RFI - Attachment 3 - Stormwater Management Plan

 CONCLUSION
This Stormwater Management Report has outlined how the stormwater run-off from the site is to be managed to
comply with the relevant requirements to minimise any adverse impacts to the downstream environment.

     •    The lawful point of discharge test for the proposed development is achieved as the development proposes
          to discharge run-off to the existing drainage feature downstream of the site to which it currently drains.
          Assessment of the impacts arising from the development have found the relative increase is insignificant to
          overall flow depth and volumes, therefore the development is considered to not impact or cause nuisance
          to the downstream properties thereby achieving lawful discharge conditions.

     •    MUSIC modelling of the stormwater treatment train within the proposed development site has shown that
          with the use of rainwater tanks, pit inserts, an end of line bioretention area and table drains acting as swales
          for run-off bypassing the bioretention area, the development will achieve the required stormwater quality
          improvements to comply with Noosa Council requirements.

     •    The proposed upgrade of Carpenters Road will provide an improvement to run-off quality through sealing
          of the gravelled surface, which will reduce sediment loads being discharged into the drainage feature. Due
          to the constrained nature of the access easement, best practice management of the run-off will rely on table
          drains providing swale treatment to convey run-off and provide further treatment in order to achieve the
          objectives of the Noosa Council Planning Scheme.

     •    An assessment of the stormwater quantity requirements was carried out in DRAINS, comparing the pre-
          developed conditions to the fully developed subdivision. The total peak increase under 2100 1% AEP flood
          conditions was found to represent only 1.3% of the existing flow rates, and a depth increase of approximately
          5mm downstream of the development. This increase is considered to be insignificant relative to the existing
          flows, and therefore attenuation will have little impacts on the flows downstream. Attenuation is therefore
          not considered to be necessary within the development.

     •    A minor drainage system consisting of inter-allotment drainage, field inlets, gully pits and stormwater lines
          will be provided in the development sized to convey the Q5 storm event. The major drainage system will
          rely on the proposed road as an overland flow path providing conveyance for larger storm events up to the
          1% AEP storm through the development.

     •    During construction, erosion and sediment control measures in accordance with best practice standards are
          to be implemented to minimise potential contaminants impacting the downstream receiving environment.
          An erosion and sediment control plan shall be developed by the contractor prior to any works commencing
          on the proposed development.

     •    The proposed development is able to be effectively managed to ensure that stormwater is captured and
          conveyed through the site, without causing nuisance flows to adjacent or downstream properties, and in
          conjunction with contribution charges towards a future treatment area, the development is able to satisfy the
          Noosa Shire Council requirements for stormwater quality and quantity.




Project number 21020                                                                                    Page 29 of 36
File RECOR Concept Stormwater Management Report - 21020.docx, 2022-09-05
Revision 0


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