Reference Douments - 132004.4029.01 & RAL22/0010

        STORMWATER QUANTITY

            3.1. Pre-Post Comparison
       The site has been modelled using the DRAINS software to assess the impact on peak flows, comparing the existing
       site conditions to the proposed development.

       In accordance with ARR2019, an Initial Loss-Continuing Loss (IL-CL) model has been used to assess the site against
       the ensemble of storm temporal patterns for the East Coast North region. The loss parameters and temporal patterns
       have been imported from the ARR Datahub, and rainfall intensities have been imported from the Bureau of
       Meteorology IFD rainfall data allowing for a 20% increase to rainfall rates to account for future climate change
       patterns.

       The parameters obtained from the Australian Rainfall and Runoff (ARR) Data Hub for the location and the rainfall
       IFD data obtained from the Bureau of Meteorology have been imported into DRAINS to generate the storm events.
       The models have been run using the ensemble of storm events for 1EY, 50%, 0.2EY, 10%, 5%, 2% and 1% Annual
       Exceedance Probability (AEP) for durations from 1 minutes to 24 hours to determine the critical storm duration and
       the mean peak flowrate from the storms. Refer to Appendix B DRAINS Modelling Parameters and Results for details
       of the parameters used and summary of the results from the modelling.

       The configuration of the catchment areas for pre-development and post-development scenarios are shown in Figure
       3.1 – DRAINS Pre-development catchment and Figure 3.2 – DRAINS Post-development catchments respectively.




                                                  Figure 3.1 – DRAINS Pre-development catchment




      Project number 20220116
      File RECOR Preliminary Stormwater Management Report - 20220116.docx, 2022-09-27                                Page 7 of 14
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