MCU14/0106 & OPW15/0001 Appendix E - Stormwater Management Plan

Noosa Civic
Stormwater Management Plan



The proposed development is predominantly located within E1 (which has a total area of 4.0ha). Noosa Plan
states that the maximum allowable plot ratio for E1 is 0.6. Therefore, the maximum GFA for E1 is 2.4ha. If
E1 was developed for a commercial use, it would require approximately 1200 car spaces for a GFA of 2.4ha.
These 1200 car spaces and their associated access roads would occupy a surface area of about 3.6ha.
Noosa Plan allows 2-3 storey buildings in area E1. Therefore, assuming that the first level is car parking and
the second and third levels are commercial space, a commercial development on E1 would equate to 1.2ha
of roofs and 2.4ha of car parking across the site. This results in green space on the site of 0.4ha.
A review of the current proposal indicates that within the same E1 area, there is 2.1ha of roof area and 1.5ha
of car parking and 0.4ha of open space. That is, there is the same amount of open space provided and
arguably a more environmentally friendly arrangement of roof/car park alignment.
As the parameters adopted in water quality modelling do not differ significantly between roofs and roads, the
proposed development is comparable with the development shown on the Shire Business Centre Map.
Consequently, we do not believe that Source modelling is required to address the underlying development
issue, relating to the area of roof and hardstand area raised by Council.
On a more fundamental basis, we do not think it is necessary to undertake catchment Source modelling for a
development application. The water quality reduction targets for the purpose of development assessment
are defined as part of the State Planning Policy, and the relevant watery quality reduction targets have been
shown to be achieved on site using MUSIC.
           Issue – Water Quantity
           The concept of the use of the car parks and bioretention basins is considered acceptable means for
           providing flood attenuation but the quantum of detention may need to be larger than that allowed for.
           Information Required
           55         Amended WBNM model and proposal plans, and potentially a hydraulic plan, to demonstrate
                      the runoff from the development can achieve the required attenuation for the proposed
                      development layout. In particular, the following needs to be addressed:
                (a)        Catchment Set-up - The WBNM model has assumed an initial loss of 7.5mm, typically
                           15mm is more appropriate for existing conditions.
                (b)        Detention Basins:
                           (i) Peak flood levels in the car park exceeds the QUDM limit of 300mm for a major
                               flood, it’s noted in minor flood peak levels exceed this limit and is typically over
                               500mm;
                           (ii) Peak levels in the Bioretention exceeds the QUDM limit of 1.2m for a 20yr ARI flood,
                                this level should be reduced;
The flood modelling has been updated to include greater detail. The details of the modelling show that the
recommended loss factors have been adopted. It is noted that the initial loss parameter was modified from
the original reporting to meet Council’s request.




QIC Noosa Civic Pty Ltd                               Version Final                                      11 May 2015
J13041R2_Final SWMP.docx                          Commercial in Confidence                                   Page 14