RFI - Attachment 7 - Updated SWMP

3.2.5.    Rainwater Tanks
Rainwater tanks are used in stormwater management to collect and store rainwater for later use. This helps
to reduce the amount of runoff that enters stormwater drainage systems and potentially causes flooding or
other issues. The collected rainwater can be used for irrigation, flushing toilets, and other non-potable uses,
reducing the demand on municipal water supplies. Additionally, the use of rainwater tanks can improve
overall water quality by reducing the number of pollutants that enter stormwater systems. In this case, the
applicant intends to use the tank for irrigation as well as internal (flushing) use. The outdoor demand
(irrigation) has been calculated as per HLW MUSIC Modelling Guidelines as 2018:

    •    Outdoor use (Irrigation) = 500 m2 (portion to be irrigated) × 85 % (pervious ground – natural turf) ×
         0.73m (annual demand – representing outdoor use in SEQ) = 310.25 kL/year (PET-Rain) option
         applied.
    •    Indoor use (toilet flushing) = 21 (per capita internal water demand – litres per person per day) ×
         100 (students) = 0.21kL/day

The site will incorporate a 15kL rainwater tank to treat half of the roof runoff and has been designed based
on based on the demand parameters mentioned above. Table 3-5 summarises the rainwater tank
parameters used for MUSIC modelling.

                Table 3-5: Rainwater Tank Parameters used for MUSIC Modelling
                  Properties of the rainwater tank                       15kL Rainwater Tank
                  Low Flow By-pass                                               0.0
                  High Flow By-pass                                             100
                  Number of Tanks                                                1

                  Volume below overflow pipe (kL)                                15


                  Depth above overflow (meters)                                 0.20

                  Surface Area (square meters)                                   7.5

                  Initial Volume (kL)                                            15


                  Overflow Pipe Diameter (mm)                                    65

                  Exfiltration Rate (mm/hr)                                     0.00




21-0211SMP01V1 | Stormwater Management Plan | Good Shepherd Lutheran College Arts Centre              Page 12