RFI - P0478-26-001_45_Maple_Street_Cooroy_SWMP

7          Conclusion
The Stormwater Management Plan for the proposed multiple dwelling development 45 Maple Street, Cooroy 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.


7.1        Hydrological and Hydraulic Considerations

Assessment of the existing site confirms that stormwater runoff generally flows towards the east in accordance
with site topography. Pre-development peak flows were estimated using both the Rational Method and DRAINS
modelling to establish a baseline for comparison.

While the Rational Method provided a suitable verification check, the DRAINS model more accurately represents
catchment behaviour, including rainfall losses, temporal variation, storage effects, and flow routing. Accordingly,
DRAINS modelling has been adopted for the final design and assessment.


7.2        Stormwater Quantity Management

The proposed development increases impervious area and runoff potential. To mitigate these impacts, a proposed
OSD tank has been incorporated within the southern portion of the site.

The detention system captures stormwater runoff and attenuates peak flows prior to discharge via the lawful point
of discharge into Council’s existing stormwater network within Myall Street. Existing overland flow paths are
maintained, and no increase in discharge to adjoining properties occurs.

Hydrological modelling confirms that post-development peak discharge rates are equal to or less than pre-
development flows for all assessed storm events up to and including the 1% AEP event, satisfying Council’s non-
worsening drainage requirements.

The detention system has been designed with appropriate storage and outlet controls to achieve compliant
discharge rates, including:

Storage volume: 75.00 m³


      •   Storage volume: 74.53 m³ for the 1% AEP event

      •   Maximum water depth: 1.49 m

      •   Lower outlet: 170 mm orifice

      •   Secondary outlet: 245 mm orifice

      •   Outlet pipe: 375 mm diameter

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




 45 MAPLE STREET, COOROY
                                         24 June 2026                                              P a g e | 19
 Stormwater Management Plan
 Client Reference: P0478-26-001
 Prepared for Myall Rise PTY LTD