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

Chapter 2 · New Conception 39
flush of roof-water (mainly for removing sediments and debris on roofs), roof-water can easily
reach very good water quality through simple treatment. Due to limited area, roof-water
utilisation systems have generally small scales and only serve the local end-users. In the
hierarchy of the IUWS, roof-water utilisation is considered for WUU and WUC. Since it
provides a good water quality, it is mostly supplied to the indoor water uses.
2.2.5.2 planning process
First of all, the local rainfall patterns should be identified, which are the preconditions for
determining the rainwater system. If the storm drain is compulsory or roof-water is adequate
and suitable for utilisation, then the following planning processes come into action. As two
independent and parallel rainwater systems, two general planning processes are developed
(Figure 21). The corresponding options are listed in Table 12 and Table 13.
Process for Planning Rainwater System
subsystem 5
Rainwater
Surface runoff
management
Roof-water
utilisation
Collection
combined
sewerage
separate
sewerage
no need
Outflow quality
B /
C (raw)
A(1)
step 1
step 1
Storage
no
yes
Collection
yes
Receptor
superior
level drain
local
water body
local
water body
step 2
Treatment
yes
step 2
Treatment
no
yes
Distribution
yes
step 3
Figure 21: Process for planning rainwater system
Infiltration
facility
For surface runoff management, firstly the type of the sewerage system is decided, i.e.
combined or separate. According to the actual situation, the storage (e.g. impoundments) is
determined afterwards. Then the dealing methods are selected, whereby water receptors
and related facilities are decided. The applicability of system options based on the types of
water entities is given on the right side of Table 12. Likewise, WUC is excluded from surface
runoff management.
In the case of groundwater recharge, if combined sewerage is used or the water quality
of surface runoff does not meet the relevant standards, certain treatment is obligatory for
protecting the groundwater. The groundwater recharge is suggested applying to UD and then
CA in consideration of the system sizes. If no additional treatment is needed, groundwater
no
yes