Risk Assessment of Toronto’s Culverts Using the Canadian Public Infrastructure Engineering Vulnerability Committee (PIEVC) Protocol

The City of Toronto utilized a risk assessment tool to help evaluate the risk of climate impacts on the City’s culverts. The PIEVC Protocol, developed by the Canadian Public Infrastructure Engineering Vulnerability Committee (PIEVC), is a step-by-step protocol in which risk scoring systems incorporate climate modeling data to outline explicit procedures to help engineers design a particular structure to withstand current and future climatic conditions. Although this study evaluated only three Toronto culverts, the results can be used to assist Toronto in incorporating climate change adaptation into the design, development and management of all of its culverts - and could be applied in other municipalities as well. The process and findings of the study of three culverts are summarized in the report Climate Change Vulnerability Assessment for Culverts.

In 2005, a severe summer storm caused $47 million Canadian in damage to Toronto’s infrastructure. During that storm, heavy rains overwhelmed a culvert and washed out a portion of Finch Avenue, a major artery north of Toronto's downtown core. The subsequent reconstruction directly cost the City millions of dollars, while the closure of Finch Avenue for 14 months caused long-term social and financial impacts to affected residents and businesses.

The main objective of the study was to identify the components (defined below) of each culvert at risk of failure, damage, deterioration, reduced operational effectiveness, and/or reduced life cycle from potential future climate changes in the 2040 to 2049 time horizon. The study found that while the three culverts generally had medium to low vulnerability to future impacts, all three culverts lack the capacity to carry the flows predicted for extreme rain events, the frequencies of which are expected to increase.

The PIEVC Protocol is a five-step process for conducting an engineering vulnerability assessment on infrastructure due to anticipated short and long-term climate change impacts; the five steps include:

  1. defining the project;
  2. gathering data about physical elements of the asset that are critical to its operation;
  3. assessing risk of failure of the asset based up the probability and severity of different weather events;
  4. analyzing the engineering to determine the capacity of the asset to withstand different loads (i.e., a certain amount of stream flow); and
  5. making recommendations for actions to reduce vulnerabilities. 

In this study, the researchers applied this five-step protocol to three Toronto culverts:

Step 1, Project Definition: Of over 150 culverts within Toronto, three were chosen for the case study because of their different engineering properties: a cast in place concrete box structure; a corrugated steel pipe (CSP) arch culvert under a large embankment; and a CSP culvert buried under the road.

Step 2, Data Gathering and Sufficiency: The specific infrastructure components of each culvert were identified along with the appropriate climate information needed to assess risk to the culvert. Examples of “components” include: road infrastructure such as pavement, sidewalk/curb, small buried utility infrastructure, and road embankments; drainage infrastructure such as inlets, outlets, and the culvert structure itself; natural features; surrounding area components such as residential units; and administration and operation components, such as emergency and operating procedures.

The climate analysis, details of which are found in Chapter 3 and Appendices A and B of the report, included two main aspects: establishing a set of climate parameters relevant to the locations of the three culverts, and establishing historic and future probabilities for the occurrence of each climate parameter (e.g., high or low temperature, heavy rainfall, heavy snow, drought, freeze-thaw). To develop future climate projections for the area for the years 2040 and 2049, the study relied on climate model outputs from Environment Canada’s Canadian Climate Change Scenario Network, the IPCC 4th Assessment Report (AR4, 2007), and the City of Toronto’s Climate Drivers Study.   

Step 3, Risk Assessment: Each culvert’s response to various climate events was evaluated by multiplying the probability of the event by the severity of its impact. The study determined, that none of the culverts were at “high risk” of impact, but many were categorized as “medium risk,” and many more that were identified as “low risk” for existing conditions changed to “medium risk” for future climate conditions.

Step 4, Engineering Analysis: Infrastructure-climate interactions with higher risk values were further analyzed. Vulnerability is assessed based upon the capacity of the infrastructure to withstand future loads. Among other individual vulnerabilities, several components of all three of the study culverts were classified as vulnerable to high-intensity, short-duration rainfall, which could exceed the culvert capacity.

Step 5, Recommendations: Specific recommendations were provided for adapting Toronto’s culverts, which may be relevant to developing adaptive responses for designed and maintaining culverts generally. For example:

  • The hydraulic capacity of culverts should be reviewed and compared with the anticipated flow conditions during large storm events. The hydraulic model results available indicate that the culverts included in this study do not have the capacity to carry the predicted flows from a high-intensity, short-duration rain event and/or a hurricane.
  • Toronto should consider a “no regrets” strategy for prioritizing culvert improvements by taking measures to mitigate infrastructure failure, such as installing upstream protective measures to prevent debris from accumulating in the culvert.
  • The City should review the policies and procedures that govern how City personnel access culverts and safely carry out their duties under extreme weather conditions.

The PIEVC Protocol risk assessment costs about $100,000, depending on the size of the infrastructure project; Toronto paid $120,000 to evaluate its three culverts.

 

This Adaptation Clearinghouse entry was prepared with support from the Federal Highway Administration. This entry was last updated on January 29, 2015.

 

Publication Date: December 2011

Related Organizations:

  • City of Toronto; Ontario, Canada

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  • Assessment

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