Technical Review of the Hydrodynamic Analysis of Jock River Reach 1 (Hwy 416 to Rideau River)

The City of Ottawa

455 Phillip Street Waterloo Ontario N2L 3X2 Canada | 11155320 | Report No 1 | May 9 2018

May 9, 2018 Reference No. 11155320

Mr. John Bougadis Senior Project Manager, Infrastructure Planning Planning, Infrastructure and Economic Development Department 110 Laurier Avenue W., 3rd Floor Ottawa, Ontario K1P 1J1

Dear Mr. Bougadis:

Re: Technical Review of the Hydrodynamic Analysis of Jock River Reach 1 Final Report Submission

GHD is pleased to provide the City Of Ottawa with the attached Final Report for the Technical Review of the Hydrodynamic Analysis of Jock River Reach 1 prepared by J.F. Sabourin and Associates Inc.

Yours truly,

Juraj M. Cunderlik, Ph.D., P.Eng. Associate, Project Manager

JC/aj/1

Encl.

GHD 455 Phillip Street Waterloo Ontario N2L 3X2 Canada T 519 884 0510 F 519 884 0525 W www.ghd.com

Table of Contents

1. Introduction ...... 1 1.1 Description of Work to be Reviewed ...... 1 1.2 Purpose of Review ...... 1 1.1 Summary of Documents Provided to Reviewer ...... 1 1.2 Summary of Communication and Site Visit by Reviewer ...... 3 1.3 Relevant Guidelines and Standards ...... 3

2. Objective of Work and Review Methodology ...... 4 1.4 Objective of Work ...... 4 1.5 Technical Review Methodology ...... 4

3. Review of Findings ...... 4 3.1 Background Information Review ...... 5 3.2 Review of Reach 1 Floodplain Suitability for Development ...... 6 3.3 Jock River Hydrological Analysis Review ...... 9 3.3.1 Summary of Previous Studies ...... 9 3.3.2 Statistical Analysis of the Jock River Flows ...... 10 3.3.3 Climatologic Analysis ...... 13 3.4 Hydrodynamic Model Review ...... 15 3.4.1 Model Selection ...... 15 3.4.2 Model Setup ...... 16 3.4.3 Model Calibration and Validation ...... 17 3.4.4 Modelling Approach ...... 17 3.4.5 Model Results ...... 18 3.5 Risk Management and Factor of Safety Review ...... 19 3.5.1 Flood Risk Characterization ...... 19 3.5.2 Sensitivity Analysis ...... 20 3.5.3 Future Watershed Development ...... 21 3.5.4 Conservative Assumptions ...... 21

4. Conclusions ...... 21

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Figure Index

Figure 3.1 The Jock River Watershed and the Study Area...... 7 Figure 3.2 Reach 1 Channel Profile...... 8 Figure 3.3 Regional Relationship between Specific Flow and Drainage Area ...... 13 Figure 3.4 Comparison of Normalized Annual Maximum Streamflow for Jock River near Richmond (WSC ID 02LA007) and Winter Snow and Mean Air Temperature for Ottawa CDA (Experimental Farm) Climate Station ...... 15

Table Index

Table 3.1 Comparison of Jock River Near Richmond (WSC ID 02LA007) 100-year Flood Estimates ...... 11 Table 3.2 Comparison of 100-year Stationary and Non-Stationary Flood Estimates for Jock River Near Richmond (WSC ID 02LA007) ...... 12 Table 3.3 Water Survey of Canada Streamflow Gauges Used in Regional Flood Frequency Analysis...... 12

Appendix Index

Appendix A Statistical Analysis of the Jock River Flows Appendix B 2D Hydrodynamic Model Review

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1. Introduction

1.1 Description of Work to be Reviewed

This Technical Report comprises the technical review of the “Hydrodynamic Analysis of Jock River Reach 1 (HWY 416 to Rideau River)” report (referred to as the “Hydrodynamic study” in this document), prepared for the Barrhaven Conservancy Inc. by J.F. Sabourin and Associates (JFSA), dated June 30, 2017.

1.2 Purpose of Review

A hydrodynamic analysis of the Jock River Reach 1 was completed to evaluate the impact of filling a portion of the floodplain, which could permit development of a large area that currently lies within the floodplain. The analysis was completed by J.F. Sabourin and Associates (JFSA, 2017).

The City retained GHD to perform a third party evaluation of the analysis to ensure that the technical approach, methodology, and assumptions utilized in the analysis are appropriate and the results are reliable in consideration of the potential risks associated with the proposed development. It is noted that the City of Ottawa (City) is responsible for associated planning, development and infrastructure approvals, and ensuring that drainage systems meet level of service targets set out in its engineering design guidelines. The Rideau Valley Conservation Authority (RVCA) is responsible for issuing permits related to the proposed filling of the floodplain and as such was involved in the peer review process.

The general purpose of the review was to answer the following key questions:

• Is the approach and methodology robust and appropriate in consideration of the potential risks associated with the development proposal and with a changing climate?

• Is the quality of input data adequate to ensure reliable results? • Have the appropriate methods/tools/assumptions been adopted to reflect hydrologic and hydraulic conditions under existing (unfilled) and future (filled) conditions? • Can the models be applied successfully to evaluate existing and future conditions of the Jock River from Highway 416 to Rideau River?

The detailed scope of the review was defined in the Terms of Reference (TOR) issued by the City on August 17, 2017.

1.1 Summary of Documents Provided to Reviewer

The following reports were provided to GHD as part of this assignment (in chronological order):

• Hydrodynamic Analysis of Jock River Reach 1 (HWY 416 to Rideau River). Prepared by J.F. Sabourin and Associates Inc. for Barrhaven Conservancy Inc., June 2017.

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• Functional Servicing Report for Minto Communities – Canada and City of Ottawa, 3311 Greenbank Road. Prepared by David Schaeffer Engineering Ltd. for the City of Ottawa, June 2017. • Kennedy-Burnett Stormwater Management Facility Project File and Functional Design Report. Prepared by CH2MHILL for the City of Ottawa, June 2017. • Functional Servicing Report for Glenview Homes (Cedarview) Ltd., 3387 Borrisokane Road. Prepared by David Schaeffer Engineering Ltd. for the City of Ottawa, May 2017. • Design Brief for the Clarke Stormwater Management Pond for the Half Moon Bay West Subdivision. Prepared by David Schaeffer Engineering Ltd. for the City of Ottawa, May 2017. • Rideau River Flood Risk Mapping from Hogs Back to Rideau Falls. Technical Memorandum, The Rideau Valley Conservation Authority, August 2016.

• Design Brief for the Interim Greenbank Stormwater Management Pond for Phases 4 and 7 of the Half Moon Bay Subdivision. Prepared by David Schaeffer Engineering Ltd. for the City of Ottawa, July 2016.

• Jock River 2016 Subwatershed Report. The Rideau Valley Conservation Authority, 2016. • Barrhaven South Master Servicing Study Addendum. Prepared by STANTEC Consulting Ltd. for the City of Ottawa, November 2014

• Ottawa River Flood Risk Mapping from Shirley’s Bay to Cumberland. Technical Memorandum, The Rideau Valley Conservation Authority, October 2014.

• Infrastructure Master Plan. The City of Ottawa, November 2013.

• Foster Stormwater Management Facility Environmental Study Report. Prepared by CH2MHILL for the City of Ottawa, October 2013.

• Summary of the Jock River Reach 2 Subwatershed Existing Conditions Report. The City of Ottawa, 2011.

• Corrigan Stormwater Management Facility Stormwater Management Report and Design Brief. Prepared by IBI Group for the City of Ottawa, July 2008. • Design Brief for Todd Pond, Half Moon Bay Subdivision. Prepared by David Schaeffer Engineering Ltd. for the City of Ottawa, April 2008. • Jock River Reach One Subwatershed Study. Final Report. Prepared by STANTEC Consulting Ltd. for the City of Ottawa, June 2007. • Jock River Flood Risk Mapping (within the City of Ottawa). Prepared by PSR Group Ltd. In association with J.F. Sabourin and Associates Inc. for the Rideau Valley Conservation Authority, June 2005.

• Secondary Plan for South Nepean (Area 8), Volume 2A of the Ottawa Official Plan. The City of Ottawa, 2003.

• Jock River Watershed Management Plan. The Rideau Valley Conservation Authority, November 2001.

