RFI - stormwater report

6 Conclusions
It can be seen from the results, presented in Table 2-6 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 that a diversion pipe be introduced between the south-east corner of
the site and the existing natural waterway approximately 100m south. The proposed
diversion pipe will redirect the change in peak flows to prevent nuisance flow from
affecting adjoining private properties and the road reserve, refer Section 3.1.7.
It has been determined from WBNM regional hydraulic routing analysis that the time
of peak flows in the local sub-catchments do not coincide to create any significant
change in peak flows associated with the change in impervious characteristics from
the developed site. Council’s non-increasing in nuisance flooding from stormwater
flows. criteria has been achieved , Table 3-5 provides a comparison of the existing and
developed (no mitigation) flows from the hydrologic model.
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, 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
   •   It is noted that there is a very minor increase in peak flow within the waterway
       traversing Pottery Street it is considered that no nuisance flooding would
       result from stormwater flows of peak flows in the 1, 2, 5, 10, 20, 50 and 100
       year ARI storm event, with site discharge being directed to a lawful point of
       discharge.




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