A flood study of the Allans Creek catchment was undertaken to define the nature and extent of flooding in the study area for a range of design rainfall events. As part of the Floodplain Risk Management Process as outlined in the Floodplain Development Manual (NSW Government, 2005) a Floodplain Risk Management Study (Cardno Lawson Treloar, 2006b) was undertaken to assess a range of flood management options for the Allans Creek Floodplain. One of the options assessed and subsequently recommended in the Allans Creek Floodplain Risk Management Plan (Cardno Lawson Treloar, 2006c) involved the removal of the median strip on the Freeway (F6).

The results of the Addendum modelling indicate that, in general, the flood behaviour in the catchment is relatively similar to that reported in the Allans Creek Flood Study (Cardno Lawson Treloar, 2006a). However, there are various local changes to the flood behaviour due to the removal of the freeway median strip mound.