to collecting good quality field data. Single point measurements of velocities are not of significant benefit due to large variations in velocity directions and magnitudes, especially at the location of the proposed crossing. Water level measurements are valuable in establishing flow rates and potentially velocities where the channel is relatively uniform and the water surface slope over the reach is the primary factor affecting the velocities within the channel. This is not 18

25 necessarily the case in this Study area however, due to the influence of winds and the expected potential for long waves to travel within the reach of interest. Furthermore, the differential in water surface elevations between Highway 401 and the LaSalle Causeway is not expected to be significant, and a meaningful differential may not be readily measured. Given these considerations, it was deemed that the field program should involve spatially distributed measurements of the primary variable of interest (velocity). An Acoustic Doppler Current Profiler (ADCP ) was used to measure the velocity at three cross sections within the Study area. The ADCP provides a velocity profile with depth in a continuous cross-sectional sense. It is most desirable to collect velocity measurements when there is a significant event that is generating good water movement; within the Study reach, this would require a significant wind event. However, the instrumentation must be towed by boat, and therefore it is difficult to obtain good data when the water surface is choppy. As a result, the field data collection was completed when wind speeds were low to moderate out of necessity due to the measurement technique. The results of the field measurements at Highway 401, the proposed crossing location and at Belle Island are presented in Figures 5.1 through 5.3. The results show that the velocities within the river are small, even at the most restricted cross section at Highway 401. While the field data does not provide a significant event condition for model calibration / verification, it does support the model results for moderate to low conditions which indicate flow velocities on the order of 0.05 m/s within the channel near Belle Island. The measurements also show flows in opposing directions in different parts of the channel, which is not uncommon in lake-type settings where winds drive currents and circulation cells are developed under the influence of the local bathymetry and shoreline geometries. 19

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27 Figure 5.1 Flow Monitoring at Highway 401: Velocity (above) Direction (below) 20

28 Figure 5.2 Flow Monitoring at Crossing: Velocity (above) Direction (below) 21

29 Figure 5.3 Flow Monitoring at Belle Island: Velocity (above) Direction (below) 22

30

31 6 Hydraulic Analyses (numerical modelling) 6.1 Approach to Modelling The objective of the numerical assessment is to provide for a comparison of the impacts of the various alternatives with existing condition scenarios, and to provide for a local assessment of hydrodynamic parameters which may influence design decisions. A twodimensional (2-D) finite element modelling approach has been taken in this project. The finite element approach permits a varied resolution of the solution domain, to permit well resolved elements in areas of interest, with relaxed sizing of elements in regions removed from those areas of interest. A 2-D (vertically averaged) model assumes that the horizontal accelerations and flow dynamics are much more relevant than the vertical accelerations and dynamics in defining the hydrodynamic conditions of interest; this is a reasonable assumption for a broad, slow-moving watercourse. A comparative modelling exercise was completed for all options using a steady state flow scenario simulated using the Finite Element Surface Water Modelling System (FESWMS). This model uses a finite element solution to the 2-Dimensional hydrodynamic equations for sub-critical and super-critical flow conditions, and includes parametric representation of pier structures within the mesh. This approach permits the definition of pier location and pier characteristics that are relevant to determining form losses under the prescribed flow conditions. It requires a relatively fine resolution of the model mesh in the vicinity of the piers, as the local losses are applied to the element in which the pier is located. This provides an efficient means of comparing various pier configurations using a relatively sophisticated modelling approach. A typical bridge pier environment where hydraulic losses are relevant is a relatively high velocity condition, consistent with fast moving river waters, for which the FESWMS model is well suited. The hydraulic conditions at the proposed site of the third crossing do not necessarily reflect this typical scenario, however, as they are generally slowmoving currents, often reversing under the influence of winds. Therefore, while the FESWMS model provides an efficient tool for a general comparison of pier alternatives in a steady state flow environment, it is not particularly well suited for detailed assessment of the more typical conditions at the proposed third crossing site. Due to this model limitation, the preferred (V pier) alternative has also been modelled in detail under the locally significant dynamic hydraulic conditions, with reversing flows driven by stresses due to wind combined with hydrologic influence (flows). This modelling has been completed using the Advanced Circulation (ADCIRC) model based on its ability to accommodate dynamic boundary conditions and multiple forcing stressors. While the model does not include a convenient pre-defined pier simulation routine, the finite element approach permits a very well refined resolution of elements in areas of interest, thereby permitting the representation of flow obstructions through detailed assignment of the model mesh structure at the proposed pier locations. This is a relatively labour and computationally intensive process. 23

