5179IWMP_Rev3

                                                                                Callaghan & Toth


5.0 FLOODING ASSESSMENT SUMMARY
Refer to Flood Assessment Report Revision 3 for the detailed flood assessment. See also Plan
2035-01 Revision E showing approximate Q100 inundation line. Below summarises the
findings of the flood assessment.

5.1      Existing Conditions

The site is traversed by one tributary of Six Mile Creek; refer to plan 2035-01 Revision E.

The site is subject to floodwaters from the adjacent watercourse and the Q100 year ARI flood
levels (see plan 2035-01 Revision E).

5.2      Proposed Drainage System and Flood Implications

The proposed residential lots front the creek’s floodway will have at least 1.0 metre freeboard to
the Year 2100 1%AEP flood level and the proposed development will therefore be adequately
flood-immune, even with a 20% impost on the design rainfalls for future climate change.

The required 100-year stormwater detention volume of 334m3 can be achieved, within the site’s
constraints, by a 342m3 open basin. A more complex modelling procedure at the Operational
Works stage, using the Bureau of Meteorology’s 2016 design rainfall data, could result in a
slightly smaller detention volume.

The open basin will have a 100-year water depth of 0.8 metres. The freeboard of 0.25 metres to
the embankment crest/footpath will be sufficient to contain the inflows from a greenhouse-
induced 20 percent increase in storm rainfall intensities.

See the Flood Study report for further details on flood modelling results.




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2035 2 Pearsons Road IWMP – Revision 3                                          April 2021