City of Peterborough Un-named City Tributaries Flood Reduction Study Master Plan Prepared by: AECOM 5600 Cancross Court, Suite A 905 501 0641 tel Mississauga, ON, Canada L5R 3E9 905 501 0181 fax www.aecom.com Project Number: 060164148 Date: March 2012 AECOM City of Peterborough Un-named City Tributaries Flood Reduction Study Master Plan Statement of Qualifications and Limitations The attached Report (the “Report”) has been prepared by AECOM Canada Ltd. (“Consultant”) for the benefit of the client (“Client”) in accordance with the agreement between Consultant and Client, including the scope of work detailed therein (the “Agreement”). 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RPT2-060164148-Final Unnamed Tribs Environmental Study Report - 2012 03 26.Docx AECOM City of Peterborough Un-named City Tributaries Flood Reduction Study Master Plan Distribution List # of Hard Copies PDF Required Association / Company Name Revision Log Revision # Revised By Date Issue / Revision Description 1 S. Hollingworth 2011 09 06 Draft Final Report Issued for City of Peterborough Review 2 S. Hollingworth 2011 10-07 Revised as per City of Peterborough Comments 3 M. Osojnicki 2012 03 26 Revised following Council Resolution AECOM Signatures Report Prepared By: Emily Cameron, P.Eng. Water Resources Engineer Report Reviewed By: Steve Hollingworth, P.Eng. Senior Water Resources Engineer RPT2-060164148-Final Unnamed Tribs Environmental Study Report - 2012 03 26.Docx AECOM City of Peterborough Un-named City Tributaries Flood Reduction Study Master Plan Executive Summary Introduction In July 2004, the City of Peterborough (the City) was hit by a severe rainfall event that caused significant flood damage. Insured private property damages reportedly exceeded $87 million while Ontario Disaster Relief Assistance Program (ODRAP) infrastructure damages of approximately $25 million were incurred. In addition, insured losses and indirect damages such as disruption in residential living conditions, loss of business, and loss of wages or income, were sustained. Shortly after the flood, the City retained AECOM (formerly UMA Engineering Ltd.) to investigate the causes and determine remedial measures to improve the operation of the drainage system and reduce the risk of damage from future flooding. AECOM undertook a City-wide Flood Reduction Master Plan Study (the Master Plan) under the Environmental Assessment Act to plan infrastructure improvements as part of the City’s overall systems, before dealing with project-specific issues. Recommendations from the Master Plan included the preparation of detailed flood reduction studies for each of the watersheds flowing through the City. Detailed studies have been completed for the seven (7) watersheds that drain through the City of Peterborough. This report constitutes the master planning process for the remaining areas within the City of Peterborough not covered by the watershed studies (i.e., un-named City tributaries). This Study was conducted as a Master Plan under the Municipal Class Environmental Assessment (EA), addressing Phases 1 and 2 of the Municipal Class EA process. In addition to public notices of the study commencement and completion, two Public Open Houses were held to present the study findings and recommendations to the public. Existing Conditions Complex hydrologic and hydraulic modelling was undertaken to assess the capacity of the existing storm drainage systems through the study area, which carry runoff from the developed portions of the study area to the Otonabee River or smaller open drainage systems. Urban flood flows were generated with the USEPA SWMM model utilizing the PCSWMM graphic user interface. The PCSWMM model was set up simulate the flows through both the piped and overland flow drainage systems simultaneously, considering pipe and catchbasin capacity, as well as the depressed areas that allow the overland flow to return to the piped systems. The PCSWMM model was calibrated using rainfall records and storm sewer flows that were recorded during the summer and fall of 2010. Finally, the HEC-GeoRAS hydraulic model was used to determine the depth and extent of flooding and flood damages along the overland flow routes based on the overland flow rates calculated by the PCSWMM model. There are three open drainage systems through the study area which required a different approach to calculate peak flow rates. SWMHYMO models were developed to calculate the peak flow rates from both the rural and urban portions of the study area draining to these systems. The HEC-GeoRAS program was then used to calculate the corresponding flood levels and extent of flooding through the open drainage systems. The models were simulated for a number of storm events, ranging from a 1 in 2 year storm to the Timmins historical storm, representing the worst storm on record that could potentially occur over the study area. The flood plains were then mapped for each these storm events. As per the procedures developed through the City-Wide Flood Reduction Master Plan, flood damage estimates were calculated as 30% of the value of any building within the flood plain for a given storm event. The assessed values of the impacted properties through the study area were based on the latest property assessments completed by the Municipal Property Assessment Corporation (MPAC), which were provided to AECOM by the City of Peterborough. RPT2-060164148-Final Unnamed Tribs Environmental Study Report - 2012 03 26.Docx i AECOM City of Peterborough Un-named City Tributaries Flood Reduction Study Master Plan A total of 214 buildings are predicted to be impacted by flooding from a 1 in 2 year storm, and a total of 444 buildings are predicted to be impacted by a 1 in 100 year storm. The average annual flood damages were determined to be approximately $15.8 Million per year. Alternative Solutions A range of alternative solutions to reduce flooding and flood damages through the study area were developed and evaluated. The following potential solutions were examined for applicability to each area affected by flooding: Do Nothing Source Controls (disconnect roof leaders from the sewer, permeable pavement, green roofs) Peak Flow Controls (stormwater management ponds, underground storage tanks) Storm Sewer Upgrades (larger pipes, new sewer systems, additional catchbasins) Overland Flow Upgrades (reconstruct streets with curb and gutter, re-grade streets to remove un- drained low areas along the profile) Flood Proofing (berms, water-tight building retrofits) The feasible alternatives for each area impacted by flooding were evaluated against a range of criteria, including cost, impacts to the natural environment, impacts on the social environment,