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Upper York Sewage Solutions Environmental Assessment Study of Potential Impacts of the Water Reclamation Centre Discharge on Flooding Potential in the East Holland River Prepared for: The Regional Municipality of York Prepared by:

OCTOBER 2012 REF. NO. 050278 (62) YORK REGION NO. 74270

Conestoga-Rovers & Associates 1195 Stellar Drive, Unit 1 Newmarket, Ontario L3Y 7B8

050278 (62) York Region No. 74270

Study of Potential Impacts of the Water Reclamation Centre Discharge on Flooding

Potential in the East Holland River Upper York Sewage Solutions EA

Table of Contents Page

1.0 Introduction 4

2.0 Methodology 7

3.0 Results 16

4.0 Summary and Conclusion 19

5.0 References 20

List of Figures Page

Figure 1.1 UYSS Service Area 2

Figure 1.2 The East and West Holland River Subwatersheds 4

Figure 2.1 Annual Maximum Instantaneous Peak Flows - East Holland River at Holland Landing 8

Figure 2.2 Existing conditions Design Flows from the Original HEC-RAS Model and Annual Maximum Instantaneous Peak Flows for East Holland River at Holland Landing 9

Figure 2.3 Existing Conditions Design Flows in the Original HEC-RAS Model and Design Flows Calculated from the Annual Maximum Instantaneous Peak Flows Using the Exponential Distribution 10

Figure 2.4 Validation of the Updated HEC-RAS Model - December 1, 2011 Event 12

Figure 2.5 The Occurrence of Annual Maximum Flows and Lake Levels in the East Holland River and Lake Simcoe 13

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List of Tables Page

Table 2.1 Summary of Model Scenarios 14

Table 3.1 Maximum and Average Changes in Water Levels in the East Holland River for Existing Conditions Design Flows 16

Table 3.2 Maximum and Average Changes in Water Levels in the East Holland River for Future Conditions Design Flows 16

List of Appendices

Appendix A Updates and Revisions Made to the Original HEC-RAS Model Appendix B cHECk-RAS Report for the Updated HEC-RAS Model Appendix C Calculated Water Levels in the East Holland River Appendix D Calculated Changes in Water Levels in the East Holland River

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EXECUTIVE SUMMARY This study evaluated the potential impacts of the Water Reclamation Centre discharge on flooding potential in the East Holland River under existing and future river flow conditions and under the condition of increased flows from the proposed Water Reclamation Centre discharge. The flooding potential in the East Holland River within the area potentially affected by the Water Reclamation Centre discharge was assessed by hydraulic floodplain modelling. A number of scenarios were considered in the modelling, reflecting different hydraulic conditions in the East Holland River and Lake Simcoe. The peak-hour Water Reclamation Centre discharge rate, which represents the worst-case flow impact, was used in all model scenarios. The study demonstrated that the Water Reclamation Centre discharge will have no significant impacts on flooding potential in the East Holland River due to the fact that the discharge represents only a small fraction of the flows in the river during flood conditions. The results showed that the Water Reclamation Centre discharge would only minimally increase water levels in the East Holland River during flood conditions. The average increase in river water levels for all scenarios ranged from 0.1 cm to 1.1 cm. The negligible increases in river levels due to the Water Reclamation Centre discharge during flood conditions are not expected to generate higher potential for river bank erosion in the East Holland River.

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Section 1.0 Introduction

This report documents the results of a study conducted to determine the potential impacts of discharge from the proposed Water Reclamation Centre on the flooding potential in the East Holland River. The study was conducted as part of the Alternative Methods stage of the Upper York Sewage Solutions Environmental Assessment (UYSS EA) and represents one of the additional receiving stream assessment studies that were identified during the Alternatives To the Undertaking stage of the UYSS EA process. As a result of a detailed assessment of potential servicing alternatives and participant input received through various consultation activities, the Innovative Wastewater Treatment Technologies (Lake Simcoe Water Reclamation Centre) alternative was confirmed as the Preferred Alternative for accommodating the growth forecasted to occur in the UYSS Service Area to 20311. As shown on Figure 1.1, the UYSS Service Area includes the growth portions of the Towns of Aurora, Newmarket, and East Gwillimbury, including Holland Landing, Queensville, and Sharon. As part of the Preferred Alternative, wastewater from growth in the Town of East Gwillimbury and a portion of the Town of Newmarket would be conveyed to a proposed Water Reclamation Centre for treatment, using environmentally sustainable wastewater purification and water recycling technologies, with surface discharge of clear treated effluent to the East Holland River and reclaimed water to serve as a non-potable water supply for irrigation and industrial processes. The Water Reclamation Centre will be designed to treat an annual average daily flow of 40 million litres per day (MLD). A preliminary study of potential impacts of the Water Reclamation Centre discharge on water quantity and quality in the East Holland River was presented in a feasibility report, entitled "Hydrodynamic and Water Quality Modelling of the Proposed Water Reclamation Centre," prepared for the Region as part of the Alternatives To the Undertaking stage of the UYSS EA. The feasibility study identified additional receiving stream assessment studies as being required for the Alternative Methods stage of the UYSS EA. The scope of the additional receiving stream assessment studies was discussed and reviewed by the Ministry of the Environment (MOE), the Ministry of the Natural Resources (MNR), and the Lake Simcoe Region Conservation Authority (LSRCA). The LSRCA requested additional information about potential impacts of the Water Reclamation Centre discharge on flooding in the East Holland River (Staff Report No. 42-11-BOD, June 13, 2011). The concern is that increased flows in the East Holland River from the Water Reclamation Centre discharge, in combination with high Lake Simcoe levels, have the potential of increasing the frequency and magnitude of flooding, resulting in more frequent overtopping of dikes and flooding of farm fields and low lying areas adjacent to the river.

1 Regional Municipality of York, Upper York Sewage Solutions Environmental Assessment, Screening Assessment of the

Alternatives to the Undertaking, August 2011.

