Success Through Resilience: Planning for resilient municipal infrastructure
Tuesday June 27 11:20am-12:45pm and 3:30:pm-5:10pm
Leads: Hazel Breton (City of Toronto), Daniel McCreery (City of Toronto), Devin Coone (City of Toronto) and Geoff Cole (City of Toronto)
Municipalities are facing unprecedented impacts to the requirement to maintain a state of good repair for their infrastructure. In particular stormwater infrastructure, including natural infrastructure such as stream corridors, are particularly subject to impacts from high intensity, short duration storm events. Traditional analyses of looking at past precipitation patterns and flow regimes are no longer appropriate. Incorporating resilience into our infrastructure requires an understanding of our changing climate, developing levels of service for key infrastructure, and recognizing the importance of the role of stream corridors to the health and well-being of the community that include supporting: biodiversity, good water quality and protection from flooding and erosion.
Keywords: Infrastructure, Planning and Master Planning, Looking Forward, Multi-objectives
Following the conference, presentations that have been made available will be linked here.
Daniel McCreery1, Rob Amos2 and Jacob Ursulak2
1City of Toronto, Toronto, Canada
2Aquafor Beech Ltd., Mississauga, Canada
Since 2020 the City of Toronto has initiated five studies, across five different subwatersheds to identify and assess erosion hazards to municipal infrastructure within Toronto’s riparian corridors. The intention of these studies is to develop a capital works program where the prioritization and allocation of resources is founded on the integration of fluvial geomorphology, water resources engineering, terrestrial & aquatic ecology, and asset management disciplines. Given the multi-objective nature of these undertakings, the City refers to these studies as Geomorphic System Master Plans (GSMPs).
This presentation will provide a summary of the continuing evolution of the Toronto GSMP program and will include an explanation of the unique challenges Toronto faces in addressing risks to infrastructure in urban watercourse systems. Key elements of the GSMP process will be covered, including structuring each study within the framework of the Municipal Class Environmental Assessment and Master Planning processes. The discussion will centre on a case study of the Mimico Creek GSMP. Highlights will include a review of the unique features of the Mimico study area including transitions from shale bedrock, to overburden and concrete lined channels as well as variations in land use from highly confined residential neighbourhoods to open park space, golf courses and industrial developments. The Mimico GSMP includes a variety of erosion related risks to infrastructure including exposed sanitary sewer crossings, failed storm sewer outfalls, and slope stability risks to private property. Working through these complex challenges has given rise to innovative approaches to field work, erosion risk analysis, design solution development and stakeholder engagement.
The presentation will also outline key considerations for completing a Toronto GSMP, such as evaluating solutions for resiliency and their inter-disciplinary and multi-objective benefits, both at a local and sub-reach scale. The discussion will also touch on the necessity to ultimately prioritize infrastructure sites in need of intervention. This insight will look at site prioritization not only on a watercourse basis (ie. a single GSMP study area), but through the lens of all the City’s watercourses, such that a defendable priority list can be generated for the entire City to address planning and budgeting requirements.
Overall, unique insight into the challenges and opportunities of assessing and prioritizing municipal infrastructure projects in a large-scale urban watercourse setting will be presented over a multi-decade horizon.
David Kynaston1, Robert Walker2 and Julie Michel1
1Aquafor Beech Limited, Mississauga,Ontario, Canada
2EBNFLO Environmental, Waterloo, Ontario, Canada
Climate change scientists are in general agreement that warmer climates will contain more frequent large storms and that storms are likely to be more severe and release more moisture. Future storms are developed based upon the concept of Probable Maximum Precipitation, wherein future warming would increase the water holding capacity and intensity of storms. Future storms are generated based upon average future temperature increases of 2 Co by 2050 and 2.75 Co by 2080.
Average air temperature increases for 2050 and 2080 were based upon Regional Climate Modelling results for the Toronto area with Greenhouse Gas emission rates (radiative forcing functions) of 4.5 W/m2. This moderate emission scenario results in steadily increasing air temperatures stabilizing towards the end of the century. The storm intensity for 7 design storms and three actual storms experienced during the period 2011 to 2016 were modified upwards to account for potential storm volume increases. The hydrologic model HSPF was run with the modified storms to generate streamflows within Mimico Creek reaches.
