Peterborough's Flood Reduction Strategy

On July 15, 2004 a severe rainfall event occurred in the City of Peterborough which resulted in a record 175 mm of rainfall, including 78 mm within an hour.  A Declaration of Emergency was made by the Mayor and the Emergency Operations Center was activated.  The City’s drainage system was unable to cope with the demands of the rainfall and significant flooding occurred to both public and private properties. 
 
As a result of the storm, the City of Peterborough developed an overall flood reduction strategy.  In 2012 Cole Engineering was retained by the City of Peterborough to conduct a Master Plan under the Class Environmental Assessment (EA) process. The project objectives were to:
  1. Identify the areas most susceptible to basement flooding across the City;
  2. Determine the most cost-effective solution to mitigate the impact of major storms in each area;
  3. Establish the preferred solution to reduce the frequency of raw sewage bypass at the wastewater treatment plant; and,
  4. Establish future sanitary sewer upgrade requirements. 

The Master Plan was completed by Cole Engineering in 2013 and provided the planning rationale and EA documentation required to proceed with the detailed design of the recommended works.  In formulating these recommendations, existing GIS (Geographic Information Systems) data was coupled with additional sewer flow monitors and rain gauges.  These were analyzed together with a City-wide hydraulic model that was developed during the same time period. 
 
Using the collected information, a feasibility review of the preferred alternatives was performed to ensure that the study recommendations were constructible and practical. An evaluation process including physical, economic, environmental and social / cultural / health implications was used to assess and evaluate the alternative solutions and select the most cost‐effective solution.
 
Cole Engineering was then retained by the City of Peterborough to provide engineering services to eliminate Inflow and Infiltration (I-I) sources in the sanitary system within the Downtown Core Area (DCA).  The DCA is a complex urban catchment with multiple hydraulic and hydrologic interactions between overland flow paths, storm and sanitary sewer networks, groundwater and Jackson Creek.  Understanding that the DCA is the prime focus of study but that upstream areas contribute sanitary flow into the DCA will be considered in identification of the priority areas proposed for investigation.  Current I-I generation and flood-causing potential are two of the main criteria in area prioritization. The I‐I Reduction project is currently underway.
Some of the field activities being performed in this project are:Rain and Flow Monitoring;
  • Smoke and Dye Testing;
  • CCTV Investigation and Pipe Condition Assessment;
  • Sewer Cleaning and Flushing;
  • Sewer Joint Testing;
  • Manhole Inspection; and,
  • Field Survey. 
  • The type of I-I sources identified and included in remedial works include:
  • Inflows from manholes covers and risers;
  • Inflows from roof downspouts;
  • Inflows from catchbasin and roof drain cross connected to sanitary sewers;
  • Inflows from overflow structures between sanitary and storm system;
  • Inflows and infiltration from Foundation Drain Collectors (FDC) and sump pumps;
  • Inflows from backflow/overflow to the Otonabee River;
  • Infiltration from sewer laterals; and,
  • Infiltration from cracks and joints in the sanitary sewer. 
Cole Engineering is currently in Phase 3 and 4 of the project (see Project Phases below), with construction scheduled for summer 2015. 
 
Any reduction in the I-I rates after repairing system ‘defects’ will be reported in an objective manner by accounting for different rain rates in different locations and times, and the amount of ‘moisture’ in the drainage system at the start and during events. It is expected that upon completion of this project, there will be a significant and tangible reduction in Inflow and Infiltration.

 
Project Phases
 


Phase 1
  • Establish Existing ‘Baseline’ Conditions;
  • Collection of Background Information and Data Gap Analysis;
  • Preliminary Area Prioritization;
  • Baseline or Pre-rehabilitation Flow Monitoring; and,
  • Field Investigations.
Phase 2
  • Preliminary Design;
  • Identification and Prioritization of I-I Sources;
  • Conceptual Remediation Plan and Preliminary Design for Rehabilitation Activities;
Phase 3
  • Communication and Public Policy Consulting;
  • Review Relevant By-laws and Regulations and Recommendations;
  • Preparation of Communication Material;
  • Communication with Public and Private Stakeholders;
Phase 4
  • Detailed Design and Construction Administration; and,
  • Acquisition of Stakeholder Approval / Permitting;
  • Tender Process;
  • Construction Administration and Site Inspection;
Phase 5
  • Post Rehabilitation Analysis;
  • ​Post-Rehabilitation Flow Monitoring; and,
  • Analysis and Quantifications.
 
Written by: Farshad Salehzadeh, April 2, 2015