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Figure 1.1: UYSS Service Area

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This report addresses the LSRCA concern by studying the potential impacts of the Water Reclamation Centre discharge on flooding potential in the East Holland River under existing and future river flow conditions and under the condition of increased flows from the proposed Water Reclamation Centre discharge. It is noted that the Water Reclamation Centre site location is subject to the EA process and has not been selected at this time. For the purposes of this study, it was assumed that the Water Reclamation Centre discharge will be to the East Holland River at Queensville Sideroad. Under the Innovative Wastewater Treatment Technologies concept, the East Holland River is the most likely receiver of the Water Reclamation Centre discharge as it is situated within the UYSS Service Area. The Holland River watershed includes the East and West Holland River subwatersheds as shown on Figure 1.2. The confluence of the East Holland River with the West Holland River (also called Schomberg River) is located near the 10th Line, approximately 5 kilometres south of Cook's Bay, which is the southern-most reach of Lake Simcoe. Lake Simcoe is part of the Trent-Severn Waterway, which is a canal system connecting Lake Ontario at Trenton to the Georgian Bay portion of Lake Huron at Port Severn. The study area includes the lower portion of the East Holland River from Green Lane East to the confluence with the West Holland River and the main branch of the Holland River (see Figure 1.2). This is the area potentially considered for the Water Reclamation Centre discharge location, and consequently, the area potentially affected by the Water Reclamation Centre discharge. In this study, the lower portion of the East Holland River within the study area limits and the main branch of the Holland River will be, for simplicity, referred to as the "East Holland River".

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Figure 1.2: The East and West Holland River Subwatersheds

Section 2.0 Methodology

Due to the interaction of the East Holland River with Lake Simcoe, the river represents a complex hydrodynamic system. The floodplain of the East Holland River is dominated by large polder areas used for intensive agricultural purposes (polder is a low-lying land enclosed by dikes). These areas are occasionally affected by flooding resulting from high Lake Simcoe levels or seiche (wind) effects, leading to overtopping of dikes and flooding of farm fields. Depending on the seasonal water levels in Lake Simcoe, the lake effect can hydraulically impact the river as far upstream as Holland Landing. The flooding potential in the East Holland River within the study area potentially affected by the Water Reclamation Centre discharge was assessed by hydraulic floodplain modelling. The U.S. Army Corps of Engineers' Hydrologic Engineering Center River Analysis System (HEC-RAS) was utilized in the modelling. HEC-RAS is a one-dimensional program for steady and unsteady flow calculations for a network of natural and constructed channels. Steady flow computational procedure is based on the solution of the one-dimensional energy equation. The momentum equation is utilized in situations where the water surface profile is rapidly varied (USACE, 2010).

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Cumming Cockburn Limited (CCL) was retained by the LSRCA in 1984 to conduct a hydraulic analysis of the East Holland River and its tributaries. The majority of the East Holland River and its tributaries were modelled in the HEC-2 format. In 2005, CCL updated the hydraulic model of the East and West Holland Rivers (CCL, 2005). The HEC-2 model format was converted into HEC-RAS version 3.1.2. Since 2005, LSRCA has updated and revised this model several times. The following is a list of revisions adopted from the HEC-RAS project description file: Original HEC-RAS model developed in version 3.1.2 LSRCA Holland River East Revised November 1, 2007 LSRCA Holland River East Revised December 11, 2009 - Insert 8447.4 9 ( Rev. 4) LSRCA Holland River East Revised March 18, 2010 - Bridge Stations adjusted at

8132.5 (Rev. 4a) LSRCA Holland River East Revised May 05, 2010 - Model of Tannery Creek, Reach 32

updated between cross-sections 8426 and 8429 as per Permit No. AP.2000.014 - Internal boundary conditions (water surface elevation) revised (Rev. 4b)

Ram Forest update (Rev. 4c) The most recent version of the model, named "HRE_rev4c" and dated June 17, 2010, was provided by the LSRCA in December 2011. This version of the model was used in the analysis presented in this study (the "original model" hereafter). The original model was imported into the latest version of HEC-RAS (version 4.1.0, as of January 2012). For the purposes of this study a number of updates and revisions were made to the model. These are summarized below. New cross-sections were added to the model to increase the density of cross-sections

and spatial detail of the original model. Several existing model cross-sections were extended horizontally to reach high ground,

to avoid the situation whereby the model is forced to extend the cross-section end points vertically for the computed water surface.

The latest bathymetric data surveyed in the spring and fall of 2011 were used to redefine low flow channels of model cross-sections.

Elevations of selected dikes along the East and West Holland Rivers were surveyed and updated in the revised model.

The geometry of bridges was updated in the model. The location of river banks, ineffective flow areas, and levees (dikes) was updated in the

model. Levees were set for the highest computed water surface elevation. Model boundary conditions (design flows and water levels) were updated in the model.

A detailed description of the changes made to the original HEC-RAS model is provided in Table A.1 in Appendix A. The updated and revised original model is referred to as the "updated model" hereafter. It is noted that, with the exception of two bridges/culverts (RS:8131.5 BR and RS:8133.5 BR, both located at reach 44: Tannery Creek) that had to be

