2508-47877 SRA - Attachment 5 - Plans and docs referenced in SARA response

                                                                                                                   ingeniir


                                          DETENTION TANK OUTLET DETAILS
                           Feature                             Size                   Height from base
                  Top of Tank Overflow             As per manufacturer                       2400mm
                                                  150mm diameter (open
                  Top Outlet                                                                 2100mm
                                                          to sky)
                  Middle Outlet                  2|150mm diameter pipes                      1550mm
                  Low Flow                            50mm diameter                              0mm
                                             Table 2: Detention tank outlet details

6.2     Detention Results

The peak water elevation achieved in the tanks by the analysis was 2100mm so falls short of discharging via
the top of tank overflow/access point.

The detention tanks are proposed to discharge to pit (6|1) and then flow into the downstream bio-retention
basin within a DN375RCP where it will then be piped to Myall Street stormwater network by 2|375 RCP. Peak
discharge rates to (6|1) are estimated at 164L/s for a 1% AEP 5 min critical storm which improves the current
estimated discharge of 198L/s.

                                         WHOLE OF SITE DETENTION SUMMARY
                                  Pre-Development                     Post-Development
                   AEP               3          Duration                          Duration         Performance
                                Q (m /s)                          Q (m3/s)
                                                 (min)                             (min)
                 63.20%             50.27                  5           32.701                5     -17.569 (65%)
                 39.35%            66.831                  5           42.835                5     -23.996 (64%)
                 18.14%            93.218                  5           58.855                5     -34.363 (63%)
                   10%            112.591                  5           70.556                5     -42.035 (63%)
                   5%             134.732                  5           83.879                5     -50.853 (62%)
                   2%             172.157                  5          120.057                5       -52.1 (70%)
                   1%             198.512                  5          163.788                5     -34.724 (83%)
                 1% 2100          238.215                  5          215.074                5     -23.141 (90%)
                                  Table 3: Comparison of pre and post development discharges

As demonstrated in Table 3, the proposed detention system successfully mitigates stormwater discharge to
pit (1|6) to achieve non worsening for the site stormwater discharge an maintain capacity in the downstream
stormwater infrastructure.


7.    FLOODING
The site is in an elevated position locally and regionally and is not known to have any flood risk. A review of
the Noosa City Councils online mapping (accessed 24/07/2025) indicates that the site is not affected by any
known flood studies. Refer 3 for an excerpt of the site report.




                                               Ingeniir Pty Ltd | 251502-SMP-01
                 ABN: 99 642 485 363 | PO Box 988 Maroochydore QLD 4558 | [email protected] | 0404157187
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