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Furthermore, the following data and information were provided by the City and the RVCA: • Location and configuration of the proposed development area (file: ConservancyLands_SubdivisionPlan.pdf) • Existing and Future Ponds Draining to Jock River (file: BarrhavenSouth_Ponds_11Oct2017.pdf) • Integrated Asset Management Approach to Watershed Based Planning & EAs (file: IntegratedAssetManagementPlanningEAsCityFULL2017.pptx) • Jock River flow and Experimental Farm data analyses (files: JockFlowsPrecip.xlsx, ClimateTempIMP.xlsx, ClimatePrecipIMP.xlsx)

• Ottawa River flow data analysis (file: OttawaRiver.xlsx)

• GIS data (LiDAR, DEM, 2005 floodplain delineation, flow paths, structures, file folders: Jock.gdb, Jock.Overviews, Raster1mBareEarth, Maps)

1.2 Summary of Communication and Site Visit by Reviewer

The following summarizes GHD’s communication with the City, RVCA, and JFSA. GHD’s site visit is also summarized.

• Request for Information (RFI) dated October 10, 2017

• Project Initiation Meeting with the City and RVCA, Ottawa, October 13, 2017

• Jock River Reach 1 Site Visit, October 13, 2017 • Teleconference with Kevin Cover (City of Ottawa), October 19, 2017, to discuss previous hydro- climatic analyses performed by the City

• Email correspondence with RVCA, October and November 2017, to request additional data and information

• Teleconference with JFSA, November 17, 2017, to discuss assumptions and results of the Hydrodynamic study

1.3 Relevant Guidelines and Standards

GHD’s assessment criteria were based on best engineering practices for professional engineers and the following published guidelines and standards (in chronological order): • Federal Floodplain Mapping Framework, Version 1.0. Natural Resources Canada and Public Safety Canada, 2017. • Guidelines and Standards for Flood Risk Analysis and Mapping. Federal Emergency Response Agency, 2017

• HEC-RAS River Analysis System. 2D Modeling User’s Manual, Version 5.0. United States Army Corps of Engineers, February 2016.

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• Guidelines and Specifications for Flood Hazard Mapping Partners. Appendix C: Guidance for Riverine Flooding Analyses and Mapping. Federal Emergency Response Agency, November 2009. • River & Stream Systems: Flooding Hazard Limit. Technical Guide, Ontario Ministry of Natural Resources, 2002. • River & Stream Systems: Erosion Hazard Limit. Technical Guide, Ontario Ministry of Natural Resources, 2002.

• Drainage Management Manual. Ontario Ministry of Transportation, 1997.

2. Objective of Work and Review Methodology

1.4 Objective of Work

The main objective of the work was to perform an independent, third party technical review of the Hydrodynamic study and provide an opinion to the City and RVCA whether the technical approach, methodology, and assumptions utilized in the analysis are appropriate and the results reliable in consideration of the potential risks associated with the proposed development.

1.5 Technical Review Methodology

The technical review was performed in general accordance with the Professional Engineers of Ontario (PEO) guideline “Professional Engineers Reviewing Work Prepared by Another Professional Engineer”, dated October 2011.

The specific tasks of the technical review were defined in TOR and included the following main tasks:

1. Background Information Review

2. Reach 1 Floodplain Suitability for Development Review 3. Jock River Hydrological Analysis Review

4. HEC-RAS Hydraulic Model Review

5. Risk Management and Factor of Safety Review

In addition, the technical review methodology included communication with the City, RVCA, and JFSA to seek clarifications as needed, and a site reconnaissance of the Jock River Reach 1 on October 13, 2017.

3. Review of Findings

This section presents the findings of GHD’s technical review of the Hydrodynamic study and relevant supplemental information. The section is organized according to the main specific tasks of the technical review as per TOR.

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3.1 Background Information Review

The 2017 Hydrodynamic study builds heavily on the 2005 Jock River flood risk mapping study (referred to as the “2005 study” in this document) prepared by PSR Group Ltd. in association with J.F. Sabourin and Associates Inc. for the Rideau Valley Conservation Authority. The 2005 study was reviewed in detail as part of this technical review. In addition, the preparation of this technical review has relied on the results and recommendations of past relevant studies and additional supplemental information summarized in Section 1.3.

The 2005 study consists of two reports: Hydrology Report (July 2004) that provides flow estimates and the Hydraulics Report (November 2004) that determines flood levels based on the flow estimates.

The regulatory flood level (RFL), used for flood risk mapping within the Rideau River watershed, is defined as the 100-year flood level (as per Section 12 of Ontario Regulation 174/06). The 100-year peak flows were estimated by flood frequency analysis (lower reach, between Richmond and the Rideau River, influenced by Richmond Fen) and hydrologic modelling (middle reach, between the Richmond Fen and Ashton).

Annual maximum daily flows from the Water Survey of Canada’s Jock River near Richmond (02LA007) streamflow station were used in the flood frequency analysis (FFA). The maximum daily flows were converted to maximum instantaneous peak flows using a scaling factor of 1.03. The Spearman test for trend detected statistically significant (decreasing) trend at a 5% confidence level. The data and the watershed characteristics were reviewed with respect to any significant changes in the watershed land use, potential river operations, and spring precipitation characteristics but no change was identified. Climate change (reduced snowpack and snowmelt due to increasing winter and spring air temperatures) was not considered in the study as a potential cause of the decreasing annual maximum flows. The Log Pearson Type III (LP3) distribution was selected as the best fitting distribution and the 100-year peak flow estimated to be 196 m3/s. It is noted that the LP3 distribution overestimated the upper tail of the empirical distribution and consequently overestimated the 100-year peak flow. However, this produced a conservative estimate of the 100-year peak flow. Prorated flows were determined for other locations of the lower reach using the Ministry of Transportation (MTO) nonlinear formula (MTO, 1997), which is appropriate for the analysis.

Hydrologic modelling was used to estimate the 100-year peak flows in the tributaries and upstream reaches of the river not influenced by Richmond Fen. The SWMHYMO (ver. 5.02 - beta) model was used for the hydrologic modelling. Two models were developed, calibrated, and validated: spring conditions (snowmelt events) model and summer conditions (storm events) model. The simulated spring and summer peak flows were compared and the larger values used as inputs to the hydraulic analysis.

The HEC-RAS (ver. 3.1.1) hydraulic model was used to estimate the regulatory flood levels corresponding to the 100-year peak flows. Model cross-sections were developed from field survey data and 0.5 m contour digital base mapping. All bridges and culverts were surveyed in the field. Downstream boundary conditions (water levels) for tributaries were based on a joint probability analysis to approximate a combined 100-year probability. The model was calibrated with observed

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water levels. The calibrated model fitted well the observed values (based on the WSC rating curve) however, underestimated the extrapolated upper tail of the rating curve by approx. 0.1 m. A sensitivity analysis was conducted based on 25% change in Manning’s roughness values.

3.2 Review of Reach 1 Floodplain Suitability for Development

The Jock River is a tributary of the Rideau River. The watershed has a drainage area of 556 km2. The watershed has a mainly rural character. Approximately 26% of the watershed is forest cover, which is less than the recommended 30% minimum. However, the watershed contains the third largest total area of wetland in the Rideau Valley (such as the Richmond Fen and Goodwood Marsh), which provides significant attenuation storage (Jock River 2016 Subwatershed Report, RVCA, 2016).

The Jock River Watershed Management Plan (RVCA, 2001) delineated four distinct reaches of the river. Reach 1 (from mouth of the river to Highway 416) is the most urbanized part of the Jock River watershed. The land use in Reach 1 is predominantly urban with limited forest cover (20%) and very limited wetland cover. Reach 1 includes the majority of the watershed population and urban development. The main growth nodes are located within this reach. About 75% of Reach 1 is expected to be urbanized in the next 20 years (RVCA, 2001). Reach 1 has been identified as an urban growth area for more than a decade (Jock River Reach 1 Subwatershed Study, STANTEC, 2007).

Figure 3.1 outlines the Jock River watershed and the study area (Reach 1). Although the Jock River has a number of built up areas the hydrologic regime does not reflect a typical urban hydrologic response. This is because the extent of the development is still relatively low in proportion to the total watershed drainage area. The proposed development area is located in the most downstream portion of the watershed. Development in this portion of the watershed cannot significantly change the watershed’s hydrologic regime and flood response, which is defined by the watershed located upstream of Reach 1 (approximately 95% percent of the watershed area is located upstream of Hwy 416). The 2005 study demonstrated that in Reach 1, the 100-year flood only increases from 196 m3/s at Hwy 416 to 205 m3/s at the confluence with the Rideau River (a 5% increase).

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Figure 3.1 The Jock River Watershed and the Study Area.

There is no flow regulation in Reach 1 with the exception of the Heart’s Desire weir, which was put in place to hold back water for aesthetic reasons. According to RVCA, the weir may affect erosion rates on the south bank of the river (RVCA, 2001). Several drains and tributaries flow into Reach 1. Most are intermittent watercourses that have flows during rain events and spring snowmelt, but dry up during the summer months. Peak flows discharged to the Jock River from the drains do not need to be controlled to existing levels since both the Jock and Rideau Rivers have adequate capacity to handle the expected increases (STANTEC, 2007).