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modified in order to run the model in the latest HEC-RAS version 4.1.0, the above changes were applied only to the model cross-sections located within the study area (downstream of Green Lane East or downstream of model cross-section No. 141, reach Holland East 28a). All existing cross-sections downstream of Green Lane East, extensions of existing cross-sections, and new cross-sections were cut from the Triangular Irregular Network data provided by the LSRCA. This format is a data structure representing a continuous surface through a series of irregular spaced points. The cross-sections were digitized using HEC-GeoRAS within ArcGIS, and were imported into HEC-RAS in a geo-referenced format. The cross-sections extracted from the Triangular Irregular Network file were checked by comparing them with the corresponding field surveyed data. Figure A.1 in Appendix A depicts the cross-sections in the original and updated HEC-RAS models. The topography of the low flow channel was updated with the bathymetric data surveyed in the spring and fall of 2011. Figure A.2 in Appendix A compares the channel bottom elevations obtained from the original and updated HEC-RAS models. The river bottom elevations from the bathymetric survey are generally higher than the bottom elevations from the original model, and reflect the sediment accumulation that has taken place in the river during recent years. Site reconnaissance and surveying were undertaken in January 2012. Model cross-sections within the study area were visited to provide additional information on hydraulic structures and dikes to supplement the Triangular Irregular Network data. Many dikes along the East Holland River were found to be recently upgraded and enlarged or upgrades were under construction. Confirmatory surface elevations were surveyed to validate the information in the existing model. The locations of levees and river banks were also updated in the model. Figure A.3 in Appendix A shows the locations of the confirmatory survey points. Table A.2 in Appendix A provides the easting, northing, and elevation data for the survey points. Model boundary conditions were also reviewed and checked against historical flow and lake level data. The existing model used the elevation of 219.52 metres above mean sea level (mAMSL) as the downstream head boundary condition, corresponding to the maximum water level at the river mouth at Cook's Bay, as determined in previous studies (CCL, 2005). Historical lake level records obtained from the Trent Severn Waterway Authority for the period 1960 to 2011 at the station closest to the mouth of the East Holland River (Lake Simcoe at Jackson Point) were reviewed and the long-term (1960-2011) average water level was calculated to be 218.88 mAMSL. The historical maximum and minimum water levels measured at this station were 219.49 mAMSL and 218.44 mAMSL, respectively. Flow boundary conditions used in the original model were also reviewed and updated. Historical flow data from the Water Survey of Canada's station East Holland River at Holland Landing (02EC009) for the period 1965 to 2011 were used to statistically estimate the design flows for common return periods. Several probability distribution functions were fitted to the historical data and their parameters estimated by the method of Linear Moments. Figure 2.1 depicts selected distribution functions fitted to the historical annual maximum instantaneous peak flow data obtained from the Holland Landing station.

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The two-parameter Exponential distribution provided the best visual fit to the annual maximum instantaneous peak flow data. The design flows estimated by this distribution function were compared against the design flows in the original HEC-RAS model. It was found that the existing conditions design flows at Holland Landing were significantly higher than the design flows estimated from the historical data. Figure 2.1: Annual Maximum Instantaneous Peak Flows – East Holland River

at Holland Landing

Figure 2.2 compares the existing conditions design flows from the original HEC-RAS model with the annual maximum instantaneous peak flows observed at the Water Survey Canada station East Holland River at Holland Landing (02EC009).

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Figure 2.2: Existing Conditions Design Flows from the Original HEC-RAS Model and Annual Maximum Instantaneous Peak Flows for East Holland River at Holland Landing

Figure 2.3 compares the design flows calculated from the annual maximum instantaneous peak flows using the Exponential distribution and the existing conditions design flows from the original HEC-RAS model. The design flows calculated from the observed instantaneous peak flow data are approximately 40 percent lower than the design flows in the original HEC-RAS model.

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Figure 2.3: Existing Conditions Design Flows in the Original HEC-RAS Model and Design Flows Calculated from the Annual Maximum Instantaneous Peak Flows using the Exponential Distribution

The design flows in the original HEC-RAS model were derived by Cumming Cockburn Limited from a calibrated hydrologic model for the East Holland River subwatershed for existing and future land use conditions. As acknowledged in the Cumming Cockburn report (CCL, 2005), "the suitability of the model to be used to estimate the return period peak flows under the design storms has not been examined against the return period flows derived from the frequency analysis of the gauged flows at hydrometric stations such as the East Holland River station 02EC009 at Holland Landing and the West Holland River station 02EC010 near Schomberg; or derived from the flood regional frequency analysis at the outlet without the gauge such as the outlets of the East and West Holland River Watersheds." Flow change locations are cross-sections at which flow boundary conditions are specified in the HEC-RAS model. In this study, the HEC-RAS design flows for existing land use conditions at the Holland Landing flow change location were replaced by the design flows estimated by the flood frequency analysis using the historical data at Holland Landing. For all other flow change

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locations downstream of Holland Landing (with the exception of tributaries), the design flows were scaled down using the ratio of design flows in the original model to the flows estimated from the historical data at Holland Landing. Using scaling ratios that are based on flows obtained from a calibrated watershed model is a more reliable approach than using ratios based solely on watershed areas. Further, the use of lower design flows in the updated model represents a more conservative approach, as the Water Reclamation Centre flow will result in a greater difference in water surface elevations compared to no Water Reclamation Centre flow. In general, the higher the design flow the smaller the difference in water surface elevations resulting from the Water Reclamation Centre flow. The updated existing conditions design flows are provided in Table A.3 in Appendix A. In addition to using the existing conditions design flows, this study also utilized design flows derived for future land use conditions. The rationale behind using the future flows was to assess the flooding potential in the East Holland River under future conditions when the Water Reclamation Centre is built and serving future development areas. The future conditions design flows were adopted from the Cumming Coburn report (CCL, 2005) and accounted for future (to-be-designed) stormwater management facilities. The future conditions design flows for the East Holland River at Holland Landing are approximately 65 to 86 percent higher than the existing conditions design flows derived from the flood frequency analysis performed in this study. It is noted that these flows represent very conservative estimates of future conditions design flows. Together with the revised existing conditions design flows, they represent a full range of variability (and uncertainty) in the magnitudes of design flows in the East Holland River. The updated and revised HEC-RAS model was validated using the Federal Emergency Management Agency (FEMA) cHECk-RAS program. This program was specially designed to verify the validity of an assortment of parameters found in the HEC-RAS hydraulic modelling program (FEMA, 2012). The cHECk-RAS program generated no errors for the updated section of the model (from Green Lane East to Lake Simcoe). The full cHECk-RAS report is available in Appendix B. In addition to validating the updated model setup and its parameters, the model was also validated with water level data measured in the field on December 1, 2011. Figure 2.4 compares the water surface elevations predicted by the updated HEC-RAS model to the water elevations surveyed in the field. The model was able to reproduce the hydraulic grade line in the river during the December 1, 2011 event very well.