32 6.2 Model Setup The hydrodynamic models used in this analysis solve the 2-D (hydrostatic) equations of motion at a large number of points (nodes) over the area of interest (model domain). These nodes are the vertices of elements that are defined over the domain, and cover the entire surface of the watercourse. The domain is forced at the nodes along the upstream and downstream boundaries by user-defined flows or water levels, and in some cases, can be forced on all nodes throughout the domain by wind stresses. Equations of momentum and continuity are solved numerically at each of the nodes. The spacing of the nodes is typically much closer in areas of interest (i.e. bridge piers) and they are adjusted as necessary to best represent the edge of the watercourse. Bed elevations are defined for each node, and elements are assigned properties to reflect flow resistance (friction) due to bed materials and vegetation influence. General hydrodynamic parameters (coefficients) are also defined. Based on the analysis of environmental variables, hydrotechnical modelling of the lower Cataraqui River (Highway 401 to LaSalle Causeway) has been undertaken for a range of boundary conditions. As previously noted the lower Cataraqui River reach is not a typical flow-dominated reach due to the relative width of the waterway at the area of interest, and the significant flood storage in the Cataraqui River. The watercourse width at this location is approximately 1 km (for comparative purposes, the watercourse at the Highway 401 crossing is in the order of 40 m wide). Flow-generated velocities at the proposed crossing location are shown in the modelling to be significantly smaller than velocities generated by wind events, or water level surges. Due to the reduced importance of the hydrologic conditions, a range of various environmental forcing conditions have been considered with respect to the potential hydrodynamic conditions at the site for existing and proposed conditions. These dynamic analyses have been completed using the ADCIRC model, which solves time dependent, free surface circulation and transport problems in two dimensions (depth integrated). The program utilizes the finite element method in space allowing the use of highly flexible, unstructured grids. The model domain is shown in Figure 6.1. Based on the analysis of environmental variables as presented in the previous sections, the following conditions have been simulated: Table 6.1: Hydraulic Modelling Boundary Conditions Boundary Condition Q (m3/s) Wind Wind Water Level Speed Direction 1. Setdown (A) 50 m 3 /s 20 m/s North 75.8 m falling 2. Setdown (B) 10 m 3 /s 20 m/s North 75.8 m falling 3. Setup (A) 4.5 m 3 /s 20 m/s South 75.8 m rising 4. Moderate-(A) 50 m 3 /s 4.5 m/s North 75.3 m constant 5. Moderate-(B) 10 m 3 /s 4.5 m/s North 75.3 m constant 6. Moderate (C) 0 m 3 /s 4.5 m/s North 75.3 m constant 24

33 As previously noted, the FESWMS model was used to compare the alternative concepts using a more simplistic approach. While the FESWMS model is also a Finite Element model, a steady state boundary condition is used for this preliminary comparison analysis. As will be discussed in following sections, the hydrodynamic conditions which represent an extreme setup condition (high south wind (20 m/s) and associated setup opposing average flow (4.5 m 3 /s)) are shown to generate the most critical conditions (largest velocities and highest water levels) in the area of the proposed bridge crossing under existing conditions. Therefore, a steady state flow boundary was applied to the FESWMS model which generated similar velocities for existing conditions. This condition was then used to force the FESWMS models with the three alternative pier concepts. A comparison of existing conditions as modelled with ADCIRC and FESWMS is provided in Figure 6.2. Modelling results are discussed in the following sections. 6.3 Existing Conditions Simulations Due to the dynamic nature of the hydraulic modelling simulations, with a surging water level in Lake Ontario, the model s solution changes with time, as the water level rises or falls in Lake Ontario. Flow and wind remain constant throughout the simulations, but due to the dynamic water level boundary, a unique solution is generated for each time step. The results presented in this report attempt to present the worst-case time step of the simulation at the proposed crossing, although conditions at one point on the cross section may be most critical at one point in time, while they are critical at a different location at a different point in time. Select results are presented within the body of the report; more detailed model results are presented graphically in Appendix B. The results of the analysis for existing conditions provide an indication of the expected velocities and water levels at the site of the proposed crossing. The water level at the proposed crossing is largely a function of the water level in Lake Ontario, and under most typical conditions on the watercourse, can be assumed to be equal to Lake Ontario levels. Under conditions of significant wind or seiches in the Lake however, the water level at the site may be slightly higher or lower than lake levels. The hydrodynamic modelling performed for this study has been completed for two water level conditions in Lake Ontario (Table 6.1). Moderate conditions have been performed with a constant water level of 75.3 m while the extreme events that will dictate the design water levels at the proposed bridge crossing have been modelled with a surging water level condition, transitioning through a surge cycle of 0.7 m over approximately 3 hours. The maximum historic recorded surge (0.7 m), combined with a 100 year wind speed is considered to be a conservative representation of a 100 year event for the project. 25

34 Figure 6.1 : Hydrodynamic Model Domain 26

35 Figure 6.2: Comparison of Existing Conditions Modelling ADCIRC (Left) and FESWMS (Right) 27

36

37 Based on the results of the analyses, there is a potential increase in water levels between Lake Ontario and the proposed bridge crossing on the order of 0.4 m, under a 100 year south wind condition. This assumes an open water condition over which winds may act on the water surface, and flows are driven in an upstream direction. The open-water design high water at the location of the proposed crossing is therefore determined as the 100 year Lake Ontario level plus this local 0.4 m increase, equating to 76.4 m. Under ice cover conditions (discussed in section 6.3.1), the Lake Ontario water level is generally lower, and with a full (static) ice cover, the winds cannot affect the water surface. Therefore, design water levels for ice cover conditions are determined based simply on the 100 Year winter water level (December through April), ignoring surge. An allowance for surge is included for floating ice considerations. The design water level conditions at the site of the proposed bridge crossing are summarised in Table 6.2. Scenario Table 6.2 Recommended Design Water Levels at Site Lake Allowance Allowance Ontario Condition Reference Design Water Level Ice Free (High) 76.0 m Surge + Wind 0.4 m 76.4 m Static Ice (High) 75.6 m none n/a 75.6 m Static Ice (Low) 73.7 m none n/a 73.7 m Dynamic Ice (High) 75.9 m surge included 75.9 m Dynamic Ice (Low) 73.6 m surge included 73.6 m Maximum velocities at the site of the proposed bridge crossing are in the order of 0.4 m/s based on the existing conditions modelling. Typical velocity conditions for setup and setdown surge conditions with high winds from North and South are presented in Figures 6.3 and 6.4 (note proposed bridge pier locations can be seen in these figures but were not modelled for existing conditions) Ice Considerations Ice forces should be considered for water levels which are relevant to ice season conditions as noted in Table 6.2 above. Ice cover on the river is variable from year to year, depending largely on climate conditions. A review of the historic ice cover charts from the Canadian Ice Service for through seasons indicates that ice cover is not typically established until mid to late December, with ice-free conditions possibly delayed as late as April 25 th. This data indicates that thick lake ice is not generally established until early February, but it can last until April. While this information is somewhat qualitative, without site specific ice measurements, it is suggested here as preliminary design guidance. Given these observations, ice-cover design water levels previously discussed were evaluated for the period of December through April. 28

