Stormwater Management Plan -OPW (A) · 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.




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A6769/25/SWMP/Rev OpW(A) – Feb 2025
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SH/PL
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