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

3.3     Developed Scenario
The proposed development has been incorporated into the WBNM model by
adjusting the site sub-catchments and the fractions impervious values. Fraction
impervious values of the existing and proposed scenarios are provided in Table 10
below.
Table 10: WBNM Sub-Catchment Fraction Impervious Values – Developed Scenario
      WBNM Sub-                          Developed Scenario      Existing Scenario
                        Area (ha)
      Catchment                            Impervious (%)         Impervious (%)
        SUB 1             0.164                 89                       69


Peak flows tabulated in this report represent the peak values extracted from the
modelled range of storm events.
Table 11: Developed Scenario WBNM Outlet Peak Flows
                    Existing Peak Flow     Developed Peak Flow    Change in Peak Flow
                           (m3/s)                 (m3/s)                (m3/s)
       1 year              0.048                   0.05                 0.002
       2 year             0.062                   0.063                  0.001
       5 year             0.078                   0.079                  0.001
       10 year            0.088                   0.089                  0.001
       20 year            0.101                   0.102                  0.001
       50 year            0.112                   0.114                  0.002
      100 year            0.125                   0.127                  0.002

It can be seen that the peak flows have increased to the catchment outlet. This is a
result of the development site increasing the impervious area. Mitigation within the
catchment will be required.




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