38 The ice forces generated at the structure are a function of the proposed bridge piers, and are therefore discussed in greater detail in Section 7. It is recommended that an ice thickness of 0.84 m be considered in the preliminary analyses and that ice strength for dynamic ice conditions should be considered to be 1100 kpa in accordance with breakup occurring at melting temperature as specified in the Canadian Highway Bridge Design Code (CSA, 2006) Erosion and Sedimentation Erosion and sedimentation in a watercourse are natural and dynamic processes, and in rivers where the bed elevation is stable over the long term, these processes are assumed to be in a dynamic, but balanced state. While the objective of this investigation is not to establish the regime of this river, it is desirable to know how the proposed structure may change the distribution of erosion and deposition potential for a given flow condition. The erosion and deposition is due to shear stresses acting on the river bed, generated by the flow movement. Bed shear (τ b ) for selected flow conditions has been estimated from the hydraulic modelling parameters using a Manning s relationship as follows: τ b =ρgv 2 n 2 /h (1/3) Where: ρ = density of water (1000 kg/m 3 ) g = gravitational acceleration (9.81 m/s 2 ) v = vertically integrated velocity magnitude (m/s) n = Manning s roughness coefficient (generally assumed as for bed conditions) h = water depth (m) The variation of bed shear with depth and velocity, as estimated by this relationship, is presented in Figure 6.5. Typical plots of the bed shear magnitude, as modelled during the extreme events (boundary conditions (1) and (3)) in the Cataraqui River, are presented in Figures 6.6 and 6.7. The potential for erosion or deposition is often assessed based on a critical shear (or velocity) value which is a function of the bed material. The geotechnical reports to date indicate that the surface bed material is muck, overlying soft to very stiff clay or silty clay. Critical shear stress values for cohesionless sediments is a function of the grain size and density and generally ranges from 0.1 N/m 2 to 1.0 N/m 2 as cited in various sources. Critical shear stress values for cohesive sediments are quite variable, but are on the order of 0.1 N/m 2 for soft clays and organics to 6 N/m 2 for silty clays. 29

39 Figure 6.3: Velocity near Proposed Crossing (Cond. 1: Setdown and North Wind) Figure 6.4: Velocity near Proposed Crossing (Cond. 3: Setup and South Winds) 30

40 Manning's Bed Shear (Pa) (n=0.025) 5 Shear Stress (Pa) Depth 0.5 m Depth 1.0 m Depth 1.5 m Depth 2.0 m Depth 2.5 m Depth 3.0 m Flow Velocity (m/s) FIGURE 6.5: Typical Manning`s Bed Shear (Pa) vs Flow Depth and Velocity The modelling of existing conditions for the extreme boundary conditions ((1) and (3)) indicates that the bed shear values are small, with a maximum in the order of 3 N/m 2. This is expected to be sufficient to disturb softer organic bed materials, silts and sands, but where vegetation has stabilized the bed, bed change may not be significant. The modelling results indicate that these higher bed shear values are not expected to be experienced across the entire width of the channel. The existing bed shear conditions have been used as a basis of comparison to assess potential impacts associated with the proposed bridge piers. 31

41 Figure 6.6 : Bed Shear at Proposed Crossing (Condition 1: Setdown + North Winds) Figure 6.7: Bed Shear at Proposed Crossing (Condition 3: Setup + South Winds) 32

42 6.4 Proposed Scenario Modelling As previously discussed, the hydrodynamic modelling has been performed for steady state and dynamic boundary conditions for the evaluation of alternative pier configurations, and for assessment of the impacts of the preferred pier alternative respectively. Based on the preferred bridge alignment determined during Stage 1, the model domain was established with a refined resolution in the vicinity of the proposed piers. The FESWMS modelling employs an empirical approach to the pier loss modelling and therefore applies the pier loss effects to the nodes of the element containing the pier. The ADCIRC model, incorporating the dynamic boundary condition, simulates the pier obstruction as a void within the mesh, and therefore, requires that the geometry of the mesh is refined sufficiently to define the pier shape. The alternative pier configurations were provided by Associated Engineering based on structural requirements. The pier shape for the Box Girder Bridge and the Tube Bridge is the same, but the Box Girder structure requires 23 piers while the Tube Bridge requires 11 piers. The Arch Bridge will use a different pier shape, and will require a pair of piers at each location, with 13 pairs of piers required overall. These piers are significantly larger in terms of their cross section perpendicular to the typical flow direction, and are less hydraulically efficient than those required for Box Girder or Tube Bridge structures. The alternative bridge pier concepts are presented in Figure 6.8. In general, the overall assumptions made for the modelling in order to improve stability (i.e. high water level conditions, smoothing of abrupt transitions in areas of less refined element resolution and representation of emergent vegetation as land masses) has been treated equally in the FESWMS and ADCIRC modelling. As suggested by the results of the existing conditions modelling, the local losses and influences on the flow conditions and water levels are insignificant due to the relatively small flow velocities, even under the most extreme boundary conditions, and the relatively small footprint of the proposed piers in comparison with the overall cross sectional area. Typical modelling results from the steady state and dynamic analyses are presented in the discussion below Steady State Simulation of All Alternatives As previously noted, a comparison of the effect of the various bridge pier alternatives under steady-state boundary conditions has been completed using the FEWMS model. The limitation of steady state boundary conditions with this conceptual pier modelling approach is not considered to be a major issue, as the comparison modelling is intended only to show the relative difference between pier impacts under any given scenario. Furthermore, the existing conditions modelling has shown that velocities are small under all conditions modelled. The FESWMS mesh is shown in Figure 6.9. The more detailed modelling of pier impacts under dynamic boundary discussions with ADCIRC is discussed in Section