The proposed development is located within the floodplain of Reach 1. The floodplain in Reach 1 is up to 2 km wide (see Figure 3.1). The river slopes are very flat, less than 0.1%. Figure 3.2 depicts the channel profile in Reach 1. During flood events, the large flood storage capacity of this area lags and attenuates the peak flows. Development in the floodplain will reduce this storage capacity, leading to increased peak flows and water levels in the downstream areas.

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Jock - Lower Reach - MArch 2005 - 1220 Plan: JFSA-2D-Inflows 4/07/2017 Jock River Reach 7 100 Legend

WS 100-Year RVCA Ground

95

90 Elevation (m)

85

80

75 0 2000 4000 6000 8000 10000 12000 Main Channel Distance (m) Figure 3.2 Reach 1 Channel Profile.

According to the Ontario Ministry of Natural Resources (OMNR), flow depths in excess of 1 m and/or flow velocities above 1 m/s can create significant hazards for developments (OMNR, 2002). The wide and flat floodplain in Reach 1 results in large ineffective flow areas with low water depths and flow velocities. The development hazard in the ineffective flow areas located in the Reach 1 floodplain is consequently considered to be low.

There are growing development pressures in Barrhaven and the surrounding area. When properly planned, new developments can lead to improved use of the land and help adapt to growing population needs. The proposed development will represent filling of about 200 ha (a floodplain storage volume of approximately 1 million m3) of existing floodplain without compensating the cut. The Provincial Policy Statement issued under the authority of the Planning Act states that new development which is susceptible to flood/erosion hazards must not be permitted to occur unless the flood/erosion hazards and environmental impacts have been addressed (OMNR, 2002).

According to the OMNR, the floodplain can often be divided into two zones: the floodway, where the majority of the flow is conveyed, and flood fringes, which exist on both sides of the floodway. Where the two zone concept is applied, the floodway is the inner portion of the flood plain, representing that area required for the safe passage of peak flow and/or that area where flood depth and/or velocities are considered to be such that they pose a potential threat to life and/or property damage (OMNR, 2002). The feasibility of the two-zone concept must be evaluated as part of an official plan update or a major official plan amendment in collaboration with the City and RVCA.

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3.3 Jock River Hydrological Analysis Review

3.3.1 Summary of Previous Studies

Single station statistical flood frequency analysis (FFA) applied to continuous streamflow records of acceptable quality provides the most accurate estimate of design flows compared to indirect approaches, such as hydrologic modelling or regional flood frequency analysis (RFFA). The Water Survey of Canada (WSC) streamflow station Jock River near Richmond (02LA007) is located at Moodie Drive just upstream of the study area. The station has been operational since 1969. At the time of the 2005 study, there were 34 years of annual maximum daily flow data available at the station, which is more than 1/3 of the 100-year return period (30 years or more are typically considered sufficient for estimating the 100-year flood). The 2005 study fitted the LP3 distribution to the annual maximum flow data and estimated the 100-year peak flow to be 196 m3/s. The LP3 distribution did not fit the upper tail of the empirical distribution well and consequently overestimated the 100-year peak flow (refer to Section 3.1). Consequently, the study provided a conservative estimate of the 100-year peak flow.

The Hydrodynamic study revisited the statistical analysis from 2005 as more than 10 years of additional streamflow data was available in 2017. The scaling factor was increased from 1.03 to 1.035. The Hydrodynamic study tested the quality of the streamflow data for statistical independence, randomness, and stationarity. The statistically significant decreasing trend detected in the 2005 study was found highly significant (1% confidence level). Further analysis was conducted to determine if the trend may be a product of climate change. The analysis involved evaluation of annual runoff coefficients calculated for the watershed. Increased variability of annual peak flows and runoff volumes was identified but no trend in runoff coefficients or annual rainfall and snowfall data was observed over time.

The LP3 distribution was fitted to the 48 years of annual maximum flow data and the 100-year peak flow was estimated to be 148 m3/s. This represents a 25% decrease compared to the 2005 estimate (196 m3/s). It is noted that the LP3 distribution fitted the upper tail of the empirical distribution much better than in the previous 2005 study. The best fitting distribution was the highly flexible 5- parameter Wakeby distribution, which produced an estimate similar to the LP3. The Hydrodynamic study acknowledged that further investigation into the frequency analysis at the Jock River station should be considered and adopted the previous 2005 estimate (196 m3/s) for the project.

Recently, RVCA performed statistical flood frequency analyses as part of the Rideau River Flood Risk Mapping Study (RVCA, 2016) and Ottawa River Flood Risk Mapping Study (RVCA, 2014). The estimated 100-year peak flows for the Ottawa River based on the longer historical streamflow records were found to be about 3% to 6% lower than those estimated in the previous study. Similarly, the updated 100-year peak flows for the Rideau River were found to be about 1.5% lower than those estimated in the previous study. It is noted that the updated 100-year peak flows were recommended and used for the flood risk mapping studies.

Sampling variability affects the results of statistical frequency analyses. Very high or low samples (outliers) can bias the frequency distribution and lead to over- or under-estimation of return period quantiles. Generally, longer data records should improve the accuracy of statistical frequency analysis by decreasing sampling variability. If the longer records remain homogeneous and

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stationarity, then perhaps there is a valid reason for adopting the more accurate quantile estimates. If, however, the updated records show statistically significant non-stationarity (trends) or heterogeneity (step changes, etc.) then potential causes (land use, climate variability/change, station relocation, new monitoring equipment, etc.) should be explored to validate the change. If the updated record is found to be heterogeneous, a split sample analysis should be performed to estimate the quantiles. If the record is non-stationary, then standard stationary flood frequency analysis is not applicable and other techniques (such as non-stationary flood frequency analysis) should be employed. This is particularly important when statistically significant increasing trends are detected in the time series. If the trend is decreasing, using the previous (larger) estimates is always conservative, however, this may also lead to overestimated regulatory flood lines and restricted land use in areas which could have otherwise been open to development.

3.3.2 Statistical Analysis of the Jock River Flows

The instantaneous annual maximum flows derived in the Hydrodynamic study are plotted in Figure A.1 in Appendix A. The Spearman test for independence indicated that the data are independent (see Table A.1 in Appendix A). The runs test for general randomness indicated that the data are random. The Mann Kendall test detected a statistically significant decreasing trend in the time series (1% level of significance). The Theil-Sen method was used to calculate the magnitude of the trend, which was -1.08 m3/s/year. The data are therefore considered non-stationary. The Mann- Whitney split sample test for homogeneity indicated that there is a statistically significant difference between the means at the beginning of the time series and the end of the time series (the time series was divided equally into two portions: the first 24 years and the second 24 years). However, this is attributable to the statistically significant trend. When the data are plotted, there is no visible evidence of a break point or a step change in the time series, which indicates that the difference in means is likely due to the statistically significant trend.

The seasonality of the annual maxima is shown in Figure A.2 in Appendix A. The month when the annual maximum streamflow occurred was used to determine the frequency of occurrence of the annual maximum in each month. It was found that 87.5% of the observed annual maximum events occurred in either March or April. A small number of annual maximum events occurred in January, February, and May, but no annual maximum events occurred in the rest of the year (June to December). The annual maximum streamflow event in the Jock River is associated with snowmelt. A trend analysis was performed on the date of the annual maximum streamflow (Figure A.3 in Appendix A). The Julian day of each annual maximum was calculated, and plotted as a time series. Visually, there is a decreasing trend observed in the time series (snowmelt events occurring earlier in the year), however, the Mann Kendall test did not detect this trend to be statistically significant (at the 5% level of significance) at this point of time. It is expected, however, that this trend will become statistically significant in the future.

The RVCA performed flood risk mapping for the Ottawa River from Shirley’s Bay to Cumberland (RVCA, 2014) and for the Rideau River from Hogs Back to Rideau Falls (RVCA, 2016). RVCA (2014) provided flood estimates for the Ottawa River at Chats Falls (WSC ID 02KF009, 1915-1994), the Ottawa River at Britannia (WSC ID 02KF005, 1961-2014), and the Ottawa River at Carillon (WSC ID 02LB024, 1933-1994). RVCA (2016) provided flood estimates for the Rideau River at Ottawa (WSC ID 02LA004, 1947-2016). Each of the four locations have longer data records than

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the Jock River. The specific flow rates (annual maximum streamflow divided by the drainage area) for the Jock River, Rideau River, and Ottawa River are compared in Figure A.4 in Appendix A. The overlapping time series of Rideau River and Ottawa River flows were correlated with the Jock River flows. The Rideau River flow at Ottawa were found to be strongly correlated with the Jock River flow (R2 of 0.89). There was a statistically significant negative trend detected for the Rideau River at Ottawa station (5% level of significance) with a magnitude of -2.13 m3/s/year. The negative trend for the Rideau River suggests that the negative trend in streamflow is not limited to the Jock River and perhaps may reflect the presence of a larger-scale hydro-climatic trend.

