UPDATED DA - Attachment 7 - Flood Impact Assessment

     3.8    Manning’s n Values

     Manning’s n roughness coefficient’s have been manually delineated for the entire contributing catchment. Refer to
     Appendix B for the Manning’s Roughness Coefficient Maps. Land uses and corresponding manning’s roughness
     coefficients for the hydraulic model are as follows:
     •        0.018 – Roads
     •        0.075 – Trees / Bushland
     •        0.05 – Grassland
     •        0.3 – Roof
     •        0.03 – Unsealed road
     •        0.015 – Water body

     3.9    Fraction Impervious

     The fraction impervious values adopted for each land use are as follows:
     •       Roads – 100%
     •       Trees / Bushland - 0%
     •       Grassland – 0%
     •       Roof– 100%
     •       Unsealed road – 50%
     •       Water body – 100%

     3.10   Topography

     Topography for the full extent of the 2D hydraulic model was created using 2015/2023 LIDAR and survey within the
     development site. The existing surface topography is shown in Figure 3-2.
     It is important to note that Council plans to construct an earthworks pad on the area to the east (labelled as RRA Pad).
     Further, the existing HES Basin is being relocated to the north-western corner of the pad. As requested by Council,
     the RRA Pad and relocated HES basin has been assumed to be present in the both the existing and developed case
     scenarios for modelling purposes.




                                     Figure 3-2 Existing Site Topography with 0.5m contours




Noosa Shire Council                                                                                     5
M25-0045Rpt – 244035– February 2025