Response to Information Request - REC13/0015

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                                                                                         Callaghan & Toth

     5         FLOODING ASSESMENT REPORT

     5.1      Existing Conditions

     This site is not subject to ponding of floodwaters from the adjacent channels and the Q 100 year
     ARI flood levels (Plan 02 shows the Q100 flood level). The buildings and carparks are above
     the Q 100 year ARI flood levels.


     5.2      Proposed Drainage System

     The road surface level is proposed to be drained to an underground drainage system capable of
     taking a Q10 flow. The overflow will discharge to the Bioretention Basin where it will alternate
     flows to be equal to pre-development concentrations.


     The habitable floor level for the proposed development is not affected by the Q 100 flood level.


     The Bioretention Basin has been modelled to act as a detention/infiltration basin. The basin size
     and weir size is sufficient to reduce the increase in runoff for a Q 10 and Q 100 storm back to
     predevelopment levels as shown in Table 5.1. Refer to attached Detail detention basin
     calculations for Q 10 Pre and Post development flow in


              TABLE 5.1:               Pre-Development and Post Development Discharges

                   Location                                Q5              Q10                       Q100
                   Pre-Development                    0.115 m3/s        0.133 m3/s               0.222 m3/s
                   Post Development                   0.118m3/s         0.128 m3/s               0.233 mJ/s




     6        CONCLUSIONS & RECOMMENDATIONS

     An integrated water management approach has been used to assess the site’s stormwater
     requirements and water management needs. In summary:

         .    The proposed four lots area can be treated by a treatment train consisting of one 25m2
              bio-retention basin.
         .    This proposed treatment train achieves the current best practice load based reduction
              targets as prescribed in the Water by Design Deemed to Comply Solutions        -




              Stormwater Quality Management (South East Queensland) version 1.0     Table A-2
                                                                                         -




         .    The new lots have sufficient flood free areas to build residential infrastructure in
              accordance with Council’s requirements.
         .    The rainwater tank and bioretention areas are able to attenuate the runoff
              concentrations back to Pre Development levels and so the development will not have an
              impact on the hydrology of the receiving waters.




                                                                                                             15
     55 Lake MacDonalld Drive   -

                                    Stage 1        SMP Revl.doc                          May 2013     1225