Appendix E - Stormwater Management Plan

                  Table 4-5:    20th Percentile Hydraulic Residence Time Results (Simplistic Approach)
                Parameter                                                   30-Year Period (1973-2003)
                Impervious Area (ha)*                                                   8.8
                Lake Volume (m3)                                                       1,840
                Pond Area (m2)                                                         1,940
                All Year Rainfall (mm)                                                  678
                Catchment Inflow (m3)                                                 59,956
                Yearly Evaporation (mm)                                                1,629
                Net Evaporation (m3)                                                       1,844
                Net Inflow (ML)                                                             58
                Net Yearly Inflow / Lake Volume Ratio                                       31
                Probabilistic Residence Time (No. of days)                                  12
         *The catchment impervious area to the central pond is consistent with MUSIC modelling areas and Fi values.

A continuous modelling approach was also undertaken using daily output from MUSIC modelling over the same 30-year
period. Using the more detailed approach, the 20th percentile HRT was determined to be 9 days, which also achieves the
required objective.

Therefore based on both the simplistic and continuous modelling approaches the Hydraulic Residence Time for the pond
will be below 15 days. This demonstrates that the required performance objective will be met.

If the water quality of the pond is found to be poor, recirculation of flows through the WQCP could be provided to increase
the turnover of water within the pond.

4.4.4.4 PROPRIETARY GROSS POLLUTANT TRAP (GPT)

A proprietary (GPT) is proposed upstream of large catchments (above 5ha) or significant areas of car parking areas
before discharging to the proposed Bioretention Basins. While GPT’s are proposed upstream of the Central Basin,
Southern Basin and Bio-Pod D2 they have not been modelled. This will make the results more conservative, as GPT’s
will capture gross pollutants and some sediments.

4.5       MUSIC MODELLING RESULTS
        This section has been updated to reflect revised modelling method and results recently approved by Council
        Officer Cherie O’Sullivan. Refer to email correspondence provided in Appendix I. Results for the updated
        modelling is presented in Table 4-6 below.

                                            Table 4-6:    MUSIC Modelling Results

                 Results at Receiving Node               Source Load    Residual Load       % Reduction
                 Total Suspended Solids (kg/yr)                 36300             7740                79
                 Total Phosphorus (kg/yr)                        76.4               23.1                70
                 Total Nitrogen (kg/yr)                          481                240                 50
                 Gross Pollutants (kg/yr)                       4620                249                 95

        The above results were approved by Council as meeting the required WQO’s.




16-001014-01B | STORMWATER MANAGEMENT PLAN                        COOROY RETIREMENT COMMUNITY, TRADING POST
(SWMP) | PALM LAKE RESORTS                                                                    ROAD, COOROY              | 21