RFI - App - Updated SWMP - 11 Robert St

LINDSAY CONSULTING PTY LTD- STRUCTURAL AND CIVIL ENGINEERS
ACN 079 744 808 ABN 61 478 386 385 GST REGISTERED, AS TRUSTEE FOR THE LINDSAY FAMILY TRUST


                    DESIGN STORM                NON-WORSENING                    ROOF AND
                  RETURN INTERVAL                    VOLUME FOR            DRIVEWAY RUNOFF
                           (AER)                     STORM (m3)                VOLUME FOR
                                                                           DESIGN STORM (m3)
                            63%                           3                            8
                            50%                           3                           10
                            20%                           4                           15
                            10%                           5                           19
                             5%                           6                           23
                             2%                           8                           29
                             1%                           9                           33


       3.      ROOFWATER DETENTION


                In relation to the minimization of the runoff from the site Lindsay Consulting Pty Ltd
                have adopted a non-worsening arrangement for the detention based on the entire site,
                based on the 0.01 AEP flow from the 5 minute storm. Based on the non-worsening
                volume of 9000 lt a 10000 lt detention tank has been adopted for the site, with the tank
                being formed using a series of dia 300 pipes under the driveway and open areas to the
                rear of the proposed units, allowing for gravity flow to the street from the overflow weir.


                The pipe tank has been provided with 2 No. access/maintenance manholes and has a fall
                from the rear to the overflow weir manhole located under the visitor carpark to the
                development.


                The flow off the site is to be limited to the 63% AEP pre-developed flow rate, as
                determined in Appendix A, and as shown in the table above. The flow has been limited
                using a 30 mm Dia low flow pipe in the detention tank weir with the weir overflow level
                set at the 0.01 AEP storm volume.


                Drawing 24-0771-OPW1 to OPW13 revision E, details the proposed water detention tank
                for the project.


                It should be noted that a small section of the driveway could not be connected into the
                detention tank as it is below the defined flood level. The grated drain at the property
                boundary was connected downstream of the detention tank to avoid backflow into the
                tank during large rainfall events.
REF: 240771                                           3                        20 October 2025