SUPERSEDED Approved Plans & Document OPW25-0042 · OPW25/0042

                     7.2 OVERALL DEVELOPMENT SITE CATCHMENT INFILTRATION –
                         QUANTITY MUSIC MODEL

                     The above Quantity MUSIC model is utilised to predict quantity of rainfall
                     infiltrated over the site for a 10-year horizon and using the Cooroy Rainfall
                     Station as a meteorological base.

                     For simplicity the model conservatively ignores bioretention, swales,
                     rainwater harvesting and reuse.

                     A separate Quality MUSIC model discussed in Section 6 is utilised to predict
                     quality of stormwater achieved prior to infiltration.


                     7.2.1 DETERMINATION OF INFILTRATION RATES FOR QUANTITY
                     MUSIC MODELLING


                     MUSIC model infiltration parameters do not consider varying infiltration
                     rates with increasing driving head whilst observations during prototype tests
                     in both 2003 and 2024 indicated a generally linear relationship.

                     For MUSIC Modelling purposes a decision was made to adopt infiltration
                     rates of 3,600mm/hour (1mm/second) as recommended for coarse sands in the
                     MUSICX1.0 modelling guidelines.

                      This rate is considered to be extremely conservative being 18 to 46 times
                     lower than those observed on site for 1m of driving head.

                     7.2.2 DETERMINATION OF EXTENDED DETENTION DEPTHS FOR
                     QUANTITY MUSIC MODELLING


                     Extended detention depth parameters were generally set to design RIP/RIC
                     depths.

                     For RIPs incorporated into the external catchment drainage line extended
                     detention depth parameters were set to the depth of RIP over-run below the
                     stormwater pipe.




                     __________________________________________________________________________

                     A6769/25/SWMP/Rev OpW(A) – Feb 2025
                                                                                                  Page 12 of 9
                     SH/PL
                                              Brah101 Pty Ltd t/as ALTA PROJECTS
Document Set ID: 23646596
Version: 1, Version Date: 21/03/2025