Attachment 4 - Stormwater Management Plan by O2 · MCU13/0251

Table 14 – Basin Performance

                                        3                                    3                               3
ARI (years)                      Pre (m /s)         Total Post (mitigated) (m /s)   Total Volume Required (m )

100                                 0.35                        0.27                          98.8

50                                  0.31                        0.25                          96.5

20                                  0.26                        0.22                          93.3

10                                  0.22                        0.20                          90.7

5                                   0.19                        0.18                          88.9

2                                   0.14                        0.14                          86.1

1                                   0.10                        0.10                          74.9



As can be seen in Table 14, the post development peak discharges have been mitigated to below the pre
development peak discharges for the 1 to 100 year ARI events. The minimum detention volume required
to maintain pre development peak flow rates is 98.8m³.

To maintain the pre-development flow rates for all ARI events, it is necessary to include an additional
control structure within the detention tank. This structure required an internal weir and orifice
arrangement to further reduce the flow rates associated with the minor ARI events.

For the purposes of this assessment, the primary chamber was assumed to have a volume of 90m³, with an
additional 10m³ of detention capacity provided by the secondary chamber. The general arrangement of
this structure is illustrated as Figure 10. The tank and outlet structure will be revised as part of the detailed
design phase when the exact configuration can be determined.




Figure 10 - Baffle Weir and Orifice Configuration




STORMWATER MANAGEMENT PLAN – PEREGIAN VILLAGE MARKET                                                      Page 17

Scanlon Property Group
R002616