102255ltr SMP Iss B

                                               4


Using the above parameters, the stormwater discharge in the pre-development and post-
development scenarios to Noosa Drive were calculated as shown in Appendix B and
summarised in Table 1 and Table 2. The results demonstrate that the peak flow discharge from
the site is increased in the post-development case. Therefore, detention of the peak
stormwater discharges is required.

              Table 1 – Site peak flow discharging to Noosa Drive (current climate)


                                             Peak Flow (l/s)
        AEP
                   Pre-development        Post-Development             Difference

        10%                37                      38                      +1
        1%                 60                      62                      +2


               Table 2 – Site peak flow discharging to Noosa Drive (2021 climate)


                                             Peak Flow (l/s)
        AEP
                   Pre-development        Post-Development             Difference

        10%                44                      46                      +2
        1%                 72                      74                      +2


  Table 3 – Infiltration trench bypass peak flow discharging to Noosa Drive (current climate)


                                             Peak Flow (l/s)
                                AEP
                                          Trench Bypass only

                                10%                 7
                                 1%                 12


The detention tank and outlets were designed in accordance with the following guideline:

   •   “On-site Underground Detention Storage Orifice Plate Sizing for Deemed-to-comply
       Detention: Fact Sheet” by Sunshine Coast Council (2018)

The detention tank storage volume was calculated as shown below:

                    𝐷𝑒𝑡𝑒𝑛𝑡𝑖𝑜𝑛 𝑣𝑜𝑙𝑢𝑚𝑒 = 90 𝑚3 ⁄𝐻𝑎 × 0.0723 𝐻𝑎 = 6.5 𝑚3

Therefore, the required detention tank volume is 6.5 m3. A detention tank, in the form of an
infiltration trench, with 6.5 m3 has been proposed for each lot.