Applications of Life-Cycle Cost Analysis in Water and Wastewater Projects: Lessons from European Experience - Governing the Nexus: Water, Soil and Waste Resources Considering Global Change - page 134

Fig. 6 Inspection costs of alternative investment-strategies. Source City of D ü sseldorf ( 2013 ,

p. 16), amended

(a) (b)

50
45
40
35

30

25
20
15
10
5
0

Lengths of sewer
Share (cumulated)

1880 1890 1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010

Year of construction

Fig. 7 a Age structure of sewage main network of a German city ( (figure on the left ). b Survival
curves for types of water mains ( (figure on the right ). Source a City of D ü sseldorf; b Herz and

Lipkow ( 2002 )

running economic depreciation curves (Herz 1996 ). With increasing planning
horizons and heterogeneity of networks, the insecurity of assumptions is increasing
and consequently the validity of results.
Long-term strategies for maintaining networks usually serve merely the principal
strategic alignment while the operative planning is principally based on technical
criteria. These day-to-day decisions impact only a few years; therefore life cycle
considerations only play a minor role.