Stormwater Management Plan - Rev 1

                                                                                     20169 - SBSMP/1
                                                                                              Page 10




5.3 On-site Detention
In order for the post-development stormwater discharge conditions to match the pre-development
conditions, it is proposed to incorporate an open detention basin with a maximum storage volume
of 240kL. The detention basin is to be located above ground within the southeast corner of the site.

The proposed OSD basin will have the following properties:

       Specified base area = 81m2;

       Specified internal depth = 1.5m;

       Low flow orifice diameter = 0.12m;

       Mid flow top of pit elevation from base of tank = 1.1m;

       Overflow weir elevation from base of tank = 1.4m;

       Overflow weir width = 7.5m;

       Required basin volume = 210kL; and

       Provided basin volume = 240kL.

The detention basin will be designed to contain all flows up to a Q20 storm event. Storm events
exceeding Q20 will be expected to sheet flow across the boundaries at or less than pre development
flows.

Refer to Appendix F for the Concept Site Levels and Drainage Plan which details the proposed on-
site detention system.


5.4 Comparison of Peak Flows at Lawful Point of Discharge
The pre-development and post-development mitigated peak flow rates were compared for each
catchment and are shown in Table 5-4 below.

                                     Table 5-4 - Comparison of Peak Flows
                                                                         XPSTORM
                                       XPSTORM
                  ARI                                              Post-development Flows
                                 Pre-development Flows
                (years)                                                  (Mitigated)
                                         (m3/s)
                                                                           (m3/s)
                   1                      0.035                            0.035

                   2                      0.043                            0.039

                   5                      0.068                            0.051

                   10                     0.087                            0.062

                   20                     0.107                            0.084

                   50                     0.128                            0.119

                  100                     0.145                            0.144




Site Based Stormwater Management Plan
Proposed Townhouse Development at 101-105 Eumundi Noosa Road, Noosaville