for leak/burst event detection than pressure signals. In view of this, it is envisaged
that future optimal sensor placement studies should focus on simultaneously considering the possibility of detecting and, most importantly, localising leaks/bursts. In
this scenario, flow measurements (usually available at the inlet of DMAs already)
can be used first to determine detection, and the pressure instruments can then be
used to determine location in addition to provide further confidence in the detection
alarms (see – e.g. [16]) and to provide information useful for root-cause identification (e.g. a flow increase and a simultaneous pressure decrease can indicate a leak/
burst in a DMA, whereas a simultaneous flow and pressure increase can indicate a
different issue such as a pressure reducing valve failure).
With regard to the problem formulation and with specific focus on the use of
hydraulic simulation packages, it is possible to state that using hydraulic models to
simulate a large number of leak/burst scenarios and then (somehow) analysing the
differences between the simulated pressures under leak/burst conditions and the
simulated pressures recorded under normal conditions are common practices
among researchers and, possibly, the only way forward. Methods that have
attempted to avoid using hydraulic models such as the structural model-based
approach proposed by Sarrate et al. [42, 44] have intrinsic limitations (see Sect. 2)
that make their use difficult for effectively solving the optimal sensor placement for
leak/burst detection and localisation problem. Therefore, it is clear that numerical
models are instrumental to the future of cost-effective monitoring of WDSs for leak/
burst detection and localisation purposes. Unfortunately, the numerous sources of
uncertainty associated with such an approach remain a key concern. Temporarily
ignoring these issues here together with issues related to increasing the complexity of
the problem formulation (and, hence, the computational burden), as they will be
discussed in further detail below, it is envisaged that more realistic modelling
practices should be taken into consideration during the development of optimal
sensor placement methodologies in the future. For example, it may be beneficial to
use pressure-driven modelling rather than demand-driven modelling as leaks and
bursts may induce pressure-deficient conditions in a network under certain circumstances. Additionally, better leak/burst localisation performance may be achieved by
more realistically simulating leaks and bursts, which may occur at any point along
the pipe (and not at nodes, as commonly done) and start at any time during the day.
With specific focus on the analysis of the differences between the simulated
pressures under leak/burst conditions and the simulated pressures recorded under
normal conditions, it is possible to observe that the development of different
approaches for performing this particular task has attracted the attention of a large
number of researchers. Generally speaking, binarisation of the residuals/sensitivity
matrix (e.g. [11, 30, 31, 49]) has been recognised as leading to a loss of information
[38]; therefore methods that make full use of the hydraulic simulation results
(e.g. [39, 63, 73, 75, 78]) should be preferred. Many of the latter methods have
been developed with the aim of addressing issues related to model, measurements
and leak/burst size uncertainties, and they are very valuable for future research. The
main findings from these studies have shown that different operating point scenarios
and demand uncertainties may significantly affect the performance of “optimal”
Review of Techniques for Optimal Placement of Pressure and Flow Sensors. . .
51
that future optimal sensor placement studies should focus on simultaneously considering the possibility of detecting and, most importantly, localising leaks/bursts. In
this scenario, flow measurements (usually available at the inlet of DMAs already)
can be used first to determine detection, and the pressure instruments can then be
used to determine location in addition to provide further confidence in the detection
alarms (see – e.g. [16]) and to provide information useful for root-cause identification (e.g. a flow increase and a simultaneous pressure decrease can indicate a leak/
burst in a DMA, whereas a simultaneous flow and pressure increase can indicate a
different issue such as a pressure reducing valve failure).
With regard to the problem formulation and with specific focus on the use of
hydraulic simulation packages, it is possible to state that using hydraulic models to
simulate a large number of leak/burst scenarios and then (somehow) analysing the
differences between the simulated pressures under leak/burst conditions and the
simulated pressures recorded under normal conditions are common practices
among researchers and, possibly, the only way forward. Methods that have
attempted to avoid using hydraulic models such as the structural model-based
approach proposed by Sarrate et al. [42, 44] have intrinsic limitations (see Sect. 2)
that make their use difficult for effectively solving the optimal sensor placement for
leak/burst detection and localisation problem. Therefore, it is clear that numerical
models are instrumental to the future of cost-effective monitoring of WDSs for leak/
burst detection and localisation purposes. Unfortunately, the numerous sources of
uncertainty associated with such an approach remain a key concern. Temporarily
ignoring these issues here together with issues related to increasing the complexity of
the problem formulation (and, hence, the computational burden), as they will be
discussed in further detail below, it is envisaged that more realistic modelling
practices should be taken into consideration during the development of optimal
sensor placement methodologies in the future. For example, it may be beneficial to
use pressure-driven modelling rather than demand-driven modelling as leaks and
bursts may induce pressure-deficient conditions in a network under certain circumstances. Additionally, better leak/burst localisation performance may be achieved by
more realistically simulating leaks and bursts, which may occur at any point along
the pipe (and not at nodes, as commonly done) and start at any time during the day.
With specific focus on the analysis of the differences between the simulated
pressures under leak/burst conditions and the simulated pressures recorded under
normal conditions, it is possible to observe that the development of different
approaches for performing this particular task has attracted the attention of a large
number of researchers. Generally speaking, binarisation of the residuals/sensitivity
matrix (e.g. [11, 30, 31, 49]) has been recognised as leading to a loss of information
[38]; therefore methods that make full use of the hydraulic simulation results
(e.g. [39, 63, 73, 75, 78]) should be preferred. Many of the latter methods have
been developed with the aim of addressing issues related to model, measurements
and leak/burst size uncertainties, and they are very valuable for future research. The
main findings from these studies have shown that different operating point scenarios
and demand uncertainties may significantly affect the performance of “optimal”
Review of Techniques for Optimal Placement of Pressure and Flow Sensors. . .
51