Swmp

6.1     Drains Analysis



To calculate the peak discharges for the site under existing (pre-development) and proposed (post-
development) conditions. Hydraulic modelling has been undertaken for the site using the software
package PC DRAINS. Modelling has established existing and proposed stormwater drainage
characteristics. This includes a climate change rainfall multiplier of 1.2 (20%)



Rainfall patterns accompanied with Initial Loss (IL) and Continuing Loss (CL) was sourced from the
Australian Rainfall and Runoff 2019 (ARR 2019) data hub for Noosaville.



Initial Losses (IL) and Continuing Loss (CL) were approximated based on the storm losses from the
ARR Data Hub, Table 6.1 below states the adopted values: -
                                 Table 6.1 - Adopted (IL) and (CL) Values

                                      AREAS             (IL)            (CL)
                                                       (mm)           (mm/hr)

                                   Impervious             1              0

                                     Pervious             31            3.4



Design ARR 2019 storms for Noosaville have been added into DRAINS accompanied with IFD rainfall
depths from the Bureau of Meteorology (BOM) website

6.1.1   Existing Catchments


Times of concentration (Tc) were calculated as defined in QUDM 2017 using a combination of standard
inlet time & overland sheet flow time. Table 6.2 displays the Adopted time of Concentrations.
                                          Table 6.2 – Tc Values

                                STATE                         (Tc) (mins)

                            Pre Development                      10

                         Post Development                         6

6.1.2   Peak Flows
The existing site consists of a dual lot undeveloped block with grass cover. The existing surface
generally falls to the north towards the Blakesley St road frontage.

The total impervious area has been estimated using the detailed site survey and was 0% Impervious
Area (Fi = 0.00).



The development consists of the construction of mixed residential unit & commercial shop development
along with a shared access driveway and ground level landscaping & courtyards area. The total pervious
area for the site was calculated to be approximately 1762m2 (Fi = 0.88).

 SCG Consulting engineers                            12                         SCG Ref: 33094(SWM).Rev A