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Figure 2.4: Validation of the Updated HEC-RAS Model – December 1, 2011 Event

The updated and validated HEC-RAS model was first run without the Water Reclamation Centre discharge and then re-run with the Water Reclamation Centre discharge added to the East Holland River flows. The Water Reclamation Centre discharge flow rate was added to all flow change locations specified in the original model downstream of the discharge location. The location of the Water Reclamation Centre discharge was assumed to be at the Queensville Sideroad for all scenarios. The peak hour flow rate of the Water Reclamation Centre discharge (112 MLD) was used in all model scenarios. It is noted that this discharge rate is 2.8 times higher than the average discharge rate (40 MLD) and represents a very conservative (worst-case) approach to the evaluation of the potential Water Reclamation Centre discharge impacts on the flooding conditions in the East Holland River. Minimum (218.44 mAMSL), average (218.88 mAMSL) and maximum (219.49 mAMSL) water levels in Lake Simcoe were considered in the modelling. Maximum flows in the East Holland River watershed typically occur in early spring, resulting from spring snowmelt events. Almost 40 percent of all historically observed annual maximum instantaneous peak flows at the Holland

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Landing streamflow station occurred in March, and almost 80 percent in the period February to April. In contrast, maximum lake levels follow the spring snowmelt and typically occur in late spring/early summer. Almost 50 percent of all annual maximum lake levels during the period 1965 to 2011 occurred in May. Figure 2.5 illustrates the lag between the occurrence of annual maximum flows and annual maximum lake levels. Figure 2.5: The Occurrence of Annual Maximum Flows and Lake Levels in the

East Holland River and Lake Simcoe

Water levels in Lake Simcoe are artificially controlled by the Trent-Severn Waterway Authority. The high water levels in the lake are generally maintained during the summer period and low levels during the winter period. Since high flows in the East Holland River rarely coincide with high lake levels, it is very conservative to use maximum lake levels in the modelling. Table 2.1 summarizes the scenarios analyzed in this study. The nomenclature used to define the scenarios in Table 2.1 has the following format: XF-YLL-W#, where XF is the type of design

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flow data (EF for Existing Flows and FF for Future Flows); YLL is the lake level (LLL for low lake level, ALL for average lake level, and HLL for high lake level); and W# is the Water Reclamation Centre discharge rate (either 0 or 112 MLD). A total of 12 scenarios were defined and analyzed in this study. Table 2.1: Summary of Model Scenarios

Scenario ID

Design flow data

Lake level (mAMSL)

WRC flow (MLD)

EF-LLL-W0 Existing 218.44 0 EF-LLL-W112 Existing 218.44 112 EF-ALL-W0 Existing 218.88 0 EF-ALL-W112 Existing 218.88 112 EF-HLL-W0 Existing 219.49 0 EF-HLL-W112 Existing 219.49 112 FF-LLL-W0 Future 218.44 0 FF-LLL-W112 Future 218.44 112 FF-ALL-W0 Future 218.88 0 FF-ALL-W112 Future 218.88 112 FF-HLL-W0 Future 219.49 0 FF-HLL-W112 Future 219.49 112

All 12 scenarios were simulated for design flows with return periods of 5, 10, 25, 50, and 100 years. Water surface elevations resulting from the regional storm were also simulated. All model runs assumed subcritical flow condition and were simulated as steady-state simulations. Bridges, culverts, and other hydraulic structures were assumed to be free of any obstruction that may reduce the hydraulic flow capacity. Section 3.0 Results

Figures C.1 to C.14 in Appendix C depict the water levels in the East Holland River calculated for existing and future conditions design flows and different lake levels. In all of the figures, the water levels calculated for the scenarios with and without the peak-hour Water Reclamation Centre discharge are visually identical (water levels for the scenarios with the Water Reclamation Centre discharge are depicted by dashed lines on Figures C.1 to C.14). Typical elevations of dikes on the left and right banks of the East Holland River are also depicted on Figures C.1 to C.14. The elevations of dikes located on the left bank of the river (looking downstream) are lower than the elevations of right bank dikes and, consequently, more prone to overtopping. However, as mentioned earlier, many dikes were found to be under construction during the site visit, and their elevations are expected to change (increase) in the near future. It is also noted that the dike elevations depicted on Figures C.1 to C.14 are just spot elevations surveyed in the vicinity of model cross-sections, and as such, they do not represent the entire dike system built along the East Holland River. Consequently, there may be dikes with elevations higher or lower than those depicted on the figures.

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It is apparent from Figures C.1 to C.14 that levels in Lake Simcoe play a crucial role in overtopping of the dikes. For example, for existing flow conditions, during low lake level conditions, the left bank dikes are expected to be overtopped under the 50-year flow event; during average lake level conditions under the 25-year flow event; and during high lake levels under the 2-year flow event. The right bank dikes have higher elevations and are expected to be overtopped only under the existing conditions regional storm flood event for all lake level conditions. For future flow conditions, the left bank dikes are expected to be overtopped during low lake levels under the 10-year flow event; during average lake level conditions under the 5-year flow event; and during high lake levels under the 2-year flow event. The right bank dikes are expected to be overtopped during low lake levels under the regional storm flood event; during average lake level conditions under the 100-year flow event; and during high lake levels under the 25-year flow event. Figures C.1 to C.14 in Appendix C also suggest that the lake effect is very pronounced for low magnitude flood events, such as the 2-, 5-, or 10-year events, and that the modelled discharge location at Queensville Sideroad is well within the zone affected by the lake level fluctuation. The lake effect diminishes for large flood events where there is only a minimal difference between the calculated water levels obtained for different lake levels (see for example Figure C.7 or Figure C.14 in Appendix C). Figures D.1 to D.6 in Appendix D depict the absolute changes in water levels in the East Holland River due to the peak-hour Water Reclamation Centre discharge for existing and future conditions design flows and different lake levels. It is apparent that the changes are largest during low lake levels and small flood events and smallest during high lake levels and large flood events. It is also apparent that the changes in water levels are very small; for the existing conditions design flows during low lake levels, only the 2-year flow event generated a change greater than 2 cm (see Figure D.1). During average lake levels, the changes generated by all flow events are below 2 cm (see Figure D.2), and during high lake levels, all changes in water levels are below 1 cm (see Figure D.3). The changes generated by future conditions flow events are even smaller (see Figures D.4 to D.6). Figures D.1 to D.6 in Appendix D also suggest that the maximum changes in river water levels are expected near the Water Reclamation Centre discharge location. The changes in water levels quickly decrease upstream and downstream of the assumed discharge location at the Queensville Sideroad, and are approaching zero at Holland Landing (upstream) and the mouth of the river (downstream). Table 3.1 and Table 3.2 summarize the maximum as well as average changes in the river water levels for all scenarios evaluated in this study. The tables show that the average changes are much smaller than the maximum changes.

