Reference Document - Flood & Stormwater Management Plan 28_8_2025

                 6. CONCLUSION
                 Colliers Engineering and Design have been engaged by PSP Developments Pty Ltd to prepare a Stormwater
                 Management Plan (SMP) in support of a development application to Noosa Shire Council (NSC) over land
                 located at 33 Pavilion Street, Pomona (Lot 4 RP809059). This investigation supports the Operational Works
                 (OPW) design for 8 residential lots. The site has an existing building at Lot 1 and no works are required to
                 create lot 1.

                 It can be seen from the results, presented in Table 3-7 that the treatment measures proposed for the
                 development site achieve the performance criteria set by the NSC Planning Scheme (2020) and SPP (July
                 2017). Annual Load Reductions of Total Suspended Solids (TSS), Total Phosphorus (TP), Total Nitrogen (TN)
                 and Gross Pollutants (GP) between the Mitigated and Unmitigated Scenarios have been achieved through
                 the upgrade of the existing bioretention basin from 80m2 to 130m2.

                 It has been demonstrated that non-worsening of peak flows has been achieved to the discharge point for
                 events up to the 1% AEP (2100) event (refer Table 2-8). The results show that there is non-worsening for
                 events up the 1% AEP (2100). The intent of sizing the detention basin is to mitigate flows up to the 10% AEP
                 storm event to ensure non-worsening of discharges into the downstream flow path. In larger events, flows
                 from the site will start to sheet flow across the rear of the site to Cooroora Creek. As the discharge point
                 for the site becomes inundated from Cooroora Creek flooding in the major storm event, it is considered
                 non-worsening has been achieved. The catchment size of Cooroora Creek reporting past the site is
                 approximately 1,400 ha and it is considered that no quantifiable change to downstream flooding conditions
                 would result.

                 This plan demonstrates that effective treatment of stormwater at the proposed development can be
                 achieved through the integration of Water Sensitive Urban Design (WSUD) principles. Through the
                 incorporation of bioretention basins, the plan successfully demonstrates:

                    Compliance with the requirements of the NSC Planning Scheme and SPPs Load Based Objectives;

                    The end of line bioretention basin is upgraded to 130m2 to cater for the proposed development.

                    Ecological sustainability in terms of the development’s impact upon receiving waters and the viability of
                     the proposed site development.

                    Non-worsening of peak flows is achieved through the upgrade of the existing basin.

                    The development is located above the regional 1% (2100) AEP flood extent with 500mm freeboard
                     recommended to future dwellings on the new allotments.

                 We therefore request Council approval of the engineering components for the proposed development with
                 reasonable and relevant conditions. Detailed design may result in changes to the proposed strategy;
                 however, the design objectives will be maintained.




                 23-0167SMP01-V4 | Stormwater Management Plan | 33 Pavilion Street, Pomona                           Page 37

Document Set ID: 24092538
Version: 1, Version Date: 02/09/2025