16-001014-01A (Swmp)

   The Load Retention Achieved (in kg/yr) was determined using the “Developed Site with External - Mitigated” model,
    estimating the amount of pollutants removed from site and External Catchment B1 and C1 as a result of the
    stormwater quality improvement devices.

Catchment B1 and C1 as shown on Drawing No. B14158.W-SK102 are external and are not part of the site area. While
External Catchment B1 and C1 have been included in the stormwater quality analysis (as runoff from these areas enter
the site and into proposed stormwater quality treatment devices), these areas are not considered a “part of the
development” or identified as ‘site area’. As such, determining the amount pollutant reduction required to meet objectives
for the site (i.e. Load Retention Target) does include the pollutants generated from the external catchment areas. The
Load Retention Achieved has been determined by the total pollutants removed by the proposed SQID’s prior to discharge
from the site.

4.4.1     METEOROLOGICAL DATA

Six-minute pluviographic data was sourced from the Bureau of Meteorology (BOM) for Cooroy Composite (Station No.
40059). In accordance with Table 3.1 from MUSIC Modelling Guidelines (2010), the 10-year period from 1st January
1973 to 31st December 1983 has been adopted for the rainfall duration. The mean annual rainfall for this period is
1,600mm. The mean annual evapotranspiration for the modelled period is 1,629mm.

4.4.2     SOURCE NODES

Source nodes are sub-catchments that are defined for MUSIC modelling purposes. The site was divided into
sub-catchments as shown in Drawing No. B14158.W-SK102 in Appendix G.

The split catchment approach has been used to set up all source nodes in MUSIC. The MUSIC Modelling Guidelines
(2010) have been used to configure three types of surfaces, Roof, Road and Ground, to be modelled for each sub-
catchment. All sub-catchments within the model extent were assigned either Urban Residential or Commercial
Residential dependent on land use. Refer to Appendix F for MUSIC node configurations for the site. Split sub-catchment
node areas were calculated based on Concept Master Plan presented in Appendix A.

Rainfall runoff parameters for all nodes were assigned as residential land-use, in accordance with Table 3.7 of the
MUSIC Modelling Guidelines (2010). Pollutant export properties for source nodes have been configured according to the
industrial land use category in accordance with Table 3.8 of the MUSIC Modelling Guidelines (2010).

Stochastic generation estimation and serial autocorrelation set to zero has also been adopted.

4.4.3     PRIMARY AND SECONDARY DRAINAGE LINKS

A combination of primary and secondary drainage links have been used in MUSIC to model minor flow diversions
adopted in the site’s internal drainage strategy. Primary and secondary drainage links have been applied in two areas of
the site as indicated below:

   Minor runoff from Southern Basin directed to Central WQCP – 63% AEP peak flows from the Southern Bioretention
    Basin (will be directed to the Central WQCP to increase turnaround time (Hydraulic Residence Time) of the Pond and
    for peak flow attenuation. This has been modelled in MUSIC by using primary drainage link to direct runoff below the
    63% AEP storm event (<1.25m3/s) to the “Central WQCP” (not modelled in MUSIC) and a secondary drainage link to
    direct runoff high-flows downstream of the Pond.

   Minor runoff (63% AEP peak flow) from Catchment B1 and B2 to Central Bioretention Basin – peak flows in the 63%
    AEP storm event will be directed towards the GPT and Central Bioretention Basin for stormwater quality treatment
    before discharging to the proposed WQCP (not modelled in MUSIC). High flows bypassing the Central Bioretention
    Basin will be directed into the WQCP. This has been modelled in MUSIC by using primary drainage link to direct



16-001014-01 | STORMWATER MANAGEMENT PLAN (SWMP)                COOROY RETIREMENT COMMUNITY, TRADING POST
| PALM LAKE RESORTS                                                                         ROAD, COOROY               | 18