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

                                                                                            Flood Hazard Assessment
                                                                   Intersection of Lake Macdonald Dr and Dianella Crt


 Flood Hazard          Classification limit      Limiting still water depth        Limiting velocity
 Classification     (D and V in combination)                 (D)                          (V)
                               m2/s                           m                           m/s
 H1                        D*V ≤ 0.3                       ≤ 0.3                        ≤ 2.0

 H2                        D*V ≤ 0.6                       ≤ 0.5                        ≤ 2.0

 H3                        D*V ≤ 0.6                       ≤ 1.2                        ≤ 2.0

 H4                        D*V ≤ 1.0                       ≤ 2.0                        ≤ 2.0

 H5                        D*V ≤ 4.0                       ≤ 4.0                        ≤ 4.0

 H6                        D*V > 4.0                         -                             -


Flood hazards for the subject site intersection have been determined for the 10% AEP, 2% AEP, and
1% AEP design flood events in accordance with the guidance in ARR Book 6 and are presented in
Map 4 to Map 6.

For the 10% AEP design flood event the intersection is not inundated and hence no flood hazard
exists within the trafficable road corridor, see Map 4. For the 2% AEP design flood event, shallow
inundation at the peak of the flood event introduces a H1 flood hazard classification across the
intersection with areas of higher classification where flow across the road concentrates and returns
to the main waterway, see Map 5. The flood hazard classifications are similar for the 1% AEP design
flood event, however, a more prominent corridor of higher H5 flood hazard exists across the
intersection, see Map 6.

Depth hydrographs were extracted from two reference points to determine the approximate
duration of inundation that could be anticipated for inundation of the intersection. The depth
hydrographs for the reference points shown on Map 6 are presented in Figure 8 and Figure 9. The
figures show the duration of inundation for the 2% AEP and 1% AEP design flood events to be less
than 1.5 hours. The actual duration of inundation will vary for each major rainfall event experienced
in the local catchment; however, the approximate duration of the design flood event provides a
reasonable indication of the duration of inundation which is also consistent with the size of the
upstream catchment that contributes flood flows to the intersection location.

The intersection is flood free and trafficable for events up to the 10% AEP.




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