Reference Documents - MCU23 0070

           STORMWATER QUANTITY

3.1        LAWFUL POINT OF DISCHARGE
The proposed lawful point of discharge is the kerb & channel on Duke Street. Currently there are two
kerb adapters fronting the site. It is proposed to utilise only the low side kerb adapter and upgrade as
required. The 1% AEP peak flow rate has been limited to 25L/s.



3.2        STORMWATER DISCHARGE STRATEGY
The fraction imperviousness increases due to the proposed development. To mitigate increase to peak
discharge rates an on-site detention tank is proposed. The tank is proposed to be located on ground
level at RL 30.26m AHD.

It is proposed to collect and convey a majority of the site runoff into the detention tank. Mitigated
flows are to be discharged on to Duke Street kerb & channel.



3.3        RATIONAL METHOD CALCULATION
The Rational Method Calculation has been undertaken for the pre-development site. Table 1 presents
the Rational Method catchment parameters. Refer to Drawings No. M3024E_DA1_SK01 in Appendix D
for the catchment plan. The fraction imperviousness has been estimated from the detailed survey
(included in Appendix A). The C10 has then been determined in accordance with Table 4.5.3 of the
QUDM (2016) and the time of concentration (Tc) based on the Standard Inlet Time in accordance with
Table 4.6.2 of the QUDM (2016).

                                Table 1 – Rational Method Calculation Parameters
                                                      Fraction
      Catchment              Area (ha)                                       C10                 Tc (mins)
                                                     Impervious
           E1                  0.0486                   57%                  0.82                     8

Site specific 2016 rainfall intensities were obtained from Bureau of Meteorology (BOM). Table 2
presents the Rational Method peak flow rates. Further details included in Appendix B.

                                      Table 2 – Rational Method Peak Flows
                                              Rational Method Peak Flows (m³/s)
                 63% AEP       39% AEP        20% AEP        10% AEP    5% AEP          2% AEP         1% AEP
      E1          0.010          0.013         0.018          0.022      0.026           0.033            0.037




SITE BASED STORMWATER MANAGEMENT PLAN – Revision B                             36 & 38 DUKE STREET, SUNSHINE BEACH
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