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

                                                                                       Flood Hazard Assessment
                                                              Intersection of Lake Macdonald Dr and Dianella Crt


6.2 Culvert blockage sensitivity
The second sensitivity test assumed an amount of blockage of the available waterway area of the
three pipe culverts which pass beneath the subject site intersection. A blockage factor was applied
based on the Australian Rainfall and Runoff Book 6 Chapter 6 guidelines. An assumed Debris
Potential (DP) of medium was adopted and an L10 value of 1.5 m assumed. The smaller culvert pipe
diameter of 1050 mm was applied as the inlet width (W) control dimension. Based on guidelines a
blockage factor of 25% was applied to the 50% AEP and 10% AEP flood event, and 50% to the 2%
AEP, 1% AEP, and 0.2% AEP flood events.

Water level (Depth) hydrographs were extracted from the results of each sensitivity analysis at
reference point A and compared to the base case results for the 10% AEP, 2% AEP, 1% AEP, and 0.2%
AEP design flood events. See Figure 13 to Figure 16.

The results show that shallow inundation to a depth of approximately 100 mm is introduced at
reference point A for the 10% AEP design flood event, see Figure 13. For the 2% AEP, 1% AEP, and
0.2% AEP design flood events inundation depths across the intersection at reference point A
increase by approximately 120 mm to 150 mm with the durations of inundation also increasing to
between 2 hours and 6 hours respectively.

The results demonstrate that for flood events with AEPs less than 10% flooding conditions across the
intersection do not change significantly in depth, however, durations of inundation may be
extended.




Figure 13 - Sensitivity analysis 25% culvert blockage for 10% AEP at Reference Pt A



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