Introduction - Pattern Recognition for Reliability Assessment of Water Distribution Networks - page 5

the water supply system of Sana'a, the capital of the Republic of Yemen, was once in every
two days. Some 20 years later, not much has changed in either of the places!

1.4 AIM OF THE STUDY

Water distribution network reliability has become an important issue emerging from
increased perception of water as economic goods, which forces water supply companies to
start managing their systems in more efficient manner. As a result, the customers'
expectations have grown substantially and water companies are confronted with situations
where they have to guarantee service levels with higher degree of confidence. To achieve this
objective, water experts have at their disposal a number of methods and a range of powerful
network modelling software that can run without much of limitations. Despite all these
advances, no universally accepted approach in defining and assessing water distribution
reliability exists in this moment. It is, above all, the complexity caused by interactions
between numerous factors that influence the service level, technical as well as managerial,
which make it difficult to address the reliability issues.

The study presented in this manuscript aims to investigate the patterns that can be possibly
used for reliability assessment of water distribution networks, focusing (1) to the node
connectivity, (2) hydraulic performance and energy balance, and (3) economics of network
construction, operation and maintenance assessed from the perspective of reliability. The
conducted research has been driven by the fact that the reliability is affected by particular
choices in all of these aspects.

Furthermore, a number of reliability measures to evaluate network resilience has been
developed and assessed to arrive at more accurate and complete diagnostics of network
performance in regular and irregular scenarios. These measures have been proposed as a part
of the methodology for snap-shot assessment of reliability based on the network
configuration and hydraulic performance. Moreover, the network diagnostics has been
developed to compare the costs of reliability increase with the consequent lowering of the
calamity impact i.e. the costs of the damage. The optimal reliability is therefore the one
achieved with the most effective investment into reconstruction and/or operation of the
network to minimize the failures and customer complaints.

Practical outcome of the research is the decision support tool for reliability-based design of
water distribution networks. This computer package named NEDRA ( NE twork D esign and
R eliability A ssessment) consists of the modules for network generation, filtering,
initialisation, optimisation, diagnostics and cost calculation, which can be used for sensitivity
analyses of single network layout or assessments of multiple layouts.

1.5 STRUCTURE OF THE THESIS

The manuscript consists of total ten chapters, seven of which are presenting the results of
particular research segments:
- Chapter 3, which deals with pressure-driven demand calculations applied to arrive at

demand calculations under stress conditions.

- Chapter 4, which explains the algorithm of network generation tool used for statistical

analyses of network patterns, and eventually as module of NEDRA decision support tool.