GHD performed a single-station frequency analysis utilizing the same distributions that were used in the Hydrodynamic study: Generalized Extreme Value (GEV), Log Pearson III (LP3), and 3- Parameter Lognormal (LNO). The analysis was performed for the entire data series: 1970 to 2017. The 100-year flood estimates are compared inTable 3.1. The Hydrodynamic study estimates were derived from the Consolidated Frequency Analysis (CFA) software package, GHD utilized both the CFA package, and the R-statistical package. The CFA package fits the distributions using the L- moment method for GEV and Wakeby, and the maximum likelihood method for LP3 and LNO. The R statistical package fits all four distributions with the L-moment method. GHD was able to exactly reproduce the Hydrodynamic study results using CFA for all four distributions. When comparing the CFA and R results, the results for GEV and Wakeby were similar, but there were significant differences for LP3 and LNO, which can be attributed to the differences between the L-moment method and the maximum likelihood method.

Table 3.1 Comparison of Jock River Near Richmond (WSC ID 02LA007) 100-year Flood Estimates

Distribution JFSA-CFA (m3/s) GHD-CFA (m3/s) GHD-R (m3/s) Generalized Extreme Value 181 181 178 Log Pearson III 148 148 195 3-Parameter Lognormal 227 227 180 Wakeby 151 151 156

The four distributions were compared both graphically and statistically. Graphically, the distributions that fit the high end of the frequency curve the best were the LP3 distribution fit by the method of maximum likelihood (calculated by CFA) and the Wakeby distribution. The statistical comparison included the correlation coefficient (R2), the chi-square (χ2), and the Kolmogorov-Smirnov statistical tests (Table A.2 in Appendix A). The Wakeby distribution had the best fit according to all three statistical tests, however, this five-parameter distribution can often overfit the empirical data. The results presented in Table 3.1 demonstrate the statistical uncertainty in the estimation of the 100- year peak flow resulting from different statistical distributions. Based on the 48 years of data available at the Jock River near Richmond, it is expected that the 100-year peak flow is within the range of 150 to 200 m3/s.

A first-order non-stationary flood frequency analysis was performed using the GEV and LP3 distributions and the method of L-moments. The non-stationary 100-year floods were estimated for the 2017 time horizons and compared with the stationary estimates (see Table 3.2). The non- stationary 100-year flood estimates are very close to the lower range (150 m3/s) of the stationary estimates summarized in Table 3.1.

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Table 3.2 Comparison of 100-year Stationary and Non-Stationary Flood Estimates for Jock River Near Richmond (WSC ID 02LA007) Distribution 2017 Stationary 2017 Non-Stationary (m3/s) (m3/s) Generalized Extreme Value 178 153 Log Pearson III 195 150

A regional flood frequency analysis (RFFA) was performed to validate the flood estimates for the Jock River. A total of five locations were used to develop the regional relationship (Table 3.3). The Hosking and Wallis homogeneity tests were applied to the region, and the region was found to be either acceptably homogeneous or possibly homogeneous according to all three tests (H1 = 1.89, H2 = 0.86, and H3 = 0.59).

Table 3.3 Water Survey of Canada Streamflow Gauges Used in Regional Flood Frequency Analysis.

Station Name Station ID Years Drainage Area (km2) Indian River Near Blakeney 02KF012 1971-2016 212 Carp River Near Kinburn 02KF011 1971-2016 258 Castor River at Russell 02LB006 1948-2016 439 Rideau River at Ottawa 02LA004 1933-2016 3,810 Ottawa River at Chats Falls 02KF009 1915-1994 89,600

The instantaneous annual maximum data for each location were downloaded from WSC. The Rideau River and Ottawa River data were adjusted by RVCA (2014 and 2016). The adjusted data from RVCA (2014 and 2016) were used. A single station frequency analysis was performed for each station to calculate the 100-year flood, using the LP3 distribution calculated with the method of maximum likelihood (CFA). The specific flow rates for each flood estimate were found, and plotted against the drainage area (Figure 3.3). The regional relationship confirms that the Jock River 100- year peak flow fits within the region.

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1

Castor River at Russell Jock River Near Richmond, 196 m3/s

) Carp River Near Kinburn 2 Jock River Near Richmond, 148 m3/s

/s/km Indian River Near Blakeney 3 Rideau River at Ottawa

0.1 Ottawa River at Chats Falls Specific Flow (m

0.01 100 1,000 10,000 100,000 Drainage Area (km2)

Figure 3.3 Regional Relationship between Specific Flow and Drainage Area

3.3.3 Climatologic Analysis

A climatologic analysis was performed to further investigate the statistically decreasing trend in annual maximum streamflow in the Jock River. The historical annual maximum events occurred predominantly in March and April as a result of snowmelt, and therefore the climatic trends in winter and spring were of particular interest in the analysis.

The climatologic analysis was performed with the data from the Ottawa CDA (Experimental Farm, EC ID 6105976) climate station operated by Environment Canada. This station is located approximately 16 km away from the Jock River Near Richmond station. To explore the trends in the winter and spring seasons, the data were divided into seasons according to the month. December, January, and February were defined as the winter months (December was attributed to the following year). March, April, and May were defined as the spring months. The winter season included the accumulation of snow, while the spring season included the snowmelt period.

Environment Canada records precipitation as either snow or rain, and also provides the total precipitation. The three time series (total precipitation for each season) are plotted in Figure A.5 in Appendix A (winter season), and Figure A.6 in Appendix A (spring season). For the winter season, there are statistically significant trends in all three variables (1% level of significance). The rain trend

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is increasing, while the trend for snow and total precipitation is decreasing. This indicates that winter precipitation has decreased since 1890, but also that a greater proportion of the winter precipitation is falling as rain. For the spring season, the trends for snow and total precipitation were not statistically significant at the 5% level of significance or lower. The spring rain trend is significant at the 5% level of significance, and is increasing.

The Ottawa CDA station data includes the daily maximum, daily minimum, and daily mean air temperatures. The trends in each of these variables are plotted in Figure A.7 in Appendix A (winter season) and Figure A.8 in Appendix A (spring season). The daily mean, maximum, and minimum air temperatures are increasing during the winter season (statistically significant at the 1% level of significance). The daily minimum air temperature is increasing the fastest. For the spring season, the daily mean and minimum air temperatures have statistically significant trends, while the trend for the daily maximum air temperature is not statistically significant at the 5% level of significance.

This significant decrease in winter precipitation in combination with significantly increasing winter air temperatures results in decreasing winter snow accumulation, more frequent occurrence of rainfall during the winter season (a greater proportion of the winter precipitation falls as rain), and declining spring snowmelt (less snowpack available at the end of winter). This climatic trend has a significant impact on the streamflow regime in the Jock River watershed, resulting in lower annual maximum streamflow (less snowmelt) and/or earlier occurrence of annual maximum streamflow events. Since no statistically significant trend was observed in the timing of the annual maximum streamflow (Figure A.3 in Appendix A), the increases in air temperature have not yet caused a significant change in the timing of the annual maximum streamflow in the watershed. Therefore, the decrease in annual maximum streamflow in the Jock River is more likely attributed to the overall decrease in winter precipitation.

The trends in the winter precipitation were further examined by calculating 30-year Theil-Sen slopes (Figure A.9 in Appendix A). The Theil-Sen slopes for total precipitation vary from positive to negative, depending on which 30-year period is analysed. Up to the mid-1940s, winter rain had a generally increasing tendency and snow was decreasing. The trend reversed between the mid- 1940s and the mid-1970s. After the mid-1970s the winter rain is again increasing and snow is decreasing, however, the last few years of record indicate that the trend may reverse again. This may indicate a possible linkage to a large scale low-frequency climate variability (such as North Atlantic Oscillation (NAO)).

The historically observed annual maximum flows in the Jock River watershed have exclusively been triggered by spring snowmelt events. The decreasing winter precipitation (snowfall) and increasing winter air temperatures provide a potential explanation why the annual maximum flows in the Jock River have been decreasing over the past decades (see Figure 3.4). This trend must however be interpreted with extreme caution considering the low-frequency climatic variability observed in the region and the limited length of streamflow data that may not be capturing the variability.

