Theoretical and Conceptual Framework - Pattern Recognition for Reliability Assessment of Water Distribution Networks - page 19

The method is illustrated on a simple system of two loops, shown in Figure 2.4 (Trifunović
and Umar, 2003). The data about the nodes and pipes are given in Tables 2.4 and 2.5,
respectively. An arbitrary demand pattern with the morning- and afternoon peaks has been
applied.

Table 2.5 Case network: pipe properties

Pipe Diameter Length Roughness Burst rate 1) Burst frequency

km -1 yr -1

mm m mm year/burst

1
2
3
4
5
6
7
8

200
200
200
150
100
100
100
150

300
300
300
400
300
300
400
400

0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.5

0.71
0.71
0.71
1.04
1.04
1.04
1.04
1.04

4.69
4.69
4.69
2.40
3.21
3.21
2.40
2.40

1) Assumed based on Gupta & Bhave (1994)

The pumping station at the source consists of two units with following characteristics:
1. P1 - duty head = 25 mwc, duty flow = 40 l/s (operated constantly).
2. P2 - duty head = 40 mwc, duty flow = 40 l/s (operated during peak supply).

Operation of the system should have met the following requirements:
- The threshold pressure of 20 mwc.

- Additionally, node 6 must keep minimum 30 mwc during the maximum peak hour.

Assuming that only the corrective maintenance is applied, Table 2.6 displays the information
about the pipe availabilities based on the information from Table 2.5 and applying Equation
2.6. The average repair time of two days has been adopted for each burst.

Table 2.6 Case network: pipe availability

Pipe Burst rate CMT A j U j

yr -1 days/year

1
2
3
4
5
6
7
8

0.213
0.213
0.213
0.416
0.312
0.312
0.416
0.416

0.426
0.426
0.426
0.832
0.624
0.624
0.832
0.832

0.9988
0.9988
0.9988
0.9977
0.9983
0.9983
0.9977
0.9977

0.0012
0.0012
0.0012
0.0023
0.0017
0.0017
0.0023
0.0023

Nine simulation runs have been conducted using EPANET software, one with the complete
system and eight by disconnecting each of the pipes, one at a time. Based on the pressure
variation in the system, the nodal reliabilities were calculated by Equation 2.9; these results
are shown in Table 2.7. The figures in bold demonstrate the principle: with all pipes
available, the pressure in node n4 is above the threshold during 14 out of 24 hours, whereas
the calculation with pipe 3 closed shows the sufficient pressure in this node during seven
hours, only. Hence, R 43 = 14/24 = 0.5833, R 4 = 7/24 = 0.2917 and RE ij = 0.5833 x 0.9988 +