43 Figure 6.8 :Alternative Pier Concepts 34

44 Figure 6.9: FESWMS Model Mesh Domain (left) and Crossing Magnification (Right) 35

45 The comparison of the V piers and concrete box piers shows that the V piers are hydraulically inefficient compare to concrete box pier alternatives. This is largely due to the larger cross section of the V pier. However in both cases the change in the WSEL is in order of (mm) for the extreme event condition simulated. The piers near the central portion of the channel generate a larger local impact on water surface elevations and velocities due to the higher velocities in this region. The piers located far from the central portion of the channel typically experience much smaller velocities and generate proportionately smaller impacts. A comparison of the impacts of the various pier alternatives on local water levels and velocities is presented in Figures 6.10 through It is obvious from the figures that the V Pier option results in a much larger relative change in velocities and water levels. It is very important to understand the scale of the absolute impacts however, as the simulation of the V Pier concept indicates that the maximum changes in water level due to the presence of the piers varies between approximately +3 mm to 1.5 mm, while changes in velocity in the region of the piers range from approximately +2.5 cm/s to 6.5 cm/s. While it is not suggested that the numerical model is accurate to within a mm in terms of water levels, or a cm/s in terms of flow velocities, it is recognized that this scale of impact is very small in terms of the overall scale of the project and the local physical processes. The results of the FESWMS analysis suggests that the impact of any of the alternatives would be considered to be negligible in comparison to typical hydraulic impacts of in water works. 36

46 Figure 6.10: Impact of Box Girder Pier Concept (Velocity above; WSEL below) (Boundary Condition 3 - Setup and South wind with average flow (4.5 m 3 /s) 37

47 Figure 6.11: Impact of Tube Bridge Pier Concept (Velocity above; WSEL below) (Boundary Condition 3 - Setup and South wind with average flow (4.5 m 3 /s) 38

48 Figure 6.12: Impact of V Pier Concept (Velocity above; WSEL below) (Boundary Condition 3 - Setup and South wind with average flow (4.5 m 3 /s) 39

49 6.4.2 Dynamic Boundary Condition Simulation of V Piers The V Pier concept has been identified as the preferred concept from various perspectives within the EA process, and is modelled in greater detail for a range of flow, wind and water level conditions in order to better describe the range of potential impacts. The ADCIRC modelling mesh is similar to that used for the FESWMS analysis, using the same model boundaries and similar resolution of elements, except within the region of the proposed crossing, where the resolution must be increased to physically define the piers. The details of the ADCIRC mesh and the resolution of the mesh near the bridge piers are shown in Figure Results from the simulation of the hydrodynamics for the existing and proposed conditions under extreme wind and surge conditions are presented in Figures 6.14 through A more complete presentation of the simulation results for the proposed conditions from the ADCIRC modelling is included in Appendix C of this report. As previously noted, for the extreme event conditions, it is assumed that the setup and setdown in Lake Ontario could approach 0.7 m in 3 hours which is used as a boundary condition for the lower Cataraqui River. This boundary condition is based on analysis of the historic measured water level at Kingston. The change in the water level generates significant flow into or out of the river. In addition to the surging water level boundary, 100 year winds are imposed on the water surface in a direction which enforces the surge generated flows. While a river flow condition is also imposed on the model at the upstream boundary, the results show that the effect of the flow is not significant in defining flow velocities within the Study area. A comparison of results for boundary conditions 1 and 2 shows the effect of an 80% reduction in the flow, from 50 m 3 /s to 10 m 3 /s. Maximum velocities within the region of the proposed bridge crossing are approximately 0.4 m/s for the case of the Lake Ontario setup with south winds and low flows. It is expected that this condition generates more significant velocities at the site due to the proximity of the proposed bridge crossing to the river narrowing at Belle Island. The numerical simulations indicate that higher velocities within this area persist for some distance upstream of the contraction, and into the region of the proposed bridge crossing. The Lake Ontario setdown condition with North winds and high flows generates velocities in the order of 0.3 m/s at the location of the proposed bridge crossing. The analysis shows that the flow velocities along the proposed bridge alignment decrease significantly towards the edges of the watercourse. This is expected to be in part due to the decreased depths, and also due to sheltering and backwater areas developed by the alignment of the channel banks. 40

50 Figure 6.13: ADCIRC Mesh and Details at Proposed V Piers 41

51 (a) Existing Conditions (b) Arch Bridge with V Piers Figure 6.14 Flow Velocities near Proposed Bridge Crossing (Boundary Condition 1 - Setdown, North Wind and High Flow (50 m 3 /s) 42

