UPDATED DA - Attachment 7 - Flood Impact Assessment

     3.0    FLOOD IMPACT ASSESSMENT

     3.1    Flood Modelling

     Flood modelling of the site was undertaken using TUFLOW, a 1D/2D hydraulic modelling software package, to ensure
     stormwater flows from upstream catchments external to the site can be conveyed through the site and to demonstrate
     that no unacceptable impacts will occur on surrounding properties as a result of the proposed development.

     Scenarios modelled as part of this investigation include:
        • Existing Case Scenario – modelling the undeveloped conditions.
        • Developed Case Scenario – modelling the site with an updated Digital Elevation Model (DEM), upgraded
             hydraulic structure at the road crossing the large clean water drain and updated Manning’s roughness
             coefficients and soil infiltration rates to represent the proposed development layout.

     Modelling was undertaken for the 50%, 10% and 1% and 1% climate change Annual Exceedance Probability (AEP)
     events.

     3.2    Hydrology

     A “Rain on Grid” modelling approach was adopted for this overland flow study and as such, no traditional hydrological
     modelling was required. The total catchment area adopted for this assessment was approximately 287 ha. Refer to
     Figure 3-1 for the overall extent of the 2D flood model and the quadtree extent for the model. This is discussed further
     in Section 3.11.




                                          Figure 3-1 Model Extent with 1m Contours




Noosa Shire Council                                                                                     3
M25-0045Rpt – 244035– February 2025