Appendix C - Stormwater Management Plan

31 October 2018


5.3.2 Stormwater Quantity Management Strategy

For the management of stormwater quantity for the proposed development, the DRAINs computer
model was used to calculate the stormwater runoff quantity for the existing site and developed site
conditions. Runoff flows for the Average Recurrence Intervals of 2, 5, 10, 20, 50 and 100 years and
durations of 5 minutes to 120 minutes were calculated to ensure that peak runoff flows from the
proposed site with detention would not exceed peak runoff flows from the existing site.

Stormwater runoff from the proposed development will be detained in a detention tank located at the
South Eastern corner of the new building.

Stormwater events varying from 5 minutes to 120 minutes were analysed with results for the peak
storm flows shown in Table 1 below.


                                             Existing Discharge                        Proposed Discharge
         ARI Year
                                             From Site (m3/sec)                         From Site (m3/sec)

             2                                        0.196                                  0.195

             5                                        0.271                                  0.254

            10                                        0.310                                  0.296

            20                                        0.359                                  0.349

            50                                        0.390                                  0.386

           100                                        0.435                                  0.435

                                       Table 1 – Existing and Developed Peak Flows

The proposed detention tank has a volume of 155m3.

5.3.3 Stormwater Quality Management Strategy

In order to satisfy the requirements of the State Planning Policy July 2017 for the adequate treatment
of stormwater runoff, mechanical treatment solutions have been provided to remove hydrocarbons,
suspended solids and nutrients prior to being discharged from site.

5.3.3.1 Potential Pollutants Generated
The pollutants that could be potentially generated as a result of the development use are as follows:

          Litter
          Sediment
          Nutrients (Nitrogen and Phosphorous)
          Hydrocarbons (oils and grease)
          Surfactants
          Pathogens/Faecal Coliforms (bacteria and viruses)

The MUSIC computer modelling program developed by the Co-operative Research Centre for
Catchment Hydrology was used to predict the performance of the proposed stormwater treatment
train.


Excellence with Economy in Engineering                                                                       10
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