LITTLE ETOBICOKE CREEK FLOOD EVALUATION STUDY SUMMARY REPORT Prepared for: CITY OF MISSISSAUGA Prepared by: MATRIX SOLUTIONS INC. Version 1.0 July 2021 Guelph, Ontario Unit 7B, 650 Woodlawn Rd. W Guelph, ON, Canada N1K 1B8 T 519.772.3777 F 226.314.1908 www.matrix-solutions.com LITTLE ETOBICOKE CREEK FLOOD EVALUATION STUDY SUMMARY REPORT Prepared for City of Mississauga, July 2021 reviewed by Amanda McKay, P.Eng. Karen Hofbauer, M.A.Sc., P.Eng. Water Resources Engineer Senior Water Resources Engineer CONTRIBUTORS Name Job Title Role Melani-Ivy Samson, M.A.Sc., E.I.T. Water Resources EIT Co-author Amanda McKay, P.Eng. Water Resources Engineer Co-author Karen Hofbauer, M.A.Sc., P.Eng. Senior Water Resources Engineer Reviewer Peter Bishop, M.Eng., EIT Water Resources EIT Modelling and Analysis Ziyang Zhang, M.Sc., EIT Water Resources EIT Modelling and Analysis DISCLAIMER Matrix Solutions Inc. certifies that this report is accurate and complete and accords with the information available during the project. Information obtained during the project or provided by third parties is believed to be accurate but is not guaranteed. Matrix Solutions Inc. has exercised reasonable skill, care, and diligence in assessing the information obtained during the preparation of this report. This report was prepared for the City of Mississauga. The report may not be relied upon by any other person or entity without the written consent of Matrix Solutions Inc. and of the City of Mississauga. Any uses of this report by a third party, or any reliance on decisions made based on it, are the responsibility of that party. Matrix Solutions Inc. is not responsible for damages or injuries incurred by any third party, as a result of decisions made or actions taken based on this report. 24603-531 LEC Summary Report R 2021-07-02 final V2.0.docx ii Matrix Solutions Inc. VERSION CONTROL Version Date Issue Type Filename Description V0.1 27-Nov-2020 Draft 24603-531 LEC Summary Report Issued to client for review 2020-11-27 draft V0.1.docx V1.0 26-Feb-2021 Final 24603-531 LEC Summary Report Issued to client 2020-02-26 final V1.0.docx V2.0 02-July-2021 Final revised 24603-531 LEC Summary Report Revisions issued to client 2020-07-02 final V2.0.docx 24603-531 LEC Summary Report R 2021-07-02 final V2.0.docx iii Matrix Solutions Inc. TABLE OF CONTENTS 1 INTRODUCTION ................................................................................................................................ 1 1.1 Purpose of this Report ........................................................................................................ 3 2 MASTER PLAN PROCESS ................................................................................................................... 3 2.1 Planning Context ................................................................................................................. 4 2.1.1 Planning Act and Provincial Policy Statement ....................................................... 4 2.1.2 Official Plan ............................................................................................................ 5 2.1.3 Ontario Ministry of Natural Resources and Forestry Floodplain Policy ................ 6 2.2 Public Consultation ............................................................................................................. 6 3 PROGRESS REPORT NO. 1: FLOODPLAIN SPILL ASSESSMENT .......................................................... 6 4 PROGRESS REPORT NO. 1A: FLOODPLAIN SPILL ASSESSMENT ........................................................ 7 5 PROGRESS REPORT NO. 2: MODELLING FOR FLOOD CHARACTERIZATION AND ANALYSIS ............ 8 6 PROGRESS REPORTS NO. 3 AND NO. 4: FLOOD CLUSTER AREAS AND GENERAL CAUSES OF FLOODING ........................................................................................................................................ 9 7 PROGRESS REPORTS NO. 5 AND NO. 6: FLOOD REMEDIATION MODELLING AND ASSESSMENT . 11 8 PROGRESS REPORT NO 7: FLOOD ALTERNATIVES EVALUATION AND REMEDIATION PLAN ......... 13 9 CONCLUSION .................................................................................................................................. 14 10 REFERENCES ................................................................................................................................... 15 LIST OF FIGURES FIGURE 1 Phase 2 Study Limit ............................................................................................................. 2 FIGURE 2 Municipal Class Environmental Assessment Process ......................................................... 4 LIST OF TABLES TABLE 1 Summary of Progress Reports ............................................................................................ 