Attachment 5 - Stormwater Managment Plan · 132007.12.8

6 Conclusions
It can be seen from the results, presented in Table 6 that the treatment proposed for
the development site achieves the performance criteria set by the NSC. Annual Load
Reductions of Total Suspended Solids (TSS), Total Phosphorus, Total Nitrogen (TN) and
Gross Pollutants (GP) between the Mitigated and Unmitigated Scenarios have been
achieved.
It is proposed for the site to implement a detention system within the site in order to
achieve Council’s non-worsening criteria. Table 13 provides a comparison of the
existing and developed (no mitigation) flows from the hydrologic model, which
highlights the need for a detention system to be incorporated into the development.
Modelling of the detention basin was carried out within the WBNM hydrology model.
Table 12 provides a comparison of the peak existing and mitigated flows. It can be
seen that the modeled mitigation solutions ensure non-worsening is achieved.
This plan demonstrates that effective treatment of stormwater at the proposed
development can be achieved through the integration of Water Sensitive Urban
Design (WSUD) principles. Through the incorporation of a bioretention and detention
system, the plan successfully demonstrates:
   •   Compliance with the requirements of NSC’s Load Based Objectives;
   •   Ecological sustainability in terms of the development’s impact upon receiving
       waters and the viability of the proposed site development; and
   •   Compliance with NSC non-worsening of peak flows in the 2, 10 and 100 year
       ARI storm event;
Preliminary design plans of the detention and bioretention system have been
prepared by TOD Consulting and are provided in Appendix 3.




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