52 (a) Existing Conditions (b) Arch Bridge with V Piers Figure 6.15 Flow Velocities near Proposed Bridge Crossing (Boundary Condition 2 - Setdown, North Wind and Moderate Flow (10 m 3 /s) 43

53 (a) Existing Conditions (b) Arch Bridge with V Piers Figure 6.16 Flow Velocities near Proposed Bridge Crossing (Boundary Condition 3 - Setup, South Wind and Low Flow (4.5 m 3 /s) 44

54 It is difficult to identify any differences in the flow velocities, with the exception of changes in the immediate vicinity of the piers. A comparison of the existing (no piers) and proposed (V piers) conditions has been developed through subtraction of the existing condition variables (velocities and water surface elevations) from the proposed condition variables in order to better represent the difference. This comparison is presented graphically in Figures 6.17 through The differences are very small overall, and it should be recognized that the number of decimals presented in the legend is not intended to reflect the expected accuracy of the modelling, but is provided in order to help to interpret the contouring of the plots. Comparing the existing condition and post-bridge construction, the maximum differences are observed in the immediate vicinity of the piers, where the flow velocity is stalled by the physical obstruction of the pier. In reality, there is a significant acceleration of flows immediately adjacent to the pier, but the region of this accelerated flow is much smaller than the resolution possible with the analysis, and is not represented in the figures. Such flow accelerations are most critical in dealing with local scour; this is discussed further in Section Modelled differences in flow velocities quickly diminish within a few elements away from the piers. The existence of the piers does not change the pattern of the current in other part of the rivers significantly. While it is important to understand that a numerical model cannot be expected to provide sub-centimeter accuracy over such a large domain, it can provide a relevant point of comparison. Impacts on water surface elevations are generally in the order of 1 to 3 mm for the extreme boundary condition scenarios. The model is not suggested to provide accuracy within the order of millimetres due to the complex nature of the hydrodynamic conditions, and the spatial and temporal variability of physical conditions within the watercourse which may influence frictional losses, but as previously noted, the results suggest a negligible impact in terms of the watercourse impacts Ice Considerations Impacts of bridges on ice conditions within a river are typically related to the potential for the piers to impede the movement of ice, thereby increasing the potential for ice jam formations. Formation of ice jams can be caused by a number of factors, with two primary mechanisms: Freeze-up jamming where low velocity sections of the river accumulate ice floes which mass together, or where frazil ice may develop, Break-up jamming where ice flows that are released from the ice pack during break-up conditions are jammed at areas of flow constriction, such as bridge piers. 45

55 Figure 6.17: Impact of V Pier Concept (Velocity above; WSEL below) (Boundary Condition 1 - Setdown, North wind and high flow (50 m 3 /s) 46

56 Figure 6.18: Impact of V Pier Concept (Velocity above; WSEL below) (Boundary Condition 2 - Setdown, North wind and moderate flow (10 m 3 /s) 47

57 Figure 6.19: Impact of V Pier Concept (Velocity above; WSEL below) (Boundary Condition 3 - Setup and South wind with average flow (4.5 m 3 /s) 48

58 The break-up jam is typically associated with larger river flows as its occurrence is often associated with the freshet period. They are developed when large ice floes are stalled at a section of river where the surface flow is restricted. As with the freeze-up jams, Froude numbers of 0.15 or greater can force the ice arriving at the jam to submerge, and potentially increase the thickness of the jam. Froude numbers associated with flow generated conditions (up to 50 m 3 /s) are less than 0.01 throughout the majority of the lower river reach, with the exception of slightly elevated values at Belle Island. While these conditions are conducive to ice floe accumulation, this is a natural condition within this watercourse, and is not influenced by the presence of the bridge. Given the Kingston Mills structures upstream, there is no significant source of ice floes to move down the system, and as previously noted, ice generally forms on the river in this location as it would in a lake setting. Furthermore, it is recognized that existing structures (Highway 401 upstream and the LaSalle Causeway downstream) are both smaller span structures than that proposed for the third crossing and would therefore constitute the primary ice passage obstruction from upstream and downstream directions. The potential for the proposed bridge to influence ice jamming is considered to be negligible based on the available information. Given that the bed elevation along the majority of crossing section is 73.5 m or lower, it is not expected that the ice sheet will be frozen to the bed throughout the majority of the channel, although thick ice conditions would approach the bed. As the ice melts, the majority of it will be free to move within the reach under the influence of winds and currents. Given the predominance of the wind influence in this reach, it is expected that ice floes may move upstream as readily as downstream. The results of the hydrotechnical analysis suggest that a current speed of approximately 0.4 m/s would be a conservative assumption for dynamic ice conditions. Wind stress on the ice sheet would also be a consideration. Under conditions where significant flow velocities are generated under an ice cover, the added friction of the ice surface can result in an increase in the hydraulic gradient. This is an especially import consideration where a bridge structure is expected to increase the potential for ice accumulation or jamming upstream of the structure, and this increased ice cover will result in an increase of the hydraulic grade line in comparison with existing conditions. However, given the negligible flow velocities at this site, and the significant proposed bridge spans which are greater than those at Highway 401 and LaSalle Causeway, the potential of the structure to impact hydraulic grade lines under ice cover conditions is considered negligible Scour and Erosion Bed shear was estimated for the existing conditions within the Study area (Section 6.3.2). The presence of the piers has been shown to have a limited influence on the local velocities, and therefore, it is expected that the influence on bed shear will also be limited. As noted, the shear forces were estimated using the relationship presented in 49

