Attachment D amended SWMP

5        Stormwater Management (Quantity)
 5.1     Hydrological Modelling
Hydrological analysis has been undertaken using DRAINS to calculate the design flow rates from the site. The
hydrological model used in DRAINS is the ILSAX model using ARR2019 methods.
Rainfall data and Temporal Patterns for the site has been obtained from the Bureau of Meteorology (BOM) and
the ARR Data hub systems.
Hydrological analysis has been undertaken using DRAINS software by Watercom to calculate the design flow
rates from the site. The hydrological model used in DRAINS is the ILSAX model using ARR2019 methods.

                               Table 1 - ILSAX Hydrological Model Parameters

                                             Parameter                           Value

                          Paved (impervious) area depression storage              1 mm

                             Supplementary area depression storage                1 mm

                           Grassed (pervious) area depression storage             5 mm

                                              Soil Type                           3/C


 5.2     Catchment Summary
Pre- and post-development catchment parameters to be used in DRAINS have been calculated based on
existing partial detailed survey data, aerial image of the site, contour data from Council’s online mapping,
information provided to us about the proposed development and methods outlined in QUDM.
Times of concentrations have been calculated based on existing partial detailed survey, contour data from
Council’s online mapping and methods outlined in QUDM.
Aerial image has been used to calculate the pre-development and external catchment fraction impervious.
Proposed site layout plans have been used to calculate the post-development fraction impervious. For the
Development Area.
Pre- and two post-development catchments are divided into two catchments; Development Area and External
Catchment. Runoff from External Catchment eventually discharge into the existing stormwater infrastructure
within Gateway Drive via Development Area.
Refer to Appendix D for the Catchment Plan.
The tables below, provide a summary of the pre- and post-development catchment characteristics used in the
DRAINS model.
                                    Table 2 –Pre-Development Parameters

                                 Catchment                 Area        F.I.      Tc(min)
                             Development Area
                                                          0.415 ha      5%          12
                               (Pre-Development)

                             Development Area
                                                          0.415 ha     95%          5
                              (Post-Development)

                            External Catchment            0.735 ha     100%         7




 BR210522_SBSMP_Rev5.docx                                                                                      Page 8 of 25