Stormwater Management Plan -OPW (A) · OPW25/0042

10.2 MAJOR EVENT OVERLAND FLOWS (>10 YEAR ARI)

Emergency overflow, for events (>Q10) which cannot be wholly conveyed by
underground pipework would be conveyed overland through the development site
via a landscaped ephemeral stream.

Previous versions of this report relied on simple manning calculations carried out at
three (3) nodes along the proposed route through the development site in order to
estimate 100 Year ARI flow characteristics and check that such flows could be
conveyed safely with the following criteria adopted:-

-Maximum velocity x depth product = 0.4m2/sec (QUDM 7.0.4.2)
-Minimum channel freeboard = 0.3m (QUDM 9.03.1)
-Minimum freeboard to any structural floor=500mm (Council Standards SC6.7).

For increased accuracy and certainty and to ensure no impacts to adjacent properties
or non-compliant flows through roadways and footpaths performance of the
ephemeral stream has now been more accurately modelled by Engeny using specialist
software.

The Engeny report is included at Appendix B and drew the following conclusions: -

Engeny Australia Pty Ltd (Engeny) have been engaged by Calile Malouf Investments Pty Ltd
to prepare a Local Overland Flow Assessment for a proposed Operational Works (OPW)
development for application resort complex and shop at 3 & 7 Serenity Close Noosa Heads
QLD 4567.

Detailed overland flow modelling has been completed at a level of detail appropriate for
Operational Works approval to confirm Alta Project’s proposed realigned drainage and
overland flow design through the site is appropriate in achieving the design requirements for
the project.

The assessment has found that flows can be appropriately managed through the site via an
overland flow path which connects into the Serenity Close cul-de-sac footpath, without
impacting adjoining properties or resulting in non-compliant flows with the road and
footpath.

The assessment found that the finished floor levels of each building achieve a minimum 0.5m
freeboard and is able to contain the severe storm event (i.e. 1% (2100) AEP fully blocked
stormwater network).

Reinforced turf is recommended for the last 20m of channel upstream of Serenity Close
(velocity up to 2.30 m/s) and rock protection be placed to manage the outlet velocities (rock
size D50 = 200mm and extend 3.6m past the outlet).


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A6769/25/SWMP/Rev OpW(A) – Feb 2025                                            Page 20 of 21
SH/PL
                     Brah101 Pty Ltd t/as ALTA PROJECTS