59 Section under the proposed hydraulic conditions. The changes in bed shear values for boundary conditions 1 and 3 are presented in Figures 6.20 and The proposed bridge piers do not result in a significant change in the overall bed shear across the channel, although they do tend to shift the flow slightly out of the central portion of the channel, increasing shear values marginally along the perimeter of the main flow areas and between the piers. Localized erosion (scour) at the base of the piers is not adequately represented by large scale numerical modelling results, and is generally addressed trough empirical scour estimates, as discussed further below. The geotechnical investigation indicates that the alluvial deposits within the Cataraqui River generally consist of a surficial layer of soft organic matter underlain by soft to very stiff clay or silty clay over a thin layer of glacial till or very dense silty sand with some gravel. Soft organic material is generally expected to be relatively mobile under higher velocity conditions, with the critical shear stress for these materials potentially as low as 0.1 N/m 2. However, given that there is no reported history of significant short term changes in depths within the Study area, it is assumed that the bed sediments have stabilized to some degree. General and local scour estimates have been completed in accordance with the OHBDC requirements and associated guidance of the MTO Drainage Management Manual (MTO, ). General scour estimates based on standard approaches are negligible for this site, given the large waterway area and minimal design flow within the reach. A broader approach to the general scour potential, based on the results of the modelling suggests that the bed shear in the vicinity of the proposed bridge crossing is on the order of 2 N/m 2. This is a relatively low shear stress for a watercourse, but may be sufficient to disturb loose organic materials, which are reported to constitute the upper portion of the river bed. It is assumed that these materials will not factor into the integrity of the structural design, and that displacement of organic materials will not be a structural concern. A more detailed evaluation of the erodibility of the upper bed materials would be necessary in order to confirm scour potential should structural design considerations rely on this material. 50

60 Figure 6.20: Change in Bed Shear (Proposed Existing) (Boundary Condition 1 - Setdown, North wind and high flow (50 m 3 /s). Figure 6.21: Change in Bed Shear (Proposed Existing) (Boundary Condition 3 - Setup and South wind with average flow (4.5 m 3 /s) 51

61 Local pier scour has been estimated based on the modified Colorado State University (CSU) technique, assuming that the piles are oriented perpendicular to the flow direction The CSU approach to estimation of scour depths is the approach recommended by the U.S. Federal Highways Administration (FHWA, 2001) as it has been found to represent the envelope of the majority of the accepted techniques and reflects a maximum expected scour depth. This approach is also accepted by MTO. In general, the empirical approaches such as the CSU technique employ very basic relationships which are primarily a function of the pier geometry and flow depth, and the estimates have been found to be overly conservative for scour predictions at wide bridge piers (Jones and Sheppard, undated). Furthermore, these relationships may not be entirely representative of the scour forming conditions for this site due to the dominant velocity drivers within the reach (winds and lake levels). The conditions generating the velocities within the Study area are quite dynamic, and sustained flow velocities are not expected to persist for any significant period of time. Nevertheless, the suggested approaches have been applied based on the proposed V-pier geometry and alignments, resulting in an estimated local scour depth allowance of 7.5 m. This is a preliminary estimate, and should be developed more fully during the detailed design process based on local bed conditions and proposed pier construction and riverbed restoration techniques. The proposed pile-supported piers to bedrock would prevent undermining of the pier footings, but exposure of any significant length of the piles should be accounted for in the structural design considerations, or appropriate scour protection should be provided as required to accommodate structural capacities. Consideration should also be given to the potential exposure of the foundation under ice loading conditions with a scoured bed. Scour protection measures for local pier scour typically involve the armouring of the local bed area. In general, rip-rap protection is not a recommended scour protection measure for protection against undermining of pier footings for new structures, and furthermore, where rock protection is provided, it is recommended that the protection is excavated into the bed such that the rock surface is generally consistent with the existing bed elevation. As previously noted, it is understood that all piers are to be founded on piles supported on sound bedrock such that there would be no structural reliance on the bearing capacity of the local bed materials. Scour protection measures should therefore be designed as required to limit the exposure of the pier supporting piles, and as required to address environmental concerns associated with erosion of contaminated sediments. Given the limited velocities within the watercourse, standard approaches to rock sizing will suggest that relatively small materials will suffice. Should scour protection measures be required, it is recommended that the sizing of materials be revisited during the detailed design stage on a pier-by-pier basis to ensure that all relevant hydraulic considerations are addressed, including the potential for ice abrasion and vessel generated wakes or propeller wash. 52

