Amended Stormwater Managment Plan

SC5594 – Walter Hay Dr, Noosaville                                                             13




4.3.3     Roughness Coefficients
The conduits and links used within the model are based on the ultimate design scenario for the internal
roadways and overland flow paths. Mannings “n” roughness coefficient values are specified as 0.014 for
RCP pipes and 0.011 for uPVC pipes.


For overland flow within the sub-catchment areas a Mannings “n” value of 0.014 for concrete areas and
0.035 for vegetated areas was adopted.


4.3.4     Storm Events
Storm patterns were setup using Australian Rainfall and Runoff storm patterns for Area 3 with intensity
frequency duration data taken for the local area. Storm durations of 10, 15, 20, 25, 30, 45, 60 and 90
minutes were investigated for the pre and post developed scenarios.


4.3.5     Backwater Condition
The subject site is not impacted by regional flooding and the proposed discharge point is at the upstream
end of the existing swale. Therefore, the outlet node identified as ‘1.0’ has been modelled assuming a free
outlet.




                                                                  Major Flood Extents




                                                             Subject Site




                               Figure 4.1 – Major Event Regional Flooding Map