The Mimico watershed spans over 78 km2 and has recorded channel flows ranging from 0.02 to almost 200.00 m3/s. Within Toronto, there are 80 sewer crossings, 25 watermain crossings, and 71 storm outfalls contributing to channel conveyance. Using topographic surveys, ground penetrating radar and pipe inverts compared to historical as-built surveys determined maximum basal scour of up to 2.7 cm/yr and bank erosion rates up to 19.0 cm/yr.
For three temporal scenarios (existing conditions, 2050, and 2080), stream power values (N/m·s) were modelled by reach for each storm event. Using a key indicator of cumulative excess stream power, rates of erosion were correlated for the future time-steps reveling rate increases in excess of 10%.
Results of climate assessment include increased erosion within the subject channel cross sections, including both horizontal and lateral degradation. These result in implications to channel design criteria, optimal design flow targets, overall longevity of restoration works, and improved climate change resiliency within Toronto watercourses.
Devin Coone1, Bill Snodgrass1 and Emma Schiller2
1City of Toronto, Toronto, Canada
2Aquafor Beech Ltd., Mississauga, Canada
Mimico Creek flows through the Greater Toronto Area, with many segments considerably straightened, realigned, and hardened to coincide with surrounding urbanization. An intricate network of buried infrastructure exists throughout the valley system, typically inset beneath the channel and floodplains. The reach adjacent to Van Dusen Blvd is located within Lower Mimico Creek, and is confined by residential, flood-sensitive properties. Within this reach, two segments of sanitary sewer infrastructure constructed between the 1950s and 1970s have become exposed by nearly 2m of shale bedrock channel incision accelerated by the pressures of urban development.
The Van Dusen Stream restoration project was a multi-objective complex channel restoration project aimed at restoring 130m of Mimico Creek to address critical infrastructure needs of the area while maintaining flood conveyance capacity. The project involved the protection of an exposed 600mm sanitary trunk sewer and a sanitary sewer siphon crossing of the creek, and replacement of a pedestrian bridge.
This presentation is divided into three elements. The hydraulic modelling and design of the project is first addressed around the balance between protecting the sewer while not impacting flood water levels. The design also needed to protect the Georgian Bay Formation shale bedrock to prevent further oxidation and erosion, as well as the encasement design implemented. The design removed a fish barrier – the excessively exposed sanitary trunk sewer crossing.
The construction of the project is the second element, including its challenges. Specific construction techniques were used to protect the sanitary trunk sewer, manage high flows during construction, and intensive stream construction within such a tight residential corridor.
The third element is the community and project management aspects of the project. This includes an overview of the communication and engagement strategies that were employed throughout the project to inform and balance the concerns of the community.
It is concluded that the Van Dusen stream restoration project was a complex multi-objective project that addressed critical infrastructure needs by restoring a portion of Mimico Creek. The project demonstrates the importance of collaboration and communication between various stakeholders, including the community, project managers, engineers, and contractors, to achieve a successful outcome.
Geoff Cole, P.Eng.
City of Toronto – Engineering & Construction Services, Toronto, ON
This presentation provides an overview of two emergency watercourse restoration projects completed by the City of Toronto’s Stormwater Management Infrastructure unit and our partners in 2022.
A storm outfall collapsed in Humber Creek near the intersection of Dixon Road and Islington Avenue in Etobcoke. The resulting erosion exposed an un-encased sanitary sewer. The City of Toronto declared an emergency to protect the at-risk sewer. This presentation will look at the steps taken to address the emergency and to complete the final restoration of the area.
The second half of the presentation will focus on the North Toronto Treatment Plant Outfall, which was determined to be at high risk of failure due to erosion in the Don River. The City declared an emergency to repair the failing outfall, and that was the start of the regulatory tango required to get approvals from various stakeholders before the emergency works could be completed.