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Table 3.1: Maximum and Average Changes in Water Levels in the East Holland River for Existing Conditions Design Flows

Lake Level 2-yr 5-yr 10-yr 25-yr 50-yr 100-yr Regional Storm Maximum change [cm] Low 2.34 1.59 1.35 1.17 0.97 0.85 0.32 Average 1.82 1.40 1.15 0.97 0.87 0.77 0.31 High 0.63 0.65 0.67 0.65 0.63 0.59 0.31 Average change* [cm] Low 1.07 0.88 0.82 0.72 0.64 0.59 0.20 Average 0.64 0.64 0.59 0.54 0.51 0.46 0.18 High 0.27 0.27 0.25 0.27 0.27 0.27 0.15

*downstream of the Water Reclamation Centre discharge point Table 3.2: Maximum and Average Changes in Water Levels in the East Holland River

for Future Conditions Design Flows

Lake Level 2-yr 5-yr 10-yr 25-yr 50-yr 100-yr Regional Storm Maximum change [cm] Low 1.55 0.95 0.79 0.64 0.55 0.48 0.20 Average 1.38 0.90 0.74 0.63 0.53 0.49 0.20 High 0.67 0.64 0.57 0.52 0.46 0.43 0.20 Average change* [cm] Low 0.81 0.63 0.53 0.42 0.36 0.31 0.11 Average 0.58 0.50 0.42 0.40 0.31 0.26 0.11 High 0.19 0.23 0.24 0.23 0.19 0.18 0.10

*downstream of the Water Reclamation Centre discharge point The results summarized in Appendices C and D and in Tables 3.1 and 3.2 confirm that the Water Reclamation Centre discharge would minimally increase water levels in the East Holland River during flood conditions; the maximum increase obtained from all 12 scenarios considered in this study was only 2.3 cm (see Figure D.1 in Appendix D). This increase was observed near the Water Reclamation Centre discharge location (Queensville Sideroad) and not in the downstream sections of the river, where farm fields and low lying areas along the river prone to dike overtopping are located. In the downstream sections of the river between Lake Simcoe and the confluence of the East and West Holland Rivers, the maximum increase was between 0 and 1 cm (see Figure D.1). Also, this 2.3 cm maximum increase was generated by a scenario which has, among all the scenarios considered, the lowest flooding potential for the following reasons:

It was generated by the existing conditions 2-year flow - a small-magnitude flood event. For comparison, for a large-magnitude (regional storm) flood event, this increase would only be 0.3 cm. Also, for future conditions 2-year flow, this increase would only be 1.5 cm.

It was obtained for low lake level; for high lake level, the increase would only be 0.6 cm.

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As expected, the modelling results suggest that the larger the flood event in the East Holland River, the smaller the increase in water levels due to the Water Reclamation Centre discharge. This is because the peak-hour Water Reclamation Centre discharge (112 MLD or 1.3 m3/s) represents only 2 percent of the magnitude of the existing conditions 2-year flow in the river at the confluence with Cook's Bay and 1.3 percent of the future conditions 2-year flow. In contrast, the 112 MLD represents only 0.6 percent of the existing conditions 100-year flow and 0.4 percent of the future conditions 100-year flow. The results also confirm that the higher the water level in Lake Simcoe, the smaller the increase in water levels due to the Water Reclamation Centre discharge. This is because of the larger volume of water available in the river during high lake level conditions. As noted previously, the maximum increase for existing conditions 2-year flow event is 2.3 cm for low lake level and 0.6 cm for high lake level. For future conditions 2-year flow, the maximum increase drops to 1.5 cm for low lake level and 0.7 cm for high lake level. For the existing conditions 100-year flow event, the maximum increase is 0.8 cm (low lake level) and 0.6 cm (high lake level) and for the future conditions 100-year flow event, 0.5 cm (low lake level) and 0.4 cm (high lake level). It is noted again that the average increases are much lower than the maximum increases (refer to Tables 3.1 and 3.2). Extreme flooding situations occur in the East Holland River when high water levels in Lake Simcoe occur simultaneously with high flood events in the river. Under these conditions however, the increase of river levels due to the Water Reclamation Centre discharge is minimal. For example, under regional storm flows and high lake levels the expected maximum increase in river levels is 0.3 cm (existing conditions regional storm) and 0.2 cm (future conditions regional storm). It is also noted that these conditions are rare; as shown previously, there is a lag between typical occurrence of annual maximum flows in the East Holland River and annual maximum levels in Lake Simcoe. Maximum flows in the East Holland River watershed typically occur in early spring, resulting from spring snowmelt events. In contrast, maximum lake levels follow the spring snowmelt and typically occur in late spring/early summer (see Figure 2.5). Section 4.0 Summary and Conclusion

This study evaluated the potential impacts of the Water Reclamation Centre discharge on flooding potential in the East Holland River. The study demonstrated that the Water Reclamation Centre discharge will have no significant impacts on flooding potential in the East Holland River due to the fact that the discharge represents only a small fraction of the flows in the river during flood conditions. The flooding potential in the East Holland River was assessed by hydraulic floodplain modelling using LSRCA's HEC-RAS hydraulic model. The model was updated and validated using the FEMA's cHECk-RAS program, as well as with observed water level data. The updated and validated HEC-RAS model was run both with and without the Water Reclamation Centre discharge added to the East Holland River flows. A number of scenarios were considered in the modelling, reflecting different hydraulic conditions in the East Holland River and Lake Simcoe.