62 It is also recommended that the scour estimates be revisited once construction techniques are confirmed to ensure that any temporary blockages of conveyance areas are accounted for in the design Summary of Impacts The results of the modelling show that the proposed structure will result in a small general increase in water levels upstream of the proposed bridge crossing under the design conditions. In reality, this impact is negligible, as the increase is most significant in the vicinity of the piers, and is modelled to be approximately 3-4 mm. This increase is due to the resistance to flow generated by the piers, associated with a change in momentum as the water is forced to move around the piers, and due to increased velocities between the piers, which in turn increase friction losses. The impact of the proposed piers on the local velocities (Figures ) is most evident in the area between the two piers of any given pair, where the flow velocity is stalled, and the comparison shows a loss of almost all of the velocity that is predicted at these nodes under the existing (pre-bridge) conditions. The result is that a slightly higher water level is required upstream of the piers to move the water through the obstruction. It is not suggested that the model is accurate on the order of millimetres, but the comparison of the pre-bridge and post-bridge conditions is considered to be relevant. Under conditions of lighter winds, lower flows or reduced setdown in Lake Ontario, the existing velocities within the channel would be reduced, thereby reducing the impacts. Impacts to velocities and circulation are also found to be negligible from a watercourse perspective, with changes in flow velocities generally less than 3 cm/s within the region of the proposed bridge crossing. A more significant localized change in velocities occurs at the piers as expected, and should be managed as required through the provision of scour protection measures. Another area which modelling shows to be influenced to a slightly greater extent is immediately south of the proposed crossing along the eastern bank of the river. Velocities are increased in this area by up to approximately 6 cm/s. While this is significant in comparison to other areas of the watercourse, it is a small change in absolute terms during an extreme event. The impact of the proposed bridge piers on sedimentation and erosion potential has been assessed through a review of bed shear conditions in the river. As with the velocities, the changes in bed shear are small. The magnitude of change is not expected to result in any significant change in deposition or erosion potential within the Study area, with the exception of localized scour processes at the proposed bridge piers. 6.5 Construction Conditions It is our understanding that the preferred means of temporary access into the Cataraqui River for bridge construction is via a dredged channel from shore so construction barges 53

63 can reach each pier location. Given the generally quiescent hydraulic conditions within the Study area, it is not expected that this change to the local bathymetry will have a significant influence on the local hydraulic conditions. The proposed (construction period) bathymetric construction could be replicated in the numerical model for assessment once confirmed, but this analysis has not been completed to date. It is expected that the dredge channel will be an area of increased deposition potential as it is generally perpendicular to the normal flow directions. A detailed evaluation of suspended sediment concentrations and characteristics would be necessary to provide a quantitative evaluation of potential deposition rates. The hydraulic nature of the region would suggest that it is depositional in nature, however, and given the established navigation channel, it is expected that deposition rates are typically small. The dredging of the work channel will require consideration of sediment quality, and potential for suspended sediment transport. Control of the suspended sediments during the dredging operations will be important as will the placement of the dredged materials. The City s past experiences (successes and challenges) with the utility crossing project for the Cataraqui River would be relevant to this project. 7 Recommendations and Design Input 7.1 Detailed Design Considerations The ability of the proposed structure to satisfy hydraulic design criteria specified in the OHBDC is based on preliminary design profiles (Associated Engineering, 2011a, b & c). The proposed bridge profiles indicate that the lowest soffit elevation would be approximately 78.8 m elevation at the west abutment. The soffit elevation over the navigation channel reaches approximately 90 m elevation. Given a design high water level of approximately 76.4 m, the proposed profile provides a minimum vertical clearance of approximately 2.4 m at the lowest soffit elevation, and is therefore well in excess of the required 1.0 m. The structural bridge deck is shown to be 2.5 m deep, and therefore, provides an additional 2.5 m freeboard above the vertical clearance. General and local scour estimates have been completed in accordance with the OHBDC requirements and associated guidance of the MTO Drainage Management Manual (MTO, ). General scour estimates based on standard approaches are negligible for this site, given the large waterway area and minimal flows generated within the reach. A broader approach to the general scour potential, based on the results of the modelling suggests that the bed shear in the vicinity of the proposed bridge crossing is on the order of 2 N/m 2, which is small, but potentially large enough to displace loose organic material or fines at the bed surface. This potential should be investigated more fully during detailed design should environmental or structural conditions dictate. It should be noted that the simulated increase in bed shear is less than 0.2 N/m 2, and therefore, the impact of the proposed works is small. Such an increase would result in an incremental increase in 54

64 the size of fines that could be mobilized under an extreme event, but would not be expected to cause a significant increase in general scour potential. Local scour potential at piers has also been estimated based on standard empirical approaches. These approaches employ very basic relationships which are primarily a function of the pier geometry and flow depth; these relationships may not be entirely representative of the scour forming conditions for this site due to the dominant velocity drivers within the reach (winds and lake levels). The conditions generating the velocities within the Study area are quite dynamic, and sustained flow velocities are not expected to persist for any significant period of time. Nevertheless, the suggested approaches have been applied based on the proposed V-pier geometry and alignments, resulting in an estimated local scour depth allowance of 7.5 m. This is a preliminary estimate, and should be developed more fully during the detailed design process based on local bed conditions and proposed pier construction and riverbed restoration techniques. The proposed pile-supported piers to bedrock would prevent undermining of the pier footings, but exposure of any significant length of the piles should be accounted for in the structural design considerations, or appropriate scour protection should be provided as required to accommodate structural capacities. Structural design of the piers and their footings should also consider the following preliminary guidance with regard to ice conditions at the site. Static Ice Water Level (mean monthly data) = 73.7 m to 75.6 m Dynamic Ice Water Levels (hourly data) = 73.6 m to 75.9 m Surge allowance for ice forces = m to m 100 year ice thickness = 0.84 m Ice strength for dynamic ice conditions should be considered to be 1100 kpa unless detailed ice studies suggest otherwise. Current speeds of approximately 0.4 m/s should be assumed for dynamic ice loading conditions. 7.2 Mitigation Opportunities Given the limited hydraulic impact of the proposed structure, it is not expected that significant mitigation efforts will be required. Detailed design should consider the benefit of more efficient pier shapes to reduce scour susceptibility and ice forces. Emergent slopes should be protected against erosion due to wave action until vegetation is established. Where deemed necessary, design of scour protection measures should be considered in association with fish habitat needs. It is suggested that measures to minimize potential for local scouring at piers should be employed to prevent displacement and transport of potentially contaminated sediments, regardless of structural needs. 55

