Appendix 4- SWMP

                                                                                                                   ingeniir


                                            DETENTION TANK OUTLET DETAILS
                           Feature                              Size                   Height from base
                  Top of Tank/Access                As per manufacturer                       1565mm
                  Top Outlet Overflow                 100mm diameter                   1380mm (in riser)
                  Middle Outlet                        50mm diameter                          970mm
                  Low Flow                             25mm diameter                          550mm
                                              Table 2: Detention tank outlet details

6.2     Detention Results

The peak water elevation achieved in the tanks by the analysis is 1230mm so falls short of discharging via the
top of tank overflow or access point.

The detention tanks are proposed to discharge to David Low way via a 100mm diameter pipes into 3.0m Long
subsoil dispersal outlets, peak discharge rates to David Low way are estimated at 25.80L/s for a 1% AEP
storm which improves the current estimated discharge of 26.36L/s.

                                      WHOLE OF SITE DETENTION SUMMARY
                                  Pre-Development       Post-Development
                  AEP                            Duration                          Duration       Performance
                                  Q (L/s)                              Q (L/s)
                                                  (min)                             (min)
                 63.20%             6.637                   5            6.417                5      -0.22 (97%)
                 39.35%             8.799                   5            8.421                5    -0.378 (96%)
                 18.14%            12.311                   5           11.657                5    -0.654 (95%)
                  10%              14.934                   5           14.061                5    -0.873 (94%)
                   5%              17.921                   5           17.060                5    -0.861 (95%)
                   2%              22.808                   5           22.779                5   -0.029 (100%)
                   1%              26.360                   5           25.432                5    -0.928 (96%)
                1% 2100            31.632                   5           30.686                5    -0.946 (97%)
                          Table 3: Comparison of pre and post development discharges to David Low Way

As demonstrated in Table 3, the proposed detention system successfully mitigates stormwater discharge to
David Low Way to achieve a non-worsening in peak discharge.


7.    FLOODING
The site is in raised elevation locally and has no known Council mapped flood risk. A review of the Noosa Shire
Council’s Intramaps system (accessed 08/09/2025) indicates that the site is not affected by riverine
Flooding or storm tide. Refer Plate 2 for an excerpt of the Council mapping.




                                              Ingeniir Pty Ltd | 245001-SMP-01
                ABN: 99 642 485 363 | PO Box 988 Maroochydore QLD 4558 | [email protected] | 0404157187
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