Environmental Engineering Reference
In-Depth Information
- The increase of pipe capacity as a means to improve the reliability has limited effect.
From some point it makes no sense to apply this measure further apart from the fact that it
inflicts possible water quality problems in the network, due to low velocities/water
stagnation. The values of NBI evaluate this moment more rigorously that the values of I n .
- Consequently, the most economic design is not necessarily the least reliable.
Similar diagrams for network options B are shown in Figures 8.26 and 8.27. Figure 8.26
shows the situation of the slope-up topography (U) of low altitude range (L) using high
investment/high operation cost scenario (HH) on the left, and high altitude range (H) using
low investment/low operation cost scenario (LL) on the right. Figure 8.27 shows the same
situation if the network is located in a slope-down terrain (D).
Investment
O&M
Toral Cost
NBI
In
Investment
O&M
Total Cost
NBI
In
1,800,000
0.90
1,800,000
0.90
1,600,000
0.80
1,600,000
0.80
1,400,000
0.70
1,400,000
0.70
1,200,000
0.60
1,200,000
0.60
1,000,000
0.50
1,000,000
0.50
800,000
0.40
800,000
0.40
600,000
0.30
600,000
0.30
400,000
0.20
400,000
0.20
200,000
0.10
200,000
0.10
-
0.00
-
0.00
-
1,000
2,000
3,000
4,000
5,000
6,000
7,000
8,000
9,000
10,000
-
1,000
2,000
3,000
4,000
5,000
6,000
7,000
8,000
9,000
10,000
Network Volume m 3
Network Volume m 3
Figure 8.26 Annual costs (US$) and reliability for 21 scenario of network B/U: left - L/HH, right - H/LL
Investment
O&M
Total Cost
NBI
In
Investment
O&M
Total Cost
NBI
In
1,800,000
0.90
1,800,000
0.90
1,600,000
0.80
1,600,000
0.80
1,400,000
0.70
1,400,000
0.70
1,200,000
0.60
1,200,000
0.60
1,000,000
0.50
1,000,000
0.50
800,000
0.40
800,000
0.40
600,000
0.30
600,000
0.30
400,000
0.20
400,000
0.20
200,000
0.10
200,000
0.10
-
0.00
-
0.00
0
2000
4000
6000
8000
10000
12000
14000
0
2000
4000
6000
8000
10000
12000
Netork Volume m 3
Network Volume m 3
Figure 8.27 Annual costs (US$) and reliability for 21 scenario of network B/D: left - L/HH, right - H/LL
The results in Figures 8.26 and 8.27 support the conclusions drawn from the analysis of the
results in Figures 8.24 and 8.25. Not surprisingly, the impact of investment costs becomes
even more dominant compared to the O&M costs, both in the HH- and LL cost options. The
reduced pumping in network options B , compared to A , is the reason for such an outcome.
There have been total 120 diagrams like in the above figures, coming out of the analysis, and
they all support the above conclusions, more or less. Figures 8.28 to 8.30 show the
correlations of all four cost options with the values of NBI calculated for 21 design scenarios
analysed in different supply and terrain configurations, and classified for three altitude
ranges. All diagrams show clearly that:
- the pipe capacity i.e. the pipe investment cost is the driving factor for network reliability,
- the tank in the B -networks has positive effect on the network reliability (when it operates
properly in combination with pumping station), as well as it reduces the total annual cost.
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