Further information re Request to Change Approval MCU 132003.221132.8

                                                                                            BROWN
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Summary of Results

   .   To gauge the effectiveness of Basins B1A and B1C, Option 2 was modelled with only the two

       basins and the original sized Twigrush Basin. Dodonaea Basin is not included in the Option 2

       model. The results indicated that the two basins upstream are not sufficient in mitigating

       peak flows with increases of up to 15%.
       Option 3 strategy incorporates basins B1A, B1C, Twigrush Basin and the Dodonaea Basin. For
       this option the reduction in Water Surface Levels     (WSL’s) in the Dodonaea     Basin   are


       significant (0.78m to 1.01m). The time in which it takes the Dodonaea basin to empty has
       reduced, up to 30 minutes shorter than previously to empty during a 100 year ARI event.
   .   The analysis of site only developed areas in Option 4 has shown that the basins can be sized

       at 40%, 55% and 65% of capacity for basin   B1A, B1C and Twigrush respectively to achieve
       the non-worsening objective. It should be noted that the analysis for this option does not

       take into account the potential for peak flows from the site and upstream catchments to

       coincide and may not be acceptable to Council.




B09182.W _Options_2_3_40NLY_130314.docx                                                      Page 5