050278 (62) York Region No. 74270



The peak-hour Water Reclamation Centre discharge rate (112 MLD), which represents the worst-case flow impact, was used in all model scenarios. The location of the Water Reclamation Centre discharge was assumed to be at the Queensville Sideroad. The modelling results showed that: The Water Reclamation Centre discharge would only minimally increase water levels in

the East Holland River during flood conditions. The maximum increase in river water levels for all scenarios ranged from 0.2 cm to 2.3 cm, and the average increase from 0.1 cm to 1.1 cm.

Lake Simcoe is an important driving force impacting flooding conditions in the East Holland River. In contrast to the expected negligible increases in river levels due to the Water Reclamation Centre discharge (less than 1.0 cm in most scenarios), the lake fluctuations can cause river levels to change by up to 100 cm.

The maximum increase of water levels in the East Holland River was observed near the Water Reclamation Centre discharge location (Queensville Sideroad) and not in the downstream sections of the river, which are prone to dike overtopping and flooding.

The magnitude of the Water Reclamation Centre discharge impacts depends on the volume of water available in the river – the larger the flood event in the East Holland River, the smaller the increase in water levels due to the Water Reclamation Centre discharge, and the higher the water level in Lake Simcoe, the smaller the increase in water levels due to the Water Reclamation Centre discharge.

The negligible increases in river levels due to the Water Reclamation Centre discharge during flood conditions are not expected to generate higher potential for river bank erosion in the East Holland River.

Section 5.0 References

Conestoga-Rovers & Associates, AECOM, and Black & Veatch. November 2011. "Hydrodynamic and Water Quality Modelling of the Proposed Water Reclamation Centre (WRC) Discharge to the East Holland River." Prepared for York Region.

Cumming Cockburn Limited (CCL). June 30, 2005. Hydrologic and Hydraulic Modeling for the West Holland River, East Holland River and Maskinonge River Watersheds. Prepared for Lake Simcoe Region Conservation Authority. 73 p.

Federal Emergency Management Agency (FEMA). 2012. cHECk-RAS 2.0.1 beta. User Guide. 30 p.

U.S. Army Corps of Engineers, Hydrologic Engineering Center (USACE). 2010. HEC-RAS River Analysis System. User's Manual. Version 4.1. 790 p.

050278 (62) York Region No. 74270



APPENDICES

Appendix A

UPDATES AND REVISIONS MADE TO THE ORIGINAL HEC-RAS MODEL

Appendix B

cHECk-RAS REPORT FOR THE UPDATED HEC-RAS MODEL

Appendix C

CALCULATED WATER LEVELS IN THE EAST HOLLAND RIVER

Appendix D

CALCULATED CHANGES IN WATER LEVELS IN THE EAST HOLLAND RIVER

050278 (62) York Region No. 74270



Appendix A

UPDATES AND REVISIONS MADE TO THE ORIGINAL HEC-RAS MODEL

050278 (62) APP A Page A-1 York Region No. 74270



Appendix A

Updates And Revisions Made To The Original HEC-RAS Model

List of Figures

Figure A.1 Original and Updated HEC-RAS Model Cross-Sections Figure A.2 Original and Updated HEC-RAS River Profile Figure A.3 Locations of the Confirmatory Survey Points

List of Tables

Table A.1 Updates Made in the Revised HEC-RAS Model Table A.2 Geographic Data of the Confirmatory Survey Points Table A.3 Existing Conditions Design Flows Used in the Revised

HEC-RAS Model




Figure A.1: Original and Updated HEC-RAS Model Cross-Sections




Figure A.2: Original and Updated HEC-RAS River Profile

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Original HEC-RAS model Updated HEC-RAS model

WRC Discharge




Figure A.3: Locations of the Confirmatory Survey Points




Table A.1: Updates Made in the Revised HEC-RAS Model River Reach Cross-section Notes Holland East 28a 141 Bank stations updated, levees modified on left bank and added on right

bank Holland East 28a 140.5 Bank stations updated, levees removed on left bank and added on right

bank Holland East 28a 140.25 Bridge opening and bridge deck data modified Holland East 28a 140 Bank stations updated Holland East 28a 139 Cross-section removed in the revised model Holland East 28a 138 Bank stations updated, levee added on right bank Holland East 28a 137 Bank stations updated, levees added on left and right banks Holland East 28a 136 Bank stations updated, levee added on right bank Holland East 28a 135 Bank stations updated, levee added on left bank Holland East 28a 134 Bank stations updated Holland East 40 133 Bank stations updated Holland East 40 132 Bank stations updated, levee added on right bank, ineffective flow areas

added Holland East 40 131.9 New cross-section Holland East 40 131.8 New inline structure with 3 gates Holland East 40 131.7 Bank stations updated, levees removed on left bank and modified on right

bank, ineffective flow areas added Holland East 40 131.6 Bridge opening and bridge deck data modified Holland East 40 131.5 Bank stations updated, levee added on right bank, ineffective flow areas

added Holland East 40 131 Bank stations updated, levee added on right bank Holland East 40 130 Bank stations updated, levee added on right bank Holland East 40 129 Bank stations updated, levee added on right bank Holland East 40 128 Bank stations updated, Levee added on left bank Holland East 40 127 Bank stations updated, levee modified on right bank Holland East 12 126 Bank stations updated, levee added on right bank Holland East 12 124 Bank stations updated, levee added on right bank Holland East 12 123 Cutline location modified, bank stations updated, levees removed on left

