Attachment 7B - Site Based Stormwater Manamgment Plan by ADG

                                                                   RACV Noosa Resort: 94-142 Noosa Drive, Noosa Heads

                                                                             ADG Ref: 22366 C R10 Rev04 14.12.22.docx

                                                                                                      December 2022




         Figure 7 - Results for Post-Development Model at Bioretention Basin (Infiltration Node)




                    Figure 8 - Results for Post-Development Model at Receiving Node


         As shown above in Figure 7, a significant pollutant reduction is shown at the bioretention basin node.
         Figure 8 illustrates that the total suspended solids, total phosphorus and gross pollutants will have a
         significant decrease with the implementation of this stormwater quality improvement device, being the
         bioretention basin. A slight increase (3.4% or 0.09 kg/yr) in total nitrogen is found in the post-
         development scenario when considering the receiving node and the existing surrounding vegetated
         surface.

         Based on a Geotechnical Report undertaken by Coffey Geotechnics for the Noosa Sanctuary Project,
         the site location has sandy soil texture up to a minimum depth of 10m, which we predict enables the
         site to infiltrate runoff. Since the majority of the stormwater runoff from the roof will be re-used by the
         rainwater tanks and the rest of the runoff is intended to infiltrate onsite through the bio-basin, no
         discharge will be proposed from the site. It is recommended that a hydraulic conductivity test be
         performed by an experienced geotechnical engineer at the detailed design phase to confirm the soils
         permeability and infiltration capability.

         Currently it is assumed that a silty sand sub-strata will have a hydraulic conductivity of approx. of
         4 × 10−6 m/s, for a 30 m2 bioretention basin infiltration area, this equates to a yearly capacity of 3,784
         𝑚3 /yr which exceeds the infiltration rate of the receiving node being 2.9 ML/yr (2,900 𝑚3 /yr). It is
         therefore understood that the existing subgrade will have sufficient capacity to infiltrate all treatable
         flows with no additional stormwater infrastructure required to be implemented to the downstream
         waterway.

         Details of the MUSIC model are attached within Appendix H for further information.

BRISBANE / DARWIN / GOLD COAST / HOBART / MELBOURNE / PERTH / SUNSHINE COAST / SYDNEY / TOOWOOMBA            Page 18