Upper South Creek Flood Study

The Study has defined design flood behaviour for the Upper South Creek area. The model used to define design flood liability is calibrated and validated and is shown to be relatively insensitive to model parameters. As such it is expected that design flood estimates are accurate, hence the model can be used with confidence in regard to safe guarding future development against risk of inundation. The range of flood heights is relatively compressed in that a relatively small difference exists between peak flood levels for design events of markedly different probability. This is a facet of the local topography i.e. relatively wide and well defined floodplain. Mapping of provisional hydraulic categories has been provided and this work identified that, based on specific criteria, the floodway area approximately corresponds to the inundation extent. This unusual result is again related to the specific topography of the study area, i.e. a well defined and high flow/storage capacity overbank area. Modelling carried out in order to assess the impact of urbanisation within the currently on-going sub-division developments of Oran Park and Turner Road has identified that urbanisation produces small impacts on the volume and peak flow of flood runoff. For downstream volume sensitive locations this can lead to an exacerbation of peak flood levels. In the 5% AEP event for example the two developments (without mitigation elements implemented in modelling) result in an increase in flood heights at Bringelly Road of 0.1 m.