**7. Long-term balanced design - carrying urban water systems into the future**

As explained before, the performance of individual components is only relevant inasmuch as it contributes to system performance. Some components will have more impact on the system than others, and the behavior of such systems is usually quite complex, giving rise in the last decades to a whole field of expertise devoted to developing and using network anal‐ ysis models, among the most advanced and useful tools in engineering.

From the viewpoint of infrastructure asset management, the notions of "system design", "preventive maintenance" and "system rehabilitation" should be seen fundamentally as part of the same long-term balanced design process.

Even in those parts of the world where service coverage has reached its effective limit, and designing new systems or system extensions appears to be a thing of the past, it must be realized that design skills and experience are just as needed in carrying present-day systems into the future as they once were in creating the first outlines.

Essentially, investing in a system over a period of time should maximize the performancerisk-cost balance while transforming the system into its ideal for the next 20 or 30 years: that which best serves the strategic objectives defined for the infrastructure as a whole, as ex‐ plained previously.

If at a strategic IAM level it is common to try to balance conflicting objectives (e.g., im‐ proving the environmental sustainability and reducing costs to ensure economic sustaina‐ bility), at the tactical and operational level, which must be aligned with the former, that is also the nature of the problem: e.g., water supply reliability is commonly achieved through pipeline redundancy, which often causes reduced flow velocities and potentiates water quality issues.

On the other hand, analyzing over long periods of time must account for what is usually a changing context: societal values and expectations evolve; regulations become more de‐ manding; technologies improve; urban areas progress; the climate and the environment fluctuate and change; natural resources become scarcer.

with the planning horizon, will be included in the tactical plan. The plan must make allow‐

The detailed diagnosis and the design and analysis of infrastructural and operational in‐ tervention alternatives are not trivial tasks and often require the use of sophisticated mod‐ eling tools. This is where the more advanced research efforts have been centered, such as mentioned in section 2 (e.g. Skipworth *et al*., 2002; Sægrov ed., 2005; Sægrov ed., 2006;

The last stages of tactical planning are the implementation, monitoring and periodic review of the plan. Implementation is materialized via operational management. Monitoring and reviewing are critical for the continuous improvement process. It is recommended that the tactical plan defines their modes, responsibilities and periodicity. Operational IAM planning

**7. Long-term balanced design - carrying urban water systems into the**

As explained before, the performance of individual components is only relevant inasmuch as it contributes to system performance. Some components will have more impact on the system than others, and the behavior of such systems is usually quite complex, giving rise in the last decades to a whole field of expertise devoted to developing and using network anal‐

From the viewpoint of infrastructure asset management, the notions of "system design", "preventive maintenance" and "system rehabilitation" should be seen fundamentally as part

Even in those parts of the world where service coverage has reached its effective limit, and designing new systems or system extensions appears to be a thing of the past, it must be realized that design skills and experience are just as needed in carrying present-day systems

Essentially, investing in a system over a period of time should maximize the performancerisk-cost balance while transforming the system into its ideal for the next 20 or 30 years: that which best serves the strategic objectives defined for the infrastructure as a whole, as ex‐

If at a strategic IAM level it is common to try to balance conflicting objectives (e.g., im‐ proving the environmental sustainability and reducing costs to ensure economic sustaina‐ bility), at the tactical and operational level, which must be aligned with the former, that is also the nature of the problem: e.g., water supply reliability is commonly achieved through pipeline redundancy, which often causes reduced flow velocities and potentiates

Malm *et al*., 2012; Renaud *et al*., 2011; Alegre and Almeida ed., 2009).

aims at implementing the interventions selected in the tactical level.

ysis models, among the most advanced and useful tools in engineering.

of the same long-term balanced design process.

into the future as they once were in creating the first outlines.

ance for the resources needed to implement it.

60 Water Supply System Analysis - Selected Topics

**future**

plained previously.

water quality issues.

The current emphasis on water-energy efficiency is driven by most of the above factors of change. However, old paradigms are broadly accepted without being questioned. For in‐ stance, drinking water networks are still designed in most developed countries to re‐ spond to fire flows. Is this the most rational approach? In the Netherlands, for instance, this paradigm is changing. Smaller diameter networks are not only less expensive but al‐ so generally behave better in terms of water quality. Firefighting is ensured from a basic trunk main grid. If paradigm shifts occur, rehabilitation interventions need to take them into account.

