Theoretical and Conceptual Framework - Pattern Recognition for Reliability Assessment of Water Distribution Networks - page 30

It has been assumed that the answers to the above questions can throw more light to the
choice between the range of operational and investment measures to improve the network
reliability. Secondly, in terms of the tool development, the conclusions should help while
analysing to which extent the irregular supply conditions can be modelled by expanding the
existing algorithms or actually transforming them into more effective ones. This issue is
specifically relevant having in mind the huge models nowadays built with the information
derived from GIS databases, which require algorithms that shall be robust enough and will
not increase the calculation times significantly.

2.7.2 Research Hypotheses

Based on the above research questions, the following research hypotheses have been tested in
this research:
1. For a given topography, network layout and demand scenario, there is a unique
reliability/resilience footprint that can be described as a function of ADF. This footprint
reflects the network buffer.
2. Reliability measures derived using demand-driven hydraulic models are less accurate than
those derived by the use of pressure-driven demand models.
3. Increasing the connectivity between the pipes improves network reliability in general. For
a given supply scheme, there is an optimal network geometry that can be described by a
'shape index', which can be correlated to other reliability measures.
4. It is possible to make a quick reliability snapshot of a network by looking at typical
hydraulic indicators. There is a clear implication from the interrelation between the
pressures, flows/velocities and network resistance, namely:
4.1. The networks with generally higher pressures, despite potential for increased
leakage, have more of a buffer to maintain the minimum service level during a single
event of the component failure.
4.2. The reliability is disproportional to the increase of the system resistance i.e. hydraulic
loss.
5. The most economic design shall always be cheaper than the most reliable design. There is
a threshold velocity and/or network resistance that can be taken as a border between the
increase of investment- or operational costs, resulting in the most effective reliability
improvement.

In summary, it can be assumed that for chosen supply scheme, network configuration,
demand scenario, and adopted preventive and reactive maintenance, it is possible to predict
an event of single component failure that will not affect the guaranteed minimum service
under irregular supply conditions.

2.8 RESEARCH METHODOLOGY

This research, compiled of the elements related to the hydraulic performance of water
distribution systems, economics of operation, maintenance and renovation of these systems,
and computer programming, is presented as an omnibus of the topics formulated from the
research hypotheses. Brought together, the outcome of the analyses of those hypotheses has
served to design a decision support tool (DST) for reliability-based design of water
distribution networks.