Hydraulic Reliability Diagram and Network Buffer Index as Indicators of Water Distribution Network Resilience - Pattern Recognition for Reliability Assessment of Water Distribution Networks - page 123

5.8 CASE: WATER DISTRIBUTION NETWORK AMSTERDAM NORTH

To demonstrate the concept on a real case network, the HRD diagram and the corresponding
NBI have been determined for the portion of water distribution network of the city of
Amsterdam, NL, shown in Figure 5.23.

Figure 5.23 Network of Amsterdam North (Courtesy: Waternet, Amsterdam)

The constructed EPANET model consists of 4552 nodes and 5044 pipes and the connection
to the rest of the network is simulated by two dummy reservoirs at fixed heads of 25 msl (on
the left side) and 21 msl (on the right side). The colours in the figure depict the hydraulic
performance of the network for snapshot simulation at the demand of 468 l/s. Most of the
pressures under normal operating conditions fall within the range of 15 to 25 mwc, with two
nodes below the PDD threshold pressure of 15 mwc (13.83 and 12.30 mwc, which is the
lowest pressure in the network, in the node connected to the right dummy reservoir). The pipe
flows are relatively low; quite some pipes have the flow rate below 1.0 l/s suggesting quite
oversized i.e. over-connected network. This is confirmed looking at the corresponding HRD
shown in Figure 5.24.

Therefore, the failure of the majority of pipes shows no loss of demand, whatsoever. The NBI
for this network has been calculated at 0.970. The average ADF for the network equals
0.9996, which indicates a highly reliable network but is in fact the result influenced by huge
amount of pipes conveying mostly small flows in a network of nearly 500 loops. The value of
ADF min is 0.761 with only 28 pipes causing the loss of demand in the network above 1 %.
Seven pipes of diameter 762 to 800 mm, connected in series in total length of 429 m create
the ADF min after any of them fails. Hence, the network is over-designed, actually. At the same
time, the calculation of resilience indices, I r , and I n , will yield the values of 0.605 and 0.560,
respectively, which is not an order of value immediately suggesting a high reliability.