For both projects, we will discuss the multiple objectives achieved by the restoration projects, the multi-disciplinary approach required to complete the restorations, the innovative approaches used to address our site challenges, how the projects incorporated climate resilience, and the inclusion of natural channel design approaches in heavily urbanized areas.
George Zeppieri1, Hazel Breton2 and Bill Snodgrass2
1Dynex Construction, Concord, Canada
2City of Toronto
Being a contractor in Toronto is more difficult (and potentially rewarding) than most other Municipalities. This presentation will provide a Contractor’s prerogative on both the tremendous challenges as well as opportunities associated with constructing within Downtown Toronto’s natural stream system. Specific references to a recent project on Mimico Creek south of Bloor Street will be used to illustrate key topics.
To start, Toronto watersheds exhibit extensive development without stormwater controls, which frequently result in uncontrollable flows associated with even minor weather events. Without appropriate planning and mitigation, flooding of a project site can result in loss of material, damage to equipment, and sedimentation downstream which are considered environmental spills.
Logistics of access include the standard heavy equipment down oversteepened slopes, bound by critical utilities, private properties, and the likelihood of other projects in immediate conflict. The Mimico project included over 10,000 tonnes of armourstone brought into the center of the City, past residential streets which had multiple houses under full reconstruction. This project was preceded by an interim repair carried out Toronto City work forces. A new bridge crossing being undertaken as part of another City initiative was added to the project, with promises of ribbon cuttings controlling the schedule.
Toronto manages their bidding process as horizontal, lump sum contracts. What does that mean? Our bid is a single line item, covering all required tasks associated with the project. For Mimico Creek at Van Dusen, the lump sum bid included extensive creek restoration, new storm sewers, full bridge replacement, and landscaping within adjacent private properties.
In addition to the practical construction, Toronto requires all works to be documented daily between the administration team and the contractor. This includes a combined effort which requires near full time office support keeping in constant contact with the in-field team, and resulting in hundreds of written documents including daily reports, quality control and materials tracking, change orders, site instructions, requests for information, and proper invoices.
Despite the challenges, these projects offer the opportunity to do some of the most challenging work on some of the Southern Ontario’s biggest stream projects.
Bill Snodgrass1, Rod Anderton2, Kumar Sivakumaran1 and Robert Chan1
1City of Toronto, Toronto, Canada
2Retired, City of Toronto, Toronto, Canada
This paper explores various Toronto Stream Restoration projects from the past two decades to evaluate elements which have enhanced the resilience of the projects. Geomorphic Systems Master Plans (GSMPs), starting with three in the Highland Creek watershed over 2005 to 2011 is one element, as the study emphasizes the complete creek/river system. Learning to work with nature is a fundamental aspirational element for (engineered) natural channel systems (NCS). Evaluating stream power and the erosion processes evident during two formative storms, the August 19 2005 and July 8th extreme storm show how nature defined the location and shape of the watercourse.
To protect sanitary sewer crossing infrastructure requires that a riffle should be located at the crossing; is this resilience?. The Valley Segment 4a project illustrates a project where multiple crossings were protected with a riffle pool system over 1.5 km creek system. Buried armourstone walls are used to protect maintenance holes from bend migration and bank erosion while permitting a softer bioengineered bank treatment outside the buried wall. Sanitary sewer crossings have additional fail- safe redundancy by using structural steel reinforcement to resist tensile forces in concrete encasement. In riffles especially upstream and downstream of sewer crossings, a rib structure is used to minimize loss of riffle stone. A complete bed cover design is used to keep the creek bed wet and minimize redox reactions in the Georgian Bay Shales. Hypothesizing the future mode of failure of a NCS design is an element to enhance resilience.
A stream inspection program has been developed which inspects for exposed infrastructure one every two to three years caused by stream erosion processes (bend migration; bank erosion, bed incision). This program has approximately 8000 points of inspections across ca 380 km of watercourse; it defines repairs needed as Emergency Works, prioritizes GSMPs and detailed design assignments. Future monitoring of completed projects will focus on the loss of depth of cover over infrastructure which is a primary criteria for when future restoration designs may be needed, and provide information for adaptive management. The conclusion is that multiple strategies and elements are needed to enhance resilience.