Attachment D amended SWMP

 5.5     Proposed Design

5.5.1    External Catchment
Runoff from the External Catchment area currently flows through the Development Area.
It is proposed to capture the flows (including up to 1%AEP design flows) from the External Catchment area and
pipe it through the Development Area and discharge to the existing infrastructure.
Refer to Appendix C for the concept stormwater layout.

5.5.2    Development Area
A new internal stormwater pit and pipe drainage system with a detention basin is proposed for the Development
Area. The proposed system will discharge to a new stormwater line within Gateway drive that connects to the
existing stormwater infrastructure that crosses Gateway Drive.

The piped flows from the External Catchment area will bypass the detention basin.

Refer to Appendix C for the concept stormwater layout sketch for the development.

5.5.3    Detention System
The following table summarises the proposed detention system characteristics:
Table 5 – Detention Basin Details

                                        Detention Basin Parameters

              Minimum surface area of the base of the basin (m2)                               97


                     Bottom of detention storage (m AHD)                                      9.100


                            Low Level Orifice Control                                1 x 240mm dia @ IL 9.100
                                                                                             mAHD

                            Mid Level Orifice Control                                1 x 350mm dia @ IL 9.700
                                                                                             mAHD

                            High Level Weir Control                                 3.6m wide @ IL 10.160 mAHD


           Top of Detention Wall Level (Including 300mm freeboard)                            10.400


                        1% AEP Storage Level (m AHD)                                          10.04


           Minimum detention volume at 1% AEP storage level (m3)                               91.2


               1% AEP Storage Level (m AHD) – Climate Change                                  10.18


  Minimum detention volume at 1% AEP storage level (m3) – Climate Change                       105


Further refinement of the detention system location, layout, sizing and outlet configuration will need to be
undertaken as part of detailed design and after revised detailed survey has been received.




 BR210522_SBSMP_Rev5.docx                                                                                 Page 10 of 25