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Normalized Annual Maximum Streamflow Normalized Snow Normalized Mean Temperature 4 4 ] -

3 3 ] -

2 2

1 1

0 0

-1 -1 Normalized Winter Mean Temperature [

-2 -2 Normalized Total Winter Snow or Annual Maximum Streamflow [ -3 -3 1960 1970 1980 1990 2000 2010 2020 Year

Figure 3.4 Comparison of Normalized Annual Maximum Streamflow for Jock River near Richmond (WSC ID 02LA007) and Winter Snow and Mean Air Temperature for Ottawa CDA (Experimental Farm) Climate Station

3.4 Hydrodynamic Model Review

3.4.1 Model Selection

One-dimensional (1D) steady flow hydraulic models are applicable to streams with well-defined open channels where flow peaks are not dominated by significant storage changes (FEMA, 2016). In wide floodplains with flat topography (such as the Jock River Reach 1) where flow is moving in two or more directions the assumption of unidirectional flow is violated and 1D hydraulic models may not provide reliable results. The 2017 Hydrodynamic study utilized a two-dimensional (2D) unsteady flow hydrodynamic HEC-RAS model to evaluate the potential effects of the proposed development on the Jock River flood levels. 2D models solve depth-averaged shallow water equations using finite difference, element, or volume solution techniques. Unlike steady state models, which assume constant peak flow within a reach and consider only conveyance, unsteady state models also compute storage along with conveyance within the floodplain (FEMA, 2016). Consequently, unsteady state 2D models can more accurately account for the movement of water and storage within a wide area of the floodplain. The main disadvantage of 2D models is their

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limited ability to simulate hydraulic structures; rating curves must be developed at specified cells to reflect control structures within the floodplain. GHD believes that the 2D hydrodynamic model should provide a more accurate representation of the hydraulic regime of the Jock River Reach 1 than the existing 1D model.

3.4.2 Model Setup

The City of Ottawa acquired LiDAR data for the area covering the Jock River Reach 1 floodplain in 2015. The processed LiDAR data provide the most recent topography information for the study area at a resolution of 1 metre. The 2017 Hydrodynamic study used the LiDAR data supplemented with survey data of the low flow channel taken from the existing RVCA 1D model for the development of the 2D model.

It is not known from the Hydrodynamic study whether the new topographic data used in the 2D model resulted in overall gain or loss of existing floodplain storage compared to the floodplain storage used in the 2005 study for the development of regulatory flood levels. This analysis should be provided in the Hydrodynamic study. GHD also noticed spikes in some cross-sections defined by the LiDAR data but assumed that these topographic irregularities have been verified in the field or smoothed by the interpolation algorithm used for defining the 2D model elevation surface.

The 2005 1D model was not updated with the LiDAR data as part of the Hydrodynamic study. However, to achieve a fair comparison of the model results, the flows generated by the 2D model representing the existing and developed flood fringe conditions were inputted back to the 1D model and the 1D model was used for generating flood elevations (JFSA, 2017). It is GHD’s opinion that the same topographic data should have been used to ensure consistent comparison of flood levels between the existing and proposed conditions.

The 2D model extends from the downstream side of Moodie Drive to the confluence of the Jock and Rideau rivers. Model domains should extend beyond the limits of the study area to eliminate the effects of boundary conditions. The upstream model limit is aligned with the location of the WSC streamflow station Jock River at Richmond and is appropriate as the 100-year peak flow does not overtop Hwy 416 in the floodplain. The downstream limit of the model is located on the Rideau River approximately 350 m downstream of the confluence of the Jock River with the Rideau River and extends to both sides of the Rideau River floodplain. This setup is unusual, typically, the downstream limit of the model is set at the confluence and the water level boundary is oriented parallel to the river channel/floodplain.

The model resolution (cell size) was set to 20x20 m (floodplain) and 10x10m cells (channel). This resolution is adequate for the floodplain but the channel resolution may be too coarse for estimating channel flow velocities accurately. In addition, the simulation time step was set to 15 seconds. This leads to Courant numbers that are greater than one, which means water can flow through more than one cell in one computational interval, and cause instability issues in the model. In fact, the 2D model contained numerous convergence warnings. GHD optimized the model settings and was able to eliminate the convergence issues.

The inflow hydrograph used in the 2D modelling adopted the spring snowmelt hydrograph derived in the 2005 study. This hydrograph is narrower than the historical spring hydrographs observed in the Jock River. A narrower hydrograph results in less flood volume being routed through the floodplain,

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which may actually underestimate the effect of the lost floodplain storage on the timing and magnitude of peak flows. A sensitivity analysis should be conducted to address the impacts of different flood hydrographs on the results of the 2D modelling.

The Diffusion Wave equations were used in the 2D model. The Diffusion Wave equations are typically not suitable for dynamic simulations of narrow flood hydrographs where the flood wave rises and falls quickly (the Diffusion Wave equations do not include the local and convective acceleration terms). GHD recommends using the Saint Venant (full momentum) equations, which can account for a wider range of hydraulic regimes more accurately. An alternative approach is to test the hydraulic solution obtained by the Diffusion Wave and Saint Venant equations, and if there are significant differences proceed with the Saint Venant solution as the full momentum answer is more accurate.

3.4.3 Model Calibration and Validation

The 2D model was calibrated to the 2005 1D model. The 2D model was refined to produce similar water level results as the 1D model. Calibration was completed by adjusting Manning's roughness values. GHD understands that the 2D model was used in conjunction with the 1D model in the Hydrodynamic study and consequently a good agreement between the two models was desired, however, the two models were based on fundamentally different topography and modelling approaches (steady state 1D versus dynamic 2D).

The 1D and 2D models were validated against water levels observed during April 1999 & April 2017 events and the results suggested that the water levels generated by both models underestimated the observed water elevations. The Hydrodynamic study acknowledges that there may be justification for further model calibration in future studies of the Jock River. GHD agrees with this statement but believes that the 2D model should have been recalibrated as part of the Hydrodynamic study to fit the observed events as opposed to the results produced by the 1D model that was found to underestimate the observed water levels.

3.4.4 Modelling Approach

If the flood fringe is encroached, the water that previously inundated the flood fringe is pushed downstream due to reduction of floodplain storage. This may result in increased upstream flood levels, increased downstream flows, velocities, and flood levels, and change in the timing of flows (OMNR, 2002, FEMA, 2016).

The 2D hydrodynamic model was developed to evaluate the impacts of filling the flood fringe on flow conveyance. The 100-year peak flow was simulated using the 2D model and the results were then applied to the existing 1D model to determine water levels.The maximum flows obtained from the 2D model were placed back into the steady state 1D model. The main reason for adopting this approach was that the existing 2005 1D model was deemed unsuitable for assessing the effects of fill placement outside of the delineated effective flow area. This is because the ineffective flow area in a 1D model is not used in the calculation of channel conveyance, and therefore, placement of fill in the ineffective flow area does not impact water levels or flows in the model (JFSA, 2017). GHD believes that this statement may be true for steady state simulations; however, in unsteady state

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simulations (including 1D HEC-RAS modelling) the ineffective area is accounted for in floodplain storage calculations.

The main concern GHD has with this modelling approach is that the two models are fundamentally different: the 1D model is steady state (the water levels in the 1D model were determined using constant peak flow), whereas the 2D model is dynamic (hydrograph with finite flood volume) and was built with different (LiDAR) topographic data. The Hydrodynamic study does not attempt to compare the 1D results with the 2D results (the 2D flow results are used as inputs to the 1D model) however, the flows generated by the 2D model correspond to different water levels in the 1D model than in the 2D model.

It is GHD’s opinion that the impact of the proposed development should be evaluated by comparing the post-development conditions to the existing conditions using the same modelling platform. Comparing the proposed condition to the regulatory flood level is not appropriate as the regulatory flood level is not a target for flood risk evaluation.

The regulatory flood level (RFL) for the Jock River Reach 1 was defined in 2005 using the RVCA 1D HEC-RAS model (2D floodplain models were not readily available at that time). The 1D model and the RFL have not yet been revised by RVCA. Considering that the 2017 Hydrodynamic study did not use the 2D model for simulating flood elevations (the 2D model was only used for estimating flow rates and the flows were used as inputs to the RVCA 1D model) an alternative modelling approach would be to adopt the RVCA 1D HEC-RAS model and perform a standard (steady or unsteady state) floodplain encroachment analysis. The model cross-sections should be updated with the new LiDAR data and the model recalibrated. The ineffective areas identified in the 1D model would have to be removed prior to the encroachment analysis (definition of the ineffective flow areas is part of the encroachment analysis).

Another approach would be to use 2D model for the encroachment analysis. This would be in line with FEMA recommendations that “if the floodway was previously determined by a one-dimensional model, 1D encroachment stations should be incorporated into a two-dimensional model and run the two-dimensional model to verify that the maximum allowable surcharge is not exceeded” (FEMA, 2016). This approach would benefit from the advantages of more accurate 2D modelling and the new topographic information that was used for developing the 2D model.

