Appendix C - Stormwater Management Plan

TfA Project Group Pty Ltd                                                                                 Stormwater Management Plan
                                                                                                               Development Application


   Table 11: Stormwater flows generated by the post-development catchment

      Catchment             Q1 (l/s)        Q2 (l/s)        Q5 (l/s)        Q10 (l/s)       Q20 (l/s)         Q50 (l/s)        Q100 (l/s)
        A (Qin)              55.25           74.71           102.47          119.85          142.62            180.49           260.83


   As can be seen from Table 12 below, the development will increase stormwater runoff for the catchment for the
   nominated ARI’s, therefore onsite stormwater detention will be required to mitigate the peak discharge and achieve
   the “no worsening” of the stormwater drainage conditions external to the site.


   Table 12: Stormwater flow differences between post and pre-development for standard ARI’s

     Change in Flow            Q1 (l/s)         Q2 (l/s)        Q5 (l/s)        Q10 (l/s)       Q20 (l/s)        Q50 (l/s)      Q100 (l/s)
              A                    17.46         23.77           31.99            37.57           44.74            56.34          64.15


   Stormwater runoff from the back of the proposed building at the Southern area (390 m2) of the site will flow
   unmitigated by passing detention. A gully pit will convey the runoff and will discharge the flow to the legal point of
   discharge on Walter Hay Drive. Table 13 shows the stormwater flow generated by the bypassing area.

   Table 13: Stormwater runoff bypassing the detention basin for the post-development catchment

     Catchment         Q1 (l/s)            Q2 (l/s)        Q5 (l/s)        Q10 (l/s)        Q20 (l/s)         Q50 (l/s)        Q100 (l/s)
      A (QoutL)             8.82           11.92           16.35            19.13            22.76              28.80            33.00


   The adjusted allowable discharge from the detention basin is shown in Table 14 below.

                                                           Qout = QoutPC – QoutL



   Table 14: Allowable stormwater discharge from the detention basin

      Catchment              Q1 (l/s)         Q2 (l/s)        Q5 (l/s)        Q10 (l/s)       Q20 (l/s)        Q50 (l/s)       Q100 (l/s)
      A (QoutPC)             37.78             50.94           70.48            82.28           97.88           124.16          142.68
       A (QoutL)              8.82             11.92           16.35            19.13           22.76            28.80           33.00
       A (Qout)              28.97             39.02           54.13            63.15           75.12            95.35          109.68


   6.2.7      Required Detention Volume


   The onsite detention volume will restrict the post-development flows to pre–development levels. The required
   detention volumes were estimated using the equation 5.04 (After Basha 1994), outlined in Section 5.05.1 of
   QUDM (2007). Table 15 shows post-development flow rates, allowable discharges from the detention basin(s),
   and the detention storage volume required to achieve the “no-worsening” of the drainage conditions external to
   the development site for the nominated ARI’s.




                            123 Eumundi Road (Cnr Walter Hay Drive), Noosaville QLD 4566                                            Page 7