The fact that most water systems are far from ideal today is a consequence of a growth proc‐ ess that has been forced to react to that changing context over the decades. Most mature sys‐ tems today are not exactly what they would be if we were to start with a clean slate. Yet, it is common to see preventive maintenance or rehabilitation strategies centered on replacing the pipes with a higher risk of failure with new pipes of the same size. Would it not make sense to try to project the best possible system for a given time horizon – 20, 30 years – and use those very same opportunities of intervention to make the present day system gradually morph into that better design?

The fact is that there are many cases when the water networks are adequately and efficiently designed and operated, meeting the hydraulic, water quality and energy targets for the present and for the expected future demands. In these cases, the key driver for rehabilitation is indeed the risk of pipe failure, usually assessed through the combination of failure proba‐ bility and component importance (in terms of the consequence its failure). Much of the lead‐ ing-edge theory and practice is tailored for these situations, where the like-for-like replacement strategy fits well.

In classical terms, infrastructures used to be seen as living through a sequence of stages, from the initial design, through constructing new (or extending), operating, maintaining and rehabilitating or replacing by new again. This is indeed the typical AM approach for other types of physical assets. In mature infrastructures, however, all these stages co-exist, and designing new, extending, maintaining or rehabilitating are fundamentally parts of the same process.

The IAM framework introduced in sections 3 to 6induces essentially one approach to the problem, illustrated in Fig. 4 in very simple terms. IAM planning starts from an existing in‐ frastructure and aims at optimizing its behavior over the analysis period, enabling a pro‐ gressive improvement of the infrastructure condition and functional response. In wellmaintained mature infrastructures, this requires that the fair value at the end of the planning horizon is not lower than the initial value.

The utility adopted the objectives and assessment criteria of the regulatory system, as they were deemed adequate for their own internal strategic purposes. Operating exclusively as a retail services utility, they selected the applicable metrics and targets from the regulatory system (Table 2). Each metric is clearly defined, with units, definition, assessment rule and

Taking these objectives into account, a SWOT analysis was carried out (Table 3).

1.1 Service accessibility Physical accessibility of the service (WS, WW)

1.2. Quality of service provided to users \*Service interruptions (WS)

2.1. Economic sustainability \*Cost coverage ratio (WS, WW)

2.2. Infrastructural sustainability \*Adequacy of treatment capacity (WS)

2.3. Physical productivity of human resources \*Adequacy of human resources (WS, WW)

3.1. Efficiency of use of environmental resources \*Energy efficiency of pumping installations (WS, WW) 3.2. Efficiency in pollution prevention Sludge disposal from the treatment plants (WS, WW)

WS: water supply services; WW: wastewater services; \*adopted by the utility to assess the strategic objectives.

**Table 2.** Objectives, assessment criteria and metrics of the Portuguese regulatory system

\*Economical accessibility of the service (WS, WW)

\*Reply to written suggestions and complaints (WS, WW)

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http://dx.doi.org/10.5772/52377

63

\*Quality of supplied water (WS)

\*Flooding occurrences (WW)

\*Non-revenue water (WS)

\*Mains rehabilitation (WS) \*Mains failures (WS)

\*Sewerage rehabilitation (WW) \*Sewer collapses (WW)

\*Adequate collected wastewater disposal (WW) \* Emergency overflow discharges control (WW) Wastewater quality tests carried out (WW) Compliance with discharge parameters (WW)

Connection to the system (WS, WW)

specification of the input variables.

1. Adequacy of the service provided

2. Sustainability of the service provision

3. Environmental sustainability

**Objectives and criteria Metrics**

**Figure 4.** The long-term balanced design planning process

The drawing board on the right-hand side is initially marked out by the green vertical lines, representing the metrics for the criteria chosen to drive the analysis. A thorough diagnosis and assessment of the current system according to those metrics is carried out (represented by the first blue horizontal at the top).

The planning board is then successively populated with the best available planning alterna‐ tives (represented by the subsequent blue lines). The intersections represent the assessment of each planning alternative for each metric. The purpose of the process is to fill out the table to the extent possible.