3 TABLE 2 Focus Area Recommendations Summary ......................................................................... 14 24603-531 LEC Summary Report R 2021-07-02 final V2.0.docx iv Matrix Solutions Inc. 1 INTRODUCTION The Little Etobicoke Creek watershed in the City of Mississauga (the City) has experienced flooding and erosion concerns recorded back to at least the 1970s. The recent large flood event on July 8, 2013, which corresponded approximately to a 350-year storm (MMM 2015), resulted in many reports of flooding-related incidents and damage, particularly in the Dixie Road and Dundas Street East area. The focus of this flood evaluation study is to characterize flooding within the Little Etobicoke Creek watershed, identify preliminary flood cluster areas, and develop flood remediation alternatives. The Little Etobicoke Creek Flood Evaluation Study is being conducted in two phases as part of a final Master Plan for the City. Phase 1 was completed in January 2018 and expanded on previous studies of the overland spill from Little Etobicoke Creek, particularly focused on the Dixie-Dundas Special Policy Area (SPA), where flood flows spill from Toronto and Region Conservation Authority (TRCA) jurisdiction lands into Credit Valley Conservation (CVC) jurisdiction lands. Phase 2 of the study was completed in February 2021 and is the subject of this report. Phase 2 of the study is focused on the Little Etobicoke Creek watershed as a whole and includes characterization of overland urban flood risk, as well as development, assessment, and recommendations for flood remediation measures. Figure 1 shows the study area, including the 2,260 ha Little Etobicoke Creek watershed. 24603-531 LEC Summary Report R 2021-07-02 final V2.0.docx 1 Matrix Solutions Inc. Etobicoke Creek Figure Date: July 6, 2020 Roads Watercourse Railway Little Etobicoke Creek Phase 2 Buildings Flood Evaluation Study Project #: 24603-155562 Little Etobicoke Catchment Phase 2 Study Limit This drawing must be used in conjuction with the attached memorandum, 'Progress Report #7: Flood Disclaimer: The information contained herein may be compiled from numerous third party materials that P. Bishop Alternatives Evalutation (June 2020)' is subject to are subject to periodic change without prior notification. While every effort has been made by Matrix K. Hofbauer the same limitations and conditions stated in the Solutions Inc. to ensure the accuracy of the information presented at the time of publication, Matrix memorandum. Solutions Inc. assumes no liability for any errors, omissions, or inaccuracies in the third party material. Figure 1 T:\24603 - Little EtobicokeCr_Flood\531\05 Analysis\GIS\BaseMap_v3.qgs|Phase 2 Study Limit (PR7 - final compiled report)|pg1|2020-07-06 1.1 Purpose of this Report Matrix has completed the Little Etobicoke Creek Flood Evaluation Study in seven sections, which are summarized in five progress reports. Due to the distinct aspects of the flood considerations throughout the watershed, these progress reports have been compiled as independent sections of this final summary report instead of consolidated into a single project report. Each of these progress reports provides details of methods and results for specific tasks within the overall project. Table 1 displays the key contents of each progress report. This summary report is intended to function as a guide to the project; each section provides a summary of each progress report to assist the reader in finding desired information. TABLE 1 Summary of Progress Reports Progress Topic Content Report No. 1 Floodplain Spill Assessment • background review (Matrix 2018) • Phase 1 2 Modelling for Flood • details of two-dimensional (2D) PCSWMM model Characterization development and Analysis (Matrix 2020a) • 2D model validation • flood risk results 3 and 4 Flood Cluster Areas and General • characterization of flooding Causes of Flooding (Matrix 2020b) • identification of flood cluster areas • identification of mechanisms of flooding • recommendations for each cluster area for further assessment 5 and 6 Flood Remediation Modelling • minor system assessment (level of service modelling) and Assessment (Matrix 2020c) • three-way coupled modelling methods • description and analysis of six key focus areas 7 Flood Alternatives Evaluation • evaluation table of remediation alternatives for the six (Matrix 2020d) focus areas • summary of recommendations for additional flood clusters • flood remediation plan 2 MASTER PLAN PROCESS The Little Etobicoke Creek Flood Evaluation Study was completed following Approach 2 of the Master Plan process (MEA 2000). Phases 1 and 2 of the Municipal Class Environmental Assessment (EA) process are included in Approach 2, as described in Figure 2. This report and the attached