3.4.5 Model Results

The Hydrodynamic study adopted the floodway boundary prescribed by the delineation of the ineffective flow area in the 2005 1D model. JFSA acknowledges that there is no record of the rationale behind the location of this boundary in the relevant floodplain mapping report (JFSA, 2017). It is GHD’s understanding that the ineffective flow area in the 1D model was not defined based on a standard hydraulic encroachment analysis and the ineffective flow area was not meant to define the flood fringe.

For the filled flood fringe scenario, the 2D model results showed that water elevation will not exceed the 100- year regulatory flood levels established by the 1D model. The maximum increase was observed upstream of Prince of Wales Dr (0.09 m). The filled flood fringe condition increased the downstream peak flows by less than 5% and decreased the timing of the peak flows by one hour.

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The results further showed that the filling the flood fringe will have a maximum velocity increase of 0.23 m/s, with an average increase of 0.015 m/s.

The Jock River Reach 1 Subwatershed Study (STANTEC, 2007) identified that the bankfull flow for the Jock River is 37.9 m3/s. Given the infrequency of the 100-year flow and the initiation of bed transport (and the likely initiation of bank erosion) at more frequent flows (bankfull/2-year flows) the morphological changes due to the velocity increase at the 100-year flow would be minimal. The Hydrodynamic study showed that the 2-year flood extent did not overlap with the proposed fill placement along the flood fringe.

Detailed technical comments on the 2D modelling performed as part of the Hydrodynamic study are summarized in Appendix B. The model deficiencies described in Appendix B are relatively minor and it is not expected that they significantly affect the modelling results presented in the study.

3.5 Risk Management and Factor of Safety Review

3.5.1 Flood Risk Characterization

Flood risks must be thoroughly evaluated and addressed for all new developments which can potentially be subject to such hazards or which can cause or aggravate existing flood/erosion hazards. As per the City of Ottawa Official Plan, development is restricted from the regulatory floodplain, however, some reduced-risk uses may be considered, subject to appropriate design considerations that mitigate and/or minimize the impact of this development on the floodplain and protect the riparian corridor functions of the Jock River (City of Ottawa, 2003).

According to the OMNR guidelines, for outer portions of floodplains that could potentially be safely developed with no adverse impacts, the Conservation Authorities in Ontario in co-operation with the watershed municipalities, have the option of selective application of the two zone (floodway - flood fringe) concept. Where the two zone concept is proposed to be applied or is considered to be a plausible option, municipalities should include policies in their official plans that explain the intent of the two zone concept and the potential ability for development of the flood fringe versus the floodway (OMNR, 2002).

The extent of the floodway should be determined based on local watershed conditions, such as critical flood depth and velocity, existing and proposed development, and the potential for upstream or downstream impacts. Generally, flow depth in excess of 1 m and/or flow velocities above 1 m/s can create significant hazards for developments (OMNR, 2002). Some Conservation Authorities have developed their own policies, for example the NVCA defines areas of acceptable risk as any portion of the lot for new development that meets the following:

• Flood depths less than or equal to 0.8 metres

• Velocities less than or equal to 1.7 m/s

• A depth-velocity product less than or equal to 0.4 m2/s • Safe access/egress provided on the municipal right-of-way

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FEMA defines low flood severity risk when the depth-velocity product is less than 0.2 m2/s and does not allow increasing water-surface elevations due to fringe development by more than 1 foot (FEMA, 2016).

The Hydrodynamic study validated the ineffective flow area presented in the 2005 study by plotting the areas where flood depths were greater than 1 m and/or flow velocities were greater than 1 m/s. The flood fringe development limits were established as the most external extent of: (1) 1D ineffective flow area, (2) meander belt width of the Jock River, (3) 2D model floodway, and (4) 30 m channel offset. This approach takes into account the three main forces that shape river systems - erosion, flooding, and slope stability (River & Stream Systems: Erosion Hazard Limit, OMNR, 2002).

3.5.2 Sensitivity Analysis

There are many sources of uncertainty involved in the estimation of flood elevations (accuracy of streamflow measurements, data sampling variability, statistical estimation uncertainty, model accuracy, etc.) as well as many unknown factors, such as climate change, that could lead to the underestimation of estimated flood elevations. Floodplain modelling should incorporate a sensitivity analysis to quantify the different sources of uncertainty. The following parameters are typically considered in sensitivity analyses (OMNR, 2002): peak flood discharge; channel and floodplain roughness; expansion and contraction coefficients; starting water levels, tidal conditions or control gate operations; channel configuration, including the spacing, location and definition of cross- sections; ice-jamming and debris blockage; and sedimentation and sand bars.

Currently, there are no provincial or federal guidelines specifying what design events should be used to evaluate the potential impacts of climate change. Future climate intensity-duration- frequency (IDF) curves can be derived from Global Circulation Model (GCM) projections and used in hydrological models to estimate the effects of climate change on design flows and flood levels. This approach is however problematic in watersheds with snowmelt-dominated flood regimes (such as the Jock River watershed) where historical observations are actually suggesting decreasing flood events as a result of increasing winter air temperatures and decreasing snowfall.

The Hydrodynamic study evaluated sensitivity of the model results to peak flood discharge. The 100-year +20% and the 350-year events were used in the sensitivity analysis to assess the potential impacts of climate change. The 100-year +20% discharge was estimated to be the equivalent of a 500-year event. Both scenarios indicated that filling the flood fringe would result in average water level increase of 6 cm with a maximum increase of 10 cm. These values are within the minimum of 0.30 m of freeboard required by RVCA in the design of flood-proofing measures for buildings and structures within or adjacent to flood prone areas.

GHD agrees that the simulated 350 and 500-year flood events should provide sufficient range for addressing the uncertainty in future flood flows in the Jock River. However, for the reasons discussed in Section 3.4.4 (Modelling Approach), it is our opinion that the water level increases obtained in the sensitivity analysis cannot be directly compared to the 1D 100-year flood elevations as the water levels between the 1D and 2D models do not match for the 100-year flood event. GHD recommends utilizing the 2D model to estimate the relative increase in water levels due to the increase in peak flows. GHD also recommends adding the Manning’s roughness to the sensitivity analysis.

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3.5.3 Future Watershed Development

Studies performed for communities experiencing urban growth should evaluate future-conditions in regulating watershed development. On a watershed-scale, the Jock River post-development hydrologic analysis (STANTEC, 2007) demonstrated that the future post-development peak flows of the Jock River are within the limit of regulatory flood flows. The spring peak flows increased by less than 1%. The analysis demonstrated that stormwater management facilities are not required to provide quantity control to maintain the regulatory floodplain within existing limits.

On the local scale, individual developments potentially affecting the floodplain storage, such as the proposed Greenbank Crossing, should be evaluated as part of the floodplain encroachment analysis. For example, the Jock River Subwatershed Study indicated that the proposed Greenbank Road bridge south abutment as well as the piers will be located within the floodplain. Infilling of 5000 m3 in the flood plain is required but there is no opportunity for compensation (STANTEC, 2007).

3.5.4 Conservative Assumptions

Floodplain studies typically adopt conservative assumptions to provide a factor of safety accounting for potential error and uncertainty. The major uncertainty in floodplain modelling is related to the limited amount of data available for calibration and validation of hydrologic and hydraulic models.

To account for potential error and uncertainty the Hydrodynamic study implemented several conservative assumptions:

• Adopting the 100-year flood derived in the 2005 study. The updated FFA performed in the Hydrodynamic study showed a significant (25%) reduction of the 100-year flood (from 196 m3/s to 148 m3/s). GHD agrees that this is a very conservative assumption; use of the updated 100- year flood would significantly reduce flood levels in the study area.

• Performing sensitivity analysis using the 350 and 500-year flood events.

• Defining the floodway/flood fringe as the most external limit of various measures addressing erosion, flooding, and slope stability.

• Blocking the entire flood fringe area including corridors along tributaries.

• Providing allowance for a 0.30 m freeboard as per the RVCA guidelines.

GHD concurs with the conservative choices made in the study but believes that the models should be recalibrated to provide a better fit to the historical spring flood events to maintain a conservative approach in terms of risk/liability.

4. Conclusions

JFSA developed a 2D hydrodynamic model to confirm the location of a flood fringe /floodway boundary and assess the potential cumulative impact on flows that could occur from the proposed flood fringe development. The results of the study showed that the proposed development will increase the flood flows by 5% and flood levels up to 0.1 m.

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The intent of this technical review was to perform an independent, third party technical review of the hydrodynamic analysis and provide an opinion to the City and RVCA whether the technical approach, methodology, and assumptions utilized in the analysis are appropriate and the results reliable in consideration of the potential risks associated with the proposed development.

The general purpose of the review was to answer the following key questions:

Is the approach and methodology robust and appropriate in consideration of the potential risks associated with the development proposal and with a changing climate?

