17 Bottlebrush Avenue, · MCU26/0001

Required Mitigation – Installation of a Detention tank

Due to the projected increase in post-development peak flows, mitigation measures are required to ensure
compliance with Noosa Shire Council stormwater management requirements and to prevent potential downstream
impacts. The most suitable solution is the use of the existing detention tank; modelling will ensure the designed
tank will achieve the following outcomes:

     •    Attenuate peak discharge by temporarily storing excess runoff and releasing it at controlled, pre-
          development rates

     •    Control flow velocities, thereby reducing the risk of downstream erosion and infrastructure overloading
          and


The detention tank will be designed to ensure that post-development peak flows do not exceed pre-development
flow conditions for all relevant design storm events. Further hydrological modelling will be undertaken to
appropriately size the tank and confirm its effectiveness in mitigating increased flow volumes and velocities.


3.4         Stormwater Detention and Mitigation Strategy
A detention tank is proposed to be utilised for stormwater attenuation and will be sized to detain all site-generated
flows. The proposed tank is to be located on the southwestern portion of the development, as shown on the Civil
Set of Plans (Drawing P0433-25-001_17_Bottlebrush_Avenue_REVA), for Council’s consideration.

The tank has been designed to detain and control stormwater flows for all assessed events, including the 1% AEP,
such that post-development peak discharges do not exceed pre-development levels. Attenuation is provided
across all assessed AEP storm events in accordance with the Queensland Urban Drainage Manual (QUDM). Refer
to Table 3-2 for tank design parameters.

As outlined in the preceding sections, the site naturally drains toward the southwest. Earthworks and site drainage
are proposed to direct all stormwater runoff to the proposed detention tank to ensure appropriate drainage
outcomes for the site. This enables controlled discharge to Council’s existing stormwater network within
Bottlebrush Avenue.

Stormwater modelling assumes the entire site will be conveyed into the detention tank. This provides a consistent
comparison between pre- and post-development conditions and demonstrates improved local drainage outcomes
Table 3-2: Detention tank parameters

 Parameter                                               Value

 Storage Volume                                          8.0 m³

 1% AEP Storage Volume                                   7.6 m³

 1% AEP Water Depth                                      0.95 m

 Lower Discharge Control                                 75 mm orifice at 28.50 m AHD

 Secondary Discharge Control                             90 mm orifice at 28.65 m AHD

 Outlet Pipe Size                                        375 mm pipe RFC Class 3

 Outlet Pipe Invert Level                                28.50 m AHD



The tank outlet will discharge via a new stormwater pipe connection into Council’s existing stormwater network
located within Bottlebrush Avenue.




 17 BOTTLEBRUSH AVENUE, NOOSA HEADS
                                        7 January 2026                                               P a g e | 14
 Stormwater Management Plan
 Client Reference: P0433-25-001
 Prepared for Made Capital PTY LTD