Appendix C - Flood Report_Sept2020

                                                                                                 Callaghan & Toth




4.0       SUMMARY
The proposed residential lots front the creek’s floodway will have at least 1.5 metre freeboard to the 100
year flood level and the proposed development is therefore expected to be adequately flood-immune, even
with a 20% impost on the design rainfalls for future climate change.

The small intrusion of the outer batter of the basin into the floodway will depreciate the 100 year floodway
storage by about 9 cubic metres, which should have practically no impact on the 100 year flood profile.

The required 100 year stormwater detention volume of 398 cubic metres can be achieved, within the site’s
constraints, by two facilities – a 351 cubic metre open basin and a 47 cubic metre EcoAid underground
facility. 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 1.05 metres. The freeboard of 0.2 metres to the
embankment crest will be sufficient to contain the inflows from a greenhouse-induced 20 percent increase
in storm rainfall intensities.




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2035 2 Pearsons Road – Flood Study                                                   September 2020