The 2D hydrodynamic model was used to evaluate the impacts of filling the flood fringe on flow conveyance. The existing and post-development 100-year peak flows were simulated using the 2D model and the results were applied to the existing 1D model to determine water levels. The main concern GHD has with this modelling approach is that the two models are fundamentally different (the 1D model is steady state and based on outdated topography whereas the 2D model is dynamic and was built with the latest LiDAR topography data); consequently the flows generated by the 2D model correspond to different water levels in the 1D model than in the 2D model.

It is GHD’s opinion that the impact of the proposed development should be evaluated by comparing the post-development conditions to the existing conditions using the same modelling platform (1D or 2D). GHD agrees with RVCA that comparing the proposed condition to the regulatory flood level is not appropriate as the regulatory flood level is not a target for flood risk evaluation.

Two alternative approaches can be utilized here. The first approach would adopt the 1D RVCA model. The 1D model should be updated with the latest LiDAR topography and recalibrated to better fit the observed historical events (the 1D model was found to underestimate water levels). An unsteady-state encroachment analysis should then be performed with the updated model to delineate the floodway and flood fringe and quantify the impacts of the proposed flood fringe development. The second approach would utilize the 2D model for the analysis, thus benefitting from the advantages of more accurate 2D hydrodynamic modelling. The 2D model would also have to be recalibrated to better fit the observed historical events (the 2D model was found to underestimate water levels).

Is the quality of input data adequate to ensure reliable results?

The Mann Kendall test detected a statistically significant decreasing trend in the time series of annual maximum flows for the Jock River. A statistically significant trend was also detected for the Rideau River, which suggests that the trend in streamflow is not limited to the Jock River watershed and may reflect larger regional hydro-climatic trends. Historically observed annual maximum flows in the Jock River watershed have exclusively been triggered by spring snowmelt events. A statistically significant trend was detected in winter precipitation and winter air temperatures. The decreasing winter precipitation (snowfall) and increasing winter air temperatures provide a potential explanation why the annual maximum flows in the Jock River have been decreasing over the past decades. This trend must however be interpreted with extreme caution considering the low- frequency climatic variability observed in the region and the limited length of streamflow data that may not be capturing the variability. For this reason, GHD does not recommend adopting the 2017 estimate of the 100-year peak flow.

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The Hydrodynamic study adopted the previous (larger) estimate of the 100-year peak flow, which is a very conservative assumption. It is beyond the scope of this review to advise how the flood regime may change in the future as a result of climate variability/change. However, it is noted that the previous (2005) estimate of the 100-year peak flow was 25% higher than the estimate derived in the Hydrodynamic study. The conservative estimate of the 100-year flood was further subject to a sensitivity analysis (100-year flood +20%, an equivalent of a 500-year flood) which should provide sufficient range for addressing the uncertainty in future peak flows in the Jock River.

Have the appropriate methods/tools/assumptions been adopted to reflect hydrologic and hydraulic conditions under existing (unfilled) and future (filled) conditions?

GHD agrees that the 2D hydrodynamic model should provide more accurate representation of the hydraulic regime of the Jock River Reach 1 than the 1D model developed as part of the 2005 floodplain mapping study. GHD reviewed the 2D hydrodynamic model in detail and identified several deficiencies, which are summarized in Appendix B of this report. It is noted, however, that the technical aspects are relatively minor and they are not expected to significantly affect the modelling results presented in the study.

A number of conservative assumptions and modelling choices were adopted in the Hydrodynamic study to ensure a robust approach to future flood risk exposure. GHD concurs with the conservative choices made in the study but believes that the models should be recalibrated to provide a better fit to the historical spring flood events to maintain a conservative approach in terms of risk/liability.

It is also recommended that other future developments potentially affecting the floodplain storage, such as the proposed Greenbank Crossing, should also be evaluated as part of the floodplain encroachment analysis to determine the combined effect of the future development of flood levels in the study area.

Can the models be applied successfully to evaluate existing and future conditions of the Jock River from Highway 416 to Rideau River?

As part of this review GHD provided a number of recommendations for improving the modelling approach presented in the Hydrodynamic study. GHD believes that once these recommendations are taken into consideration and implemented the models will be suitable for evaluation of existing and future conditions of the Jock River from Highway 416 to Rideau River.

In conclusion, there are growing development pressures in Barrhaven and the surrounding area. The proposed development will represent filling about 200 ha (a floodplain storage volume of approximately 1 million m3) of existing floodplain without compensating the cut. The Provincial Policy Statement issued under the authority of the Planning Act states that new development which is susceptible to flood/erosion hazards must not be permitted to occur unless the flood/erosion hazards and environmental impacts have been addressed.

The feasibility of the two-zone concept must be evaluated as part of an official plan update or a major official plan amendment in collaboration with the City and RVCA. According to the OMNR Technical Guide (OMNR, 2002): “during the preparation of an official plan update or a major official plan amendment affecting flood plain areas, the municipality in conjunction with the Conservation Authority or Ministry of Natural Resources, should include policies addressing:

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• Existing areas of the municipality utilizing the two-zone concept and/or • A framework for analysing potential areas of two-zone application, including both land use considerations and technical flood plain information and • The inter-relationship between the official plan, zoning by-law and the Conservation Authority’s Fill, Construction and Alteration to Waterways Regulation.

The Regional Engineer of the Ministry of Natural Resources shall be involved in decision making regarding potential application of a two-zone concept.”

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Appendices

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Appendix A Statistical Analysis of the Jock River Flows

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Figure Index

Figure A.1 Annual Maximum Flows in the Jock River Near Richmond (WSC ID 02LA007) ...... 2 Figure A.2 Seasonality of Annual Maximum Flows in the Jock River Near Richmond (WSC ID 02LA007) ...... 3 Figure A.3 Occurrence of Annual Maximum Flows in the Jock River Near Richmond (WSC ID 02LA007) ...... 4 Figure A.4 Comparison of Trends in Specific Flows for Jock River Near Richmond and Rideau River and Ottawa River Stations ...... 5 Figure A.5 Winter Precipitation Trends for Ottawa CDA (Experimental Farm) Climate Station ...... 6 Figure A.6 Spring Precipitation Trends for Ottawa CDA (Experimental Farm) Climate Station ...... 7 Figure A.7 Winter Air Temperature Trends for Ottawa CDA (Experimental Farm) Climate Station ... 8 Figure A.8 Spring Air Temperature Trends for Ottawa CDA (Experimental Farm) Climate Station ... 9 Figure A.9 30-year Theil-Sen Slopes for Winter Precipitation for Ottawa CDA (Experimental Farm) Climate Station ...... 10

Table Index

Table A.1 Data Screening Results for Jock River Near Richmond (WSC ID 02LA007) ...... 1 Table A.2 Distribution Fitting Test Results for Jock River Near Richmond (WSC ID 02LA007) ...... 1

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Table A.1 Data Screening Results for Jock River Near Richmond (WSC ID 02LA007)

Test Test Value Accept or Reject H0 and Interpretation Significance Spearman test for 0.164 Accept H0 5% independence The null hypothesis is that the correlation is zero. Spearman test for 0.464 Reject H0 1% trend The serial (lag-one) correlation is non-zero, and display a highly significant trend. Mann-Kendall -0.327 Reject H0 1% There is a monotonic trend in the time series. Run test for general 1.167 Accept H0 5% randomness The null hypothesis is that the data are random Mann-Whitney -2.639 Reject H0 1% The difference between the two samples is non-zero.

Table A.2 Distribution Fitting Test Results for Jock River Near Richmond (WSC ID 02LA007)

Statistical Distribution Fitting Method R2 Chi-square Kolmogorov- 2 2 Smirnov (R =1 is ideal) (χ =0 is ideal) (K-S=0 is ideal) Generalized Extreme L-Moments 0.9789 4.691 0.0267 Value Log Pearson III L-Moments 0.9762 9.955 0.0535 Maximum Likelihood 0.6025 106.836 0.1261 3-Parameter L-Moments 0.9841 6.0778 0.0666 Lognormal Maximum Likelihood 0.9745 3.811 0.0239 Wakeby L-Moments 0.9988 0.955 0.0124

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160

140

120 /s) 3

100

80

60 Annual Maximum Streamflow (m 40

20

Statistically significant trend at 1% significance level 0 1960 1970 1980 1990 2000 2010 2020

Figure A.1 Annual Maximum Flows in the Jock River Near Richmond (WSC ID 02LA007)

GHD | Technical Review of the Hydrodynamic Analysis (Hwy 416 to Rideau River) | Appendix A | 11155320 (1) | Page 2

Figure A.2 Seasonality of Annual Maximum Flows in the Jock River Near Richmond (WSC ID 02LA007)

GHD | Technical Review of the Hydrodynamic Analysis (Hwy 416 to Rideau River) | Appendix A | 11155320 (1) | Page 3

