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

Chapter 3 · Decision Support Model (IUWS-DSM) 75
Above all, all cost functions and sheets are country or region based. Unless two countries
have very similar conditions, including economic, social and government aspects, the
individual cost functions and sheets should be generated based on the local statistics.
3.4.2.2 intake and treatment facilities
Concerning the IUWS-DSM, as discussed in § 2.1.4.2, the treatment facilities of both raw
water and sewage in are categorised into certain steps. The cost functions can therefore set
up for each step. A blank sheet is set up in Table 31 as the pattern. If the cost functions are
unavailable and the project data are inadequate, it is suggested to use the Stage2 of raw
water treatment and Grade2 of used water as the base, where the costs of other steps are
obtained by multiplying the coefficients with the base. Thereby, the relative costs can be
obtained and compared.
In order to more precisely represent the reality, certain ranges of system sizes are often
established and each range has its specialised cost functions. Consulting USEPA (1979a)
and USEPA (1979b), two levels are suggested and taken for the IUWS-DSM (Table 31).
Table 31: Table of cost functions (or coefficients) for different treatment steps (as pattern)
level range [m 3 /d] Stage1 Stage2 Stage3 Stage4
1 < 4.000
2 > 4.000
level range [m 3 /d] Grade1 Grade2 Grade3 Grade4 Grade5
1 < 4.000
2 > 4.000
The construction cost of intake facilities is various that depends every much on the actual
conditions. It can be also rough estimated as the portion of the total waterworks cost.
Reliable intake systems may represent as much as 20% of the total investment of the water
treatment plant (AWWA & ASCE 1998).
As introduced above, several methods are available to estimated O&M costs. The
individual cost functions can be generated. The O&M costs can also be lumped together with
the construction cost, or estimated as the portion of construction cost.
3.4.2.3 conveying system
In urban area, the underground pipes are mostly used. Hence, two critical parameters are
usually taken into account for cost calculation, i.e. the pipe diameter and the excavation
depth, whereby the cost function of Eq. (9) is often used. If only pipe diameter is considered,
Eq. (7) is used. Ong (1988) summarised the empirical cost functions of sewer, which all are
the nonlinear functions of pipe diameters and the excavation depth is not always considered.
Using Eq. (9), Clark et al. (2002) generate the cost functions for each step of pipe
construction, such as trenching and excavation, backfill and compaction, etc. The IUWS-
DSM suggests using the single function representing all construction cost of pipes. In the