RFI - ATTACHMENT A - SBSMP - Rev 2

                                                                                         20169 - SBSMP/2
                                                                                                  Page 10




5.3 Downstream Pipe Infrastructure Considerations
The existing 225 to 450mm diameter stormwater line traversing the rear of Lots 45, 46 and 62 on
SP132578 and Lots 42-44 on SP144002 has been modelled within PC DRAINS to determine its
capacity to take post-development mitigated flows from the development. The subsequent
longitudinal sections and calculations table have been exported from PC DRANS and outlined
within the drainage plans attached in Appendix F.

It was determined from the results of PC DRAINS modelling that the downstream stormwater
drainage infrastructure has capacity to convey up to 67L/s from the proposed development.
Subsequent XPSTORM detention modelling has taken this capacity into account.


5.4 XPSTORM Modelling
5.4.1 Intensity Frequency Distribution
The IFD data and temporal patterns used for the XPSTORM modelling has been obtained from the
Bureau of Meteorology for the following coordinates:
       Latitude -26.406
       Longitude 153.050

Refer to Appendix G for a copy of the BOM IFD data table.

5.4.2 Initial and Continuing Losses
Initial and continuing losses were approximated based on the storm losses obtained from ARR Data
Hub for the aforementioned coordinates. Refer to Table 5-4 below for the adopted initial and
continuing losses.
                           Table 5-4 – Adopted Initial and Continuing Losses

                             Designation              Initial Loss     Continuing Loss

                           Impervious Areas               0.0               0.0
                            Pervious Areas               25.0               2.5


5.4.3 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 254kL. 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 = 223m2;

       Specified internal depth = 1.15m;

       Low flow orifice diameter = 0.14m;

       Overflow weir pit elevation from base of tank = 1.03m;

       Required basin volume = 230kL; and

       Provided basin volume = 256kL.

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