160 Statistically non-significant trend at 5% significance level

140

120

100

80

60

40 Julian Dayof Annual Maximum Streamflow

20

0 1960 1970 1980 1990 2000 2010 2020

Figure A.3 Occurrence of Annual Maximum Flows in the Jock River Near Richmond (WSC ID 02LA007)

GHD | Technical Review of the Hydrodynamic Analysis (Hwy 416 to Rideau River) | Appendix A | 11155320 (1) | Page 4

Rideau River at Ottawa Ottawa River at Carillon Ottawa River at Chats Falls Jock River Near Richmond 0.35 Rideau River at Ottawa: Statistically significant trend at 5% significance level

0.3

0.25 ) 2

/s/km 0.2 3

0.15 Specific Flow (m

0.1

0.05

0 1900 1920 1940 1960 1980 2000 2020 2040

Figure A.4 Comparison of Trends in Specific Flows for Jock River Near Richmond and Rideau River and Ottawa River Stations

GHD | Technical Review of the Hydrodynamic Analysis (Hwy 416 to Rideau River) | Appendix A | 11155320 (1) | Page 5

Snow Rain Total 350 Statistically significant trends at 1% significance level

300

250

200

150

100

Total Total Winter Precipitation (mm for Rain, cm for Snow)50

0 1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010 2020

Figure A.5 Winter Precipitation Trends for Ottawa CDA (Experimental Farm) Climate Station

GHD | Technical Review of the Hydrodynamic Analysis (Hwy 416 to Rideau River) | Appendix A | 11155320 (1) | Page 6

Snow Rain Total 400 Rain: Statistically significant trend at 5% significance level

350

300

250

200

150

100 Total Total Spring Precipitation (mm for Rain, cm for Snow) 50

0 1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010 2020

Figure A.6 Spring Precipitation Trends for Ottawa CDA (Experimental Farm) Climate Station

GHD | Technical Review of the Hydrodynamic Analysis (Hwy 416 to Rideau River) | Appendix A | 11155320 (1) | Page 7

Daily Mean Temperature Daily Maximum Temperature Daily Minimum Temperature 30 Statistically significant trends at 1% significance level

20 C)

° 10

0

-10

-20

-30 Winter Average/Extreme Temperature (

-40

-50 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010

Figure A.7 Winter Air Temperature Trends for Ottawa CDA (Experimental Farm) Climate Station

GHD | Technical Review of the Hydrodynamic Analysis (Hwy 416 to Rideau River) | Appendix A | 11155320 (1) | Page 8

Daily Mean Temperature Daily Maximum Temperature Daily Minimum Temperature 40

30

20 C) °

10

0

-10

-20

Spring Average/Extreme Temperature-30 (

-40

Daily mean and daily minimum: Statistically significant trends at 1% significance level -50 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010

Figure A.8 Spring Air Temperature Trends for Ottawa CDA (Experimental Farm) Climate Station

GHD | Technical Review of the Hydrodynamic Analysis (Hwy 416 to Rideau River) | Appendix A | 11155320 (1) | Page 9

Total Rain Snow 2.5

2

1.5

1

0.5

0

-0.5

-1

-1.5 Sen Slope for Winter Preciptation (mm/yr or cm/yr) - -2 year Theil

- -2.5 30 -3 1900 1920 1940 1960 1980 2000 2020 Midpoint of 30-year Period

Figure A.9 30-year Theil-Sen Slopes for Winter Precipitation for Ottawa CDA (Experimental Farm) Climate Station

GHD | Technical Review of the Hydrodynamic Analysis (Hwy 416 to Rideau River) | Appendix A | 11155320 (1) | Page 10

AAAppendixAAAAppendixAppendixppendixppendixppendixppendixppendix MHOQKNBCDR SEPFLJI 2D Hydrodynamic Model ReviewTitle

GHD | City of Ottawa – Technical Review of the Hydrodynamic Analysis | 11155320 (1) Comment Description

1 The energy slope is set to 0 for the 2D area inflow boundary conditions. This energy slope is used by the program to compute the normal depth and then to distribute flow along the boundary condition line. A normal depth water flow cannot have a zero energy slope.

2 The internal 2D area connections named “6550-Wormhole” and “3699-Wormhole” are used to transfer inflow from the 2D area boundary into the main channel. Taking 6550-Wormhole as an example, the area bounded within the “6550-Dam” is more than 2,000 m2 in area, and the maximum depth in this area is above 1 m in the “Jock_v09-Existing-Unsteady-100yr” plan. Using the peak flow rate of 5 m3/s, the hydraulic retention time in this closed area is longer than 6 minutes. The retention effect can significantly change the culvert flow. The figure below shows a comparison between the inflow hydrograph at “BC Line 6550” and the outflow at 6550-Wormhole. Figure 1 indicates that the wormhole culvert cannot deliver an identical inflow hydrograph from the 2D area boundary into the main channel. The outflow is extracted from the DSS file.

GHD | Technical Review of the Hydrodynamic Analysis (Hwy 416 to Rideau River) | Appendix B | 11155320 | Page 1 Comment Description

3 The model used 20 m cells for the floodplain and 10 m cells for the main channel, as well as a 15 s computational interval. The maximum velocities in the main channel, in the “Jock_v09-Existing- Unsteady-100yr” plan, are around 1 m/s. Therefore, the Courant numbers are larger than one in the main channel, which means water can flow through more than one cell in one computational interval, and cause instability issues in the model.

The model resolution is adequate for the floodplain but the channel resolution may be too coarse for estimating channel flow velocities accurately.

It is recommended to reduce the cell sizes and/or the computational interval to check if the water surface elevation or other parameters are significantly different. If they are, the smaller cell size or the shorter computational interval should be used instead.

4 The computational messages show convergence warnings in every plan. These convergence warnings are generated when the maximum iterations are reached but the element is not solved within the pre-defined numerical tolerance (0.003 m in this model) during a given time step. The convergence flag “1” indicates that the computation is converging when the maximum number of iterations is reached. Using a larger number for the Maximum Iterations option will solve these convergence warnings. Reducing the computational interval or the cell size can also improve the numerical stability. In the “Jock_v09-Existing-Unsteady-100yr” plan, many convergence warnings are generated for cell number 27086. The area around this cell should be investigated.

5 The implicit weighting factor (Theta) defines the weighting of the spatial derivatives between the current solution time line and the previously solved solution time line. A Theta of 1.0 indicates a more stable but less accurate solution. A Theta of 0.6 will provide a more accurate but less stable solution. A test between the two Thetas should be performed to confirm the use of Theta of 1.0.

6 The Diffusion Wave equations are typically not suitable for dynamic simulations of narrow flood hydrographs where the flood wave rises and falls quickly (the Diffusion Wave equations do not include the local and convective acceleration terms). The modeling should test the hydraulic solution obtained by the Diffusion Wave and Saint Venant solutions and if there are significant differences proceed with the Saint Venant solution as the full momentum answer is more accurate.

GHD | Technical Review of the Hydrodynamic Analysis (Hwy 416 to Rideau River) | Appendix B | 11155320 | Page 2 Comment Description

7 In the “Jock_v09-Existing-Unsteady-100yr” plan, a water leak with a total volume of 187 m3 (0.02%) is identified in the area to the west of the Half Moon Bay Public School on the right bank of the Jock River, as shown in Figure below. Water leaks can reduce the water volume and underestimate the flooding area. Break lines should be utilized to delineate the cells and ensure the faces are placed on top of the ridge.

8 The internal 2D area connections “North-FloodFring” and “6550-wormhole” include cell face numbers 41113 and 43104 (see Figure below). The weir elevations assigned to the two faces are around 91 m in “6550-wormhole”, and 100 m in “North-FloodFring”. The inconsistency in weir elevations may cause an error.

GHD | Technical Review of the Hydrodynamic Analysis (Hwy 416 to Rideau River) | Appendix B | 11155320 | Page 3 Comment Description

9 Internal 2D area connections are set up for Hwy 416 and other roads. The embankment elevations are set up very close to the centerline terrain elevations. In HEC-RAS 2D, the hydraulic property tables can capture the terrain elevations and calculate hydraulic parameters accordingly. A 2D area connection is unnecessary unless the embankment is higher than the terrain.

10 An error message occurs when trying to check the internal 2D area connection named “RailStrandherd-” in the geometry file “Jock_v09-Existing”.

11 The downstream limit of the model is located on the Rideau River approximately 350 m downstream of the confluence of the Jock River with the Rideau River and extends to both sides of the Rideau River floodplain. This setup is unusual, typically, the downstream limit of the model is set at the confluence and the water level boundary is oriented parallel to the river channel/floodplain.

GHD | Technical Review of the Hydrodynamic Analysis (Hwy 416 to Rideau River) | Appendix B | 11155320 | Page 4