Stormwater Management Plan MCU17/0014

BORNHORST + WARD | DOONELLA STREET UNITS


                     Table 1: Pre and Post Development Peak Stormwater Discharge to the Southeast Corner of Lot 32 Doonella
                                                                   Street.


                                                      Parameter                             Existing   Developed   Difference
                                                      Area (ha)                             0.2519      0.2519       0.00

                                                      Fraction Impervious (fi)               30%         85%          55%

                                                      Coefficient of Runoff (C10)            0.76        0.86        0.10
                                  Catchment Details




                                                      Time of Concentration (min)            16.5        11.5         5.0
                                                      1 year Rainfall Intensity (mm/hr)      81.1        95.8        14.7
                                                      2 year Rainfall Intensity (mm/hr)      103.1       121.7       18.6
                                                      5 year Rainfall Intensity (mm/hr)      127.5       150.1       22.6
                                                      10 year Rainfall Intensity (mm/hr)     141.5       166.4       24.9
                                                      20 year Rainfall Intensity (mm/hr)     160.8       188.9       28.1
                                                      50 year Rainfall Intensity (mm/hr)     186.0       218.2       32.2
                                                      100 year Rainfall Intensity (mm/hr)    205.2       240.6       35.4
                                                      100% AEP (m3/s)                       0.0345       0.047       0.012
                                                      50% AEP (m3/s)                        0.0466       0.063       0.016
                                  Discharge




                                                                      3
                                                      20% AEP (m /s)                        0.0644       0.087       0.022
                                                                      3
                                                      10% AEP (m /s)                        0.0753       0.101       0.026
                                                                  3
                                                      5% AEP (m /s)                         0.0898       0.121       0.031
                                                                  3
                                                      2% AEP (m /s)                         0.1138       0.153       0.039
                                                      1% AEP (m3/s)                         0.1309       0.168       0.037

                    As indicated in the table above, the peak discharge from the development to the southeast corner of lot 32
                    Doonella Street will increase in the developed scenario. To ensure that there will be no impact on the
                    downstream infrastructure or properties as a result of the development, construction of a detention system is
                    proposed to mitigate the expected discharge increase. The detention system proposed is a below ground
                    storage tank.

         4.1.3      Detention System

                    Peak discharges for the development will increase as a result of the proposed development. In order to
                    mitigate these flows a detention system is proposed. An initial detention sizing has been completed using the
                    Rational Method to estimate the size of the system. The detention volume required to mitigate peak flows
                    from the proposed development to pre-developed conditions is 45m3. It is proposed to provide this volume in
                    a below ground storage tank near the lawful point of discharge, in the southeast corner of lot 32 Doonella
                    Street. Refer to the Stormwater Layout Plan within Appendix B for further information.

         5.         STORMWATER QUALITY

                    The following is an extract from Part E: Interim Development Assessment Requirements within State Planning
                    Policy which describes developments that the policy is applicable to:

                              Receiving waters – a development application for any of the following:


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 Level 4, 67 Astor Terrace, Spring Hill, Qld 4000                                                                            Page 5
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