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

Noosa Civic
Stormwater Management Plan




4                Response to Information Request
Noosa Shire Council requested additional information in their information request dated 12 February 2015
(ref MCU14/0106, OPW15/0001). A response to the items related to the stormwater management are
detailed below.
           HYDROLOGY
           Issue – Water Quality
           The layout and quantum of bio-basins need to be confirmed via a refined MUSIC model that reflects
           the site layout, rather than the broad simplified approach taken in the SWP.
           Information Required
           50         Revised MUSIC modelling to demonstrate the proposed stormwater quality objectives can
                      be achieved for the proposed development layout. In particular, the following needs to be
                      addressed:
                (a)        Catchment Set-up - The MUSIC model has used 1 catchment only whereas the
                           developed scenario will have several catchments draining to a least 4 different areas.
                (b)        Rainfall Set-up - The MUSIC model does not appear to have used the Cooroy
                           Composite Station
                (c)        40059 for the model (i.e. 1973 -1983) as stated in the report and as per the guidelines.
                           The model should be revised to incorporate this station.
                (d)        Bioretention Basins: As the basins will be used for flood attenuation, the basins should
                           be checked to ensure velocities are kept below the Water By Design’s “WSUD Technical
                           Design Guidelines for SEQ” Velocities should be in the range of 0.5m/s for minor floods
                           (2-10yr ARI) & 2.0m/s for Major Floods (50-100yr ARI) + plus risk assessment of erosion
                           potential.
The MUSIC modelling has been updated to include additional detail in the catchment setup to reflect the
multiple outlet configuration. The rainfall data used in the assessment is consistent with the reporting and
guidelines. Details of the MUSIC modelling outputs are contained in Section 3.
No bio-retention basins are to be used for flood attenuation and therefore are not at risk of erosion from high
velocities resulting from flooding. The bio-basins in the car park do not have any direct inflows and are
ponding only, hence no adverse velocities are anticipated.
           Issue – Water Quality
           The submitted MUSIC model does not appear to consider the impacts of waters from catchments
           F1, G1 and H on the overall stormwater quality.
           Information Required
           51         Demonstrate how waters from these catchments (F1, G1 and H) will be considered in the
                      MUSIC model and consistent with the proposed design.
Catchment F1, G1 and H will as part of this development be diverted around the bio-retention treatment
measures. The small amounts of additional roads and hardstand within catchments F1 and G1 will be
treated by the vegetated corridor for treatment in the corridor vegetation.
Catchment H will ultimately be developed and include its own treatment measures, thus ultimately changing
the way that the catchment will be drained. As currently proposed, the only developed portion of the
catchment will be runoff from roads. This runoff will be drained to the bio-basin proposed in the centre of the
roundabout. An interim diversion bund will direct the runoff from H past the proposed bio-basin.




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