Final Engineering services report _62 Lake Macdonald Drive · OPW25/0057

                                                                                      Flood Hazard Assessment
                                                             Intersection of Lake Macdonald Dr and Dianella Crt


4.3 Model Roughness
The observed land uses for the 2D model surface for the existing catchment condition is shown in
Map 3.

The corresponding Manning’s n surface roughness values for each surface type are presented in
Table 4-1.

Table 4-1 Flood model surface roughness

 Catchment Surface              Assumed
                               Manning’s n
 Openspace                        0.08
 Residential                      0.12
 Rural residential                0.06
 Waterway                         0.12
 Roads                            0.015



4.4 Validation
Design discharge hydrographs were exported from the local high-resolution flood model results
immediately upstream of the intersection and compared to design discharges extracted from the
Cooroy Creek flood model.

Design discharge hydrographs show good consistency across all flood events. Refer to Figure 1 to
Figure 6.




Figure 1 - 50% AEP design discharge comparison




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