65 References Acres, Study of the Operation of the Rideau Cataraqui System. Report to Rideau Canal- Parks Canada and Department of Indian and Northern Affairs. Acres Rideau Canal Water Management Study. Report to Canadian Heritage Parks Service. Associated Engineering, 2011a. Bridge Pier Locations Option 1: Arch Configuration. Dwg. No SK R2, February 2011 Associated Engineering, 2011b. Bridge Pier Locations Option 2: Tube Configuration. Dwg. No SK R2, February 2011 Associated Engineering, 2011a. Bridge Pier Locations Option 3: Girder Configuration. Dwg. No SK R2, February 2011 Bowfin Environmental Consulting Ltd., Fisheries Background Review: City of Kingston Environmental Assessment Third Crossing of the Cataraqui River. CHS (Canadian Hydrographic Service), Canadian Ice Service (CIS), Environment Canada, Canadian Standards Association (CSA), Canadian Highway Bridge Design Code. Standards Council of Canada. Golder and Associates, Preliminary Geotechnical Considerations City of Kingston EA Study, Third Crossing of the Cataraqui River. Technical Memorandum to City of Kingston, October 23, J.L.Richards (JLR), City of Kingston Third Crossing of the Cataraqui River Environmental Assessment: Stage 1 Summary Report. April 9, Jones, J. Sterling and Sheppard, D. Max, Undated. Scour at Wide Bridge Piers. U.S Federal Highway Administration. Ontario Ministry of Natural Resources (MNR), Great Lakes St. Lawrence Ricer System and large inland lakes: Technical Guides for flooding, erosion and dynamic beaches in support of natural hazards policies 3.1 of the provincial policy statement. Watershed Science Centre, Trent University. Ontario Ministry of Transportation (MTO), Directive B-100: MTC Design Flood Criteria. Provincial Roads Ministry Directive. 56

66 Ontario Ministry of Transportation (MTO), Drainage Management Manuals (Parts 1 4). Drainage and Hydrology Section, Transportation Engineering Branch, Quality and Standards Division. Ontario Ministry of Transportation (MTO), Exceptions to the Canadian Highway Bridge Design Code CAN/CSA-S6-00 for Ontario June Excerpt from Structural Manual Division 1, Engineering Standards Branch. Ontario Ministry of Transportation (MTO), Exceptions to the Canadian Highway Bridge Design Code CAN/CSA-S6-00 for Ontario June Excerpt from Structural Manual Division 1, Engineering Standards Branch. Ontario Power Authority, Undated. United States Environmental Protection Agency (USEPA), Great River Ecosystems Field Operations Manual. Report No. EPA/620/R-06/002. Wortley, C. Allen Great Lakes Small-CraftHarbour and Structure Design for Ice Conditions: An Engineering Manual. Univeristy of Wisconsin Sea Grant Institute. 57

67 Appendix A Study Area Photos

68

69 Bascule Lift Bridge (West End) LaSalle Causeway Fixed Bridge Structure (East End) LaSalle Causeway

70 Highway 401 Crossing Cataraqui River Poor circulation and water quality south shore of Belle Park

71 Looking northwest towards John Counter Blvd. along north shore of Belle Park Looking southwest towards John Counter Blvd from east riverbank

72 River narrows moving north towards Highway 401 Typical wetland vegetation root mat in northern portion of Study reach

73 Appendix B Existing Condition Simulations

74

75 Existing Conditions : Boundary Condition 1 (Setdown with 20m/s Wind (North) and 50 m 3 /s)

76 Existing Conditions : Boundary Condition 2 (Setdown with 20m/s Wind (North) and 10 m 3 /s)

77 Existing Conditions : Boundary Condition 3 (Setup with 20m/s Wind (South) and 4.5 m 3 /s) Hydrotechnical Analysis December, 2011

78 Existing Conditions : Boundary Condition 4 (Constant WSEL with 4.5m/s Wind (North) and 50 m 3 /s)

79 Existing Conditions : Boundary Condition 5 (Constant WSEL with 4.5m/s Wind (North) and 10 m 3 /s)

80 Existing Conditions : Boundary Condition 6 (Constant WSEL with 4.5m/s Wind (North) and 0 m 3 /s)

81 Appendix C Proposed Conditions Simulations (V Piers)

82

83 Proposed (V Pier) Conditions : Boundary Condition 1 (Setdown with 20m/s Wind (North) and 50 m 3 /s)

84 Proposed (V Pier) Conditions : Boundary Condition 2 (Setdown with 20m/s Wind (North) and 10 m 3 /s)

85 Proposed (V Pier) Conditions : Boundary Condition 3 (Setup with 20m/s Wind (South) and 4.5 m 3 /s)

86 Proposed (V Pier) Conditions : Boundary Condition 4 (Constant WSEL with 4.5 m/s Wind (North) and 50 m 3 /s)

87 Proposed (V Pier) Conditions : Boundary Condition 5 (Constant WSEL with 4.5 m/s Wind (North) and 10 m 3 /s)

88 Proposed (V Pier) Conditions : Boundary Condition 6 (Constant WSEL with 4.5 m/s Wind (North) and 0 m 3 /s)