17 Bottlebrush Avenue, · MCU26/0001

5        Conclusion
The Stormwater Management Plan for the proposed multi residential dwelling at 17 Bottlebrush Avenue, Noosa
Heads has been prepared to demonstrate compliance with the stormwater management requirements of Noosa
Shire Council, QUDM and relevant State Planning Policy provisions. The assessment incorporates detailed
hydrological modelling, comparison against existing conditions, and the development of an effective stormwater
management strategy that mitigates potential impacts arising from the proposed works.

Hydrological and Hydraulic Considerations

Assessment of the existing site confirmed that stormwater runoff naturally flows towards the southwest following
the existing topography, discharging into downstream Bottlebrush Avenue. Pre-development peak flows were
calculated using both the Rational Method and DRAINS modelling, providing a reliable baseline for comparison with
post-development scenarios.

The comparative assessment demonstrated that while the Rational Method provides reasonable estimates, the
DRAINS model more accurately captures hydrologic and hydraulic behaviour, including rainfall losses, temporal
storm patterns, storage and flow routing. This model was therefore used for the final design.

Stormwater Quantity Management

Post-development conditions introduce increased impervious areas, resulting in higher runoff volumes and
elevated peak flow rates. To ensure no worsening of drainage conditions downstream, a detention tank has been
incorporated into the proposed stormwater management strategy.

Modelling of the proposed detention tank demonstrates that post-development peak flows are attenuated to at or
below pre-development levels for all assessed storm events, up to and including the 1% AEP event. This satisfies
the intent of QUDM and Council stormwater objectives for lawful, non-worsening discharge.

The detention tank has been designed to provide adequate flood storage and controlled discharge via an orifice
and overflow system. Key design parameters include:

    •   Storage volume: 8.0 m³

    •   1% AEP event Storage volume: 7.6 m³

    •   Maximum water depth: 0.95 m

    •   Lower outlet: 75 mm orifice

    •   Secondary outlet: 90 mm orifice

    •   Outlet pipe: 375 mm diameter discharging to Council’s lawful point of discharge in the stormwater network
        located in Bottlebrush Avenue

These design elements ensure safe and effective management of stormwater flows generated by the
development.

Stormwater Quality Management

Although the development does not trigger the State Planning Policy (SPP) thresholds requiring formal post-
construction stormwater quality treatment, best-practice measures have been incorporated to support good water
quality outcomes.

These include:


    •   Providing an effective stormwater drainage layout that conveys and attenuates runoff before discharge


 17 BOTTLEBRUSH AVENUE, NOOSA HEADS
                                       7 January 2026                                            P a g e | 17
 Stormwater Management Plan
 Client Reference: P0433-25-001
 Prepared for Made Capital PTY LTD