Decision Support Tool for Design and Reliability Assessment of Water Distribution Networks - Pattern Recognition for Reliability Assessment of Water Distribution Networks - page 246

9.3.6 Available Demand Fraction and Coverage

The network diagnostics module establishes the values of available demand fraction based on
the results of PDD simulations for consecutive failure of links, one at a time. This includes
pumps and valves, except those in initially closed status. The drop of demand will be
compared with the full demand i.e. the one calculated in DD mode. This means that the
demand drop from the low pressures in PDD mode, caused by low supplying heads despite
all links being functional, will also be considered as an irregular situation.

In the single network menu option, the ADF can be displayed for all the pipes, while for the
multiple network simulations two values will be shown: the average one and the one for the
most critical pipe failure, causing the lowest ADF . Next to that, the nodal ADF will be
divided into ten categories, at the increments of 10%, displaying the number of nodes within
each category, as well as the percentage of total original demand affected with the failure.
This analysis, done for the worst case pipe failure, will depict the spatial distribution of
demand loss in the first case, and its severity, in the second case. Based on these results, it
becomes more clear whether the calamity affects large or low number of nodes, and if it has
happened to moderate or severe extent.

9.3.7 Economic Considerations

Economic considerations in the network diagnostics module are founded on the engineering
economy concepts discussed in Chapter 8. Based on the selected loan conditions and
inflation, the investment costs will include the annuities, while the operational costs will
include the actual energy consumption in case of pumping used for water conveyance; this is
done from the results of PDD simulations. The pipe costs are calculated for actual length and
diameter, while the investment costs into the pumps and storage are based on the storage
volume and maximum installed capacity of pumping stations. For the time being, there is no
automatic link between the pipe costs used in the network diagnostics module and the GA
optimiser (which is also the case with PDD threshold pressure). These values therefore have
to be synchronised manually during the analyses. Logically, all the figures will be shown for
the entire network, and all the networks listed in the EPAinpfiles.txt file.

9.4 CASE STUDY

NEDRA has been illustrated on a synthetic case of a reservoir and 50 demand nodes. The
location of the source and the nodes prepared in EPANET is shown in Figure 9.4a showing
the nodal elevations (in msl), and 9.4b showing the baseline demands (in l/s).

The case reflects a gravity supply situation on a terrain descending from the reservoir for
some 45 m. The total demand of 305 l/s is distributed over relatively wide area within the
distance to the most faraway node of roughly 16 km, calculated based on the nodal
coordinates. The head of the reservoir is 50 msl.

The network generation has taken place in various configurations settings, both in random
and non-random mode. Total 13,000 networks have been generated.