C6361-22-ENG - Feb 2023 - V1

6.3   Stormwater Quantity Management


Refer to Engineering Drawing C6361/22/P05 and P07-08 attached as Appendix B for
details of proposed stormwater drainage.


Development works within the subject site will increase the total impervious percentage
of the northern and southern catchments from 0% to 10% and 0% to 40% respectively.
The total Time of Concentration (TOC) will remain similar in the developed case due to
upstream contributing catchments.


When considered as part of the total catchments contributing stormwater runoff to the
northern and southern flow paths, these changes will increase the total impervious
percentage from 0% to 6% and 0% to 2.8% (respectively). These changes to catchment
drainage characteristics will result in minor increases to peak discharge at the northern
and southern legal points of discharge.


Refer to Table 6.3a-b for a summary of the pre and post developed flows for the northern
and southern catchments. Refer to Appendix D for detailed Rational Method calculations.


               Table 6.3a Pre Vs Post Developed – Southern Flow Path – CMT 1
                         AEP     Q Pre      Q Post   Variance
                                 (m3/s)     (m3/s)
                         63%      6.14      6.15       0.04%
                         39%      8.18      8.18       0.04%
                         18%     11.37     11.38       0.04%
                         10%     13.79     13.79       0.04%
                          5%     16.57     16.58       0.04%
                          2%     21.17     21.18       0.04%
                          1%     24.425    24.434      0.04%




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