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  • Writer's pictureMark Reiner, PhD, PE

The Repair vs Replace Debate – from a City’s Perspective

Updated: Oct 22, 2020

By: Mark Reiner, PhD, PE; Steve Fisher, PhD, PE; and Andrew Fang, PhD

The RABID paradigm is so inaccessible for maintaining distributive urban infrastructure that the cost of proactive maintenance is weighed against the direct costs of reacting to asset failure. It is the indirect costs of infrastructure failure and the hazards of repair vs replacement that a city should better understand.

As stated in Part 1a, a utility’s best practice KPI may not correlate with the resilience goals of the city that the utility serves, or even the goals of professional engineering associations. For example, consider how the same KPI example from Part 1a (15 water main breaks/100 miles of pipe/year) is viewed by the American Society of Civil Engineers (ASCE). In ASCE’s quadrennial Report Card (2017), the 240,000 annual water main breaks experienced in the U.S. each year is presented as an unacceptable outcome of aging infrastructure. However, with approximately 1.2 million miles of water mains in the United States, the 240,000 annual breaks equate to 20 breaks per 100 miles/yr. As shown on Figure 3, there is a narrow range (5 breaks per 100 miles) between what the water utility perceives as best practice (15 breaks) with what ASCE considers as unacceptable (20 breaks). This creates confusion for city-leadership and is illustrated on Figure 3.

Figure 3: The Narrow Range of Communicating Best Practices and Unacceptable to the Public

From a city’s perspective, the lack of meaning behind this water utility KPI (breaks per 100 miles of pipe/yr) cannot be understated. Whereas the utility views any failed asset within their system as part of this KPI, whether a small-diameter residential water main break or a large-diameter main break, the city’s perspective is based on the where, when, and how much disruption does a failed asset cause. That is, any disruption to city life is measured by the city KPI of how many complaints are received. Consider the scale of the two water main breaks illustrated in Figure 4.

Figure 4 highlights the differences in perspective between the utility and the city it serves. The water utility perspective is based on anticipated direct costs under pre-failure probabilities. While the city’s perspective is of post-failure economic consequences (‘indirect’ costs, discussed in next blog) that disrupt city-life. Currently, there is not a methodology that cities apply to determine where infrastructure failure would actually be ‘disruptive’ – and why. Developing these city-centric KPIs is the focus of Parts 2 and 3 of this blog.

Repair vs Replacement and Hazardous Older Weak-Links

Figure 4 also illustrates one common priority that both the utility and the city share – restore service as quickly as possible. The quickest method to stop a leak is to repair an isolated section without replacing the entire failed segment of water main (i.e. from ‘bell-to-bell’). What is left behind is depicted in Figure 5, each side of the patched (repaired) section continues to age in place. That is, a symptom is cured by repairing the failure, but the disease remains. This hurried approach ignores a significant consequence that all cities will face when choosing the ‘repair’ side in the repair vs replace debate [1]. And, the repair choice will continue to be made until the ‘true costs’ are better understood. A quick repair leaves a series of weak links that culminate to create a long-term risk of major disruption to city-life. This quick repairing results in a patchwork of remaining vulnerable, and potentially Hazardous, Older Weak-Links (HOWL) across the city that only fosters continued asset failures. As a system is only as resilient as the weakest link, this is a form of 'technical debt'. HOWL is depicted on Figure 5.

Figure 5: Hazardous Older Weak-Links (HOWL) in the Potable Water Sector

For example, the Los Angeles Department of Water and Power (LADWP) communicates with the city that its potable water system experiences an average of three water main breaks per day. But, LADWP might not communicate the potential consequences of a water system that, by 2030, will have 90 percent of its water mains (6,800 miles of the total 7,600 miles) exceeding the AWWA recommended service-life. While most water main breaks are barely noticed, others are very significant and the city does not have a KPI quantifying how disruptive one break might be over another.

Here, we introduce two areas within Denver, Colorado that we plan on developing as case studies to illustrate HOWL. Site 1 is near the corner of West 29th Street and Zuni Street where on January 28th, 2017, a 130-year-old, 24” diameter water main broke a short-distance from where the main broke the previous year. To add to the frustration of this one neighborhood, the same location suffered yet a third break on July 5th, 2017. These breaks resulted in flooded basements, closed streets, and closed highway lanes. Downstream and across an interstate highway, a parking lot and complete lower level of a commercial building was flooded in chest-deep water. Finally, after three consecutive breaks at the same location, this segment of main was completely replaced. The disruption and costs experienced by the residents, businesses, and repurposed city personnel have not been quantified – these are indirect costs from the utility’s perspective. Site 2 is located near the massively busy intersection of Colorado Blvd and Mississippi where a water main break occurred on August 8th, 2019 and shut down the road for several hours during weekday commuting. Another water main break occurred near the same location on August 29th, 2019. These breaks were preceded by events in January 2019 and January 2016 at the same location that shut down Colorado Blvd for more than 24 hours. The approach to determining whether these sites are ‘disruptive’ and what indirect costs were paid are the topics covered in Parts 2 and 3 of this blog series.

Conclusion Part 1

The inaccessibility of RABID has led to deferred maintenance that is the cause of the decaying infrastructure issues most cities currently face (see this link for the reasons we prefer the term ‘decay’ while other associations use ‘aging’). On one hand, the message from the ASCE is very clear – aging infrastructure is plaguing our cities. The ASCE has consistently made the recommendation in the Report Card, that

“…Americans must be willing to pay, rates and fees that reflect the true cost of using, maintaining, and improving all infrastructure…”.

The problem has always been calculating, and explaining, what the ‘true cost’ is and why individual citizens should care. On the other hand, utilities are not communicating system age, despite the unambiguous warning from the same association that issues the best practice of 15 breaks/100 miles of main/year – the AWWA:

"…aging water mains are subject to more frequent breaks and other failures that can threaten public health and safety (such as compromising tap water quality and fire-fighting flows). Buried infrastructure failures also may impose significant damages (for example, through flooding and sinkholes), are costly to repair, disrupt businesses and residential communities, and waste precious water resources. These maladies weaken our economy and undermine our quality of life."

We conclude this blog in Parts 2 and 3 with specific steps for cities to determine what areas should not be disturbed by road closures due to maintenance, repair, operations, and failures (MROF) and what ‘true costs’ are already being paid by utility end-users in the city.

Parts to this blog series:


[1] This blog is not intended to weigh in on the economics of rehabilitating infrastructure to extend the remaining useful life. Rather, the point being made is the outcome from a city perspective when failed infrastructure is simply repaired vs replaced.

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