Chapter 3 Decision Support Model (IUWS-DSM) - Tubdok

76 New Conception and Decision Support Model for IUWS
case of pipes retrofitting, besides using Eq. (7) or Eq. (9), the coefficients can be applied to
the costs between replacement and new construction. For example, Burnside 2005 applied
the factor of 0,75 to the replacement cost curves for new construction situations.
Cost
= a + b ⋅ D
c
+ d ⋅ H
e
+ f ⋅
( D ⋅ H)
where: Cost – average cost, local currency
D – diameter of pipe, mm
H – depth of excavation, m
( Clark
et al., 2002)
a, b, c, d, e, f – coefficient, - (estimated using regression techniques)
Besides mathematical functions, the certain cost tables can also be used. Pipes have
numerous different diameters. In such situation, the single cost function may not contently
represent all conditions, so the cost tables are adopted. Table 32 gives a blank sheet of
average pipe costs as a pattern. The frost line has the notable impacts on the exaction depth,
especially to the small-diameter pipes. Thus, the condition of frost may be included.
Table 32: Sheet of average pipe costs based on pipe diameters (as pattern)
no. pipe
diameter
[mm]
1 < 150
2 150 – 250
3 250 – 400
4 400 – 500
5 500 – 600
6 600 – 800
... ...
... 2500 – 3000
costs [m.u./m] (new)
frost non-frost
distribution transm. distribution transm.
Abbreviations: m.u. – monetary unit; transm. – transmission
( 9)
costs
[m.u./m]
(retrofit)
Pipe material is another key factor influencing the pipe costs. As comparing and selecting
pipe materials are not the focusing point of the IUWS-DSM, the most common pipe materials
are used, and they keep the same in all system alternatives.
If the geological conditions need to be involved, the additional cost can be added or
specific coefficient can be used. For example, Burnside (2005) adds the additional allowance
for rock conditions.
As to population densities, intuitively it directly affects the sizes of pipe systems. Nevertheless,
after surveying 3895 medium and large sizes of water systems, USEPA (2006)
found that population density has no significant improvement to the simpler cost model