LATE RFI - Revised SWMP

     2.3. Proposed Development Drainage Pattern

           2.3.1 Stormwater Concept
The future sites will contain individual dwelling homes typical of low density residential allotments. The downstream
environment is typically rural in character however is zoned low density residential that may be developed in the
future.

The proposed internal drainage relies on overland surface flows from the proposed allotments to discharge run-off
from the development. Run-off from the roof area will discharge via downpipes to the ground through a gravel trench
to act as an energy dissipator. Impervious areas of development including the driveway will be graded to fall towards
the pervious ground area to the west with the overland flows remaining dispersed as they discharge downstream
consistent with the existing conditions.

Upstream flows from the existing access easement and adjacent properties to the east will be diverted around the
proposed lots along the northern site boundary. A table drain along the property boundary will carry run-off along
the eastern and northern boundary of the site. The run-off will be discharged through a level spreader positioned
along the western boundary of the site, distributing the flows over a minimum 4m width to minimise impacts to any
future downstream development and reducing risk of scour from the outlet. The table drain will be contained within
a drainage easement to the benefit of the upstream properties.

The roof and allotment drainage system for the proposed site shall be designed to comply with:

     1. Noosa Shire Council Planning Scheme Policy (PSP) - Engineering Design Standards – Roads, drainage and
        earthworks;

     2. The Queensland Urban Drainage Manual (QUDM); and

     3. AS/NZS 3500.3:2015 - Plumbing and Drainage Part 3: Stormwater Drainage.

Refer to Appendix A Proposed Development Plan for the proposed stormwater drainage layout plan illustrating
the concept described above.



           2.3.2 Lawful Point of Discharge
The site typically drains west towards the large undeveloped rural parcel downstream of the site. The lawful point
of discharge test, as described in Section 3.9.1 of QUDM, requires:

       •    The development does not change the flow characteristics leaving the site; or
       •    The proposed development will not alter the sites stormwater discharge in a way that may substantially
            damage a third-party property; or
       •    The location of the discharge from the site is under lawful control of the government or other statutory
            authority from whom permission to discharge has been received; or
       •    An authority to discharge has been obtained.

An assessment of the site, considering a future impervious fraction of 40%, has found that total peak flows will
increase by an insignificant amount within context of the large allotments and low-density character of the locality.
Refer to Section 3.1 for details. As the peak increases are small for all events, attenuation is not considered
necessary to mitigate flows to predevelopment levels. Upstream flows which will be diverted around the proposed
allotments, are discharged at the downstream boundary by level spreader which will ensure the flows are
dispersed and unlikely to result in scour or concentrated flow paths that would impact upon the downstream
property.

The proposed discharge from the site will therefore not alter run-off conditions in a way that may substantially
damage third party property and the site will remain generally consistent with the existing drainage characteristics.
The proposed point of discharge is therefore able to achieve a lawful point of discharge for the development.



Project number 20220217
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File 20220217 Pavilion St SWMP Rev1.docx, 2023-04-19 Revision 1

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