20220206 48 Elm St SWMP

     2.3. Proposed Development Drainage Pattern

          2.3.1 Stormwater Concept
It is proposed to provide a kerb along the eastern edge of the proposed carpark. The kerb will grade downhill from
south to north and be free draining. A new grated field inlet will be constructed over the existing 300mm diameter
roofwater pipe located in the north eastern corner of the existing easement. Paved surfaces and driveway areas in
the eastern portion of the site will be graded towards the proposed kerb. The propsoed kerb will direct stormwater
runoff to the proposed grated inlet pit. It is proposed to provide a 150mm high kerb around the proposed inlet pit
to ensure the runoff is collected and ponded on the proposed inlet.

Roof run-off, which makes up the majority of the site, will be collected by downpipes and discharged to a 13kL in-
ground detention tank. The tank will attenuate roof water flows so that the outflow from the entire site will not
increase over existing conditions. The outlet from the detention tank will discharge to the proposed grated inlet pit.

All gutters, downpipes and roofwater pipes will need to be designed to convey the 1% Annual Exceedance
Probability (AEP) storm to the proposed detention tank.

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.

A copy of the proposed stormwater drainage plan for the development is provided in Appendix A.


          2.3.2 Lawful Point of Discharge
Under existing conditions, the site naturally drains north towards pearl street, with roof run-off piped to a kerb
adaptor outlet in Pearl Street where it is captured by downstream stormwater pits. 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.

The site will make use of stormwater attenuation to ensure that peak flow rates arising from the proposed
developed will not exceed the existing site’s peak flow rates. Run-off from the development will be piped directly
to the existing roofwater line located within the easement along the eastern boundary of the site. Stormwater
runoff in excess of the capacity of the existing network will discharge from the site as overland flow to Pearl Street.

The proposed discharge from the site will not increase run-off to the downstream environment, and the site will
discharge to the existing infrastructure, therefore resulting in no worsening to existing conditions. The proposed
drainage system is therefore able to achieve a lawful point of discharge for the development.



     2.4. Flood Considerations
Review of the Noosa Shire Council Intramaps flood layers including the Flood Hazards Overlay has identified that
the site is located outside of any flood or inundation areas within the locality indicating it is not expected that the
proposed development will be subject to flooding.

Project number 20220206                                                                                Page 6 of 19
File 20220206 48 Elm St SWMP, 2023-02-03 Revision 1

P +61 7 5211 1003             A 75 Noosa Drive, Noosa Heads Qld 4567   E [email protected]       recorconsulting.com