and added on right bank, ineffective flow areas added Holland East 12 122.5 Bridge opening and bridge deck data modified Holland East 12 122 Cutline location modified, bank stations updated, levee added on right

bank, ineffective flow areas added Holland East 12 121 Bank stations updated, levee added on left bank Holland East 12 120 Cutline location modified, bank stations updated, levee added on right

bank Holland East 12 119 Bank stations updated, levee added on right bank Holland East 12 118 Cutline location modified, bank stations updated, levee modified on left

bank Holland East 12 117.5 Bridge opening and bridge deck data modified




River Reach Cross-section Notes Holland East 12 117 Cutline location modified, bank stations updated Holland East 12 116 Bank stations updated Holland East 12 115 Bank stations updated, levee added on left bank Holland East 12a 114 Bank stations updated Holland East 12a 113 Bank stations updated, levee added on right bank Holland East 12a 112.5 New cross-section Holland East 12a 112 Cutline location modified, bank stations updated, levee added on right

bank Holland East 12a 111.5 New cross-section Holland East 12a 111 Bank stations updated, ineffective flow areas added Holland East 12a 110.5 New cross-section Holland East 12a 110 Bank stations updated, levee modified on right bank Holland East 12a 109 Cutline shortened in left and right bank, bank stations updated, levee

added on right bank Holland East 12a 108 Cutline location modified, bank stations updated, levees removed on left

and right bank Holland East 13 107.7 Cutline location modified, bank stations updated , levees modified on left

bank and removed on right bank, ineffective flow areas added Holland East 13 107.6 Bridge opening and bridge deck data modified Holland East 13 107.5 Cutline location modified, bank stations updated , levees modified on left

bank and removed on right bank, ineffective flow areas added Holland East 13 107 New cross-section Holland East 13 106 Cutline shortened on left and right bank, bank stations and levees

updated on left and right bank Holland East 13 105 Cutline location modified, bank stations and levees updated on left and

right bank Holland East 13 104 Cutline shortened on left bank and extended on right bank, bank stations

and Levees updated on left and right bank Holland East 13 103.5 New cross-section Holland East 13 103 Cutline extended on left and right bank, bank stations and levees updated

on left and right bank Holland East 13 102 Cutline extended on left and right bank, bank stations and levees updated

on left and right bank Holland East 13 101 Cutline extended on left and right bank, bank stations and levees updated

on left and right bank Holland East 13 100.5 New cross-section Holland East 13 100 Bank stations updated, levees removed on left bank and modified on right

bank




Table A.2: Geographic Data of the Confirmatory Survey Points

Point ID X [m] Y [m] Elevation [m] J16.001 620906.6 4883501.6 224.855 J16.002 619457.3 4887461.4 220.421 J16.004 619206.6 4887730.2 220.322 J16.005 619120.2 4887616.5 220.684 J16.008 619356.2 4887358.7 221.284 J16.012 619238.5 4887230.3 221.258 J16.013 617740.7 4888035.4 220.234 J16.014 617497.2 4889260.5 219.595 J16.018 619763.5 4888950.3 220.361 J16.019 621544.9 4889964.5 221.028 J16.020 622979.6 4892432.7 222.332 J16.021 619605.0 4893474.6 219.159 J16.023 619359.6 4893572.9 219.270 J16.024 618995.3 4892803.9 219.570 J16.025 618077.8 4890989.0 219.646 J16.026 617104.3 4890668.9 219.994 J16.027 617975.5 4895293.6 219.508 J16.028 618216.0 4895372.2 219.447 J16.029 617410.8 4895104.2 220.361 J16.030 616621.0 4892721.1 221.740 J16.031 619998.2 4887784.5 221.229 J16.032 619877.7 4888379.2 220.696 J17.001 618120.9 4889367.0 219.447 J17.002 618289.8 4889910.2 219.698 J17.003 618313.5 4890487.8 219.397 J17.004 618115.7 4890508.8 219.635 J17.007 617961.3 4889976.8 219.615 J17.008 617958.0 4889976.2 219.780 J17.009 619717.2 4889187.9 219.942 J17.010 621333.6 4889075.7 220.934 J17.012 620794.6 4888895.3 220.401 J17.013 620947.9 4888728.0 220.211 J17.016 620749.6 4889084.7 219.470 J17.017 620751.5 4889083.0 220.045 J17.020 621318.7 4889284.0 220.667 J17.024 620764.1 4893738.8 219.786 J17.025 618701.0 4891460.3 220.765 J17.026 619264.8 4891502.3 219.714




Point ID X [m] Y [m] Elevation [m] J17.028 619355.1 4891232.7 220.107 J17.029 619014.1 4892713.3 219.370 J17.033 618843.0 4892719.8 219.888 J17.034 618807.9 4893797.3 220.753 J17.036 619065.1 4894799.8 219.602 J17.037 618208.6 4895196.8 219.448 J17.038 618272.2 4895244.6 219.080 J17.039 617097.8 4890684.5 219.820 J17.040 618375.9 4891425.6 220.305 J17.041 618381.1 4891427.8 219.147

Table A.3: Existing Conditions Design Flows used in the Revised

HEC-RAS Model (in m3/s)

River Reach Cross-section 2-yr 5-yr 10-yr 25-yr 50-yr 100-yr Regional Storm Holland East 28a 145 23.46 35.83 45.42 58.97 69.11 79.44 401.51 Holland East 28a 140.5 24.05 36.80 46.62 60.35 70.78 80.86 398.99 Holland East 40 133 26.95 41.01 51.90 66.10 77.12 87.64 403.49 Holland East 12 126 28.73 44.00 55.56 70.83 82.39 93.94 422.30 Holland East 12 121 28.99 44.06 55.50 70.89 82.81 94.24 414.33 Holland East 12 115 26.49 41.68 51.54 64.30 73.71 83.42 361.86 Holland East 12a 114 26.49 41.68 51.54 64.30 73.71 83.42 361.86 Holland East 13 107.7 25.89 40.28 49.44 62.62 71.98 81.46 331.55 Holland East 13 104 25.04 40.89 51.06 64.96 75.21 85.56 347.18 Holland East 13 102 62.93 98.69 123.18 156.11 180.21 201.68 529.46

