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

Chapter 3 · Decision Support Model (IUWS-DSM) 55
The water demand of UD is the summation of the demands of its WUU. Since one UD
contains a number of WUU and each WUU can have several possible water demands, the
water demand of UD can be many possibilities due to the combination. As explicated in
2.2.1.3, the simplication is taken in order to reduce the variations, whereby only the same
water usage scenarios are summed, e.g. scenario 1 of all WUUs in the same UD are
summed as scenario 1 of water usage for the UD. The water usage of CA is carried out in
the same ways but with the summation of its UD. Such kind of summation represents the
extreme situations covering the range where other possibilities fall into. As the planning tool
for the early phase of projects, such simplification is appropriate as it generates suitable
solutions but dramatically reduce the calculation work.
UD can have individual water sources, but with the second priority. It means in normal
situation the water supplied from CA is considered for UD in the first. Only when the source
water from CA has either quantity shortage or quality issues, the local water sources in UD
will be taken into account. In CA, local water sources are always considered firstly, where
external sources have lower priorities. More detailed decision making mechanism and rules
for water source selection are given in § 3.3.1.
Though having redundant water sources result in a more secure supply system, it causes
also a more complicated and expensive system. Initially it is not in the concern of this model,
and it keeps open for planners to consider redundant water sources in their systems.
The methods for determining the sizes of WIS are described in § 3.4.1. The methods for
estimating system costs and evaluating energy consumption are introduced and discussed in
§ 3.4.2 and § 3.4.3. The comparison methods are explicated in § 3.5.
3.3 Decision making policies
If there is more than one option, the decision has to be made. Following the design
procedure and based on the subsystem options, a flowchart is developed, whereby the
positions for making decisions are clearly revealed (Figure 27). Three blocks are built up
from top to bottom in Figure 27. The first block water usage & sources just represents Stage
One of the planning procedure shown in Figure 25. The third bock subsystem options &
applicability summarises the information from Table 8, Table 9, Table 10, Table 11, Table 12
and Table 13, which determines the WIS that is calculated in Stage Two. The second block
decision making positions that connects two parts is just the critical place where the proper
dicisions have to be made, which are identified as follows:
1. selection of water sources,
2. supply methods of desired water,
3. collection and transport methods of used water and rainwater,
4. utilisation methods of used water,
5. utilisation methods of rainwater.
The corresponding decision making policies are thereby developed.