Request to Amend Application and Response to DSDIP's Information Request · MCU14/0009

3.4      Mitigated Scenario
When comparing the peak flows in the existing and developed scenario, increases in
the peak discharge occur at the catchment outlet. As a result a detention system will
be required in order to achieve non-worsening from the site.
All modeling parameters remain consistent between the developed and mitigated
scenarios, with the addition of a detention system before outlet to site (refer
Appendix 1). The storage details included within the model are provided in Table
15.
Table 15: Storage and Outlet Details of Underground Detention System

         Storage
                      Storage Height     Outlet Configuration      Peak 100yr WSL
         Volume

                                       1 x 300mm at RL0.0m; and
           10m3            0.3m                                        RL0.3m
                                       1.5m wide weir at RL0.22m


A comparison of the peak flows between the existing, developed and mitigated
scenarios are presented below in Table 16. It can be seen that non-worsening of
peak flows are achieved at each outlet to the site.
Table 16: Comparison of Existing, Developed and Mitigated WBNM Outlet Peak Flows
                   Existing Peak   Developed Peak   Mitigated Peak     Change in Peak
                    Flow (m3/s)      Flow (m3/s)     Flow (m3/s)        Flow (m3/s)
      1 year           0.048            0.05             0.044             -0.004
      2 year          0.062            0.063             0.062               0
      5 year          0.078            0.079             0.078               0
      10 year         0.088            0.089             0.088               0
      20 year         0.101            0.102             0.101               0
      50 year         0.112            0.114             0.112               0
   100 year           0.125            0.127             0.123             -0.002



WBNM outputs are provided in Appendix 2 of this report.




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