050278 (62) York Region No. 74270



Appendix B

cHECk-RAS REPORT FOR THE UPDATED HEC-RAS MODEL

050278 (62) APP B Page B-1 York Region No. 74270



Appendix B cHECk-RAS Report For The Updated HEC-RAS Model










050278 (62) York Region No. 74270



Appendix C

CALCULATED WATER LEVELS IN THE EAST HOLLAND RIVER

050278 (62) APP C Page C-1 York Region No. 74270



Appendix C

Calculated Water Levels in the East Holland River

List of Figures

Figure C.1 Water Levels in the East Holland River for Existing Conditions 2-year Design Flows and Different Lake Levels With and Without the Peak-Hour Water Reclamation Centre Discharge

Figure C.2 Water Levels in the East Holland River for Existing Conditions 5-Year Design Flows and Different Lake Levels With and Without the Peak-Hour Water Reclamation Centre Discharge





Figure C.7 Water Levels in the East Holland River for Existing Conditions Regional Storm Flows and Different Lake Levels With and Without the Peak-Hour Water Reclamation Centre Discharge

Figure C.8 Water Levels in the East Holland River for Future Conditions 2-year Design Flows and Different Lake Levels With and Without the Peak-Hour Water Reclamation Centre Discharge









Figure C.14 Water Levels in the East Holland River for Future Conditions Regional Storm Flows and Different Lake Levels With and Without the Peak-Hour Water Reclamation Centre Discharge




Figure C.1: Water Levels in the East Holland River for Existing Conditions 2-year Design Flows and Different Lake Levels With and Without the Peak-Hour Water Reclamation Centre Discharge

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High Lake Level Average Lake Level Low Lake Level Level with WRC

Channel Bottom Left Dyke Right Dyke

WRC Discharge




Figure C.2: Water Levels in the East Holland River for Existing Conditions 5-year Design Flows and Different Lake Levels With and Without the Peak-Hour Water Reclamation Centre Discharge

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Figure C.3: Water Levels in the East Holland River for Existing Conditions 10-year Design Flows and Different Lake Levels With and Without the Peak Hour Water Reclamation Centre Discharge

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WRC Discharge




Figure C.7: Water Levels in the East Holland River for Existing Conditions Regional Storm Flows and Different Lake Levels With and Without the Peak Hour Water Reclamation Centre Discharge

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WRC Discharge




Figure C.8: Water Levels in the East Holland River for Future Conditions 2-year Design Flows and Different Lake Levels With and Without the Peak Hour Water Reclamation Centre Discharge

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WRC Discharge




Figure C.14: Water Levels in the East Holland River for Future Conditions Regional Storm Flows and Different Lake Levels With and Without the Peak Hour Water Reclamation Centre Discharge

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050278 (62) York Region No. 74270



Appendix D

CALCULATED CHANGES IN WATER LEVELS IN THE EAST HOLLAND RIVER

050278 (62) APP D Page D-1 York Region No. 74270



Appendix D

Calculated Changes in Water Levels in the East Holland River

List of Figures

Figure D.1 Changes in Water Levels in the East Holland River Due to the Peak Hour Water Reclamation Centre Discharge for Existing Conditions Design Flows and Low Lake Levels

Figure D.2 Changes in Water Levels in the East Holland River Due to the Peak Hour Water Reclamation Centre Discharge for Existing Conditions Design Flows and average Lake Levels

Figure D.3 Changes in Water Levels in the East Holland River Due to the Peak Hour Water Reclamation Centre Discharge for Existing Conditions Design Flows and High Lake Levels

Figure D.4 Changes in Water Levels in the East Holland River Due to the Peak Hour Water Reclamation Centre Discharge for Future Conditions Design Flows and Low Lake Levels

Figure D.5 Changes in Water Levels in the East Holland River Due to the Peak Hour Water Reclamation Centre Discharge for Future Conditions Design Flows and Average Lake Levels

Figure D.6 Changes in Water Levels in the East Holland River Due to the Peak Hour Water Reclamation Centre Discharge for Future Conditions Design Flows and High Lake Levels




Figure D.1: Changes in Water Levels in the East Holland River Due to the Peak Hour Water Reclamation Centre Discharge for Existing Conditions Design Flows and Low Lake Levels

-0.5

0.0

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2-Year 5-Year 10-Year 25-Year 50-Year 100-Year Regional Storm

Lake Simcoe

Queensville Side Rd




Figure D.2: Changes in Water Levels in the East Holland River Due to the Peak Hour Water Reclamation Centre Discharge for Existing Conditions Design Flows and Average Lake Levels

-0.5

0.0

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Lake Simcoe

Queensville Side Rd




Figure D.3: Changes in Water Levels in the East Holland River Due to the Peak Hour Water Reclamation Centre Discharge for Existing Conditions Design Flows and High Lake Levels

-0.2

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Lake Simcoe

Queensville Side Rd




Figure D.4: Changes in Water Levels in the East Holland River Due to the Peak Hour Water Reclamation Centre Discharge for Future Conditions Design Flows and Low Lake Levels

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Lake Simcoe

Queensville Side Rd




Figure D.5: Changes in Water Levels in the East Holland River Due to the Peak Hour Water Reclamation Centre Discharge for Future Conditions Design Flows and Average Lake Levels

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Lake Simcoe

Queensville Side Rd




Figure D.6: Changes in Water Levels in the East Holland River Due to the Peak Hour Water Reclamation Centre Discharge for Future Conditions Design Flows and High Lake Levels

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Queensville Side Rd

Study of Potential Impacts of the Water Reclamation Centre ... · due to the Water Reclamation Centre discharge during ... Reclamation Centre discharge on flooding potential in ...

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