Identification of Critical Pipes Using a Criticality Index in Water Distribution Networks
Round 1
Reviewer 1 Report
The paper evaluates an important aspect of criticality index in water distribution network. However, there are different aspects of the paper that are of concern. The authors proposed their own way of measuring criticality index. But, there is no real data to support the success of their model. It is mainly a demonstration of a hypothetical network without any verification. The authors are claiming this to be an improvement from previous literature. However, without demonstration of real data, how can this be assessed? Some improvement of writing can be done. For example “For all the networks, the more critical pipes are likely located near the Source” – more than what? The abstract stops at explaining the methodology of the research. However, there should be a few sentences on the results and conclusions. The introduction is brief and literature review is limited. The authors are advised more relevant references. The authors are missing references on vulnerability assessment, a key component of resiliency. For example: Impacts of Water Quality on the Spatiotemporal Susceptibility of Water Distribution Systems in Clean Soil Air Water. Many references were used very superficially with only one sentence of what the study proposed. However, it doesn’t go to an extent of the outcome of this study. Anyone can propose anything, the suitability can only be examined through outcome. In the last sentence of the section 1, the authors used “well-known” to cite RI. I would advise to actually cite the paper. Well-known is a subjective term and shouldn’t be used like this. The authors mentioned about four benchmark networks. However, are these hypothetical networks or real networks. No details of them are provided. The authors used unit value of water from reference 18, which is a 2004 paper, 15 year old price? Water quality index measurement based on water age degradation is a very crude estimation. I understand combining multiple parameters are not easy. However, if one water quality parameter that represents the water quality variation, that should be residual chlorine. Most software models (EPANET) include in itself chlorine decay models. That should have been considered, in place of water age. I would advise the section 4 to be renamed as “Examples of Application” since there is no real data to verify the model. In the section 4.4, the authors compared the results with RI. However, without real data, it was not possible to demonstrate whether the proposed indexes are better than traditional RI.Author Response
Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The manuscript focuses on a common problem in water distribution systems analysis, that is, the identification of the most critical components. To this purpose, the authors introduce four indices accounting for supply shortage, economic value loss, pressure decline, and water age degradation. These indices are evaluated on four benchmark networks, for which multiple hydraulic simulations have been carried out (more specifically, the authors removed one pipe at a time and calculated the value of each index for each pipe).
In the followings, I provide my opinion on this work, focussing primarily on novelty, rationale, and experimental approach.
Novelty and rationale. My understanding from the Introduction is that the main novelty behind this work is the idea of introducing indices that provide specific information on the most vulnerable network components. This contrasts with the established approach of calculating indices that provide an assessment for the entire network. Unfortunately, the review of the state-of-the-art is rather weak: the authors provide a long, unstructured list of previous contributions, but do not clearly identify the research gaps that this work aims to address.
Experimental approach. This is—in my opinion—the weakest part of the manuscript. I have indeed the following major concerns:
- The economic index (eq. 2) depends on two very important parameters, namely the unit values of water for domestic and industrial users. These values are taken from a previous work (that apparently focussed on agricultural water management) without any reasoning or justification.
- The first and third indices (i.e., social and hydraulic) explicitly depend on the water pressure throughout the networks. Yet, the authors do not provide any information about the calculation of pressure with EPANET. Note that the default setting of EPANET builds on a demand-driven engine, which provides unreliable estimation of the pressure. In other words, a decent calculation of these indices would require (1) the use of a pressure-driven engine, and (2) a convincing explanation of the parameters used for such engine.
- The authors use a design of experiment in which “the individual pipes are closed one at a time sequentially”. In my opinion, this is a rather narrow scenario: pipes do not necessarily fail sequentially! Pipe failure can be caused by many different events—such as poor maintenance, earthquakes, pressure spikes—that could create many different conditions.
- There is no discussion (or treatment) of the hypothesis on which the experiments are built. Note that the end results would depend on many factors, such as the water demand at the nodes, the kind of user at each node (domestic vs industrial), or the length of the simulations. These factors add to the other mentioned above.
The overarching conclusions of this work are rather shallow (e.g., "Correlating the criticality with several pipe parameters, it was generally found that the pipes with large sizes and serving high-demand nodes tend to show greater criticality”). In my opinion, these indices do not add much to the existing literature on water distribution systems analysis, and their use in the manuscript is based on experiments that present several flaws.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
This paper deals with the problem of identification of critical pipes using critically indexes in water distribution networks. In particular, four different criticality indexes are proposed: Social Index, Economic index, Hydraulic index and water quality index. Four different benchmark networks are used to compute the different criticality indexes.
The topic of the paper is interesting and it is well-written in general. My main concern is about details of the computation of some variables of the defined indexes,
In particular, I do not see how EPANET can compute supplied demand at node j after an event (i.e., isolation of pipe i) and pressures in this event: i.e. $Q_{e,j}$ and $P_{e,j}$, using flow chart of Figure 1 using EPANET simulator. I could imagine that we could impose, for example, demand in nodes as normal operation and the result of the simulation could be feasible (it is possible to satisfy specified demands) or not feasible (if would be possible to satisfy specified demands). In the first case the difference of normal operation and isolation of pipe I would be in the obtained values in nodes $P_{n,j}$ and $P_{e,j}$. So, Could you specify how $Q_{e,j}$ and $P_{e,j}$ are computed?
Another variables that should be better described and specified how the can be computed are water age at node j after the event and normal water age at node j: $T_{n,j}$ and $T_{e,j}$ respectively.
On the other hand, I do not see how take into account different operating points defined for example by means of inlet flows and pressures that will correspond with different hours of the day. As water distribution networks are non-linear systems it would be nice to consider the different possible operation points. Did you consider different operating conditions in the computation of the criticality indexes?
Regarding the WDN described in Figure 2 that are used as application examples: do they correspond to real networks or know benchmarks? If yes, please provide some information and if not justify why these networks are used as case studies.
Finally, it would be nice to show at least in one of the benchmark networks the inlet flow and pressure profile to illustrate its normal operation.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The responses are reasonable enough. I approve the current version of the paper.
Reviewer 2 Report
The authors have clarified my doubts; these improvements are now reflected in the manuscript. Overall, the contribution of this study is still marginal, or insignificant, to an international audience. I will leave up to the AE to recommend the next course of action.
Reviewer 3 Report
All my comments have been satisfactorily addressed in the new version of the paper.
