2576 - SBSMP-01 (Feb 2026)

                                         MITIGATED CASE - COMBINED
                                                 Peak Flow Rates - Q (m3/s)
                          AEP            EXISTING       MITIGATED        Difference
                         63.2%             0.197           0.188            -4.6%
                          50%              0.242           0.230            -5.0%
                          20%              0.457           0.368           -19.5%
                          10%              0.485           0.444            -8.5%
                          5%               0.578           0.530            -8.3%
                          2%               0.725           0.614           -15.3%
                          1%               0.801           0.668           -16.6%
             Table 4-10 WBNM discharge flow rates from the site for the mitigated post-development scenario



To suitably attenuate flows at LPOD1, a detention basin will be integrated with the proposed
bioretention system. The basin features a weir height of 1.35m from the base, providing a
storage volume of 472m³. The weir is 5m wide, designed to operate with less than 10mm
depth of flow. Outlets include a 300 mm orifice for low flows, a 300 mm orifice outlet located
0.45m above the base, and a 375 mm orifice outlet located 0.6m above the base for mid flows.
The location of the detention basin is shown in Drawing C300 in Appendix A.


No stormwater flow mitigation measures are proposed for Catchment 2 flowing to LPOD2, as
the area of 349 m² is considered sufficiently small, with a maximum discharge of 29 L/s in a
1% AEP event, for any adverse effects from uncontrolled discharge to be negligible.




2576-SBSMP-01_Version 1.0 (February 2026)                                                                 Page 20 of 23
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